Maximum Percent of Post-Consumer
Recycled Polypropylene in an
Interior Hard Trim Panel
An Investigation into the Feasibility, Environmental Impact, and
Performance of Increasing Post-Consumer Recycled Polypropy-
lene Content in Automotive Interior Components

Master’s thesis in Product Development

JULIA EKENER
AGNES SUNDSTRÖM

DEPARTMENT OF INDUSTRIAL AND MATERIALS SCIENCE

CHALMERS UNIVERSITY OF TECHNOLOGY
Gothenburg, Sweden 2025
www.chalmers.se

www.chalmers.se




Master’s thesis 2025

Maximum Percent of Post-Consumer Recycled
Polypropylene in an Interior Hard Trim Panel

An Investigation into the Feasibility, Environmental Impact, and
Performance of Increasing Post-Consumer Recycled Polypropylene

Content in Automotive Interior Components

Julia Ekener
Agnes Sundström

Department of Industrial and Materials Science
Division of Engineering Materials

Chalmers University of Technology
Gothenburg, Sweden 2025



Maximum percent of recycled PP in an interior hard trim panel
An Investigation into the Feasibility, Environmental Impact, and Performance of
Increasing Post-Consumer Recycled Polypropylene Content in Automotive Interior
Components
JULIA EKENER & AGNES SUNDSTRÖM

© JULIA EKENER, 2025.
© AGNES SUNDSTRÖM, 2025.

Supervisor: Marko Bek, Industrial and Materials Science
Examiner: Roland Kádár, Industrial and Materials Science

Master’s Thesis 2025
Department of Industrial and Materials Science
Division of Engineering Materials
Chalmers University of Technology
SE-412 96 Gothenburg
Telephone +46 31 772 1000

Cover:

Typeset in LATEX, template by Kyriaki Antoniadou-Plytaria
Printed by Chalmers Reproservice
Gothenburg, Sweden 2025

iv



Maximum percent of recycled PP in an interior hard trim panel
An Investigation into the Feasibility, Environmental Impact, and Performance of
Increasing Post-Consumer Recycled Polypropylene Content in Automotive Interior
Components
JULIA EKENER
AGNES SUNDSTRÖM
Department of Industrial and Materials Science
Chalmers University of Technology

Abstract
This study examines the influences PCR PP has on mechanical properties, aesthet-
ics, CO2 footprint, and the effects from aging. The purpose of the project is to aid
Volvo Cars in updating their material composition of hard trim interior panels by
recommending a suitable percentage of PCR PP to use. The investigated materials
have been 30% PIR PP, 30% PCR PP, 40% PCR PP, 50% PCR PP, 60% PCR PP,
and 70% PCR PP with the same amount of additives. To understand this influ-
ence, methods such as aging, tensile testing, impact testing, differential scanning
calorimetry, perceived quality assessment, and CO2 footprint calculations were per-
formed. The findings indicate that the mechanical properties are strongly limited by
the impact strength, which decreases with the amount of PCR PP. This limits the
recommendation for Volvo Cars to 30% PCR PP to be used. Regarding appearance,
the perceived quality assessment shows that a switch to the highest material stud-
ied, 70% PCR PP, is possible. The tests performed present that aging for 500h and
1000h affects the crystallinity, resulting in varied outcomes for the studied mechan-
ical properties. The CO2 footprint overall decreases with the amount of PCR PP
content. Although, between 30% PIR PP and 30% PCR PP there is an increase in
the CO2 footprint. Further studies should explore the effects on the full components
instead of material samples, along with additional tests of the same kind as those
conducted to further strengthen the results.

Keywords: PCR, PIR, tensile test, impact strength, crystallinity, DSC, molecular
weight, carbon footprint

v





Acknowledgements
We would like to express our deepest gratitude to our supervisor, Marko Bek, and
examiner, Roland Kádár, for their continuous support, valuable guidance, and con-
structive feedback throughout the course of this project. Our sincere thanks also go
to our opponents, Sigrid Wirdheim and Aron Uggla, for their insightful comments
and suggestions. We are also grateful to our supervisor at Volvo Cars, Patrik Lilje-
vide, for unwavering support, insightful guidance, and helpful feedback throughout
the duration of this project. Moreover, we would like to acknowledge the rest of the
team at Volvo Cars, including Hanna Ahlström, Sven Karlsson, and Lucas Scheuer
for their collaboration, guidance, and assistance in this project. We also express
gratitude for Polykemi for allowing us to visit their factory, where we had the op-
portunity to explore their processes and ask numerous questions. Their hospitality
and willingness to share valuable insights greatly contributed to the success of this
project.

Julia Ekener and Agnes Sundström, Gothenburg, May 2025

vii





List of Acronyms

Below is the list of acronyms that have been used throughout this thesis listed in
alphabetical order:

CO2e Carbon Dioxide Equivalent
DSC Differential Scanning Calorimetry
EoL End-of-Life
GHG Greenhouse Gas
GU Gloss Unit
GWP Global Warming Potential
PCR Post-Consumer Recycled
PIR Post-Industrial Recycled
PP Polypropylene

ix





Contents

List of Acronyms ix

List of Figures xiii

List of Tables xv

1 Introduction 1
1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1.1 Current situation . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.2 Collaborating Company - Volvo Cars . . . . . . . . . . . . . . 2
1.1.3 Collaborating Companies - Polykemi & Rondo Plast AB . . . 3

1.2 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Aim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 Research questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.5 Limitations and Demarcations . . . . . . . . . . . . . . . . . . . . . . 4
1.6 Social and ethical aspects . . . . . . . . . . . . . . . . . . . . . . . . 5

2 Research background 7
2.1 Automotive Interior Hard Trim Panels . . . . . . . . . . . . . . . . . 7
2.2 Polypropylene as a Material . . . . . . . . . . . . . . . . . . . . . . . 7
2.3 Post-Consumer and Post-Industrial Recycled material . . . . . . . . . 9
2.4 Mechanical recycling . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.5 Chemical recycling . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.6 Feedstock of Post-Consumer Recycled Plastic . . . . . . . . . . . . . 12
2.7 Carbon footprint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.8 Tensile test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.9 Impact test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.10 Differential Scanning Calorimetry . . . . . . . . . . . . . . . . . . . . 14
2.11 Aging of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.12 Perceived quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.13 Polykemi’s and Rondo’s functions and processes . . . . . . . . . . . . 17
2.14 Sample Production Details . . . . . . . . . . . . . . . . . . . . . . . . 20

3 Methods 23
3.1 Literature review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.2 Interviews and study visits . . . . . . . . . . . . . . . . . . . . . . . . 23
3.3 Aging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

xi



Contents

3.4 Tensile tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.5 Impact tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.6 Differential Scanning Calorimetry . . . . . . . . . . . . . . . . . . . . 30
3.7 Perceived Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.8 Calculation of Carbon footprint . . . . . . . . . . . . . . . . . . . . . 36

4 Results 39
4.1 Tensile tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.2 Impact tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.3 Differential Scanning Calorimetry tests . . . . . . . . . . . . . . . . . 43
4.4 Perceived Quality assessment . . . . . . . . . . . . . . . . . . . . . . 47
4.5 Carbon footprint calculations . . . . . . . . . . . . . . . . . . . . . . 50

5 Discussion 51
5.1 Potential sources of error . . . . . . . . . . . . . . . . . . . . . . . . . 51
5.2 Material tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

5.2.1 Evaluation of DSC tests . . . . . . . . . . . . . . . . . . . . . 52
5.2.2 E-modulus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
5.2.3 Stress at Yield Point . . . . . . . . . . . . . . . . . . . . . . . 53
5.2.4 Strain at Yield Point . . . . . . . . . . . . . . . . . . . . . . . 54
5.2.5 Strain at Breakage Point . . . . . . . . . . . . . . . . . . . . . 55
5.2.6 Impact test . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
5.2.7 Perceived Quality . . . . . . . . . . . . . . . . . . . . . . . . . 57

5.3 CO2 footprint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
5.4 Material recommendation for Volvo Cars . . . . . . . . . . . . . . . . 58
5.5 Future work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

6 Conclusion 61

References 63

A Appendix 1 I
A.1 Notes from interviews and study visits . . . . . . . . . . . . . . . . . I

A.1.1 Notes from study visit at Polykemi and Rondo with Patrik
Axrup, Johan Svenmo and Patrik Lindqvist (Date: 2025-02-25) I

A.1.2 Interview with Inger Jacobsson and Hanna Ljungholm at the
Perceived Quality department (Date: 2025-03-17) . . . . . . . III

A.2 Tensile test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV
A.2.1 Stress-strain diagrams . . . . . . . . . . . . . . . . . . . . . . IV
A.2.2 Tensile tests - All parameters . . . . . . . . . . . . . . . . . . VIII

A.3 DSC values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . XVIII
A.4 Impact test - results . . . . . . . . . . . . . . . . . . . . . . . . . . . XIX

xii



List of Figures

1.1 The hard trim panels . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Close-up of one of the hard trim panels, the threshold . . . . . . . . . 3

11figure.caption.8
2.2 Color space used in PQ via (Mouw, 2018) . . . . . . . . . . . . . . . 16
2.3 The shredded PCR PP that arrives to Rondo . . . . . . . . . . . . . 18
2.4 The erema extruder machine that removes contamination . . . . . . . 19
2.5 The extruded contamination by the erema machine . . . . . . . . . . 19
2.6 The granules created by the erema machine . . . . . . . . . . . . . . 19
2.7 Closeup of the granules . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.8 The spaghetti-liked strings cooling down i water right after being

extruded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.9 The spaghetti-liked strings drying and on their way to be cut into

granules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3.1 Description and purpose of aging at Volvo Cars . . . . . . . . . . . . 24
3.2 Highlighted part shows the temperature these samples should be ag-

ing in . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.3 Bags filled with samples placed on the car floor . . . . . . . . . . . . 25
3.4 Close-up of the bags placed on the car floor . . . . . . . . . . . . . . 25
3.5 Samples spread out on the car floor during aging . . . . . . . . . . . . 25
3.6 Putting on the reflexive points . . . . . . . . . . . . . . . . . . . . . . 26
3.7 Test specimen with reflexive dots . . . . . . . . . . . . . . . . . . . . 26
3.8 Cameras locating the reflexive points . . . . . . . . . . . . . . . . . . 26
3.9 Test specimen during tensile test . . . . . . . . . . . . . . . . . . . . 26
3.10 Conditioning the samples . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.11 Cutting the samples into the correct size . . . . . . . . . . . . . . . . 28
3.12 How the samples were cut . . . . . . . . . . . . . . . . . . . . . . . . 29
3.13 A sample ready for impact testing in the machine . . . . . . . . . . . 29
3.14 The impact test machine . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.15 The result shown by the machine after a test . . . . . . . . . . . . . . 29
3.16 Cutting out the small samples . . . . . . . . . . . . . . . . . . . . . . 30
3.17 Making sure the samples fit in the pan . . . . . . . . . . . . . . . . . 30
3.18 Weighing the samples . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.19 Making a hole in the DSC-pan lid . . . . . . . . . . . . . . . . . . . . 31
3.20 Placing the lid on the pan with the sample in . . . . . . . . . . . . . 31
3.21 Pressing the lid and pan together . . . . . . . . . . . . . . . . . . . . 31

xiii



List of Figures

3.22 Placing the pans in the machine . . . . . . . . . . . . . . . . . . . . . 32
3.23 The machine performing the DSC-test . . . . . . . . . . . . . . . . . 32
3.24 Example of graphs from the DSC-test for 50% PCR PP . . . . . . . . 33
3.25 Samples in Spectralight . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.26 Samples in Spectralight . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.27 The Spectrophotometer tool used to measure the color of the material 35
3.28 Different nozzles for the tool that decides how much light should be

let in . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.29 The Spectrophotometer in use . . . . . . . . . . . . . . . . . . . . . . 35
3.30 The Glossmeter tool . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.31 The Glossmeter in use . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.32 The hard trim panel parts with their separate names . . . . . . . . . 37

4.1 The average E-modulus . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.2 The average stress at yield point . . . . . . . . . . . . . . . . . . . . . 41
4.3 The average strain at yield point . . . . . . . . . . . . . . . . . . . . 41
4.4 The average strain breakage point . . . . . . . . . . . . . . . . . . . . 42
4.5 The average impact strength for the tested materials . . . . . . . . . 43
4.6 The total average crystallinity . . . . . . . . . . . . . . . . . . . . . . 44
4.7 The total average peak temperature . . . . . . . . . . . . . . . . . . . 44
4.8 The average crystallinity of the big peak . . . . . . . . . . . . . . . . 45
4.9 The average peak temperature of the big peak . . . . . . . . . . . . . 45
4.10 The average crystallinity of the small peak . . . . . . . . . . . . . . . 46
4.11 The average peak temperature of the small peak . . . . . . . . . . . . 46
4.12 The ratio in crystallinity between the small peak and the big peak . . 47

A.1 The stress-strain curves for 30% PIR, note that there are 10 tests for
the unaged . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V

A.2 The stress-strain curves for 30% PCR . . . . . . . . . . . . . . . . . . V
A.3 The stress-strain curves for 40% PCR . . . . . . . . . . . . . . . . . . VI
A.4 The stress-strain curves for 50% PCR . . . . . . . . . . . . . . . . . . VI
A.5 The stress-strain curves for 60% PCR . . . . . . . . . . . . . . . . . . VII
A.6 The stress-strain curves for 70% PCR . . . . . . . . . . . . . . . . . . VIII
A.7 Values for big and small peak together, and the small big peak . . . . XVIII
A.8 The values for the small peak . . . . . . . . . . . . . . . . . . . . . . XIX

xiv



List of Tables

3.1 The part weights of the hard trim interior panels . . . . . . . . . . . 37

4.1 Results of the visual assessment . . . . . . . . . . . . . . . . . . . . . 47
4.2 Results of the color measurements . . . . . . . . . . . . . . . . . . . . 48
4.3 Results of the color measurement compared to the reference and the

approved tolerance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.4 Results from the gloss measurement compared to the reference and

the approved tolerance . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.5 CO2e values for the different materials . . . . . . . . . . . . . . . . . 50

xv



List of Tables

xvi



1
Introduction

This chapter introduces the project, providing an overview of its background and
context. It outlines the key limitations and ethical considerations associated with
the project, while also detailing the aims, purpose, and research questions that guide
the study.

1.1 Background
Following, the background for the project will be presented. It will describe the
current situation and present collaborating companies.

1.1.1 Current situation
Plastic is widely used today across industries such as packaging, construction, and
technology due to its versatility, durability, and cost-effectiveness. This widespread
use has raised significant environmental, social, and health concerns due to the in-
sufficient waste management and reliance on fossil fuels for production. The levels of
production and consumption of today are increasingly recognized as having reached
unsustainable levels (Walker & Fequet, 2023).

Half of all plastic produced today is designed for single-use purposes, which im-
plies that it is used once and then wasted. Approximately 98% of single-use plastic
products are produced from virgin feedstock, which means that the plastic used is
fully newly produced and contains no percent recycled plastic. The production, use
and disposal of virgin plastic based on conventional fossil fuel is estimated to repre-
sent 19% of the global carbon budget by 2040 ( The United Nations Environment
Programme, 2025). The use of recycled plastics instead will not only benefit the
global carbon budget, but also addressing the depletion of fossil fuel resources by
eliminating the need for their use in the production of new plastic materials (Tide
Earth, 2024)

At the end of 2017, looking at all plastic waste ever produced, only 10% had been
recycled. 76% ended up in landfills and the remaining 14% was incinerated. The
inadequate recycling practices lead to the long-term pollution as plastics can persist
in ecosystems for centuries. These numbers recognizes the need for improved circular
economy and to address the full life cycle of plastics (Grabiel, Gammage, Perry, &
Dixon, 2022)

1



1. Introduction

1.1.2 Collaborating Company - Volvo Cars
Volvo Cars, a global automobile manufacturer originating in Sweden, operates six
major production facilities around the world and markets its vehicles in more than
100 countries. The company has committed to achieving net zero emissions in their
full value chain by 2040. To accomplish this ambitious goal, Volvo Cars must adopt
innovative and forward-thinking approaches to sustainability. As many components
of their automobiles consist of polymers, which have significant adverse effects on
the environment, this is an area where they can develop to reduce their carbon
footprint (CO2 footprint) (Volvo Cars, 2025). Furthermore, the European Union,
in 2023, presented a proposal on circularity requirements for vehicle design and
end-of-life (EoL) vehicle management. It includes a requirement that each new
vehicle include at least 25% of post-consumer recycled (PCR) plastic, and 25% of
that material should come from recycled end-of-life vehicles (European Commission,
2023). This may also be a significant motivator for development.

To minimize their CO2 footprint and follow the regulation that may be implemented,
Volvo Cars would like to decrease the amount of virgin polypropylene (PP) in their
hard trim panels, shown in Figures 1.1 and 1.2. The hard trim panels consist
of: pillars, for example where the seatbelt is located, there are both upper and
lower pillars, threshold, and tailgate panel and window frame located in the trunk.
Because of safety reasons only lower pillars are made out of recycled material since
the upper pillars have airbags inside them. Today their hard trim panels consist
of 30% post-industrial recycled (PIR) PP. The goal is to use as high percentage of
recycled PP as possible in their hard trim panels while still meeting technical and
aesthetic requirements. The materials that will be investigated in this project are
PCR PP since that is the change that Volvo Cars aims to implement.

Figure 1.1: The hard trim panels

2



1. Introduction

Figure 1.2: Close-up of one of the hard trim panels, the threshold

1.1.3 Collaborating Companies - Polykemi & Rondo Plast
AB

Polykemi is a family-owned company that produces tailor plastic compounds accord-
ing to the requirements of their costumers. The company does not have a standard
product, instead they produce what the customer requests. Their compounds are
based on virgin material and/or high-quality recycled raw materials, customized
with the help of relevant reinforcing agents and additives. The high-quality recycled
raw materials that the company uses come from Rondo. Polykemi has production
sites in Sweden, the United States, and China that all use local suppliers. The
total production capacity is estimated to be 130 000 tons, with their biggest cus-
tomer segment being the automotive industry (Axrup, Lindqvist, & Svenmo, 2025),
(Polykemi, 2025).

Rondo Plast AB, known as Rondo, is a subsidiary of Polykemi, with a business
idea focused on providing recycled technical polymers through grinding, quality
assurance, and re-granulation. The company started in 1980. Prior to that, the
operations were a division within Polykemi, but the time had come for it to function
as an independent company. Initially, the company handled a lot of polyethylene
and polystyrene but gradually evolved into a complete plastic recycling company
handling all types of plastics. Today, it is one of the most modern plastic recycling
companies in Northern Europe, specializing in technical plastics (Axrup et al., 2025),
(Rondoplast, 2025).

1.2 Purpose
The purpose of this study is to support Volvo Cars in updating the composition of
recycled plastic and virgin material in the production of hard trim interior panels.
This study will provide a starting point for future research by identifying an area
that offers potential to optimize the percentage of recycled material, rather than
providing an exact optimal figure.

3



1. Introduction

1.3 Aim
The aim of this project is to determine the maximum feasible percentage of post-
consumer recycled polypropylene that can be utilized in the hard trim interior panels
used by Volvo Cars. This without compromising the technical or aesthetic require-
ments while reducing their CO2 footprint.

1.4 Research questions
The project will be guided by four research questions. They are the following:

• What is the maximum percentage of PCR PP that can be incorporated into
interior hard trim panels while maintaining the same, or increasing, mechanical
properties as the currently used material?

• What is the maximum PCR PP limit that can be applied while still meeting
the aesthetic requirements for interior hard trim panels?

• How does aging of PCR PP affect the mechanical properties?
• How does the CO2 footprint of the interior hard trim panels change depending

on the amount of recycled content?

1.5 Limitations and Demarcations
The project will be based on one of Volvo Cars’ supplier of the PP granules, Polykemi
who has provided material samples with different percentages of recycled PP. More-
over it will be based on Polykemi’s subsidiary Rondo, who is responsible for upgrad-
ing the PCR material to re-granulate for Polykemi to use.

Recycling of plastic and how to use it differs between both countries and companies.
Therefore it is most efficient to focus the research on Polykemi’s and Rondo’s PP
granules since that is what Volvo Cars uses today for the panels. The samples were
ordered in advance of the project start due to time constraints. Thus, the ordered
samples with respective percentages of recycled PP selected by Volvo Cars will be
used. The project’s own time limit, 21 weeks, implies that the material will not
be able to be aged for as long as would be desirable. The aging performed in the
project will be 500h and 1000h, which is considered a limitation.

Moreover, the tests and analyzes performed in the study will be based on the dog-
bone and plate samples provided. This implies that tests and analyses of the actual
components are not included in this project.

Lastly, as mentioned in Section 1.2, the results from the study will not imply an
exact percentage of recycled PP that should be implemented in the hard trim interior
panels but more of a guidance of what could be used. This will provide support for
future research for Volvo Cars and guide their upcoming decision making.

4



1. Introduction

1.6 Social and ethical aspects
In a project of this nature, it is crucial to take into account the societal, ethical, and
ecological aspects that may be impacted. This section will touch upon these aspects
and some possible affects. An ethical consideration that needs to be considered is
related to material sourcing and material production. This includes ensuring that
the recycled PP used is ethically sourced and not tied to exploitative labor practices
or unregulated waste management systems. This aspect is also considered a societal
aspect since it is equally important that the recycled PP does not compromise safety
features or release harmful substances in any phase of the life cycle.

Moreover, it is important to present the percentage of recycled content and its
environmental benefits honestly in the marketing and communication to avoid any
suspicions of greenwashing, meaning a company appearing more sustainable than
they are (Cambridge University Press, 2025).

Furthermore, it is essential to develop hard trim interior panels that can themselves
be recycled after the vehicle’s end of life, to maintain the circular economy principles.
This includes ensuring that the PP is of high quality to facilitate recycling, as well
as ensuring that the panels can be easily separated from the vehicle during waste
management. This aspect can also be considered an ecological aspect since the
design to easily separate the panels will contribute to a higher amount of material
being recycled and thereby minimizing the landfill waste.

5



1. Introduction

6



2
Research background

This chapter provides an overview of the essential background information related
to the project. It outlines key concepts and relevant topics that inform the project’s
objectives and context.

2.1 Automotive Interior Hard Trim Panels
Automotive trims are plastic components that can be installed both inside and
outside of the vehicle. The inside trims, or interior trims, serve both aesthetic and
functional purposes. This since they are designed to elevate the visual appeal of
the interior while being functional and providing safety. Moreover, the trims are
used to conceal the intricate electrical and mechanical components that manage the
vehicle’s locks, windows, and other features (Shaisundaram & Vignesh, 2023).

The interior hard trims of cars are manufactured using injection molding. The
method implies that thermoplastic resin pellets are melted, injected into a mold,
and then cooled back to a solid state in a new shape (Shaisundaram & Vignesh,
2023). Injection molding allows for complex geometries with tight tolerances, of-
fers high repeatability and reliability, and is very efficient (Sybridge, 2023). Hard
trims manufactured through injection molding provide various vital functions such
as protecting passengers from sharp edges and corners, offer good stability and duc-
tility, are capable of withstanding high temperatures, provide stiffness performance
when subjected to load, ensuring a tight fit during assembly, and lastly exhibit good
impact resistance (Shaisundaram & Vignesh, 2023).

2.2 Polypropylene as a Material
PP is a type of thermoplastic polymer which implies that the material becomes
soft and moldable when heated up, and solidifies again when cooled down. This
process is reversible, meaning that the material can be heated, shaped, and cooled
multiple times without significantly degrading (Press, 2025). The polymer is derived
by combining propylene molecules. Most propylene monomer comes from the steam-
cracking process where naphtha, which is a fraction of crude oil, is heated to break
it down. In this cracking process propylene is mostly a by-product since the target
product is ethylene monomer. Because of this propylene is produced at various
ratios depending on the crude oil feedstock. Today many cracking processes contain
a propylene plant closely connected to being able to effectively collect the propylene

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2. Research background

from the cracking process (Shubhra, Alam, & Quaiyyum, 2011).

The melting point of PP is influenced by several factors, leading to a melting point
that is not a fixed value, but rather a range of values. One of the key factors is
the molecular weight distribution. PP can consist of molecules of varying lengths
(molecular weights). The longer chains can interact more strongly, which may raise
the melting point, while the shorter chains may melt at a lower temperature. More-
over, the melting point also depends on the crystallinity, which means the degree
of crystallinity in the polymer. Higher crystallinity implies more ordered regions,
thus not amorphous, which means higher melting temperatures and vice versa. The
factor of additives may also affect the melting point of the material. PP is often
not a clear material since it is often mixed with various additives and fillers. These
additives, depending on what they are, can both raise or lower the melting point.
Furthermore, the processing conditions affects the melting temperate. This since the
way the polymer is processed can affect the final structure of the PP. For example,
slow cooling often implies higher crystallinity, compared with fast cooling that often
results in a more amorphous structure. It is also possible that the PP can crystal-
lize into different structures or polymorphs within the material. This means that
different areas of the material may have its own melting point. The typical melting
point for PP falls within a range of approximately 160°C to 170°C, depending on
the specific characteristics and conditions of the material (Prototyping, 2025).

PP is a highly versatile material with a wide range of properties and characteristics.
The properties include (British Plastics Federation, 2025), (RT Prototype, 2025):

• Semi-rigid - meaning that it combines both flexibility and stiffness.
• Translucent - enables some light to pass through while still maintaining its

structural integrity.
• Good chemical resistance - can maintain the integrity, strength, and func-

tionality even when exposed to harsh chemicals over time.
• Tough - ability to withstand physical stress and impact without easily break-

ing or deforming.
• Good fatigue resistance - endure repeated stress or bending without losing

its shape or mechanical properties.
• Integral hinge property - it can bend repeatedly without cracking.
• Good heat resistance - it can tolerate relatively high temperatures before

it begins to deform or lose its functionality.
• Low water absorption rate - has a low tendency to absorb water or moisture

from its surroundings, meaning it is considered hydrophobic.

Moreover, the density of PP is 905 kg/m3, which is considered relatively low. The
lower density makes PP lightweight, which is beneficial for applications where weight
reduction is important, such as automotive parts (British Plastics Federation, 2025).

8



2. Research background

2.3 Post-Consumer and Post-Industrial Recycled
material

When recycled plastic is used, it can be either PCR or PIR. Which of them to use
depends on a lot of factors such as the required quality, the available feedstock and
the price (Alcion, 2025).

PIR refers to plastic discarded from the industry. It is the material that does
not make it to the market and can be waste from packaging, scraps, electronic
components, and cut-offs from the production process. Since it has not been used
as a product the material is often of good quality and can be recycled and reused for
the same product or a new (Alcion, 2025). This also means that the waste is clean
and without any contamination, making it easier to recycle (Machinery, 2025).

PCR is plastic that has been gathered, sorted, and processed for reuse after it has
served its purpose as a consumer product. In other words, it is plastic that has
been used by consumers, recycled, and then repurposed to create new products.
Examples of household or commercial waste that contribute to PCR plastic include
PET bottles and shampoo containers. The advantages of incorporating PCR into
manufacturing include that it minimizes plastic waste in landfills and saves natural
resources, since it reduces the need to extract and process virgin raw materials.
However, a limitation with PCR plastics may imply a reduction in the quality and
durability of the material compared to virgin plastic (Alcion, 2025). Furthermore,
inconsistent color dispersion may affect the overall color of the desired part which
implies an increase of needed additives such as pigment. The increased additives
may in turn affect the mechanical properties of the material (Packaging, 2021).

2.4 Mechanical recycling
To reduce the environmental impact and resource inefficiency of plastics, scholars
agree that prioritizing recycling over energy recovery and landfilling is essential. In
addition to this, efforts should focus on decreasing plastic production, encourag-
ing reuse, and increasing consumer awareness of waste management (Commission,
2023). One way, and the main way, of recycling plastics is through mechanical recy-
cling. This recycling method implies processing of waste into secondary raw material
without substantially changing the chemical structure of the material. In the case
of plastics this implies that the polymer chains are not chemically disrupted in the
recycling process (Royal Society of Chemistry, n.d.), (Shen & Worrell, 2024).

To convert the plastic waste into secondary raw materials five steps are followed. The
first step is to sort and separate the waste according to its shape, density, size, color
or chemical composition. The collected mix of plastic will typically include various
types, particularly if PCR waste. PIR waste on the other hand is usually relatively
pure. PCR waste normally contains non-plastic contaminant, such as small metal
pieces, wood chips, or labels, which must be removed firstly. To further enhance the
material quality the plastics need to be separated into different types, however, this

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2. Research background

task is proven very complex. Multiple methods and techniques are used in various
combinations to perform this task. Common methods include, (Commission, 2023),
(Shen & Worrell, 2024):

• Eddy current separator - when an electric current that occurs when chang-
ing the magnetic field within a conductor and is used to separate nonferrous
metals.

• Sink-float separation - when waste is separated based on the specific weight
of the material relative to the fluid.

• Drum separators/screens - separates materials based on the particle size.
• Induction sorting - when the material is sent over a conveyor belt with a

series of inductive sensors underneath that has the ability to locate different
types of metal.

• X-ray technology - can distinguish between different types of material based
on density, and near infrared sensors (NIR), that can distinguish between
different materials based on the way they reflect light.

The attainable level of purity implies a balance between energy costs and market
demands, this leads to that some impurities are inevitable. The maximum achievable
purity that can be accomplished when separating mixed plastic waste is around 94-
95%. High-quality recycled materials suitable for manufacturing require a purity
level of at least 98%. Because of this, further refining is crucial (Commission, 2023),
(Shen & Worrell, 2024).

The next step is if the plastic is not processed at the sorting site, in that case it
undergoes a baling process where the material is shredded to make transportation
easier (Commission, 2023), (Shen & Worrell, 2024).

The third step implies a decontamination process to remove further impurities and
contaminants from the plastic. This is done by washing the material. Either cold or
hot water, up to 60°C, may be used even though the usage of cold water may result
in an increased use of chemicals and mechanical energy. The wastewater from the
washing is often treated in-house for reuse. The washed flakes are then dried until
they contain less than 0.1% of the total weight of the flakes moisture and are ready
for reprocessing (Commission, 2023), (Shen & Worrell, 2024).

The final step includes that the plastic is ground into smaller flakes. The most
applied technique for this is extrusion. This technique implies that the material
is firstly blended and then injected in the extruder. There it comes in contact
with a rotating screw that forces the plastic flakes forward into a heated barren at
the desired melt temperature. The pressure causes the plastic beads to gradually
mix and melt as they are forced through the barrel. The melt is then degassed to
eliminate oils, waxes, and lubricants. Lastly, the molten plastic is pushed through
a sieve to filter out impurities, cooled, and pelletized. After extrusion phase the
pellets are ready for the final processing where they are used to create the final
product (Commission, 2023), (Shen & Worrell, 2024).

Today, mechanical recycling is the top option for recycling of plastics since it has the
lowest carbon footprint and is optimal in terms of minimizing overall environmental

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2. Research background

impact. A limitation with mechanical recycled plastics is that it tends to continu-
ously degrade in the process and are thus unable to retain quality after one or more
recycling loops (Commission, 2023). Moreover is the potential risk of introduction of
impurities, frequently due to inadequate sorting practices (Royal Society of Chem-
istry, n.d.). Furthermore, a central limitation is that mechanical recycling can only
handle specific (homogeneous) plastic types and requires thorough pre-sorting and
cleaning. A consequence of this is that the method is unsuitable for a significant
portion of end-of-life plastics collected (Commission, 2023), (Shen & Worrell, 2024).

Another consequence of mechanical recycling is that it exposes the material to
thermo-mechanical and thermo-oxidative conditions. These conditions can trigger
a range of degrading reactions such as chain scission, branching, and eventually
cross linking. Chain scission refers to the breaking of polymer chains into shorter
segments, leading to the formation of low molecular weight chains, and is the most
dominant consequence, see Figure 2.1 (Zhang et al., 2024). The shorter molecular
chains, or lower molecular weight, will have a lower boiling and melting point com-
pared to the original molecules (Higginbotham, 2020). Lower molecular weight will
also make the material respond easier to stress, since it increases mobility of the
molecules. Thus, the strength and E-modulus will be reduced with shorter chains.
Longer chains lead to more entanglement which makes the material stretch more
before rupturing and have higher impact resistance due to more energy needing to
break the bonds (Bamberger Amco Polymers, 2024). The degree of degradation is
affected by several factors, including extrusion speed, processing time, presence of
oxygen, and temperature (Zhang et al., 2024).

Figure 2.1: Chain scission via (Hollaway, 2013)

2.5 Chemical recycling
Even though plastics are generally recycled mechanically, some plastics can not be
recycled this way. The reasons for this may, for example, be because of the charac-

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2. Research background

teristics of the material or due to low purity. The low purity may be a consequence
of being mixed with other plastics, being composites, being laminated with multiple
layers, or containing additives and fillers (Shen & Worrell, 2024). An alternative
to mechanical recycling is chemical recycling. The name chemical recycling is an
umbrella term that describes a range of different technologies to recycle EoL materi-
als. In common with all different technologies, they include changes in the chemical
structure of the material with the intent of producing basic chemicals or feedstock
for the chemical industry that can be turned into, in this case, new plastic. Chemical
recycling has the capacity to treat more heterogeneous plastic waste streams with
certain levels of contamination compared to mechanical recycling, which does not
have this potential. However, chemical recycling has other limitations. The high en-
ergy intensity of the processes involved makes the method economically challenging,
therefore relying profoundly on the demand for recycled feedstock. Furthermore,
chemical recycling plants are in need of a stable and continuous supply of feedstock
in large enough quantities to remain economically viable. Another issue involves
production losses and the resulting changes in yields, which are greatly affected by
the quality of the feedstock. In addition, there may be a range of co-products, such
as fuels (Commission, 2023).

2.6 Feedstock of Post-Consumer Recycled Plastic
In 2022 Naturvårdsverket did a mapping of plastic flows in Sweden with data col-
lected from 2020. The data is for all types of plastic, not just PP which is the
material of interest, but still represents recycling rates in Sweden. From the specific
flow of plastic, meaning a specific type of product category that has been separated
and not mixed with others, was the total amount of waste 644 000 tons. Packaging
(PP plastic) generated the most waste with approximately 320 000 tons. In the
mixed flow, plastic made up between 690 000 and 1 million tones. The construction
industry generated about 120 000 tons of plastic waste, followed by the automotive
and tire industry which contributed with 94 000 tons. These are the largest flows
that can be traced back to a product category or source. Of all this plastic waste,
approximately 120 000 tons were material-recycled in 2020. More than 1 100 000
tons of the plastic waste went to energy recovery and about 76 000 tons of plastic
and rubber waste was used in the cement industry (Naturvårdsverket, 2024).

In 2021 the average plastic waste of a person living in the European Union was
36,1kg. Between 2010 and 2021 the amount of plastic packages generated per person
increased by 29% (+8,1kg per person). The total amount of plastic waste in the EU
2021 was 16,13 million tons, of which approximately 6,56 million tons were recycled
(Europaparlamentet, 2024).

2.7 Carbon footprint
The CO2 footprint refers to the total amount of greenhouse gas (GHG) emissions
that are produced directly or indirectly by an activity, such as producing a prod-

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2. Research background

uct, or accumulated during a product’s life cycle. In recent years, it has been used
as an indicator of environmental sustainability and can help find hotspots and im-
provement areas (Scrucca, Barberio, Fantin, Porta, & Barbanera, 2021). The CO2
footprint is calculated by multiplying the activity data, for example amount of ma-
terial used, electricity consumed, transportation, with the activity emission factor
(Dormer, Finn, Ward, & Cullen, 2013). The emission factor is a value that repre-
sent the amount of GHG emitted and can be expressed as a CO2 equivalent (CO2e).
Since the emissions contributing to global warming are not just carbon dioxide, a
CO2e is used which is a measure of the effect of different GHGs. It converts all
GHGs into the equivalent amount of carbon dioxide with the same global warming
potential (GWP) (Commission, n.d.-a). The GWP is used to describe how potent a
greenhouse gas is based on how long it remains active in the atmosphere. Currently,
the GWPs used are calculated over 100 years and carbon dioxide is the reference
with a 100 years GWP of 1 (Commission, n.d.-b).

Only using the carbon footprint can be misleading since environmental problems
include more than climate change, such as resource use, toxicity impact, and eu-
trophication. Thus it is important to not only rely on the carbon footprint when
evaluating the total environmental impact (Scrucca et al., 2021).

2.8 Tensile test
A tensile test helps to select a material since tensile properties are often included in a
requirement list. It determines the material’s tensile strength by stretching a sample
in a machine until breakage. The sample is often shaped as a dog bone, meaning
bigger ends for the machine to grip and a smaller gage that deforms. The primary
focus is on creating a stress-strain curve. During the test the force is recorded as a
function of the elongation of the sample. That function is then normalized to the
dimension of the sample to get the stress-strain curve since then it is independent
of the specimens dimensions.

Among the various mechanical tests conducted on thermoplastic polymers, the ten-
sile test is the most poorly understood, with its results frequently misinterpreted and
misapplied. Originally adapted from materials exhibiting linear elastic stress-strain
behaviors, this test is not always suitable for polymers. Nevertheless, standardized
methods like DIN 53457 and ASTM D638 are available for assessing the stress-strain
characteristics of polymeric materials (Osswald, Baur, Brinkmann, Oberbach, &
Schmachtenberg, 2006).

2.9 Impact test
An impact test is used to evaluate a material’s ability to absorb energy during
a sudden or impact load. The primary goal is to assess a material’s toughness
(Callister & Rethwisch, 2017).

Using the absorbed energy the impact strength can be calculated. According to the

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2. Research background

ISO 179-1:2023(E) for an unnotched sample the impact strength is calculated as:

acU =
(

Wc

h · b

)
× 103 (2.1)

Where Wc is the corrected energy, in joules, absorbed by breaking the test speci-
men, h is the thickness, in millimeters, of the test specimen, and b is the width, in
millimeters, of the test specimen.

2.10 Differential Scanning Calorimetry
Differential scanning calorimetry (DSC), is an efficient analytical tool used to iden-
tify and characterize the physical properties of a polymer. Properties such as melting
temperatures, crystallization, mesomorphic transition temperatures, meaning the
temperatures at which a material transitions between different structural phases,
can be determined using this method (RISE, 2025), (Schick, 2009).

The percentage of crystallinity of the material analyzed by DSC is calculated using
the following formula (NETZSCH Analyzing & Testing, 2025):

Crystallinity (%) =
(

∆Hm − ∆Hc

∆H0
m

)
× 100 (2.2)

Where ∆Hm is the measured melting enthalpy, ∆Hc is the cold crystallization en-
thalpy (if present), and ∆H0

m is the melting enthalpy of a 100% crystalline polymer.
The value for ∆H0

m is the same for each type of material and can therefore be found
in literature, for PP the value is 207 J/g. The subtraction that occurs in the numer-
ator, ∆Hm − ∆Hc, takes the enthalpy area of the melt and subtracts the enthalpy
area of the post-crystallization or cold-crystallization, that can be calculated from
the DSC-diagram. The result of the calculation gives the crystallinity as a percent-
age. The amorphous content can be determined by subtracting the crystallinity
percentage from 100 (NETZSCH Analyzing & Testing, 2025).

Amorphous materials are defined by a short-range order, with atoms bonded in ran-
dom and disordered spatial arrangements. The reason for this structure are factors
that do not allow the formation of a regular arrangement, usually by a rapid solidi-
fication method (Xu & Xu, 2017), (Tanzi, Farè, & Candiani, 2019). Some materials,
especially many polymers, can have macromolecules that are efficiently packed in
some regions, that produces a higher degree of long-range order, while other regions
have a short-range order. This implies that some regions may be crystalline while
others are amorphous. Materials with this structure are called semicrystalline ma-
terials. In materials that have an amorphous structure the molecules are bonded
together by weak bonds, this implies lower mechanical properties compared to ma-
terials with a crystalline structure (Tanzi et al., 2019). Because of the more ordered
and packed structure in a crystalline material, it will affect the ability to deform.
Thus, an increase in crystallinity will lead to a greater stiffness and a higher melt-
ing temperature. It also implies reduced ductility, since more order will limit the
movement of molecular chains, which makes it more brittle (Chanda, 2013). The

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2. Research background

molecular weight will also affect the crystallinity, shorter chains can form crystals
more easily and faster since they are not as entangled as longer chains tend to be.
However, a material with a lower molecular weight can be weaker in strength even if
they have a higher degree of crystallinity (Whisnant, 2022). The crystallite size can
also effect the mechanical properties of the material (Whisnant, 2023). Crystallites
can make the material less prone to crazing and shear yielding, these are mechan-
ical properties that help to absorb energy (Ludwig & Davidenkov, 2003). Factors
that affect the crystalline structure and degree of crystallinity is, for instance, the
processing conditions and cooling rates (Strasser & Hanss, 2023).

2.11 Aging of material
To determine how components and materials will change over time, the method ag-
ing or artificial aging is used. This method implies that the material or component
is exposed to a condition, such as radiation, heat, or chemicals, during a determined
period of time to simulate real life aging. The determined time period that a compo-
nent or material should be exposed to the relevant condition depends on factors such
as what material/component it is, in what environment the material/component is
expected to be used in, or how the material/component is expected to be used. The
advantage with artificial aging is the possibility to accelerate the aging process and
get results faster compared to having to age the material or component naturally
which might take years (Izdebska, 2016).

When aging is carried out with heat, it is performed in a chamber with a constant
temperature where the material is placed. The heat will cause thermal degradation,
which in the case of a polymer implies a change in the structure due to shortening
of its chain. Thermal degradation can occur in the whole volume of the polymeric
material and will affect the properties of it. Thus it is important to understand what
influence aging and degradation have when choosing and sourcing a material, not
only for the main use, but also for storage of the material and recycling (Izdebska,
2016).

Furthermore, the crystallization will also be affected by the heat. A temperature
closer to the melting temperature during a longer time period will enable more
movement of the polymer chains. They can fold into a more structured order, and
an increase in crystallinity will occur (Nurazzi et al., 2023).

2.12 Perceived quality
Perceived quality (PQ) refers to the impression the customer gets of a product,
service, brand, or business derived through sight, sound, touch, and scent (Roffey,
n.d.). Having the term "perceived" in its name suggest a factor of subjectivity, but it
is not fully subjective or objective. Though PQ is how and what the customer feels
about a product, which will be person depending. A first impression and opinion
is formed within minutes and determines if a customer trust a product, if it is of
high quality or not. What is evaluated is often not tied to actual reliability, such as

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2. Research background

strength, durability. Therefore it is important to consider PQ so that the customer
will accept the product, but also develop them to be reliable (Solin & Curry, 2023).

At Volvo Cars perceived quality on interior plastic components is done by analyz-
ing the color and gloss of the material. This implies both visual observation and
measuring of the material and comparing with a master (the reference). The visual
observation is performed in a light booth that illuminates a predetermined amount
of light. In the booth the component is observed from different angles next to the
master. The color, gloss, embossing (surface), and defects are of interest. Since the
assessment is done by humans there is a risk that the result is subjective. Therefore,
it is always done by at least two people, and if they disagree a third party is brought
in. Measurements are also conducted to compare with the visual outcome; however,
greater emphasis is placed on visual assessment, as it reflects what the customer
will ultimately perceive. This implies that if a material passes visual assessment
but measurements indicate it falls outside the specified tolerances, it will still be
considered acceptable (Jacobsson & Ljungholm, 2025).

Measured parameters are color and gloss, which is done using a spectrophotometer
tool and a glossmeter respectively. A spectrophotometer illuminates the sample with
a controlled light source and measures how the sample interact with the light. A solid
sample will absorb some of the wavelengths from the light and reflect some. The
reflected light hits a detector that measures the intensity of specific wavelengths
of the visible spectrum. For example, if a sample absorbs all light over visible
ranges and reflects none of visible wavelengths, it will appear black (X-Rite, 2022).
Since there are many parameters that affect how colors are perceived by human
eyes, the International Commission on Illumination (CIE) has created a model that
standardized and simplifies color communication. It is called L*a*b or CIELAB,
and uses a color space, see Figure 2.2, to distinguish color differences with three
values: L, a; and b.

Figure 2.2: Color space used in PQ via (Mouw, 2018)

"L" stands for lightness; "a" represents the green-red axis, and "b" the blue-yellow
axis, and these are the values the spectrophotometer measures. The master is set at

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2. Research background

the origin of the circle which the measurements are compared to, giving the values:
∆L, ∆a, and ∆b (Datacolor, 2023).

The gloss, or specular reflection, of the material is measured with a glossmeter. It
projects a beam of light at a fixed intensity and angle. The amount of reflected light
at the same but opposite angle is measured by a detector. The result is given in
Gloss Units (GU) which is a scale ranging from 0 to 100, where 0 is perfectly matte
and 100 is glossy. It is based on a reference that is a highly polished black glass
standard with a defined 100GU at the specified angle (Instruments, 2025).

2.13 Polykemi’s and Rondo’s functions and pro-
cesses

A primary part of Polykemi’s industry implies working with recycled material. This
means that Polykemi is not the original source of the material that they use. Instead,
they obtain and purchase recycled material. As a result, it becomes crucial to know
the origin of the recycled material and prioritize traceability. The purpose of this
is to understand its previous use, identify the raw material, and verify that the
material is in fact recycled. To do this Polykemi has to work closely with their
sources and rely on their trustworthiness. As a result, they mainly source recycled
material from manufacturing companies in the form of PIR material, as they can
trace the raw material throughout the entire production process, and less from
recycling companies where the origin is less traceable. Comprehending the origin
of the material is easier to do with PIR material due to the fact that it is mainly
bought directly from manufacturing companies that handle the material from raw
material. Sources of PIR material can include, for example, packaging, spills, and
nonwoven fabrics. The traceability with PCR on the other hand is more difficult.
The reason for this is that the origin of the material is most often unknown. Sources
of PCR material can, for example, come from communal recycling (chairs, plastic
crates, toys etc.) and household recycling (food packaging, bottles, bags etc.), but
can also be marine ropes and ship’s ropes (Axrup et al., 2025).

Polykemi’s PCR material is delivered to them from their subsidiary Rondo, who
handles the upgrading of the sourced recycled material. This implies to upgrade
sourced recycled material of inadequate quality into better quality. Polykemi receives
re-granulated PCR without contamination such as heavy metals, paper remnants,
or wood chips. Before arriving to Polykemi and Rondo the material has undergone
many processes such as being collected, sorted and washed. These processes are
not usually being handled by the same operators, thus the traceability and origin is
difficult to determine. The long process and many steps to obtain the PCR material
require a well-built infrastructure that makes the PCR material more expensive
than the PIR material. The many steps of the process also lead to a higher CO2e
compared to the respective PIR material. This is the reason why PCR is currently
not used as widely. At Polykemi PCR material is only used when requested by the
customers (Axrup et al., 2025).

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2. Research background

The process of Polykemi being able to deliver PP components consisting of recycled
material begins at Rondo. The PCR PP arrives to Rondo mixed and shredded,
ahead of this it has already been washed, see Figure 2.3. Despite the fact that the
material has been washed it is in the majority of cases still dirty and contaminated,
for example containing traces of metal, paper remnants or wood chips. To determine
if this is the case, lab tests on the received PCR PP is performed. These test include
for example an XRF-test, or X-ray Fluorescence, that determines if there is any
contamination, mainly heavy metals, in the material.

Figure 2.3: The shredded PCR PP that arrives to Rondo

To remove dirt and contamination the material is filtered through an erema extruder
machine. This machine uses a laser filter to remove any impurities and then gran-
ulates the material, see Figures 2.4, 2.5, 2.6, 2.7. Following this step, additional
lab tests are performed , where the now filtered granulates, are again examined
to see if they contain dirt or impurities. Other mandatory lab tests are melting
index, fluidity, and mechanical properties to ensure that the quality is sufficient.
After these tests, the material is labeled according to its quality. After labeling,
the granulate is ready to be sent to Polykemi for production of the requested final
material-compound (Axrup et al., 2025).

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2. Research background

Figure 2.4: The erema extruder
machine that removes

contamination

Figure 2.5: The extruded
contamination by the erema

machine

Figure 2.6: The granules
created by the erema machine

Figure 2.7: Closeup of the
granules

The granulate arrives at Polykemi from Rondo. Polykemi’s task is then to create
a material compound that is requested by the costumer. This compound is made
by mixing granulate from suppliers and qualities to obtain the desired properties.
Other additives such as pigment and fiberglass are also added, depending on the
customer’s requirement. Virgin material is also added to the compound to stabilize

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2. Research background

it and obtain better quality, but also to facilitate the coloring of the material. Since
the PCR material contains a mix of colors, additional pigment is required to receive
the desired color. To ease the coloring some virgin material may therefore be added
since it is easier to color. When the desired mix is completed, the compound is
then put in an extruding machine that uses two screws and heats the mixture to
245-250◦C where it is extruded into long spaghetti-like strings, see Figures 2.8 and
2.9. They are then immediately cooled down in water and dried. Finally, they are
cut into new granulates and packaged, ready to be sent to customers (Axrup et al.,
2025).

Figure 2.8: The spaghetti-liked
strings cooling down i water
right after being extruded

Figure 2.9: The spaghetti-liked
strings drying and on their way

to be cut into granules

Regarding the available feedstock of PCR PP it is good and sufficient according
to Polykemi. Furthermore Polykemi states that they are able to produce upgraded
PCR PP of good and consistent quality even if the source of material varies (Axrup
et al., 2025).

2.14 Sample Production Details
In this project, the material samples that have been analyzed and tested have been
provided by Volvo Cars’ supplier Polykemi. The samples were produced using the
method mentioned in Section 2.13. On the request of Volvo Cars’, they delivered six
variants of plastic to investigate, all with a different percentage of recycled plastic
in them. All samples were made with the same amount of additives and color
pigments for charcoal solid. The additives were 17% of talc, UV, impact resistance,
and scratch resistance. The different variants were as follows:

20



2. Research background

• 30% PIR PP, 45% virgin material, additives
• 30% PCR PP, 45% virgin material, additives
• 40% PCR PP, 35% virgin material, additives
• 50% PCR PP, 25% virgin material, additives
• 60% PCR PP, 15% virgin material, additives
• 70% PCR PP, 5% virgin material, additives

An amount of 35 dogbones of each percentage and a number of 10 plates of each
percentage were provided. They were produced using injection molding with the
following settings:

Dogbones:
Injection molding: Arburg 470C screw Ø 35mm
Clamping force: 50 ton
Temperature profile cylinder: 230 – 230 – 230 – 220 – 200 – 40
Temperature tool: 40°C

Plates:
Injection molding: Arburg 420C screw Ø 30mm
Clamping force: 100 ton
Temperature profile cylinder: 240 – 240 – 235 – 235 – 230 – 40
Temperature tool: 50°C

21



2. Research background

22



3
Methods

This chapter outlines the methods utilized in the project, detailing the procedures
and techniques used. It also provides a rationale for the selection of these methods,
explaining their relevance and suitability for addressing the research objectives.

3.1 Literature review
The project commenced with a literature review to establish a broader perspective
regarding the background for the project and acquire knowledge on relevant subjects
such as PP as a material, different recycling methods, the tests that was to be
performed in the project etc. The literature review was performed by brainstorming
relevant and important subjects to understand and examine. When the preliminary
list was completed the research began by searching for literature and sources related
to the subjects. Search engines used for this task were Google, Google Scholar and
Chalmers Library. The result of the literature review can be found in the research
background, see Chapter 2.

3.2 Interviews and study visits
Interviews where held with personnel at Volvo Cars, Polykemi and Rondo. The aim
with the interviews was to collect information on how processes are performed and
gain more understanding regarding the subject. The main study visit was made
to Polykemi and Rondo located in Ystad where a interview with Johan Svenmo,
Patrik Axrup, and Patrik Lindqvist was held. At Volvo Cars interviews were con-
ducted with Hanna Ljungholm and Inger Jacobsson from the PQ department. The
interviews that were conducted were unstructured to allow the respondent to speak
freely and elaborate on their thoughts. In an unstructured interview, the questions
and in which order they are asked do not have to be set before. It is a flexible way
of interviewing adapting the conversation to the situation and following interesting
threads that emerge during the interview (George, 2022a). They are usually used
for qualitative data, meaning non-numerical (George, 2022b). Questions were pre-
pared beforehand but were asked as deemed appropriate. They were recorded and
notes were also taken during the meeting. Since most of the information from the
interviews was used as background information, no transcription was done. Instead,
a summary of the notes was done which can be found in the Appendix A.

23



3. Methods

3.3 Aging
To determine if and how the materials would be affected by time, aging was carried
out, see Figure 3.1. 20 samples of each percentage were aged in 80◦C without
humidity, ten samples for 500h, and ten samples for 1000h. 1000h corresponds to
3 years in hot market, mentioned in Figure 3.1. If following Volvo Cars’ standards,
see Figure 3.2, the samples should be aging in 75◦C, but in this case 80◦ C was
used instead, as an oven with that temperature was available during the short time
span of this project. The aging was performed without no humidity because PP is
a hydrophobic material, see section 2.2.

Figure 3.1: Description and purpose of aging at Volvo Cars

Figure 3.2: Highlighted part shows the temperature these samples should be
aging in

The samples were put into bags of ten and marked with their respective percentage
and for how long they would be aged, see Figure 3.4. All the bags were then spread
out on the floor of a car that also would be aged for the same amount of time and the
same temperature, see Figures 3.3, 3.4, and 3.5. The car, with the samples placed
on the floor, was then driven into a big "oven" in the form of a container with an
inner temperature of 80◦ C. Before the aging began the samples were taken out of
their respective bags and spread out upon it on the car floor. After three weeks,
meaning 500h, the first samples were removed from the oven and after six weeks,
meaning 1000h, the rest were collected.

24



3. Methods

Figure 3.3: Bags filled with samples placed on the car floor

Figure 3.4: Close-up of the bags
placed on the car floor

Figure 3.5: Samples spread out
on the car floor during aging

3.4 Tensile tests
Tensile tests were carried out in order to be able to measure the mechanical prop-
erties of the materials. All tensile tests were performed at room temperature in the
material lab at Volvo Cars. A tensile testing machine by the brand Zwick Roell was
used. Five samples were used for each aging point, thus 15 in sum, for one material,
and 90 samples in total were tested.

Before the tests could be performed the test specimens were marked with two re-
flexive points with a distance of 80mm using a machine, see Figure 3.6 and 3.7. The
points are marked for two cameras to be able to measure the distance during the
elasticity phase.

25



3. Methods

Figure 3.6: Putting on the
reflexive points

Figure 3.7: Test specimen with
reflexive dots

The width and thickness of the rectangular middle part of the samples was measured
and then entered in the machine program called TestXpert. The sample is first
locked at the top, then the machine resets the force to 0 newton in the specimen,
and then the bottom part of the sample is secured. A distance of 115mm was
established between the locking points in the machine. The test started with that
the two cameras located the marked reflexive points, thereafter the machine began
to apply a force and drag until the sample broke, see Figures 3.8 and 3.9.

Figure 3.8: Cameras locating
the reflexive points

Figure 3.9: Test specimen
during tensile test

After the elastic phase the cameras stopped measuring the distance and from it
was based on the lower beam in the machine. TestXpert produced a stress-strain
curve for each test and a list of other measurements. Among these measurements

26



3. Methods

E-modulus, stress at yield point, strain at yield point, and strain at breakage were
deemed necessary to further analyze. The E-modulus calculated by the program
was determined using the secants method. For the secants method the beginning
of the tensile modulus determination was set to 0,1% strain and the end to 0,15%
strain. In this case, the ultimate tensile strength, meaning the maximum stress, and
the yield stress had the same value, therefore, only one had to be evaluated. The
values were averaged and visualized in bar charts for easier comparison, see Section
4.1 for all results. After the first tests of the unaged material were performed, it
was discovered that what was thought to be 30% PCR PP was actually 30% PIR
PP due to a miscommunication the supplier. The data was still used in the analysis
since it had been obtained, but for further tests only five samples were used, as for
the other material. Thus, the result for the unaged 30% PIR PP consists of the
result from ten samples.

3.5 Impact tests
The execution of the impact tests was carried out with ISO 179-1:2023(E) as a
guideline. The only part that deviated from the standard is that the absorbed
energy, W, by the machine should be in the range of 10% to 80% of the available
energy at impact, in this case meaning between 0,75 J and 6,0 J. To fulfill this the
machine needs to be calibrated carefully, which requires many additional samples to
perform impact tests on. The reason why this could not be achieved in the project
was simply that there were not enough samples to calibrate the machine sufficiently.
This lead to the fact that 20, of the total 90, impacts tests had values greater than
80% of the available energy at impact. According to Kai Kallio, Material Specialist
at Volvo Cars, who helped with the execution of the impacts tests, this is from Volvo
Cars’ perspective, acceptable since the ISO standard is typically used as a guideline
rather than strict rules. However, it is a potential source of error that should be
considered when analyzing the results.

The initial step of the impact testing involved conditioning the samples by placing
them in a conditioning room with the following parameters: 23◦C±2◦ and 50%±5%
humidity. The samples were placed in the conditioning room for approximately 22h,
see Figure 3.10.

Before actual testing could be carried out, the machine needed to be calibrated. This
was done by performing impact tests on some unaged 30% PCR PP samples and
changing the size of the gap where the samples lays in the machine, depending on
the absorbed energy of the tests used for calibrating. The bigger the size of the gap
the lower the absorbed energy, since the supports of the specimens moves further
apart. The goal was to get an absorbed energy around 5 J, meaning approximately
71% of the allowed absorbed energy, since the hypothesis was that the unaged 30%
PCR PP samples were thought to be on the tougher side. This would imply that the
other samples would hopefully be in the allowed range as well. The allowed range
is, according to ISO 179-1:2023(E), between 10% and 80% of the available energy at
impact. The size of the gap that ended up being used for the testing was 31,55 mm.

27



3. Methods

Ideally, the machine calibration would include testing on all of the different samples
to make sure that all would be in the allowed range. Unfortunately, there were not
enough extra samples available apart from unaged 30% PCR PP samples, which is
why these were used. This led to the machine being not perfectly calibrated.

The next step included cutting of the bigger end parts of the samples to be able
to place the sample straight later on in the impact testing machine. The cutting
was done with a cutter, see Figure 3.11, and the result after the cutting is shown in
Figure 3.12.

Figure 3.10: Conditioning the
samples

Figure 3.11: Cutting the samples
into the correct size

The length of the cut samples does not have to be exactly the same for every
sample according to ISO 179-1:2023(E). When calculating the impact strength, the
ISO standard only takes into account thickness and width. The next step was to
perform the actual impact tests. This was carried out by placing and aligning the
cut samples in the machine, see Figure 3.13.

28



3. Methods

Figure 3.12: How the samples
were cut

Figure 3.13: A sample ready for
impact testing in the machine

Then the testing could start, all tests were performed at room temperature. Two
buttons were pressed at the same time, which caused the pendulum in the machine,
see Figure 3.14, drop and hit the sample placed at the bottom. Thereafter it was
observed if the sample broke completely, hinge broke, partial broke, or did not break
at all. Moreover, the absorbed energy shown at the top of the machine on the display,
see Figure 3.15, was noted.

Figure 3.14: The impact test
machine

Figure 3.15: The result shown
by the machine after a test

This was repeated 15 times for each material, five samples for each aging point, in
total 90 tests. When all impact tests were performed and all results were noted,
the impact strength calculations could be performed. The Charpy impact strength

29



3. Methods

of unnotched specimens, acU , expressed in kilojoules per square meter, is calculated
with the following formula:

acU = Wc

h · b
× 103 (3.1)

where Wc is the energy, in joules, absorbed by breaking the test specimen, h is the
thickness, in millimeters, of the test specimen, and b is the width, in millimeters, of
the test specimen.

3.6 Differential Scanning Calorimetry
To perform the DSC test, small samples were cut from the original dog bone samples,
each containing different percentages of PCR PP. To be able to perform the test the
samples needed to weigh between 5-10 mg. They were carefully cut with knives and
weighed to ensure that the weight was within the required range, see Figure 3.16.
Once verified, the samples were placed in the small DSC pan to confirm they fit
properly, see Figure 3.17. Two samples were cut from each percentage of the unaged
material and two samples each of 40% and 70% PCR PP that had been aged for
500h, a total of 16 samples. The reason for why aged 40% and 70% PCR PP was
selected was to examine the two tests with the greatest difference regarding recycled
content and to examine if aging affected the DSC result. The 30% PIR PP material
aged for 500h would have given a greater difference in recycled content, but since
this was the reference sample and not a material of interest in this project, the aged
40% PCR PP was used instead. The reason why the aged 30% PCR PP was not
examined is because it was not done aging at the point for the DSC test. However,
using the 40% PCR PP and 70% PCR PP was sufficient enough for the purpose of
investigating if and how aging affected the crystallinity.

Figure 3.16: Cutting out the small
samples

Figure 3.17: Making sure the samples
fit in the pan

The samples were then prepared for testing. It started with a pan that was placed
on a scale that was then tared so that the sample could be placed there and weighed
again, see Figure 3.18. A hole was punched into the lid using a needle to prevent
pressure from building up in the pan during the test, see Figure 3.19.

30



3. Methods

Figure 3.18: Weighing the
samples

Figure 3.19: Making a hole in
the DSC-pan lid

The lid was then placed on the pan, see Figure 3.20, and then placed in a tool that
sealed them together by pressing down the lid, see Figure 3.19.

Figure 3.20: Placing the lid on
the pan with the sample in

Figure 3.21: Pressing the lid
and pan together

The prepared sample could then be placed in the DSC-machine, see Figure 3.22.
In the computer program, called STAR, the respective weight of the samples and
placement of the pan in the machine were entered to keep track of the different
samples.

31



3. Methods

Figure 3.22: Placing the pans
in the machine

Figure 3.23: The machine
performing the DSC-test

The machine had been programmed to first melt the material, going from -50◦C
to 200◦C, then down to -50◦C to once again be heated up to 200◦C and melt the
material a second time. These temperatures are based on the melting point and
the glass transition temperature that PP has. In the machine the temperature
changed with 10◦C/minute. In addition, 50ml nitrogen/min was pumped into the
surrounding environment in the machine prevent the material from reacting with its
surroundings. The 16 tests lasted approximately 20h altogether. When one test was
performed, the machine automatically performed a new test on the next sample, see
Figure 3.23. Afterwards a graph for each sample was given showing the heating and
cooling process in three separate curves, see Figure 2.10.

32



3. Methods

Figure 3.24: Example of graphs from the DSC-test for 50% PCR PP

Using STARe Evaluation software the enthalpy could be calculated for the heating
curves, see curve 1 (red) and curve 3 (green) in Figure 2.10, by doing integration.
Curve 2 (blue) was not used because it shows the cooling stage of the process which
is not of interest. From the first heating curve, the crystallinity can be calculated
on the basis of thermal history and how the material has been processed, such as
using injection molding. In the second heating curve, all previous processing and its
influence are removed, and the pure material can be analyzed (BARLOG Plastics
GmbH, n.d.). Since the material in the final component is made by injection mold-
ing, the crystallinity in the first curve is more accurately represented. Therefore,
only the crystallinity from the first curve will be analyzed.

Notice that there is a big peak on each graph with a smaller peak on the left. A peak
represents that the material melts. The enthalpy, and in turn the crystallinity, was
calculated separately for both peaks together, only the big peak, and only the small
peak. There was no clear smaller peak for 30% PIR PP and thus the crystallinity
could only be calculated for the big peak. Since two tests were performed for each
material, the average was taken of them and then visualized in bar charts. Further-
more, the peak temperature, meaning the melting temperature, was also illustrated,
see Section 4.3 for results.

3.7 Perceived Quality
Perceived quality tests were carried out to determine the perceived quality factors
of the recycled PP samples. The first test performed was to visually investigate the
samples against the master, also called the reference material, in a light booth. In
this case the master was a PP plate with the identification number 9123691, with
a uni grain surface, in the color charcoal-solid and the value 1,9 in GU. The light-
settings of the light-booth was set to D65, 6500 Kelvin and 1329 lux, this was to

33



3. Methods

represent the environment of daylight. The samples, one at a time, together with the
master, were then placed in the light booth beside each other to visually investigate
the differences regarding color, gloss, embossing and defects, see Figure 3.25 and
3.26. The tests were performed by the two experienced perceived quality operators
Hanna Ljungholm and Inger Jacobsson.

Figure 3.25: Samples in
Spectralight

Figure 3.26: Samples in
Spectralight

The next test included measuring the color of the samples. This was done using
a spectophotometer, see Figure 3.27. When using this tool, different nozzles can
be used to determine how much light should be allowed in during the test. In this
case the tool was set to the light-setting D65 with a specular component included
(SCI), this to represent the environment of daylight. The test begun by measuring
the master and setting its measurements to represent the origin. Thereafter, the
samples were measured one by one and their differences were compared with the
set origin. Three measuring points were taken for each sample. The tests were
performed simply by pressing the nozzle of the spectrophotometer against the sample
and taking the measurement, see Figure 3.29. The results were given in delta L, a
and b. The color and light tolerances for dark interior colors, as appropriate for the
samples in these tests, are as follows:

• ∆L (Lightness): Tolerance ±0.5
• ∆a and ∆b (Color components in the a- and b-axes): Tolerance ±0.2

34



3. Methods

Figure 3.27: The
Spectrophotometer tool used to

measure the color of the material

Figure 3.28: Different nozzles
for the tool that decides how
much light should be let in

Figure 3.29: The Spectrophotometer in use

The last test was to measure the gloss of the samples. This was performed using
a Glossmeter, see Figure 3.30. The test began by firstly measuring the GU of the
master, which in this case was measured to 1,9. After that, the samples’ GU were
measured one by one and noted, also taking three measuring points for each sample.
The tests are executed by simply pressing the Glossmeter on the sample and taking
the measurement, see Figure 3.31. The gloss tolerance for dark interior colors, as
appropriate for the samples in these tests, is ±0,3.

35



3. Methods

Figure 3.30: The Glossmeter
tool

Figure 3.31: The Glossmeter in
use

Using the three measuring points for each parameter, an average was calculated to
compare with the reference and create bar charts. These can be seen in Section 4.4.

3.8 Calculation of Carbon footprint
The CO2 footprint calculations are based on CO2e data supplied by Polykemi. The
values are based on Cradle-to-gate ISO 14044:2016, background data Ecoinvent 3.9
evaluated with Environmental Footprint 3.1. Moreover, the values are based on
the samples provided and used in the project, which in turn come from a PCR PP
source in Sweden with washing in Sweden. However, the PCR PP provider has not
yet fully completed their LCA which implies that the provided CO2e values may
be considered indicative at present. If future sourcing were to come from other
countries, these values would most likely be higher considering the additional need
for transport and the energy type used when washing (Axrup et al., 2025).

The CO2e values used in the calculations are the following (Axrup et al., 2025):

• 30% PIR PP: 1,55 kg CO2e/kg
• 30% PCR PP: 1,63 kg CO2e/kg
• 40% PCR PP: 1,44 kg CO2e/kg
• 50% PCR PP: 1,24 kg CO2e/kg
• 60% PCR PP: 0,90 kg CO2e/kg
• 70% PCR PP: 0,85 kg CO2e/kg
• Virgin PP material: 2,16 kg CO2e/kg

The weights used in the calculations are presented in Table 3.1 and were provided
by Emma Johansson (personal communication, April 3, 2025), a developer at Volvo

36



3. Methods

Cars. They are based on a car of the size of Volvo Cars’ XC40, which approximately
weighs 1 800kg (Volvo Car Sverige AB, 2020). Only parts consisting of the used
material, recycled PP, are used in the calculations, these values are written in bold.

Table 3.1: The part weights of the hard trim interior panels

Part: Amount of part: Material: Weight/part (g): Total weight (g):
A piller upper 2 Textile covered PC/ABS 382 764
A piller lower 2 Recycled PP 77 154
B piller upper 2 Virgin material 794 1588
B piller lower 2 Recycled PP 553 1106
C piller upper 2 Virgin material 484 968
C piller lower 2 Virgin material (in some cars recycled PP) 639 1278
Belt outlet 2 PC/ABS 137 274
Sill front 2 Recycled PP 228 456
Sill extension left 1 Recycled PP 256 256
Sill extension right 1 Recycled PP 278 278
Sill rear 2 Recycled PP 292 584
Brackets sill rear 2 Fiberglass reinforced PP (recycled PP) 22 44
IC ramp 2 Fiberglass reinforced PP (recycled PP) 164 328
Bracket D piller 2 Fiberglass reinforced PP (recycled PP) 138 276
Tail gate panel 1 Recycled PP 2112 2112
Panel window front left 1 Recycled PP 471 471
Panel window front right 1 Recycled PP 365 365

Figure 3.32 shows the parts in Table 3.1.

Figure 3.32: The hard trim panel parts with their separate names

The CO2e calculations consisted of adding all the weights of the parts consisting
of the material used, recycled PP, which gives the total weight of the parts with
the relevant material. Thereafter the total CO2e was calculated by multiplying
the total weight together with each of the CO2e values for the different types of

37



3. Methods

recycled PP. When the values were given, they were also converted to the carbon
footprint of a 33cl aluminum can of Coca Cola to put the value in perspective (CO2
Everything, n.d.). An approximation of 200 000 cars produced a year was used in
the calculations, this is based on the size of Volvo Cars’ factory in Torslanda (Volvo
Car Sverige AB, 2024).

38



4
Results

This chapter presents the results obtained from the various tests conducted during
the project. It provides a descriptive overview of the findings, highlighting key data
and observations.

4.1 Tensile tests
The performed tensile tests results is presented in stress-strain curves and a list of
measured parameters, see Appendix A.2. The following parameters were used to
illustrate the trends in mechanical properties in bar charts:

• Et [MPa] - E-modulus
• σY [MPa] - Stress at yield point
• εY (corrected) [%] - Strain (elongation) at yield point, corrected means it has

been adjusted to better reflect the actual deformation
• εB [%] - Strain at breakage point

Note that in the bar charts, the bars representing unaged 30% PIR PP, consist of
a mean value calculated from ten test results instead of five, as for the rest. This
is due to a misunderstanding that the unaged 30% PIR PP was initially thought to
be unaged 30% PCR PP.

The bar charts for the E-modulus, stress at yield point, strain at yield point and
strain at breakage can be seen in Figures 4.1 - 4.4. The error bars represent the
range between the lowest and highest values.

39



4. Results

Figure 4.1: The average E-modulus

The E-modulus has a, in general, balanced trend. Exceptions are 30% PIR PP aged
1000h, 30% PCR PP aged 500h, 50% PCR PP aged 1000h, and 70% PCR PP aged
500h which all show different amounts of variance.

40



4. Results

Figure 4.2: The average stress at yield point

The stress at yield point have an overall increasing trend, both between material
groups and within material groups. The material groups 30% PIR PP and 30%
PCR PP are the only exceptions.

Figure 4.3: The average strain at yield point

41



4. Results

The strain at yield point shows signs of a uniform trend, with exceptions of 30%
PIR PP aged 1000h and 30% PCR PP aged 500h. The trend within each material
group is that the strain at yield point decreases between uaged and aged 500h.

Figure 4.4: The average strain breakage point

Strain at breakage point has a wide distribution of test results both between material
groups and within the material groups. Moreover, the error bars presented show a
wide spread. The largest error bar presented is for the unaged 30% PIR PP that
ranges between approximately 70%-168% of the mean average value.

4.2 Impact tests
Figure 4.5 shows the bar chart that represents the result of the impact tests where
the different bars illustrate the average impact strength in KJ/m3 for the respective
materials and aged materials.

42



4. Results

Figure 4.5: The average impact strength for the tested materials

The impact strength presents an overall declining trend between the material groups.
Within the material groups the result is mixed. Furthermore, the bar chart shows
a wide distribution of error bars.

4.3 Differential Scanning Calorimetry tests
Following are the results of the DSC tests, both the degree of crystallinity and the
peak temperature, presented in bar charts. The results for the total crystallinity
and observed peak temperature can be seen in Figures 4.6 and 4.7, the crystallinity
and observed peak temperature of the big peak in Figures 4.8 and 4.9, and the
crystallinity and observed peak temperature of the small peak in Figures 4.10 and
4.11. Note that for 30% PIR PP there was no clear smaller peak and is thus left
empty in the bar chart. Also observe that for the temperature charts the Y-axis
does not begin at 0, this to facilitate comparison.

The complete list with values obtained from the DSC tests used to calculate the
crystallinity is shown in the Appendix A.3.

43



4. Results

Figure 4.6: The total average crystallinity

The total average crystallinity can be seen in Figure 4.6, where a trend of increase
can be observed.

Figure 4.7: The total average peak temperature

The total average peak temperature has a varying result with no clear observed

44



4. Results

trend as can be seen in Figure 4.7.

Figure 4.8: The average crystallinity of the big peak

Figure 4.9: The average peak temperature of the big peak

Figures 4.8 and 4.9 present the average crystallinity of the big peak and the average
peak temperature for the big peak. It shows that the average crystallinity has a

45



4. Results

decreasing trend and that the average peak temperature has a diverse result with
no clear trend.

Figure 4.10: The average crystallinity of the small peak

Figure 4.11: The average peak temperature of the small peak

46



4. Results

Figures 4.10 and 4.11 present the average crystallinity of the small peak and the
average peak temperature for the small peak. It can be seen that the average
crystallinity is increasing, and the average peak temperature has a varying result,
where no clear trend can be observed.

Figure 4.12: The ratio in crystallinity between the small peak and the big peak

The bar graph, seen in Figure 4.12, shows the ratio between the small and big
peaks. The bars represent the number of percentages that the size of the small peak
represents of the big peak.

4.4 Perceived Quality assessment
The results of the visual assessment can be seen below in Table 4.1.

Table 4.1: Results of the visual assessment

Sample: Color Gloss Embossing Defect
30% PIR PP Slightly light but ok Ok Ok Flashes, not ok
30% PCR PP Slightly light but ok Slightly glossy but ok Ok -
40% PCR PP Slightly light, slightly blue but ok Slightly glossy but ok Ok Flashes, not ok
50% PCR PP Borderline, slightly light and slightly blue but ok Slightly glossy but ok Ok Flashes, not ok
60% PCR PP Borderline but ok Slightly glossy but ok Ok Flashes, not ok
70% PCR PP Borderline but ok Slightly glossy but ok Ok Flashes, not ok

All samples were approved by visual assessment, even though there are defects in
the form of flashes that are not ok. The flashes were a little bit of extra material
on the sides as a result of the production of the plate, this may therefore not be the
case for the final component. If that were to be the case on the final component,
then that would need to be addressed.

47



4. Results

In table 4.2 the measured values from the color and gloss assessment are presented
and in table 4.3 and table 4.4 they are compared with the reference.

Table 4.2: Results of the color measurements

Sample Color Gloss
∆L ∆a ∆b GU

30% PIR PP
1,15 -0,12 -0,26 1,90
1,18 -0,12 -0,23 1,90
1,28 -0,12 -0,26 1,80

Average 1,20 -0,12 -0,25 1,87

30% PCR PP
1,09 -0,10 -0,04 1,80
1,02 -0,09 -0,03 1,90
1,10 -0,10 -0,04 1,80

Average 1,07 -0,10 -0,04 1,83

40% PCR PP
1,52 -0,13 -0,20 1,80
1,48 -0,13 -0,19 1,80
1,50 -0,12 -0,18 1,80

Average 1,50 -0,13 -0,19 1,80

50% PCR PP
1,79 -0,15 -0,27 1,90
1,76 -0,14 -0,25 1,90
1,74 -0,13 -0,23 1,80

Average 1,76 -0,14 -0,25 1,87

60% PCR PP
1,86 -0,14 -0,27 1,80
1,76 -0,15 -0,27 1,80
1,77 -0,13 -0,21 1,80

Average 1,80 -0,14 -0,25 1,80

70% PCR PP
1,86 -0,16 -0,22 1,90
1,90 -0,16 -0,22 1,90
1,88 -0,15 -0,22 1,90

Average 1,88 -0,16 -0,22 1,90

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4. Results

Table 4.3: Results of the color measurement compared to the reference and the
approved tolerance

Color
Sample: Reference ∆L Tolerance ∆a Tolerance ∆b Tolerance
30PIR 0 1,20 ± 0,5 -0,12 ± 0,2 -0,25 ± 0,2
30PCR 0 1,07 ± 0,5 -0,10 ± 0,2 -0,04 ± 0,2
40PCR 0 1,50 ± 0,5 -0,13 ± 0,2 -0,19 ± 0,2
50PCR 0 1,76 ± 0,5 -0,14 ± 0,2 -0,25 ± 0,2
60PCR 0 1,80 ± 0,5 -0,14 ± 0,2 -0,25 ± 0,2
70PCR 0 1,88 ± 0,5 -0,16 ± 0,2 -0,22 ± 0,2

Table 4.4: Results from the gloss measurement compared to the reference and the
approved tolerance

Gloss
Sample: GU Reference Tolerance

30% PIR PP 1,87 1,9 ± 0,3
30% PCR PP 1,83 1,9 ± 0,3
40% PCR PP 1,80 1,9 ± 0,3
50% PCR PP 1,87 1,9 ± 0,3
60% PCR PP 1,80 1,9 ± 0,3
70% PCR PP 1,90 1,9 ± 0,3

When comparing the results from the color measurements to the reference, they are
outside the tolerance. The measuring of the gloss is within the tolerance.

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4. Results

4.5 Carbon footprint calculations
Using Table 3.1 the total weight of the relevant parts was calculated to be 5,782kg.
Using this total weight, the CO2e for the different categories was calculated and is
shown in Table 4.5. The value in column " Yearly (200 000 cars) CO2e" in the table
is translated into the corresponding amount of Coca Cola cans to easier comprehend
the values.

Table 4.5: CO2e values for the different materials

Material CO2e/kg Total CO2e Yearly (200 000 cars) CO2e Amount of Coca Cola cans
30% PIR PP 1,55 8,96 1 792 420 10 543 647
30% PCR PP 1,63 9,42 1 884 932 11 087 835
40% PCR PP 1,44 8,33 1 665 216 9 795 388
50% PCR PP 1,24 7,17 1 433 936 8 434 917
60% PCR PP 0,90 5,20 1 040 760 6 122 117
70% PCR PP 0,85 4,91 982 940 5 782 000

Virgin PP 2,16 12,49 2 497 824 14 693 082

Shown in Table 4.5 the CO2e is the highest for virgin PP. Moreover, there is a
decrease of CO2e with more PCR content. However, the CO2e for 30% PIR PP is
lower than the value for 30% PCR PP.

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5
Discussion

This chapter explores and interprets the results in relation to the research questions.
The discussion also highlights any patterns, implications, and potential limitations
identified during the project. Additionally, it suggests potential directions for future
research.

5.1 Potential sources of error
During the testing of the materials, there have been a couple of potential sources of
error that could affect the results. Being aware of these is important when analyzing
the results and if replicating the study and/or continuing it. The first potential error
could be the number of samples that were used for each test. Since the material had
already been ordered prior to the study, there was a limited number of samples to
work with, five samples for each test and for each point of aging. A higher number
for each test could have given a more secure result and less distribution. Calibrating
the impact test machine would also ideally require a greater number of samples, as
mentioned in Section 3.5. If more material from Polykemi had not been acquired
during the project, the initial amount of samples would not have been enough. Since
the additional material was acquired late in the project, these samples unfortunately
did not have the time to age, which led to a shortage of aged samples.

When aging the materials they were placed on the floor of a car, as mentioned in
Section 3.3. This meant that one side of each sample was not in contact with the
hot air. To avoid this, aging by hanging the samples, so that all sides are exposed
to hot air, could have given a different result with a greater difference between
the aged materials and thus more accuracy. This knowledge was gained after the
commencement of the aging. However, it is possible that because the materials aged
for a longer time period, the sides of the samples were still sufficiently in contact
with the hot air. But the effects were not investigated further, and therefore the
consequences are unknown.

When doing the impact tests conditioning was carried out on the samples first. The
conditioning step was not performed for the tensile tests. Having done conditioning
to all samples before the tests would give them more equal conditions and a more
fair comparison. This was not done because the method was not known at the time
the tests were performed.

In conclusion, many of the mentioned potential sources of error could have been

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5. Discussion

prevented by a more thorough test plan prior to starting the tests. Consulting more
experts to get a clearer picture of what needed to be done together with investigating
related ISO standards could have been done.

5.2 Material tests
Below follows a discussion regarding the test results and how to interpret them.
Furthermore, it is explained if the actual result corresponds to the expected result
from theory.

5.2.1 Evaluation of DSC tests
Figure 4.6 illustrates the total crystallinity of the different groups of materials used
in the project. It shows that the total crystallinity is overall considered equal but
that it gradually increases slightly with more recycled content. Moreover, all samples
are approximately almost 30% crystalline, which implies that 70% of the material
is amorphous.

As mentioned in Section 2.11, the crystallinity increases with aging. This shows
proof in Figure 4.6 where the bars for 40% and 70% PCR PP aged 500h are higher
than the bars with the same material, but unaged.

Furthermore, Figures 4.8 and 4.10 reveal the crystallinity of the so-called big and
small peaks that constitute the total crystallinity shown in Figure 4.6. Figure 4.12
presents the ratio between the small and big peaks where it can be seen that the size
of the small peak varies approximately between the range of 0,6%-2,5% of the size of
the big peak. Interestingly, Figure 4.8 expose that if the small peak is excluded from
the total crystallinity, the crystallinity would instead decrease with more recycled
content. This demonstrates that the crystallinity of the content of the small peak
compensates for the crystallinity of the big peak which results in a gradually increase
of total crystallinity.

The DSC-tests reveal that there is a so-called small peak that melts before the main
big peak. Figures 4.9 and 4.11 present the melting temperature of the respective
peaks. These figures clarifies that the big peak has a considerably higher melting
point, for example, the melting point between the peaks for 30% PCR PP differs
almost 40◦C. This proves that the material is not homogeneous. The small peak
could portray the additives, but since all of the tested materials contain the same
amount of additives there should be no size differences between the small peaks of
all materials in that case. Furthermore, the DSC-test results for 30% PIR PP should
then also include a small peak which it does not. This implies that the small peak
is the result of something that the PIR PP does not include. Moreover, Figure 4.11
reveals that the small peaks in fact have melting temperatures, this proves that the
small peaks are not due to some remains of dirt from the recycled content either.
The explanation behind the small curves could, therefore, depend on the material
structure resulting from recycling. As mentioned in Section 2.4, the material de-
grades when mechanically recycled by chain scission, forming low molecular weight

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5. Discussion

chains. These shorter molecular chains will have lower melting points, which is what
can be seen when analyzing Figures 4.9 and 4.11. To strengthen this theory further
it can be seen that the crystallinity for the small peak increases with the recycled
content. This implies that the size of the small peak increases with the recycled
content as well since the crystallinity is calculated by integration, as mentioned in
Section 3.6. This would imply that the amount of short molecular chains increases
with the recycled content, which is reasonable since the greater the amount of re-
cycled content, the higher the concentration of shorter molecular chains. Moreover,
Section 2.10 explains that the shorter molecular chains tend to crystallize easier,
which further strengthens the theory.

5.2.2 E-modulus
Figure 4.1 illustrates a bar chart of the average E-modulus for the tested materials.
It shows an overall uniform result with relatively small error bars. The error bars
ranges within approximately 89%-110% of the average E-modulus value, on the
majority of samples. Exceptions are for 30% PIR PP aged 1000h and 70% PCR PP
aged 500h that both have greater error bars and stand out from the overall uniform
length of the bars. In addition,