Effect of rheology and crystallinity on
processing and barrier properties of
PHA

Degree project in Innovative and Sustainable Chemical Engineering

AMIT KUMAR SIVA KUMAR

DEPARTMENT OF INDUSTRIAL AND MATERIALS SCIENCE

CHALMERS UNIVERSITY OF TECHNOLOGY
Gothenburg, Sweden 2023
www.chalmers.se

www.chalmers.se




Master Thesis 2023

Effect of rheology and crystallinity on processing
and barrier properties of PHA

AMIT KUMAR SIVA KUMAR

Department of Industrial and Materials Science
Chalmers University of Technology

Gothenburg, Sweden 2023



Effect of rheology and crystallinity on processing and barrier properties of
PHA
AMIT KUMAR SIVA KUMAR

© AMIT KUMAR SIVA KUMAR, 2023.

Supervisor(s): Ebrahim Shokri, Stora Enso ®
Gisela Cunha, Stora Enso®
Professor Roland Kádár, Chalmers University of Technology®
Examiner: Professor Roland Kádár, Chalmers University of Technology

Master Thesis 2023
Department of Industrial and Materials Science
Chalmers University of Technology
SE-412 96 Gothenburg
Sweden
Telephone +46 31 772 1000

Cover: Carton used on Food service packaging.

Typeset in LATEX, template by Kyriaki Antoniadou-Plytaria
Gothenburg, Sweden 2023

iv



Abstract
Plastic pollution is one of the major problems that the world is facing at present.
Different industrial sectors contribute to this and the packaging sector is one of
the main contributors. According to the statistics, the packaging sector alone con-
tributes to 60% of the total plastic pollution. This creates the need for the packaging
industry to become more sustainable and produce more environmentally friendly
products. There are various types of packaging products and this thesis is focused
on food packaging. In food packaging a plastic layer is used to act as a barrier
against, for example, gases, such as oxygen and carbon dioxide, and sunlight, as
these can decrease the shelf life of the packaged food. However, the plastic film is
produced from fossil-based resources and is not biodegradable. The replacement of
the conventional plastic barriers with a bio-based polymer is one possible solution
to move towards more sustainable packaging materials. For this purpose, a class
of bio-based polymers named polyhydroxyalkanoates (PHAs) have been studied in
this project. Four different types of PHAs have been characterized using techniques
such as DSC, TGA, and DMA, among others. Rheological characteristics were
also studied to improve the PHA processing and coating onto paperboard at a pilot
scale. Additionally, water vapor barrier properties of the different PHA samples and
PHA-coated paperboard were measured and the effect of PHA molecular weight and
crystallinity on these was also assessed. From this study, it was observed that PHA
with higher molecular weight showed better performance in terms of mechanical
properties and barrier properties. Moreover, PHA crystallinity has also been shown
to play an important role in terms of barrier properties alongside molecular weight.
Regarding rheological properties, it was verified that PHA with higher molecular
weight has higher melt viscosity, which makes the material stable at higher tem-
peratures but at the same time, hinders the production of proper coating onto the
paper-board. For a better understanding of how PHA processing through extrusion
coating can be improved in practice, further studies are required, for instance, the
change of processing parameters and the compounding of PHA with other compo-
nents/polymers.

Keywords: Packaging, polyhydroxyalkanoates, barrier properties, rheological prop-
erties, crystallinity, extrusion coating

v





Acknowledgements
First, I would like to thank my supervisors Ebrahim Shokri, Gisela Cunha and Prof.
Roland Kádár for giving me the opportunity to do my thesis under them and for
the opportunity to do my thesis at Stora Enso. I had constant support and advice
from you and thank you for allowing me to explore freely this topic.

I would also like to thank Mikael Pelcman from Stora Enso and Marko Bek from
Rheology and Processing Soft-Matter team at Chalmers for their help during my
lab work.

Finally, I would also like to extend my gratitude to the entire team at Stora Enso
and the Rheology Processing of the Soft-Matter team at Chalmers for their valuable
inputs during my thesis period

Amit Kumar Siva Kumar, Gothenburg, 2023

vii





List of Acronyms

Below is the list of acronyms that have been used throughout this thesis:

PLA Polylactic acid
PHA Polyhydroxy alkaonate
PCA Polycaprolactone
LPB Liquid packaging board
PE Polyethylene
SCL Short chain length
MCL Medium chain length
P3HB Poly(3-hydroxybutyrate)
P(3HB-co-3HV) Poly(3-hydroxybutyrate-co-3hydroxyvalerate)
P(3HB-co-3HH) Poly(3-hydroxybutyrate-co-3-hydroxyhexonate)
LDPE Low density polyethylene
CO2 Carbon dioxide
O2 Oxygen
N2 Nitrogen
WVTR Water vapour transmission rate
OTR Oxygen transmission rate
Tm Melting temperature
Tc Crystallisation temperature
Tg Glass transition temperature
PET Polyethylene terephthalate
CH4 Methane
PHBV Polyhydroxybutyrate–co-hydroxy valerate
H2O Water
HDPE High density polyethylene
DSC Differential scanning calorimetry
TGA Thermogravimetric analysis
DMA Dynamic mechanical analysis
SEM Scanning electron microscopy
ICP-OES Inductively coupled plasma optical emission spectroscopy
FTIR Fourier transform infrared spectroscopy
PBS Polybutylene succinate



x



Nomenclature

Below is the nomenclature of indices, sets, parameters, and variables that have been
used throughout this thesis.

Mw Molecular weight
G” Loss modulus
G′ Storage modulus
E Elastic modulus
σ Tensile stress
ϵ Tensile strain
τ Shear stress
L/R Length/Radius
∆P Pressure loss
τ True (corrected) shear stress
γ̇ True(corrected) shear rate
τa Apparent shear stress
γ̇a Apparent shear rate
ηa Apparent viscosity
ηs Corrected(true) viscosity
δ Phase angle

xi





Contents

List of Acronyms ix

Nomenclature xi

List of Figures xv

List of Tables xvii

1 Introduction 1
1.1 Plastic materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Bio-based and biodegradable polymers . . . . . . . . . . . . . . . . . 2

1.2.1 PLA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2.2 PHA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2.3 Other biopolymers . . . . . . . . . . . . . . . . . . . . . . . . 5

1.3 Packaging material . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3.1 Packaging demands . . . . . . . . . . . . . . . . . . . . . . . . 6

1.3.1.1 Packaging systems and types . . . . . . . . . . . . . 6
1.3.1.2 Packaging properties . . . . . . . . . . . . . . . . . . 7
1.3.1.3 Barrier properties . . . . . . . . . . . . . . . . . . . . 7

1.3.1.3.1 WVTR test . . . . . . . . . . . . . . . . . . 7
1.3.1.3.2 OTR test . . . . . . . . . . . . . . . . . . . 8
1.3.1.3.3 Grease barrier test . . . . . . . . . . . . . . 8

1.3.1.4 Stiffness(mechanical properties) . . . . . . . . . . . . 8
1.3.1.5 Sealing properties . . . . . . . . . . . . . . . . . . . . 8

1.3.2 Liquid packaging board structure . . . . . . . . . . . . . . . . 8
1.4 Extrusion coating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.5 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.6 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2 Materials and Methods 12
2.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.2 Experimental methods . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.2.1 Film preparation . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.2.2 Differential Scanning Calorimetry(DSC) . . . . . . . . . . . . 13
2.2.3 Thermogravimetric Analysis(TGA) . . . . . . . . . . . . . . . 14

xiii



Contents

2.2.4 Dynamic Mechanical Analysis(DMA) . . . . . . . . . . . . . . 14
2.2.5 Fourier Transform Infrared Spectroscopy(FTIR) . . . . . . . . 15
2.2.6 Mechanical Properties . . . . . . . . . . . . . . . . . . . . . . 15

2.2.6.1 Tensile testing . . . . . . . . . . . . . . . . . . . . . 15
2.2.6.2 Seal strength testing . . . . . . . . . . . . . . . . . . 15

2.2.7 Rheological properties . . . . . . . . . . . . . . . . . . . . . . 16
2.2.7.1 Rotational rheometry . . . . . . . . . . . . . . . . . 16
2.2.7.2 Capillary rheometry . . . . . . . . . . . . . . . . . . 17

2.2.8 Water Vapour Transmission Rate(WVTR) . . . . . . . . . . . 19

3 Results and Discussion 20
3.1 DSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.2 TGA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.3 DMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.4 FTIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.5 Mechanical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3.5.1 Tensile testing . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.5.2 Heat sealing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.6 Rheological properties . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.6.1 Thermal stability of PHA . . . . . . . . . . . . . . . . . . . . 29
3.6.2 Relaxation behaviour of PHA . . . . . . . . . . . . . . . . . . 30
3.6.3 Frequency sweep test and Non-Newtonian behaviour . . . . . 33
3.6.4 Melt Viscosity . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

3.7 WVTR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

4 Conclusion and Future work 37
4.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.2 Future work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

A Appendix 1 I
A.1 DSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I
A.2 Rheological properties . . . . . . . . . . . . . . . . . . . . . . . . . . II

A.2.1 Thermal stability of PHA . . . . . . . . . . . . . . . . . . . . II
A.3 Mechanical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . III

A.3.1 Heat sealing test . . . . . . . . . . . . . . . . . . . . . . . . . III

xiv



List of Figures

1.1 Classification of biodegradable polymers[1] . . . . . . . . . . . . . . . 2
1.2 PLA structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 General structure of polyhydroxyalkanoates in which R represents (CH2 4
1.4 Cellulose structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.5 Starch structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.6 LPB structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.7 A. Shows the typical cross-section scheme of the most important parts

of the extrusion process; B. Extrusion of PHA film at pilot scale; C.
Extrusion-coated paperboard at pilot scale . . . . . . . . . . . . . . . 10

2.1 A.Sample pack setup in hot press B.Schematic representation of the
setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.2 Sample structure used for I. Seal strength testing(ISO 11607); II.
Tensile testing(ISO 527-1) . . . . . . . . . . . . . . . . . . . . . . . . 16

2.3 Cross-sectional view of a capillary rheometer . . . . . . . . . . . . . . 17
2.4 Bagley correction graph . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.5 Shear rate profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.1 DSC curves obtained in different (I)heating and (II)cooling cycles . . 20
3.2 DSC curves of PBS obtained in different heating(I) and cooling(II)

cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.3 TGA results for the different PHAs studies and LDPE. (Note: The Y-

axis of the TGA curves were offset for better visibility of the different
thermograms.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

3.4 DMA curves for (I)PHA A, (II)PHA B, (III)PHA C, and (IV)PHA D 24
3.5 FTIR spectra PHA A(Red), PHA B(black), PHA C(green), PHA

D(blue) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.6 Seal strength of (I)PHA A, (II)PHA B, (III)PHA C and (IV)PHA D

hot-pressed films at varying temperatures . . . . . . . . . . . . . . . . 27
3.7 Thermal stability of the (I)LDPE 175 at ◦C, (II)PHA A at 175◦C,and

(III)PHA A at 160◦C . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.8 Amplitude sweep graph for (I)LDPE, (II)PHA A, (III)PHA B, (IV)PHA

C, and (V)PHA D . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.9 Frequency sweep graph (I)LDPE, (II)PHA A, (III)PHA B, (IV)PHA

C, (V)PHA D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

xv



List of Figures

3.10 Complex viscosity graphs for (I)LDPE, (II)PHA A, (III)PHA B,
(IV)PHA C, (V)PHA D . . . . . . . . . . . . . . . . . . . . . . . . . 33

3.11 Melt viscosities for LDPE and PHA studied . . . . . . . . . . . . . . 34
3.12 WVTR results of PHA films (top) and PHA-coated paperboards (bot-

tom) at normal (left) and tropical conditions (right). . . . . . . . . . 35
3.13 WVTR vs degree of crystallinity of PHA at normal(blue) and tropical

conditions(orange) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

A.1 DSC graph of PHA B (I). Heating cycles (II). Cooling cycles . . . . . I
A.2 DSC graph of PHA C (I). Heating cycles (II). Cooling cycles . . . . . I
A.3 DSC graph of LDPE . . . . . . . . . . . . . . . . . . . . . . . . . . . II
A.4 Thermal stability of PHA’s (I)PHA B at 175◦C, (II)PHA B at 160◦C,

(III)PHA C at 175◦C, (IV)PHA C at 160◦C, (V)PHA D at 175◦C,
(VI)PHA D at 160◦C . . . . . . . . . . . . . . . . . . . . . . . . . . . III

A.5 Thickness variation of the film used for heat sealing (I)PHA A, (II)PHA
B, (III)PHA C, (IV)PHA D . . . . . . . . . . . . . . . . . . . . . . . III

xvi



List of Tables

1.1 Mechanical properties of two of the most common PHAs and LDPE[2] 4

2.1 Qualitive molecular weight of the different PHAs studied . . . . . . . 12
2.2 Summary of the conditions used to prepare PHA and LDPE films

with hot-press . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.3 Rotational rheometer measurement conditions . . . . . . . . . . . . . 17

3.1 DSC results for the PHAs studied and LDPE . . . . . . . . . . . . . 22
3.2 Percentage of crystallinity for the different PHAs studied and LDPE . 22
3.3 Tg values obtained in this study by DMA for all the PHA samples. . 25
3.4 Summary of mechanical properties for all four PHA samples. . . . . . 26
3.5 Cross over frequencies for LDPE and different PHAs studied . . . . . 32

xvii



1
Introduction

1.1 Plastic materials
Conventional plastics are materials made of synthetic polymers. The first fully
synthetic plastic was developed in the beginning of 20thcentury. The invention of
synthetic plastics made petroleum companies partner up with chemical companies
for large-scale production, as their raw material is one of the byproducts of process-
ing crude oil. The first use of synthetic polymer or plastic was during World War
II as insulation in radar cables. In the modern world, synthetic plastics are widely
used in many industries, including packaging, agriculture, food, consumer products,
automobile, medical, and aerospace. The massive and irresponsible consumption of
plastics since their industrialization has led to worldwide pollution and other envi-
ronmental issues, and the packaging sector has been one of the biggest contributors
to this. Households contribute to more than 60% of the consumer plastic waste,
most of which is single-use plastic that takes decades to decompose[1].

Existing literature on marine litter worldwide shows that plastics contribute to 60-
80% of total marine debris. Out of this debris, plastics deriving from packaging
materials are one of the most common[3]. The problem with plastics made of syn-
thetic polymers does not stop in marine pollution. In fact, of the total plastics
produced worldwide each year, 20% to 25% end up in landfills[4]. This creates a
significant strain on municipal budgets for clearing the landfills and following the
environmental norms and regulations for discarding plastic waste[1]. The economic
burden of moving and recycling plastic waste outweighs that of making new plastic.
Thus, more sustainable alternatives are required, and plastics derived from bio-based
and biodegradable polymers can be part of the solution.

Bio-based polymers are generally classified into three categories.
•Polymer produced by chemical synthesis using renewable bio-based monomer.
•Polymer directly removed from the biomass.
•Polymer directly produced by microorganisms or genetically modified bacteria

Biodegradable plastics, on the other hand, are defined as polymers that resemble
normal plastics but that will break down in nature in the presence of water and
microorganisms after being disposed of. Biodegradable plastics can be either bio-
based or derived from fossil resources. However, the latter type is less common.
Extensive research is being conducted to change the characteristics of polymers so

1



1. Introduction

they can break down more easily into their constituents upon disposal, to minimize
their environmental impact[1].

The image below depicts a summary of biodegradable polymer types.

Figure 1.1: Classification of biodegradable polymers[1]

1.2 Bio-based and biodegradable polymers

1.2.1 PLA
PLA is a semicrystalline polymer prepared by polycondensation of lactones or con-
densation of hydrocarbonic acid[5]. It is biodegradable under composting conditions
at elevated temperatures and possesses moderately good mechanical properties [6].
The image below depicts the PLA structure.

Figure 1.2: PLA structure

2



1. Introduction

Since PLA is bio-based and generally biodegradable, it is currently being widely
used in packaging and medical applications[5]. The mechanical, thermal, and rhe-
ological properties of the PLA are determined by its Tg temperature. The melt
viscosity of the PLA determines the flow conditions and has a significant impact
on the processing time[5]. Based on the PLA molecular weight, its processing con-
ditions for extrusion coating on paperboard can vary. For higher molecular weight
PLA, the melt viscosity is in the range of 500-100 Pa, and for low molecular weight
PLA the polymer melt behaves like a Newtonian fluid( i.e, a fluid that behaves
like water)[5]. The crystallinity of PLA is also one of the important factors for the
extrusion coating process. PLA with semi-crystalline structure shows higher shear
viscosity compared to amorphous PLA within the same processing conditions. The
PLA melt also shows a shear thinning behavior with increasing shear rate[5]. Due to
the weakening of the interaction of molecular chains at higher shear rates and am-
plitudes, the shear viscosity also decreases[5]. Thus, the structure and crystallinity
of the polymer are important factors affecting the processing conditions.

The thermal properties of the PLA are also determined by its molecular weight and
the polymerization conditions [5]. In general, the Tg value of PLA lies in the range
50 - 80◦C and Tm in the range 130 - 180◦C[5]. The exact value of the Tg and Tm
depends on the molecular weight[5].

PLA’s mechanical properties vary; it can be either stiff or elastic and soft. PLA is
usually compared to PET and it possesses higher tensile strength and tensile mod-
ulus than the latter. Its tensile strength is about 59 MPa and the tensile modulus
is about 3.8 GPa[5]. PLA also shows superior barrier properties than PET overall.
It has better resistance to CO2, N2 and CH2, but low resistance to O2 compared to
PET[5].

1.2.2 PHA
Polyhydroxyalkanoates (PHAs) are a class of naturally occurring bio-based polyesters
that are produced by several bacteria[7]. Under certain unbalanced growth condi-
tions, and in the presence of too much carbon, a variety of microorganisms accu-
mulate PHAs as inclusion bodies[8]. PHAs were first discovered in 1926. Since
then, they have attracted interest for use in various applications because of their
biodegradability, bio-compatibility, and ability to be manufactured from natural car-
bon sources[9]. PHA polymers backbone is made up of a monomer called R-Hydroxy
fatty acid and each monomer contains a saturated alkyl group[10]. However, the
side group can also be an unsaturated alkyl group or a branched alkyl group, but
the occurrence of the latter is quite uncommon[10]. The image below shows the
general structure of PHAs.

3



1. Introduction

Figure 1.3: General structure of polyhydroxyalkanoates in which R represents (CH2
)xCH3 moieties

PHAs are generally classified into different types based on the number of carbon
atoms in their respective monomers. A short chain length (SCL) PHA contains 3
to 5 carbon atoms and a medium chain length (MCL) PHA contains 6 to 14 carbon
atoms[11]. The average molecular weight (Mw) of PHAs is determined by their chain
length. In general, the Mw of PHAs is around 50,000-1,000,000 Da and varies with
PHA producer[12]. Since their discovery, there are only a few PHA types that have
started to be commercialized in recent years. The most common and currently com-
mercialized PHAs are P3HB, (or simple PHB), P(3HB-co-3HV) (or simply PHBV),
P(3HB-co-3HH) (or simple PHBH) and P(3HB-co-4HB) (or simply P3HB4HB)[13].

Depending on the grade and structure, PHAs Tm is in the range of 120-180◦C and
Tg in the range of -20◦C to -+15◦C. Based on the monomer units present in its
structure, PHA can show a wide range of mechanical properties. For instance, a
short-chain length (SCL) PHA-like polyhydroxybutyrate (PHB) is considered brit-
tle and has a low impact strength. For co-polymers like poly(hydroxybutyrate-co-
hydroxyvalerate) (PHBV), the properties of PHA can be varied by changing the
valerate content. The modulus of elasticity of PHA ranges from 0.08GPa to 3.5GPa
(very ductile)[5]. The tensile modulus and tensile strength of some PHA are shown
in the table below alongside those of LDPE

Table 1.1: Mechanical properties of two of the most common PHAs and LDPE[2]

Polymer type Tensile modulus(GPa) Tensile strength(MPa)
PHB 1.7-3.5 40

PHBV 0.7-2.9 30-38
LDPE 0.2 10-15

The water vapor permeability of PHA is claimed to be of the same level as that of
PET. PHAs are highly biodegradable and their degradation can take place both in
the presence or absence of enzymes [5]. Even though PHAs possess properties com-
parable to those of fossil-based polymers, one of the main disadvantages of PHAs

4



1. Introduction

is the fact that the difference between their processing temperature and thermal
degradation temperature is too low, which makes it difficult to properly process the
material without triggering thermal decomposition.

1.2.3 Other biopolymers
The growing demand for sustainable materials has brought much attention to cel-
lulose. Cellulose is a polysaccharide and the most abundant naturally occurring
biodegradable polymer on earth[5]. The image below depicts the cellulose structure.

Figure 1.4: Cellulose structure

The hydroxyl groups in cellulose structure allow the formation of a vast hydrogen
bonding network, which makes cellulose strong and insoluble in most of the solvents,
including water[5]. Despite being insoluble in water, cellulose is highly hydrophilic
and can absorb high amounts of water and swell. Cellulosic materials have in gen-
eral very good mechanical properties but have usually high permeability to air and
water[5]. To compensate for the poor barrier performance, cellulose is generally
combined with other synthetic materials.

Starch is another abundant polysaccharide like cellulose and its characteristics are
also studied for usage as a bio-based barrier in packaging materials. The structure
of the starch is shown below.

Figure 1.5: Starch structure

Starch has two main components, amylose and amylopectin. It has generally low
stability under stress and its amylose component is soluble in water[5]. In terms
of mechanical properties, these can greatly vary due to the big variation of molar

5



1. Introduction

masses of amylose and amylopectin. Like cellulose, starch is also biodegradable and,
due to this, it is typically used as a natural filler in polyolefins, such as high-density
polyethylene (HDPE).

1.3 Packaging material
Bio-based and biodegradable polymers for packaging materials have drawn increas-
ing attention globally. As mentioned earlier, the use of bio-based polymers can
greatly decrease toxicity and increase the chances of biodegradability and sustain-
ability of end products. In addition, the carbon footprint can also be reduced[14].

One of the main components of fiber-based packaging materials is paperboard. Pa-
perboard provides the necessary mechanical support but needs additional compo-
nents to enhance the barrier performance of the packaging material. The barrier
properties, such as against odor, moisture, grease, oxygen, and water[14], are typi-
cally improved by coating the paper board on both sides with synthetic polymers.
As mentioned above, since the invention of packaging materials, fossil-based poly-
mers have been widely used as barrier coating due to their easy processability and
relatively low price.

Plastic waste (19.4%) is the second most common waste after paper and cardboard
(40.6%) within packaging materials. Packaging waste reached 178 kg per capita
in 2019 and it has been reported that Ireland is at the top of the members in
the European Union when it comes to packaging waste, while Sweden is in 22nd
place[14]. Though Sweden is almost at the bottom, efforts are still being taken
to further reduce the environmental impact. Stora Enso, the renewable materials
company, is making efforts from its side to minimize waste production and its impact.

1.3.1 Packaging demands
1.3.1.1 Packaging systems and types

Food packaging technology is constantly improving in response to modern soci-
ety’s expanding challenges and requirements[15]. The packaging industry employs
a diverse range of materials and printing processes to create packages that look at-
tractive and help us keep the packaged product safe[6]. Packaging systems also play
a crucial role in marketing by providing an opportunity to differentiate the products
and make them more attractive. In general packaging systems can be divided into
three types.

• Primary packaging: These are the packaging types that come in direct contact
with the food. Some examples of primary packaging are laminated pouches, plastic
containers, C arton packages, etc.

• Secondary packaging: This type of packaging usually holds together individual
units of goods. Some examples of secondary packaging are plastic crates, plastic

6



1. Introduction

trays, etc.

• Tertiary packaging: This type of packaging deals with the type of packaging used
to transport for example large quantities of wood from one place to another. Some
examples are wooden containers, wooden pallets, etc.

The primary packaging system is important because it comprises food packaging.
Within the primary packaging, usually a barrier material protects the food from
carbon dioxide, oxygen, and water vapor, among others. There are various types
of materials that can be used as barriers. Some of the most used barrier materials
are metals, glass, plastic, and laminates. Among these packaging materials, LDPE
plastic, as mentioned above is the most widely used in today’s scenario.

1.3.1.2 Packaging properties

When it comes to packaging materials, various demands arise throughout the entire
value chain of the product. Most of the properties are associated with the polymer
used. The properties of importance can be divided into three main categories
• Barrier properties
• Stiffness(i.e.,mechanical properties)
• Sealing properties

1.3.1.3 Barrier properties

In a fiber-based packaging context, a barrier is a layer of material that is coated or
laminated onto paperboard to prevent the migration of unwanted substances like
water, into the packaging, thus increasing the shelf-life of the food product. The
migration of oxygen must also be prevented, as it can change the nutritional value
of the product. The barrier material must also hinder the penetration of light, as
it can induce chemical processes, such as photo-oxidation, vitamin loss of the food
product, etc.

The barrier properties are usually tested with three main types of experiments.
• Water Vapour Transmission Rate(WVTR) test to assess water vapour barrier
performance
• Oxygen Transmission Rate(OTR) test to assess Oxygen barrier performance
• Grease barrier test to assess grease barrier performance.

1.3.1.3.1 WVTR test The WVTR test is a standard test (ASTM F1249-20)
that measures how much water vapor can transit through the thickness of the pack-
aging material. The instrument measures the weight increase of the material over
the period of the experiment. The test can be done at different temperatures and
relative humidity conditions, but most commonly is done at i) normal conditions –
23◦C and RH=50% and/or ii) tropical conditions – 38◦C and RH=80%.

7



1. Introduction

1.3.1.3.2 OTR test The OTR test (ASTM D3985-17) is done to measure how
much oxygen can transit through the thickness of the packaging material. It is
one of the important tests as oxygen can change the nutritional value and odour of
the food product. In this test, the packaging material sample is usually placed in
a chamber, and oxygen is allowed to pass through it. A sensor placed inside the
instrument measures the amount of oxygen that is passed in a fixed interval of time
and the test is complete when the amount that passes through the film becomes
constant.

1.3.1.3.3 Grease barrier test Grease barrier is also one of the important tests
that are measured on polymer-coated paperboard. There are different ways to assess
oil and grease barrier properties. One way is to test how much time it takes for oily
or greasy substances used in food to penetrate through the coated paperboard, for
example, mayonnaise, chicken fat, etc. Another way is to use the KIT method
and test if twelve liquid solutions with different polarities can penetrate the coated
paperboard. The highest numbered solution that remains on the surface of the
paperboard without causing failure is reported as the ‘kit rating’ (maximum 12).

1.3.1.4 Stiffness(mechanical properties)

Stiffness provides information about the behavior of a material when an external
force is applied, i.e., it tells the extent to which it can resist deformation in re-
sponse to that force. Stiffness is one of the important properties because, from the
preparation of the packaging material to the end use of the package, the material
is subjected to different types of forces and bending. So, the packaging material
must have the capacity to be bent and withstand different forces during converting.
To assess the stiffness of the material, Elastic Modulus can be determined through
tensile testing, and/or bending resistance can be analyzed.

1.3.1.5 Sealing properties

Selability and seal strength are also important parameters of a packaging material.
A packaging material should have good sealing so that the packaged content doesn’t
get leaked through the seal. Depending on the structure of the packaging material,
different sealing techniques can be used, namely: heat sealing, cold sealing, and
ultrasonic sealing. In the case of a heat-sealed material, the sealing strength is
measured by first heat-sealing the packaging material sample at a particular tem-
perature, pressure, and time, and then measuring the force required to break apart
the seal, which is done by pulling away the material near the seal area using a tensile
tester.

1.3.2 Liquid packaging board structure
Liquid packaging board (LPB) has been used for the production of food containers
for liquids and creamy substances for more than 40 years. It is used to protect
and transport food, and to avoid its contamination by external sources. A typical

8



1. Introduction

structure of aseptic LPB is shown in Figure1.6

Figure 1.6: LPB structure

The above picture depicts the different layers present in an aseptic LPB, mean-
ing an LPB that requires a long shelf-life, even at ambient conditions. In order
to protect the food, four layers are typically present on the inner side of the pa-
perboard (i.e., towards the packaged product), and one of the plastic layers is the
one in contact with the food. The outer side of the paperboard is known as the
printing surface, on which information about the product and brand are printed.
On the top of the printing surface another plastic layer is added, typically named
the condensation layer. Today most of the plastic laminates used in LPB contain
low-density polyethylene (LDPE). Depending on the application of the LPB, the
number of layers can vary. While typical aseptic LPB contains both LDPE and
aluminum layers, LPB for shorter shelf-life applications contains only LDPE. Be-
ing LDPE derived from fossil-based resources and not biodegradable, to produce
more sustainable packaging materials, and in specific LPB, one needs to focus on
the replacement of LDPE by other more sustainable alternatives. In this project
polyhydroxyalkanoates (PHA) were chosen for this purpose.

1.4 Extrusion coating
Extrusion coating is one of the first processes designed to extrude thermoplastic
polymers onto flexible substrates. Since its introduction, extrusion coating has been
continuously developed over the years and nowadays it turned into one of the most
used processes for extrusion and lamination of plastics [16].

The first extrusion coating was done with polyethylene on the paperboard. Since
then it has been used for the extrusion of different polymers and for various appli-
cations. In extrusion coating a thin film of hot molten polymer comes out the of
extruder and is passed to a cooled nip reel assembly (Figure1.7A). The length and
thickness of the extruded film are determined by the type of die utilized. Typically,

9



1. Introduction

the extrusion coating of a polymer film on a paperboard leads to a coat weight in
the range of 10-75 g/m2. The part of the equipment that coats the polymer film
onto the paperboard is also sometimes called a laminator[16]. The molten polymer
that comes out of the die is pulled towards the nip, which is formed by a chill roll
and a rubber pressure roll. The substrate (e.g., paperboard) is fed continuously and
it is pressed with the polymer melt. Due to the compression force applied by the
pressure roll, the polymer melt gets adhered to the substrate[16].

The position of the chill roll with respect to the die is of critical importance. The
melt entry angle and height from which the chill roll is placed (air gap) also determine
how well the polymer can be coated on the paperboard. The polymer melt must be
fluid enough to flow onto the surface of the substrate continuously and it is cooled
immediately so bonds get formed with the substrate. The thickness of the coated
film on the substrate depends on the relative velocity of the extruder to the chill
roll. The pressure roll is associated with a backup roll that removes the heat from
the former while being cooled with water at a temperature in the range of 15-20◦C
[16]. The image below demonstrates the extrusion process.

Figure 1.7: A. Shows the typical cross-section scheme of the most important parts of
the extrusion process; B. Extrusion of PHA film at pilot scale; C. Extrusion-coated
paperboard at pilot scale

1.5 Objectives
The main objectives of this Master thesis project were
• To characterize different PHA samples in terms of properties relevant to their pro-
cessing within extrusion coating: melting temperature, glass transition temperature,
crystallinity, thermal stability, and rheological properties of the polymer melt.

10



1. Introduction

• To evaluate some of the properties of the produced PHA-based materials relevant
for packaging materials: heat seal strength, mechanical and water vapor barrier
properties.
• To understand how the rheological properties of PHA may affect the extrusion
coating process.
• To assess how PHA crystallinity may affect barrier properties of ensuing materials.
• For this purpose, both hot-pressed PHA films, prepared in-house, and PHA-coated
paperboard, produced at pilot scale, were analyzed.

1.6 Limitations
In this thesis only technical properties of different PHA types and samples pre-
pared thereof were assessed. Other aspects that are usually of interest when a new
polymer is to be introduced into the packaging world, such as feedstock, geograph-
ical availability, and cost, were not in focus. Moreover, due to time constraints,
normal for a Master thesis project, the type of characterization to be done on the
PHA samples was limited to a number of prioritized parameters, and some other
relevant properties were not assessed, for instance, recyclability and compostabili-
ty/biodegradability of the PHA-based materials.

There were also some technical constraints worth mentioning: i) since no extruder
was available in-house, PHA films were produced at lab-scale with a hot-press in-
stead; ii) since technical issues (i.e., related to PHA stickiness) were encountered
when trying to analyze Mw of the PHA samples using Gel Permeation Chromatog-
raphy (GPC), one needed to rely on Mw information present on the technical data
sheet of the material.

11



2
Materials and Methods

2.1 Materials
Four different PHA types in granulate form were studies. The four PHA types
will be termed throughout the thesis as PHA A, PHA B, PHA C, and PHA D.
In the table below, information obtained from the respective technical data sheets
regarding the molecular weight of the four PHA types is listed. Along with these
PHA and LDPE coated paper board were obtained from the pilot trials and the
average thickness of the samples was 280µm.

Table 2.1: Qualitive molecular weight of the different PHAs studied

Material
type Molecular weight

PHA A Low molecular weight
PHA B Medium molecular weight
PHA C High molecular weight

PHA D High molecular
weight(blend with PBS)

2.2 Experimental methods

2.2.1 Film preparation
Films of all four PHA types and also LDPE (reference) with an average thickness
of 45µm were produced in-house by compression moulding using a Collin hot-press.
Prior to hot-pressing, the granulates (except LDPE) were dried at 60◦C for 4 hours
to remove any residual water that could evaporate and originate bubbles during hot-
pressing. The hot-press was set to 175◦C (120◦C for LDPE) and the mould setup
(Figure2.1) was pre-heated at this temperature. Release films were placed on metal
plates and the metal frame was placed on the bottom metal plate. The metal frame
dimensions were 14 cm x 14cm with a thickness of 0.1 mm. The polymer granulates
were placed in the center of the frame and the top metal plate was brought down into
contact with the bottom metal frame to melt the granulates without any additional
pressure. The granulates were left to melt for 14 min and then a pressure of 100 bar
was applied for 2 min. After pressing, the mould setup was taken out and left to

12



2. Materials and Methods

cool down for 3 minutes. Then the polymer films were carefully removed from the
release films. The table below summarizes the conditions used to prepare the films.

Figure 2.1: A.Sample pack setup in hot press B.Schematic representation of the
setup

Table 2.2: Summary of the conditions used to prepare PHA and LDPE films with
hot-press

Material
type

Pre heat-
ing tem-
perature
(◦C)

Preheating
timing (h)

Melting
tem-
per-
ature
(◦C)

Melting
time
(min)

Pressure
applied
(bar)

Pressure
applied
timing
(min)

PHA A 60 4 175 14 100 2
PHA B 60 4 175 14 100 2
PHA C 60 4 175 14 100 2
PHA D 60 4 175 14 100 2

LDPE no preheat-
ing - 120 14 100 2

2.2.2 Differential Scanning Calorimetry(DSC)
DSC is a thermal analysis technique that can provide various polymer character-
istics, such as melting temperature, glass transition temperature, crystallization
temperature, enthalpy of fusion, etc., by measuring the difference in the amount
of heat required to increase the temperature of a polymer sample and reference as
a function of temperature. The reference sample(Platinum crucible pan), is also
exposed to the same conditions as polymer sample[17].

DSC measurements were done using a TA Instruments Q2000 device. Four heating
and cooling cycles were measured. In the heating cycles, 10mg polymer samples
were first equilibrated at -20◦C for 5 min and then heated to 190◦C with a heating

13



2. Materials and Methods

rate of 20◦C/min. In the cooling cycles, the samples were then kept at 190◦C for 2
min before being cooled down to -20◦C at the same rate used for heating. Nitrogen
was used as purging gas and the flow rate was kept at 50 ml/min. For all PHA
samples, the first cycle was disregarded for further calculations since it is usually
associated with the polymer’s thermal history.

Alongside with the Tm and Tc, the crystallinity (in percentage) was also calculated
from the DSC curves for the different PHA’s. Crystallinity for each PHA sample was
calculated based on the ratio between its melting enthalpy and that of a 100% crys-
talline PHA polymer, which was obtained from the literature. The same procedure
was followed for analyzing PBS.

2.2.3 Thermogravimetric Analysis(TGA)
TGA analysis is a technique in which the polymer sample is subjected to a defined
temperature program. In this analysis, the temperature is raised at a constant rate
and the mass of the material is recorded with the rise in temperature[18]. TGA
provides a good insight into the thermal stability of the material since it enables to
assess at what temperature the material starts degrading (thermal degradation).

TGA analysis was done using a TA Instruments Q5500 device. The samples were
first equilibrated at 40◦C and then heated to 105◦C with a heating rate of 5◦C/min.
Then the samples were kept isothermal for 20 min and then again heated to 700◦C
with a heating rate of 5◦C/min. At 700◦C the samples were also kept isothermal
for 20 min. The obtained thermograms depict the mass change with respect to the
increasing temperature. Air was used as purging gas with a flow rate of 10 ml/min.

2.2.4 Dynamic Mechanical Analysis(DMA)
DMA is used to investigate the molecular relaxation in polymers and to calculate
inherent mechanical and flow properties as a function of time and temperature.
DMA can be used to find in an accurate way the glass transition temperature (Tg)
of a polymer. In DMA, the storage modulus (G′) and the loss modulus (G”) of the
material is measured while ramping the temperature at a constant amplitude. With
the value of G′ and G”, one can determine tan(δ). Then, the Tg is obtained as the
peak value in the Temperature vs tan(δ) graph[19]

DMA evaluation was done with an Anton Paar MCR702 Twindrive rotational rheome-
ter. The analysis was carried out at the temperature range of -40◦C to +40◦C. First,
the strain sweep test was done to determine the linear viscoelastic region. From the
strain sweep test, the strain of 0.008% was selected. The dimensions of the films
used for the testing were 12mm x 20mm. Once the sample was mounted the tem-
perature was decreased to -40◦C at a cooling rate of 8◦C/min. A constant normal
force of -0.04N was applied to keep the sample in tension as the films were thin.
Then, at the constant strain of 6 rad/s, the temperature was raised to +40◦C at the
heating rate of 2◦C/min. The data was recorded and the temperature was brought

14



2. Materials and Methods

back again to room temperature before the next sample was loaded.

2.2.5 Fourier Transform Infrared Spectroscopy(FTIR)
FTIR is one of the analysis techniques used to characterize the chemical composition
of polymeric materials. In this project, FTIR was performed using a Bruker Plat-
inum device coupled with an ATR cell. The analysis was done with an accumulation
of 24 scans and the resolution of 1cm-1 was used to record the spectra.

2.2.6 Mechanical Properties
The mechanical properties of interest in this project were tensile strength, tensile or
Elastic modulus, and heat seal strength.

2.2.6.1 Tensile testing

The tensile modulus, also known as elastic modulus or Young’s modulus, gives
information about the linear elasticity of the material. The elasticity of the material
is evaluated based on the relationship between deformation and the force or power
required for this deformation to happen. Young’s modulus is given by the equation:

E = σ/ϵ (2.1)

E = Elastic modulus
σ = Stress
ϵ = Strain

The maximum stress and the elongation a material can handle before it breaks
can be measured during tensile testing. The tensile testing was performed using
a Zwick/Roell machine equipped with a 100 N load cell. For every experiment, a
preload of 0.2 N was applied to keep the film in tension as the films were thin. The
films used for the experiment were cut into dumbbell shapes of 30mm x 5mm using
a die cutter with the right dimensions (see Figure2.2) and the test was performed
at a speed of 50 mm/min as per ISO standard. For each PHA type, 10 replicates
were analyzed and the average values were then calculated.

2.2.6.2 Seal strength testing

One of the important requirements for a packaging material is its sealability and
seal strength. The heat sealing test was performed by first using a Param HST-H3
heat sealer device to seal the polymer films and subsequently, the force required to
break the sealing, meaning the seal strength, was then evaluated using an Instron
5969 tensile tester. The hot-pressed films were cut into dimensions of 60mm x 15mm.
Then two samples of the same type of PHA film were pressed together at the top (see
Figure2.2) under a specific sealing temperature with a dwell time of 1 second and
pressure of 200 kPa. The heat sealing was performed at six different temperatures:
175◦C, 180◦C, 185◦C, 190◦C, 195◦C and 200◦C. Then, as mentioned above, the seal
strength of the samples was tested using a tensile testing machine by clamping the

15



2. Materials and Methods

lower ends of both films to one of the two clamps. A 500 N sensor was used as a
load cell and a pre-load of 4 N was applied to keep the sample under tension. The
test was performed at the speed of 50 mm/min and the force required to break the
seal was recorded. This test was performed on 5 replicates for each PHA type and
for each temperature, and then average values were calculated.

Figure 2.2: Sample structure used for I. Seal strength testing(ISO 11607); II. Tensile
testing(ISO 527-1)

2.2.7 Rheological properties
Rheology refers to the study of matter when subjected to flow or deformation. Rhe-
ological measurements can provide information on how to achieve a uniform coating
of a certain polymer on paperboard without defects. Some of the defects that can
be avoided are bubbles, streaks, edge defects, etc.

2.2.7.1 Rotational rheometry

Rotational rheometry measurements were done using an Anton Paar MCR702 Twin-
Drive instrument. The rotational rheometer was used to study the thermal stability
of the material, together with strain sweep and frequency sweep tests. The rheome-
ter was equipped with a convection oven CTD450. A cone-plate measuring geometry
having 2◦ angle and 25 mm diameter and the bottom with a flat plate of 30mm di-
ameter was used. For each test, the oven was pre-heated to the desired temperature
and then the polymer granulates were loaded. The distance between the top and
bottom plate was 0.106 mm (standard for the measuring geometry used). The ta-
ble below summarizes the measurement conditions used for the different rheological
tests.

16



2. Materials and Methods

Table 2.3: Rotational rheometer measurement conditions

Test type Amplitude-
Strain(%) Frequency(Hz) Temperature(◦C)

Thermal
stability 0.05 1 175 and 160

Strain
Sweep test 1 to 1000 1 160

Frequency
Sweep test 1 0.01 to 100 160

2.2.7.2 Capillary rheometry

A Göttfert RG20 capillary rheometer was used to measure the melt viscosity at
processing-relevant shear rates. After setting the test temperature, the cylindrical
barrel of 15 mm diameter was filled with polymer pellet which were let to melt down
for 10 min. Then the piston was lowered to the measuring position. The rheome-
ter measures the shear rate and shear stress based on the value of pressure, piston
speed, and capillary die used. The pressure measurement is done above the capil-
lary die in the barrel, hence a correction factor was applied to get the actual shear
stress. The basic rheological properties in capillary rheometry are determined based
on Newtonian fluid assumption, thus a shear rate correction was also applied to get
the true shear rate. Once the true shear rate and shear stress were estimated, the
true melt viscosity (η) was calculated. The image below depicts the cross-sectional
view of the capillary rheometer.

Figure 2.3: Cross-sectional view of a capillary rheometer

BAGLEY CORRECTION
The Bagley correction is used for shear stress correction. At first, a capillary die
of diameter 1 mm and length 20 mm is used and apparent values of shear rate and
shear stress are measured. Then the capillary die is changed to that of a diameter

17



2. Materials and Methods

of 1 mm and length of 0.2 mm and the shear rate and shear stress are measured
again. The true shear stress is calculated as follows

Figure 2.4: Bagley correction graph

τ = (∆P )/2 ∗ (L/R + e) (2.2)

∆P = Pressure difference between inlet and outlet
L/R = length by radius ratio of capillary dies
e = Indicates the extrapolated value to x axis

For a given shear rate, pressure values as well as their corresponding L/R ratio are
taken from both capillary dies. The values are plotted with pressure at the y-axis
and L/R ratio at the x-axis, this gives a two-point straight line. This line is extrap-
olated to the x-axis which gives e value. These values are substituted in the formula
above to get true shear stress (τ). Corrected shear stress values were calculated for
every shear rate using the steps described.

WEISSENBERG-RABINOWITSCH CORRECTION
The different polymer melts showed shear thinning flow behaviour. Due to this,
shear rates (γ̇) at the wall are high, but the instruments assume a Newtonian flow
behaviour (see Figure2.5) and only measure the apparent shear rates. Hence, a
correction factor must be introduced to get corrected true shear rates.

Figure 2.5: Shear rate profile

18



2. Materials and Methods

The shear rate was corrected using the formula below

γ̇ = ((3 ∗ n + 1)/(4 ∗ n)) ∗ γ̇a (2.3)

To find the value of n the power law model was used

τ a = K ∗ γ̇a
n (2.4)

τ a = shear stress apparent
K = flow index
γ̇a = apparent shear rate

Taking logs on both sides gives

log(τ) = n ∗ log(γ̇a) + log(k) (2.5)

This equation is of the form Y = Mx + C where C represents the interception
and M represents the slope,here n represents the slope and log(k) represents the y-
interception. These equations are applied for every shear rate to get true shear rates

Once the true shear rate and stress are obtained the true melt viscosity(ηs) is cal-
culated using the formula below.

ηs = τ/γ̇ (2.6)

2.2.8 Water Vapour Transmission Rate(WVTR)
Water vapour transmission rate (WVTR) analysis was done to assess the barrier per-
formance of both the hot-pressed PHA films and PHA-coated paperboards against
moisture. The analysis was done using a ProUmid dynamic vapour sorption ana-
lyzer. The samples were cut into round shapes of a diameter of 7 cm possessing
six small holes in the circumference for screwing the samples onto the chamber. In
each chamber, 5 grams of molecular sieves were placed so that the bottom was fully
covered. The samples were then placed and screwed onto the chamber. The barrier
properties were assessed under two different environmental conditions: normal con-
ditions - 50% relative humidity and temperature of 23◦C and tropical conditions -
80% relative humidity and temperature of 38◦C.

19



3
Results and Discussion

3.1 DSC
The DSC measurements were carried out to get more information about the differ-
ent PHA types studied in this project and find, among other things, their melting
temperature, which can give a good understanding of the optimal operating tem-
perature for the extrusion coating process. The image below shows an example of
the DSC curves obtained in the different heating and cooling cycles for PHA A and
PHA D (the DSC curves for the other PHA types can be found in the appendixA.1
and A.2)

(a) PHA A

(b) PHA D

Figure 3.1: DSC curves obtained in different (I)heating and (II)cooling cycles

20



3. Results and Discussion

From the image above, it is possible to observe that there are two endothermic peaks
in the heating curves of PHA A (Figure:3.1 (a)-I) and three endothermic peaks in
those of PHA D (Figure:3.1 (b)-I). For the other PHA types, only 2 endothermic
peaks were observed as in the case of PHA A (FiguresA.1 and A.2). The presence
of two endothermic peaks indicates that PHA A, PHA B, and PHA C contain two
different polymers that melt at different temperatures, which is in tune with the
information in the technical data sheet. In the case of PHA D, which was known
from the beginning to be a blend with PBS, apart from the two peaks corresponding
to two different polymers (also in tune with the information in the technical data
sheets), its DSC heating curves also showed a third peak likely assigned to PBS. To
corroborate that PBS was really present in PHA D, DSC measurement was also car-
ried out for pure PBS. The DSC results for PBS(Figure:3.2) showed that its melting
temperature is around 114◦C, which is in tune with the temperature at which the
third peak appears in the heating curves of PHA D.

Figure 3.2: DSC curves of PBS obtained in different heating(I) and cooling(II) cycles

PHA A and PHA C also showed two exothermic peaks during the crystallization
process, which indicated that the two constituent polymers don’t co-crystallize at
the same temperature.

The table below summarizes the average values of Tm,Tc and Tg of the different
PHAs studied and of LDPE. The melting enthalpy of PHA D alone was calculated
by integrating two peaks of PHA and neglecting the PBS associated peak.

21



3. Results and Discussion

Table 3.1: DSC results for the PHAs studied and LDPE

Material
type

Average melting
temperature (°C)

Average crys-
tallisation
temperature
(°C)

Average melting
enthalpy (J/g)

PHA A Tm1 = 135.1, Tm2 =
147.7 78.3 61.3

PHA B Tm1 = 128.1, Tm2 =
144.6 70.6 59.2

PHA C Tm1 = 136.0, Tm2 =
153.3 68.0 42.1

PHA D Tm1 = 131.7, Tm2 =
151.6, Tm3 = 114.1 58.1 25.1

LDPE Tm1 = 107.2 95.4 127.2

As could be expected, there seems to be a certain correlation between Tm and Mw;
PHA samples with the lowest Mw (PHA A and PHA B) generally presented the
lowest Tm values, while PHA samples with the highest Mw (PHA C and PHA D)
presented the highest Tm values.

Based on the melting enthalpy values, the crystallinity of each PHA type was calcu-
lated. The melting enthalpy of a 100% crystalline polymer(146 J/g) was taken from
the literature [20]. The crystallinity was also calculated for LDPE (the reference
sample) taking into account its melting enthalpy value. The melting enthalpy of
100% crystalline LDPE(293J/g) was also taken from the literature[21]. The table
below summarizes the crystallinity for the different PHA types and LDPE

Table 3.2: Percentage of crystallinity for the different PHAs studied and LDPE

Material
type

Average melting
enthalpy of sample
(J/g)

Melting en-
thalpy of
100% crys-
talline poly-
mer(J/g)

Crystallinity(%)

PHA A 61.3 146 41
PHA B 59.2 146 40
PHA C 42.1 146 29
PHA D 25.1 146 17
LDPE 127.2 293 43

PHA and PHA B seem to have similar crystallinity to that of LDPE, PHA C and
PHA D have significantly lower crystallinity, being PHA D apparently the least
crystalline material. The blending with PBS may have contributed to this low
crystallinity[22]. The crystallinity values are also used in the section below to try
to identify the impact of crystallinity on the water vapor barrier properties of the
different PHA samples. In general, it is believed that by increasing the crystallinity

22



3. Results and Discussion

of a polymer, its WVTR should decrease. Nonetheless, it is worth noting that sev-
eral other factors also have an effect, such as the molecular weight and degree of
polymerization of the polymer, the quality of the coated film etc.

3.2 TGA
The TGA analysis can provide useful information about the maximum recommend-
able temperature to process PHA during extrusion coating. The thermograms of the
different PHA types and LDPE in the image below show how their mass is affected
by increasing temperature.

Figure 3.3: TGA results for the different PHAs studies and LDPE. (Note: The Y-
axis of the TGA curves were offset for better visibility of the different thermograms.)

From the figure above it can be seen that all PHA samples start to thermal degrade
steeply at the temperature range 245-257◦C. However, the onset of thermal decom-
position starts already at around 190◦C. At this temperature, PHA likely starts
depolymerizing and slowly decomposing up to the point at which the decomposition
is then very fast (245-257◦C). LDPE, on the other hand, starts to slowly decompose
at around 219◦C and the pronounced degradation happens only at 423◦C. This in-
dicates that PHA is less thermally stable than LDPE, as already reported in the
literature[23]. The thermogram of PHA D also showed a second smaller decompo-
sition step at around 295◦C (Figure3.3), likely attributed to the presence of PBS
in this PHA blend. This is in tune with the literature, in which it is reported that
PBS starts to degrade at around 300◦C[24].

23



3. Results and Discussion

3.3 DMA
Since the glass transition temperature (Tg) could not be retrieved by DSC, DMA
was also carried on all the PHA samples. The Tg is a very relevant parameter for
amorphous and semi-crystalline polymers (which is the case of the PHAs studied)
and provides information about the temperature at which the polymer changes from
a glassy state to a flexible rubbery state. As explained in the experimental section,
the Tg value was taken as the temperature at which the maximum Tan(δ) value
is attained in the temperature vs Tan(δ) curve (Figure3.4). The value of δ was
calculated as the ratio between G” and G′.

Figure 3.4: DMA curves for (I)PHA A, (II)PHA B, (III)PHA C, and (IV)PHA D

From the DMA curves above, one can observe that the Tan(δ) curve is very noisy
for all the PHA samples. Thus, the estimated Tg values listed in Table:3.3 are only
approximate. The reason for the noise, also observed for the G’ and G” curves,
could be related to the nature and physical stability of the PHA films, since these
were rather thin(80-90µm).

24



3. Results and Discussion

Table 3.3: Tg values obtained in this study by DMA for all the PHA samples.

Material
type Tg(◦C)

PHA A 12
PHA B 10
PHA C -2
PHA D -4

The Tg values obtained for PHA C and PHA D are similar to those reported in
the respective technical data sheets, which were measured using DSC. However, for
PHA A and PHA B, much higher Tg values were obtained by DMA in this study,
compared to those reported in the technical data sheets using DSC. The reason
for this significant difference is not well understood, and more studies would need
to be carried out to clarify this. Nonetheless, if one looks only at the Tg values
obtained in this study, there seems to be a correlation between these and the Mw
of the different PHA samples. Surprisingly, PHA with lower Mw (PHA A and PHA
B) had higher Tg values, and PHA with higher Mw (PHA C and PHA D) had lower
Tg values. These results contradict the established overall qualitative dependence
of Tg on Mw, in which Tg is expected to increase with increasing Mw. On the other
hand, the results correlate with the fact that typically higher degree of crystallinity
of the polymer (lower amount of amorphous regions) leads to increased Tg. This
then indicates that for PHA materials, the degree of crystallinity has a stronger
effect on Tg than Mw per se.

3.4 FTIR
FTIR spectroscopy was used to characterize the chemical composition of the different
PHA samples. The obtained FTIR spectra can be seen in Figure3.5 below. All PHA
samples presented similar FTIR spectra. The peak at 1719cm-1 is assigned to the
presence of C=O vibration from the ester function in PHA. The peaks at 1179cm-1

and 1129cm-1, represents C-O stretching and those at 1044cm-1 and, 979cm-1 are
attributed to C-H bending vibration. The peak at 1274cm-1 may indicate the pres-
ence of amine moieties. Since PHA don’t normally possess amine groups in their
structure, this suggests the presence of amine-containing additives. Further studies
would be required to find the type and exact composition of the additives but this
was out of scope for this project.

25



3. Results and Discussion

Figure 3.5: FTIR spectra PHA A(Red), PHA B(black), PHA C(green), PHA
D(blue)

3.5 Mechanical properties

3.5.1 Tensile testing
Tensile testing was performed on films of all PHA types in order to determine the
mechanical properties of the different materials. The results are summarized in the
table below

Table 3.4: Summary of mechanical properties for all four PHA samples.

PHA
Type

Tensile
stress(N/mm2) Strain(%) Young’s

Modulus(N/mm2)
PHA A 32.4 ± 6.2 2.8 ± 0.1 11.7 ± 1.04
PHA B 33.3 ± 9.6 3.1 ± 0.2 11.0 ± 0.9
PHA C 20.6 ± 1.6 8.2 ± 7.3 3.6 ± 1.7
PHA D 20.5 ± 1.4 5.6 ± 0.7 3.6 ± 0.2

There are several factors that can affect the tensile strength (tensile stress) of poly-
mers, namely temperature, strain rate, molecular weight, degree of crosslinking, and
crystallinity[25]. Since all PHA samples were tested at the same environmental con-
ditions (23◦C and RH=50%) and strain rate, and there is no indication that the
polymers are crosslinked, the discussion of mechanical properties will focus mainly
on molecular weight and crystallinity. Tensile strength is expected to increase with
increasing Mw since more entanglements can occur between the polymer chains and
more force is needed to loosen up those entanglements[26] Surprisingly, the results
show the opposite behaviour, i.e., PHA A and PHA B that have lower Mw than
PHA C and PHA D (according to the respective technical data sheets), possessed

26



3. Results and Discussion

higher tensile strength. On the other hand, it is also known that tensile strength is
expected to increase with increasing crystallinity, since the intermolecular bonding
within the polymer chains increases[27]. The results show that PHA C and PHA
D, which had the lowest crystallinity, were the ones presenting the lowest tensile
strength, as would be expected. These results then indicate that, under the testing
conditions used, the crystallinity of PHA had a stronger influence on the mechanical
properties than Mw. Strain results also align with crystallinity results, i.e., PHA
with higher crystallinity (PHA A and PHA B) deformed less before breaking (lower
strain values). From the results, one can also conclude that the presence of PBS in
PHA D didn’t have a very big impact on the mechanical properties if one compares
the strength and Elastic modulus values obtained for PHA C and PHA D, which
have similar Mw according to the technical data sheets.

3.5.2 Heat sealing
In order to understand the optimal conditions to heat-seal the PHA films produced
in-house and to analyze how strong the ensuing seals were, a heat-sealing test was
performed at different temperatures (pressure and dwell time were kept constant),
which was then followed by heat seal strength test. With this sequence of tests, it
was not only possible to understand the influence of temperature on sealing, but
also the maximum force the ensuring seals could withstand. The graphs in the
image below show how the different temperatures used for heat sealing affected the
strength of the formed seals for the different PHA films produced.

Figure 3.6: Seal strength of (I)PHA A, (II)PHA B, (III)PHA C and (IV)PHA D
hot-pressed films at varying temperatures

27



3. Results and Discussion

The results show that the temperature really had an impact on the strength of the
formed seals,i.e., on the force required to break the seals. For PHA C it is possible
to observe that increasing temperature up to 195◦C led to increased seal strength.
This trend was not so evident for the other PHA samples, for which the seal strength
varied randomly with changes in temperature. However, all PHA samples obtained
the highest seal strength at 195◦C, which indicates that this was the most adequate
temperature to heat seal PHA samples. This temperature is 42-77◦C higher than
the Tm of the different PHA samples, thus the PHA samples were likely fully melted
during heat-sealing. The absence of a clear relationship between temperature and
force required to break the seal (i.e., seal strength) for PHA A, PHA B, and PHA
D, may be related to the big variation in film thickness(60 - 90µm) for these samples
(much more than for PHA C films). It is known that for thicker samples, at the
same heat-sealing temperature, the strength required to break the seal increases[28].
Thus if some films of the same PHA type were thicker than others, it also influenced
the seal strength results. Above 195◦C, as indicated by TGA results, PHA starts
to thermally decompose. Thus, the seal strength decreased for all PHA samples at
200◦C, even if the dwell time used to heat-seal the samples was only 1 second.

Interestingly, there seems to be a good correlation between seal strength and crys-
tallinity of PHA. Considering the maximum seal strength at 195◦C, it is possible
to observe that seal strength increased with decreasing PHA crystallinity in the or-
der: PHA A (8.7N) < PHA B (9.1N) < PHA C (13.7N) < PHA D (15.6N). It is
known that the seal initiation of semi-crystalline polymers, like the different PHA
materials in this study, occurs when the amorphous fraction increases by heating,
as the crystalline regions start disassembling and the polymer chains become more
mobile[29]. Thus, under the heat-sealing conditions used in this study, i.e., for a
short dwell time of 1 second, it was easier for the samples with lower crystallinity
( meaning a bigger fraction of amorphous regions) to fully fuse and create a good
seal. Also there seems to be a good correlation between seal strength and Mw at
195◦C, and seal strength seems to increase with increasing Mw: PHA A (8.7N) <
PHA B (9.1N) < PHA C (13.7N) < PHA D (15.6N).

3.6 Rheological properties

The rheology measurements are important for creating and preventing coating flaws
on the paperboard. The measurements of interest in this thesis were,
• Melt viscosity
• Extensional viscosity
• Strain sweep test
• Frequency sweep test

These tests can show how the polymer melt behaves and how they behave when
exposed to higher shear rates at the processing conditions.

28



3. Results and Discussion

3.6.1 Thermal stability of PHA
As mentioned above, PHAs can degrade when exposed to high temperatures(which
are below those of the thermal decomposition of conventional fossil-based polymers).
Thus, when exposed to high temperatures, some PHA polymers can show a drop in
viscosity, which interferes with the change in viscosity upon increasing shear rate,
and this can provide the wrong value of melt viscosity[24]. So it is primarily nec-
essary to determine the safe operating temperature for measuring the rheological
properties.

To assess the thermal degradation of the polymer, the loss modulus(G”) and stor-
age modulus(G′) are measured with respect to a constant amplitude of 0.05 and
frequency of 1Hz. For reference, the same measurement is also done for LDPE.

Figure 3.7: Thermal stability of the (I)LDPE 175 at ◦C, (II)PHA A at 175◦C,and
(III)PHA A at 160◦C

From the figure above, one can see that the G′ and G” lines for LDPE are straight
which indicates that the material is stable at 175◦. However, for PHA A, one can

29



3. Results and Discussion

see that, the G′ and G” lines create a declining slope with increasing time. This
indicates that the material starts to degrade with time at temperatures above its
melting point, likely due to a decrease in molecular weight. The slope is steeper for
PHA A at 175◦C which was the material preparation temperature and pilot plant
processing temperature. However, the degradation process seems to be slower for
PHA A at 160◦C. This phenomenon is observed for other PHA samples as well Fig-
ureA.4. To weaken the influence of thermal degradation on rheological data, the
measurement temperatures were kept at 160◦C.

3.6.2 Relaxation behaviour of PHA
The linear viscoelastic region of the polymer amplitude sweep was assessed with a
constant frequency of 1Hz. The amplitude sweep provides the limit of the linear
viscoelastic region and the range in which the frequency sweep test can be operated.
The images below represent the amplitude sweep test of LDPE and PHA’s.

30



3. Results and Discussion

Figure 3.8: Amplitude sweep graph for (I)LDPE, (II)PHA A, (III)PHA B, (IV)PHA
C, and (V)PHA D

The graphs in Figures3.8 indicate that G′ lines are horizontally straight for all PHA’s
and LDPE at frequency range 0.1Hz to 10Hz. This indicates the linear viscoelastic
region of these polymers, and from this, a constant frequency of 1Hz was taken
for the frequency sweep test. Apart from this, it was possible to observe that at
any given point in the viscoelastic region the value of G” is greater than G′, which
indicates that all the samples showed fluid structure and behave as viscoelastic fluid.

The frequency sweep test is also useful to obtain more characteristic information
about polymer melt. The viscoelastic properties of the polymer may change over
time and these oscillation measurements can be useful to determine their long-time
behaviour. Figure3.9 shows the cross-over of G” and G′ along with phase angles.

31



3. Results and Discussion

Figure 3.9: Frequency sweep graph (I)LDPE, (II)PHA A, (III)PHA B, (IV)PHA C,
(V)PHA D

The crossover point indicates the phase transition of the material and it shows the
time taken by each material to change from elastic material(before cross-over fre-
quency) to viscous material(after cross-over frequency). The table below summarizes
the cross-over frequencies.

Table 3.5: Cross over frequencies for LDPE and different PHAs studied

Material
type

Cross over fre-
quency(Hz) G”(Pa) G′(Pa)

LDPE 0.1 27463 27651
PHA A 0.1 61739 61993
PHA B 0.25 61201 63983
PHA C 0.15 65020 65020
PHA D 0.1 69582 71704

The cross-over frequency values in the table above indicate that for lower and higher
molecular weight PHA’s the time taken to change into viscous behaviour is the same
as that for LDPE. The graph in the image above also indicates the Phase angle(δ)
for LDPE and PHAs. The Phase angle is a relative measure of the material’s viscous
and elastic properties. For LDPE and PHAs, it is possible to observe that at lower
frequencies the phase angle is almost 90◦ indicating that these materials are of a
viscous nature. Therefore they do not possess a yield stress.

32



3. Results and Discussion

3.6.3 Frequency sweep test and Non-Newtonian behaviour
In the frequency sweep test, the complex viscosity was measured over a range of
frequencies. The frequency sweep graph is shown in the image below. It is possible
to observe that there are two complex viscosities lines for each PHA. The complex
viscosity indicates the frequency sweep from 100Hz to 0.01Hz and the complex
viscosity reverse indicates the frequency sweep from 0.01Hz to 100Hz

Figure 3.10: Complex viscosity graphs for (I)LDPE, (II)PHA A, (III)PHA B,
(IV)PHA C, (V)PHA D

33



3. Results and Discussion

From Figure:3.10, it is observed that both viscosity curves showed the same path for
LDPE. However, this was not the case for the PHAs. For PHAs, from the interme-
diate to high-frequency range(0.1Hz to 100Hz), all showed shear thinning behaviour,
proving the polymer melt is a Non-Newtonian fluid. From low to intermediate fre-
quency range(0.01Hz to 0.1Hz), there is a sudden drop in viscosity in the complex
curves except for PHA D. The sudden drop in viscosity might be attributed to the
thermal degradation of the polymer. For PHA D alone, the complex viscosity is
the same for both viscosity curves. This indicates that the blending with PBS may
have improved the thermal stability of this PHA. Another reason for the increase
in stability could be the monomer ratio, as different PHAs have different monomer
ratios.

3.6.4 Melt Viscosity
The melt viscosities were measured with a capillary rheometer. As mentioned ear-
lier, capillary rheometers were used to measure melt viscosity at process-relevant
shear rates. The melt viscosities were measured by going from higher shear rates to
lower shear rates.

The image below represents the corrected melt viscosities of LDPE and of all four
PHA studied. From this image, it is possible to observe that with an increase in
shear rate, the melt viscosities decreases, which indicates the polymer melt has
shear thinning behaviour, even at higher shear rates. The line of viscosity s almost
straight for LDPE. However, for PHAs the viscosity lines have more fluctuations.
These fluctuations indicate that PHAs are pressure-sensitive materials. Among the
PHAs studied, the line of PHA D is a close resemblance to that of LDPE, which
suggests that with an increase in the molecular weight and blending with other
polymers(in this case PBS), the material stability can also be increased.

Figure 3.11: Melt viscosities for LDPE and PHA studied

34



3. Results and Discussion

3.7 WVTR
The water vapour transmission rate of all PHA films and some of the PHA-coated
paperboards (with PHA A, PHA C, and PHA D) was assessed at two different
environmental conditions: normal (23◦C and RH=50%) and tropical (38◦C and
RH=80%). From Figure3.12, it is observed that all samples presented higher WVTR
values than the reference sample (LDPE) in all conditions. This shows that PHA
materials still require some developments in order to attain as good water vapor
barrier performance as LDPE-based materials.

Figure 3.12: WVTR results of PHA films (top) and PHA-coated paperboards (bot-
tom) at normal (left) and tropical conditions (right).

At normal conditions, PHA C (both in the form of film and coated paperboard)
showed the lowest WVTR values. Nonetheless, it is worth noting that samples
containing PHA C were the ones possessing high variation in film/coating thick-
ness. Interestingly, in tropical conditions, the paperboard coated with PHA C still
presented the lowest WVTR value, but not the PHA C film. Instead, at these con-
ditions, PHA B film was the one presenting the lowest WVTR value, which was
close to that of PHA A film.

If one only looks at the WVTR results obtained for the PHA films (Figures3.12
top), it seems that at normal conditions (lower relative humidity – RH=50%), Mw
of PHA played a bigger role than PHA crystallinity, in the sense that PHA C

35



3. Results and Discussion

and PHA D were the samples presenting the lowest values. Conversely, at tropical
conditions (higher relative humidity – RH=80%), the crystallinity of PHA seems to
have had a stronger effect than Mw of PHA, as PHA A and PHA B were the ones
with lower WVTR values. Figure3.13 also corroborates this conclusion. Whereas at
normal conditions there seems not to be any correlation between WVTR values and
degree of crystallinity (R2=0.3), At tropical conditions one can see a good correlation
between these two parameters and a trendline with R2=0.93 can be obtained.

Figure 3.13: WVTR vs degree of crystallinity of PHA at normal(blue) and tropical
conditions(orange)

For PHA-coated paperboards, the WVTR values under both normal and tropical
conditions increased in the order PHA C< PHA A< PHA D. The reason for this
behavior is not well understood and more studies would be required to draw any
good conclusions. It is still worth noting that when it comes to extrusion-coated
paperboards, factors other than the PHA characteristics start playing an important
role in water vapor barrier performance, including film homogeneity, edge stability,
pinholes, etc.

36



4
Conclusion and Future work

4.1 Conclusion
In this project four different PHA types were evaluated. The melting temperature,
glass transition temperature, and degradation temperature were determined to bet-
ter understand the thermal behavior of the materials and try to improve their pro-
cessing conditions. From the DSC and DMA analysis, it was found that increased
molecular weight of PHA generally led to increased melting temperature and de-
creased glass transition temperature. TGA analysis showed that the PHA polymers
start decomposing already at temperatures around 190◦C, so temperatures lower (or
at least not much higher) than 190◦C would be recommended for real-life processing.

PHA crystallinity also seems to play an important role both in tensile strength and
heat-seal strength of PHA materials; tensile strength seems to increase with in-
creasing crystallinity, whereas heat-seal strength seems to increase with decreasing
crystallinity (and increasing Mw). The highest heat seal strength for all four PHA
types was obtained at 195◦C, and above this temperature the strength started to
decrease, likely due to thermal decomposition.

The rheological studies showed that PHAs are not thermally stable at high temper-
atures, and the time period that a material is exposed to high temperatures is of
importance. The rheological studies also showed that with a higher shear rate, the
material showed shear thinning fluid behavior and no yield stress, which makes it
easier to coat on paperboard. However, for the high molecular weight PHAs, coating
can be more difficult as the melt viscosities are also higher.
Finally, the WVTR of the different PHA samples was evaluated to assess their
water vapor barrier performance. It was shown that both molecular weight and
crystallinity of the polymer play an important role when it comes to WVTR but
at different environmental conditions. The former plays a bigger role at normal
conditions (23◦C and RH=50%), whereas the latter plays a more significant role at
tropical conditions (38◦C and RH=80%).

4.2 Future work
Some future work could include
• Measuring the Mw values of PHAs.

37



4. Conclusion and Future work

• Measuring the melt flow index of the polymers to obtain more information on the
flow of the polymer on the paperboard.

• Testing the grease barrier performance against different types of food products
such as mayonnaise, oil, chicken fat etc.

• Testing the swelling of the PHA materials when exposed to water.

38



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41



A
Appendix 1

A.1 DSC
The below pictures shows the DSC graph of other PHA’s.

Figure A.1: DSC graph of PHA B (I). Heating cycles (II). Cooling cycles

Figure A.2: DSC graph of PHA C (I). Heating cycles (II). Cooling cycles

I



A. Appendix 1

Figure A.3: DSC graph of LDPE

A.2 Rheological properties

A.2.1 Thermal stability of PHA

II



A. Appendix 1

Figure A.4: Thermal stability of PHA’s (I)PHA B at 175◦C, (II)PHA B at 160◦C,
(III)PHA C at 175◦C, (IV)PHA C at 160◦C, (V)PHA D at 175◦C, (VI)PHA D at
160◦C

A.3 Mechanical properties

A.3.1 Heat sealing test

Figure A.5: Thickness variation of the film used for heat sealing (I)PHA A, (II)PHA
B, (III)PHA C, (IV)PHA D

III



DEPARTMENT OF INDUSTRIAL AND MATERIAL SCIENCE
CHALMERS UNIVERSITY OF TECHNOLOGY
Gothenburg, Sweden
www.chalmers.se

www.chalmers.se

	List of Acronyms
	Nomenclature
	List of Figures
	List of Tables
	Introduction
	Plastic materials
	Bio-based and biodegradable polymers
	PLA
	PHA
	Other biopolymers

	Packaging material
	Packaging demands
	Packaging systems and types
	Packaging properties
	Barrier properties
	WVTR test
	OTR test
	Grease barrier test

	Stiffness(mechanical properties)
	Sealing properties

	Liquid packaging board structure

	Extrusion coating
	Objectives
	Limitations

	Materials and Methods
	Materials
	Experimental methods
	Film preparation
	Differential Scanning Calorimetry(DSC)
	Thermogravimetric Analysis(TGA)
	Dynamic Mechanical Analysis(DMA)
	Fourier Transform Infrared Spectroscopy(FTIR)
	Mechanical Properties
	Tensile testing
	Seal strength testing

	Rheological properties
	Rotational rheometry
	Capillary rheometry

	Water Vapour Transmission Rate(WVTR)


	Results and Discussion
	DSC
	TGA
	DMA
	FTIR
	Mechanical properties
	Tensile testing
	Heat sealing

	Rheological properties
	Thermal stability of PHA
	Relaxation behaviour of PHA
	Frequency sweep test and Non-Newtonian behaviour
	Melt Viscosity

	WVTR

	Conclusion and Future work
	Conclusion
	Future work

	Appendix 1
	DSC
	Rheological properties
	Thermal stability of PHA

	Mechanical properties
	Heat sealing test