Mekaniska och aktiva egenskaper hos strukturer av nanokristallin cellulosa
Ladda ner
Typ
Examensarbete på kandidatnivå
Bachelor Thesis
Bachelor Thesis
Program
Publicerad
2023
Författare
Barnå, Gustav
Benjaminsson, John
Clark, Malte
Lundström, William
Preinitz G¨ardinge, Viktor
Young, Alexander
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Nanotechnology is a field of science involving the manipulation of structures smaller than 100 nanometers, often involving
singular molecules or atoms. At this scale, unique material properties that enable new and interesting applications
appear. Nanocellulose is a nanomaterial with promising future prospects in this area of research, mainly because of its
renewable and biocompatible properties. Furthermore, it is very suitable for chemical modification as the large amount
of hydroxyl and sulfate groups easily allow for substitution reactions, in addition to coordination with cations.
One purpose of this study was to investigate the possibility of chemically modifying nanocellulose such that it reversibly
changes its physical structure when exposed to an external stimuli. More specifically, the possibility of achieving
it trough a mechanism known as piezoelectricity, where a material contorts or vibrates as a current or voltage is applied
to it, or vice versa, was investigated. Another purpose was to determine the effect of different factors in the manufacturing
process on the resulting structure and material properties of nanocellulose-based aerogels. Lastly, gaining insight
into how molecular interactions between cellulose crystallites affect observed macroscopic phenomena was a key focus
of the study. A major challenge with producing films and aerogels that can bend and compress, respectively, from a
renewable and natural source such as cellulose, is its fragility and stiffness. This problem emphasizes the importance
of chemical modification and its ability to alter the structure of nanocellulose on a molecular scale, such that it obtains
the desired properties. Research on which additives successfully increase the flexibility and piezoelectric properties
of nanocellulose is therefore a central part of this review. In order to accomplish this, the task was divided into three
main steps. Firstly, manufacturing nanocrystalline cellulose by hydrolysis of microcrystalline cellulose (MCC) with
sulfuric acid, followed by producing nanocellulose-based films and aerogels. Secondly, identifying chemical additives
or modifications of the cellulose crystallites that provide the durability necessary to repeatedly change the macroscopic
structure without fracturing. Additionally, inducing piezoelectric qualities in films by a similar methodology. Thirdly,
a quantitative comparison of the mechanical and electrical properties of films and aerogels that passed the initial trials.
Consequently, the effects of the chemical modifications and other factors was determined.
Triethanolamine proved to be especially successful as a plasticizing additive for the films, providing the greatest
increase in flexibility and durability. Moreover, including azetidinium salts in the manufacturing of films resulted in the
emergence of stronger piezoeletric effects compared to alternatives, such as triethanolamine and tartaric acid. Aerogels
frozen in carbon dioxide ice baths crystallize into a more uniform directional structure, characterized by a distinct
horizontal surface layer and vertical fibers throughout, in comparison to their counterparts produced by freezing at -80
°C followed by freeze-drying. Furthermore, this resulted in a more reflective and lustrous surface with better rebound
and less structural damage when compressed. In conclusion, modifying nanocellulose films with triethanolamine and
azetidinium salts provided the desired mechanical and electrical properties respectively. Moreover, including PVA as
an additive followed by freeze drying in carbon dioxide ice baths resulted in more structured, durable and flexible
aerogels.