An Investigation of Mixed Cellulose Esters and Acyclic Polyacetates: Effects of Side-Chain Lengths and Degrees of Ring-Opening
Doctoral thesis, 2023
Bio-based polymers produced from natural sources are gaining an increased interest as potential replacement for today’s conventional fossil-based plastic polymers. Their use is already wide in many large-scale industrial areas such as healthcare, personal care, and food.
To widen the potential of biopolymers in new applications such as plastics, their properties need to be tuned by modification to handle factors like relative humidity, which is especially important for gas barriers in food packaging. This thesis explores the effect of two structural variations of cellulose esters, one where the average side-chain length is increased, going from
cellulose acetate to cellulose acetate propionate and then cellulose acetate butyrate, and another where the polymer backbone of cellulose acetate is ring-opened. These two modifications affect the glass transition temperature, an important structural factor. The effect of the average side-chain length is explored to a greater extent where they are studied for impact on mechanical properties, water content, water sorption at different RH, the kinetics of water sorption at different RH, mechanical properties at different RH and oxygen permeation at different RH. The focus is on how water interacts with the different esters with regard to the average side-chain length and how water affects their properties. An increase of average sidechain length and the ring-opening were shown to decrease the glass transition temperature.
Together with the water sorption and Hansen solubility parameter, it was concluded that longer average side-chain length screens out hydrogen bonding between the polymers. The studies on the average side-chain length and water sorption indicated that water entering the cellulose acetate creates clusters. These formed water clusters create cavities in the polymer which makes the polymer hold more water than before introducing of the water clusters. Oxygen permeation studies on prewetted films prove that these cavities created by water clustering are still present after drying the material at 0% RH and thus resulted in a higher oxygen permeation compared to films that had not been exposed to higher than 50% RH.
To widen the potential of biopolymers in new applications such as plastics, their properties need to be tuned by modification to handle factors like relative humidity, which is especially important for gas barriers in food packaging. This thesis explores the effect of two structural variations of cellulose esters, one where the average side-chain length is increased, going from
cellulose acetate to cellulose acetate propionate and then cellulose acetate butyrate, and another where the polymer backbone of cellulose acetate is ring-opened. These two modifications affect the glass transition temperature, an important structural factor. The effect of the average side-chain length is explored to a greater extent where they are studied for impact on mechanical properties, water content, water sorption at different RH, the kinetics of water sorption at different RH, mechanical properties at different RH and oxygen permeation at different RH. The focus is on how water interacts with the different esters with regard to the average side-chain length and how water affects their properties. An increase of average sidechain length and the ring-opening were shown to decrease the glass transition temperature.
Together with the water sorption and Hansen solubility parameter, it was concluded that longer average side-chain length screens out hydrogen bonding between the polymers. The studies on the average side-chain length and water sorption indicated that water entering the cellulose acetate creates clusters. These formed water clusters create cavities in the polymer which makes the polymer hold more water than before introducing of the water clusters. Oxygen permeation studies on prewetted films prove that these cavities created by water clustering are still present after drying the material at 0% RH and thus resulted in a higher oxygen permeation compared to films that had not been exposed to higher than 50% RH.
water interactions
oxygen permeation
storage modulus
ring-opening
water sorption
cellulose esters
side-chains
acyclic cellulose acetate
KE-salen, kemigården 4.
Opponent: Prof. Minna Hakkarainen, Division of Polymer Technology, Kungliga Tekniska Högskolan i Stockholm, Sverige.
Author
Robin Nilsson
Chalmers, Chemistry and Chemical Engineering, Applied Chemistry
Experimental and simulated distribution and interaction of water in cellulose esters with alkyl chain substitutions
Carbohydrate Polymers,;Vol. 306(2023)
Journal article
Screening of hydrogen bonds in modified cellulose acetates with alkyl chain substitutions
Carbohydrate Polymers,;Vol. 285(2022)
Journal article
The fact that plastics are made from non-renewable resources is becoming a problem for society. Scientists are looking at different ways to replace traditional plastic with plastics made from renewable resources such as wood. When referring to materials from nature that can replace different types of plastic the term “bio-based polymers” is widely used. Bio-based polymers are already used in, for example, healthcare, personal care, and food industries. However, in order to be able to use them for a wider range of applications, researchers need to modify their properties to make them behave more like traditional plastic. One of the major components of wood and other plant-based materials is cellulose, which is a bio-based polymer that shows a lot of potential. Both because of its large availability and because it can be modified in several different ways. One way of modifying cellulose is to create cellulose esters.
This thesis has explored the properties of different modified versions of cellulose-esters. You can think of cellulose-esters as long chains, with short chains sticking out, like branches. The structural modifications studied in this thesis included varying the average side-chain length (the length of the branches), by attaching different groups of different lengths to the cellulose. Another modification studied in this thesis is called ring-opening. This can be described as taking some of the links of the long chain and opening them. The polymer chain will still be a chain, but the ring-opening will cause it to behave slightly differently. These structural modifications were observed to affect the glass transition temperature (the temperature range where a material goes from stiff and glassy to soft and pliable, but not melted) of the polymers, where an increase of both average side chain length and the degree of ring opening led to increased mobility/flexibility of the polymers and thus decreased the glass transition temperature. The study found that longer average side-chain lengths reduced hydrogen bonding between the polymers, resulting in more flexible polymers. It also decreases the water sensitivity of the polymers, making them more water resistant. For cellulose acetate (the shortest side-chain tested), it was observed that they formed water clustering at high relative humidity, which means that tiny water droplets were created inside the material. When comparing wetted and non-wetted materials it was shown that the clusters leave cavities in the material that does not fully disappear when the material is dried.
These findings have important implications for the development of bio-based polymers. By modifying the structure of cellulose esters, researchers can tune their properties to handle environmental factors such as relative humidity. This could create new applications for these bio-based polymers, particularly in areas such as food packaging, where gas barriers are essential. Furthermore, understanding how water interacts with bio-based polymers could lead to further research in this area. Ultimately, bio-based polymers could help us move towards a more sustainable future by reducing our reliance on fossil fuels.
This thesis has explored the properties of different modified versions of cellulose-esters. You can think of cellulose-esters as long chains, with short chains sticking out, like branches. The structural modifications studied in this thesis included varying the average side-chain length (the length of the branches), by attaching different groups of different lengths to the cellulose. Another modification studied in this thesis is called ring-opening. This can be described as taking some of the links of the long chain and opening them. The polymer chain will still be a chain, but the ring-opening will cause it to behave slightly differently. These structural modifications were observed to affect the glass transition temperature (the temperature range where a material goes from stiff and glassy to soft and pliable, but not melted) of the polymers, where an increase of both average side chain length and the degree of ring opening led to increased mobility/flexibility of the polymers and thus decreased the glass transition temperature. The study found that longer average side-chain lengths reduced hydrogen bonding between the polymers, resulting in more flexible polymers. It also decreases the water sensitivity of the polymers, making them more water resistant. For cellulose acetate (the shortest side-chain tested), it was observed that they formed water clustering at high relative humidity, which means that tiny water droplets were created inside the material. When comparing wetted and non-wetted materials it was shown that the clusters leave cavities in the material that does not fully disappear when the material is dried.
These findings have important implications for the development of bio-based polymers. By modifying the structure of cellulose esters, researchers can tune their properties to handle environmental factors such as relative humidity. This could create new applications for these bio-based polymers, particularly in areas such as food packaging, where gas barriers are essential. Furthermore, understanding how water interacts with bio-based polymers could lead to further research in this area. Ultimately, bio-based polymers could help us move towards a more sustainable future by reducing our reliance on fossil fuels.
Subject Categories
Polymer Chemistry
Analytical Chemistry
Polymer Technologies
Textile, Rubber and Polymeric Materials
Materials Chemistry
Organic Chemistry
Areas of Advance
Materials Science
ISBN
978-91-7905-857-9
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5323
Publisher
Chalmers
KE-salen, kemigården 4.
Opponent: Prof. Minna Hakkarainen, Division of Polymer Technology, Kungliga Tekniska Högskolan i Stockholm, Sverige.