Bio-based polymers are produced using renewable resources and are thus aimed to be more environmentally friendly as well as circular in nature. As opposed to conventional, fossil-based or petroleum-derived polymers, replacements that have plant-based origins are expected to be less polluting in terms of both the manufacturing process and disposal.
Extensive research has been conducted over that past decade or so to determine the best possible sources of these renewable raw materials. The considerations have included not only the ease of supply and prolificacy, but also end-of-life treatments, reusability, recyclability and the likes. Other coveted characteristics include biodegradability and composability.
In this blog, we will consider a few examples of the composition of bio-based polymers currently being researched, tested or used.
- BIO-POLYETHYLENE (Bio-PE)
Microbial PE or green PE can be manufactured from the dehydration of ethanol produced by microbial fermentation. Bioethanol can be derived from sugarcane or other renewable feedstock including sugar beets and starch crops like maize, wood, wheat and corn. Sugarcane juice with high sucrose content is preferred for anaerobic fermentation to synthesize bioethanol. In this case, bio-based polyethylene has exactly the same chemical, physical, and mechanical properties as petrochemical polyethylene.
Natural Bio-Based Polymers
This is a subset class of bio-based polymers which are found naturally, such as proteins, nucleic acids, and polysaccharides (collagen, chitosan, etc.).
- STARCH
Starch is the end product of photosynthesis in plants. It is a natural carbohydrate-based polymer and is abundantly available in nature from sources including wheat, rice, corn, and potato. Starch would be categorized as a thermoplastic. Addition of plasticizer changes the thermal and mechanical properties of starch as a biopolymer to various degrees. Starch’s molecular structure makes it difficult for it to display ductility; it also suffers from retrogradation which makes it brittle over time.
- CELLULOSE
Cellulose is another natural biopolymer. It is found in the cell walls of plants. The primary raw material sources used in the production of cellulosic plastics are cotton fibers and wood. Plant fiber is dissolved in an alkali and carbon disulfide to create viscose. Viscose is then reconverted to cellulose in the form of cellophane following a sulfuric acid and sodium sulfate bath. Currently, there are two processes used to separate cellulose from the other wood constituents (Yan et al. 2009). Both sulfite and pre-hydrolysis kraft pulping, use high pressure and chemicals to separate cellulose from lignin and hemicellulose which leads to an attainment of greater than 97% cellulose purity. The main derivatives of cellulose for industrial purposes are cellulose acetate, cellulose esters (molding, extrusion, and films), and regenerated cellulose for fibers.
Cellulose is a hard polymer and has a high tensile strength of 62 to 500 MPa and elongation of 4% (Bisanda and Ansell 1992; Eichhorn et al. 2001). In order to overcome the inherent processing problems of cellulose, it is necessary to modify, plasticize, and blend with other polymers. The mechanical and thermal properties vary from blend to blend depending on the composition.
