# Bio-Based Polymers with Potential for Biodegradability
## 4 Other Bio-Based Polymers with Potential for Biodegradability
### Compatibilizers, Biocomposites and Biofibers  
Despite their great positive environmental impact, most bio-based and biodegradable polymers' mechanical properties are inferior to their petroleum-based counterparts. Compatibilizers and/or reinforcing agents, such as inorganic fillers and fibers [176], are often added to bio-based polymers in order to improve their mechanical properties and make them suitable for structural applications. For instance, the non-renewable, biodegradable polymer, poly(butylene adipate-_co_-terephthalate) (PBAT) [194], has been blended with PLA in order to confer flexibility and a higher elongation at break in comparison to other biodegradable polymers. The blend, however, exhibits poor thermal and mechanical properties. Compatibilizers that are of considerable toughness, such as poly(butylene succinate) (PBS), PHBV and the non-renewable, biodegradable polymer poly(butylene succinate-_co_-adipate) (PBSA) [194] were added to a PLA/PBAT blend, resulting in a slight decrease of thermal properties and an increase in melt flow with PBS, while no change was observed with PBSA or PHBV [195]. The chemical structures of PBAT, PBS, and PBSA are provided in Figure 5.  
Figure 4: Chemical structure of (**a**) amylose; and (**b**) amylopectin.  
Triglycerides and epoxidized oils have been investigated as compatibilizers with PLA because of their ester or epoxy groups, which can be degraded by microorganisms. Some oils also contain fatty acids with carbon-carbon double bonds that can act as reactive sites for crosslinking, creating a stronger polymer network. Recent studies have tested the mixture of deodorization oil condensates with PLA and report an increase in ductility in comparison to pure PLA. Deodorization oil condensates are mixtures of different molecules found in vegetable oils [196]. These molecules are recovered via a vacuum steam distillation process, in which steam is passed through the vegetable oil at a very low pressure and high temperature [196].  
Bio-fibers or reinforcements have also become increasingly popular as low cost and renewable reinforcing agents. Two common bio-based reinforcing agents are lignin and cellulose. Lignin is more sensitive to light degradation than cellulose. Cellulose is more sensitive to heat degradation than lignin. These factors can affect the choice of bio-based reinforcement [197]. Generally, these biopolymers are highly hydrophilic, but they are typically added to hydrophobic polymer matrices, compromising reinforcement and matrix adhesion. In order to improve reinforcement-matrix adhesion, cellulose treatment that decreases hydrophilicity has been proposed. Grafting techniques have also become popular and can be categorized into three groups, namely grafting of fiber with a single monomer, grafting with a mixture of two or more monomers, and grafting with the polymer directly. Along these lines, bio-based and biodegradable PHBV oligomers have been prepared by transesterification, and PHBV-graft-ethyl cellulose copolymers have been synthesized using 1,6-hexamethylene diisocyanate (HDI) as a grafting agent. In comparison with neat PHBV, the crystallinity of the grafted copolymer decreased and the moisture resistance was improved [198].