Thermal and Mechanical Properties of Polyhydroxyalkanoates

Moreover, PHB thermally decomposes at temperatures just above its melting point. A short exposure of PHB to temperature near 180°C could induce a severe degradation accompanied by the production of the degraded products of olefinic and carboxylic acid compounds, e.g., crotonic acid and various oligomers through the random chain scission reaction that involves a cis-elimination reaction of/3-CH and a six-member ring transition [16-18]. 

The very low resistance to thermal degradation seems to be the most serious problem related to the processing of PHB. 

Other approaches to improve the properties of PHB is the production of derivatives based on PHB via the biosynthesis of copolyesters containing PHB units with other 3-hydroxyalkanoates units [19], such as poly [3-hydroxybutyrate-co-hydroxyvalerate] [PHBV] [20] or poly [3-hydroxybutyrate-co-3-hydroxyhexanoate] [21], with different molar ratios of hydroxycarboxylic acids. This approach has been investigated extensively [22] because it can 

As reported above, the addition of plasticizers is considered a relatively simple route to modify the thermal and mechanical properties of polymers. Blending polymers with plasticizers may modify the physical properties of polymers and a decrease in processing temperature can be achieved. Thus, PHB is commonly blended with plasticizers and nucleation agents that lead to a lower glass temperature and lower crystallinity due to the formation of numerous, small, and imperfect crystallites. 

---