Basic PHB Degradation
Basic PHB Degradation Mechanism The melting point of 3-PHB is 1°C. By producing copolymers such as PHBV the melting point is reduced to around 1°C when % by weight of the valerate units are incorporated randomly in the polymer chain. This reduction in the melting point enables a wider melt processing window and also reduces the overall brittleness compared to PHB. Increasing the valerate content or using longer chain co monomers can further reduce the melting point but may also reduce the rate of crystallization which can lead to processing inefficiencies due to longer cycle times. Although the pure PHB is still produced, most common PHA’s are copolymers designed to have a wider processing window and a spectrum of properties from rigid to ductile materials. Other than these drying requirements and the relatively narrow processing temperatures PHA’s are otherwise readily processed on conventional melt processing equipment. Fig.3 Bathroom Accessories, Photo: PolyOne Due to the difficulties in processing the 3 –PHB the industry either produces copolymers, as discussed above or PHB is compounded with other materials to reduce degradation and improve processability. In conclusion, PHA’s are a diverse class of polymers produced by many natural or modified microorganisms. Although the technology has been known for long time in academia the spectrum of products now becoming commercially available are showing promise in a variety of traditional and new commercial applications By varying the co monomer ratio and type, rigid to elastomeric products can be produced This family of unique microbial polyesters would appear to have a bright future in the emerging renewable resource based polymer industry. References: [1] Ronny Purwandi – Fermentation Production of Polyhydroxyalkanoates. www.adm.hb.se/~RPU/download/ PHA_presentation_show_rev.pps [2] Biotechnological approaches for the production of polyhydroxyalkanoates in microorganisms and plants — A review. Pornpa Suriyamongkol Et. Al. [3] EP 1 0 20 A1 Xuejun Chen- Tianan Biologic [4] Madison LL, Huisman GW. Metabolic engineering of poly (3-hydroxyalkanoates): from DNA to plastic. Microbiol. Mol. Biol. Rev. 1999; 3:21–3. [] Hablot E et al., Thermal and thermo-mechanical degradation of poly(3-hydroxybutyrate)-based multiphase systems, Polym. Degrad Stab (200), doi:10.101/j.polymdegradstab.200.11.0 18 PDST31_proof _ 11 December 200 _ 4/9. Fig. 4 PHA pellets 38 bioplastics MAGAZINE [03/09] Vol. 4
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