Polymer blends with polyhydroxyalkanoates

Other blends such as polyhydroxyalkanoates (PHA) with cellulose acetate (208), PHA with polycaprolactone (209), poly(lactic acid) with poly(ethylene glycol) (210), chitosan and cellulose (211), poly(lactic acid) with inorganic fillers (212), and PHA and aUphatic polyesters with inorganics (213) are receiving attention. The different blending compositions seem to be limited only by the number of polymers available and the compatibiUty of the components. The latter blends, with all natural or biodegradable components, appear to afford the best approach for future research as property balance and biodegradabihty is attempted. Starch and additives have been evaluated ia detail from the perspective of stmcture and compatibiUty with starch (214). 

Based on current standard testing methods and specifications, several renewable resource polymers may be considered biodegradable, the foremost being starch blends, cellulosic derivatives, polyhydroxyalkanoates and poly(lactic acid). Several new and old condensation polymers based on monomers obtained from fossil resources, such as polycaprolactone and the Bionolle series from Japan (Showa High Polymers) based on suucinic acid, are also acceptable by current standards, as are there blends with natural polymers such as starch. 

Abstract The present chapter deals with a brief account on various types of natural polymers such as cellulose, chitin, starch, soy protein, casein, hemicellu-loses, alginates, polylactic acid and polyhydroxyalkanoates etc. Blends, composites and nanocomposites based on these polymers have been very briefly discussed. Finally the applications, new challenges and opportunities of these biomaterials are also discussed. 

Some synthetic polymers like, polyurethanes, specifically polyether-polyurethanes, are likely to be degraded by microbes but not completely. However, several polymers such as, polyamides, polyfluorocarbons, polyethylene, polypropylene, and polycarbonate are highly resistant to microbial degradation. Natural polymers are generally more biodegradable than synthetic polymers specifically, polymers with ester groups like aliphatic polyesters [1]. Therefore, several natural polymers such as cellulose, starch, blends of those with synthetic polymers, polylactate, polyester-amide, and polyhydroxyalkanoates (PHAs) have been the focus of attention in the recent years [3]. 

Polyhydroxyalkanoate is a polyester identified in 1925 by the microbiologist Maurice Lemoigne. It can be synthesised by various bacteria (Alcaligenes Eutrophus, cyanobacteria). Lower concentrations of carbon, nitrogen and phosphorus sources increase the yield and the quality of the polymers produced (Steinbiichel, 2002). There are numerous potential applications for PHA (cosmetics containers, disposable articles, medical implants, paper coatings). Moreover, PHA can be formulated in many grades, from elastic products to crystalline ones, it is a good candidate for blends and easy to process with traditional equipment (Whitehouse, 2000). 

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