Polycaprolactone 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). 

Polyhydroxyalkanoates, which are produced by bacterial synthesis, are well known to biodegrade (32) under anaerobic conditions, and several studies have been reported and compared with S3uithetic polyesters such as polycaprolactone... 

Among the most important biodegradable polymers, we can specially mention thermoplastic starch (TPS), polylactide (PLA), polycaprolactone (PCL), and polyhydroxybutyrate and polyhydroxyalkanoate (PHA) due to their promising properties. 

FIGURE 16 Representative melting and glass transition temperatures of bio and fossil based polymers (PCL-Str - Polycaprolactone/Starch blends, PC - Polycaprolactone, mcPHA - medium chain Polyhydroxyalkanoates, Ali-coPES - Aliphatic (co)Polyesters, PUBAf -Polyhydroxy Butyrate/valerate, and PEA - Polyester Amides). 

The compatibility of the individual components of polymeric blends can lead to significant effects on the degradation of the polyhydroxyalkanoate component. This has been illustrated in a study on blends of PHB homopolymer with polycaprolactone, poly( 1,4-butylene adipate) and polyvinyl acetate [57]. Blends over wide composition ranges were incubated as thin films in aqueous solutions of an extracellular PHB depolymerase at 37 °C. The relative degradation rates were related to the miscibility and microstructure of the polymeric phases. For blends where PHB formed the continuous phase, degradation was relatively fast. 

NATCO = Natural Absorbent Technology Co., PPT, Inc. = Planet Polymer Technologies, Inc. TPS, Inc. = Texas Polymer Services, Inc. PCL = polycaprolactone, PHA = polyhydroxyalkanoates, PLA = poly(lactic acid), PVA = poly(vinyl alcohol), ns = not specified. 

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. 

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