Temperature aliphatic polyester degradation

C and is easily processable, whereas the homopolymers do not melt before the onset of thermal degradation, at temperatures as high as 500°C.73,74 Varying copolymer composition permits the adjustment of melting temperature and of other properties (e.g., solubility) to desired values. This method is frequently used for aliphatic and aromatic-aliphatic polyesters as well. 

Polyesters offer multiple options to meet the complex world of degradable polymers. All polyesters degrade eventually, with hydrolysis being the dominant mechanism. Degradation rates range from weeks for aliphatic polyesters (e.g. polyhydroxyalkanoates) to decades for aromatic polyesters (e.g. PET). Specific local environmental factors such as humidity, pH and temperature significantly influence the rate of degradation. 

Typical diol-diacid type biodegradable aliphatic polyesters, PBA and PBS, were degraded in a diluted toluene solution by the immobilized lipase CA which exclusively formed the cyclic oligomers. Their composition was partially dependent on the degradation conditions, such as the enzyme concentration and temperature. On the other hand, in a more concentrated condition, the cyclic oligomer was readily repolymerized by the ring-opening polymerization. 

Tokiwa and Suzuki already proposed in 1977 a correlation between the melting temperature of a polyester and its biodegradability. Based on this attempt, we plotted the degradation rate of different aliphatic polyesters against the difference of melting temperature (maximum of the melt peak in the DSC) (Fig 1). 

Figure 1. Rate of the hydrolysis of different aliphatic polyesters with a lipase from Pseudomonas sp. at different degradation temperatures. Left side correlation with the melting point of the polyesters right side correlation with the difference between melting temperature and degradation temperature...

PBS and its copolymers can be degraded in various environments, such as natural water, soil burial, activated sludge, and compost. The environmental biodegradation rate is sensitive to both the properties of the polyester and the environment, e.g., the microorganisms, nutrient, temperature, and humidity. Eor instance, Bionolle has different biodegradation rates in various enviromnents, as presented in Table 7 (Fujimaki 1998). Table 8 shows biodegradation properties of several aliphatic polyesters in different waters (Kasuya et al. 1998). It has been demonstrated that... 

Polycaprolactone Poly-e-caprolactone (PCL) is a semicrystalline, thermoplastic, linear aliphatic polyester synthesized by the ring-opening polymerization of e-caprolactone and is produced commercially by Union Carbide-Dow (Midland, MI) and Rhone-Poulenc (Collegeville, PA). This polymer has a melhng point of approximately 62°C and a glass transihon temperature of approximately -60°C. PCL is readily degraded and mineralized by a variety of microorganisms [45] ... 

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