Semi-crystalline biodegradable polyesters crystallinity

The control of biodegradation rate is of critical importance for many applications of degradable polymers. Amorphous polyesters absorb water and hydrolyse much more rapidly than crystalline materials. Consequently, in partially crystalline polymers, hydrolysis occurs initially in the amorphous phase and continues more slowly in the crystalline phase. This selective degradation leads to an increase in crystallinity by chemicrystallisation. A very similar selective abiotic oxidation process occurs in the semi-crystalline polyolefins which fragment rapidly due to failure at the crystallite boundaries. 

In an attempt to gain an element of control over the mechanical, physical and degradation properties of PLA, large-scale efforts are currently underway to chemically and physically modify PLA throng copolymerization and physical blending with prudently chosen secondary constituents. Without immediate consideration for the issue of financial accessibility of PLA-based products, a logical, con lementary conqx)nent to PLA is poly(8-caprolactone)[PCL]. PCL is a flexible, semi-crystalline(Tg -60°C, Tm 60°C) aliphatic polyester with unique biodegradation characteristics and superior thermal and hydrolytic stabihty. ... 

PCL is semi-crystalline polyester that exhibits good mechanical properties, biodegradability, biocompatibility and miscibility with various polymers. 

Most of the polyesters are semi-crystalline polymers, althongh their copolymers are often intrinsically amorphous. The crystalline phase is difficult for water to penetrate and hydrolyse. The degree of crystallinity can increase significantly during biodegradation in both initially amorphous and semi-crystalline polymers. This is because the cleavage of the polymer chains provides extra mobility to the chains and leads to further crystallisation. The model has to consider the interplay between the hydrolysis reaction and crystallisation. 

Modelling degradation of semi-crystalline biodegradable polyesters... 

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