Hydrolytic and Enzymatic Degradation of PLA

Hydrolysis, also known as hydrolytic degradation, is the major degradation mechanism of PLA. It is an autocatalytic process yielding carboxylic acid, i.e. the lactic acid helps to catalyze the hydrolysis process. This has been observed in a study, where a thick sample was immersed in a buffer of pH 7.4 at 37°C bulk hydrolysis occurred at a higher rate than the surface hydrolysis (Henton et al., 2005). This can be explained by the fact that the surface of the thick PLA sample was in contact with the buffer and the lactic acid generated from the hydrolysis of PLA end group at the surface could easily 

The study of PLA hydrolysis has been performed in aqueous media, such as phosphate-buffered solutions or water, at 37°C to simulate its degradation in body fluids at the appropriate temperature. Studies have also been done at higher temperatures, in acidic solutions, alkaline solutions or buffered solutions, with the addition of enzymes, in order to determine the hydrolytic effects of PLA under severe and accelerated conditions (Tsuji et ah, 2004). When hydrolysis of crystallized PLLA was carried out at temperatures below its melting point, it was found that the amorphous region suffered substantial 

Tsuji (2002) conducted an investigation into the hydrolysis of an amorphous form of PLA, to determine the effects of L-lactide content, tacticity and enantiomeric polymer blends. In this work four samples were prepared—poly(D,L-lactide), poly(L-lactide), poly(D-lactide) film and the blend sample of poly(L-lactide) and poly(D-lactide). The results are sununa-rized in Table 7.4, which also covers a complementary study that explored the effects of hydrolysis in terms of molecular weight and its distribution, glass transition temperature, crystallization temperature, melting temperature and mechanical properties. 

Although the weights of PLA films do not show significant losses over time, the average molecular weight, M, changes 

Properties Form of PLA Before After Hydrolysis Hydrolysis  

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