Enzymatic Degradability of PLLA Films

PLLA is a crystallizable polymer with melting temperature at around 175°C. Semicrystalline PLLA films can be prepared by various techniques, such as solution casting with a slow evaporation rate of solvent, isothermal crystallization from the melt, and annealing of amorphous samples. Since PLLA has a glass transition temperature (Tg) of 60 C, which is higher than room temperature, a completely amorphous film can be obtained by melt quenching. 

FIGURE 22.3 Enzymatic hydrolysis rate of PLLA films as a function of the inverse of molecular weight (M ). Reprinted with permission from Ref. 12. Copyright 2001, American Chemical Society. 

On the other hand, the nonlinear relationship of hydrolysis of semicrystalline PLLA films can be accounted for in terms of successive hydrolysis reactions of amorphous and crystalline regions on the film surface. It is known that the enzymatic degradation of PLLA film by proteinase K progresses on a film surface as a heterogeneous reaction. If the surface of semicrystalline PLLA film is occupied by PLLA 

Furthermore, it was reported that among the semicrystalline PLLA films with similar crystallinity, the films annealed at a higher temperature were more resistant to enzymatic degradation [14]. It is suggested that the lamellar crystal size of PLLA also plays a decisive role in the enzymatic degradation process. A similar dependence of the enzymatic erosion rate of semicrystalline PLLA on crystal size has been confirmed by Kurokawa et al. [28] 

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Effects of Surface Properties on Enzymatic Degradability of PLLA Films... 

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