Biodegradable cellulose diacetate-graft-poly(L-lactide)s: enzymatic hydrolysis behavior and surface morphological...

Enzymatic hydrolysis of selected copolymers of cellulose diacetate-graft-poly(L-lactide)s (CDA-g-PLLAs) were conducted with proteinase K for film specimens, which were solely quenched from the molten state or, further, annealed at temperatures below or above their glass transition temperatures. The hydrolysis rates depended seriously on the thermal history, as well as on the graft modification. Especially, the heat treatment, followed by physical aging or crystallization of the originally amorphous materials, was a key factor to control subtly their enzymatic degradation behavior. Atomic force microscopy revealed that the enzymatic hydrolysis transformed the surface of the respective films into a more undulated one with a number of fine protuberances, for example, of several hundred nanometers in height and a few micrometers in width. Attenuated total reflection FTIR spectroscopy ensured selective release of lactyl units from the surface region. In visual appearance, some degraded films exhibited even an iridescent color due to an effect of interference of visible light reflected on the surface. These observations suggest a conception of "spatiotemporally controlled degradation", leading to a new method not only for regulation of the overall rate of degradation but also for fine surface abrasion of polymer materials.