A SPECTROPHOTOMETRIC METHOD FOR DETECTION OF ENZYMATIC DEGRADATION OFTHIN POLYMER-FILMS

An assay method has been developed for monitoring the enzymatic degrad ation of thin films of translucent polymers. The method was based on t he observation that when a solution-cast film of poly(3-hydroxybutyrat e-co-3-hydroxyvalerate) (PHBV) was exposed to a solution of a depolyme rase from Pseudomonas lemoignei, the surface of the film roughened and the film became visibly turbid, This increase in turbidity could be m easured spectrophotometrically and was reproducible during the initial stage of degradation. Turbidity correlated very closely with film wei ght loss early in the degradation but reached a maximum value before e xtensive degradation had taken place. For a given set of films, this c orrelation was independent of the concentration of the enzyme used, al though it did vary with the mode of enzyme exposure. The turbidity was associated with the exposure of crystalline domains due to the remova l of amorphous material from the film surface. The increase in crystal linity at the surface was verified by attenuated total reflectance inf rared spectroscopy (ATRIR). In conjunction with SEM, weight loss, and ATRIR, the film turbidity assay provided much semiquantitative insight into the mechanism of the enzymatic degradation reaction. This assay was used to study the enzymatic degradation of films of PHBV solution blended with cellulose acetate esters (CAE). The presence of only 25% of CAE of degree of substitution 2.9 severely hampered the enzymatic d egradability of PHBV, a result which is consistent with the environmen tal degradation of these same samples exposed to activated sludge.