Enzymatic degradation of atactic poly(R,S-3-hydroxybutyrate) induced by amorphous polymers and the enzymatic degradation temperature window of an amorphous polymer system

The phase structure and biodegradability were investigated for amorphous blends of chemosynthetic fully amorphous atactic poly(R,S-3-hydroxybutyrate) (a-PHB) with atactic poly(methyl methacrylate) (PMMA) and atactic poly(R,S-lactide) (a-PLA). The differential scanning calorimetry thermal analysis indicated that a-PHB/PMMA blends were partially miscible while a-PHB/a-PLA blends were miscible in the studied composition range. The biodegradations of the blends were carried out in phosphate buffer solution in the presence of bacterial poly(R-3-hydroxybutyrate) extracellular depolymerases purified from Alcaligenes faecalis T-1 and P. stutzeri. Although a-PHB in the pure state was not degraded by these depolymerase, it was degraded by blending with PMMA and a-PLA. The results demonstrated that the enzymatic degradation of a-PHB can be induced by amorphous polymers such as PMMA and a-PLA. Also, the biodegradation rate of a-PHB in the blends decreased drastically when the degradation temperature is too much away from the polymer glass transition temperatures. On the basis of these results, a temperature window of the enzymatic degradation was first proposed for the blend and the essence of induced degradation was discussed.