Selective enzymatic degradations of poly(L-lactide) and poly(epsilon-caprolactone) blend films

Solution cast films were prepared from poly(L-lactide) (PLLA) and poly(epsi lon -caprolactone) (PCL) as well as from three blends, namely B75, B50, and B25 with PLLA/PCL proportions of 75/25, 50/50, and 25/75, respectively. Th e enzymatic degradation of square samples (10 x 10 x 0.2 mm) cut from the f ilms was investigated at 37 degreesC in a pH = 8.6 Tris buffer containing p roteinase K or in a pH = 7.0 phosphate buffer containing Pseudomonas lipase . It was confirmed that proteinase K can degrade amorphous domains of PLLA, but cannot degrade crystalline PLLA or PCL. In contrast, Pseudomonas lipas e can degrade both amorphous and crystalline PCL but cannot degrade PLLA. T he two faces of solution cast films showed different morphologies due to th e solvent evaporation process. The lower face appeared more crystalline tha n the upper face because of the plasticizing effect of solvent entrapped in side which allowed crystallization to proceed. Therefore, the lower face wa s more resistant to enzymatic attack by proteinase K in the cases of PLLA a nd the blends. The two polymers in the blends exhibited well separated crys talline domains. PCL seemed to constitute the continuous phase of the blend s with formation of large size spherulites when the PCL content was over 50 %. The selective degradation of PCL or PLLA components revealed the inner m orphology of the blends where microspherelike or islandlike patterns were o bserved.