Control of racemization for feedstock recycling of PLLA

Poly(L-lactide) (PLLA) is considered to be a possible candidate for feedstock recycling because thermal degradation of PLLA can result in the recovery of its monomer, L,L-lactide. One of the serious problems concerning the feedstock recycling of PLLA has been the racemization of lactide. To control the racemization in the pyrolysis of PLLA, various calcium compounds, which are relatively safe chemicals, were added to the PLLA. Consequently, the calcium compounds, especially calcium oxide, effectively decreased the pyrolysis temperature of PLLA and led to predominant L,L-lactide formation in the specific range of 250-300 degreesC. For PLLA containing calcium oxide, at temperatures above 250 degreesC, L,L-lactide formation was predominant. This demonstrates the possibility of a practical way of recycling PLLA feedstock to optically pure L,L-lactide.