Selective depolymerization of poly-L-lactic acid into L,L-lactide from blends with polystyrene

Poly(L-lactic acid) (PLLA) is a candidate for feedstock recycling materials, because it easily depolymerizes back into the cyclic monomer, L,L-lactide. In order to examine the depolymerization of PLLA from a blend with polystyrene (PS), wep repared the polymer blend and we thermally degraded it with a degradation catalyst: magnesium oxide (MgO) in a TG/DTA and Py-GC/MS. TG curves of PLLA/PS [50:50(wt/wt)] and PLLA/PS/MgO [50:50:5(wt/wt/wt)] clearly showed two-step weight-loss profiles, in which MgO promoted the PLLA degradation selectively, decreasing the temperature range more than 60 degrees C. To clarify the influence of PS ingredient, we analyzed the thermal degradation data. The analytical results showed that, even in the presence of MgO, PS had no effect on the depolymerization of PLLA, and that PLLA was effectively depolymerized into L,L-lactide with a low racemization ratio.