Effect of layered double hydroxides on the thermal degradation behavior of biodegradable poly(l-lactide) nanocomposites

This study elucidates the thermal degradation behavior of biodegradable poly(l-lactide) (PLLA)/layered double hydroxide (LDH) nanocomposites was explored using thermogravimetric analysis (TGA) and pyrolysis-gas chromatography/mass spectroscopy (Py-GC/MS) in an inert atmosphere. PLLA/LDH nanocomposites were fabricated using PLLA and organically-modified magnesium/aluminum layered double hydroxide (P-LDH) in tetrahydrofuran solution. According to the TGA results, the thermal stability of PLLA/P-LDH nanocomposites was significantly lower than that of pure PLLA matrix, perhaps because P-LDH provides thermal acceleration of the degradation of the underlying polymer from the heat source. The identification of the thermal degradation products by Py-GC/MS evidently shows that introducing P-LDH into PLLA leads to a remarkable change during the thermal degradation process. The main reaction route of neat PLLA was through inter- and intra-transesterification to generate lactides and oligomer. The primary volatile products obtained from PLLA/P-LDH nanocomposites were lactides regardless of the temperature of degradation. These results suggest that the thermal degradation behavior of PLLA/P-LDH nanocomposites is governed by the preferential formation of lactide by the unzipping depolymerization reaction, which is catalyzed by Mg and Al components in P-LDH.