Thermal degradation of poly(caprolactone), poly(lactic acid), and poly(hydroxybutyrate) studied by TGA/FTIR and other analytical techniques

Thermal degradation of three biodegradable polyesters: poly(caprolactone), poly(lactic acid), and poly(hydroxybutyrate), was studied by thermogravimetry coupled to Fourier Transform Infrared Spectroscopy TGA/FTIR before and after they were partially degraded. TGA curves and Gram-Schmidt plots showed only one decomposition stage for both poly(caprolactone), PCL, and poly(lactic acid), PLA. In contrast, poly(hydroxybutyrate), PHB, exhibited two degradation stages by TGA, but only one region of evolved gases was appreciated in the Gram-Schmidt plot. It was established that hexenoic acid, epsilon-caprolactone, and small fragments of polymeric chains are the main degradation products of PCL, which were simultaneously released during thermal decomposition of this polymer. Meanwhile, carboxylic acid, aldehydes, and lactide monomer and/or oligomers were evolved from degradation of PLA. Finally, carboxylic acids and ester moiety were detected in the course of degradation of PHB; thus, random chain scission reaction took place during thermal decomposition of this polymer. Results from the spectroscopic characterization (FTIR and H-1 NMR) of partially degraded samples supported the degradation mechanisms suggested by TGA/FTIR studies.