Py-GC/MS as a means to predict degree of degradation by giving microstructural changes modelled on LDPE and PLA

The degree of changes in the patterns and ratio of peaks (oligomers) in pyrograms from pyrolysed polymers exposed to hydrolysis (chemical and/or biological) and oxidation are related the extent of degradation and could be used to predict life-time. PLA and LDPE with enhanced degradability (LDPE with LLDPE, corn starch and pro-oxidant [SBS + manganese stearate (MB)] were used as models for hydrolysable and oxidisable polymers and pyrolysis gas chromatography mass spectrometry (Py-GC/MS) analysed for its versatility show differences in microstructure of polymers. In parallel size exclusion chromatography (SEC), gas chromatography mass spectrometry (GC-MS) and Fourier transform infrared spectroscopy (FTIR) gave other signs of degradation. Pyrolysed LDPE samples gave fragments constituting a triplet from C-6, to C-30, With a peak maxima at C-10, C-14 and C-18 expect for LDPE with pro-oxidant and starch exposed to thermo-oxidation. This sample instead had a high amount of C-9 fragment which is related to hydrogen abstraction occuring along the chain. FTIR showed that this samples had formed higher amounts of carbonyl compounds at the surface. Thermogravimetry analysis (TGA) gave changes in the constituents of the LDPE with starch, pro-oxidant and starch. By fractionated Py-GC-MS at 400 and 500 degreesC, acetaldehyde, acrylic acid, lactoyl acrylic acid, two lactide isomers and cyclic oligomers up to pentamer were identified in poly(lactide) (PLA). The ratio of meso-lactide to D, L-lactide was lower in the biotically hydrolysed PLA, while the PLA matrices changes of unaged and chemically hydrolysed samples gave quite similar pyrograms. Thus, the most severly thermo-oxidised LDPE-sample had in a large peak at the C-9 fragment opposite to the other LDPE-samples while the most severly hydrolysed PLA (biotically hydrolysed) had a ratio of meso-lactide to D,L-lactide quite different from unaged and chemically hydrolysed sample. (C) 2001 Elsevier Science Ltd. All rights reserved.