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

摘要

The degree of changes in the patterns and ratio of peaks (oligomers) in pyrograms from pyrolysed polymers exposed to hydro- lysis (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) ana- lysed for its versatility show differences in microstructure of polymers. ln parallel size exclusion chromatography (SEC), gas chro- matography 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-oxi- dant and starch. By fractionated Py-GC-MS at 400 and 500℃, 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 dif ferent from unaged and chemically hydrolysed sample.