Solid-phase extraction and subsequent gas chromatography mass spectrometry analysis for identification of complex mixtures of degradation products in starch-based polymers

A solid-phase extraction (SPE) method, using silica bonded with aminopropyl groups, was developed to separate highly complex mixtures of degradation products into three fractions. The SPE allowed the subsequent GC-MS identification of nearly 140 thermo-oxidation products of starch-based polymer blends, consisting of 70% starch and either ethylene maleic anhydride (EMA) or ethylene vinyl acetate maleic anhydride (EVAMA). It was thus possible to identify several homologous series of degradation products such as n-alkanes and 1-alkenes, 1-alcohols, 2-ketones, aldehydes, carboxylic acids and dicarboxylic acids. The homologous series of dicarboxylic acids ranged from butanedioic acid (C-4) to nonadecanedioic acid (C-19) and was for the first time identified in thermo-oxidized starch-based blends with polyethylene (PE), Hydrocarbons of even carbon number were formed to a larger extent than those with an uneven carbon number in the starch-EMA blend and the ratio n-alkane to 1-alkene increased (i.e. relatively more alkane is formed) under more severe thermo-oxidation conditions. The same phenomenon was not observed in the starch-EVAMA blend. Formic acid, acetic acid and gamma-butyrolactone were the most predominant degradation products in both materials. Typical starch degradation products were difficult to resolve but we identified 2-hexanone, formic acid and acetic acid, which also have been reported previously to be degradation products of starch. The molecular mass measurements showed that the starch-EVAMA blend starts to degrade earlier than the starch-EMA, but on the other hand, at a lower rate. A good correlation between the decrease in M(n) and the amount of degradation products formed was observed. A higher degree of cross-linking occurred in the starch-EVAMA blend in comparison with the starch-EMA blend and, in parallel, qualitatively and quantitatively more degradation products are formed in the starch-EMA blend.