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 aminop ropyl groups, was developed to separate highly complex mixtures of deg radation products into three fractions. The SPE allowed the subsequent GC-MS identification of nearly 140 thermo-oxidation products of starc h-based polymer blends, consisting of 70% starch and either ethylene m aleic anhydride (EMA) or ethylene vinyl acetate maleic anhydride (EVAM A). It was thus possible to identify several homologous series of degr adation products such as n-alkanes and 1-alkenes, 1-alcohols, 2-ketone s, aldehydes, carboxylic acids and dicarboxylic acids. The homologous series of dicarboxylic acids ranged from butanedioic acid (C-4) to non adecanedioic acid (C-19) and was for the first time identified in ther mo-oxidized starch-based blends with polyethylene (PE), Hydrocarbons o f 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 t o 1-alkene increased (i.e. relatively more alkane is formed) under mor e severe thermo-oxidation conditions. The same phenomenon was not obse rved in the starch-EVAMA blend. Formic acid, acetic acid and gamma-but yrolactone were the most predominant degradation products in both mate rials. Typical starch degradation products were difficult to resolve b ut we identified 2-hexanone, formic acid and acetic acid, which also h ave 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 l ower rate. A good correlation between the decrease in M(n) and the amo unt of degradation products formed was observed. A higher degree of cr oss-linking occurred in the starch-EVAMA blend in comparison with the starch-EMA blend and, in parallel, qualitatively and quantitatively mo re degradation products are formed in the starch-EMA blend.