Oxidative Degradation of Polyether In Contact with Minerals

Abstract: Oxidative degradation of adhesives based on silane terminated polypropylene oxide and polypropylene oxide (PPO) was studied. The combination of rapeseed oil and PPO as plasticizer in the parquet adhesive gave rise to oxidative degradation in contact with screeds of certain minerals. In order to investigate the degradation process in parquet adhesive two experimental approaches were employed in parallel. The first method was ageing of a solid adhesive-screed system at elevated temperature. It was done in order to evaluate the effect of contact between adhesives and screed in different adhesive-screed systems. Another purpose was also to identify the degradation procedure in a system resembling reality. The second method used was ageing of a soluble mixture of pure PPO with selected plant oils; in order to study the affect of oils unsaturations on the PPO by FTIR. FTIR was used to monitor the degradation of samples after different exposure periods. Unfortunately, interference from the adhesive additives made monitoring of the degradation process difficult in this approach. On the other hand, the optical inspection of the samples degradation process gave a clearer overview. A second method, looking only at two components mixed e.g. PPO and Oil, gave clear FTIR spectra showing that the oxidation process of rapeseed oil started in the period before fifteen days ageing at 75 oC. The combination of FTIR and optical inspection gave a clear image of the adhesive degradation process. Interaction between unsaturated carboxylic acid in the vegetable oils and PPO can increase the degradation rate of parquet adhesives by a radical mechanism. Another parameter affecting the degradation is the interfacial interaction between adhesive containing PPO-Rapeseed oil as plasticizer and screed with high alkalinity, porosity and humidity. The alkaline and humid conditions in the screed probably increase the hydrolysis of rapeseed oil. Further, the porosity of the screed provides a large surface area enabling the plasticizer to be exposed to plenty of oxygen from the air. Therefore, the plasticizer is not only exposed to hydrolysis but also oxidation. This would support the observation of migration of the rapeseed oil, since it is known that carboxylic acid has affinity to calcium sulfate anhydrite in the screed material. Migration and oxidation of rapeseed oils carboxylic acid generate radicals, which accelerate the degradation of PPO in the adhesive film. This process correlated with disappearance of PPO absorbance band from the spectrum.