Examination of a low density polyethylene (LDPE) film after 15 years of service as an air and water vapour barrier

A low density polyethylene (LDPE) film used as an air and water vapour barr ier for 15 years in an exterior wooden wall construction has been examined regarding ageing properties. The wall in question was part of a small house used for building material testing purposes only. During its use, the majo r part of the him was firmly pressed between plywood boards made of spruce and plasterboards. By pure chance, however, parts of the him had been hangi ng loose over the plasterboard into the room and thus exposed to room tempe rature air as opposed to the rest of the film. Different parts of the same LDPE film had thus been exposed to natural ageing in different environments allowing for interesting comparisons to be made. Tensile testing, size exc lusion chromatography (SEC), oxygen induction temperature measurements, W a nd FTIR spectroscopy, and MALDI mass spectrometry have been used to examine the differently aged parts of the LDPE film. It was found that the him con tained the antioxidant beta-(3,5-ditert-butyl-4-hydroxyphenyl)-propionic oc tadecyl ester (trade name Irganox 1076). Despite the fact that the part of the film found inside the wall had lost about 75% of its initial antioxidan t concentration as compared to the part exposed to the room's environment, the latter had a substantially lower stabilising power as indicated by a co nsiderably lower oxygen induction temperature. Most likely,the antioxidant has been "deactivated" through its protective action in preventing oxidativ e degradation of the polymer of the "room" film. The loss of antioxidant in the "wall" film can most likely be attributed to migration and loss to the surrounding wall construction materials. Despite substantial losses of act ive antioxidant for both parts of the him, through different mechanisms, bo th parts have retained their tensile properties as indicated by normal valu es of elongation- and stress-at-break. Furthermore, the SEC chromatograms i ndicate no degradation of the polymer in neither parts of the film. Accordi ngly, the polymer itself seems not yet to have been affected by ageing. (C) 2001 Elsevier Science Ltd. All rights reserved.