Microstructural examination of welded environmentally stress cracked polyethylene.

摘要

Microstructural examination of surfaces has been shown to be useful in investigating the brittle failure of creep tested polyethylene. In order to examine the fine scale microstructure of polyethylene, the surface must be etched. Permanganic acid etching has been well proven at revealing the fine scale microstructure of polyethylene. However, as permanganic acid etching is chemically dangerous and the size of the specimen that may be etched is limited. UV Ozone was examined as a possible alternative. The UV Ozone etching technique is simple; requiring only a low pressure mercury lamp which emits the 254nm and 185nm wavelengths. This technique, however, did not prove to be nearly as effective as permanganic acid in revealing fine scale microstructures.;The surfaces of welded 32060 Dow HDPE were examined. Microstructural differences were noticed across the weld zone and between the weld zone and the bulk; the greatest microstructural difference being across the weld interface. Samples of welded and non-welded polyethylene were creep tested in methanol until failure. Microstructural observation of the surface in the plane of the applied stress revealed the occurrence of microcracking, indicative of brittle failure. Microcracks in the welded specimen were observed at the weld interface and throughout the weld zone. The failure of the welded specimens through the weld zone is attributed to changes in morphology between the weld zone and the non-welded zone.