The role of a heat affected zone (haz) on mechanical properties in thermally welded low density polyethylene blown film

摘要

Low density polyethylene (LDPE) thin films are produced by blown film extrusion. THe control of key variables during processing is important in the development of optimized microstructure and mechanical properties. Joining several extruded film pieces by thermal welding is common in industry to produce finished prodcucts. It has bee reported in the literature that the welding process impacts the cold brittleness temperature of a film and weld system. This observation is confirmed in this work. There have also been reports in the literature of changes in polymer microstructure and properties adjacent to thermal welds in non-film applications such as pipe welding. This Heat Affected Zone (HAZ) has been observed here for the first time in the thin films. The size of the HAZ is shown to scale with welding temperature. Evidence correlating the size of the observed HAZ to the degree of change in cold brittleness temperature is also presented.