Effect of a separator in a sheet die on the anisotropy of tear strength of extruded medium density polyethylene

Abstract

Sheets of medium density polyethylene (MDPE) were extruded through a slit die containing an internal separator. Thus, the melt stream was momentarily split before emerging from the die. A line of separation was evident in the extruded sheets. It is attributed to incomplete welding or healing. Measurements of tear energy G, revealed that the extruded sheets were anisotropic and that the weld line was extremely weak after extrusion start-up, only about V5 of the strength elsewhere. As extrusion continued, the strength of the weld line increased to reach that of the bulk material after about 10 min. This is attributed to an increasing temperature of the melt in the die region, aiding interdiffusion. A sample containing 30% by weight of short glass fibers showed less initial weld-line weakness but the weld line remained weak in this case, even after long extrusion times.

The anisotropy of slow crack growth in polyethylene pipes

“…For ABS a straightforward correlation of molecular orientation, which was measured by using thermal conductivity and thermally induced shrinkage, with critical strain was observed. Gent, et aL (4), have found the extrusion temperature dependence of the anisotropy in an extruded medium density PE by measuring the tear energy. They found that when the die temperature of the extruder is 150°C.…”

Unique Slow Crack Growth Behavior of Isotactic Polypropylene: The Role of Shear Layer-Spherulites Layer Alternated Structure

“…Ludwig et al discovered that polyethylene (PE) with a broad molecular weight distribution has superior long-term mechanical properties [ 13 ]. Meanwhile, many researches have proven that the formation of a shish-kebab structure and more perfect crystals can help to enhance the resistance of polymer to SCG to a large extent [ 11 , 14 , 15 ].…”