Crystalline-State Extrusion of Low Density Polyethylenes.
Abstract
Three low density polyethylene, one long branched (A) and two linear (B and C), have been solid-state extruded at several constant temperature from ambient to 8 deg C and to draw ratios < 8. The initial densities and melt indices of A, B and C are 0.920, 0.920 and 0.935 g/cc, and 1.9, 0.8 and 1.2 respectively. Melt-crystallized cylindrical billets were extended through conical dies in an Instron Capillary Rheometer. The linear polymers were found to draw by extrusion more readily than the branched; all three strain-harden. Density, birefringence, tensile and thermal properties have been evaluated as functions of extrusion temperature and draw ratio. Despite a measured loss via die swell, substantial orientation takes place during solid-state extrusion as evidenced by increases in transparency, birefringence and tensile modulus (up to 4.5 times that of the original isotropic polymer). Depending on the polymer and the draw temperature, density does go through a minimum or shows a monotonic increase with draw by extrusion. A minimum in modulus is also observed at low draw and at all draw temperatures for all three polymers. The highest tensile moduli achieved are 0.73, 0.46 and 1.5 GPa for A, B and C respectively at their highest draw ratio. The melting point for polymer B decreases with extrusion draw ratio, whereas it remains constant after a small initial drop, for the two others. For all three low density polyethylenes, birefringence increases rapidly with extrusion draw and then levels off at high draw.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 15, 1983
- Accession Number
- ADA142017
Entities
People
- C. Benelhadjsaid
- R. S. Porter
Organizations
- University of Massachusetts Amherst