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Polymer Science & Engineering
Year Degree Awarded
Three low density polye thylenes , one long branched (A) and two linear (B and C), have been solid-state extruded at different temperatures from ambient to 80°C and to draw ratios _< 8. The densities and melt indices of A, B and C are 0.920, 0.920 and 0.935 g/cm3 , and 1.9, 0.8 and 1.2 respectively. Melt crystallized billets were extruded through conical dies in an Instron Capillary Rheometer. The linear polymers draw more easily 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 some loss through die swell, substantial orientation takes place during solid-state extrusion as evidenced by increases in transparency, birefringence, tensile modulus (up to 4.5 times that of the original isotropic polymer) and thermal conductivity. No ma j or changes in crystallinity were observed as assessed by density and DSC measurements. Depending on the polymer and the draw temperature, density does go through a minimum or shows a monotonic increase with draw.