• The Optimal Design and Manufacture of Thin-Walled Polystyrene Structures

      Unwin, A.P.; Ugail, Hassan; Bloor, M.I.G.; Wilson, M.J. (2005)
    • Suppression of necking in polyethylene.

      Unwin, A.P.; Duckett, R.A.; Ward, Ian M.; Collins, T.L.D.; Sweeney, John; Coates, Philip D. (2002)
      The deformation behavior of a particular grade of high-density polyethylene prepared in a number of different ways has been examined. The samples all have an initially isotropic crystalline texture but differ in the levels of network preorientation surviving as a legacy of the melt processing history. Measurements of shrinkage and shrinkage force have been used to characterize this network, and the results suggest that the density of active chains is much lower than found in the main molecular network operating during solid-state drawing. The subnetwork properties vary depending on the level of extrusion and rate of cooling experienced during processing, with those entanglements surviving in the oriented melt at the point of crystallization having a long relaxation time. The presence of this subnetwork can lead to the suppression of necking during subsequent solid-state deformation. The implication is that simple processing procedures can be devised to remove or control the instability associated with necking.