Production of UHMWPE sheet materials

A ram extrusion process for preparing UHMWPE panels of widths of 0.4 m or greater, comprising:

• providing a slit die having a width of 0.4 m or greater which has a substantially rectangular cross-section proximate its exit under ram extrusion operating pressure, the die having a top portion and a bottom portion defining a slit therebetween, and an inlet face and an exit face, and having a plurality of independently controllable transverse cooling zones in each of the top portion and bottom portion, said cooling zones located proximate the exit face of the die and positioned across the width of the die such that the temperature of the cooling zones may be adjusted to vary the temperature of respective portions of the slit die transverse to the exit face;
• incrementally introducing UHMWPE particles into the die under pressure from a ram;
• heating the UHMWPE particles to at least crystalline melt temperature of UHMWPE to form a substantially continuous molten thermoplastic;
• cooling the UHMWPE to a temperature below the crystalline melt temperature while within the die and while maintaining contact with walls of the die;
• extruding from the slit of the slit die a solidified UHMWPE panel product, and restraining movement of the panel product away from the die by a back pressure device to produce a back pressure within the die.