Ultradrawing of thermoplastics by solid state coextrusion illustrated with high density polyethylene

Ultra‐thin films of high density polyethylene of high orientation have been produced by the recently developed technique of solid state coextrusion. The films were prepared under moderate conditions, without lubricant in continuous lengths by extruding through conical dies of extrusion draw ratio up to 36. This is a draw ratio higher than achievable by conventional solid state extrusion at comparable processing conditions through slit dies. The ultra‐thin films of high orientation were transparent and exhibited dead bend. The physical and mechanical properties were evaluated and compared with the properties of the same high density polyethylene extruded through a slit die. The increase in the melt point, crystallinity, tensile modulus, and birefringence indicates that the method is very efficient for the production of ultra‐thin and highly oriented films. An experimental technique is also presented for preparing billets of controlled and uniform initial morphology and free of voids.