Push–pull extrusion: A new approach for the solid‐state deformation illustrated with high density polyethylene

Abstract

SynopsisThe crystalline state deformation of high density polyethylene has been examined a t an extrusion draw ratio of 30 over a range of temperatures and pressures. The experiments involve combined pushing (extrusion) and pulling through a conical die. The pressure dependence of the extrusion rate through conical dies is given by a logarithmic relation and the temperature dependence by an activation energy of -95 kcal/mole. An equation established for the total applied force linearly relates the pulling and extrusion pressure components and represents a force balance at the die entrance and exit. Steady-state extrusion, with or without pulling, was feasible in a pressure range beyond which fractures occurred owing to strain rate and shear or tensile failure. Under some circumstances the extrusion rate was increased by ten times. The mechanical properties and mode of deformation were not affected by pull load and fibers with a tensile modulus of 55 GPa were produced a t T < 110°C.

Drawing and extrusion of semi-crystalline polymers

“…The application of a force on the back of the billet (ram extrusion) [297], or a uniform pressure (hydraulic extrusion) [298,299], or traction of the extrudate [300] does not substantially change the resuks. A higher temperature [301] or an added lubricant [49][50][51] reduces the friction on the die, and thus the transverse, but not the longitudinal velocity gradient.…”

The Structure and Properties of Typical Melt-spun Fibres

“…Developments in tlie formation of ultra-oriented polyethylene fibre from its melt were reported by several authors [424][425][426][427][428][429][430][431][432].…”

“…Extension rate, pressure, temperature, draw ratio, and molecular weight were studied in the light of microstructural details of the drawn fibres [424][425][426][427][428][429][430].…”

Die geometry induced heterogeneous morphology of polypropylene inside the die during die-drawing process

“…The basic idea of polymer processing is to build a polymer network in which polymer chains are ideally stretched so that each chemical bond could help taking load, yet not too extended to protect the system from peeling apart [4]. There are lots of effective processing methods being well-developed currently, such as die drawing [7][8][9], extrusion [10][11][12], spinning [13,14], rolling [15], etc.…”