Aj. Prins et al., BIAXIAL ORIENTATION OF LINEAR POLYETHYLENES USING THE COMPRESSIVE DEFORMATION PROCESS, Polymer engineering and science, 37(2), 1997, pp. 261-269
The tensile properties of three grades of linear polyethylene were enh
anced by a factor of as much as 15 using a melt/solid phase compressiv
e deformation process that produced equi-biaxial planar orientation in
the sheet. Ultra high molecular weight polyethylene wi th planar isot
ropy and an in plane modulus of 10 GPa and a tensile strength of 330 M
Pa was produced using this method. It was found that the molecular wei
ght had a significant influence on the optimum processing temperature,
the ultimate biaxial deformation ratio and hence the ultimate tensile
properties. High density polyethylene processed under ideal condition
s had a tensile modulus of 2.3 GPa and a tensile strength of 250 MPa.
The tensile strength increased linearly with increasing biaxial deform
ation ratio and the tensile modulus increased non-linearly with increa
sing biaxial deformation ratio. The deformation rate and the dwell tim
e did not have a significant effect on the tensile properties. Shrinka
ge tests showed that biaxial deformation was less effective than uniax
ial deformation in inducing orientation of the polymer chains, however
differential scanning calorimetry results were consistent with the pr
esence of extended chain crystals in very highly oriented ultra high m
olecular weight polyethylene sheets.