Effects of orientation on mechanical properties of uniaxially oriented polystyrene films

Oriented samples of polystyrene have been produced by drawing at temperatures just above the glass transition range. Birefringence measurements have been used to characterise the degree of orientation. Mechanical measurements of elastic modulus and tensile yield stress have been made in the direction of drawing and it has been established that the birefringence value does not uniquely determine the mechanical properties—samples drawn to a high draw ratio at high temperatures have a higher modulus and yield stress than samples drawn at lower temperatures and lower draw-ratios to the same birefringence. The results are explained qualitatively by the convective constraint release theory of McLeish et al.