MEASUREMENT OF INTERNAL-STRESSES IN CHEMICALLY CROSS-LINKED HIGH-DENSITY POLYETHYLENE

Residual stresses in injection-moulded high-density polyethylene bars have been assessed by the stress-relaxation procedure of Kubát and Rigdahl, and also by the layer removal technique. Stresses were found to be tensile in the interior and compressive near to the surface. The introduction of cross-links through moisture-activated alkoxysilyl groups grafted onto the polyethylene molecules was found to increase the value of the internal stress parameter derived from the relaxation experiments and also to produce higher stress values by the layer removal analysis. Some of the relaxation curves have been analysed in addition by the technique due to Li and the significance of the internal stress parameter, σi obtained by the two different relaxation analyses is discussed. © 1979 Chapman and Hall Ltd.