Mechanical properties of oriented low-density polyethylene with an oriented lamellar-stack morphology

A quantitative study was undertaken of the anisotropy of low-strain mechani cal behavior for specially oriented polyethylene with controlled crystallin e and lamellar orientation. The samples were prepared by the die drawing of injection-molded rods of polyethylene and annealing. This produced a paral lel lamellar structure for which a simple, three-dimensional composite lami nate model could be used to calculate the expected anisotropy. Experimental data, including X-ray strain measurements of the lateral crystalline elast ic constants, showed good quantitative agreement with the model prediction. The X-ray strain measurements confirmed that the amorphous regions exert l arge constraints on the crystalline phase in the lateral directions, where an order of magnitude difference was found between the measured apparent la teral crystalline compliances in the lamellar-stack sample and the expected values for a perfect crystal. (C) 2000 John Wiley & Sons, Inc.