Oil Barrier Polymer Alloy for Rotational Moulding Applications

Abstract

Blow moulded polymer alloys, with a dispersed nylon laminar phase, have been proven to be effective barrier materials to permeating hydrocarbons. These phases are prepared by the shear stretching of the polymer alloy in the blow moulding stage. DuPont has successfully implemented this technology under the brand name Selar RB. This research aims to adapt this lamina morphology to a rotational moulding process. As rotational moulding is a low to zero shear process, optimisation of the starting materials and process procedure was performed to promote the formation of the laminar phase. Two nylons were investigated in an attempt to form the dispersed phase laminar morphology. Elvaloy PTW was identified as the optimal compatibilizing agent between nylon and polyethylene. Nylon 6 containing polymer alloy samples, with varying levels of Elvaloy PTW, were moulded at temperatures above and below the melting temperature of the nylon. Nylon multi-polymer containing polymer alloy samples were only moulded at temperatures above the nylons melting temperature. The optimum temperature for the high temperature process of both polymer alloys was found to be 250oC. Samples to be rotationally moulded were produced by twin-screw extrusion. All samples contained 12.5% nylon by weight and had an Elvaloy PTW level of range from 45% to 5%, in relation to the nylon concentration. The samples were then rotationally moulded into the proposed oil barrier structure. Samples were tested for their phase morphology, barrier properties and mechanical properties. Scanning electron microscope tests showed that there was no formation of the proposed r phase for any of the rotationally produced samples. A xylene permeation test showed that the rotationally moulded products did not perform as effective a barrier as did Selar RB. The mechanical testing showed an increase in both the impact resistance and the flex modulus with the addition of the Elvaloy/nylon species. As the level of Elvaloy was increased from 5% to 45% in relation to the nylon content, the impact resistance increased, whereas the flexural modulus decreased. The proposed mechanism of producing an oil barrier material, consisting of laminar nylon layers, in a rotational moulding system, was not achieved in this study. It is apparent from this research, that the rotational moulding cycle does not induce enough shear on the molten polymer alloy to extend the spherical regions into a laminar morphology.