THE INFLUENCE OF VISCOSITY RATIO ON THE MORPHOLOGY AND MECHANICAL PROPERTIES OF POLYAMIDE 6/NATURAL RUBBER BLENDS

F.H. AXTELL, P. PHINYOCHEEP, AND P. MONTHACHITRA

ABSTRACT: Natural rubber samples were prepared having a wide range of molecular weights using two techniques: mastication, and reaction with phenylhydrazine. The rheological properties of polyamide 6 and the natural rubbers were determined. Blends of polyamide 6 and the natural rubbers were prepared by melt blending. The blends were tested for their impact strength and other properties. The molecular weight of the natural rubber controlled the viscosity ratio of the blend components during mixing. The dispersion of the natural rubber in the polyamide 6 was found to be dependent on the viscosity ratio of the blends. The dispersion of the masticated natural rubbers were better than the liquid natural rubbers. The blend impact strength was found to be dependent on the degree of dispersion, with the best impact strength at a mean rubber particle size of 0.33 microns and a particle size range of 0.20-3.00 microns. The dependence on the rubber molecular weight of the rubber was significant, with low blend impact strength at molecular weights below 10,600. At higher rubber molecular weights the natural rubber toughened the polyamide significantly, reaching a peak Charpy impact strength of 18 kJ/m² at a rubber molecular weight of 290,000. This blend was prepared having a viscosity ratio of 0.65 during mixing. The effect of molecular orientation and crystallisation behaviour were studied and found to be minor. The uncrosslinked natural rubber toughened the polyamide 6 without loss of hardness but with a drop in the heat distortion temperature.

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Department of Chemistry, Faculty of Science, Mahidol University, Rama VI Road, Bangkok 10400, Thailand.

Received November 29, 1992