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

Natural rubber samples were prepared having a wide range of molecular weights using two techniques: mastication, and reaction with phenylhyd razine. The rheological properties of polyamide 6 and the natural rubb ers were determined. Blends of polyamide 6 and the natural rubbers wer e prepared by melt blending. The blends were tested for their impact s trength and other properties. The molecular weight of the natural rubb er controlled the viscosity ratio of the blend components during mixin g. The dispersion of the natural rubber in the polyamide 6 was found t o be dependent on the viscosity ratio of the blends. The dispersion of the masticated natural rubbers were better than the liquid natural ru bbers. The blend impact strength was found to be dependent on the degr ee of dispersion, with the best impact strength at a mean rubber parti cle size of 0.33 microns and a particle size range of 0.20-3.00 micron s. The dependence on the rubber molecular weight of the rubber was sig nificant, 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 48 kJ/m2 at a rubber molecular weight of 290,000. This blend was prep ared having a viscosity ratio of 0.65 during mixing. The effect of mol ecular orientation and crystallisation behaviour were studied and foun d to be minor. The uncrosslinked natural rubber toughened the polyamid e 6 without loss of hardness but with a drop in the heat distortion te mperature.