Compatibilising additives for enhancing the interaction at the phase interface in thermoplastic vulcanisates based on rubbers of different polarity and polypropylene*

Abstract

The possibilities of increasing the interaction between the components of previously developed thermoplastic vulcanisates based on polypropylene and a combination of isoprene and nitrile butadiene rubbers were studied. The morphology of the composites was recorded by means of optical microscopy using an analytical complex based on a Leica DM-2500 optical microscope, a Leica DFC-420C digital high-resolution colour camera with a Peltier cooling system, and a specialised computer desk. The parameters of crystallisation of polypropylene were measured by differential scanning calorimetry using a DSC 204F1 Phoenix instrument (Netzsch). The physicomechanical properties of the vulcanisates were also determined. Maleinised polypropylene, a copolymer of ethylene with vinyl acetate, and their mixtures were used as compatibilising additives. Maleinised polypropylene was introduced together with polypropylene in a quantity of 1–10 parts; no changes in properties were observed with increase in the dosage above 4 parts, so this dosage was used. The copolymer of ethylene with vinyl acetate (1–10 parts) was introduced into the rubber phase at the stage of rubber mix preparation specially to improve the compatibility of polypropylene and nitrile butadiene rubber. The introduction of maleinised polypropylene leads to an increase in the workability and in the level of elastic strength properties, in particular the tensile elastic modulus and hardness. A considerable increase in the uniformity of distribution of components throughout the volume, a finer dispersion of the rubbers in the polypropylene matrix, and a reduction in the number of pores in the material were shown, and also an increase in the degree of polypropylene crystallinity measured under experimental conditions. The most positive effect is observed with the combined introduction of the copolymer of ethylene with vinyl acetate and the maleinised polypropylene: the nominal stress under elongation increases by 34%, and the elongation at break by 15%. The combined introduction of the compatibilising additives improves the compatibility of the components of the system, the phase boundaries become more diffuse, there is a reduction in the optical density of rubber-rich zones, and these zones are penetrated by polypropylene fibrils.