Desenvolvimento de compósitos de matriz PA6/EVA com carbonato de cálcio com potencial aplicação na indústria automobilística

Abstract

The automotive industry is responsible for a large share of the of the global market consumption of polymeric materials, which represent today the second predominant material in vehicles. Polymers combine properties such as flexibility in processing, good chemical resistance, low density and low cost. Polyamide 6 (PA6) is an engineering polymer widely used in automotive parts, replacing metal parts, which motivates the development of mixtures and composites that optimize its properties, particularly toughness, which can be obtained by the addition of an elastomeric phase. However, this usually leads to loss of rigidity and mechanical strength of the matrix. A balance between rigidity and toughness can be achieved with the addition of rigid particles to PA6 blends. Seeking to meet specifications of the automotive industry regard to the application performance of PA6 composites in corrugated pipes, in this study PA6 composites with poly(ethylene-co-vinyl acetate) (EVA) with calcium carbonate (CaCO3) were developed. In the initial stage PA6/EVA blends with 10, 20 and 30% by weight of EVA were prepared and then PA6/CaCO3 composites with 10, 20 and 30 parts per hundred resin (phr) of two CaCO3 types, natural and precipitated, produced by twin screw extrusion. PA6/EVA blend shows immiscibility, with loss of mechanical and thermal properties compared to the neat PA6, providing increased impact resistance and elongation at break. The blend with 10% (w/w) EVA shows the most satisfactory results of the proportions studied. For the composites, the presence of both CaCO3 types improves PA6 flexural and impact strength and elastic modulus, with loss of tensile strength. The increase in heat deflection temperature is the most significant improvement on the composites, reaching 170%. While the best results for natural CaCO3 occur in the presence of 30 phr, for precipitated CaCO3 the best performance is observed in composites with 20 phr, since in larger quantities the particles form agglomerates. Based on these results, two PA6 composites with 10% by weight EVA and 20 phr of natural and precipitated CaCO3 were developed. Morphological analysis shows that CaCO3 particles are preferentially located in the PA6 matrix, which leads to an increase in composite stiffness and reduction of toughness. Finally, PA6/EVA/CaCO3 corrugated pipes were produced by single screw extrusion in industrial scale, for performing testing according to the specific standard for use as protection for electrical wires. The pipes produced with the composites show greater dimensional stability compared to the standard, produced with PA6, improving impact and compression resistance. However, the reduction of flame resistance disables the pipe with precipitated CaCO3 for use, while the pipe with natural CaCO3 proves to be the best option for replacing PA6 corrugated pipes.