Avaliação do efeito da adição de nanopartículas de carbonato de cálcio nas propriedades físico-mecânicas do polipropileno

Abstract

Composites of polypropylene and calcium carbonate in nanosized scale were prepared by melt processing in a twin screw extruder. Statistical analysis (experimental design) was performed to evaluate the effect of the following variables: content of calcium carbonate, screw rotation and profile on the properties of the materials. The mechanical properties were determined by means of tensile tests (ASTM D 638), flexural strength (ASTM D 790) and impact resistance (ASTM D 256). The processability of the materials was evaluated by means of the melt flow index (ASTM D 1238). The scanning electron microscopy was used to evaluate the dispersion of filler in the matrix and to obtain information about the interfacial adhesion between calcium carbonate particles and polymer matrix. The results showed that the filler content is the most significant variable on the flexural modulus values. The filler concentration and screw rotation are the variables that exert the most significant effect on the impact properties. As the concentration of nanoparticles increases, an increase in flexural modulus and impact resistance is observed. The increase of the screw speed leads to a reduction of the impact properties. The screw configuration is the most significant variable on the mechanical strength of the materials. Higher values of tensile strength were obtained when a high shear screw configuration was employed. The screw speed is the most significant variable on the Young's modulus values. The increase of the screw rotation and a high shear screw profile lead to polypropylene higher Young's modulus values. Scanning electron microscopy showed that a good dispersion of nanoparticles in the polymer matrix was not achieved, despite of using particles coated with calcium stearate. Better flexural and impact properties were obtained at 350 rpm using the low shear screw configuration. However, the tensile properties were reduced. In order to obtain nanocomposites of polypropylene and calcium carbonate, other processing conditions and filler coating procedures should be tried.