Modulação da morfologia e dos comportamentos térmico e mecânico do polietileno de alta densidade (PEAD) com a incorporação de etileno-acetato de vinila (EVA) e baixas concentrações de nanotalco sintético

Abstract

HDPE is a polymer widely used in industry, but it has some limitations of use as engineering material, a portion due to its fragility mainly under conditions of high pressure, low temperature and high deformation speed. The synthetic nanotalc is still a poorly studied filler, but it exhibits attractive lubricating properties, in addition to a high surface area and appreciable nanometric/submicrometric condition, so it is supposedly an attractive filler for improving the deformation capacity of polymeric systems. Binary and ternary blends of HDPE and HDPE/EVA with the incorporation of 1% m/m of talcs were prepared by mixing in the molten state in a twin-screw extruder followed by injection molding. Three types of talc were evaluated: natural microtalc (TN), semicrystalline synthetic nanotalc (NTC) and amorphous synthetic nanotalc (NTA). The TN had a micrometric size, while the synthetic talc showed a nanometric/submicrometric condition and with a specific surface area about 80 times greater than the TN. The investigation of HDPE/EVA/NTA ternary nanocomposites was carried out using different characterization techniques. The thermal properties were examined by thermogravimetric analysis (TG) and by differential scanning calorimetry (DSC) and showed that the thermal stability of the nanocomposites was slightly improved with NTA incorporation. The morphology of the nanocomposites, using scanning electron microscopy (SEM), revealed the NTA deeply embedded in the polymer matrix, a homogeneous distribution between the phases, in addition to changing the morphology of the 50EVA/NTA sample from sea-island to co-continuous, as well as refinement of size of the EVA phase. The dynamic mechanical properties of the samples were analyzed using the dynamic mechanical thermal analyzer (DMA). The results showed that the storage modulus increased with a diffuse pattern with NTA addition, while the tan  curve showed a prominent peak for the nanocomposite with 50% m/m of EVA (50EVA/NTA) around the EVA Tg, besides immiscibility between the polymeric phases. The mechanical properties of nanocomposites were studied by tensile and impact tests. A remarkable behavior was verified for the 50EVA/NTA nanocomposite that showed a super ductility characteristic, with an increase in the elongation at rupture of 4.8 and 2.4 times in relation to the pure HDPE and the related blend. The investigation of HDPE/talc binary composites was conducted to evaluate the role of different types of talc. The thermal stability of the composites has moderately improved with the incorporation of talcs. The morphology of the binary composites revealed that the particles of the synthetic talcs were normally homogeneously dispersed and deeply incorporated into the HDPE, whereas the TN presented higher levels of aggregated particles. DMA results showed that the addition of talcs to pure HDPE caused an appreciable increase in the storage modulus over a wide temperature range. The tan  curves indicated that the damping behavior of the composites was relatively reduced. The mechanical tests indicated that the composites showed a slight increase in the elastic modulus. However, composites showed a moderate drop in tensile strength and impact resistance, while ductility showed a significant gain for the HDPE/NTA sample, with an increase of 50% when compared to pure HDPE. The research evidenced that the NTA, with a low-level concentration, can be used as a differentiated filler, of high effectiveness, to improve the ductility and the stiffness/deformability balance of HDPE and HDPE/EVA blends. This new feature enables HDPE to new applications where superior mechanical properties are required, especially ductility, as well as qualifying NTA as a promising lubricating agent, with the potential to meet the mechanical requirements of other polymeric systems.