Dispersão em polietileno de masterbatch de PE/PA seletivamente reticulado: Influência de propriedades reológicas e condições de extrusão

Abstract

The present work evaluated the influence of rheological parameters of different matrices of high-density polyethylene (HDPE), along with processing parameters (screw design) in twin-screw extrusion, over the dispersion and distribution of a masterbatch consisting of a compatibilized blend of HDPE and selectively crosslinked PVA, as well as the mechanical and rheological properties of the diluted products, which contained 5 and 10 wt% of PVA. In the tensile test, it was clear that PVA content, as well as HDPE rheological properties and processing parameters directly affected the properties of the mixtures, especially stress and elongation at break, which were the best metrics in the tensile test. In general, better dispersion conditions, more viscous HDPEs and lower PVA contents led to better tensile properties, where the polyethylene with the highest viscosity showed decreases in stress and elongation at break up to 2x lower in percentage terms compared to the PE with the lowest viscosity. Few exceptions were noted, especially for yield stress and strain. The tensile impact test demonstrated that the addition of PVA particles have not led to increase in toughness of HDPE but to a reduction of impact strength, with a drop of up to 30% for the more viscous PE. The results presented opposite trends to what was expected and observed in uniaxial tensile and rheological analysis, when comparing processing conditions and polymer selection. These results might be related to greater degradation due to a more severe processing condition, or even by the addition of a HDPE vehicle of different molar mass. Rheological tests (parallel plates in small angle oscillatory shear (SAOS)) demonstrate that properties such as complex viscosity, loss and storage modulus and tan δ, varied more intensely for lower viscosity matrices, better dispersion conditions, and finally, for higher PVA contents, as predicted by the theoretical foundation, where it was considered that better dispersion and distribution, therefore, larger exposed surface area of matrix-particle interface would lead to a higher shift in rheological properties. For example, increases of more than 100% in storage modulus compared to the neat polymer were observed for the less viscous PE, while increases around 13% for the higher viscosity PE were obtained. Finally, in terms of visual evaluation of dispersion via optical microscopy for 5 wt% of PVA, there is a perception that the tested polyethylenes with highest and lowest viscosities presented better dispersion and particle distribution for the more severe processing condition, meanwhile the PEs of intermediate viscosity presented basically equivalent aspects between different screw designs. The more viscous polyethylene displayed better mixture characteristics than the others, the PEs with intermediate viscosities had very similar microstructures, and the less viscous PE presented the worst aspect, as expected.