Propriedades reológicas de blendas de polietilenos de fonte renovável: correlação com a estrutura molecular.

Abstract

The aim of this work is to evaluate the rheological behavior of high density biopolyethylene/linear low density linear biopolyethylene (BioHDPE/BioLLDPE) blends, containing 0-100% of BioLLDPE, at low and high shear rates and to correlate the results with the molecular structure of individual polymers. It was observed from complex viscosity curves (*) as a function of angular frequency () that the viscosity of BioLLDPE, at low frequencies, is much higher than that of BioHDPE, which can be attributed to the higher molar mass of BioLLDPE besides it has -oleophilic branching of 1-butene type. The viscosity of the BioHDPE/BioLLDPE blend increased with the increase of BioLLDPE content. Through the storage modulus (G ') vs , damping factor (tan ) vs  and spectrum relaxation plots it was observed, at low frequencies, that BioLLDPE is more elastic than BioHDPE and presented longer relaxation time. For BioHDPE /BioLLDPE blends there was a monotonic increase of G 'and reduction of tan  slope with increasing BioLLDPE concentration, indicating a more elastic behavior and resulting in longer relaxation times. Cole-Cole (imaginary viscosity – ‖ vs real viscosity - '), Han (G' vs loss modulus - G‖) and van-Gurp Palmen (phase angle -  vs complex modulus G*) plots suggest that the BioHDPE and BioLLDPE are possibly miscible in the molten state. It was observed that the BioHDPE and BioLLDPE polymers in addition to the BioHDPE/ BioLLDPE blends obey the principle of time-temperature superposition. BioHDPE/ BioLLDPE blends with higher BioHDPE concentrations showed less extrudate swelling and less flow instability. Based on the results it was observed that there is a strong dependence of the rheological properties of the blends on the molecular structure of the individual polymers and that the blends with higher contents of BioHDPE presented better processability at the high shear rates.