Reactive melt modification of polyethylene by ethyl acrylate/acrylic acid copolymers: rheology, morphology and thermal behavior

Abstract

Polyethylene (PE) was in situ grafted and blended with ethyl acrylate and acrylic acid copolymer units and the rheology, morphology and thermal behavior of samples were investigated and correlated to grafting efficiency. The ethyl acrylate and acrylic acid monomers were copolymerized in three different amounts of monomers (i.e., 5, 15 and 25 wt%) and three different amounts of 2,2′-azobisisobutyronitrile (AIBN) initiator (i.e., 0.2, 0.3 and 0.4 wt%). The reactive melt blending of the synthesized copolymers, PE and dicumyl peroxide (DCP) were carried out in a co-rotating, 40 L/D twin screw extruder. The grafting percentage, determined by using chemical titration and Fourier transform infrared (FTIR) methods, increased at higher amounts of reactive monomers and AIBN and a maximum of 6 % was achieved. The thermal behavior of PE were studied by differential scanning calorimeter (DSC) and no remarkable changes was observed in melting (T m = 127.0 ± 2 °C) and crystallization (T c = 113.6 ± 2 °C) temperatures. The crystallinity of PE decreased from 53.5 to 43.8 %, with increase in grafting density. Investigating the gel content showed that only in samples that contained the highest amounts of acrylic monomer, i.e., 25 wt%, an increase in gel content was observed by increasing the total peroxide. The maximum value of gel content was 23.6 %. Increase in acrylate and AIBN percentages showed increase in viscosity and damping factor and decrease in storage modulus in rheological study of the samples and the results were proved by morphological study of the samples using scanning emission microscopy (SEM).