Rheological behaviour of LDPE/EVA-c blends. I. On the effect of vinyl acetate comonomer in EVA copolymers

Low-density polyethylene (LDPE) has been the subject of several rheological studies trying to correlate rheological features with molecular parameters. As the ethylene vinyl acetate copolymer (EVA-c) and LDPE are obtained through the same polymerization process, it has been long assumed that both materials would exhibit a similar viscoelastic response. However, a recent work has put forward the question as to whether the presence of vinyl acetate (VAc) units could modify the expected viscoelastic behaviour. In order to further explore this effect, we have carried out a dynamic viscoelastic study in a series of seven EVA-c. At a first step, it will be shown that EVA-c presents a thermorheological complex behaviour. It will be shown that Newtonian viscosity (η0) values are conspicuously higher than those reported for LDPE of similar molecular weight (Mw). Furthermore, a concurrent lower elastic character of the EVA-c samples is observed. The results are discussed in terms of molecular architecture and molecular weight distribution (MWD). However, a final explicit VAc content dependence of the viscoelastic properties up to 30% by weight of this comonomer is not observed.