Rheological and mechanical properties of PEO/block copolymer blends

Small quantities of block copolymers from two families, styrene-butadiene-methylmethacrylate (SBM) and methylmethacrylate-butylacrylate-methylmethacrylate (MAM) have been added to a polyethylene oxide (PEO) in order to improve its processability, namely increasing its elastic modulus without increasing too much its shear viscosity. The copolymers contain one block of polymethylmethacrylate (PMMA) that is compatible with PEO; the other blocks create nano phases, dispersed in the PIED matrix. Considerable efforts were devoted to finding the best blending method, either melt processing or solution casting. PEO is very sensitive to shear, and was found to degrade both in the bulk and in solution. Degradation, which cannot be avoided, was quantified through intrinsic viscosity measurements. The rheological characterization of blends containing 1, 2, and 5 wt% block copolymer was carried out. The elastic modulus was found to increase more than the complex viscosity. Blends obtained by solution casting technique gave better results. The elongational viscosity obtained for one blend containing 5 wt% of SBM showed a slight increase with respect to the pure PEO. Mechanical properties were then investigated, through tensile tests and dynamic mechanical analysis in flexion and in torsion; the copolymer generally enhanced the mechanical properties.