Elongational viscosity for miscible and immiscible polymer blends. II. Blends with a small amount of UHMW polymer

The effect of miscibility on elongational viscosity of polymer blends was i nvestigated in homogeneous, miscible, and immiscible states by the blend of 1.5 wt % of ultrahigh-molecular-weight (UHMW) polymer. The matrix polymer was either poly(methyl methacrylate) (PMMA), or poly(acrylonitrile-co-styre ne) (AS) that has a comparable elongational viscosity value. The homogeneou s blend consisted of 98.5 wt % of PMMA and 1.5 wt % of UHMW-PMMA. The misci ble blend was composed of AS and UHMW-PMMA at the same ratio. The immiscibl e blend was a combination of AS and UHMW-polystyrene (PS) at the same ratio . The strain-hardening behavior of the different blends were compared with that of pure PMMA. It was demonstrated that 1.5 wt % of UHMW induces a stro ng strain-hardening property in the homogeneous and miscible blends but was hardly changed in the immiscible blend. The optical microscope observation of the immiscible blend suggested that the UHMW domains were stretched, bu t that the degree of domain deformation was less than a given elongational strain. It was concluded that the strain-hardening property is strongly aff ected by the miscibility of UHMW chain and matrix. The strong strain-harden ing property is caused by the deformation of the UHMW polymer. UHMW chains are stretched when they are entangled with surrounding polymers. However, U HMW chains in an immiscible state are not so deformed because of viscosity difference and no entanglements between domain and matrix. A smaller degree of UHMW chain deformation in immiscible state results in weaker strain-har dening property. (C) 1999 John Wiley & Sans, Inc.