Polyblends. II. Isochronal viscoelastic parameters for polyblends of butadiene–acrylonitrile elastomers and copolymers of vinyl stearate and vinyl chloride

Abstract

AbstractIsochronal viscoelastic parameters were obtained for the polyblends of nitrile rubbers with internally and externally plasticized poly(vinyl chloride) (PVC) whose mechanical properties were studied in the previous paper. Thus, the room‐temperature mechanical properties of the previous paper were extended to included a wide temperature range in this work. Phase immiscibility, indicated by the observance of two glass transition temperatures, using differential scanning calorimetry, was observed for most of the polyblends. In contrast, blend compatibility was indicated by mechanical measurements, because the inflection temperatures of the isochronal curves (Ti) shifted with blend composition. It was concluded that mechanical spectroscopy‐monitored volume elements large enough to include contributions to viscoelastic response from both phases; this caused the curves to shift with composition. On the other hand, the much shorter‐range segmental responses characteristic of Tg produced transitions at the discrete temperature intervals representative of each phase. Using a relation between torsional stiffness at room temperature and tensile strength, failure strengths with respect to temperature were estimated and compared at varied free‐volume increments (T − Tg) up to 50°C. Approximate equivalence was found by this procedure for fillers of bulk PVC and those containing 21 wt‐% of both internal and external plasticizer, in analogy with findings for mechanical property optimization of the previous paper. Low‐temperature properties and viscoelastic response of the polyblends containing vinyl stearate copolymers were greatly improved over their neat state. In addition, data from isochronal temperature–composition diagrams suggested viscoelastic equivalence, but greater ease of processability for the blends containing vinyl ester, compared to the others.