Mechanical and viscoelastic properties of semi‐interpenetrating polymer networks of poly(vinyl chloride)/thermosetting resin blends

Abstract

AbstractSemi‐interpenetrating polymer networks (SIPNs) of PVC/thermoset were prepared by premixing porous, 150 μm diameter particles of PVC and a small quantity (from 5 to 15% by weight) of a single thermosetting liquid preresin from one of five types (e.g. methylene bis‐phenyl diisocyanate (MDI), oligomeric MDI isocyanates (PAPI), toluene diisocyanate (TDI) prepolymer, epoxy, and vinyl ester resins, respectively). Two roll milling of these mixtures was followed by hot‐press curing. Mechanical testing indicated that most of these blends exhibited increased tensile, impact, and flexural strengths. The strength increments were greater when going from 0 to 5% thermoset content than when going from 5 to 10% or 10 to 15% thermoset. In many cases, increasing thermoset content from 10 to 15% gave slightly decreased or unchanged tensile, impact, and flexural strengths. This behavior is in accord with a “thermoset dilution effect” in PVC. Most of these SIPN blends exhibited a tan δ peak temperature lower than that for pure PVC in the glass transition region. The tan δ peak temperatures were progressively lowered as the amounts of thermoset increased. Also, a single distinct peak existed in the E″ curves for most of the blends. Only the PVC/epoxy (90/10) blend showed two peak maxima in E″ vs. temperature curves. All blends exhibited peak E″ values at a lower temperature than those of PVC which had been exposed to the same processing temperatures. These observations seem to rule out the presence of large domains of PVC, which are phase‐separated from PVC/thermoset SIPN, and pure thermoset domains. A substantial amount of the added thermoset appears to exist in SIPN type phases in these five blend types.