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

Semi-interpenetrating polymer networks (SIPNs) of PVC/thermoset were prepar ed by premixing porous, 150 mu m diameter particles of PVC and a small quan tity (from 5 to 15% by weight) of a single thermosetting liquid preresin fr om one of five types (e.g. methylene bis-phenyl diisocyanate (MDI), oligome ric MDI isocyanates (PAPI), toluene diisocyanate (TDI) prepolymer, epoxy, a nd vinyl ester resins, respectively). Two roll milling of these mixtures wa s followed by hot-press curing. Mechanical testing indicated that most of t hese blends exhibited increased tensile, impact, and flexural strengths. Th e strength increments were greater when going from 0 to 5% thermoset conten t than when going from 5 to 10% or 10 to 15% thermoset. In many cases, incr easing thermoset content from 10 to 15% gave slightly decreased or unchange d 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 delta peak temperature lower than that for pure PVC in the glass trans ition region. The tan delta peak temperatures were progressively lowered as the amounts of thermoset increased, Also, a single distinct peak existed i n the E " curves for most of the blends, Only the PVC/epoxy (90/10) blend s howed two peak maxima in E " vs. temperature curves. All blends exhibited p eak E " values at a lower temperature than those of PVC which had been expo sed to the same processing temperatures. These observations seem to rule ou t the presence of large domains of PVC, which are phase-separated from PVC/ thermoset SIPN, and pure thermoset domains. A substantial amount of the add ed thermoset appears to exist in SIPN type phases in these five blend types .