Natural rubber-polystyrene interpenetrating polymer networks as impact modifier

Abstract

Natural rubber-polystyrene interpenetrating polymer networks (IPNs) were synthesized by emulsion polymerization process. A prevulcanized natural rubber latex was coated with a shell of polystyrene (PS). The bipolar redox initiating system tertbytyl hydroperoxide/tetraethylene pentamine promoted a core-shell arrangement. IPNs polymerization was carried out by varying concentrations of the initiator, emulsifier, crosslinking agent, reaction time, and reaction temperature. The optimum conditions were the initiator concentration of 1.5 phr, the crosslinking agent concentration of 0.25% wt of monomer, emulsifier concentration of 1.5% wt of monomer, and temperature of 60 ํC for 2 hours. Both IPNs and semi-IPNs were prepared and characterized by evaluating their morphology and mechanical properties. The morphologies of resulting latex IPNs were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). From this experiment, IPNs showed higher tensile strength, modulus, tear strength and finer phase distribution than the corresponding semi-IPNs, while the latter exhibited higher elongation at break. IPNs products were used as an impact modifier in polypropylene (PP). The IPNs products (10, 15, 20 and 25 phr) and PP blends were prepared. The effects of IPNs products content on tensile strength and hardness decreased with increasing the IPNs product content, but impact strength increased with the increasing IPNs product content. The appropriate amounts of IPNs products used were 10 and 15 phr.