Development of layered silicates montmorillonite filled rubber-toughened polypropylene nanocomposites (RTPPNC)

Abstract

Polypropylene is an outstanding thermoplastic with respect to its attractive combination of low cost and extraordinary versatility in terms of properties and applications. However, the increasing demand of polypropylene for various applications requires greatly improved physical and mechanical properties. Recently, the addition of nanoscopic fillers of high anisotropy instead of conventional reinforcing agents renders the polymer/nanoclay nanocomposites to exhibit interesting structure-property relationships and promising application perspectives. However, the low temperature impact properties polypropylene nanocomposites limit some of its application. In order to achieve improved impact properties, impact modifiers polyethylene octene known as polyolefin elastomer have been added to toughen the polypropylene nanocomposites. Rubber toughened polypropylene nanocomposites containing difference content of organoclay and polyethylene octene were compounded in a twin-screw extruder. The mechanical properties of the nanocomposites were determined on injection-molded specimens in tensile, flexural and impact tests. From the tensile and flexural tests, the optimum loading of organoclay in nanocomposites was found to be 6 wt%. Maleic anhydride modified polypropylene was used as compatibilizer to mediate the polarity between the clay surface and PP. The modulus and strength of polypropylene nanocomposites were improved in the presence of polypropylene grafted maleic anhydride and achieved optimum modulus and strength at a compatibilizer content of 6wt% for the blend. The morphology of the nanocomposites was studied by scanning electron microscopy and X-ray diffraction. X-ray diffraction results showed the formation of nanocomposites as the organoclay was intercalated by polypropylene macromolecules. Incorporation of polypropylene grafted maleic anhydride could improve the degree of intercalation and hence resulting in better dispersion in the polypropylene matrix. Izod impact tests indicated that the polyethylene octene and maleated polyethylene octene were very effective in converting brittle polypropylene nanocomposites into tough nanocomposites. Scanning electron microscopy study revealed a two-phase morphology which was clearly visible for all systems and the droplets of elastomer dispersed uniformly within the blends. Thermogravimetric analysis showed that thermal stability of nanocomposites significant increased with the incorporation of small amounts of organoclay in a platelet form. The essential work of fracture was used to evaluate the fracture toughness of the rubber toughened polypropylene nanocomposites. Essential work of fracture measurements indicated that the specific essential work of fracture decreased with increasing organoclay content. However, additions of polyethylene octene and maleated polyethylene octene are beneficial in enhancing the specific essential work of fracture of the polypropylene nanocomposites.