Structural and mechanical behavior of polypropylene/maleated styrene-(ethylene-co-butylene)-styrene/sisal fiber composites prepared by injection molding

Hybrid composites consisting of isotactic poly(propylene) (PP), sisal fiber (SF), and maleic anhydride grafted styrene-(ethylene-co-butylene)-styrene copolymer (MA-SEBS) were prepared by melt compounding, followed by injection molding. The melt-compounding torque behavior, thermal properties, morphology, crystal structure, and mechanical behavior of the PP/MA-SEBS/SF composites were systematically investigated. The torque test, thermogravimetric analysis, differential scanning calorimetric, and scanning electron microscopic results all indicated that MA-SEBS was an effective compatibilizer for the PP/SF composites, and there was a synergism between MA-SEBS and PP/SF in the thermal stability of the PP/MA-SEBS/SF composites. Wide-angle X-ray diffraction analysis indicated that the alpha form and beta form of the PP crystals coexisted in the PP/MA-SEBS/SF composites. With the incorporation of MA-SEBS, the relative amount of beta-form PP crystals decreased significantly. Mechanical tests showed that the tensile strength and impact toughness of the PP/SF composites were generally improved by the incorporation of MA-SEBS. The instrumented drop-weight dart-impact test was also used to examine the impact-fracture behavior of these composites. The results revealed that the maximum impact force (F-max), impact-fracture energy (E-T), total impact duration (t(r)), crack-initiation. time (t(init)), and crack-propagation time (t(prop)) of the composites all tended to increase with an increasing MA-SEBS content. From these results, the incorporation of MA-SEBS into PP/SF composites can retard both the crack initiation and propagation phases of the impact-fracture process. These prolonged the crack initiation and propagation time and increased the energy consumption during impact fracture, thereby leading to toughening of PP/MA-SEBS/SF composites. (C) 2002 Wiley Periodicals, Inc.