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Properties and morphology of injection- and compression-molded thermoplastic polyurethane/polypropylene-graft-maleic anhydride/wollastonite composites

The mechanical properties, morphology, thermal stability and flammability of thermoplastic polyurethane/polypropylene-graft-maleic anhydride/wollastonite composites (TPU/PP-g-MA/wollastonite) were investigated. TPU was melt mixed with two loadings of PP-g-MA (5 and 10 phr) and subsequently with 5 phr PP-g-MA and four loadings (10, 20, 30 and 40 phr) of wollastonite mesh size 2000 microparticles on a twin screw extruder. The extrudates were pelletized and then molded into test specimens by injection- and compression-molding. The stiffness and thermal stability of the TPU were found to be improved as a result of the incorporation of PP-g-MA and wollastonite, although the extent of such depended upon and varied with the processing technique. The injection-molded specimens exhibited a higher tensile strength and elongation at break, and a lower Young’s modulus, than the compression-molded specimens of the same composition. The limiting oxygen index values were slightly increased by the presence of wollastonite in the composites. Moreover, the morphologies of the injection- and compression-molded samples observed by scanning electron microscopy showed the orientation and nonorientation of the wollastonite microparticles, respectively.