Preparation And Properties Of Calcium Sulfate Whisker/Polypropylene Composite Materials

Polypropylene(PP)can be used to engineering material owing to that it has the advantages of excellent mechanical properties,high crystallinity,good heat resistance,excellent chemical stability,good resistance to bending fatigue and good crack resistance.But the strength and toughness of the PP material often cannot be both achieved in one material,because the material tends to have high strength and low toughness,or high toughness and low strength.Therefore,in practical applications,PP was usually modified in a targeted manner to improve strength or toughness to expand it fields of use.In this paper,the modified calcium sulfate whiskers was used as the main filler for modifying PP to improve its mechanical properties.And,the mechanical properties,crystallization,rheology,processing and other properties of modified calcium sulfate whiskers(OCSW)/PP composites were studied in detail.Firstly,the titanate coupling agent(NDZ)was used to modify the CSW and it is found that NDZ was grafted onto CSW with different grafting rates.And then,OCSW/PP composites were prepared via melt blended method.The results show that NDZ can significantly improve the compatibility of OCSW and PP.A good interfacial effect is found between the PP matrix and OCSW.OCSW plays the role of a stress concentration in the composites and performs a significant reinforcing effect on the matrix.Secondly,different PP composites were prepared via melt blended method with a graft ratio of 2.0 wt% OCSW.The performance results of OCSW/PP composites show that OCSW/PP composites have better comprehensive mechanical properties,lower critical contents of induced ?-crystal nucleation and lower crystallization temperature compared with those of CSW/PP composites.As the contents of OCSW increase,the tensile strength,flexural strength and impact strength of OCSW/PP composites increased first and then decreased,when the contents of OCSW is 5 wt%~10 wt% that the composites has the optimal mechanical properties.OCSW also has great influences on the rheological properties and dynamic mechanical properties of PP.OCSW has a viscosity-increasing effect on the PP melt.As the contents of OCSW increases,the crystal size of the composites decreases gradually.The optimum injection molding process of OCSW/PP composites is at 190? of barrel temperature and 30? of mold temperature.Thirdly,the foaming properties of OCSW/PP composites show that the composite has the best comprehensive mechanical properties when the contents of OCSW is 4 wt%.When the same amount of foaming agent is added that the composite material can obtain smaller cell size compared with that of pure PP without OCSW.OCSW is oriented in the cell wall what to enhance the cell wall and improve the tensile strength and compressive strength of the composite.But the cell collapse when the contents of OCSW is above 6 wt%.Finally,when the OCSW and glass fiber(GF)are used to synergistically modify PP,the results show that OCSW and GF have synergistic enhancement effect on PP.When the contents of OCSW is 3 wt% and the contents of GF is 20 wt% that the composite has the best comprehensive mechanical properties.OCSW and GF also have synergistically nucleation effect of induced ?-crystal.When the contents of OCSW is 5 wt% and the contents of GF is 20 wt%,the relative contents of ?-crystal in PP reaches 0.5.As the contents of OCSW increases,the melt viscosity and shear storage modulus of the composite decrease gradually.