Research On Properties And Reinforcing&Toughening Mechanisms Of PP/Wollastonite Composites

Polypropylene is one of the five common thermoplastics, and it can be used in thechemical equipment as an effective substitute for the part of iron and steel. However, it hasseveral shortcomings, such as low strength, poor thermal stability, high notch sensitivity,especially poor impact resistance at low temperatures,which seriously hindered its furtherapplication in the chemical equipment. In order to improve its mechanical and thermalproperties, PP/wollastonite composites, PP/PP-g-MAH/wollastonite composites andPP/surface treated wollastonite composites were prepared. And its mechanical property,thermal property and flow performance were analyzed and discussed. The major conclusionsas follows:With the increase of wollastonite content, modulus of PP composites increasedsignificantly. At the same time, tensile strength, fracture strength and bending strength tendedto increase and then decrease. But notched impact strength increased gradually. Whilenon-notched impact strength behaved in the opposite way. Compared with other systems, thePP composite material system which was filled with surface treated wollastonite showed thebest mechanical properties. Depending on SEM images, we could find that wollastoniteparticle could uniformly disperse in the PP matrix when its content was less than10phr(perhundred resin). And the bond situation between the surface treated wollastonite and PP wasbetter than others.Wollastonite could play the role of heterogeneous nucleation in PP composite. Whenwollastonite content was less than10phr, it could effectively improve the crystallinity ofcomposite materials. Moreover, wollastonite could improve the thermal stability of PP.Compared with other systems,the system of surface treated wollastonite was the best.Although wollastonite reduced the melt flow rate of PP, it also decreased the influence oftemperature on the density.Finite element analysis software ANYSY was used to stimulate the interface stressdistribution when PP composite was under tensile stress. Results showed that the maximumtensile stress occured in the mutation of wollastonite where the obvious stress concentrationphenomenon appeared. And the matrix near the mutation existed an obvious compression area which was easy to cause shear yield. With the increase of interface layer thickness andmodulus, stress concentration effect reduced and the internal stress of composite materialstended to be uniform.On the basis of three different systems, the effect of different treatment methods on themechanical property was studied. And we concluded that when wollastonite content was lessthan10phr, its high modulus and fiber structure in PP matrix could promote thecrystallization of the composite material with the heterogeneous nucleation effect. And therewas a good adhesion interface in PP/surface treated wollastonite system. Stress concentrationcaused by wollastonite led the matrix near the particles to debond and yield firstly and sliverlines caused by the particles were both major cause of toughening effect.