Study On The Preparation And Properties Of The Composites Blending With Polypropylene And Calcium Carbonate Whiskers

As a single-crystal and fibrous material, calcium carbonate whiskers possess the excellent properties such as structural integrity, high strength, thermal stability and lower price, and they have been become a new kind of polymeric additive. When calcium carbonate whiskers are filled in polymer material, they can improve the strength and toughness of the matrix. Meanwhile, they can reduce the costs of the composites. In this article, the sodium stearate was used to treat the surface of calcium carbonate whiskers and the influence factors, such as surfactant dosages, treated temperature and time, were investigated. Then, the composites were prepared by blending polypropylene and the treated calcium carbonate whiskers with three methods of melt-moulding, extrusion-moulding and extrusion-molding. The influences of calcium carbonate whiskers in composites were evaluated by differential scanning calorimetry, thermo-gravimetric analysis, X-ray diffraction, mechanical performance, scanning electron microscope and so on.The results indicated that sodium stearate has well effect on surface modification of calcium carbonate whiskers. The optimal treatment conditions was following:the content of the coupling agent was 4.5%, the treatment time was 50min and the treatment temperature was 40℃. Three processing methods all showed that the structure of the polypropylene filled with calcium carbonate whiskers were a-crystal form and the crystallization temperature all moved to the low temperature. The thermal stability of the composites make better than the unfilled polypropylene.Tensile fracture mode of the composites prepared through melt-moulding processing converted from brittle fracture to ductile fracture and the bend experiment showed ductile fracture. Compared with the pure polypropylene, tensile strength of the composites decreased a little, but the elongation at break increased. As the weight percent of the whiskers was within the range from 5% to 10%, the bending stress almost increased 11.5%. When the content of the whiskers was 5%, bending strain at break increased by 173%.Tensile fracture modes of the composites prepared through extrusion-moulding method were ductile fracture at 5% whisker content and brittle fracture at 15% whisker content. Furthermore, the bend style exhibited ductile fracture.When the whisker volume was 5%, tensile stress increased the maximum as 18.2MPa and the elongation at break was the maximum as 9.24%. Calcium carbonate whiskers played a role of the toughening and reinforcing, especially the toughening. When the weight percent of the whiskers was 5%, bending stress increased by 23.4%. As the weight percent of the whiskers was within the range from 5% to 10%, the bending strain at break increased about 59%.Compared with two other methods described above, tensile model of the composites prepared through extrusion-molding method showed having a yield point. The yield stress decreased a little and the tensile fracture stress increased by 32.1%. Moreover, the bending stress increased obviously and the maximum was 39.5MPa as the content of the whiskers was 15%. Viewed the tensile section by scanning electron microscopy, calcium carbonate whiskers acted the toughening and reinforcing functions.