PVT Property Of Carbon Fiber Filled Polymer And Its Application In Controling The Accuracy Of Products

PVT property is one of the inherent properties of the polymer, which is also a principal part of simulation analysis and experimental research of the injection molding. The addition of carbon fiber will have different effects on the PVT properties and then affect the accuracy of the injection products. In order to probe into the effect of carbon fiber on the PVT properties and the accuracy of injection products, the PVT properties of the carbon fiber filled polypropylene and polycarbonate had been studied respectively. Based on the PVT data, the PVT state equation was established. The effect of carbon fiber and PVT properties on the precision of products was studied through the simulation analysis and the actual injection, which provided a theoretical basis for controlling the precision of injection molding products of carbon fiber filled polymer. The main work and conclusions are as follows:1?A PVT test device was designed based on the principle of piston-cylinder dilatometer, and an annular sample was used as test sample. Compared with the conventional apparatus, this device can reduce the radial temperature gradients of the sample during cooling because of its ability to rapidly cool both sides of the annular sample simultaneously, and apply shear on the sample as well. The coupling interaction of cooling and shear can make the testing process similar to the real injection, and the PVT properties obtained under the condition close to that of injection molding.2?The PVT properties of different carbon fiber filled polypropylene and polycarbonate were studied. The results showed that the specific volume of isobaric gradient of carbon fiber filled polypropylene was higher than that of pure one, but the polycarbonate was on the contrary. Since partial volume of the polycarbonate was occupied by carbon fiber that has a smaller specific volume, the specific volume of carbon fiber filled polycarbonate was lower than that of the pure one consequently. Carbon fiber raised the crystallization temperature of polypropylene to some extent, because carbon fiber played a role of heterogeneous nucleation. Since the carbon fiber inhibited the development and diffusion of homogeneous nucleation of polypropylene, the range of crystallization temperature became narrow, resulting in the specific volume variation of crystallization decreased.3? Based on the PVT data, the Tait equation was established to describe the PVT properties of the composites. Volume shrinkage and warping of injection molded products for four kinds of materials were studied respectively via simulation analysis and actual injection, and the role of PVT properties played in this process was researched subsequently. The results showed that the spring-back of polymer made the volume shrinkage of warping less than that of packing, and the former was more close to the actual shrinkage. The decrease of volume shrinkage of carbon fiber filled polypropylene was five times that of carbon fiber filled polycarbonate, which demonstrated the more obvious effect of carbon fiber on the inhibition of contraction of crystalline polymer. The reason of the appearance above is that the carbon fiber could influence the crystallization process of polypropylene, making the specific volume variation of crystallization decrease. The shrinkage in the flow direction of carbon fiber filled polypropylene products and carbon fiber filled polycarbonate were less than that of vertical flow direction, and the shrinkage in two directions of their pure polymer products were almost the same. The reason is that the carbon fiber orients in the flow direction and restrict the stress relaxation of the polymer chain in this corresponding direction.