Toughening And Strengthening Mechanism Of Thermoplastic Matrix Polyphenylene Sulfide(PPS) And Its Aviation Composites And Their Crystalline Structural Evolution

Owing to the highstrength and modulus,thermal stability and precise moldability, polyphenylene sulfide(PPS) is widely applied as high-performance engineering plastics used in the aviation composite matrix. But strength of thermoplastic carbon fiber composite material represented by PPS base, which need to be further improved to replace thermosetting materials for large-scale use in aviation field, is relatively lower than thermosetting carbon fiber composite material. The weakness of fiber reinforced resin matrix composites mechanical lies in the interface and the matrix. This paper used the regulation of PPS crystallization structure to realize the PPS matrix strengthening and toughening. Eventually we establish a high strength molding method of PPS/CF composites. The main research results are as follows.This paper used PIF moulding to do the strengthening and toughening modification of the resin matrix. The effect of molding process parameters such as temperature, pressure etc. were investigated. We found that PIF processing could markedly increase the material performance of PPS. The tensile strength and impact strength respectively markedly increased from 85.17 MPa to 186.42 MPa and 37.93kJ/m2 to 81.29kJ/m2 under the following laboratory conditions: molding temperature is 210?, the molding pressure is 615 MPa, the compression ratio is 3.0. We also use SEM, DSC SAXS and WAXD and other detection means to analyze microstructure and crystal structure. We found that the lamellae of PPS is broken, orientation and ordered arrangement under the stress and shear field during the PIF forming process. These crystalline fragments remain the long periods of original lamellae, and the fold chains of them exhibit a preferred orientation along the flow direction, but it keeps the original crystallinity and melting point. In the PIF molding PPS, the weak interfaces between crystalline area and amorphous area are along the direction of FD orientation, which leading silver lines and holes along the direction of FD extensions appear in fracture surface. Fracture surface is increased, presentsing ductile fracture microstructure. This is the major reason of PPS material increased toughness and strength.In order to apply PIF forming to PPS matrix composites and avoid interfacial failure of CF-PPS, breaking off of CF or issues such as, we improved PIF molding process to make plastic deformation occurs during the crystallization——Cooling PIF(CPIF) molding. The results showed that this method could also increase the mechanical properties of materials. The comprehensive mechanics performance of the material to achieve high value under the following laboratory conditions: cooling rate is 42.14?/min, molding temperature is 150?, the molding pressure is 320 MPa, the compression ratio is 1.69. The tensile strength and impact strength respectively markedly increased to 120.36 MPa and 40.21kJ/m2, increasing by 40% and 10% respectively compared with raw materials. When molding temperature is 270?, the tensile strength and impact strength respectively increased by 15% and 33% comparing with raw materials. Increasing cooling rate properly can make the PPS form smaller crystalline grains. After CPIF molding, c axis of lamellae oriented along the FD orientation and formed multistage weak interface, The two points make the material have higher strength. Smaller crystalline grains forming by CPIF molding is harder to deformation along the FD orientation comparing with the crystalline grains forming by PIF. That is why the improvement of comprehensive mechanical properties forming by CPIF is not high as PIF forming. For all this, strength and toughness properties have significantly developed comparing with raw materials.At the same time this paper also explored the possibility of applying the PIF forming in the CF and CFF reinforced composites. SEM observations showed that the interfaces adhesion between CFs and PPS is still strong and the matrix is full of silver lines and holes, presentsing ductile fracture microstructure. This brought to a great increase of both strength and toughness to about 2 folds,when the composites were processed at 240? and under 263 MPa. Results in DSC and XRD measurements indicated more orderly layered stack microstructure and c axis of PPS lamellae paralleled to the orientation of FD. PIF-processing. The tensile strength and impact strength of PPS/CFF increased by 8.1% and 14% respectively and bending strength and the interlaminar shear strength have no significant decline. It was observed from metallographic microscope that the interfaces adhesion between CFF and PPS were still stronger and porosity did not increased.