| Continuous fiber reinforced thermoplastic composites(CFRTP)have many advantages,such as light weight,high strength,corrosion resistance,good impact resistance,weldability,green environmental protection and recyclability.It has been widely used in automotive industry,aerospace,bridge construction,wind power and other fields,and has increasingly become a research hotspot of resin-based composites.At present,the main method of industrialized production of CFRTP is melt impregnation,but the thermoplastic polymer has a high melt viscosity(100-10000 Pa S),which makes it difficult to fully penetrate the high content reinforced fibers with thick-scale to prepare high performance CFRTP products with large-scale and complex structure.In this study,based on the anionic polymerization of monomer of polyamide-6(PA-6),the PA-6 material system was innovatively applied to the pultrusion process.Complete impregnation of high content reinforced fibers has been achieved with ultra-low viscosity monomers(caprolactam).CFRTP sheets with excellent mechanical properties were successfully manufactured based on the self-built experimental platform of reactive injection pultrusion.At the same time,the impregnation model and heat transfer-reaction coupling model in pultrusion process were systematically studied and the related process parameters were optimized.The thermal properties,mechanical properties and microstructures of pultruded composites under different processing parameters were analyzed,and the relationship between processing parameters and properties of composites was revealed.The main research works are as follows:1.By analyzing the mechanism of anionic polymerization of caprolactam,various factors affecting the polymerization were summarized,and the effects of the content of activator and initiator on the reaction rate and the properties of anionic polymerization PA-6(APA-6)were investigated.On this basis,the PA-6 raw material system suitable for pultrusion process was optimized,and the molecular weight distribution and physical properties of APA-6 and extrusion grade PA-6 were compared.The feasibility of APA-6 as matrix of thermoplastic composites was determined.2.According to the characteristics of anionic polymerization of caprolactam,a resin injection moulding device with functions of on-line mixing of two components,vacuum dewatering and nitrogen protection was designed and developed.A new type of double-convergence conical impregnation die was designed to meet the impregnation requirements of fiber bundles.CFRPT sheets with high fibre content(70wt%)and high performance were successfully prepared using the self-built experimental platform.The flexural strength and modulus are as high as 1061 MPa and 38 GPa respectively,and the interlaminar shear strength is as high as 71.5 MPa.3.Based on Darcy's law,the impregnation model of pultrusion process was established by using finite volume method,and the multiphase flow of moving porous media in the model was solved by ANSYS CFX software.The effects of pultrusion speed and injection pressure on impregnation time and resin back-flow distance were analyzed theoretically.4.Based on the theory of heat transfer and resin reaction kinetics,a two-dimensional heat transfer-reaction coupling model of pultrusion process was established.The effects of die temperature,pultrusion speed and fiber content on the temperature and monomer conversion of the composites were analyzed.5.The effects of die temperature and fiber content on thermal properties,mechanical properties and microstructures of composites during pultrusion were investigated,and the relationship between process parameters and properties of composites was revealed. |
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