Study On The Impregnation Mechanism And Technology Of Long Fiber Reinforced Polypropylene Composites

China is the main country for automobile production and sale.A large number of automobile consumption has brought about serious problems such as energy consumption and environmental pollution.The lightweight of automobile has become one of the major ways to fix this problem.Thermoplastic resin matrix composites are characterized by recyclability,environmental friendliness,high strength,and low density,which have been important ways for automotive lightweighting.The process of melt impregnation is the main selection for the production of continuous fiber-reinforced thermoplastic composites due to its simple process and ease of industrialization.In this study,the melt impregnation die was designed,and the melt impregnation production line of continuous fiber reinforced thermoplastic composite was independently built up.Through the research on the impregnation and fiber fracture mechanism during the melt impregnation process,the relationships among structural parameters,process parameters and physical properties parameters of the impregnation die were established together with the degree of impregnation equation and the probability distribution equation of the fiber bundle breakage.The parameters of melt impregnation die were optimized using the impregnation degree equation and the fiber bundle fracture probability distribution equation.Experimental research was also conducted on the melt impregnation process parameters and the fiber bundle spreading process.A new method of fiber bundle spreading was used to study the effects of different fiber distribution methods on the mechanical properties of continuous fiber-reinforced polypropylene(GF/PP)composite prepreg.Firstly,the permeability of unidirectional glass fiber bundles impregnated with high-viscosity resin was measured via the experiments with the conditions of different fiber volume fractions.Then,the unidirectional glass fiber permeability expression was fitted using matlab software according to the experimental results.Based on the lubrication approximation principle and Darcy's law,the prepreg impregnation level expressions including the structural parameters of the impregnation die,the physical properties parameters,the fiber bundle structural parameters,and the process parameters were proposed.From the point of view of mechanical balance,the force of the fiber bundle during the melt impregnation process was analyzed.According to the traction force of the fiber bundle and the Weibull probability distribution function,the facture probability distribution function of the fiber containing the structural parameters,process parameters,physical properties and other parameters of the impregnation die were established.The effect of process parameters,physical parameters and structure parameters on the impregnation degree of prepreg and the probability distribution of fiber bundle fracture was analyzed theoretically.Secondly,according to the proposed impregnation degree equation and fiber bundle fracture probability distribution equation,‘Design Expert' software was used to optimize the structural parameters of the impregnation mold.In the meantime,a melt impregnation process line of continuous fiber-reinforced thermoplastic composite was set up,and the melt impregnation die was designed as well.The experiments were conducted to investigate the impregnation die and the results were in good agreement with the optimization results.Next,experimental studies were conducted on the fiber bundle inlet tension and traction speed in the melt impregnation process parameters.The effect of the inlet tension on the mechanical properties of continuous glass-fiber-reinforced polypropylene(GF/PP)composites was investigated through an independent fiber bundle inlet tension collection system.The experimental results showed that under the current process conditions,the fiber bundle inlet tension increases.The best mechanical properties of GF/PP prepreg were achieved at 15N and cladding angle of 622°.The traction speed determines the production efficiency and product quality.Under the current process conditions,the lower the traction speed,the better the mechanical properties of the prepreg.However,the efficiency will be reduced.Therefore,under the premise of meeting the quality requirement,the traction speed should be increased as much as possible to increase the practical production efficiency.Finally,the high-voltage electrostatic field defibrillator and airflow-roller spreading were designed.The effects of the two methods on the mechanical properties of continuous glass fiber-reinforced polypropylene(GF/PP)composite prepreg were investigated.Using the principle of the electrostatic field force of the polar material in the high voltage electrostatic field,a high-voltage electrostatic separator device was designed,which effectively improved the uniformity of the fiber bundle and reduced the damage of the fiber to the fiber.Experiments showed that under the current process conditions,the mechanical properties of GF/PP composite prepreg are optimal when the distance between upper and lower plates is 20cm and the high voltage electrostatic field voltage is 30kV.An airflow-roller combined spreading device was designed.Through opening the air-slot,the air-flow spreading is introduced,which reduces the mechanical friction force between the glass fiber bundle and the roller surface and the damage of the glass fiber tow,and makes the spreading of the glass fiber bundle more uniform.Experiments showed that under the current process conditions,the GF/PP composite prepreg has the optimal performance when the gas flow rate is 4.5m3/h and the airflow pressure is 0.2MPa.