Morphology And Mechanical Properties Of Overflow Water-Assisted Co-Injection Molding Glass Fiber Reinforced Polypropylene

Glass Fiber Reinforced Polypropylene(GFRPP)is a kind of polymer composite material,which is made by adding a certain content of glass fiber and other additives on the basis of pure polypropylene material.The addition of glass fiber can improve the mechanical properties of the product,reduce the cost of material and expand the adaptability of material.Water-Assisted Co-Injection Molding(WACIM)is a new type of injection molding that combines Co-Injection Molding(COIM)and Water-Assisted Injection Molding(WAIM),the technology can be used to produce multi-layer structure hollow products.In this paper,the pure polypropylene is used as the inner layer of the product,and GFRPP is used as the outer layer of the product.The Overflow Water-Assisted Co-Injection Molding(WACIM-O)process is used as the research object,the effect and mechanism of the residual wall thickness(RWT)distribution,microscopic morphology,and mechanical properties were studied.At the same time,through the existing simulation results,the flow field distribution during the filling process is used to reveal the evolution result of the glass fiber orientation in the outer melt.Through the combination of experimental and simulation results,the application of glass fiber reinforced polypropylene can be promoted effectively in WACIM,which is a complex and has a good development prospect process.The main research contents and conclusions of this paper are as follows:(1)The process principles and processes of WAIM,COIM,and WACIM are described,and the research situation at home and abroad is briefly described.The research of glass fiber reinforced composites and its application in injection molding process are briefly introduced,and the research direction of this paper is determined.(2)The WACIM-O experiment platform was built,and the related equipment and materials were prepared.The influence of process parameters on the RWT of pipes was studied by single-factor experiment.The results show that the total RWT decreases with the increase of outer melt temperature,which is mainly contributed by the decrease of outer layer RWT.With increase of the water injection delay time and internal and external melt switching time,the inner and outer layer RWT show an increasing trend.With the increase of the mold temperature,the inner and outer layer RWT show a decreasing trend.When the injection pressure of inner melt is 8MPa,the total RWT is at the minimum,which is mainly contributed by the variation trend of the inner layer RWT.The water injection pressure has no obvious influence on the inner and outer layer RWT.The orthogonal experiment of six process parameters was carried out,and the RWT of pipes was optimized by using the range of each factor.The proportion of influence degree of process parameters to the each RWT is obtained.Finally,the parameter combination for obtaining the optimal RWT of pipes is determined.(3)The effect of glass fiber content on the RWT and microstructure of WACIM-O pipes with GFRPP as outer layer and PP as inner layer was investigated.It is found that when the glass fiber content is 10%-30%,the inner and outer layer RWT fluctuates in a small range,and the total RWT has no obvious change.When the glass fiber content is 30%-40%,all the RWT show an increasing trend.Microscopic observation of sample wall thickness layers with different glass fiber contents shows that there are differences in the orientation of glass fibers between the near module wall layer,the lateral middle layer and the lateral near-interface layer of the samples.When the glass fiber content is the same,the orientation degree of the glass fiber along the flow direction gradually increases from near module wall layer to the lateral near-interface layer.When the glass fiber content gradually increases,the degree of mutual interference between the glass fibers increases,making it easier to break,and randomly distributed short glass fibers were produced,making the glass fibers have a lower degree of orientation at the same module wall layer.According to the existing simulation results,the formation reason of glass fiber orientation is analyzed by using the flow field distribution characteristics during WACIM-O filling process,revealing its internal mechanism and confirming the microscopic observation results.(4)The effect of process parameters on the tensile strength of pipes was investigated through tensile testing.It was found that with the outer melt temperature increased,the tensile strength of GFRPP WACIM-O pipes gradually decreased.With the water injection delay time and the internal and external melt switching time increased,the tensile strength increased first and then decreased.While the mold temperature and water injection pressure increase,the tensile strength decreased first and then increased.The injection pressure of inner melt has an irregular influence on the tensile strength.When the pipes of the orthogonal experiment method were stretched,it is found that the sample No.10 has the highest tensile strength and the sample No.7 has the lowest tensile strength.Then the range of tensile strength of each group pipes was compared,it is found that the influence degree of each factor on the tensile strength is from strong to weak: outer melt temperature>water injection delay time>water injection pressure>internal and external melt switching time> injection pressure of inner melt >mold temperature.The final combination of process parameters to obtain the maximum tensile strength is: outer melt temperature is 220°C,water injection delay time is 8s,injection pressure of inner melt is 9MPa,mold temperature is 40°C,water injection pressure is 8MPa,internal and external melt switching time is 7s.The tensile strength of the pipes with glass fiber content of 10%,20%,30%,and 40% is analyzed.The results show that when the glass fiber content is within 30%,the tensile strength increased with the increase of the glass fiber content.When the glass fiber content exceeds 30%,the tensile strength will be reduced.