Research On The Preparation And Microcellular Injection Molding Process Of Basalt Fiber Reinforced Polypropylene Composites

Polypropylene(PP)is widely used in industrial fields due to its light weight,low cost,nontoxic,tasteless and easy recovery.However,PP has poor impact resistance and low melt strength,which is often solved by blending modification.Basalt fiber(BF),as a new natural and environment-friendly material with excellent mechanical properties,biocompatibility and high cost performance,is regarded as a good alternative to glass fiber and carbon fiber.In recent years,BF has gained widespread attention in reinforced polymer applications.Microcellular plastic parts can be fabricated by microcellular foam injection molding technology with complex shapes,light weight and high specific strength.This promising technology can endow products with special properties such as sound insulation,heat insulation and vibration damping.However,the current research on BF/PP composites lags behind the engineering applications,some systematic researches are conducted urgently.The effects of BF on the mechanical and physical properties of PP.the interfacial strengthening mechanism between BF and PP and the foaming properties of BF/PP composites should be further investigated.In this paper,BF/PP composites were firstly prepared suceessfully,and the effects of fiber content on mechanical properties,heat resistance and thermomechanical properties of BF/PP composites were quantitatively analyzed.The improvement effect of the Polypropylene grafted with maleic anhydride(PP-g-MAH)on the interfacial bond strength between BF and PP matrix was also investigated.based on the aboved investigation,the effects of fiber content.compatibilizers and process parameters on the cell structure of the composites were systematically studied.Lightweight composite foams with uniform and dense cell structure was successfully prepared finally with excellent impact resistance and thermal insulation properties.The main work is as follows:The effects of BF content on the mechanical properties,heat deflection temperature crystallization and rheological behavior of BF/PP composites were investigated.The heat deflection temperature,tensile strength and flexural strength of the composites were improved with the increase of BF content.Comparing to pure PP,the heat deflection temperature of 30 wt%BF/PP composites exhibits a significant augment of 85%.from 62.2℃ to 115.1℃.The tensile and flexural strengths of the composites were increased by 33.6%and 64.2%,respectively.The highest impact strength of composites was reached with 20 wt%fiber content,which was improved by 27.8%compared to PP.Meanwhile,the crystallinity of the PP matrix and the viscoelastic properties of the melt were improved with the introduce of BF.Based on the 20 wt%BF/PP composite system,the effect of PP-g-MAH on the enhancement of the interfacial bonding properties between BF and PP matrix was investigated.The results demonstrated that the polar groups reacted with the hydroxyl groups on the surface of BF,which significantly improved the interfacial bonding strength between the fibers and the matrix.The addition of 3 wt%PP-g-MAH endows the composites with the best overall mechanical properties.Its tensile strength,flexural strength and impact strength increased by 24.7%,46.9%and 77.5%,respectively,compared to the 20 wt%BF/PP composites.Moreover,the crystalline properties,composite viscosity,thermal stability and heat resistance of the composites were also enhanced.The effects of different process parameters on the cell structure of 20 wt%BF/PP composites using Core-back foam injection molding were investigated.The results showed that the increasing N2 concentration could improve the cell density and refine the cell size.the augment mold temperature leads to larger cell size and lower cell density as well as uniformity,but it is beneficial to increase the expansion ratio and reduce the skin thickness.The packing pressure has less influence on the cell structure,but excessive packing pressure will cause the merge,collapse and aggregation of bubble,hence forming large-sized cells.The packing time has the greatest influence on the cell structure.By increasing the packing time,the cell size decreases continuously while the cell density and skin thickness increase significantly.Too short packing time leads to large and unevenly distributed cells,while too long packing time severely restricts the growth of cells,hence the foaming is not sufficient.Lightweight BF/PP composite foams with uniform and dense cells,good impact resistance and thermal insulation properties were prepared by regulating the mold opening distance and fiber content.The results showed that the expansion ratio of the composite foam constantly improved with the increase of mold opening distance,and the thermal conductivity gradually decreased from 252.2 to 144.7 mW/mK.indicating a significant improvement in thermal insulation performance.The uniform and dense cell structure as well as the fiber skeleton contribute to maintain the stability of the material specific strength,which leads to the remarkable improvement of the flexural modulus and impact strength of composite foams.At the weight reduction ratio of up to 50%,the flexural modulus and impact strength of the composite foam can still maintain more than 90%of the unfoamed PP samples.