Study On Process Control And Properties Of Polypropylene Composites By Microcellular Injection Molding

Polypropylene(PP)foams are widely used because of comprehensive performance.But melt strength of PP is poor,and cells are easy to merge or collapse,so the cell structure is not good.At the same time,the traditional processing methods of PP foams also have some disadvantage such as complicated process control,heavy pollution,high equipment investment and high energy consumption.Mechanical blending is believed to be a simple and economical method to improve the properties of PP foams.And producing microcellular products without any modification to conventional injection machine has the advantage of low equipment investment cost.According to the difference of the compatibility between the additive materials and PP,Ethylene Vinyl Acetate(EVA),High Density Polyethylene(HDPE),Acrylonitrile Butadiene Styrene(ABS)and Polycarbonate(PC)were selected to be blended with PP.And different PP composites and foams are fabricated by injection molding with a chemical foaming agent after adjusting injection parameters.The impact of different materials on properties of PP composites was explored after a series of tests.At last,talcum powder and glass fiber were added to prepare PP composites and foams,and the influence of two inorganic materials on cell structure of PP composites was explored.PP was blended with EVA,HDPE,ABS,PC,talcum powder and glass fiber with different mass ratios,and the injection molding parameters were adjusted to prepare different PP composites in a traditional injection machine,and corresponding PP foam composites were prepared by adding appropriate amounts self-made foaming agent.Tensile test of PP composite standard molding injection bars was performed using an electronic universal testing machine to obtain the mechanical properties of different PP composites.Differential scanning calorimetry(DSC)and dynamic thermomechanical analyzer(DMA)were used to characterize the crystallinity and heat resistance of different PP composites.Different PP composites' processing torque was tested with a torque rheometer.At last,microscopic morphology and microcellular structure of composites were observed by scanning electron microscopy(SEM)after being soaked in liquid nitrogen and quenched.With the addition of EVA,tensile strength and Young's modulus of PP/EVA composites decreased,but composites showed excellent ductility;the crystallization ability of PP decreased,and all of melting temperature,crystallization temperature and crystallinity decreased;the balance torque of PP blend system increased,and the melt strength of PP increased;when the mass ratio of EVA and PP was 50/50,the compatibility between the two phases was the best,corresponding foamed composite had the best cell structure with the smallest cell size and the highest cell density.However,EVA's improvement in foaming performance of PP is limited compared with neat PP foam.HDPE's addition reduced composites' tensile strength and Young's modulus.The strain was as high as 530% when PP/HDPE=25/75,which was extremely good.The crystallization behavior of PP phase was restricted,and parameters such as melting temperature,crystallization temperature and crystallinity decreased to varying degrees.The melt strength of system increased significantly.When PP/HDPE was 25/75,the compatibility between PP and HDPE and the foaming performance were best,and cell density was improved to nearly 40 times comparing to neat PP foam.After ABS was added,tensile strength and Young's modulus of PP/ABS composites increased,but the elongation at break decreased sharply;the crystallization ability of PP decreases,and rystallization temperature,initial crystallization temperature and crystallinity decreased to varying degrees;the crystallization performance of PP was greatly improved with the addition of compatibilizer.The compatibility between ABS and PP is bad,ABS was distributed in a spherical shape in PP matrix and provided extra cell attachment points.The foaming performance of composites was significantly better than that of PP.The size of the dispersed phase was reduced after adding compatibilizer,and the cell structure of the corresponding foamed material was further improved.Tensile strength and Young's modulus of PP/PC composites increased with PC's addition,and the ductility was at a lower level.PP's melting temperature,crystallization temperature and initial crystallization temperature decreased deeply.The compatibility between PP and PC is very poor,so phase separation was obvious and large PC aggregates can be observed clearly;the foamed composites had better cell structure compared with PP foam.After adding the compatibilizer,foaming performance of PP/PC was improved.The introduction of talc powder greatly improved the rigidity of PP composites,and Young's modulus of increased significantly.Talc powder was uniformly dispersed in the polymer matrix and a large number of nucleation sites were promoted to promote PP heterogeneous nucleation.PP's melting temperature,crystallization temperature and initial crystallization temperature were greatly increased;the foaming performance of the PP foams was also significantly increased,the cell size was reduced to about 50 ?m,and the cell density is more than 35 times higher than that of the PP.However,too much talcum powder tended to agglomerate and caused the foaming performance to decline;adding appropriate amount of LDPE can increase the strength of melt and reduce the content of talcum powder.When the ratio of MPP:PP:LDPE=2:1:1,the micropore size and cell density were the best.Glass fiber(GF)with an original length of 12 mm was added to PP for blending,and the optimal processing conditions were determined by orthogonal test;the optimal PP/GF composite and foamed materials were tested,and the tensile strength and residual fiber length were positively correlatedt,injection foam molding was conducive to reduce the fracture of glass fiber in composites,mechanical strength was better than solid parts,while the addition of glass fiber also improved the foaming performance of PP composites.In this paper,different PP composites and foams were prepared.The influence of different compatible polymers and inorganic fillers on both mechanical properties and foaming performance of PP was analyzed,and it was confirmed that preparation of PP foamed composites with good cell structure by chemical foaming and injection molding is feasible.This paper provides theoretical and practical guidance and reference for improving PP melt strength and improving PP foaming performance.And the research in this paper is also of great significance to promote the understanding of the relationship between material components,processing technology,microporous structure and mechanical properties of PP microcellular materials under different conditions.