Structure And Properties Of Micro-Injection Molded Products Based On Polypropylene/Polyethylene Terephthalate Microfibrillar Composites

As one of the general-purpose resins with the smallest density,polypropylene(PP)is widely used in various fields of national economy and social development due to its advantages of abundant sources,low price,easy processing and good comprehensive performance.With the development of the industry and the advancement of technology,general-purpose PP has been unable to meet the requirements of lightweight,highperformance,and functional plastic products.The engineering modification of PP has become the focus of domestic and foreign academic and industry attention.The chemical modification effect by means of copolymerization and crosslinking is remarkable,but the cost is high and the process is complicated;the modification process of melt blending and the third phase filler is simple,but the modification process is greatly affected by the phase morphology of the blend and the dispersion of the filler.The modification effect is unstable.Micro-injection molding has been more and more widely used in various industries due to its advantages of high efficiency and high precision.Academics and industries have gradually carried out research on the microinjection molding process of composite materials.The existence of micro-scale effects makes micro-injection products internal There is a special "skin-core" structure different from conventional injection molding,which directly affects the dimensional stability and mechanical properties of micro-injected products.In view of the above technical problems,this paper introduces the PP modified composite material into the micro-injection molding process.Based on the control of the viscosity ratio,components and interfacial compatibility in the PP/PET composite material system on the microfibrillation process of the PET dispersed phase,the PP modified phase is discussed.The reinforcement mechanism of the fiber network in the matrix reveals the intrinsic relationship between the microstructure and mechanical properties of PP/PET microinjection products under the influence of PET microfibrillation.Relevant research will help to broaden the material range of microinjection molding products,and provide a new idea for improving the mechanical properties of micro-injection molding products.The specific research contents are summarized as follows:1.Preparation and properties of PP/PET microfibrillated compositesBased on the "melt blending-hot drawing" one-step process,PP/PET microfibrillated composites with fiber diameters of 280-460 nm were successfully prepared continuously by adjusting the viscosity ratio,components and external drawing conditions.The study found that the PET microfibers were entangled with each other in the PP matrix to form a three-dimensional network and were uniformly dispersed.The isothermal crystallization study found that the PET microfibers could provide PP with more nucleation points and increase the crystallization rate by 25 times;viscoelasticity tests confirmed the three-dimensional network.The existence of the structure significantly improves the viscoelasticity of PP and hinders the relaxation of molecular chains;compared with pure PP,the tensile yield strength of microfibrillated PP/PET composite products can be increased by 28%,and PET microfibers can effectively transmit tensile stress.2.The effect of interfacial interaction on the PET microfibrillation processThe compatibilizer PP-g-MAH was introduced into PP/PET blends to control the phase interface,and PP/PET/PP-g-MAH ternary microfibrillated composites.The study found that the introduction of compatibilizers on the one hand enhanced the interfacial bonding force through the transesterification reaction and improved the compatibility of the system,on the other hand,it also hindered the deformation and orientation of the PET microfibers along the stretching direction.In the composition with a ratio of 90:10:2,the tensile strength is increased by 16.3%compared with pure PP,and the toughness is also increased by more than 10%.3.Study on the relationship between the structure and mechanical properties of PP/PET/PP-g-MAH microfiber composites micro-injection productsMicro-injection molding was performed on microfibrillated composite materials with different components.Compared with pure PP micro-injection products,the polarization infrared test results after ultra-thin slices found that the existence of PET fiber network structure in the composite material makes the micro-injection products"skin-core" structure.Taken from the homogenization,that is,the thickness ratio of the skin layer and the degree of orientation are significantly reduced,and the degree of molecular chain orientation of the core layer is significantly improved.Further research by nanoindentation test found that the hardness and modulus of the core layer of the insitu microfibrillated composite micro-injection product were slightly higher than that of the skin layer.The macroscopic mechanical tensile test found that compared with pure PP,the microfiber composite micro-injection product with a composition of 90:10:1 increased the yield strength by nearly 30%,and the fracture toughness increased by 23%.