Study On In-Situ Reaction Molding Technology And Biphasic Interface Evolution Of Single Polymer Composites

Single polymer composite(SPC)is a novel material with high strength,high modulus and good recyclability.It has a wide application prospect in the automotive industry.However,the traditional thermoforming methods have technical bottlenecks such as narrow temperature window,difficult to infiltrate high proportion fibers,low degree of interface molecular chain entanglement,which are difficult to meet the manufacturing requirements of large parts with complex shape in the automotive field.Therefore,this paper proposes a new method of in-situ reaction molding to prepare SPC.In this method,polymer fibers are wound on a frame and placed in the mold,the same polymer monomer is injected into the mold cavity and initiated to polymerization,to obtain SPC with homogeneous two-phase structure.Compared with the traditional thermoforming method,this forming method has the outstanding advantages of wide temperature window and easy infiltration.It is especially suitable for producing products with large size and high reinforcement proportion.In the process of in-situ reaction molding,the fiber will dissolve from the surface to the core when immersed in the liquid monomer,and a special transition structure will be formed on the interface.In this process,the physical dissolution of fibers and the chemical polymerization of monomers affect each other and form a strong coupling relationship,resulting in the nonlinear evolution characteristics of molecular polymerization,de-orientation and crystallization at the two-phase interface in time and space,which has become a key scientific problem that determine the mechanical properties of SPC.Therefore,this study will focus on the interface evolution of SPC,and reveal the influence law of physical dissolution,chemical polymerization and their coupling on the micro interface structure of SPC.This study will establishe the structure-performance relationship between process parameters,microstructure and macro properties,and obtain the process control strategy of in-situ reaction molding in SPC’s preparation.This study will open up a new way for the lowcost and efficient preparation of SPC.Following results are get in this study:(1)The in-situ reaction molding method and device of SPC are innovatively developed.The evolution law of two-phase interface formed by fiber dissolution is revealed.The coupling relationship between fiber dissolution and monomer polymerization process and their influence on the macro mechanical properties of SPC are clarified;The process control strategy based on "dissolution window" is innovatively proposed,which provides a theoretical basis for effectively reinforcing SPC.Based on the above control strategy,the dissolution damage of reinforcing fibers is reduced by increasing the dosage of additives and shortening the polymerization time.Nylon based SPC with significant reinforcing effect is prepared.The tensile strength is improved by 42.4% at low fiber content(15%).(2)The influence of molding temperature on the evolution process of two-phase interface and macro mechanical properties of SPC is revealed.The way to determine the range of process window under the synergistic effect of additive dose and molding temperature is expounded.The results show that increasing the molding temperature can promote the dissolution of the interface.Excessive dissolution of fibers under high temperature and poor interface bonding under low temperature are the reasons for the deterioration of SPC performance.Therefore,there is an optimal molding temperature to optimize the mechanical properties of SPC.Increasing the dosage of additives can reduce the fiber dissolution at high temperature and improve the monomer conversion at low temperature,which will expand the molding temperature range to effectively reinforcing SPC.(3)The effects of the fiber type and proportion on the two-phasic interface and macro properties of SPC are clarified,SPC with 50% fiber proportion is prepared,which has a tensile strength of 154.49 mpa,and the tensile strength is 116.3% higher than that of virgin PA6.It is found that increasing the proportion of reinforcing fiber will introduce more inhibitor,slow down the polymerization rate of monomer and intensify the dissolution of fibers.These two effects promote each other,resulting in the serious de-orientation of molecular chains at the interface and the formation of oligomers with plasticizing effect,which will significantly reduce the reinforcing effect of SPC.By selecting PA66 fibers that are not easily dissolved in monomers as the reinforcement,the dissolution under high fiber proportion can be reduced.The inhibitor in the fiber core is prevented from seeping with the dissolution,so that the monomer reaches higher conversion.Therefore,the reinforcing effect of SPC is improved.(4)It is proposed to restrict the fiber to slow down the interfacial dissolution rate,so as to reduce the coupling effect of fiber dissolution and monomer polymerization.A programmable fiber winding device with constant preload is developed,and the effects of winding preload and winding structure on the two-phase interface and macro properties of SPC are explored.The results show that the restraint of fiber can reduce the interfacial dissolution,inhibit the formation of oligomers and improve the reinforcing efficiency of products.Further,by using the small angle staggered winding mode,the problem of difficult infiltration in the unidirectional winding mode at high preload is solved.By adopting the above fiber constraint optimization measures,the "dissolution window" of molding is expanded and the mechanical properties of SPC are improved.(5)Based on the principle of in-situ reaction molding,the structural reaction injection molding of polyurethane based SPC and the photopolymerization injection molding of polymethylmethacrylate(PMMA)based SPC were proposed.The reaction injection molding equipment suitable for the above molding process was developed,and SPC with significant reinforcing effect was prepared.The interface evolution law in the forming process of the two kinds of SPC is revealed.The results show that polyurethane fiber cannot be significantly dissolved at the interface,and the interface bonding mainly depends on the fullness of infiltration.By optimizing the injection speed parameters,the interface can be more fully infiltrated,and the reinforcing effect of SPC is improved;PMMA fiber can be significant dissolved at the interface.By increasing the initial viscosity of monomer and increasing the irradiation energy of photopolymerization,the polymerization rate is accelerated,the dissolution damage of reinforcing fiber is reduced,and the reinforcing effect of SPC is significantly improved.