The Synthesis And Application Study Of Crystalline Resin Used In SMC

Low pressure sheet molding compound (LPSMC) is a new-style molding technique of fiber reinforced polyester compounds. Being distinguishable from traditional SMC adopting chemic thickening by using alkaline earth oxide or hydrate as thickening agents, LPSMC technique adopts physical thickening by using crystalline polymer with reaction activity as thickening agent. LPSMC compounds have better viscosity stablility at room temperature, and better thermal rheology property. Besides, its molding pressure and temperature are far lower than traditional SMC. Therefore, the technique declines the investment at a great extent of equipment and mould, which will develop the application domain of LPSMC as a result.The synthesis of crystalline polymer used as physical thickening agent is one of the pivotal technique of LPSMC. In this paper, a crystalline polymer—PEG₆₀₀₀-MAH, was synthesized successfully by using maleic anhydride(MAH) to modify polyethylene glycol(PEG₆₀₀₀). Testing results of X-ray diffraction showed that PEG₆₀₀₀-MAH possessed well crystalline property; testing results of DSC indicated that the melting point of PEG-MAH was about 63.5℃, which was propitious to the molding process of compounds. Besides, according to the testing results of infrared spectroscopy before the modifying reaction and after the reaction, PEG₆₀₀₀-MAH possessed reaction activity to participate in the copolymerization of unsaturated polyester(UP).When PEG and PEG₆₀₀₀-MAH were used as toughening agents of UP, it was shown that PEG could improve the toughness of UP with a evidently drop of its tensile strength and bending strength, and PEG₆₀₀₀-MAH also could improve the toughness of UP, but meanwhile, the declining extent of tensile strength and bending strength was far lower than that by using PEG. In addition, according to TG analysis, it was indicated that the copolymer of UP possessing 10% PEG₆₀₀₀-MAH had good thermal stability.In this paper, the viscosity of blend by adopting heating, shearing, melting and frozen treatment was larger than that of the direct blend method by a magnitude, through comparing different thickening technics. Besides, viscosity stability of the treatment was better. It was shown that additive quantity of 10% PEG₆₀₀₀-MAH was appropriate, considering thickening effect and that the mechanical properties could not be harmed at a great extent. Besides, the solubility parameters of PEG₆₀₀₀-MAH and UP were calculated and mensurated by using Small group-contribution method and turbidity titrimetry respectively, and it was proved that PEG₆₀₀₀-MAH was a appropriate physical thickening agent of UP. According to the analysis of solubility parameters and microcosmic morphology, the thickening effect of PEG₆₀₀₀₀-MAH to UP was the results contributed by follow two ingredients together: when PEG₆₀₀₀-MAH melted and dispersed in UP system, one part of PEG₆₀₀₀-MAH would separate out as crystallite after frozen treatment, so the thickening effect would be reached; the long molecule chain of another part of PEG₆₀₀₀-MAH which had not separated out from the system, would be frozen in the blend system, and the thickening effect would also be obtained by hydrogen bond and inter-molecule force.In this paper, correlated kinetic parameters and kinetic equation of the autocatalytic empirical kinetic model of LPSMC system are determined by using isothermal DSC to scan the system thickened by crystalline polymer (PEG₆₀₀₀-MAH). By using the obtained model equation to predict the curing kinetics of the system at 390k, the predicted results were basically identical with the testing results at 390k. According to the variation characteristics of the viscosity during the gelation process, the gel-time of the system at different curing temperature was obtained by mensurating the viscosity of the system . Besides, the gelling theory model of LPSMC system was also successfully established through linear regression. All of these above could provide necessary theoretical reference to the establishment and optimize of molding technics of LPSMC.