| As a kind of advanced composite material,sheet moulding compound(SMC)has gained wide attention since its inception.And it has been widely used in automotive industry for its advantages such as excellent processing performance,good mechanical properties,and designability of materials.It has played a great role in promoting automotive lightweight and the development of new energy vehicles.However,the curable shrinkage rate of the unsaturated resin matrix used in SMC is larger(7%-10%),and this kind shrinkage may cause deformation and warpage of the product in the molding process,affecting the dimensional accuracy and the surface quality.Severe conditions can cause cracking of the product,while the unsaturated resin matrix has a lower heat resistance,which limits its application.At present,the method of maintaining low shrinkage of the unsaturated polyester resin is mainly achieved by adding a low profile additive(LPA).However,due to the addition of LPA,the mechanical properties of the resin after curing are greatly reduced.Therefore,it is very important to achieve good mechanical properties while achieving low shrinkage.In this study,a new type of LPA was developed by using vinyl ester resin as a resin matrix,which could improve the mechanical properties of the resin system under the condition of low shrinkage.In this paper,the surface modification of styrene butadiene styrene block copolymer(SBS)and graphene oxide(GO),which has better anti shrinkage properties,was selected from the molecular structure design and the anti-shrinkage mechanism of LPA.Firstly,the product of SBS-g-VAc was obtained by grafting polyvinyl acetate(PVAc)to SBS by bulk polymerization.The grafting reaction was successfully carried out by FT-IR and 1H NMR.Secondly,GO was prepared by modified Hummer method.The silane coupling agent KH570 was grafted onto GO surface(KH570-GO).The reaction was confirmed by FT-IR and XPS,and the reaction mechanism of KH-570 and GO was analyzed.The thermogravimetric analysis confirmed that the heat resistance of KH570-GO increased by about 20°C.The compatibility analysis and test show that the grafted SBS and vinyl ester resins had good compatibility,and the dispersion of the resin in the resin is uniform and the diameter of the particle was between 0.5-2?m.After optimization of the low shrinkage formula,the optimal content of composite LPA was 9% SBS-g-VAc and 0.5% KH570-GO,and the shrinkage of the resin system was 1.92%.The curing kinetics of the resin system was analyzed by DSC,and the activation energy of the curing reaction was calculated as Ea=176.76 k J/mol,the reaction order n=0.96,and the reaction rate equation was obtained.The tensile strength and tensile modulus of the resin cast specimens added with the composite LPA increased by about 21% and 8%,respectively,and the elongation at break increased by about 39%.Through SEM image analysis,the fracture morphology was more rough with the addition of KH570-GO,which plays a role in filling micropores and dispersing loads.The addition of composite LPA increased the glass transition temperature of the resin system from 108.6°C to 128.5°C,increasing its thermal stability.The interfacial shear strength,tensile and bending properties of carbon fiber SMC composites with composite LPA has been improved.In the SEM image,it was observed that the surface of the broken carbon fiber was coated with resin residue,demonstrating that the addition of the composite LPA increased the wettability and interfacial bonding strength of the resin system,and enhanced the stress transmission between the resin and the fiber,thus improving the mechanical properties of the composite material. |
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