Preparation And Properties Of The Bio-based Unsaturated Polyester Resin System And Its Reinforced Composites

Unsaturated polyester is a type of polyester that containing double bond in backbone,and having number average molecular weight（M_n）of about 1000 to 2000g/mol.Industrially,unsaturated polyester resins are cured by a free radical polymerization of the liquid mixture with diluent vinyl monomers.Current unsaturated polyesters are often use styrene as the diluent.They are facing the challenges of the consumption of petroleum resources and the damages on the ecological environment and human health.The first part of this work proposes a novel blending solvent of epoxidized soybean oil（AESO）and glycidyl methacrylate（GMA）to dilute a bio-based unsaturated polyester（UPOEM）,which was synthesized by ethylene glycol（EG）,oxalic acid（OA）,and maleic anhydride（MA）via a melt polycondensation.The resulting unsaturated polyester systems have low viscosity,high bio-based content,good storage stability,and improved wettability with reinforcing fibers.Viscosity tests showed that GMA effectively reduce the viscosity of AESO/UPOEM systems,and the viscosity values of resin solutions decreased with the increase of GMA content.When20 wt%GMA mixed to a AESO/UPOEM mixture with mass ratio of 100:300,the resulting solution shows a low viscosity not more than 780 mPa·s,which is only5.4%of that of the general AESO/UPOEM mixture,and keeps the yellow solution transparent and a constant viscosity at room temperature for more than 30 days.After composited the unsaturated polyester systems with cotton fabrics,green composites were prepared via a free radical polymerization performed at 100°C for 2 hours and150°C for 3 hours,under a pressure of 15 MPa in a hot pressing machine,and using a mixture of tert-butyl peroxybenzoate（TBPB）and isophorondiamine（IPDA）as initiator.The tensile and thermo-mechanical properties of the resulting green composites were examined by universal testing machine,dynamic mechanical analysis（DMA）and thermogravimetric analysis（TGA）,respectively.The results showed that the composites have good tensile strength close to 30 MPa,and their glass transition temperature（T_g）and thermal decomposition temperature(T_d5%)are greater than 90°C and 248°C,respectively.Thus the bio-based unsaturated polyester systems have a great potential for various industrial applications.The second part was based on the previous work to further improves the bio-based content of the resin system and the mechanical and thermal properties.A series of itaconic acid-based unsaturated polyesters（UPEOI）were prepared by melt polycondensation using itaconic acid（IA）,ethylene glycol（EG）and oxalic acid（OA）.The UPEOI were diluted using 30 wt%dimethyl itaconate（DI）as the reactive diluent.The obataining unsaturated polyester systems have low viscosity,all-biobased content,good storage stability,and improved wettability with reinforcing fibers.After composited the unsaturated polyester systems with cotton fabrics,composites were prepared via a free radical polymerization performed at 110°C for 3 hours,under a pressure of 15 MPa in a hot pressing machine,and tert-butyl peroxybenzoate as initiator.The tensile fracture surface morphology of the composites was observed by SEM and it was found that the fibers and resin are regularly broken.The mechanical and thermal properties of the resulting green composites were examined by universal testing machine,dynamic mechanical analysis（DMA）and thermogravimetric analysis（TGA）,respectively and test results show that the tensile breaking strength was higher than 30 MPa,and their glass transition temperature（T_g）was as high as 108.2oC and the thermal decomposition temperature(T_d5%)is above 230.8oC.In this paper work,high-performance thermosetting resin was prepared by replacing of petroleum-based counterparts with renewable resources.The result establishes the experiments and theoretical foundation for the development of bio-based polymer materials.