Preparation And Properties Of Bio-based Unsaturated Polyester And Its Nanocomposites

Since the industrialization of unsaturated polyester（UP）resin,the technical level of UP industry has been greatly developed due to the need of improving its performance,broaden its application field and the promotion of the technical progress of related industries,and the new varieties of high performance and functional constantly appear.Based on the consideration of ecology and sustainability,in recent years,the study of fully bio-based UP has attracted wide attention.According to the current research,the replacement of petroleum-based UP by fully bio-based is still face with many challenges,mainly including two points（1）Due to the limitation of upstream industry,the types of bio-based monomers and diluents are limited.However,the development of high-performance UP often has specific requirements on the structure of UP prepolymer and diluent,which limits the design of the molecular structure of fully bio-based UP.It is also necessary to design and synthesize a certain component in the UP system,and the synthesis process tends to be complex.（2）At the present stage,the fully bio-based UP does not have cost advantages over petroleum-based UP,and its market advancement depends on the development of the upstream industry while functionalized products need to be developed to increase its added value.Based on the above analysis,in this paper,bio-based isosorbide（IS）was used as the rigid unit,itaconic acid（IA）provided the cross-linking reaction site,1,3-propanediol（PD）and succinic acid（SA）regulated the stiffness and flexibility of molecular chains.According to the principle of similar solubility,commercially available bio-based dimethyl itaconic acid（DMI）was selected as the active diluent,the fully bio-based UP was prepared by heat curing process.Cinnamyl cellulose nanocrystals（Cin-CNC）and lignin nanoparticles（LNP）were used as functional additives to enhance the mechanical properties of fully bio-based UP while endowing it with UV resistance.Specific research content are as follows:（1）Bio-based IS was used as the rigid unit,IA provided the cross-linking site,PD and SA regulated the molecular chain stiffness and flexibility,and DMI was selected as the active diluent,a series of fully bio-based UP with different chemical structures were prepared by adjusting the monomer feed ratio,purifying the prepolymer and optimizing the curing process.Flourier transformed infrared spectroscopy（FTIR）,nuclear magnetic resonance（¹H NMR）and gel permeation chromatography（GPC）tests showed that the fully bio-based UP was successfully prepared.Rotational rheometer test showed that fully bio-based UP had good processing performance,with a viscosity of 400～840 m Pa·s at 25℃and 1.0 s^-1.Mechanical properties,dynamic thermomechanical analyzer（DMA）and thermogravimetric analyzer（TGA）tests showed that when the feeding molar ratio of IA,PD and IS was 1.0:0.7:0.4,the comprehensive properties of cured fully bio-based UP were the best,with tensile strength and flexural strength of 68.60 MPa and 98.37 MPa,storage modulus（’）and glass transition temperature（T_g）of 3504 MPa and 124.7℃,respectively,and thermal decomposition temperature(T_d5%)of 262.3℃.（2）Cinnamoyl cellulose nanocrystals（Cin-CNC）were prepared by acylation reaction using cellulose nanocrystals（CNC）prepared by sulfuric acid hydrolysis as raw materials and cinnamoyl chloride as modified monomers.Cin-CNC were introduced as a functional additive into the fully bio-based UP to prepare UP/Cin-CNC nanocomposites.By elemental analysis,FTIR,nuclear magnetic resonance(¹³C NMR),ultraviolet visible spectrophotometer（UV-vis）and X-ray diffraction（XRD）characterization,the cinnamyl cellulose nanocrystalline（Cin-CNC）were successfully prepared,with the degree of substitution increasing from 0.32 to 1.69,the absorption capacity of Cin-CNC to UVA and UVB regions increased gradually,but the degree of crystallinity decreased.The mechanical properties,DMA and TGA tests showed that when the degree of substitution of Cin-CNC is 0.87 and the addition amount is 1.0%,the tensile strength,’,T_gand T_d5%of UP/Cin-CNC were 59.45 MPa,3413 MPa,115.9℃and259.8℃,respectively,compared with UP,it increased 4.87 MPa,389 MPa,5.2℃and7.00℃,respectively,and the UV-vis and UV-aging tests showed that the addition of Cin-CNC improved the UV resistance of UP.（3）The UP/LNP nanocomposites were prepared by using LNP prepared by dissolution precipitation method as a functional additive and fully bio-based UP as a matrix.FTIR,UV-vis,TGA and scanning electron microscopy（SEM）tests showed that LNP was prepared successfully and its main chemical structure did not change,it as rod-like structure with length of 180～220 nm and diameter of 30～36 nm.Mechanical properties and TGA tests showed that when LNP content was 0.5%,the elastic modulus and T_d5%of UP/LNP were2223 MPa and 259.7℃,respectively,which increased by 271 MPa and 6.0℃compared with UP.The UV-vis and UV aging tests showed that LNP increased the UV resistance of UP,and had a certain effect on the transparency of UP.