| Oil is the main energy in the world today.With the rapid development of China’s economy,oil resources are decreasing.Looking for bio-based resources,developing "environment-friendly" materials and implementing of sustainable development have become an important direction for industrial development.The bio-based materials that have been industrialized today are basically aliphatic polyesters,but most aliphatic polyesters have many drawbacks such as poor brittleness,poor thermal stability and poor mechanical properties,which makes aliphatic polyesters unable to meet the requirements of materials Performance requirements,restricting the development of bio-based polyester.Thermotropic liquid crystal is an ester-based polymer containing an aromatic ring in the main chain.Its unique molecular chain structure makes that the rigid molecular chain is easy to order along a certain order.This orientation can improve the mechanical properties of fiber materials.But because above its melting point or glass transition temperature,it will appear the liquid crystal state.At low viscosity and low shear,the liquid crystalline chain can maintain a high degree of orientation,so the thermotropic liquid crystal has excellent molding process performance and mechanical properties.These properties make up for the drawbacks of the aliphatic polyesters,expanding the application of materials.But bio-based liquid crystal polyester has not been widely studied,so to carry out the study of bio-based liquid crystal material is very meaningful.In this paper,copolyester was synthesized via bio-based liquid crystalline monomer p-hydroxybenzoic acid(HBA),vanillic acid(VA)and p-hydroxyphenylpropionic acid(HPPA)which can be derived from lignin.The bio-based liquid crystal copolyester was synthesized by two-step acetylation and melt polymerization.Chemical structure,crystalline properties,thermal properties and mechanical properties of different monomer ratio of copolyesters were studied.There are many problems such as high melt viscosity,low molecular weight and easy decomposition;the solid phase polymerization can solve these problems.The effects of different solid-phase temperature on the crystallinity,liquid crystal properties,melt flowability and mechanical properties of copolyester were discussed.(1)The structures of monomers and acetylated monomers were characterized by IR(FTIR)and 1H NMR(1HNMR).It was showed that acetylation of HBA,VA,HPPA have high purity and hydroxyl has been completely converted to acetoxy.(2)A series of binary copolyester HBA / VA were prepared by melt polymerization.Copolyester was characterized by 13 C nuclear magnetic resonance analysis(13C NMR),Fourier transform infrared(FTIR),powder X-ray diffraction(XRD),hot-stage polarizing microscope(POM),differential scanning calorimetry(DSC),thermo-gravimetric analysis(TG)Melt index(MI)and micro-control electronic universal testing machine.It was showed that binary copolyester was successfully polymerized.When the content of HBA was more than 30%,the copolyester showed different fabric structure under polarized microscope,and the copolyester with 70% HBA content showed bright color stripe texture;the melting point of copolyester is a range of 220 ~ 350 ℃,But the higher content of VA copolymer and VA homopolymer cannot melt;With the increase of VA content,the decomposition temperature of HBA / VA decreased gradually.The copolyester has good melt flowability above the melting point of 10 ℃,and its tensile properties are tested.(3)A series of HBA / VA / HPPA ternary copolyesters were prepared by two-step melt polymerization.The structure,crystallinity,liquid crystallinity,thermal properties and mechanical properties of copolyester were characterized.The FTIR and 13 C NMR proved that the copolyester is successfully polymerized;By XRD analysis,it was found that the crystallinity of copolyesters increased gradually,because the aliphatic segment in HPPA increased the flexibility of the copolyester to make the copolyester more easily crystallized.copolyesters are liquid crystal and show a different fabric structure under the polarized Microscope.The melting point of copolyester is the range of 230 ~ 260 ℃,the initial decomposition temperature is in the range of 300 ~ 410 ℃,the decomposition temperature increases first and then decreases.Because when the addition of HPPA is less,the decomposition temperature of the copolyester is influenced by the steric hindrance of the OH in the ortho position,and when the content of the HPPA is increased,the aliphatic segment of HPPA decreases the rigidity of the copolyester and the decomposition temperature decreases.When the amount of HPPA is 15%,the decomposition temperature of copolyesters is the highest,the residual carbon is the largest and the mechanical properties are better.The tensile strength,initial modulus and elongation at break are 6.7 MPa,0.13 GPa,6.6 %.(4)In the process of melt polymerization of copolyester,with the extension of reaction time,the polymerization reaction enters the later stage,The molecular weight of copolyester increased rapidly,but the viscosity of the system increased sharply and the stirring was difficult.Therefore,polyester production process often use solid-phase polymerization to improve the molecular weight of the polymer.The solid phase polymerization of HBA / VA / HPPA copolyester at 180 ℃,190 ℃ and 200 ℃ was carried out,and the crystallinity,liquid crystallinity,melt flowability and mechanical properties of copolyester were characterized.It was showed that the crystallinity of copolyester increases with the increase of the solid phase polymerization temperature.After the solid phase polymerization,the liquid crystalline structure of copolyester has obviously changed and the structure of this liquid crystal will become more and more obvious as the solid phase temperature increases.Solid-phase polymerization reduces the melt index of the copolyester and increases the tensile strength,because the molecular weight of the copolyester is improved after solid-phase polymerization. |
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