Poly(Ethylene Furan-dicarboxylate):from Synthesis To Structrure-properties

Poly(ethylene furandicarboxylate)(PEF)is a newly emerged biobased polyester synthesized from biobased monomer furandicarboxylic acid(FDCA)and ethylene glycol(EG).It is reported that PEF possesses excellent thermo-mechanical properties comparable to its petroleum-based counterpart,poly(ethylene terephthalate)(PET)and low prospective cost.Especially,it has at least one order of magnitude higher gas barrier property than PET.Therefore,PEF is a promising polyester material that will partially substitute PET and will find som new applications.Currently,the research and development of PEF is just in the ascendant.However,according to published reports,there still are many problems to be solved in the synthesis,structure-property relationship and applications of PEF.In our preliminary study,we also found that PEF discolored seriously during its synthesis by esterification-melt polycondensation method and had poor crystallizability and poor mechanical properties.These key problems should be solved for R&D of PEF.Aiming at these problems,fundamental researches including identification of impurities and purification of FDCA,screening of catalysts,optimization of synthesis route and conditions,identification and controlling/tuning of chemical structure of PEF,relationship between chain structure and crystallization,accelerating crystallization by nucleating agent and mechanical properties have been done in this study.First,it is found via 1H NMR analysis that there are many impurities,typically,2-carboxyl furfural and acetic acid,in commercially provided FDCA.These impurities are responsible for the discoloration and depressed molecular weight growth during synthesis of PEF.An effective purification method,namely,acetic acid refluxing plus pH swing,was developed and all the impurities had been successfully removed from FDCA.Using purified FDCA,the discoloration was significantly depressed and the molecular weight growth of PEF was clearly improved.Second,it is found that there are not only ethylene furandicarboxylate(EF)units but also diethylene glycol furandicarboxylate(DEF)units(about 10 mol%)in PEF synthesized by ordinary esterification-polycondensation route under commonly used conditions.The DEF units were formed through etherification side reaction between terminal hydroxyl ethylene groups.And we reasoned that the existence of DEF units resulted in deterioration of crystallizability of PEF.Therefore,the effects of catalyst,diol/diacid or diol/diester ratio,esterification or transesterification time on generation of DEF units were investigated in both esterification-polycondenation and transesterification-polycondensation routes,and effective control/tuning of DEF content in PEF was realized.It was found that DEF content in PEF was lowered down by using transesterification-polycondensation route,using antimony catalyst,reducing diol/diacid or diol/diester ratio,or reducing time of esterification or transesterification.PEF with DEF content as low as 0.5 mol%was successfully synthesized via transesterification-polycondensation route using tin-antimony binary catalyst at low diol/diester ratio.Then,the effects of DEF content and molecular weight on crystallization as well as crystallization kinetics of PEF were investigated detailedly.It is found that(1)the crystallizability of PEF decreased when the DEF content or molecular weight increases;(2)PEF can crystallize completely from melt at a cooling rate of 10?/min when the DEF content is 1.2 mol%or less;(3)and PEF loses its crystallizability from melt at a cooling rate of 10?/min when the DEF content is 3.5 mol%or more.Therefore,tuning from amorphous to completely crystallized PEF has been realized via tuing its DEF content.This result also verifies our previous reasoning.This is the first time to realize complete nonisothermal melt crystallization of PEF and to reveal the relationship between crystallization and chemical structure of PEF.To further improve the crystallizability of PEF,nucleating agents for PEF were screened.It is found that talc is a good nucleating agent that can effectively accelerate crystallization of PEF.Finally,nearly colorless transparent high molecular weight PEF was successfully synthesized from purified FDCA or dimethyl furandicarboxylate(DMF)and EG via both synthetic routes with the aid of a stabilizer.After crystallization treatment,white colored PEF was obtained.These PEF resins exbited very high tensile modulus and tensile strength,3.7 GPa of 77.1 MPa respectiely.The tensile properties are the best rusults ever reported up to now.In summary,afer the researches on synthesis and structure-properties of PEF in this study,an effective purification method of FDCA was invented,the true chemical structure of PEF and the effect of DEF content on crystallization were revealed,the controlling or tuning of DEF content in PEF was realized via synthesis and further improvement of crystallization of PEF was realized via incorporating talc as a nucleating agent,and finally,high molecular weight PEF with satisfactory color,good crystallizability and mechanical properties has been successfully synthesized.These results have laid a good foundation and therefore will be very helpful for further R&D of PEF.