Bio-based Poly (Ethylene 2,5-Furandicarboxylate) And Its Copolyester Synthesis And Performance Studies

Bio-based poly?ethylene 2,5-furandicarboxylate??PEF?is synthesized from bio-based 2,5-furanedicarboxylic acid?FDCA?or its derivatives and ethylene glycol?EG?through direct esterification or transesterification.Currently the research is mainly focused on the exploration of polymerization conditions and copolymerization modification of beverage packaging materials.And PEF is the most promising bio-based polyester to replace petroleum-based polyethylene terephthalate?PET?.In the polymerization process of bio-based PEF,the esterification rate and molecular weight of PEF may be affected by many factors such as feed ratio,catalyst type,esterification time/temperature,and polycondensation time/temperature.Therefore,suitable polymerization conditions should be selected.In addition,in the application of PEF,there are still some shortcomings such as low viscosity of polyester,slow crystallization rate,high brittleness,poor mechanical properties and difficult degradation of products.As known,poly?ethylene glycol??PEG?is a long chain of flexible hydrophilic polyethers,and is a kind of modified component to improve the hydrophilicity,crystallinity,and degradability of polymers.At present,there are many researches on improving hydrophilicity and degradability of conventional polyester by introduction of PEG,but there is still no research on improving the hydrophilicity and degradability of furan polyester by using PEG.In this study,based on the principle of transesterification,soft segment PEG is introduced into the PEF segment by copolymerization method to prepare series of copolyesters with a soft and hard segment block coexisting,which is expected to improve the crystallization behavior of the copolymers.Meanwhile,the prepared copolyesters are endowed with certain hydrophilicity and degradability.Based on the above discussion,this paper mainly studies the following work:?1?Synthesis and Properties of Bio-based Poly?ethylene 2,5-furandicarboxylate?In this chapter,bio-based PEF was prepared from bio-based dimethyl 2,5-furandicarboxylate?2,5-DMFD?and ethylene glycol though transesterification.In this study,the effects of feedstock ratio on esterification rate and intrinsic viscosity were investigated.It is found that when DMFD:EG=1.8,the esterification rate and intrinsic viscosity of the obtained polymer are the highest,about 93.8%and 0.61 dL/g,respectively;At the same time,according to a large number of small experiments,the catalyst required for the polymerization is determined to be ethylene glycol oxime?Sb?EG?₃?,the esterification and polycondensation time are 4 h,respectively,and the esterification and polycondensation temperatures are 190°C and 235°C,respectively.The prepared product was characterized by nuclear magnetic and infrared methods,and the results show that the obtained product is the target product PEF.The thermal properties were characterized by differential scanning calorimetry?DSC?and thermal analyzer?TGA?.The results show that the obtained product has good thermal stability,and the glass transition temperature?T_g?is about 87.2°C.The melting point?T_m?is approximately 211.6°C.The crystallization rate of PEF is found to be very slow by DSC,and only a small crystallization peak appeared at a temperature drop rate of 1°C/min.Therefore,in order to investigate the crystallization behavior of PEF,the isothermal crystallization kinetics of PEF was studied.It is found that the temperature of PEF corresponding to the fastest crystallization rate is at 165°C,and its semi-crystallization time is about 11.2 min,which is much lower than that of PET.?2?Synthesis and Properties of Bio-based 2,5-furandicarboxylic Acid-based CopolyestersTo deal with the problems of polyester brittleness,poor mechanical properties caused by low molecular weight of polyester and slow crystallization rate,and difficult degradation in the preparation and application process of bio-based PEF,a flexible hydrophilic polyether segment is introduced into PEF chain.PEG is used as the component to be introduced into PEF chain in the polycondensation stage.Polyethylene glycol 2,5-furandicarboxylate-co-2,5-furandicarboxylate?PEGF?with soft and hard segment block is obtained.By changing the addition contents and the molecular weights of PEG?contents of10wt%,20wt%,40wt%and 60wt%,respectively,molecular weights of 600 g/mol,2000 g/mol,6000 g/mol and 10000 g/mol,respectively?,a series of PEGFs are successfully prepared.And the intrinsic viscosity of the product are between 0.62-0.99dL/g,respectively.The structures of the prepared products were characterized by nuclear magnetic and infrared.The results show that the content of PEG in the PEGFs is basically consistent with the actual feed,and the synthesized product is the target polymer.The thermal properties of the products were characterized by DSC and TGA,the results show that the addition of PEG would slightly reduce the thermal stability,melting point and glass transition temperature of the PEGFs.Based on the results of DSC method,the addition of PEG can increase the crystallization rate of the PEGFs.When the PEG content is 40wt%and the molecular weight is 2000 g/mol,the crystallization rate of the copolyester is the fastest.Besides that,we have also systematically investigated the hydrophilicity and degradability of PEGFs.Compared with PEF,the introduction of PEG increases the hydrophilicity of the PEGFs,and the surface contact angle of the PEGFs reduces from91.9°to 37.6°,indicting the increase of their hydrophilicity.In addition,the introduction of PEG imparts certain degradability to the PEGF.In the neutral phosphate buffer solution at 37°C,the maximum mass loss can reach about 15%.Finally,this study conducts a preliminary study on the degradation mechanism of PEGFs.The results showe that the co-hydrophobic coexistence of PEGFs promotes the attack of ester bonds by water molecules,which causes the ester bond to be break,leading the polymer achieve certain degradation property.The introduction of PEG can be optimized the performance of PEGFs to a certain extent.This research may lay a theoretical foundation for the application of bio-based polyester instead of petroleum-based polyester.