Rheological Properties Of Poly(Ethylene 2,5-Furandicarboxylate)(PEF) And Diffusion/Sorption Behavior Of Small Molecules In PEF

The development and application of bio-based polymers can fundamentally control the "white pollution",and reduce the consumption of petroleum resources,which is conducive to the realization of carbon peaking and carbon neutralization.Polyethylene terephthalate(PET)synthesized from petroleum-based terephthalic acid(TPA)is gradually being replaced by the bio-based polymers.However,the commercial biopolymers such as poly(lactic acid)(PLA),poly(3-hydroxyalkanoate)(PHA),poly(butylene succinate)(PBS)exhibit poor mechanical properties and poor heat resistance compared with PET because of the lack of rigid aromatic ring structure in these biopolymer chains.The structure and physical properties of 2,5-furandicarboxylic acid(2,5-FDCA)are similar to those of TPA.2,5-FDCA can be prepared from biomass like cellulose and sugars and other biomass.PEF synthesized from 2,5-FDCA has more excellent physicochemical properties,such as higher glass transition temperature(Tg),better gas barrier,higher strength and modulus,etc.PEF is considered to be the most promising substitute for petroleum-based PET and can be applied as packaging materials,spinning,engineering plastics and so on.PEF has not yet achieved industrialized commercial production due to the lack of basic data.To solve such problems,a lot of work has been done in this thesis.Rheological experiments of PEF were conducted in a wide shear range of shear rate for polymerization and processing.In addition,the sorption and diffusion behaviors of small molecules in PEF were studied based on the gravimetric method and molecular dynamics(MD)simulation.(1)The rheological properties of PEF.The rheological data can provide data support for process conditions setting and machine design in polycondensation process,spinning,extrusion and injection molding process.PEF is proved to be a complex viscoelastic fluid dominated by viscous property.The apparent viscosity of PEF decreases with the increase of shear rate,temperature and the decrease of intrinsic viscosity in the range of test temperature(230-260℃).The viscous flow activation energy decreases with the increase of shear rate;the non-Newtonian index(0.57-0.91)increases with the increase of temperature and the decrease of intrinsic viscosity.The dynamic rheological data can reflect the structure of the material.The results show that the loss modulus G" is much larger than its elastic modulus G’,which means the rheology of PEF is dominated by viscous property.The first normal stress difference N1 of PEF was calculated and compared with that of PET.(2)The diffusion characteristics of ethylene glycol(EG)and acetaldehyde(AA)in PEF.The diffusion characteristics of small molecules in PEF provide an important theoretical basis for the separation and removal of volatiles and the design of process conditions in the final polycondensation and solid state polycondensation.The diffusion coefficients of EG and AA in PEF matrix were studied based on the gravimetric desorption experiments and diffusion mathematical model.Molecular dynamics simulation(MD)was used to analyze the effects of free volume,temperature,polymerization degree,and small molecular species on diffusion behavior from a microscopic point of view.The predicted results of molecular simulation were in good agreement with the experimental data.Above the glass transition temperature,the relationship between the diffusion coefficient of EG in PEF and temperature is:D=5.29×10-6 exp(-39050/RT),and the relationship between the diffusion coefficient of AA in PEF and temperature is:D=6.02×10-6 exp(-37700/RT).(3)The solubility behavior of CO2 in PEF at a wide temperature range.The adsorption isotherm of CO2 in PEF was measured by magnetic suspension balance,and the all-atom simulation systems(about 20,000 atoms)were established by MD method to simulate the sorption behavior of CO2 in PEF.The solubility of CO2 in PEF matrix was calculated by different statistical methods.Henry coefficient and dissolution enthalpy of CO2 in PEF were calculated according to Henry’s law and Van’t Hoff equation.The sorption of CO2 in PEF is an exothermic process,and the solubility of CO2 in PEF increases with the decrease of temperature(308-513 K)and the increase of pressure(0-4 MPa).When the sorption of CO2 in PEF occurs at a temperature lower than the glass transition temperature,the relationship between Henry coefficient and temperature is:ln Hp=ln0.002+23170/RT.When the sorption of CO2 in PEF occurs at a temperature higher than the glass transition temperature,the relationship between Henry coefficient and temperature is:ln Hp=ln 0.002+23170/RT.