Preparation And Scale-up Research Of High Intrinsic Viscosity Polytrimethylene Terephthalate For Fibers

Polytrimethylene terephthalate(PTT)is a new type of thermoplastic polyester material with excellent performance.With high strength,toughness and heat resistance,but also good chemical stability and easy processing characteristics.PTT is widely used in fibers,carpets,fabrics,thirn films and the field of thermoplastic engineering materials.Although its performance is very excellent,the equilibrium constant of polymerization is small,the synthesis of the PTT resin products with high intrinsic viscosity technology is difficult.This is a technical bottleneck for the industrialization of PTT.In this paper,PTT resins with high intrinsic viscosity were successfully synthesized by direct esterification polycondensation.And the intrinsic viscosity of synthesized PTT resin was more than 0.92 dL/g.The torque value can reveal the change of PTT viscosity,so we used the torque value to track the change of PTT viscosity during the polycondensation process.The effects of the ratio of alcohol and acid,polycondensation time,polycondensation temperature,catalyst,vacuum and stirring speed on PTT with high intrinsic viscosity was studied.The optimum synthetic conditions of PTT with high intrinsic viscosity were investigated.Meanwhile,polymerization kinetics of PTT was studied by the method of intrinsic viscosity and torque.The structure and properties of PTT resins were characterized by FTIR.TGA,XRD and DSC.The results showed that the intrinsic viscosity of PTT resins synthesized was more than 0.90 dL/g,when the ratio of alcohol and acid was more than 1.4:1.With the increase of ratio of alcohol and acid,the corresponding esterification reaction time was shorted,the intrinsic viscosity of synthesized PTT varied little.Polymerization temperature had an important effect on preparing high intrinsic viscosity PTT.When polymerization temperature was less than 250 ?,the intrinsic viscosity of PTT resin obtained was less than 0.9 dL/g.When the polymerization temperature was higher than 265 ?.the intrinsic viscosity of PTT resin increased slightly in polycondensation prophase and then decreased significantly.Side reaction and thermal degradation were intensified.Therefore,the polymerization temperature was kept in 250-265 ?:.Catalyst was added by two times,it could increase the catalytic activit,and the content of catalyst was 1900ppm.The high vacuum degree of the system is beneficial to move byproducts.The vacuum pressure preparing high intrinsic viscosity PTT was less than 100 Pa.The fast stirring rate make material contacted fully,the collision probability of functional groups was increaseed,and the interface updated was accelerated,which was in favour of the positive reaction of polymerization.In this study,we used the paddle agitator to maintain a speed of 150 r/inin.Polymerization kinetics of PTT was studied by intrinsic viscosity method and torque method,and polycondensation reaction order of PTT was 2.Polymerization activation energy of PTT obtained by intrinsic viscosity method was 33.14 kJ/mol,and polymerization activation energy of PTT obtained by torque method was 101.32 kJ/mol.The TGA results showed that PTT resin had good thermal stability.The temperature of 5 wt%weight loss of PTT resin was 360-373 ?.Molecular weight has no effect on the thermal stability of PTT resin.The XRD spectra of PTT resin with different intrinsic viscosity show several obvious diffraction peaks,and the peak angle of the diffraction peaks occur between 10° and 30°,and the the strongest diffraction peak appeared at 24.5°,and the second appeared at 15.9°.PTT resins with different molecular weights were no shift of the position(20)in the diffraction peaks,indicating that the crystal unit cell of PTT does not change.DSC test results show that the melting temperature of the PTT samples with different intrinsic viscosity was 221-228 ?,the crystallization temperature was 183-196?,the melting enthalpy was 45.84-68.56 J/g,the crystallization enthalpy was 44.47-61.66 J/g,and the crystallinity of the PTT with different intrinsic viscosity calculated by the melting enthalpy was 30-48%.DSC test results show that the PTT samples with different intrinsic viscosity showed double melting peaks during the secondary heating process.Generally,the multiple melting behaviors could be considered to be related to the effec t of secondary crystallization during DSC cooling trace.Based on the small experimental conditions,scale-up research of PTT in 5 L reactor was carried out.The effects of polymerization time,catalyst,dosage,nitrogen and alkyd ratio on PTT polymerization were studied.The results show that PTT with high intrinsic viscosity was difficult to be obtined when the polymerization time was too short in the amplification system,and the depolymerizing reaction and the degradation reaction of the PTT resin would be aggravated when the polymerization time is too long.Polymerization time in the amplification system was kept in 3.5-4.0 h.The dosage of catalyst should be increased by 20%.In the reactor with the same volume,the intrinsic viscosity of PTT was increased when the materia were reduced properly.Injecting nitrogen into the reaction reactor in the polycondensation stage could promote the move of byproducts,but the flow rate of nitrogen should be controlled very small.In the scale-up experiment of PTT,vacuum had an important effect on preparing PTT resin with high intrinsic viscosity.When the vacuum of the equipment was poor,it is difficult to move byproducts out of system and PTT resin with high intrinsic viscosity was not obtained.