Preparation Of High Intrinsic Viscosity Polytrimethylene Terephthalate Resins For Fibers

The polytrimethylene terephthalate(PTT)is a kind of crystalline thermoplastic polyester materials.The molecular chain of PTT has a spiral structure,exhibiting inherent elasticity and good processability.PTT possesses toughness,good mechanical strength and heat resistance.The fibers prepared from PTT exibit high tensile resilient rate and lower modulus than those of polyethylene terephthalate(PET)and polybutylene terephthalate(PBT).PTT fibers also have a good dyeability compared with polyamide(PA)fibres.Therefore,PTT resins can be applied in the fields of synthetic fibers and engineering plastics.However,the synthesis of high intrinsic viscosity PTT was difficult.Only Shell Group of Companies and DuPont Company can manufacture the high intrinsic viscosity PTT.The preparation and production technology of PTT in domestic is not mature enough.In the present study,the high intrinsic viscosity PTT was synthesized from terephthalic acid and 1,3-propylene glycol by direct esterification polycondensation.The intrinsic viscosity of synthesized PTT was more than 0.9 dL/g and the viscosity average molecular weight of PTT was greater than 5.0×104 g/mol.The content of carboxyl end group of the prepared PTT was less than 15μmol/g.The effects of polymerization temperature,polymerization time,stirring strength,vacuum and ratio of raw materials to reactor volume on the intrinsic viscosity of PTT were investigated.The structure and properties of PTT were characterized by FTIR,Ubbelohde viscometer,TGA,polarizing optical microscope.The results showed that polymerization temperature had an important effect on preparing high intrinsic viscosity PTT.When the polymerization temperature was lower than 260℃,the intrinsic viscosity of PTT obtained was less than 0.9 dL/g,in the temperature range,the higher polymerization temperature was good for synthesizing higher intrinsic viscosity of PTT.When the polymerization temperature was higher than 270℃,PTT obtained was less than 0.9 dL/g,and with increase of polymerization temperature,the intrinsic viscosity of PTT decreased sharply.The polymerization temperature was kept in 260-270℃ for preparing high intrinsic viscosity of PTT.Polymerization time had an effect on synthesizing PTT.When the polymerization time was less than 6 h,the intrinsic viscosity of PTT obtained was less than 0.9 dL/g,the degradation reaction and other side reaction would gradually be strengthen with.a longer polymerization time.The polymerization time of 6 h was used to prepare the high intrinsic viscosity PTT.The stirring rate,stirring apparatus,vacuum,ratio of raw materials to reactor volume are very important factors for removing the byproducts from the system.The TGA results showed that PTT had good thermal stability.The temperature of 5%weight loss of PTT with different intrinsic viscosity of 0.5043-1.0643 dL/g,was in the range of 360-374℃.The temperature of maximum degradation rate was in the range 398-405℃.The crystallization behavior of PTT was also studied by polarizing optical microscope.The spherulite crystals were observed in the PTT resins with black cross extinction phenomenon under polarizing optical microscopy.The isothermal crystallization rate was 0.3567μm/s,at 190℃and 0.0370μm/s,at 210℃,respectively.During isothermal crystallization under higher temperature,band structure was formed in the PTT spherulite crystals.In the nonisothermal crystallization process,the band structure was found at the center of the crystal.The lab-scale study is the basis of industrial process development.We selected filtering experience amplification method to prepare high intrinsic viscosity PTT.The intrinsic viscosity of synthesized PTTs was greater than 0.9 dL/g with the amplification of 2 to 50 times of raw materials.Reducing the ratio of raw materials to reactor volume was beneficial to prepare PTT with high intrinsic viscosity.The ratio of raw materials to reactor volume could be less than 0.8668 kg/L.