Study On Synthesis Of PET/PPG Copolyesters And Preparation Of Its Fibers

Poly(ethylene terephthalate)(PET) has been widely employed in synthetic fibers, plastics with excellent physical, chemical and mechanical properties, including very good water and moisture barrier, heat resistance, fatigue resistance, abrasion resistance and good dimensional stability. However, PET is a linear semi-crystalline polymer with a lower crystallization rate and only when conditions are appropriate, can it form better crystal. Therefore, it is not suitable for high-speed processing such as injection moulding to yield engineering plastic and ultrahigh speed spinning to prepare fiber having some specific properties. Lots of works have been done on PET with physical and chemical modifications to enhance the overall crystallization property of PET. Nevertheless, the modified PET obtained by the means of physical modifications which is usually blended with nucleating agent such as clay, metal oxides and inorganic salts would show poor miscibility and durable resistance. And the modified PET obtained by the means of chemical modifications which is usually copolymerized with comonomer units such as ionomer, arylate(e.g. imide) would be expensive. This study introduce poly(propylene glycol) to PET by copolymerization to prepare copolyesters with excellent crystallization rate and low cost. The novel materials would retain the advantages of PET, and introduce the special performance of PPG.The main research content and conclusions are as follows:1. A novel copolyester, i.e., poly(ethylene terephthalate)/poly(propylene glycol)(PET/PPG) was synthesized. Intrinsic viscosity and viscosity average molecular weight of the copolyesters were obtained by the Ubbelohde viscometer. And chemical structure was characterized and confirmed by proton nuclear magnetic resonance(1H-NMR) spectra.2. The non-isothermal crystallization process of copolyesters was studied by differential scanning calorimetry(DSC). The non-isothermal crystallization kinetics of the copolyesters was analyzed by Avrami, Ozawa, Mo’s, Kissinger and Dobreva methods, respectively. The results show that the crystallization rate of PET is apparently enhanced with incorporating a small amount of PPG, which is first raised and then reduced with increasing amount of PPG in the copolyesters at a given cooling rate. And PET/PPG containing 0.60 mol% PPG exhibits the highest crystallization rate. The process of crystal nucleation and growth is mainly three-dimensional growth with both instantaneous and sporadic nucleation mechanisms. Meanwhile, the non-isothermal crystallization process and isothermal crystallization process of the copolyesters was studied by polarized optical microscopy(POM). The results show the crystal of PET/PPG is much smaller and denser(particularly for PET/PPG with 0.60 mol% PPG), which well confirms that PET/PPG copolyesters can have superior crystallizablity to the neat PET and PET/PPG with 0.60 mol% PPG has the most highest crystallizablity. The data obtained by X-ray diffraction(XRD) also supports the results.3. PET/PPG fiber was prepared by the melt spinning method, then stretched and wound. The results of dynamic thermomechanical analysis(DMA) of the modified PET fibers suggest that the molecular chain of PET/PPG exhibits better flexible and damping capacity. In addition, the results indicate that the modified copolyester fibers exhibit better toughness and thermal properties.