Synthesis And Properties Of Low-melting-point Ptt

Poly(trimethylene terephthalate) (PTT) has attracted much interest from its excellent elastic resilience, colorableness, stain-resistance and other properties, so there were many reports about modified PTT recently. There was a potential value of that low-melting point polyester used as non-woven fabric and hot-melt adhesive; however, there was little research about low-melting point PTT. In this paper, isophthalic acid (IPA) and polyethylene glycol (PEG) were used to modify poly(trimethylene terephthalate) to obtain a novel copolyester with low melting point and spinnability, poly(trimethylene terephthalate isophthalate-co-polyethylene glycol) (PTTI-PEG). First, IPA was imported to PTT (IPA/TPA: 10/90, 20/80, 30/70 and 35/65, molar ratio) to obtain a series of PTTI, and then PEG units were imported to PTTI to get PTTI-PEG. The structure and composition of PTT and its copolymers was invested by Fourier transform infrared spectrometry (FT-IR) and nuclear magnetic resonator (~1H-NMR) respectively. Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA) and Wide-angle X-ray diffraction (WAXD) were used to analyze the thermal and crystal properties of PTT and its copolymers. The rheological properties of PTT and its copolymers were detected by capillary rheometer; these can provide basic data for spinning of PTTI-PEG.DSC showed that the melting temperature of PTTI decreased and the crystal temperature increased with the amount of IPA increased, as well as the crystallinity of PTTI decreased. There was no crystallinity when the molar ratio of IPA to TPA exceeded 30/70. In order to improve the crystallinity, PEG units were imported to PTTI at the polycondensation stage. DSC and WAXD showed that PEG can improve the crystallinity. The non-isothermal crystallization behaviors of PTT, PTTI and PTTI-PEG were analyzed by the modified Avrami equation, the Avrami exponents n of PTT and PTTI were approximately from 4 to 5, and it was assumed that the nonisothermal crystallization mechanism for PTT and PTTI was the combination of homogenous and heterogeneous nucleation. The crystallization mechanism may be greatly affected by impurity. The average Avrami exponent n of PTTI-PEG was 2.26, and it was assumed that the crystallization mechanism was heterogeneous nucleation because PEG units could induce crystallization in spite of destroying the regularity of the chain segment after the introduction of IPA, resulting in the imperfect crystallite morphology. The activation energy of PTTI-PEG was high, suggesting that the crystallization rate was more sensitive to the temperature. Therefore, it was of great importance to control the temperature in spinning process.The rheological properties of PTT, PTTI and PTTI-PEG were good through the rheological analysis. The shearing viscosity of PTT, PTTI and PTTI-PEG decreased with the shear rate increasing, exhibiting shear thinning behavior, which suggested that they belonged to typical pseudoplastic fluids. Moreover, the non-newtonian indexes gradually increased close to 1 with the test temperature increased. The flow activation energy of PTTI-PEG at low shear rate was higher than at high shear rate, demonstrating that the shearing viscosity at low shear rate was more sensitive to the temperature than at high shear rate. The flow curves of PTTI-PEG were similar as PET and PTT's, suggesting that the spinnability of PTTI-PEG was good.