Melt crystallization studies of poly(trimethylene terepthalate)(PTT)

The isothermal melt crystallization of poly(trimethylene terephthalate) (PTT) was investigated using differential scanning calorimetry (DSC), optical microscopy and FTIR spectroscopy. Melt crystallization was carried out inside the DSC and inside the oven and the results from both methods are compared. Difference in final crystallinity between these two methods was attributed to the rate of cooling after melt crystallization. Triple melting endotherms were dominant at Tc below 195°C while double melting endotherms were dominant at Tc above 195°C. Melting peaks from high to low were labeled as Tm1, Tm2, Tm 3, respectively. Tm2 disappeared at above Tc =190°C while melting peak, Tm3 increased in intensity with increasing Tc, Tm 3 was attributed to the melting of primary crystallites formed during melt crystallization while Tm1, T m2 were attributed to crystals formed by lamella thickening during secondary crystallization. Equilibrium melting temperature, T m0 of 238°C was obtained by plotting Tm 3 against Tc and it was in good agreement with previously reported values.; Difference in crystallinity between melt crystallized PTT films before and after cooling to room temperature was attributed to additional crystallization occurred during cooling to room temperature. Crystallization kinetics of isothermal melt crystallization of PTT was determined by DSC. The crystallization process took about 30 to 45 minutes depending on Tc for completion. The t1/2, increased with increasing Tc as expected and the average value of Avrami exponent, n, of 2.6 was obtained for the PTT melt crystallized from 190 to 205°C from the Avrami plot, suggesting spherulitic morphology with heterogeneous nucleation. Our polarized optical microscopic observation confirms the melt crystallized PTT crystallized in spherulitic morphlogy and size of the spherulites increased with increasing Tc.; Mid IR spectroscopy was used to determine the conformational changes during melt crystallization of PTT. Bands at 1577, 1173, and 976 cm -1 were assigned to the amorphous phase while the bands at bands at 933, 947 and 1358 cm-1 were attributed to crystalline phase. The presence of weak bands at 933, 947 and 1358 cm-1 in the amorphous spectrum suggested that gauche methylene conformation is also present in the amorphous phase. In the present study, we separated the crystalline and amorphous gauche conformation. It was found both crystalline and the amorphous gauche conformation increases with increasing Tc while trans conformation decreased with increasing Tc.