Orientation Of Polymer Crystallization Kinetics Parameters Of The Analytical Method Of Study

In this paper, the kinetics of non-isothermal crystallization of oriented polymer was investigated by using DSC method with a constant heating rate. A kinetic model was established to describe the crystallization process of oriented polymer. A crystallization kinetic equation was proposed to match this model. Novel methods were put forward to obtain the kinetic parameters of crystallization from DSC heating curve and used to analyse the kinetics of crystallization of oriented PET fibers. The results indicated that more kinetic parameters can be obtained by using the new methods. Compared with the other methods, the theoretical curves calculated from the new methods show a good agreement with the experimental data.First, the PET as-spin fibers were used to prepare the oriented PET fibers with different orientation.. The tests of non-isothermal crystallization kinetics of the PET as-spun fibers and oriented PET fibers under fixed length and relaxed conditions were carried out by the means of differential scanning calorimetry(DSC) .Compared with PET as-spin fibers, the cold crystallization peaks move towards the lower temperatures and become very dispersive in the DSC curves of oriented PET fibers. Enlarging the crystallization peaks we found the dispersive DSC curves are made up of several overlapping peaks. The existence of overlapping peaks in the oriented PET fibers was also confirmed by the isothermal DSC method. So a kinetic model describing the crystallization process of oriented polymer was established and a kinetic equation matching the model was proposed. Two new methods obtaining the kinetic parameters of crystallization from DSC heating curve were put forward. They involved decomposing the overlapping peaks and fitting whole curve. The new methods were used to investigate the kinetics of crystallization of oriented PET fibers. The results showed that more kinetic parameters can be obtained by using either of the two methods. It was also found that the parameters are more reliable with the combination of the two methods.. Compared with the methods in the literature, the combined method proposed by us are preferable.In this paper the crystallization kinetics of oriented PET fibers were analyzed by using a model that involved three different crystallization processes. The results showed that compared with the amorphous PET fiber, the rate constant of crystallization of oriented PET fibers increase quickly in the lower temperatures and decreased in thehigher temperatures. It was speculated that owing to drawing , the order of segments improve and the amount of primary nucleation increase , so crystallization rate constant increase substantially in the lower crystallization temperatures. The decrease of rate constant of crystallization in the higher temperatures is related to the less amount of the amorphous portion in the oriented PET fibers. The first two processes provide Avrami exponents of 1~2 and the last process display Avrami exponents of 3~4. From the Avrami exponent values, we speculated that in the lower crystallization temperatures, the crystal morphology may be rod with predetermined nucleation and sporadic nucleation respectively. In the higher crystallization temperatures, the crystal morphology may be the incomplete spherulite. The crystallization process of oriented PET fibers is also related to the state of samples in the DSC pan.