Polymer In The Finite Volume Element In The Isothermal Crystallization Kinetics Study

In this paper, the course of isothermal crystallization kinetics of polymer in limited volume unit is simulated by use of the method of Monte Carlo. Four factors influenting on the course of polymer in the limited volume unite isothermal crystallization are analyzed under the given conditions. The four factors are sample volume shrinkage, the change of the linear growth rate of entities G, the change of sample thickness and the change of the number of nuclei. Then the validity of Avrami equation and Price equation is evaluated. And the quantitative data are obtained that the four factors influent on the parameters of polymer crystallization kinetics. Moreover, the turning point that isn't yet reported by relative literature before is found in the earlier stage of crystallization when the sample thickness reduce to the desired value. Some conclusions from simulating experiments are validated though the experiments of the hot stage polarizing microscopy(HSPOM) and differential scanning calorimetry(DSC).Firstly, the computer simulating model of the limited volume unit is established. Then PET is chosen as sample. Generally, under predetermined nucleation condition, the course of PET isothermally crystallized at 170 C in limited volume unit is simulated. It is shown that the value of the Avrami exponent n decreases because of the limited volume. Volume shrinkage of sample results in the increasing of the value of the crystallization rate vc and the decreasing the values of the Avrami exponent n in the primary crystallization and s, defined as the relative crystallinity degree when experiment data deviate theoretical predicting straight line. Compared with the Avrami equation, the Price equation hardly makes progress on describing the behavior of polymer later stage crystallization. When the linear growth rate of entities G reduces, the value of vc reduces too. However, the values of Avrami exponent and s are hardly affected by the value of G. The conclusions are approved by the data fromHSPOM experiment. The sample thickness declining, provided the number of nuclei per unit volume fix, the value of the Avrami exponent n falls, but the values of vc and s almost don't change. When the value of thickness reduce to the average diameter of entities, the turning point turn up after the course of crystallization has begun soon. The conclusion is testified by the DSC experiment. In the experiment of the number of nuclei change, there are two nucleation conditions considered. Under predetermined nucleation condition, with the number of nuclei decreasing, the values n and vc drop and the value of s ascends. When being sporadic nucleation condition, four cases are considered that the number of nuclei increase with time by different ways. In every case, if the initial number of nuclei go up, the value of the Avrami exponent n goes down approximately from 4 to 3, on the contrary, the value of vc moves up. The different ways of the number of nuclei increasing with time vary the influence extent of the value of s. And the exponential growth of the number of nuclei has sharper effect on the course of crystallization than the linear growth of its.