Research On The Crystallization Of The Surface Modified PEO Particles

The improved Wurster equipment was designed on the base of the principle of the Wuester equipment. On this equipment, the polyethylene glycol (PEO) particles were modified by the method of fluidized coating. PEO particles were used as the core and the Ethyl Cellulose (EC) as the surface. We researched the crystallization of the different molar mass PEO particles, including the isothermal crystallization and non-isothermal crystallization of the PEO particles. We try to probe into a new equation that is suitable for the cooling process of the non-isothermal crystallization.The result shows that the improved Wurster equipment is quite suitable for making the surface modified PEO particles. The content and the thickness of the surface modified PEO' wall can be obtained by using the melting heat or the crystallization heat analysis in case that the surface materials is no heat effect in the temperature range of phase change of the PEO particels. The thickness obtained from the of phase change is consistent with the one obtained from the optical microscope. The crystallization of the surface modified PEO particles ends in case that the fronts of the spherulites in the surface modified PEO particles arrive the wall until the spherulities filled the confined volume. But the fronts of the spherulites in original PEO particles are likely to reach inside of adjacent PEO particles owing to conglutination PEO particles after melted. The half times of the crystallization and the fastest time of the crystallization of the surface modified PEO particles are shorter than those of the original PEO particles. The crystallization peak position of the surface modified PEO particles shifts to higher temperature in case that the PEO particles' diameter is less than 400μm.The t_1/2 of the PEO particles crystallization was longer as the isothermal temperature increased; The t_1/2. of the PEO particles crystallization is larger with the molar mass of the PEO increasing. The sporadic nucleation brings on two crystallization peaks appear in the DSC curves.Under the non-isothermal crystallization process, the t_1/2 of the PEO particles were shorter as the cooling rate increasing, the heat of the crystallization increases. The Avrami exponent n is close to 3 which is independent the cooling rates. By contrasting the surface modified PEO particles to the orignal PEO particles, the speed constant of the crystallization of the surface modified PEO particles was smaller in the first stage of crystallization, but larger later.The differential equation for non-isothermal crystallization which was obtained byconsidering the K(T) as the Gaussian equation can analysis the cooling non-isothermal crystallization quite well in case that the Avrami exponent n was confirmed.