Poly(ethylene terephthalate) (PET) systems containing different concentrations of sodium benzoate (SB) as crystallization promoters have been studied by small-angle light scattering (SALS). We report here that the mechanism of action of organic nucleating agents such as sodium benzoate completely differs from the generally accepted model, at least in the case of polyesters. The nucleating agent reacts as a true chemical reagent with the molten macromolecules and produces ionic end-groups which are responsible for the acceleration of the crystallization rate. This phenomenon is called "chemical nucleation". In the case of chemical nucleation, the nucleation process can be divided into a "hetrogeneous particle nucleation" performed by the unreacted salt and a "homogeneous nucleation" due to the polymer-sodium(metal) salt formed during the mixing. The morphology and the overall rate of crystallization of poly (ethylene terephthalate) were measured by means of scattering and transmission of depolarized light. The influence of crystallization temperature and concentrations of nucleating agent was investigated. Increasing crystallization temperature decreases the rate of crystallization. Efficacious nucleating agent increases the rate of crystallization occur over a wider range of crystallization temperature.
