Study On Preparation Of BaSO₄ Submicro-particles And Core-shell Polycarbonate/BaSO₄ Submicron Composite Particles By Solventing-out Process

Generally, micronization is mostly carried out in industrial production by two common techniques, recrystallization and comminution. However, these two methods have some drawbacks such as large particle size with wide size distribution, high thermal and mechanical stress, environmental pollution problems and so on. Therefore, it is desirable to explore alternative methods, which at least partially overcome these problems. Solventing-out crystallization is widely used for isolation and purification in the traditional industries, especially in the field of organic compound. Nevertheless, there is little research on the preparation of submicron polymer particles by solventing-out crystallization.Antisolvent crystallization is gaining more and more attention . The technique which is often called 'extractive', 'solventing-out', or 'salting-out' crystallization is an interesting energy-saving alternative for evaporative crystallization, provided that the antisolvent can be separated at low (energy) costs. The aim of this work is to find a simple, suitable and commercially viable process that needs to be low cost and involve both continuous operation and a high production rate to prepare ultrafine polymer particles or nano-particles.The system of solventing-out crystallization is made up of three parts such as target component, main solvent and antisolvent. The solventing-out crystallization is based on the remarkable difference of target component's solubility in the main solvent and antisolvent. Adding antisolvent to the main solvent will decrease the capacity of dissolving target component, and a large fraction of the target component will be precipitated because it's solubility in the main solvent has been decreased. In a precipitation process, the appearance of a new solid phase from a solution is only possible if supersaturation conditions are established . From a thermodynamic point of view, three main properties should be considered in the selection of process conditions in order to perform a successful micronization:1. high solubility of target component in the main solvent;2. insolubility of target component in the antisolvent;3. the main solvent and antisolvent are completely miscible.The process of solventing out can be divided into two steps: dissolution process and crystallization process. The crystallization process involves two simultaneous processes: crystal nucleation and growth. During the crystallization process, new particles are created by nucleation events and the rate of nucleation plays an important role in the final characteristics of particles such as particles size, particle size distributions, etc. Thereforethe nucleation is the key step in the solventing-out crystallization, and it will effect on the conditions of crystal growth also by changing the number of nuclei and consuming the content of solute in the mother liquor. In order to prepare utralfine particles, we must keep the nucleation rate much quicker than the crystal growth rate.A micronization technique using solventing-out crystallization is described for the preparation of submicron BaSO4 particles. The submicron BaSO4 particles were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), laser diffraction-based particle size analyzer and X-ray diffraction (XRD). The product was obtained as spherical particles with mean sizes from 160-750 nm. The effects of feed method, feed concentration, feed rate, agitation intensity and crystallization temperature in the solventing-out process were investigated. A well-efficiency dispersant was selected. The experimental results indicate that lower crystallization temperature, reversed feed method, higher feed rate; controlling solution concentration to a certain extent and faster agitation rate will lead to producing smaller BaSO4 particles. Furthermore, the purity of submicron BaSO4 particles prepared by solventing-out crystallization is upon to 99.7%, and it indicates that the solventing-out crystallization is not only a micronization technique but also an...