Study On Direct Defoaming Technology And Equipment Of In-situ Bubble Stretching (ISBS) Method

With the flourishing development of nano-composites, more and more scientific research focuses on this field. Due to their low surface energy, small particle size and thermodynamic instability, nano-particles usually aggregate during preparation, storing and application process, and then they lose their functions. So the dispersion of nano-particles in nano-size is crucial in the preparation of polymer-based nano-composites. In order to resolve the aggregation of nano-particles in polymers, many methods such as oscillator field, ultrasonic, etc. have been attempted. For nano-materials with bedded structure like montmorillonite, in-situ intercalation polymerization was used, and other methods were also reported such as sol-gel process, organic/inorganic composite membrane, etc. which have showed their limitations during their applications. For instance, oscillator field and ultrasonic method have many inconveniences when exerted on the object, and they also showed low efficiency. In-situ intercalation polymerization only functions for nano-materials with bedded structure. In order to solve the dipersion problem of nano-particles in polymers, professor Wu Daming put forward a method of ISBS to realize a better dipersion. The results showed that, better dipersion was achieved by ISBS method, but the properties declined because of the existence of bubbles, so it is necessary to do defoaming treatment to nano-composites, in order to avoid aggregation of nano-particles in polymers. The current defoaming process is mainly through windblast crush, twin screw extruder, and injection machine. This paper studied direct defoaming method using twin screw extruder. The foamed polymer melt from single screw extruder was directly leaded into the twin screw extruder to defoam without a mesh cooling process. The process above avoided energy cost during the cooling and reheating process which would cause adverse effects on polymer properties, and it also reduced processing steps, simplified the production techniques and finally improved the production efficiency.In this paper, tandem defoaming technology and equipment for direct defoaming was introduced and applied. It was studied whether the re-aggregation of nano-particles would occur after the direct defoaming. Electron microscope and mechanical properties were tested. Conclusions are as follows:1. Using tandem defoaming technology and equipment to defoam is feasible. Good product can be abtained under the conditions that:the nose pressure of twin-screw extruder is about 25bar, and rotate speed 180-200rpm.2. Tandem defoaming technology is tested to be feasible through the comparasion and calculation of distributions of nano-powders using electron microscope. After two-stage defoaming and injection molding of nanocomposites prepared by ISBS method, nano-particles don't re-agglomerate.3. Notched impact strength of PPR/nano-CaCO3 composites increases with the addition of inorganic particles. The addition of nano-CaCO3 has a limitation. When it is in a certain value, the impact strength reaches the maximum value and when above, the impact strength will decrease. In this paper,20phr of addition is the best.4. Whether the nano-powders will re-aggregate relies on the additive amount. Re-aggregation rate will rise if it is above a certain value because it has exceeded the critical value of inorganic particle to re-aggregate.