Feature

Mixing Technology for High Performance Polymer Compounds

Posted on 02 February, 2010 | Tags: Plastics Processing

Knowledge towards replacing conventional plastics with biodegradable plastics is getting impetus. The key to produce good quality bio-plastics involves integration of technology within the process to ensure total homogeneity of compounding resin for desired results.

 

Plastics have become an important part of the modern life and are used in different sectors of applications like packaging, building materials etc.  Though plastics are most often used as carry bags, but disposal of these plastics poses serious threats to the environment. This problem is very acute in developing countries where the economic growth as well as urbanization is taking place at a rapid pace, such as India.
 Right from the disposal, conventional plastics create major problems for the environment when littered around e g careless disposal of plastic bags results in clogging of drains, blockage in the porosity of soil and problems for ground water recharge. Presence of plastics in soil disturbs microbial activity.  When dropped in water, plastics float on the surface and block the way of oxygen into water. This leads to decrease in volume of dissolved oxygen in water, which can result in endangering marine life.
Dioxins are highly toxic products obtained while the plastics are manufactured. When plastics are burned, Polychlorinated Byphenyls (PCB) is emitted, which are extremely hazardous in nature. Plastics always creat setbacks for environment. The alternative ways of manufacturing plastics using environment friendly products are imminent to curb the harmful effect on the environment.

Bio Plastics
Bio-plastics are biodegradable plastics with components derived from renewable raw materials like abundant agricultural or animal resources, such as cellulose, starch, collagen, casein, soy protein, polyesters and triglycerides. Use of these sources on a large scale will eventually help reduce consumption of non-renewable sources like petroleum, natural gas and coal and simultaneously contribute towards waste management. When exposed to sun and air over a period of time, these plastics degrade without causing any harm to the environment.
Though there has been an increase in demand of bio-plastics but acceptance of biodegradable polymers will depend on various factors: 

• Consumer's response to cost
• Possible legislation by Government
• Achievement of total biodegradability

Bio-plastic composite polymers resin compound are produced by proprietary technology. High performance engineered polymers compounding process demands good mixing technology that involves powder compound homogeneous mixing with uniform sticky liquid binder coating for further extrusion process to get consistent pellet quality, which in turn goes through the blow up process to get desired shape of bio-degradable bags and other consumable industrial package. 

Compound Mixing Critical for Desired Product Quality
Toshniwal Mixer has proven performance to meet bio-degradable plastics resin compound mixing process.
Construction: The mixer is horizontal with two counter-rotating shafts with welded paddles that lift the material in the centre of the mixer in weightless whirls, which ensures a high level of homogeneity.
Optimal Mixing takes place in Weightless Zone Condition. The weightless zone ensures low friction between the particles resulting in gentle mixing of the product, which in turn safeguards even the most fragile particle from being crushed. As a result wear and tear on the mixer and paddles are comparatively low.  Mixing process ensures total homogeneity irrespective of size, shape and density of the particles in short time.
Mixers offered by Toshniwal to process resins are very effective in carrying out plastic resin compound mixing process. The mixers offer various advantages as the process of mixing is carried out gently that results in maintaining total homogeneity in the final product. In addition process has high production capacity with reduced mixing time. As a result the process is completed in lesser time and significant reduction can be  observed in operating cost.

Spraying and Coating
Adding a Sticky liquid such as oil/ binder etc helps bind fine particles to coarser particles. This reduces the chance of segregation and thus results in better finished mixed quality and it becomes ideally much more homogenous mixture.
Spray atomization is used for addition of sticky liquid. Most effective spray can be achieved by heating the liquid without deteriorating the quality in order to increase its flow ability and ease of atomization. Otherwise diluting the liquid with water or suitable solvent media also results in achieving desired spray parameter. Better atomization results in better absorption or coating of the liquid into powder homogeneous mixing and less build up on mixer parts.
Mixing technique of the equipment eliminates the direct spray by means of creating stream of material and also contributes towards dispersion of liquid and smaller particles in the mixture.
Best way to apply sticky liquids in the mixer in order to limit the amount of built up on parts of mixer is illustrated in Fig 1. By adopting this approach, it is possible to use the stream of particles rebounding from the flow distortion bar (FDB) to shield the paddle system from the direct spray.  This gets the sticky liquid into the mixing material before it comes in contact with mixer parts.  The particles of powder mix are surrounded by the sticky liquid droplets in such a way that the risk of covering the bottom and the sides of the mixer gets greatly reduced.

Mixing Theory
There is a theory in mixing called 'Levy flight' that consists of convection, diffusion, ie consists of relatively long movement of particles, whereas the particles get very intimately mixed followed by new long movements of particle and so on. This is to avoid any operational problems while the mixer is filled with two materials of different type in each end of mixer. Convection and diffusion together are extremely important to achieve desired homogeneity in the product. As only for diffusion without convection, the process would take a very long time to achieve total homogeneity of the mixture.
On the other hand, if we are going to rely only on the convection and diffusion is not a part of the process, there will be a need to cut through the mixture and move particles all the time, which will also be a very time consuming and impractical before the mixture gets homogenized.
Thus it is important that mixer uses combination of convection and diffusion in the process to achieve desired results in reasonable time. The mixer can operate in weightless conditions so that there is no segregation of ready mixed material and results can be achieved in extremely short period with high degree of precision.

Article Courtesy: Toshniwal Systems & Instruments Pvt Ltd
Email : mixer@toshniwal.net