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extrusion is considered as the best “net

extrusion is not considered as an extrusion part. It is just a tool to give the material a specific shape. Rotation of the twin screw can be co-rotating or counterrotating, intermeshing or nonintermeshing according to the formulation being processed. Many factor play a vital role in the process like screw rotation speed (SRS) and its length, temperature of the extrusion barrel and die, viscosity of the material. Now with the development of computer and finite element analysis, process can be well simulated to get good productivity and low residence time. There are some steps which is followed during the production of composites. First of all, polyolefin transit from solid phase to liquid phase using heater and the melted material start to move toward the die. Another material being put in the barrel from the side feeder which is then meshed by rotating screw and make the homogeneous mixture which is then being shaped by passing through die. In the final stage, product is shaped and cools down. Extrusion is generally done for the composites of polyolefin with wood or kenaf fiber. 1.1.2 Injection moulding-  Extrusion process which is oldest and successful method to produce composites is limited to the simple basic structure of the final product like pipes, cylinder sheet etc. for a complex geometry they have to use some other technique. 6 Injection moulding is the technique which overcomes these issues. It is use to produce high precession parts of composites with complex 3D structure at a very low cost. Injection moulding is considered as the best “net shape” (“net shape” is the term to produce the desirable product with only one process) manufacturing process because of its simplicity, reliability, versatility and efficiency. 7 Among all the processing method for polymers, one third of the polymers are processed by injection moulding. First of all, mixture of ingredients is heated in a barrel which is after melting forced to put in a mould under very high pressure and temperature. The above was the basic function of the injection moulding. For the production of composites by this method, improvement was done by placing a auger inside a cylinder which on rotation mix the melted material in a cylinder before pushing forward in the mould. 6, 8 Besides of many advantage of the injection moulding like complex structure production and automation it has some serious drawback like it is not preferred over short production runs due to high cost tooling, auxiliary equipment and mold. Also the product result is unpredictable from barrel to mold processing due to lack of scientific understanding. Moreover complicated behavior of polymeric materials makes it more unfavorable.9-10    Fig. 2 Design of injection moulding machine (Source: http://www.myplasticmold.com/injection-molding-process.html) 1.1.3 Calendering- Calendering is the process in which material is passed through a series of heated roller to decrease its thickness and making of thin sheets of the order of 1 mm to thin film transistor. The cost of the equipment is quite high but once the production start it works continuously. First calendaring machine was patented by Edwin Chaffee in 1833 to make various rubber based life vests.11 Most of the polyolefin composites with paper, wool, and silk or with other natural fiber to improve the surface properties are done with calendaring. For the production of composites, two or more materials are passed through a same roller which on heating make the materials melt and make the multi layered composites in the output.12  1.1.4 Pultrusion- Pultrusion is similar to extrusion with the only difference that the work piece is pulled from the die that’s why pultrusion is the combination of the words “pull” and “extrusion”. First of all in 1950s Sir Brandt Goldsworthy used pultrusion technique for the production of fishing rods of glass reinforced polymer. Before this, pultrusion was only used in particular sectors like civil-engineering for the constant cross-sectional and high tolerance. There are many significant improvements in the last 70 years and nowadays it is the most cost efficient method for the production of composites. Like extrusion it can continuously give product having constant and straight cross-sectional profile. The common example of pultrusion material is the putruted rods reinforced in the concrete during the construction of buildings.  In the process, strands or plys are pulled from a desired liquid filled bath resin which is then gathered in a particular shape and enter in a heating die. In the heating die, material gets s and gets cross linked with each other which on then come out from a die to give it a desired cross-sectional profile. After coming out from a die it is cooled down and become solid which is the cut with saw into a desired length. It is the fastest process for the production of composites and like extrusion the output profile of the product depends upon the die opening.  Pultrusion is cost-effectiveness at high productivity as well as high raw material conversion efficiency. Fiber-matrix coupling and its ratio can be adjusted according to the desired properties of the material.13-15 Besides all above technique, some other techniques are also followed such as thermoforming and compression moulding. These two techniques are generally not for synthesis but it seems more like to give the shape to the composites material. Compression machine is generally more like a press which is oriented vertically with top and bottom halves which is completely interlocked with each other. Product is placed between these two halves


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