ppt
1-Introduction Polymers are blended with their compounding ingredients in extruders. The blending of basic components such as antioxidants and light stabilisers is done either during the last stages of the polymerisation process or soon after in an extrusion step which is followed by granulation. In fact most if not all plastic granules sold in bags, have been subjected to the effects of heat as well as shear, once after their production and another time at the compounders who produce special grades and colours. Compounding extruders are classified in single screw and twin screw extruders. The mixing effect of single screw extruders relies on the shear generated between the walls of the barrel and the screw. The shear mixing of twin screw extruders is more efficient and as a result the polymer is subjected to less thermal history.
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