Paper Topic:

Polymer Processing

Polymer Processing

The modern chemical industry produces a wide range of synthetic materials , many of which are applied in construction . The most important products are the polymers and polymer composites . A polymer is a very large molecule comprising hundreds or thousands of atoms . The polymer concept emerged in the 1920s , and since then the number of polymers has increased spectacularly . There are three large groups : thermoplastics thermosets and elastomers . Thermoplastics and thermosets together form the plastics group (Mauskopf 76 . The most widely used thermoplastics are : polyvinyl chloride (PVC , polyethylene (PE , polypropylene

(PP ) and polystyrene (PS . They melt on heating and may be processed by a variety of techniques such as moulding (e .g . injection moulding , calandering extrusion , and thermoforming all these processes usually involve heating . Thermosets , or thermosetting resins , include alkyds , amino and phenolic resins , epoxies and polyurethane (PU . The beginning of commercial production of some polymers and their two predecessors occurred as follows natural rubber , UK /USA , 1839 cellulose nitrate , USA , 1870 polystyrene , Germany , 1930 polyvinyl chloride , Germany /USA , 1933 polyurethane , Germany , 1943 epoxy , USA , 1947

As the name implies , polymer composites are made from two or more components . One of these may be an additive or fibre , and foaming agents , which are used to process foamed polymers , are frequently used Fibres can be made from glass , carbon or a polymer such as aramid (Kevlar . In fibre-reinforced polymer composites , the fibres are embedded in some form of plastic , termed a matrix (Mauskopf 45 Polymethylmethacrylate and polycarbonate are used to produce organic glass . PU and PS are much used in heat insulating materials or as components thereof . These are just some of the basic examples of the manifold uses of polymers

Plastics and the composites manufactured from them have low moduli of elasticity . The required rigidity of a structure must therefore be derived from the shape rather than from the material . Shapes with high rigidity are three-dimensional surface structures such as domes , shells or folded plates . To achieve or increase rigidity , fibre-reinforced sheets in appropriate forms are used , e .g . by troughing , ribbing , or supporting the sheet in a sandwich structure . Corrugated sheets are rigid in one direction but not in the other . In sandwich panels , the polymer foam constitutes the core the two faces may be metal sheets or some form of hardboard . The use of a soft cover layer such as is also possible . The most productive technology for making sandwich panels is continuous manufacture . The two cover faces are produced from coated steel or aluminium sheet coils , which are corrugated with rollers . The foam is produced , equally continuously , between the two metal faces of the future sandwich panels . Following heat treatment and a hardening of the foam , the three-layer sandwich is cut to its definitive length . Such sandwich panels are used for both external walls and roofs

Fabrics made from glass and /or synthetic fibres , saturated and coated and plastic membranes are relatively new building materials . Their two main uses are in roofing and soil mechanics...

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