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Plastic processing

Plastics are polymers formed through polymerization reactions that join small organic molecules into long chains. Monomers are the basic building blocks that undergo polymerization to create polymers. There are two main types of polymerization: addition polymerization and condensation polymerization. Addition polymerization involves breaking carbon double bonds in monomers to form chains, producing thermoplastics. Condensation polymerization reacts two different organic molecules to form plastic molecules and byproducts. A variety of additives can be mixed with plastics to modify properties, improve performance, or reduce costs.

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 Plastics(polymers) are formed when small organic molecules are stitched together to form a long chain. This process is called polymerization.  Those organic molecules suitable for polymerization are called monomers.  A monomer is the single building block used in creating the polymer.  It is necessary for a monomer to be at least bifunctional(capable of forming two covalent bond) to polymerize.  Some monomers are polyfunctional, capable of forming three or more bonds. These can form three-dimensional arrangements of chain called a network.
polymerization is generally of two types:  Addition polymerization  Condensation polymerization  It consists of breaking the double carbon bond (C=C) in bifunctional polymers so that the chain can be formed.  Addition polymerization to produce thermoplastic materials. Some plastic materials made by AP- I. Poly- styrene(CH2=CH-C6H5) II. Poly -vinyl chloride(CH2=CHCl) III. Ploy- propylene(CH3CH=CH2) IV. Poly-methyle methacrylate(CH2=CC3O2H4) V. Poly-vinyl acetate(CH3COOCH=CH2) VI. Poly-ethylene(CH2=CH2)
Conti…..  In this polymerization, two different organic molecules react to form a plastic molecules. The reaction generally results in the separation of a small molecules such as H2O as a by-product.  Typical plastic materials formed by CP: I. Poly-epoxy(araldite) II. Poly-phenol formaldehyde(Bakelite) III. Polyamide(Nylon) IV. Poly-urathane
A no. of additives are normally used with plastic materials to modify their behaviour, improve properties or reduce the overall cost thereby increasing the range of application of plastic. Examples:  Plasticizers: these are mixed with plastic to improve their flow characteristics & decrease their brittleness.  Fillers: these are inexpensive materials that are added to plastic to reduce their cost.  Flame retardants: these are added to plastic to reduce the flammability of plastic by preventing oxygen reaction & charring.  Reinforcing agent: these are the materials that are specifically added to plastic materials to raise their mechanical properties.  Stabilizers: are used to stabilize the properties of the plastic throughout its useful life  Colourants: are used to give colour to the plastics.
Polyethylene polyamides phenolics silicones Polypropylene acetals unsaturated polyester urethanes Polystyrene,PVC cellulosics ureas melamines Polymeric materials plastics elastomers thermoplastic thermosetting Commodity plastics Engineering plastics Commodity plastic Engineering plastics
1. It is the process of confining the material in a closed cavity and then allowing it to flow from only one opening so that the metal will take the shape of the opening. The operation is identical to the squeezing of toothpaste out of a toothpaste tube. 2. Extrusion can be used to process most thermoplastics. 3. It is possible to combine a variety of resins to gain special physical, biological or chemical properties.
 Injection moulding is similar to pressure die casting.  In this process, plastic material in a highly softened state is forced to flow at high pressure through a nozzle into the mould cavity, the plastic solidifies in the die and then is ejected by opening the die.  Injection moulding pressure usually ranges from 70MPa to 200MPa. .
Plastic processing