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properties & uses of PVC

Comprehensive study notes, diagrams, and exam preparation for properties & uses of PVC.

Properties & Uses of PVC (Polyvinyl Chloride)

Definition

Polyvinyl Chloride (PVC) is a widely used thermoplastic polymer synthesized by the polymerization of vinyl chloride monomer (VCM). It is the world's third-most widely produced synthetic plastic polymer, characterized by its versatility, durability, and resistance to chemical corrosion.

Main Content

1. Chemical Structure and Polymerization

  • PVC is produced through addition polymerization, where vinyl chloride molecules ($CH_2=CHCl$) link together to form a long chain.
  • The presence of the chlorine atom in the polymer chain gives PVC high polarity, which contributes to its rigidity and flame-retardant properties.
       H   Cl      H   Cl
       |   |       |   |
  --- C - C --- C - C ---
       |   |       |   |
       H   H       H   H

  (Repeating unit of PVC)

2. Physical Properties

  • PVC has high mechanical strength and hardness, making it ideal for structural applications.
  • It is naturally rigid; however, it can be made flexible by adding plasticizers (such as phthalates), leading to two distinct types: Rigid PVC (uPVC) and Flexible PVC.

3. Thermal and Chemical Resistance

  • PVC exhibits excellent resistance to acids, alkalis, and various chemicals, preventing degradation in harsh industrial environments.
  • It has low thermal conductivity and is self-extinguishing, meaning it does not easily support combustion when the source of fire is removed.

Working / Process

1. Monomer Synthesis

  • The process begins by reacting ethylene with chlorine to produce ethylene dichloride (EDC).
  • EDC is then cracked at high temperatures to produce Vinyl Chloride Monomer (VCM) gas.

2. Polymerization

  • The VCM gas is polymerized through suspension, emulsion, or bulk polymerization techniques.
  • Suspension polymerization is the most common, where VCM droplets are suspended in water with a catalyst to form PVC resin beads.

3. Compounding and Molding

  • The raw PVC resin is mixed with stabilizers, lubricants, and plasticizers to create a "compound."
  • This compound is then processed using extrusion (for pipes) or injection molding (for fittings) to form the final product.

Advantages / Applications

  • Construction Industry: Used extensively for water supply pipes, sewage systems, window frames, and electrical conduits due to its resistance to rust and weathering.
  • Medical Sector: Flexible PVC is used for blood bags, tubing, and surgical gloves because it is easy to sterilize and chemically inert.
  • Electrical Insulation: Used as a protective sheath for electrical cables because of its excellent dielectric strength and non-flammability.

Summary

Polyvinyl Chloride (PVC) is a versatile thermoplastic created from vinyl chloride monomers. It is valued for its strength, chemical resistance, and ability to be transformed from rigid structural material into flexible plastic through the addition of additives. PVC is essential in construction, medicine, and electrical industries. Important terms to remember include Vinyl Chloride Monomer (VCM), Plasticizers, Polymerization, and uPVC (unplasticized PVC).

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