Polyvinyl Chloride (PVC): Preparation, Properties and Uses

Preparation of Polyvinyl Chloride (PVC)

PVC is synthesized by the polymerization of vinyl chloride monomer (VCM). The monomer is derived from chlorine and ethylene.

Steps in the Manufacturing Process:

1. Production of Vinyl Chloride Monomer (VCM):
   • Ethylene (C₂H₄) is chlorinated to form ethylene dichloride (EDC).
   • EDC is cracked at high temperature (500°C) to produce VCM and HCl.
2. Polymerization Methods:
   • Suspension Polymerization (Most Common): VCM droplets are suspended in water with initiators (e.g., peroxides) and stabilizers. Produces ~80% of global PVC.
   • Emulsion Polymerization: VCM is emulsified in water with surfactants; yields fine PVC particles used in pastes.
   • Bulk Polymerization: Conducted in absence of solvent or water; used for high-purity PVC.

Key Reaction:
n CH₂=CHCl → [-CH₂-CHCl-]_n

Properties of Polyvinyl Chloride (PVC)

Physical Properties:

Property	Value/Description
Density	1.3–1.45 g/cm³
Melting Point	100–260°C (depending on plasticizers)
Appearance	White, brittle solid (rigid); flexible when plasticized
Solubility	Insoluble in water; soluble in ketones, esters

Chemical & Mechanical Properties:

• High Chemical Resilience: Inherently highly resistant to corrosive acids, alkalis, inorganic salts, and alcohols.
• Flame Retardancy: The structural chlorine content provides exceptional natural flame resistance (self-extinguishing properties).
• Dielectric Strength: Functions as an excellent high-voltage electrical insulator.
• Thermal Vulnerability: Possesses relatively poor thermal stability; degrades rapidly above 140°C while off-gassing toxic HCl fumes.
• UV Degradation: Susceptible to photo-degradation unless formulated with stabilizing chemical UV absorbers.

Commercial Formulations:
• Rigid PVC (uPVC): Unplasticized, high-strength polymer primarily utilized for infrastructure plumbing and architectural profiles.
• Flexible PVC: Heavily modified with plasticizers (such as phthalates) to provide extreme flexibility for wire jackets and medical films.

Uses of Polyvinyl Chloride (PVC)

Major Applications:

• Construction (50% of PVC use):
  • Pipes and fittings (water supply, drainage)
  • Window frames, doors, roofing membranes
  • Flooring, wall coverings
• Electrical & Electronics:
  • Cable insulation and sheathing
  • Wire coatings
• Packaging:
  • Blister packs, cling films
  • Bottles (non-food), containers
• Healthcare:
  • Blood bags, tubing, IV bags (flexible, sterile-grade PVC)
  • Medical gloves, masks
• Automotive:
  • Interior trim, underbody coating
  • Seals, dashboards
• Consumer Goods:
  • Credit cards, inflatable products
  • Raincoats, footwear, garden hoses

Macro Statistics: Global production hovers around 40 million metric tons annually, retaining its position as the world's 3rd most widely manufactured synthetic plastic polymer.

References: IUPAC, PlasticsEurope, Industrial Polymer Chemistry