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The polymer cannot be used in its natural state, but compounding it offers
enormous range of properties from rigid products (window frames) to flexible soft
material (sheets, pipes, hoses) and this ability of being used in either the rigid or soft
(plasticised) forms doubles the market for this exceptionally safe material. There
are more compounding recipes for PVC than for any other polymer.
PVC compounds can be extruded, injection, compression or Blow moulded or
calendared to give variety of products, either rigid or flexible depending on the
amount and type of plasticizers used.
Processing: Drying before processing is highly recommended, moisture rate
should be lower than 0.3%
PVC is sensitive to the heat and on thermal decomposition evolves HCI gas hence
suitable stabilizers are to be used during processing
For Moulding Melt temperature should lie between 170 and 210°C. Mould
temperatures of 20 to 60°C are more suitable. Mould shrinkage lie between 0.2 and
0.5%.Screw with an L/D ratio of 15 to 18 is recommended.
For Extrusion temperatures are 10-20°C below injection moulding temperatures in
order to avoid premature thermal degradation.
12) Rigid PVC:
Is strong, good combination of stiffness and impact strength, has excellent solvent
stress cracking resistance, weatherproof, flame resistant with good overall
mechanical properties, better chemical resistance than plasticized PVC, good
dimensional stability at room temperature, Low cost, good electrical insulation and
vapour barrier properties, FDA Compliant.
Density 1.35 - 1.5 g/ cm 3
Glass transition temperature 60 - 100 °C
Max / Min continuous Service temperature 50 - 80 °C / -10 - 1 °C
Limitations: Difficult to process, Low continuous service temperature of 50°C,
tends to degrade at high temperatures, Becomes brittle at 5°C (without impact
modifiers and/or processing aids), Limited solvent stress cracking resistance,
Some plasticized materials are susceptible to microbiological attack and staining,
High specific gravity for plastic material.
Applications:
• Building: Waste water pipes & fittings, grating covers, guttering, roofing sheets,
sanitary installations, window frames, fencing fascia boards.
• Electrical : Insulation pipes, panels, electricity distribution boxes, switches,
telephone and plug housings, battery terminals.
• Engineering: Pressure pipes, ventilation ducts, thermostat housings, fittings, pipe
connections, claddings, ventilators.
• Packaging: Disposable pots, Food containers, pen cases, oil and beverage
bottles.
13) Plasticised PVC:
Is easier to process than rigid PVC, Low cost, soft, flexible and transparent, good
resistance to UV, Flexible, high ratio of strength to weight, Good resistance to acids,
alkalis, oils and many corrosive inorganic chemicals, Good electrical insulation

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