Basic Forms of PVC
Polyvinyl Chloride is widely available in two broad categories: Flexible and Rigid. But there are more types like CPVC, PVC-O and PVC-M.
Plasticized or Flexible PVC (Density: 1.1-1.35 g/cm3): Flexible PVC is formed by the addition of compatible plasticizers to PVC which lower the crystallinity. These plasticizers act like lubricants resulting in a much clearer and flexible plastic. This type of PVC is sometimes called as PVC-P.
Unplasticized or Rigid PVC (Density: 1.3-1.45 g/cm3): Rigid PVC is a stiff and cost-effective plastic with high resistance to impact, water, weather, chemicals and corrosive environments. This type of PVC is also known as UPVC, PVC-U or uPVC.
Chlorinated Polyvinyl Chloride or perchlorovinyl: It is prepared by chlorination of PVC resin. High chlorine content imparts high durability, chemical stability and flame retardancy. CPVC can withstand a wider range of temperatures.
Molecular Oriented PVC or PVC-O: It is formed by reorganizing the amorphous structure of PVC-U into a layered structured. Bi-axially oriented PVC has enhanced physical characteristics (stiffness, fatigue resistance, lightweight, etc.).
Modified PVC or PVC-M: It is an alloy of PVC formed by addition of modifying agents, resulting in enhanced toughness and impact properties.
Key Facts About Rigid and Flexible PVC
Rigid PVC
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Strength:
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Low cost & high stiffness
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Intrinsic flame retardant
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FDA compliant & also suitable for transparent applications
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Better chemical resistance than plasticized PVC
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Good electrical insulation & vapor barrier properties
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Good dimensional stability at room temperature
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Limitations:
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Difficult to melt process
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Limited solvent stress cracking resistance
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Becomes brittle at 5°C (when not modified with impact modifiers and/or processing aids)
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Low continuous service temperature of 50°C
Flexible PVC
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Strength:
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Low cost, flexible & high impact strength
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Good resistance to UV, acids, alkalis, oils and many corrosive inorganic chemicals
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Good electrical insulation properties
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Non-flammable & versatile performance profile
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Easier to process than rigid PVC
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Limitations:
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Properties can change with time, due to plasticizer migration
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Attacked by ketones; some grades swollen or attacked by chlorinated and aromatic
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hydrocarbons, esters, some aromatic ethers and amines, and nitro- compounds
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Tends to degrade at high temperatures
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Non-suitable for food contact with some plasticizers
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Lower chemical resistance than rigid PVC