Chlorinated polyvinyl chloride
|This article does not cite any references or sources. (December 2009)|
|Chlorinated polyvinyl chloride|
|Young's modulus (E)||2.9-3.4 GPa|
|Tensile strength (σt)||50-80 MPa|
|Elongation at break||20-40%|
|Notch test||2-5 kJ/m2|
|Glass temperature||106 - 115 °C|
|Melting point||395 °C|
|Vicat B||106 to 115 °C|
|Thermal conductivity (k)||0.16 W/(m·K)|
|Linear Expansion Coefficient (α)||8 x 10−5 /K|
|Specific heat (c)||0.9 kJ/(kg·K)|
|Water absorption (ASTM)||0.04-0.4|
CPVC is PVC (polyvinyl chloride) that has been chlorinated via a free radical chlorination reaction. This reaction is typically initiated by application of thermal or UV energy utilizing various approaches. In the process, chlorine gas is decomposed into free radical chlorine which is then reacted with PVC in a post-production step, essentially replacing a portion of the hydrogen in the PVC with chlorine.
Depending on the method, a varying amount of chlorine is introduced into the polymer allowing for a measured way to fine tune the final properties. The chlorine content may vary from manufacturer to manufacturer; the base can be as low as PVC 56.7% to as high as 74% by mass, although most commercial resins have chlorine content from 63% to 69%. As the chlorine content in CPVC is increased, its glass transition temperature (Tg) increases significantly. Under normal operating conditions, CPVC becomes unstable at 70% mass of chlorine.
Various additives are also introduced into the resin in order to make the material processable. These additives may consist of stabilizers, impact modifiers, pigments and lubricants.
CPVC shares most of the features and properties of PVC. It is also readily workable, including machining, welding, and forming. Because of its excellent corrosion resistance at elevated temperatures, CPVC is ideally suited for self-supporting constructions where temperatures up to 200 °F (90 °C) are present. Due to its specific composition, dealing with CPVC requires a specialized solvent cement, with high strength solvent cement variants being first introduced in 1997 by Weld-On, then followed closely by other products such as Henkel's Tangit line. The ability to bend, shape, and weld CPVC enables its use in a wide variety of processes and applications. It exhibits fire-retardant properties.
Comparison to polyvinyl chloride (PVC)
CPVC can withstand corrosive water at temperatures greater than PVC, typically 40°C to 50°C (104°F to 122°F) or higher, contributing to its popularity as a material for water piping systems in residential as well as commercial construction.
The principal mechanical difference between CPVC and PVC is that CPVC is significantly more ductile, allowing greater flexure and crush resistance. Additionally, the mechanical strength of CPVC makes it a viable candidate to replace many types of metal pipe in conditions where metal's susceptibility to corrosion limits its use.
CPVC is similar to PVC in resistance to fire. It is typically very difficult to ignite and tends to self-extinguish when not in a directly applied flame.
Due to its chlorine content, the incineration of CPVC, either in a fire or in an industrial disposal process, can result in the creation of chlorinated dioxins.