Chlorinated polyvinyl chloride
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Chlorinated polyvinyl chloride (CPVC) is a thermoplastic produced by chlorination of polyvinyl chloride (PVC) resin. Uses include hot and cold water pipe, and industrial liquid handling.
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Production Process
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 the base PVC 56.7% to as high as 74%, although most commercial resins have 63 to 69% chlorine. As the chlorine content in CPVC is increased, its glass transition temperature (Tg) increases significantly.
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.
Physical Properties
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 (93°C) are present. The ability to bend, shape, and weld CPVC enables its use in a wide variety of process applications including tanks, scrubbers, and ventilation systems. It exhibits excellent fire resistance, chemical resistance, and is readily available in sheets, rods, and tubing.
| STRUCTURE | amorphous | |
| Density | 320 lb/ft³ | 1.56 g/cm³ |
| Water absorption rate | 0.15% | |
| Elongation | 40% | |
| Tensile strength | 8700 psi | 60 Mpa |
| Compression strength | 14,500 psi | 100 MPa |
| Flexural strength | 15,500 psi | 107 MPa |
| Flexural modulus | 435,000 psi | 3 GPa |
| Impact (IZOD) | 12 ft·lbf/in | 640 N |
| UV resistance | Poor | |
| Transparency | Clear | |
| Coefficient of expansion | 0.00004 | |
| Hardness | R110 | |
| Melting point | 175 °F | 79 °C |
Uses
CPVC is a popular engineering material due to its relatively low cost, high glass transition temperature, high heat distortion temperature, chemical inertness, and flame and smoke properties. CPVC is used in a variety of industrial applications where a high functional temperature and resistance to corrosive chemicals are desirable. Besides pipe and fittings, it is used in pumps, valves, strainers, filters, tower packing, and duct, as well as sheet for fabrication into storage tanks, fume scrubbers, large diameter duct, and tank lining.
Pipe
In use as plumbing materials, CPVC exhibits comparatively high impact and tensile strength and is non-toxic. In pressurized systems, it can be used with fluids up to 80°C and higher in low-pressure systems. It does require specialized solvent cement for assembly. Depending on local building codes, it can be used in hot and cold water systems as well as hot and cold chemical distribution systems in conditions where metal pipe is not indicated.
Comparison to Polyvinyl Chloride (PVC)
Chemical Resistance
CPVC, unlike PVC exhibits excellent resistance to acids while sharing its excellent resistance to bases. Additionally it exhibits excellent resistance to salts and aliphatic hydrocarbons. Being a non-conductive long chain polymer, CPVC is also immune to galvanic corrosion.
Since the chemical properties of resins may vary according to the amount of chlorination and the types and quantity of additives, manufacturers recommendations should be consulted before designing material handling systems using CPVC.
Heat Resistance
CPVC can withstand corrosive water at temperatures 40C to 50C greater than PVC, contributing to its popularity as a material for water piping systems in residential as well as commercial construction.
Mechanical Properties
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.
Fire Properties
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 dioxins.
