Chlorinated polyvinyl chloride

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 mass based chlorine content may vary from the base PVC 56.7% to as high as 74%, although most commercial resins have mass of chlorine from 63% to 69%. As the chlorine content in CPVC is increased, its glass transition temperature (T_g) 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 processible. 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 (90 °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.

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 as well as PVC exhibits a good resistance to acids and bases (depending on the acid/base). There are several cases, where it is useful to stay with PVC (e.g. ammonia hydrous solution, hydrofluoric acid). 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 40 °C to 50 °C (70 °F to 90 °F) 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.