Polyvinyl Chloride

Nov. 15, 2002
Among the vinyl polymers and copolymers, the polyvinyl-chloride (PVC) thermoplastics are the most commercially significant.

Among the vinyl polymers and copolymers, the polyvinyl-chloride (PVC) thermoplastics are the most commercially significant. With various plasticizers, fillers, stabilizers, lubricants, and impact modifiers, PVC is compounded to be flexible or rigid, opaque or transparent, to have high or low modulus, or to have any of a wide spectrum of properties or processing characteristics.

PVC resin can also be chlorinated (CPVC) and it can be alloyed with other polymers such as ABS, acrylic, polyurethane, and nitrile rubber to improve impact resistance, tear strength, resilience, heat-deflection temperature, or processibility.

PVC compounds are processed by extrusion, injection molding, calendering, compression molding, and blow molding. PVC coatings are applied by fluidized-bed and electrostatic powder-coating methods. The resins are also used for dip molding and coating, in the form of plastisols and organosol dispersions or water dispersions (latexes). Cellular PVC products are made by introducing gas into the resin during molding or extrusion. Foams can be open or closed cell, and can be elastomeric or rigid, depending on plasticizer content.

PVC compounds can be made waterwhite in flexible compounds, very clear in rigid compounds, and they can be pigmented to almost any color.

Properties: With so many property variations attainable by compounding methods, no single compound can be considered typical of polyvinyl chloride. For example, creep rate of rigid compounds is so low and predictable that they can be used to make pressure pipe for water distribution; flexible compounds can be soft enough, yet impermeable, so that they are used for baby pants and for an excellent imitation suede, or they can be transparent, nontoxic, and tough enough to be used for mineral-water bottles.

Rigid PVC, sometimes called the "poor man's engineering plastic" is a hard, tough material that can be compounded to a wide range of properties. Noteworthy among its properties is low combustibility; it has high resistance to ignition and is self-extinguishing. It also provides good corrosion and stain resistance, thermal and electrical insulation, and weatherability. However, PVC is attacked by aromatic solvents, ketones, aldehydes, naphthalenes, and some chloride, acetate, and acrylate esters. Some impact modifiers used in rigid PVC reduce chemical resistance. In general, normal-impact grades have better chemical resistance than the high-impact grades.

Most PVC compounds are not recommended for continuous use above 140°F. Chlorination increases heat-deflection temperature, flame retardancy, and density and extends the continuous-use temperature to 176 to 212°F, depending on the amount of chlorination.

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