Polyvinyl Chloride

Details

Material hierarchy: Polymer - Thermoplastic - Vinyl Plastic

Polyvinylchloride (PVC) is a widely used plastic whose properties can be varied by combining additives with the polymer. In particular, plasticizers are used to achieve thermoplastics ranging from rigid PVC (no plasticizers) to flexible PVC (high proportions of plasticizer). The range of properties makes PVC a versatile polymer, with applications that include rigid pipe (used in construction, water and sewer systems, irrigation), fittings, wire and cable insulation, film, sheets, food packaging, flooring, and toys. PVC by itself is relatively unstable to heat and light, and stabilizers must be added to improve its resistance to these environmental conditions. Care must be taken in production and handling of the vinyl chloride monomer used to polymerize PVC, due to its carcinogenic nature.

Polyvinyl Chloride is abbreviated PVC. Polyvinyl chloride is one of the world's most widely used plastics. Its acceptance comes from the polymer's versatility; it can be utilized in rigid compounds or blended with plasticizers to produce flexible grades.

Most PVC is made via suspension polymerization. A small amount is made by mass polymerization, and plastisols and organosols are produced by the emulsion processs.

Rigid PVC compounds normally contain resin, a heat stabilizer, and an impact modifier such as ABS or chlorinated polyethylene. Powder compounds are made by combining the ingredients in a high-intensity mixer. Pelletized compounds are made on twin-screw extrusion lines.

Flexible PVC compounds contain plasticizers to soften the resin. These additives are high-voiling solvents for PVC such as dioctyl phthalate (DOP) and didecyl phthalate (DDP). The plasticizers also act as processing aids.

Because it degrades relatively easily and because the degradation products are corrosive, the processing of PVC requires special care. Machinery surfaces that come in contact with the polymer should be corrosion-resistant (e.g., chrome-plated). Flow paths should be as smooth as possible with no "dead areas" where material can collect and degrade. With proper precautions, rigid PVC can be processed as easily as other thermoplastics.

PVC resin is self-extinguishing. In a fire, however, it produces hydrochloric acid and other toxic and corrosive chemicals. It can be burned in a properly designed incinerator without releasing any of these chemicals into the atmosphere.

A chief limitation of PVC is its heat resistance. Its heat distortion temperature is only about 160°F at 264 psi. Allying with ABS and other polymers can improve PVC's performance at higher temperatures.

Polyvinyl chloride (PVC) is a strong, durable plastics material. It mixes easily with lubricants, fillers, and colorings to make plastics with many different properties. There are two basic types of PVC plastics--rigid and flexible. Products made of rigid PVC plastic include bottles, pipes, siding, and window sashes. Flexible PVC plastic products include rainwear, shower curtains, garden hoses, and electrical insulation.

PVC is a synthetic polymer. A polymer is a long, chainlike molecule. The "links" are repeating patterns of simple groups of atoms called monomers. PVC is made from vinyl chloride monomers, each consisting of two carbon atoms, three hydrogen atoms, and one chlorine atom. PVC is a thermoplastic--that is, it softens and melts at high temperatures.

The most common method of making PVC is suspension polymerization. In this process, vinyl chloride monomer--a gas--is fed into water under pressure. There, the monomers link up to form the polymer.

Manufacturers make PVC plastic products by extrusion (pushing melted plastic through an opening), injection molding (forcing it into a mold), and calendering (pressing it between rollers to form sheets).

Vinyl chloride can also form many copolymers, polymers made up of more than one monomer. The most important of these contains vinyl chloride and vinyl acetate. This copolymer is used for floor tiles.

Because PVC plastics contain many ingredients, they are difficult to recycle. However, recyclers commonly grind them into powders that are used as fillers.

The first PVC became available in the late 1920's. Production accelerated during World War II (1939-1945), when PVC was used in synthetic rubber and in insulation for electric wires and cables.

PVC Type I and II are amorphous thermoplastics, and have continuous use temperature range of -4°$ (-20°C) to 140°F (60°C). It's difficulty to machine is low. It has high impact resistance, high stiffness, and good chemical resistance. It provides excellent electrical insulation. Type II PVC can be used for colder applications.


ProsCons
  • Very versatile, can be utilized in rigid compounds or blended with plasticizers to produce flexible grades
  • degrades relatively easily and the degradation products are corrosive. In a fire, however, it produces hydrochloric acid and other toxic and corrosive chemicals.
  • Its heat distortion temperature is only about 160°F at 264 psi.


Common Applications

Almost three-quarters of the rigid PVC produced goes into building and construction applications. Most is processed via extrusion into products such: Packaging is another major market for PVC. Rigid grades are blown into bottles and made into sheet for thermoforming boxes and blister packs. Flexible compounds are made into food wrap. Other markets for PVC include: PVC dispersion resins in the form of plastisols and organosols are processed by spray and dip coating, casting, and slush molding. The resin is fused by heat, and the solvents are removed. Applications include: