Polyvinyl chloride

Description

Polyvinyl chloride, commonly abbreviated PVC, is the thirdmost widely produced plastic, after polyethylene and polypropylene. PVC is used in construction because it is more effective than traditional materials such as copper, iron or wood in pipe and profile applications. It can be made softer and more flexible by the addition of plasticizers, the most widely used being phthalates. In this form, it is also used in clothing and upholstery, electrical cable insulation, inflatable products and many applications in which it replaces rubber. Pure polyvinyl chloride is a white, brittle solid. It is insoluble in alcohol, but slightly soluble in tetrahydrofuran.

Physical properties

PVC is a thermoplastic polymer. Its properties for PVC are usually categorized based on rigid and flexible PVCs.Mechanical propertiesPVC has high hardness and mechanical properties. Electrical propertiesPVC is a polymer with good insulation properties but because of its higher polar nature the electrical insulating property is inferior to non polar polymers such as poly ethylene and poly propylene.

History

PVC was accidentally discovered at least twice in the 19th century, first in 1835 by French chemist Henri Victor Regnault and then in 1872 by German chemist Eugen Baumann. The presence of chloride groups gives the polymer very different properties from the structurally related material polyethylene.

Uses

Rubber substitutes, electric wire and cable-coverings, pliable thin sheeting, film finishes for textiles, non-flammable upholstery, raincoats, tubing, belting, gaskets, shoe soles.

Definition

ChEBI: A polymer composed of repeating chloroethyl units.

General Description

Poly(vinyl chloride) [PVC] is a polymer which is mostly prepared from vinyl chloride monomer. In most cases PVC is mixed with heat stabilizers, lubricants, plasticizers, fillers, and other additives.

Hazard

Decomposes at 148C, evolving toxic fumes of hydrogen chloride. Pneumoconiosis, lower respi- ratory tract irritant, and pulmonary function effects. Questionable carcinogen.

Industrial uses

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. Plastisols are used extensively for coating glass bottles and glass fabrics. The dispersion types of resins are used in flexible molding compounds. Such formulations consist of a vinyl paste resin, a suitable plasticizer such as dioctyl phthalate, and a stabilizer (usually a compound of lead). Flexible molds are widely applied to plaster casting and encapsulation of electronic circuits with epoxy resins.

Safety Profile

Chronic inhalation of dusts can cause pulmonary damage, blood effects, abnormal liver function. “Meat wrapper’s asthma” has resulted from the cutting of PVC films with a hot knife. Can cause allergic dermatitis. Questionable carcinogen with experimental tumorigenic data. Reacts violently with F2. When heated to decomposition it emits toxic fumes of Cland phosgene.

Additives to finished polymer

The product of the polymerization process is unmodified PVC. Before PVC can be made into finished products, it always requires conversion into a compound by the incorporation of additives such as heat stabilizers, UV stabilizers, lubricants, plasticizers, processing aids, impact modifiers, thermal modifiers, fillers, flame retardants, biocides, blowing agents and smoke suppressors, and, optionally pigments.The choice of additives used for the PVC finished product is controlled by the cost performance requirements of the end use specification e.g. underground pipe, window frames, intravenous tubing and flooring all have very different ingredients to suit their performance requirements.Heat stabilizersOne of the most crucial additives are heat stabilizers. These agents minimize loss of HCl, a degradation process that starts above 70 °C. Once dehydrochlorination starts, it is autocatalytic. Many diverse agents have been used including, traditionally, derivatives of heavy metals (lead, cadmium). Increasingly, metallic soaps (metal "salts" of fatty acids) are favored, species such as calcium stearate. .

Chlorinated PVC

PVC can be usefully modified by chlorination, which increases its chlorine content to 67 %. The new material has a higher heat resistance so is primarily used for hot water pipe and fittings, but it is more expensive and it is found only in niche applications, such as certain water heaters and certain specialized clothing. An extensive market for chlorinated PVC is in pipe for use in office building, apartment and condominium fire protection. CPVC, as it is called, is produced by chlorination of aqueous solution of suspension PVC particles followed by exposure to UV light which initiates the freeradical chlorination.

Sustainability

The Olympic Delivery Authority (ODA) has chosen PVC as material for different temporary venues of the London Olympics 2012. The ODA want to ensure to meet the highest environmental and social standards for the PVC materials. E.g. temporary parts like Roofing covers of the Olympic Stadium, the Water Polo Arena and the Royal Artillery Barracks will be deconstructed and a part will be recycled in the Vinyloop process. Dan Epstein Head of Sustainable Development at Olympic Delivery Authority (ODA) The ODA after initially rejecting PVC as material has reviewed its decision and develop a policy for the use of PVC. The PVC policy has focused attention on the use of PVC across the project and highlighted that the functional properties of PVC make it the most appropriate material in certain circumstances. Environmental and social impacts across the whole life cycle played an important role, with e.g. the rate for recycling or re-use and the percentage of recycled content.