Polyvinyl chloride

+ Mechanical properties Elongation at break 20–40% Notch test 2–5 kJ/m2 Glass Transition Temperature Melting point to Effective heat of combustion 17.95 MJ/kg Specific heat (c) 0.9 kJ/(kg·K) Water absorption (ASTM) 0.04–0.4 Dielectric Breakdown Voltage 40 MV/m

Polyvinyl chloride, alternatively poly(vinyl chloride), colloquially vinyl or polyvinyl, abbreviated PVC, is the world's third-most widely produced synthetic polymer of plastic (after polyethylene and polypropylene). About 40 million tons of PVC are produced each year.

PVC comes in rigid (sometimes abbreviated as RPVC) and flexible forms. Rigid PVC is used in construction for pipes, doors, and windows. It is also used in making plastic bottles, packaging, and bank or membership cards. Adding plasticizers makes PVC softer and more flexible. It is used in plumbing, electrical cable insulation, flooring, signage, phonograph records, inflatable products, and rubber substitutes. With cotton or linen, it is used in the production of canvas.

Polyvinyl chloride is a white, brittle solid. It is soluble in ketones, chlorinated solvents, dimethylformamide, THF and DMAc.

Discovery PVC was synthesized in 1872 by German chemist Eugen Baumann after extended investigation and experimentation.Baumann, E. (1872) "Ueber einige Vinylverbindungen" (On some vinyl compounds), Annalen der Chemie und Pharmacie, 163 : 308–322. The polymer appeared as a white solid inside a flask of vinyl chloride that had been left on a shelf sheltered from sunlight for four weeks.

In the early 20th century, the Russian chemist Ivan Ostromislensky and Fritz Klatte of the German chemical company Griesheim-Elektron both attempted to use PVC in commercial products, but difficulties in processing the rigid, sometimes brittle polymer thwarted their efforts. Waldo Semon and the B.F. Goodrich Company developed a method in 1926 to plasticize PVC by blending it with various additives, including the use of dibutyl phthalate by 1933.

Production Polyvinyl chloride is produced by polymerization of the vinyl chloride monomer (VCM), as shown.

About 80% of production involves suspension polymerization. Emulsion polymerization accounts for about 12%, and bulk polymerization accounts for 8%. Suspension polymerization produces particles with average diameters of 100–180 μm, whereas emulsion polymerization gives much smaller particles of average size around 0.2 μm. VCM and water are introduced into the reactor along with a polymerization initiator and other additives. The contents of the reaction vessel are pressurized and continually mixed to maintain the suspension and ensure a uniform particle size of the PVC resin. The reaction is exothermic and thus requires cooling. As the volume is reduced during the reaction (PVC is denser than VCM), water is continually added to the mixture to maintain the suspension.

Microstructure The polymers are linear and are strong. The monomers are mainly arranged head-to-tail, meaning that chloride is located on alternating carbon centres. PVC has mainly an atactic stereochemistry, which means that the relative stereochemistry of the chloride centres are random. Some degree of syndiotacticity of the chain gives a few percent crystallinity that is influential on the properties of the material.

About 57% of the mass of PVC is chlorine. The presence of chloride groups gives the polymer very different properties from the structurally related material polyethylene.Handbook of Plastics, Elastomers, and Composites, Fourth Edition, 2002 by The McGraw-Hill, Charles A. Harper Editor-in-Chief. At 1.4 g/cm3, PVC's density is also higher than structurally related plastics such as polyethylene (0.88–0.96 g/cm3) and polymethylmethacrylate (1.18 g/cm3).

Producers About half of the world's PVC production capacity is in China, despite the closure of many Chinese PVC plants due to issues complying with environmental regulations and poor capacities of scale. The largest single producer of PVC as of 2018 is Shin-Etsu Chemical of Japan, with a global share of around 30%.

Additives

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 (but not necessarily all of the following) such as heat stabilizers, UV stabilizers, plasticizers, processing aids, impact modifiers, thermal modifiers, fillers, flame retardants, biocides, blowing agents and smoke suppressors, and, optionally, pigments.David F. Cadogan and Christopher J. Howick "Plasticizers" in Ullmann's Encyclopedia of Industrial Chemistry 2000, Wiley-VCH, Weinheim.

The choice of additives used for the PVC finished product is controlled by the cost performance requirements of the end use specification (underground pipe, window frames, intravenous tubing and flooring all have very different ingredients to suit their performance requirements). Previously, polychlorinated biphenyls (PCBs) were added to certain PVC products as flame retardants and stabilizers.

Plasticizers

Among the common plastics, PVC is unique in its acceptance of large amounts of plasticizer, yielding physical properties that range continuously from a rigid solid to a soft gel, and almost 90% of all plasticizer production is used in making flexible PVC.David F. Cadogan and Christopher J. Howick "Plasticizers" in Ullmann's Encyclopedia of Industrial Chemistry 2000, Wiley-VCH, Weinheim. The majority is used in films and cable sheathing. Flexible PVC can consist of over 85% plasticizer by mass, but unplasticized PVC (UPVC) should not contain any.

+ PVC properties as a function of phthalate plasticizer level Plasticizer content (% DINP by weight) Specific gravity (20 °C) Shore hardness (type A, 15 s) Flexural stiffness (Mpa) Tensile strength (Mpa) Elongation at break (%) Example applications Rigid 0 1.4 900 41 <15 Unplasticized PVC (UPVC): window frames and sills, doors, rigid pipe Semi-rigid 25 1.26 94 69 31 225 Vinyl flooring, flexible pipe, thin films (stretch wrap), advertising banners Flexible 33 1.22 84 12 21 295 Wire and cable insulation, flexible pipe Very Flexible 44 1.17 66 3.4 14 400 Boots and clothing, inflatables, Extremely Flexible 86 1.02 < 10 Fishing lures (soft plastic bait), polymer clay, plastisol inks

Phthalates

The most common class of plasticizers used in PVC is phthalates, which are diesters of phthalic acid. Phthalates can be categorized as high and low, depending on their molecular weight. Low phthalates such as bis(2-ethylhexyl) phthalate (DEHP) and dibutyl phthalate (DBP) have increased health risks and are generally being phased out. High-molecular-weight phthalates such as diisononyl phthalate (DINP) and diisodecyl phthalate (DIDP) are generally considered safer.

While DEHP has been medically approved for many years for use in medical devices, it was permanently banned for use in children's products in the US in 2008 by US Congress; the PVC-DEHP combination had proved to be very suitable for making blood bags because DEHP stabilizes red blood cells, minimizing hemolysis (red blood cell rupture). However, DEHP is coming under increasing pressure in Europe. The assessment of potential risks related to phthalates, and in particular the use of DEHP in PVC medical devices, was subject to scientific and policy review by the European Union authorities, and on 21 March 2010, a specific labeling requirement was introduced across the EU for all devices containing phthalates that are classified as CMR (carcinogenic, mutagenic or toxic to reproduction). The label aims to enable healthcare professionals to use this equipment safely, and, where needed, take appropriate precautionary measures for patients at risk of over-exposure.

Heat stabilizers

PVC is more thermally labile that other commodity polymers. Onset for degradation is near 250 °C whereas polyethylene is stable to 400 °C. Heat stabilizers minimize loss of HCl. Diverse agents have been used including, traditionally, derivatives of heavy metals (lead, cadmium). Metallic soaps (metal "salts" of fatty acids such as calcium stearate) are common in flexible PVC applications.

BaZn stabilisers have successfully replaced cadmium-based stabilisers in Europe in many PVC semi-rigid and flexible applications.

In Europe, particularly Belgium, there has been a commitment to eliminate the use of cadmium (previously used as a part component of heat stabilizers in window profiles) and phase out lead-based heat stabilizers (as used in pipe and profile areas) such as liquid autodiachromate and calcium polyhydrocummate by 2015. According to the final report of Vinyl 2010, cadmium was eliminated across Europe by 2007. The progressive replacement also of lead-based stabilizers gave a 75% reduction from 2000 to 2010. This was accompanied by the corresponding growth in calcium-based stabilizers as an alternative to lead-based stabilizers, also outside Europe.

Properties PVC is a thermoplastic polymer. Its properties are usually categorized based on rigid and flexible PVCs.

Property Unit of measurement Rigid PVC Flexible PVC Density. g/cm3 1.3–1.45 1.1–1.35 Thermal conductivity. W/(m·K) 0.14–0.28 0.14–0.17 Yield strength 4,500–8,700 1,450–3,600 31–60 10.0–24.8 Young's modulus. psi 490,000 — 3.4 — Flexural strength (yield) psi 10,500 — MPa 72 — Compression strength psi 9,500 — MPa 66 — Coefficient of thermal expansion (linear) mm/(mm °C) 5×10−5 — Vicat B °C 65–100 Not recommended Resistivity. m 1016 1012–1015 Surface resistivity Ω 1013–1014 1011–1012

Notes

Thermal and fire The heat stability of raw PVC is very poor, so the addition of a heat stabilizer during the process is necessary in order to ensure the product's properties. Traditional product PVC has a maximum operating temperature around 60 °C (140 °F) when heat distortion begins to occur. As a thermoplastic, PVC has an inherent insulation that aids in reducing condensation formation and resisting internal temperature changes for hot and cold liquids.

Applications

Pipes Roughly half of the world's PVC resin manufactured annually is used for producing pipes for municipal and industrial applications. In the private homeowner market, it accounts for 66% of the household market in the US, and in household sanitary sewer pipe applications, it accounts for 75%. PVC sewage plumbing uses rigid unplasticized PVC. Buried PVC pipes in both water and sanitary sewer applications that are 100 mm (4 in) in diameter and larger are typically joined by means of a gasket-sealed joint. The most common type of gasket utilized in North America is a metal-reinforced elastomer, commonly referred to as a Rieber sealing system.

Electric cables PVC is often used as the insulating sheath on electrical cables. PVC is chosen because of its good electrical insulation, ease of extrusion, and resistance to burn.

In a fire, PVC can form hydrogen chloride fumes; the chlorine serves to scavenge free radicals, making PVC-coated wires fire retardant. While hydrogen chloride fumes can also pose a health hazard in their own right, it dissolves in moisture and breaks down onto surfaces, particularly in areas where the air is cool enough to breathe, so would not be inhaled.

Construction

PVC is widely and heavily used in construction and building industry, For example, vinyl siding is used extensively as a popular low-maintenance material, particularly in Ireland, the United Kingdom, the United States, and Canada. The material comes in a range of colors and finishes, including a photo-effect wood finish, and is used as a substitute for painted wood, mostly for window frames and sills when installing insulated glazing in new buildings; or to replace older single-glazed windows, as it does not decompose and is weather-resistant.