Polyvinyl chloride

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. The mechanical properties enhance with the molecular weight increasing, but decrease with the temperature increasing. The mechanical properties of rigid PVC (uPVC) is very good, the elastic modulus can reach to 1500-3,000 MPa. The soft PVC (Flexible PVC) elastic is 1.5- 15 MPa. However, elongation at break is up to 200% -450%. PVC friction is ordinary, the static friction factor is 0.4-0.5, the dynamic friction factor is 0.23.Thermal propertiesThe heat stability of PVC is very poor, when the temperature reaches 140 °C PVC starts to decompose. Its melting temperature is 160 °C. The linear expansion coefficient of the PVC is small and has flame retardancy, the oxidation index is up to 45 or more. Therefore, the addition of a heat stabilizer during the process is necessary in order to ensure the product's 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. On both occasions the polymer appeared as a white solid inside flasks of vinyl chloride that had been left exposed to sunlight. 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 blocked their efforts. Waldo Semon and the B.F. Goodrich Company developed a method in 1926 to plasticize PVC by blending it with various additives. The result was a more flexible and more easily processed material that soon achieved widespread commercial use. Polyvinyl chloride is produced by polymerization of the monomer vinyl chloride (VCM), as shown.MicrostructureThe polymers are linear and are strong. The monomers are mainly arranged head-to-tail, meaning that there are chlorides 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.

Production Methods

In chlorinating polyethylene, chlorine atoms substitute for hydrogen atoms of the polyethylene chain in both crystalline and amorphous regions. The most common chlorination method is treating polyethylene powder in an aqueous suspension that contains hydrochloric acid and a free-radical initiator with chlorine gas. After the desired level of chlorination is obtained, the CPE is water washed and dried, and an antiblocking agent is then added.

Application

PVC's relatively low cost, biological and chemical resistance and workability have resulted in it being used for a wide variety of applications. It is used for sewerage pipes and other pipe applications where cost or vulnerability to corrosion limit the use of metal. With the addition of impact modifiers and stabilizers, it has become a popular material for window and door frames. By adding plasticizers, it can become flexible enough to be used in cabling applications as a wire insulator. It has been used in many other applications.PipesRoughly half of the world's polyvinyl chloride resin manufactured annually is used for producing pipes for municipal and industrial applications . In the water distribution market it accounts for 66 % of the market in the US, and in sanitary sewer pipe applications, it accounts for 75 % . Its light weight, low cost, and low maintenance make it attractive. However, it must be carefully installed and bedded to ensure longitudinal cracking and overbelling does not occur. Additionally, PVC pipes can be fused together using various solvent cements, or heat-fused (butt-fusion process, similar to joining HDPE pipe), creating permanent joints that are virtually impervious to leakage.Electric cablesPVC is commonly used as the insulation on electrical cables; PVC used for this purpose needs to be plasticized.Unplasticized polyvinyl chloride (uPVC) for constructionuPVC, also known as rigid PVC, is extensively used in the building industry as a low-maintenance material, particularly in Ireland, the United Kingdom, and in the United States. In the USA it is known as vinyl, or vinyl siding . 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 double glazing in new buildings, or to replace older single-glazed windows. Other uses include fascia, and siding or weatherboarding. This material has almost entirely replaced the use of cast iron for plumbing and drainage, being used for waste pipes, drainpipes, gutters and downspouts. uPVC does not contain phthalates, since those are only added to flexible PVC, nor does it contain BPA. uPVC is known as having strong resistance against chemicals, sunlight, and oxidation from water.Clothing and furniturePVC has become widely used in clothing, to either create a leather-like material or at times simply for the effect of PVC. PVC clothing is common in Goth, Punk, clothing fetish and alternative fashions. PVC is cheaper than rubber, leather, and latex which it is therefore used to simulate.HealthcareThe two main application areas for medically approved PVC compounds are flexible containers and tubing: containers used for blood and blood components for urine or for ostomy products and tubing used for blood taking and blood giving sets, catheters, heartlung bypass sets, haemodialysis set etc. In Europe the consumption of PVC for medical devices is approximately 85.000 tons every year. Almost one third of plastic based medical devices are made from PVC.FlooringFlexible PVC flooring is inexpensive and used in a variety of buildings covering the home, hospitals, offices, schools, etc. Complex and 3D designs are possible due to the prints that can be created which are then protected by a clear wear layer. A middle vinyl foam layer also gives a comfortable and safe feel. The smooth, tough surface of the upper wear layer prevents the build up of dirt which prevents microbes from breeding in areas that need to be kept sterile, such as hospitals and clinics.Other applicationsPVC has been used for a host of consumer products of relatively smaller volume compared to the industrial and commercial applications described above. Another of its earliest mass-market consumer applications was to make vinyl records. More recent examples include wallcovering, greenhouses, home playgrounds, foam and other toys, custom truck toppers (tarpaulins), ceiling tiles and other kinds of interior cladding.

Definition

ChEBI: A polymer composed of repeating chloroethyl units.

Preparation

In commercial practice, poly(vinyl chloride) is mainly prepared by suspension polymerization whilst bulk and emulsion polymerization are used to a lesser extent. The homopolymer is seldom made by solution methods. (a) Bulk polymerization The only commercially successful bulk polymerization process for poly(vinyl chloride) is that developed by Pechiney St. Gobain (now Rhone-Poulenc Industries) (France). This process is conducted in two stages, permitting better control of particle morphology than is possible with a one-stage process. The first stage is carried out in a stainless steel reactor, jacketed for heating and cooling and fitted with a reflux condenser and high speed agitator. About half of the monomer required for the final amount of polymer is fed into the reactor together with an acyl peroxide or peroxydicarbonate initiator. In the first stage, polymerization is carried out at about 60-75°C and 0.5-1.2 MPa (5-12 atmospheres) for a short time (about 20 minutes) to give a conversion of about 8%. At this point the product consists of small particles of polymer dispersed in liquid monomer (since the polymer is insoluble in the monomer). The size of the polymer particles is determined principally by the rate of agitation and must be carefully controlled since it affects the final processing properties of the polymer. A mean particle diameter of about 10-5 cm is usual for the first stage product (pre-polymer). For the second stage of the process, the seed is transferred into a larger reactor, jacketed for heating and cooling and fitted with a reflux condenser and low speed agitator. Additional monomer is added to the reactor together with a further quantity of initiator such as diisopropyl peroxydicarbonate. In the second stage, polymerization is carried out at a constant pressure of about 1 MPa (10 atmospheres) while the temperature rises from about 55°C to 75°C. Reaction proceeds for 3-5 hours until a conversion of about 80% is reached. At this point the product is in the form of a powder containing absorbed monomer. Unreacted monomer is distilled off and recycled and the remaining product is degassed in vacuo using steam or nitrogen as a carrier. The final product consists of particles (about 10-2 cm in diameter) which are agglomerates of smaller particles (about 10-4 cm in diameter). (b) Suspension polymerization The principal characteristics of suspension polymerization have been described in the previous discussion of polystyrene. Typically, the suspension polymerization of vinyl chloride is carried out batch-wise in a stirred reactor, jacketed for heating and cooling. The reactor is also connected to a vacuum line. (c) Emulsion polymerization Poly(vinyl chloride) prepared by emulsion techniques contains soap residues and, as a result, the heat and colour stabilities and the electrical insulation properties are rather poor compared to those of suspension polymer. Nevertheless, emulsion polymer is manufactured for pastes which find use in noncritical applications. There is also some direct use of poly(vinyl chloride) latices for coating and impregnating paper and textiles. Emulsion polymerization is carried out in a pressure reactor of the type used for suspension polymerization.

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. PVC resin can also be chlorinated (CPVC) and it can be alloyed with other polymers such as ABS (acrylonitrile butadiene styrene), acrylic, polyurethane, and nitrile rubber to improve impact resistance, tear strength, resilience, heat-deflection temperature, or processibility.PVC is a hard, flame-resistant, and chemicalresistant thermoplastic resin. The resin is available in the powder form, as a latex, or in the form of plastisol. PVC resin, pigments, and stabilizers are milled into plasticizers to form a viscous coating material (plastisol) that polymerizes into a tough elastic film when heated. 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.

Safety

DegradationPlastics, like most materials, degrade, albeit slowly, in all environmental settings by means of bio-degradation, photodegradation, thermo-oxidative degradation or hydrolysis. Degradation is a chemical change that drastically reduces the average molecular weight of the polymer. Since the mechanical integrity of plastics invariably depends on their high average molecular-weight, any significant extent of degradation inevitably weakens the material. Weathering degradation of plastics results in their surface embrittlement and microcracking, yielding microparticles that continue on in the environment, known as microplastics. Microplastics concentrate Persistent Organic Pollutants (POPs). The relevant distribution coefficients for common POPs are several orders of magnitude in favor of the plastic medium. Consequently, the microparticles laden with high levels of POPs can be ingested by organisms in the biosphere. Given the increased levels of plastic pollution of the environment, this is an important concept in understanding the food web.PlasticizersIt has been claimed that some plasticizers leach out of PVC products. However, it has been difficult to prove that plasticizers readily migrate and leach into the environment from flexible vinyl articles because they are physically and tightly bound into the plastic as a result of the heating process used to make PVC particles. Vinyl products are pervasive — including toys, car interiors, shower curtains, and flooring — and initially release chemical gases into the air. Some studies indicate that this outgassing of additives may contribute to health complications, and have resulted in a call for banning the use of DEHP on shower curtains, among other uses.EU decisions on phthalatesRisk assessments have led to the classification of low molecular weight and labeling as Category 1B Reproductive agents. Three of these phthalates, DBP, BBP and DEHP were included on annex XIV of the REACH regulation in February 2011 and will be phased out by the EU by February 2015 unless an application for authorisation is made before July 2013 and an authorisation granted. DIBP is still on the REACH Candidate List for Authorisation. The European Union Copyright ? Tarek Kakhia. All rights reserved. http://tarek.kakhia.org has confirmed that DEHP poses no general risk to human health. The summary of a comprehensive European risk assessment, involving nearly 15 years of extensive scientific evaluation by EU regulators, was published in the EU Official Journal on February 7, 2008.The assessment demonstrated that DEHP poses no risk to the general population and that no further measures need to be taken to manage the substance in any of its key end-use applications. This confirms an earlier opinion of member state experts and an opinion from the EU Scientific Committee for Toxicity, Ecotoxicity and the Environment (CSTEE) adopted in 2004. The only areas of possible risk identified in the assessment relate to : The use of DEHP in children's toys. Under regulations introduced in January 2007 DEHP is no longer permitted in toys and childcare articles in the EU. Possible exposure of workers in factories. Adequate precautions are already taken based on occupational exposure limit values and some localised environmental exposure near to factories. The use of DEHP in certain medical devices. An EU Scientific Review was requested to determine whether there may be any risk from the use of DEHP in certain medical applications (children and neonates undergoing long-term blood transfusion and adults undergoing long-term haemodialysis). In 2008 the European Union's Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) reviewed the safety of DEHP in medical devices. The SCENIHR report states that certain medical procedures used in high risk patients result in a significant exposure to DEHP and concludes there is still a reason for having some concerns about the exposure of prematurely born male babies to medical devices containing DEHP . The Committee said there are some alternative plasticizers available for which there is sufficient toxicological data to indicate a lower hazard compared to DEHP but added that the functionality of these plasticizers should be assessed before they can be used as an alternative for DEHP in PVC medical devices. Risk assessment results have shown positive results Copyright ? Tarek Kakhia. All rights reserved. regarding the safe use of High Molecular Weight Phthalates. They have all been registered for REACH and do not require any classification for health and environmental effects, nor are they on the Candidate List for Authorisation. High phthalates are not CMR (carcinogenic, mutagenic or toxic for reproduction), neither are they considered endocrine disruptors. In the EU Risk Assessment the European Commission has confirmed that Di-isononyl phthalate (DINP) and Di-isodecyl phthalate (DIDP) pose no risk to either human health or the environment from any current use. The European Commission's findings (published in the EU Official Journal on April 13, 2006) confirm the outcome of a risk assessment involving more than 10 years of extensive scientific evaluation by EU regulators. Following the recent adoption of EU legislation with the regard to the marketing and use of DINP in toys and childcare articles, the risk assessment conclusions clearly state that there is no need for any further measures to regulate the use of DINP. In Europe and in some other parts of the world, the use of DINP in toys and childcare items has been restricted as a precautionary measure. In Europe, for example, DINP can no longer be used in toys and childcare items that can be put in the mouth even though the EU scientific risk assessment concluded that its use in toys does not pose a risk to human health or the environment. The rigorous EU risk assessments, which include a high degree of conservatism and built-in safety factors, have been carried out under the strict supervision of the European Commission and provide a clear scientific evaluation on which to judge whether or not a particular substance can be safely used. The FDA Paper titled "Safety Assessment of Di(2- ethylhexyl)phthalate (DEHP)Released from PVC Medical Devices" states that [3.2.1.3] Critically ill or injured patients may be at increased risk of developing adverse health effects from DEHP, not only by virtue of increased exposure relative to the general population, but also because of the physiological and pharmacodynamic changes that occur in these patients compared to healthy individuals.

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.