Polyvinyl chloride, more correctly but unusually poly(vinyl chloride), commonly abbreviated PVC, is the third-most widely produced synthetic plasticpolymer, after polyethylene and polypropylene.
PVC comes in two basic forms: rigid (sometimes abbreviated as RPVC) and flexible. The rigid form of PVC is used in construction for pipe and in profile applications such as doors and windows. It is also used for bottles, other non-food packaging, and cards (such as bank or membership cards). 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 plumbing, electrical cable insulation, imitation leather, signage, inflatable products, and many applications where it replaces rubber.
Pure poly (vinyl chloride) is a white, brittle solid. It is insoluble in alcohol but slightly soluble in tetrahydrofuran.
PVC was accidentally synthesized in 1872 by German chemist Eugen Baumann. The polymer appeared as a white solid inside a flask 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 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. 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 vinyl chloride monomer (VCM), as shown.
The 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.
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 (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. 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. Previously, polychlorinated biphenyls (PCBs) were added to certain PVC products as flame retardants and stabilizers.
Most vinyl products contain plasticizers which dramatically improve their performance characteristic. The most common plasticizers are derivatives of phthalic acid. The materials are selected on their compatibility with the polymer, low volatility levels, and cost. These materials are usually oily colourless substances that mix well with the PVC particles. About 90% of the plasticizer market, estimated to be millions of tons per year worldwide, is dedicated to PVC.
Bis(2-ethylhexyl) phthalate was a common plasticizer for PVC but is being replaced by higher molecular weight phthalates.
One 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. Addition levels vary typically from 2% to 4%. The choice of the best heat stabilizer depends on its cost effectiveness in the end use application, performance specification requirements, processing technology and regulatory approvals.
Rigid PVC applications
Regular PVC (polyvinyl chloride) is a common, strong but lightweight plastic used in construction. It is made softer and more flexible by the addition of plasticizers. If no plasticizers are added, it is known as uPVC (unplasticized polyvinyl chloride), rigid PVC, or vinyl siding in the U.S. 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 substitution of lead-based stabilizers is also confirmed in the same document showing a reduction of 75% since 2000 and ongoing. This is confirmed by the corresponding growth in calcium-based stabilizers, used as an alternative to lead-based stabilizers, more and more, also outside Europe.
Tin based stabilizers are mainly used in Europe for rigid, transparent applications due to the high temperature processing conditions used. The situation in North America is different where tin systems are used for almost all rigid PVC applications. Tin stabilizers can be divided into two main groups, the first group containing those with tin-oxygen bonds and the second group with tin-sulphur bonds. According to the European Stabiliser producers most organotin stabilisers have already been successfully REACH registered. More chemical and use information is also available on this site.
Flexible PVC applications
Flexible PVC coated wire and cable for electrical use has traditionally been stabilised with lead but these are being replaced, as in the rigid area, with calcium based systems.
Liquid mixed metal stabilisers are used in several PVC flexible applications such as calendered films, extruded profiles, injection moulded soles and footwear, extruded hoses and plastisols where PVC paste is spread on to a backing (flooring, wall covering, artificial leather). Liquid mixed metal stabiliser systems are primarily based on barium, zinc and calcium carboxylates. In general liquid mixed metals like BaZn, CaZn require the addition of co-stabilisers, antioxidants and organo-phosphites to provide optimum performance.
BaZn stabilisers have successfully replaced cadmium-based stabilisers in Europe in many PVC semi-rigid and flexible applications according to the European producers.
PVC is a thermoplastic polymer. Its properties are usually categorized based on rigid and flexible PVCs.
PVC 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) are very good; the elastic modulus can reach 1500-3,000 MPa. The soft PVC (flexible PVC) elastic is 1.5–15 MPa.
Thermal and fire properties
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. PVC starts to decompose when the temperature reaches 140 °C, with melting temperature starting around 160 °C. The linear expansion coefficient of rigid PVC is small and has good flame retardancy, the Limiting oxygen index (LOI) being up to 45 or more. The LOI is the minimum concentration of oxygen, expressed as a percentage, that will support combustion of a polymer and noting that air has 20% content of oxygen.
PVC is a polymer with good insulation properties, because of its higher polar nature the electrical insulating property is inferior to non polar polymers such as polyethylene and polypropylene. Since the dielectric constant, dielectric loss tangent value, and volume resistivity are high, the corona resistance is not very good, and it is generally suitable for medium or low voltage and low frequency insulation materials.
PVC is used extensively in sewage pipe due to its low cost, chemical resistance and ease of jointing. 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, PVC scrap has become a popular material for window and door which is 50% less than the cost of wooden window and door. 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. In 2013, about 39.3 million tonnes of PVC were consumed worldwide. PVC demand is forecast to increase at an average annual rate of 3.2% until 2021.
Roughly 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.
In February 2007 the California Building Standards Code was updated to approve the use of chlorinated polyvinyl chloride (CPVC) pipe for use in residential water supply piping systems. CPVC has been a nationally accepted material in the US since 1982. The United States Department of Housing and Community Development prepared and certified an environmental impact statement resulting in a recommendation that the Commission adopt and approve the use of CPVC. The Commission’s vote was unanimous and CPVC has been placed in the 2007 California Plumbing Code.
In the United States and Canada, PVC pipes account for the largest majority of pipe materials used in buried municipal applications for drinking water distribution and wastewater mains. Buried PVC pipes in both water and sanitary sewer applications that are 4 inches (100 mm) 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.
Polypropylene raw material is a white color thermoplastic material that is produced by polimerization of propylene (adding propylene monomer molecule to each other and forming big propylene molecule chains) which is obtained from ‘‘Naphta’’ – a derivative of crude oil. In production of Polypropylene raw material, 97 % crude oil is used.Just because of this,its availability and price level is fully dependenton the world’s crude oil market.
After a series of complex chemical reactions,ethylene molecules are inserted on the molecular chain of propylene. Ethylene molecules are added to the polypropylene molecular chain with a percentage of 1-7 %. By doing this, the physical properties of the Polypropylene raw material like ring stiffness, heat resisstance, electric connectivity, hardness, softness, etc. are improved. The percentage of the ethylene molecules inserted in the polypropylene molecular chain determines the physical properties of the final raw material. By regulating the ethylene percentage, excellent heat and pressure strength are given to the raw material.
Polypropylene raw material has extraordinary strength against high temperatures and high pressures. In our daily life, we use the three types of polypropylene raw material being:
- Polypropylene Homopolymer (does not contain any ethylene molecules.It is very soft material which is used in production of non-pressure items like sheets,plastic houseware,plastic bags, etc.).
- Polypropylene Bloco Copolymer (contains up to 3 % ethylene molecules.This raw material can be used in production of polypropylene pipes to be used only for cold water transfer.
- Polypropylene Random Copolymer (contains ethylene between 3-7 %. It is used in production of high pressure pipes which can be used at temperatures till 90°C).
We have available:
- Complete Range of Polypropylene Pipe made to DIN and ISO standards and accompanying Butt Weld or Socket Fusion Weld Fittings;
- Upon special request PP Electro-fusion fittings;
- Engineering sheets in various colours, dimensions and materials, including PP, HDPE, PVDF, LLDP;
- HDPE/PP/PVDF welding rod and solid rods.
- Full range of Industrial valves with instrumentation to cater for every need and application.
The rapid improvements in plastic technology has resulted in important progress in raw materials production. PE32-LDPE type polyethylene, which was improved in the 1950’s was successfully used in drinking water piping systems at low pressures.
Polyethylene producers improved after PE63 to PE80 (=6.30 Mpa) as second generation products. Thus PE80 raw material started being produced for water pipes and natural gas networks. Subsequently, in 1999, PE100, the third generation raw material, proved to be highly economic with excellent performance. PE100’s greatest advantage is having high stretching resistance and security coefficient. For example, pipes permitted working pressure is 10 bar if it is produced from PE80 material, but complies with SDR11, and 16 bar when PE100 is used.
Essentially this means that pipes produced with PE100 allow for use in higher pressures with less wall thickness. Pipes produced with PE100 provide more quality while saving 30% material, at lower costs.
Depending on molecular weight, Polyethylene is either unimodal or bimodal. PE100 is bimodal polyethylene. A good quality Polyethylene should have high molecular weight. If Polyethylene material does not have high molecular weight, it cannot be processed well. So, the PE pipe would not be at desired mechanical properties and strength. High durability and required mechanical properties of Polyethylene pipe could only be obtained by bimodal Polyethylene raw material (PE100). Bimodal Polyethylene is fabricated by a mixture of two different molecule weights that meet with previous requirements. Bimodal molecule’s structure, contains both long polymer chains of a polymer grain that strengthens the pipe and short polymer chains that gives plasticity to product in a polymer particle in the most suitable and optimum way. Besides, combination of long and short chain adds high strength to PE100 against stretch and high resistance against elongational cracking
Properties of Polyethylene (PE) Pipes and Fittings:
Some of the advantages of PE100 pipe and fittings are:
- Not affected by earthquake because of flexible structure, absorbs some degree of extension at areas where landslide is possible.
- Maintain flexibility features at temperatures down to -40°C.
- Small diameters can be transported in coils by allowing easy handling at site.
- High resistance to chemicals, no corrosion.
- High abrasion resistance, resistant to worn out. No cancerous effect as no molecule transfers to fluid.
- No corrosion from fluid flow and/or ground structure.
- Low density, 8 times lighter than steel.
- Resistant to strokes from variable flow pressures.
- Lifetime of minimum 50 years under normal operating pressure.
- 100% leak-free with high quality and easy welding methods, no waste at montage.
- Hygienic, no effect on colour and taste of water.
- High stroke resistance in low temperatures.
- Ease in transportation.
- Resistance to weather conditions and UV.
- Resistance to strike and breakings.
- No need to cathodic protection.
- Various welding methods are applicable.
Compared to other type of pipes which convey abrasive slurries, Polyethylene has highest resistance against abrasion with its very low friction coefficient. Its widespread usage and some laboratory tests has shown that PE’s performance exceeds the performance of metallic pipe systems. PE pipes has become the ideal choice for viscous applications with its elasticity, lightness, and easy montage. Abrasive filling stuff has minor exterior effect on PE. If the pipe is cut with a sharp tool, and the cut deepness was more than %10 of wall thickness, damaged part should be replaced with a new one.
PE pipes can be used in range of temperatures -50°C to +60°C. Higher temperatures reduce the hardness and stretch tension. Like all other thermoplastics, PE also shows bigger thermal expansion than metals. PE’s thermal expansion coefficient is 0,15-0,2 mm/mK and this value is 1,5 times higher than PVC. PE’s thermal conductivity is 0,38w/mK and this characteristic is more economic comparing to metal systems, such as copper.
Reaction to Combustion
Polyethylene is combustive material, burns drop by drop without soot. Toxics is released to atmosphere when burns. Generally most harmful churn is carbon monoxide. Carbon monoxide, carbon dioxide and water produced when PE is burned. PE is self combustible at temperature of +350°C. Ideal fire extinguisher is water, foam and/or carbon dioxide.
PE is highly resistant to chemical attacks with its non-polar structure like high molecular weighted hydrocarbons. PE does not decay, is not worn out or weakened mechanically by electrical or chemical reactions. Not only is PE highly resistanct to acids but also to alkaline solutions, solvents, alcohol and water with low resistance against oxidant acids, ketones, aromatic hydrocarbons and chloral hydrocarbons. Level of chemical resistance, depends on chemical’s concentration, temperature and working pressure. These three specifications determine the life span of the pipe.
We have available:
- Complete range of HDPE Pipes in PE100 material manufactured according to SABS Standards from 16mm to over 1 meter.
- Accompanying ranges of Butt, Socket Fusion, Electro-fusion welded fittings.
- Clamp saddles with O’RINGS for mechanical jointing or electrofusion weld.
- Special fabrications.
- HDPE Engineering sheets.
- Welding rods and solid bars.
- Geomembranes for dam linings.
- Greenhouse materials
Polyvinlidene Fluoride is a unique thermoplastic with excellent chemical and physical properties, even at low temperatures. Safe working temperatures range from -40ºC to +120ºC, with short term use possible at temperatures well above this level.
Its special properties allow it to be used for very aggressive fluids as it is resistant to most inorganic acids and basis, and to aliphatic and aromatic hydrocarbons, organic acids, alcohols and halogenated solvents, even in high concentrations. Although expensive compared to other thermoplastics, PVDF offers an economically attractive alternative to many “exotic” materials and/or in process lines where limited working life of other materials necessitates frequent replacement.
PVDF has and has considerable resistance to abrasion. It is also non-toxic and can be used for high purity applications.
PVDF pipe systems are connected by using heat fusion welding machines, either using socket fittings or butt fusion welding the fittings directly to the pipes. Special heat radiation machines are available for welding in clean applications, where no contact between the pipes and fittings is permitted.