PVC full form is Polyvinyl Chloride and it is the third most widely produced synthetic polymer around the world where about 40 million tonnes of PVC is produced every year. Polyvinyl chloride which is PVC full form is actually a plastic that is commonly abbreviated as PVC in hardware stores. PVC has two basic forms in which one is rigid and the other one is flexible. The rigid one is mostly used for profile applications such as doors and windows and is mainly put to use in the construction of pipes. Apart from these applications, it is also used for the production of making plastic bottles, non-food packaging, food-covering sheets and plastic cards. It can also be made softer and more flexible by the addition of more plasticizers among which the most common and widely used plasticizer is phthalates. In this flexible plastic form, it is used for plumbing, wire insulation, imitation leather, flooring, signage, phonograph records, inflatable products, and many applications where it has successfully replaced the application of rubber. It is also used for the production of canvas by jointly using cotton and linen.
Pure PVC is a brittle white solid that is insoluble in alcohol but slightly soluble in tetrahydrofuran. PVC is structurally Vinyl polymer. The chemical polyvinyl chloride formula is (C₂H₃Cl)ₙ or alternatively, it can be written as the repeating units of the monomer CH₂=CH-Cl. The polyvinyl chloride structure is very similar to that of the polythene except that the hydrogen atom attached to every carbon in the backbone chain is replaced with a chlorine atom. It is generally synthesized by the free radical polymerization of vinyl chloride. The IUPAC name of polyvinyl Chloride is given as poly(1-chloroethylene) while its common names include Polychloroethene. Therefore the structure of polyvinyl chloride is expressed as follows:-
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Some of the physicochemical properties of PVC is as follows:-
Properties of Polyvinyl Chloride
|
Physicochemical Properties |
Values |
|
Chemical formula |
(C₂H₃Cl)ₙ |
|
Appearance |
Brittle solid, white in appearance |
|
Odour |
odourless |
|
Solubility in water |
insoluble |
|
Solubility in alcohol |
insoluble |
|
Solubility in tetrahydrofuran |
Slightly soluble |
|
Magnetic susceptibility |
−10.71×10⁻⁶(SI, 22 ⁰C) |
|
Density |
Rigid PVC: 1.3 to 1.45 g/cm³ Flexible PVC: 1.1 to 1.35 g/cm³ |
|
Thermal conductivity |
Rigid PVC: 0.14–0.28 W/(m·K) Flexible PVC: 0.14–0.17 W/(m·K) |
|
Melting temperature |
212-500 ⁰F or 100 to 260 ⁰C |
|
Heat deflection temperature |
92⁰C or 198⁰F |
|
Tensile strength |
Flexible PVC: 6.9 – 25 MPa (1000 – 3625 PSI) Rigid PVC: 34 – 62 MPa (4930 – 9000 PSI) |
|
Specific gravity |
1.35 – 1.45 |
|
Yield strength |
Rigid PVC: 4500-8700 psi Flexible PVC: 1450-3600 psi |
|
Rigid PVC: 31-60 MPa Flexible PVC: 10-24.8 MPa |
|
|
Young’s module |
Rigid PVC: 490,000 psi |
|
Rigid PVC: 3.4 GPa |
|
|
Flexural strength (yield) |
Rigid PVC: 10,500 psi |
|
Rigid PVC: 72 MPa |
|
|
Compression strength |
Rigid PVC: 9500 psi |
|
Rigid PVC:66 MPa |
|
|
Coefficient of thermal expansion (liner) |
Rigid PVC: 5 x 10⁻⁵ mm / (mm ⁰C) |
|
Vicat B |
Rigid PVC: 65-100⁰C Flexible PVC: Not recommended |
|
Resistivity |
Rigid PVC: 10¹⁶ Ω m Flexible PVC: 10¹² – 10¹⁵ Ω m |
|
Surface Resistivity |
Rigid PVC: 10¹³ – 10¹⁴ Ω Flexible PVC: 10¹¹ – 10¹²Ω |
Mechanical Properties of PVC are as Follows:-
|
Mechanical properties |
Values |
|
Elongation break |
20–40% |
|
Notch test |
2–5 kJ/m² |
|
Glass transition temperature |
82 ⁰C (180 ⁰F) |
|
Water absorption (ASTM) |
0.04–0.4 |
|
Effective heat of combustion |
17.95 MJ/kg |
|
Specific heat |
0.9 kJ/(kg·K) |
|
Dielectric breakdown voltage |
40 MV/m |
Some of the Characteristic Properties of Polyvinyl Chloride are as Follows:-
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PVC has high Mechanical properties and hardness. As the molecular weight increases, the mechanical properties are also enhanced but it happens with the decrease in the temperature. As the temperature increases the mechanical properties decrease.
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Because of the high polar nature of PVC, it is considered a good insulator. Electrical insulating property is less as compared to non-polar polymers such as polythene and polypropylene. It is generally suitable for low voltage and low-frequency insulating materials.
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PVC has good resistance properties towards acid salt-based fats and alcohols and that’s why it is also resistant to the corrosion effect of sewage. That is why it is used widely as a sewer pipe system.
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Since PVC fabric is resistant to water, therefore, it is widely used in coats, skiing equipment, shoe, jackets, aprons and sports bad for its weather resistance property.
Polyvinyl Chloride Preparation
Polyvinyl chloride is produced by the polymerization of vinyl chloride monomers. The two most commercially viable methods for the production of polyvinyl Chloride are Emulsion Polymerization and Suspension Polymerization. Suspension polymerization accounts for 80% of the synthesis of polyvinyl chloride whereas emulsion polymerization accounts for only 12% of the total synthesis of polyvinyl chloride. Suspension polymerization results in the formation of particles with a bigger diameter of size 100–180 μm, whereas emulsion polymerization results in the formation of smaller particles of size around 0.2 μm.
VMC is introduced in the reactor along with water and other polymerization initiated and additives. The content within the reactor vessel is pressurized and the contents are continuously mixed to maintain the suspension so as to ensure uniform particle size of the PVC resin. This reaction needs cooling as it is an exothermic reaction. Water needs to be continuously added to this reaction as the volume while the reaction proceeds reduces so as to maintain the suspension of the mixture.
The polymerization reaction of the VMC is initiated firstly e by the compounds referred to as initiators that are mixed into the droplets. This reaction then transferred to the radical chain reaction as the compound started breaking down. Both are considered as the typical initiators as both have fragile oxygen bonds. Some of the initiators initiate the reaction quickly but they also rapidly decay and other initiators have different effects. Thus a combination of the two different initiators is used to produce a uniform polymerization rate. Post the polymer when it grows 10 times its size the short polymer settles into the droplets VCM. And therefore the reaction continues with the precipitated short polymer and those which have swollen particles. The average molecular weight that the molecules of the polymer weigh are about the range of 1,00,000 to 2,00,000 and the average molecular weights range from 45,000 to 64,000.
The PVC salary is the guest and stripped after the reaction has been completed to remove access BCM which is then recycled. In order to remove water, the polymer is then passed through a centrifuge. Then a hot air bed is introduced in order to fir drive the salary and the powder that is ultimately formed is sieved before pelletization or storage. Normally the PVC that is formed has less than 1 part per million content of VCM. Some of the other production processes such as micro-suspension polymerization on emulsion polymerization produce smaller particle sizes of PVC that have slightly different properties and a different set of applications.
Ethylene feedstock on nap feedstock are the two compounds from which PVC may be manufactured. However in China, though the feedstock is abundant the main starting material for the calcium carbide process is coal. Vcm is 10 formed by conversion of the generated acetylene which usually is involved in the use of Mercury base catalyst. This process generates a lot of waste and is a very energy-intensive process.
Polyvinyl Chloride Uses
The major uses of polyvinyl chloride are as follows:-
1. Building and Construction: About three-quarters of the total polyvinyl chloride that is produced goes for long-lasting buildings and construction applications. Since it has low greenhouse gas emission properties and conservation of resources and energy therefore it has been seen that it is effective in protecting the environment in the long run. Poly million chlorides have strong resistance to moisture and abrasion and therefore it is ideal for windows, roofing and cladding, fencing, decking, wallcovering and flooring.
2. Wires and Cables: Polyvinyl chloride has the property to which then the tough conditions of building walls suggest a change in the temperature and exposure to dampness. This is the only reason that it is the most trusted and prevalent material which is used in electric wiring and cables.
3. Water Pipes: PVC creates virtually leak-free pipes and does help conserve energy and water. These are not prone to corrosion and they have very good resistance to environmental stress. The rate of breakage of PVC is of very low percentage and has about as low as 1% of breakage rate of cast metal systems. Since the build-up in the PVC piping is very low therefore it improves the functionality and also increases the energy efficiency.
4. Packaging: It maintains the integrity of the product inside including the medicines as it is very durable, dependable and light well along with being flexible for packaging. Clear polyvinyl chloride is used in tamper-resistant over-the-counter medications and for consumer products, it is used in shrink wrap. For clamshell packaging and blisters, rigid Vinyl films are used in order to protect medicines, personal care products and other household goods.
5. Health Care: Through IV bags and medical tubing polyvinyl chloride plays a critical role in safely dispensing life-saving medicines. The blood collection bag that was made from the PVC is considered as a significant breakthrough of PVC the blood bags became flexible and unbreakable and therefore enhanced the development of ambulatory medicines along with serving as the foundation for modern blood banks.
6. Household Products: The durability, affordability and water resistance of PVC makes a deal for raincoats, shower curtains, boots etc.