office
(+91)(0512) 2690015
fax (+91)(0512) 2690015
Mobile (+91) 9839033104
Polyvinyl chloride, (IUPAC Poly(chloroethanediyl))
commonly abbreviated PVC, is a thermoplastic polymer. It is a vinyl
polymer constructed of repeating vinyl groups (ethenyls) having one
of their hydrogens replaced with a chloride group.
Polyvinyl chloride is the third most widely produced plastic, after
polyethylene and polypropylene.PVC is widely used in construction
because it is cheap, durable, and easy to assemble. PVC production
is expected to exceed 40 million tons by 2016.
It can be made softer and more flexible by the addition of
plasticizers, the most widely used being phthalates. In this form,
it is used in clothing and upholstery, and to make flexible hoses
and tubing, flooring, to roofing membranes, and electrical cable
insulation. It is also commonly used in figurines and in inflatable
products such as waterbeds, pool toys, and inflatable structures.
Preparation
Polyvinyl chloride is produced by polymerization of the vinyl
chloride monomer (VCM), as shown.Since about 57% of its mass is
chlorine, creating a given mass of PVC requires less petroleum than
many other polymers.[citation needed] However, because PVC also has
a much higher density than hydrocarbon polymers, and chlorine
production has its own energy requirements, this ends up being of
little practical relevance in the production of most solid objects.
By far the most widely used production process is suspension
polymerization. In this process, VCM and water are introduced into
the polymerization reactor and a polymerization initiator, along
with other chemical additives, are added to initiate the
polymerization reaction. The contents of the reaction vessel are
continually mixed to maintain the suspension and ensure a uniform
particle size of the PVC resin. The reaction is exothermic, and thus
requires a cooling mechanism to maintain the reactor contents at the
appropriate temperature. As the volumes also contract during the
reaction (PVC is denser than VCM), water is continually added to the
mixture to maintain the suspension.
Once the reaction has run its course, the resulting PVC slurry is
degassed and stripped to remove excess VCM (which is recycled into
the next batch) then passed though a centrifuge to remove most of
the excess water. The slurry is then dried further in a hot air bed
and the resulting powder sieved before storage or pelletization. In
normal operations, the resulting PVC has a VCM content of less than
1 part per million.
Other production processes, such as micro-suspension polymerization
and emulsion polymerization, produce PVC with smaller particle sizes
(10 μm vs. 120-150 μm for suspension PVC) with slightly different
properties and with somewhat different sets of applications.
The product of the polymerization process is unmodified PVC. Before
PVC can be made into finished products, it almost 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.[5]
Properties
The properties for PVC are usually categorized based on rigid and
flexible PVCs.Property Rigid PVC Flexible PVC
Density [g/cm3][6] 1.3–1.45 1.1–1.35
Thermal conductivity [W/(m·K)][7] 0.14–0.28 0.14–0.17
Yield strength [MPa][6] 31–60 10–25
Young's modulus [psi] 490,000[8]
Flexural strength (yield) [psi] 10,500[8]
Compression strength [psi] 9500[8]
Coefficient of thermal expansion (linear) [mm/(mm °C)] 5×10−5[8]
Vicat B [°C][7] 65–100 Not recommended
Resistivity [Ω m][9][10] 1016 1012–1015
Surface resistivity [Ω][9][10] 1013–1014 1011–1012
History
PVC was accidentally discovered at least twice in the 19th century,
first in 1835 by Henri Victor Regnault and in 1872 by 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 (polyvinyl chloride) 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.
Applications
PVC's intrinsic properties make it suitable for a wide variety of
applications. It is biologically and chemically resistant, making it
the plastic of choice for most household sewerage pipes and other
pipe applications where corrosion would limit the use of metal.
With the addition of impact modifiers and stabilizers, it becomes 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 is also used to make vinyl records.
Clothing
PVC 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 and alternative fashions. PVC is
cheaper than rubber, leather, and latex and so it is more widely
available and worn.
PVC fabric has a sheen to it and is waterproof. It is commonly used
in coats, skiing equipment, shoes, jackets, aprons, and bags because
of this.