POLYVINYL CHLORIDE ( PVC)

Polyvinyl Chloride (PVC) is an odorless and solid plastic. The basic structure of this polymer

is (C2H3Cl)n. The degree of polymerization varies from 300 to 1500.

1) MONOMERS of PVC

Vinyl chloride monomer (VCM) is the key material which PVC is made. ( CH2 = CH – Cl )

a)Source of VCM

Vinyl chloride monomer does not occur naturally in the environment. It is manufactured

by the chemical industry (manufacture of polyvinyl chloride, ethylene dichloride, methyl

chloroform (1,1,1 trichloroethane), caprolactam, vinyl acetate, and vinylidene chloride) and

the plastics industry.Landfills containing vinyl chloride or other chlorinated hydrocarbons may

release vinyl chloride monomer. The treatment of wastewater containing vinyl chloride or

chlorinated hydrocarbons may release vinyl chloride.

b)Manufacturing of VCM

1- Production from Acetylene

Acetylene reacts with anhydrous hydrogen chloride gas over a mercuric chloride

catalyst to give vinyl chloride:

C2H2 + HCl → CH2=CHCl

The reaction is exothermic and highly selective. Product purity and yields are generally very

high.

This was the most common industrial route to VCM, before ethylene became widely

distributed. When VCM producers shifted to using the thermal cracking of EDC described

above, some used byproduct HCl in conjunction with a colocated acetylene-based unit. The

hazards of storing and shipping acetylene meant that the VCM facility needed to be located

very close to the acetylene generating facility.

2- Production from Ethylene

There are two ways to manufacture VCM from ethylene (obtained from thermal

cracking); the direct chlorination method and oxychlorination method:

Direct chlorination

The production of vinyl chloride from 1,2-dichloroethane (EDC) consists of a series of

well-defined steps. EDC is prepared by reacting ethylene and chlorine. In the presence of

iron(III) chloride as a catalyst, these compounds react exothermically:

CH2=CH2 + Cl2 → ClCH2CH2Cl

This process is very selective, resulting in high purity EDC and high yields. However

any dissolved catalyst and moisture must be removed before EDC enters the VCM

production process.

Thermal cracking

When heated to 500 °C at 15–30 atm (1.5 to 3 MPa) pressure, EDC vapor decomposes

to produce vinyl chloride and anhydrous HCl.

ClCH2CH2Cl → CH2=CHCl + HCl

The thermal cracking reaction is highly endothermic, and is generally carried out in a fired

heater. Even though residence time and temperature are carefully controlled, it produces

significant quantities of chlorinated hydrocarbon side products. In practice, EDC conversion

is relatively low (50 to 60 percent). The furnace effluent is immediately quenched with cold

EDC to stop undesirable side reactions. The resulting vapor-liquid mixture then goes to a

purification system. Some processes use an absorber-stripper system to separate HCl from

the chlorinated hydrocarbons, while other processes use a refrigerated continuous distillation

system.

Oxychlorination

Modern VCM plants use recycled HCl to produce more EDC via oxychlorination, which

entails the reaction of ethylene, oxygen and hydrogen chloride over a copper(II) chloride

catalyst to produce EDC:

CH2=CH2 + 2 HCl + ½ O2 → ClCH2CH2Cl +H2O.

The reaction is highly exothermic.Due to the relatively low cost of ethylene, compared to

acetylene, most vinyl chloride has been produced via this technique since the late 1950s.

This is despite the lower yields, lower product purity and higher costs for waste treatment.

By-products of the oxychlorination reaction, may be recovered, as feedstocks for chlorinated

solvents production. One useful byproduct of the oxychlorination is ethyl chloride, a topical

anesthetic.

Figure 1 : Notation of direct chlorination, oxychlorination and cracking

c) Physical properties of VCM

VCM is a colourless gas with a molecular weight of 62.5 and boiling point of -13.9°C,

and hence has a high vapour pressure at ambient temperature. , it is extremely flammable

and unstable. It has a mild, sweet odour. The threshold for detecting odour is 3000 parts per

million. VCM is soluble in many organic solvents but is not soluble in water It is therefore

manufactured under strict quality and safety control..

Specific gravity: 0.9106

Melting Point: -153.8

Relative vapour density: 2.2

Flash point: -77.8

d) Manufacturers of VCM

Global capacity for VCM was about 76 billion pounds (35 million metric tons) in 2005.

The Dow Chemical Company and its consolidated subsidiaries (“Dow”) are one of the largest

producers of VCM in the world. Dow has VCM manufacturing facilities in Freeport, Texas,

Plaquemine, Louisiana, and Schkopau, Germany. A VCM manufacturing facility located in

Fort Saskatchewan, Alberta, Canada, was shut down in 2006. Dow has roughly 5.1 billion

pounds (2.4 million metric tons) of VCM capacity at the remaining facilities.

Table 1:  VCM capacity and production trends (in thousand metric tonnes)

Region North

Am.a

W.

Europe

Japan Other

Asia b

Otherc Total

Annual Capacity,

1992

6540 6315 2485   7860

(rest of

world)

23200

Annual Capacity,

1996

8027 6420 3189 4236 4461 26333

Operating rate 1996 92% 89% 88% 91% 70% 87%

Actual Consumption

1996d

6723 5266 2486 4877 3462 22814

Regional Avg. Growth

1996-2001 (%)

4.0 2.0 -0.5 9.5 6.5 5.0

             

e) VCM production in TURKEY

Vinyl chloride monomers are manufactured in PETKİM petrochemical holding in

Turkey. PETKİM has a capacity of VCM 142000 tons/years.

2) SYNTHESIS MECHANISMS of PVC

This is the case for PVC, which is made from vinyl chloride monomer known usually by

its initials VCM through polymerisation.

The process of `polymerisation' links together the vinyl chloride molecules to form

chains of PVC. The PVC produced in this way is in the form of a white powder. This is not

used alone, but blended with other ingredients to give formulations for a wide range of

products.

VCM is polymerized via free-radical methods . VCM has a liquid density at normal

polymerization temperature between 0.85-0.9 g/cm. The polymer has a density of 1.4 g/cm3

which is a sign of the large shrinkage during polymerization.

Figure 2 : Free radical mechanism of PVC .

3) MANUFACTURING of PVC

There are four polymerization routes for the manufacture of PVC. They are as

follows :

Process Route % of World Production

a. Suspension Polymerization 80

b. Emulsion Polymerization 10

c. Bulk or Mass Polymerization 8-10

d. Solution Polymerization 0-2

First, the raw material VCM is pressurised and liquefied, and then fed into the

polymerisation reactor, which contains water and suspending agents in advance. Through

high-speed agitation within the reactor, small droplets of VCM are obtained. Next, the initiator

for polymerisation is fed into the reactor, and PVC is produced by reaction under a few bar at

40 - 60°C.?PVC obtained through suspension polymerisation is suspended in water as

particles of 50~200 ?m diameter (in slurry form). Thereafter the slurry discharged from the

polymerisation reactor is stripped of residual monomer, dehydrated, dried and the particle

size controlled by screening to yield PVC in the form of a white powder. The un-reacted VCM

is entirely recovered through the stripping process, and after purification, recycled as raw

material for reuse in this process. PVC resin produced via this ‘suspension’ process is

referred to within the industry using the abbreviation S-PVC.

Emulsion polymerisation and bulk polymerisation are alternative, much less extensively

employed, technologies to manufacture PVC. Emulsion polymerisation produces finer resin

grades having much smaller particles, which are required by certain applications. This type of

resin is sometimes called ‘paste’ PVC and referred to within the industry using the

abbreviation P-PVC to distinguish it from S-PVC.

Kinetic features of manufacturing proceses:

The following significant features are common for bulk-, suspension- and emulsion

polymerization.

1. The reaction is autocatalytic from the on set of reaction.

2. The reaction order, with respect to the initiator, is close to 0.5.

3. Molecular weight does not depend upon the conversion or the initiatorconcentration.

Molecular weight and molecular weight distribution are similar for bulk and emulsion

polymerization.

4) PROPERTIES OF POLYVINYL CHLORIDE

Polyvinyl chloride has a chemistry and a physical structure that makes it

broadly unique in the polymer world. PVC (often referred to vinyls or vinyl resins) is

made commercially at several molecular weights, depending on the intended

applications: from Mw = 39000 g/mol, to Mw = 168000 g/mol

Chemical structure of PVC

Polyvinyl Chloride is similar in structure to polyethylene, but each unit contains a

chlorine atom. The chlorine atom renders it vulnerable to some solvents, but also makes it

more resistant in many applications. PVC has extremely good resistance to oils (except

essential oils) and very low permeability to most gases. Polyvinyl chloride is transparent and

has a slight bluish tint. Narrow-mouth bottles made of this material are relatively thin-walled

and can be flexed slightly. When blended with phthalate ester plasticisers, PVC becomes

soft and pliable, providing the useful tubing to be found in every well-equipped laboratory.

Physical properties of PVC

PVC has an amorphous structure with polar chlorine atoms in the molecular structure.

Having chlorine atoms and the amorphous molecular structure are inseparably related.

Although plastics seem very similar in the context of daily use, PVC has completely different

features in terms of performance and functions compared with olefin plastics which have only

carbon and hydrogen atoms in their molecular structures.

Chemical stability is a common feature among substances containing halogens such as

chlorine and fluorine. This applies to PVC resins, which furthermore possess fire retarding

properties, durability, and oil/chemical resistance.

PVC Strenght

PVC is extensively used for municipal water supply/sewage pipes, spouts, profiles, etc.,

since its mechanical properties such as tensile strength and tensile modulus are better than

those of other general purpose olefin plastics, and these products are robust and durable.

When plasticisers are added, PVC shows rubber-like elasticity with high tensile

strength and fatigue strength, and can be used for industrial hoses, gaskets, automobile

parts, and electric cable covering.

Tensile strength

Figure shows the comparison of tensile strength of PVC products with other plastics.

The tensile strength is expressed in terms of the maximum stress per unit area of the cross

section when the test piece breaks by applied loads to both ends of the test piece. (An index

to show the magnitude of force at break, when both ends of the test piece are pulled apart)

--Tensile strength of various plastics

Tensile modulus

Figure shows the comparison of tensile modulus of PVC products with other plastics.

The tensile modulus is also known as the Young’s Modulus, which is expressed in terms of

the ratio between the tensile stress per unit area of the cross section and the elongation in

the direction of the tensile stress. Plastics possessing large tensile modulus have a small

stress-strain ratio. In other words, the tensile modulus is an index showing the magnitude of

elongation, when a test piece is pulled apart. It is the equivalent of the spring constant.

--Young's modulus of various plastics

Bending strength

Figure shows the bending strength of PVC products in comparison with other plastics.

It is expressed in terms of the maximum stress upon break of the test piece, where the test

piece is supported at two points apart and a vertical stress load is applied at the centre. (An

index to show the magnitude of force at break, when the test piece is bent).

--Bending strength of various plastics

Impact strength

The glass transition temperature (second order transition point) of PVC is over 70°C.

The result is low impact strength at room temperature, which is one of the disadvantages of

PVC. There are many ways to measure impact strength. Figure shows the results of

energies absorbed by test pieces when they are fixed and hammered to break (impact

failure). Higher values show higher impact strength.

Creep properties

Plastic products are said to show a ‘creep behaviour’, where the product is deformed at

room temperature as time elapses when an external force is applied continuously.

--Creep properties of various thermoplastics

The phenomenon is also known as cold flow. When plastics are used for construction or

industrial applications, cold flow is an especially important point to be considered. Under

normal environmental conditions, rigid PVC products show very little creep and are superior

in comparison with other plastic products such as PE or PP. Therefore, PVC is used in

various interior and exterior construction materials (e.g., ducts, panels, window frames and

decks) and electric or machine parts.

Plasticising

PVC is a polar polymer with strong intermolecular forces, therefore it is rigid at room

temperature. On the other hand, when a plasticiser is added upon fabrication, flexible PVC

products are obtained. This versatility is a major advantage of PVC.PVC products without

any plasticisers are called rigid PVC products, while PVC products that include plasticisers

are called flexible PVC products. The softness of the flexible PVC products is obtained as a

result of plasticisers coming between molecules to separate them, reducing intermolecular

forces.

Chemical Resistance

Since the main chain of the polymer is made by single bonds of carbon atoms, PVC has

excellent chemical resistance, as with other general-purpose plastics such as PE, PP, or PS.

The chart shows the chemical resistance of PVC in comparison with other plastics.

Some of the engineering plastics and specialty resins are susceptible to acid or alkali,

and some plastics have excellent chemical resistance properties, such as polyfluorocarbons.

PVC has excellent chemical resistance together with good mechanical properties, therefore

is used for chemical storage tanks, plastic valves/flanges, drainage/sewage pipes, and plant

piping.

5) OVERWİEV of PAST,CURRENT and FUTURE CAPACITY in the PVC INDUSTRY

Polyvinyl chloride plastics are the second largest class of theromoplastics in the world,

after the polyethylenes.  Global PVC production capacity amounted to approximately 26

million metric tons (57 billion lbs.) in 1997 and is expected to increase by approximately 5.5%

per year through the year 2002.  Thus, world PVC production capacity is expected to reach

34 million metric tons (75 billion lbs.) by the year 2002.  From 1992 to 1997, PVC production

capacity rose an average of 2% per year, actually going down in Europe.  Regions of

greatest PVC capacity growth into the next millennium include Asia, Eastern Europe, the

Middle East, and South/Central America.  Per capita PVC consumption in these areas is in

the range of 2 kg compared to 6-8 kg in North America, Western Europe and Japan.  These

three countries/regions account for approximately 60% of PVC production.  To satisfy quickly

growing demand in Asia, Latin America and Eastern Europe, mainly due to large investments

in construction and infrastructure, 3.4 million metric tons of capacity are expected to be

added in developing countries by 2001.  Capacity in Asia (except for Japan) is expected to

almost double by the year 2002.

Table 2 :Regional PVC Capacity and Expected Expansions (in thousands of metric tons per

year)

Region 1992 1997 2002 Avg. Annual growth %

North America 5210 (only U.S.) 7730 9350 4

Western Europe 6335 6185 6320 0.5

Japan 2375 2772 2772 0

Other Asia   5755 10150 12

Other regions 9620 (all other

regions)

     

     Africa   370 370 0

     Middle East   940 1095 3

     South America   1240 1550 4.5

     Eastern

Europe

  840 2380 23

     Oceania   200 200 0

Total 23540 26032 34187 5.5

(Source:  SRI International)

PVC is currently produced by approximately 150 companies in 50 countries.  Table 3

shows that PVC production is highly concentrated in a few large companies, with the top 10

PVC producing companies amounting for more than 40% of global capacity.  Formosa

Plastics (Taiwan) accounts for approximately 8% of global PVC production

capacity. Operating rates (actual production/capacity) range from 90% in North America to

70% in other regions.  With the exception of Shin-Etsu (Shintech), all of the largest PVC

producers have captive sources of VCM (Shin-Etsu purchases theirs from Dow, though the

proposed Shintech plant in Louisiana would have a captive source of chlorine and VCM). 

Consumption of PVC in the world

Global consumption of PVC reached a level of about 31 million tons in 2005. PVC is a

matured polymer with average growth rate less than World GDP, but is seeing good growth

in Asia due to more emphasis on infrastructure and construction. In fact, markets indicate

that the power of business in PVC and related sectors are surely shifting to Asia, where PVC

is growing at about 7% or almost at the same rate as Asia's GDP growth. North America as

well as Europe are both matured markets for PVC. These regions are expected to grow at

less than 3% in the coming five years. Asia is therefore expected to have a larger share in

PVC consumption as compared to Europe and North America by 2010. 

The global plastics additives market was about 9.9 million tons in 2004, valued at

US$19 billion. Overall, the additives market is expected to grow at 4% AAGR from 2004 to

2009. While Europe, North America and Asia-Pacific (excluding China) are growing at about

3%, China is predicted to grow at 8-10%. The other smaller market regions are also poised

to grow at 5-6% through 2009. India could be the next big growth area. 

PVC consumes more than 65% of the total volume of 9 million tonnes of additives, with major

portion of this volume arising from plasticizers. Additives for PVC excluding plasticizers,

amount to a volume of over 2 million tons. The regional distribution of additives in 2005 has

reached a level of 23% in Asia. Europe continues to be the largest region with almost 25% of

the total global consumption currently. PVC wire and cable sector also consumes lead

stabilizers and will continue to use them because of inherent advantages offered by lead in

terms of superior electrical resistance. While wire and cable sector constitutes only about 2-

3% of the total PVC consumption, it requires heavy dosage of lead stabilizer at about 2-3%

level. Lead stabilizers are being phased out in Europe. It is expected that by 2010, lead will

be replaced by lighter metals like calcium or zinc, as well as organic stabilizers. Most of the

replacement of lead will take place in pipe sector. The wire and cable sector is expected to

stay with lead stabilizer longer until a suitable alternate is developed matching technical

performance of lead. All the developments in this area still continue to be deficient. 

PVC melt gets stuck on hot metal during processing. It therefore requires higher level

of lubricants that prevent sticking of PVC melt to hot metal. In addition, improving flow by

addition of PVC compatible additives called internal lubricants are also used. Lubricants of all

types are added at about 0.5-1% levels. Obviously 15% of the PVC additives comprise of

lubricants. 

PVC requires the largest dosage among all other polymers. Antioxidant is generally

used by polyolefins, but PVC is quite resistant to oxidative degradation. However the dosage

of antioxidant is lower than 0.2% compared to average 2-3% of heat stabilizer used in PVC.

Antioxidant therefore has only has 1% share of the global additive consumption by volume.

PVC manufacturing in TURKEY

PVC is manufactured in PETKİM holding in Turkey which has the capacity of 150000

tons/years.

6) PVC and THE ENVIRONMENT

Because of its extraordinary stability, PVC is difficult to dispose of. It is not

biodegradable and unlike polyethylene and many other plastics it is only very slowly

decomposed by exposure to the sun.

When PVC is burned it gives off hydrochloric acid and some of the chlorine combines

with other material to form very toxic and stable organochlorine compounds such as dioxins.

See also Introduction (Persistent Organic Pollutants).In some countries the use of building

materials containing PVC is prohibited, mainly because of the very toxic fumes which are

formed when there is a fire. In Australia, some local councils are promoting the use of

alternatives to PVC pipe, such as aluminium and clay.It is possible to recycle PVC by melting

and remoulding it, but there is little recycling of PVC in Australia; the recycling code number

for PVC is 3.

Health effects

When the monomer is polymerised to form the plastic it is no longer toxic, but a very

small amount of the monomer remains in the product. PVC intended for use with food is

made to very stringent specifications and, in Australia, must not contain more than five ppm

of vinyl chloride monomer. It is important that only 'food-grade' PVC be used with food as

ordinary PVC may contain much more of the toxic monomer. This can diffuse out of the

plastic into the food, particularly if the food is oily or strongly acid or alkaline. For example, do

not use garbage cans for making fruit drinks or pickled cabbage, or for storing edible oil.

7) USES of PVC

PVC is used extensively within the construction industry for the following products:

* Pipes and fittings

* Siding

* Windows

* Flooring

* Fencing

* Decking

* Roofing

* Wall coverings

* Wire and cable products

* Transport and packaging materials

* Medical supplies

* Consumer products (such as credit cards and toys)

8) REFERENCES

- Allen, D. T. "Chapter 4 - Industrial Ecology". Green Engineering. United States

Environmental Protection Agency.

- Chemical Economics Handbook Report Vinyl Chloride Monomer (VCM), SRI Consulting,

July 2006, pages 4, 10, 11, and 20.

- faculty.ksu.edu.sa/alhajali/ChE534_CourseNotes/PVC.pdf

- aquaticpath.umd.edu/appliedtox/wendy.pdf

- www.npi.gov.au/substances/vinyl-chloride-monomer/index.html

- www.pvc.org/en/p/vinyl-chloride-monomer-vcm

- earth911.com/recycling/construction/pvc/facts-about-pvc/

- www.vinylchem.com/news.html

- www.safersolutuions.org.au/a/180?task=view

GÖZDE SALKIÇ

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