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POLYVINYL CHLORIDE

(PVC)

Term Paper

For the partial fulfilment of course:

ME 6720 POLYMERS-I

By

Sai Goutham Soma

U00732813

Wright State University

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Structure

The strongest non-covalent bond after hydrogen bond is dipole-dipole

interaction as in 𝐶 − 𝐶𝑙 in the polyvinyl chloride. The electronegativity

difference between the atoms involved in the polar bond is large and hence

it is weaker than the hydrogen bond.

Polyvinyl chloride often termed as PVC is made from its monomer unit

vinyl chloride (𝐶𝐻2 = 𝐶𝐻𝐶𝑙) which is toxic gas at normal conditions. The

polymerized vinyl chloride which is obtained by catalytic polymerization

is a homopolymer. The homopolymer obtained is brittle, hard and also

difficult to process as the reaction cannot be controlled. PVC has a linear

structure which forms long chains. But homopolymer PVC is not used for

commercial use. So some additives are added to make it copolymer and

also for the ease of reaction.

PVC is classified as amorphous polymer. Crystallinity varies from 5-15%.

Crystallinity increases rapidly if the reaction is taking place below the room

temperature. Branching depends mostly on the reaction temperature. It is

directly proportional to the reaction temperature.1

Both isotactic and syndiotactic formations occur in the PVC. The head to

tail configuration that is carbon atom having pendant Cl atom attaching

with the non-pendant carbon atom of the other monomer is predominant

than head to head and tail to tail bonding.5

(Fig from Polymer science)

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Properties

Polyvinyl chloride is a thermoplastic made of 57% chlorine (industrial

grade salt) and 43% carbon (from oil / gas). Compared to other plastics

PVC has some unique properties which makes it different from others.

Mechanical properties

It has better tensile strength and tensile modulus than other olefin

polymers.

The elastic modulus of rigid PVC range from 1500-3000MPa

whereas for plasticized or soft PVC it is from 1.5-15MPa.

Flexural strength is about 10,500psi whereas compression strength

is about 9500psi. Specific gravity of PVC is 1.4.

Rigid PVC shows less creep.

Chlorine atom which is larger and almost equal to the size of carbon make

the chain to uncoil, rotate, disentangle and deform by viscous flow. Cl atom

is largely attracted by the hydrogen atom in the adjacent chain forming

hydrogen bonding. Due to this PVC is more rigid than other polymers

Thermal properties

PVC is poor conductor of heat and start to decompose at 140℃.

Melting point of PVC is 160℃, thermal expansion coefficient is

5 × 10−5/℃ and thermal conductivity is 0.14-0.28 W/m°𝐾.

Due to main chain high flexibility the heat distortion or softening

temperature of PVC is less and ranges from 54~80℃.

It is generally fire retardant. When PVC is burnt HCl gas which is

denser than air is produced there by relieving oxygen from the

vicinity which makes it self –extinguishing.

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The glass transition temperature of PVC is about or more than80℃.

This can be varied up to 100℃ depending upon the use such as hot

water pipes.

Electrical properties

PVC have good dielectric constant and so insulating properties

which makes it use for electrical appliances.

Due to large dielectric constant losses of PVC, makes it possible of

high frequency welding.

Dielectric constant varies from 2.7 to 3.1, dielectric strength-

14KV/mm and volume resistivity is about 10^16 Ohm-cm.

Optical properties

PVC is generally amorphous and so transparent. Rigid PVC

products have high transparency compared to plasticized PVC.

The polar and amorphous nature of PVC makes it have good

adhesion and printing properties.

Refractive index of PVC is 1.54.

Other properties

It has good chemical resistance towards acids, alkalis, salts,

oxidizing solvents. 2

Effect of plasticizers and other additives

PVC before processing into final products is modified or not depending on

the type of application. The unmodified PVC is known as rigid PVC

whereas the modified PVC is called soft or plasticized PVC. The PVC is

modified by adding plasticizers. The plasticized PVC is also called vinyl.

Other additives include heat stabilizers, lubricants, processing aids,

thermal modifiers, UV stabilizers, fillers and flame retardants, biocides,

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blowing agent, smoke suppressors, impact modifiers and color pigments

depending on the applications.

Plasticizers are more like a copolymer than additives. It inherits plastic

properties to the polymer. Commonly used plasticizers include diisononyl

phthalate (DINP), di-2ethylhexyl phthalate (DEHP) and diisodecyl

phthalate (DIDP). Other than phthalates, adipates and trimellitates are also

used for low temperature resistance and heat resistance respectively.

Stabilizers include metal compounds, lead stabilizers, cadmium stabilizers,

organo tin stabilizers, calcium-zinc stabilizers, Barium-zinc stabilizers and

more. Stabilizers mainly protect from thermal degradation. Metal

compounds prevent chain reaction of decomposition of the chain and also

from daylight and weathering. Pb stabilizers are used for excellent

electrical properties and water resistivity, Ca-Zn stabilizers are used for

blood bags, toys and food packaging.7

Applications

For typical applications PVC can be used after it is extruded or molded by

injection molding process or blow molded or other for its final use. Its

intrinsic properties makes vast use in the regular life.

Mechanical properties applications

PVC is extensively used for making pipes which include household

and industrial purposes. It is used for sewage by the municipality.

Its light weight, strong and durable nature makes its use

construction. It is used to make windows, claddings, fittings, roof

ceiling and flooring.

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It is used in light weight furniture like tables, skiing equipment etc.

PVC is used to make clothing which replace leather, latex etc. it is

used to make water proof clothing like rain coats and jackets.

Other applications include making toys, automotive appliances,

balls, pools (paddling) etc.

Electrical purposes

The electrical properties makes it useful for insulating of electrical

cables.

Biodegradable properties applications

Coming to healthcare it plays a vital role. PVC with DEHP (Di-

2ethylhexylphthalate) is used or making blood bags. It is also used

in heart and lung equipment, catheters and cannulae, surgical gloves,

Inhalation masks, packing for medicines, tubing for nerve flow like

dialysis and urine continence, syringes etc.

PVC is also used in packaging extensively. Packing equipment for

food products, medicines, toiletries, electronic parts and accessories,

tools, toys and bottle sieving, tapes for adhesion. 2

Processing

Specific application: PVC rigid pipes

Polymerization

First the monomer is obtained by

Direct reaction of acetylene with HCl.

𝐶𝐻 ≡ 𝐶𝐻 + 𝐻𝐶𝑙 → 𝐶𝐻2 = 𝐶𝐻𝐶𝑙

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Reaction of ethylene with chlorine.

𝐶𝐻2 = 𝐶𝐻2 + 𝐶𝑙2 → 𝐶𝐻2 = 𝐶𝐻𝐶𝑙

Oxy-chlorination

1

2𝑂2 + 𝐶𝑙2 + 2𝐶2𝐻4 → 2𝐶𝐻2𝐶𝐻𝐶𝑙 + 𝐻2𝑂

The obtained vinyl chloride undergoes free radical polymerization to form

its polymerized product poly vinyl chloride.4

𝐻2𝐶 = 𝐶𝐻𝐶𝑙 + 𝑅 → 𝑅 − 𝐶𝐻 − 𝐶𝐻𝐶𝑙 ∙

𝑅 − 𝐶𝐻 − 𝐶𝐻𝐶𝑙 ∙ +𝐶𝐻 = 𝐶𝐻𝐶𝑙 → 𝑅 − 𝐶𝐻 − 𝐶𝐻𝐶𝑙 − 𝐶𝐻 − 𝐶𝐻𝐶𝑙 ∙

𝑅 − 𝐶𝐻 − 𝐶𝐻𝐶𝑙 − 𝐶𝐻 − 𝐶𝐻𝐶𝑙 ∙ +𝐶𝐻 = 𝐶𝐻𝐶𝑙 → −(−𝐶𝐻 − 𝐶𝐻𝐶𝑙−)n

Processing of PVC

Commercial preparation of PVC is done by suspension polymerization

mostly. Other processes include emulsion and bulk polymerization which

are used less frequently.

The vinyl chloride monomer generally called as VCM is prepared by

ethylene processed from crude oil and chlorine from rock salt obtained

from sea water. It is generally followed by oxychlorination technique.

Coming to suspension polymerization VCM which is pressurized and

liquefied is fed into the polymerization reactor. The polymerization reactor

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contains water and suspension agents. The reactor is agitated with high

speed so that small droplets of VCM are obtained. Then the initiator is fed

into the reactor in which the reaction takes place under low pressure

at 40℃ − 60℃. PVC is obtained by suspending in water to get particles of

size 50𝜇𝑚 − 200𝜇𝑚 diameter in slurry form. The slurry is then discharged

from the reactor to stripper which separates slurry from the residual

monomer. The VCM which didn’t react or remained is collected through

stripping process and is purified to use it again in the next process.

The separated slurry is sent into the centrifuge where excess water is

removed. The dehydrated slurry is sent into the drier where the white

powdered PVC is obtained. By sieving the white powdered PVC in the

sieve machine particles of the required size is obtained.3

The PVC thus obtained by suspension polymerization is called S-PVC.

About 80% of the PVC is manufactured by suspension polymerization.

The PVC obtained by emulsion polymerization is called P-PVC to

distinguish from S-PVC obtained by suspension. Emulsion polymerization

is used to get finer grades of PVC. The advantage of bulk polymerization

is PVC obtained is free from impurities but heat removal is main problem.5

Manufacturing of rigid PVC pipes

PVC rigid pipes are manufactured by extrusion process. Extrusion is a

process through which plastic is melted and then extruded into required

profiles. This process is only applicable for continuous profiles only. The

obtained continuous profiles are cut to length. Extrusion is used for profiles

like pellets and rods, solid profiles like rods, pipe and tubing, sheets and

extruded flat film, coating of wire and cable, blown films, synthetic fibers

and so on.

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Extrusion

In extrusion process the raw plastic or polymer is fed into the extruder

cylinder or barrel via hopper. The raw material feed may be granules,

powder, some cases additives are also mixed. The cylinder consists of a

screw called as extrusion screw. It is specially designed for the mixing and

forward movement of plastic in the barrel. The extrusion screw turns inside

the barrel which then conveys the forward movement of the plastic into the

heated region. The plastic which is heated by the external source as well as

by the friction developed inside by moving parts melts the plastic. The

screw forwards the molten plastic into a hole and enters into special screen

which filters the contaminants out. The molten plastic then moves into a

die to get required profile. Then the output is cooled by sealed water bath

so that no stresses or holes or collapsing of the profile occurs. Some other

auxiliary equipment is used to pull the extrudate out at a continuous rate.

The plastic obtained after cooling is a continuous profile is cut to length.

After certain time the friction and pressure would be enough to maintain

the temperature inside the barrel. So the heater would be switched off to

avoid energy losses. Extrusion lines can be very long.1

Extrusion Screw (Fig from www.pvc.org)

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PVC pipe extrusion

The rigid PVC is hard and brittle which makes it break easily. So in order

to be less prone to impact modifiers are added. Some of the modifiers used

are methacrylate butadiene styrene terpolymers (MBS), chlorinated

polyethylene (CPE) resins. These are known as impact modifiers. DuPont

Dow Elastomers using hydrocarbon rubbers and chlorinated polyethylene

as impact modifiers claim the following compositions:

a vinyl chloride polymer,

2 to 20 parts by weight of at least one ethylene/alpha-olefin

copolymer per 100 parts vinyl chloride polymer, said

copolymer having a density of 0.858 to 0.91 g/cc and having

a melt index from an I10 value of 0.1 to an I2 value of 10, and

To less than 1 part by weight of at least one randomly

chlorinated polyolefin per 100 parts of vinyl chloride

polymer.6

Other additives such as UV stabilizers which include benzo-phenones are

also added. These are mixed in the hopper in proper ratio and sent into the

extrusion barrel. The die used for the processing of these pipes is called

spider die. This die consists a mandrel which acts an obstruction and allows

the formation of pipe.1

Spider die (Fig from 1)

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The polymer mixture is heated up to 150℃. The plastic is heated in three

blocks of heaters with temperature varying in each block from low to high.

The molten plastic is sent in the die after passing through the filter screen

and then the profile is obtained. The pipe profile should not be disturbed

so that flaws don’t occur. It is cooled in sealed water bath. There is puller

which keeps the output profile even. The pipe is then cut to length by the

cutter and sent to packing.1

Rigid PVC pipes

The rigid pipes commonly produced is PVC pipe-Schedule 40. The

samples are sent to the lab for testing. The hardness is tested by Rockwell

hardness test and the thermal tests, pressure tests are also done. The below

are the specifications of Schedule 40

Outer diameter as much as 0.405 inch to 24 inch.

Thickness may vary from as much as 0.109inch to 0.500inch.

The typical temperature that a rigid pipe will resist is about 140℉.

Pressure varies in between 120psi to 810psi.8

All PVC Schedule 40 pipe shall be manufactured from a Type I, Grade I

Polyvinyl Chloride (PVC) compound with a Cell Classification of 12454

per ASTM D1784.8

The average degree of polymerization of the PVC resin used in the making

of rigid pipes is usually in between 950-850.

After Polyethylene and Polystyrene Polyvinyl chloride is mostly produced

in the world. As per 2007 the amount of PVC produced in the USA and

Canada is about 6426 thousand metric tons which account to $17.7 billion

market.

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References

1. Strong A. Brent (1996), Plastics Materials and Processing 3rd

edition, New Jersey, Pearson Education.

2. Harold A. Sarvetnick (1977), Polyvinyl Chloride, R. E. Krieger

Publication Company.

3. Burgess, R.H (1982), Manufacturing and processing of PVC, New

York, Ed., MacMillan.

4. Coroyannakis Panayotis E, Polymerization of vinyl chloride (1978),

Open Access Dissertations and Thesis, Paper 347.

5. Leonard I. Nass, Charles A. Heiberger (1986), Encyclopedia of PVC

Volume 1, 2nd edition, Markel Dekker, INC.

6. Gary R. Marchand, Mark T. Berard, US patent 6706815 B2.

7. ASM International, Engineering Materials Handbook Vol2

Engineering Plastics.

8. ASTM, Rigid PVC pipes specifications and properties.