Poly vinyl chloride – its properties, preparation and uses

Jan 27 • General • 30260 Views • 10 Comments on Poly vinyl chloride – its properties, preparation and uses

poly vinyl chloride

1. abbreviated as PVC
2. Used in construction because it is more effective than wood , iron and copper.
3. Can be made softer by using plasticisers mostly phthalates .
4. used in clothing ,upholstery                                                                                               

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PROPERTIES

1. white, brittle solid                                                                                                                2.insoluble in alcohol                                                                                                                 3.soluble in tetrahydrofuran

PHYSICAL PROPERTIES:

1.thermoplastic polymer                                                                                                                                            2.rigid and flexible

MECHANICAL PROPERTIES:

1.High hardness                                                                                                                                            2.mechanical properties enhance with the molecular weight increasing, but decrease with the temperature increasing.                                                                                                                                  3.elastic modulus can reach to 1500-3,000 MPa.                                                                                             4.elongation at break is up to 200% -450%.                                                                                  5.PVC friction is ordinary                                                                                                                   6. the static friction factor is 0.4-0.5                                                                                                7.the dynamic friction factor is 0.23.

THERMAL PROPERTIES:

1.heat stability of PVC is very poor, when the temperature reaches 140 °C PVC starts to decompose.                                                                                                                                          2. Its melting temperature is 160 °C.                                                                                                          3.The linear expansion coefficient of the PVC is small and has flame retardation.                                  4. the oxidation index is up to 45 or more.

ELECTRICAL PROPERTIES:

1.PVC is a polymer with good insulation properties but because of its higher polar nature the electrical insulating property is inferior to non polar polymers such as POLYETHYLENE.

2.As the dielectric constant, dielectric loss tangent value and volume resistivity are high, the corona resistance is not very good, it is generally suitable for medium or low voltage and low frequency insulation materials

Chemical structure:

H Cl

|   |

– C – C –

|      |

H   H

 PREPARATION:

poly vinyl chloride is prepared by polymerisation of monomer vinyl chloride

– About 80 percent of polymerisation includes suspension polymerisation.

-12% emulsion polymerisation and 8% bulk polymerisation.

Process :  VCM and water are introduced into the reactor and a polymerization initiator, along with other additives. The reaction vessel is pressure tight to contain the VCM. 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 cooling. As the volume is reduced during the reaction (PVC is denser than VCM), water is continuously added to the mixture to maintain the suspension.

The polymerization of VCM is started by compounds called initiators that are mixed into the droplets. These compounds break down to start the radical chain reaction. Typical initators include dioctanoyl peroxide and diacetyl peroxydicarbonate, both of which have fragile O-O bonds. Some initiators start the reaction rapidly but decay quickly and other initiators have the opposite effect. A combination of two different initiators is often used to give a uniform rate of polymerization. After the polymer has grown by about 10x, the short polymer precipitates inside the droplet of VCM, and polymerization continues with the precipitated, solvent-swollen particles.

Once the reaction has run its course, the resulting PVC slurry is degassed and stripped to remove excess VCM, which is recycled. The polymer is then passed though a centrifuge to remove water. The slurry is further dried in a hot air bed, and the resulting powder sieved before storage or pelletization. Normally, the resulting PVC has a VCM content of less than 1 part per million.

USES:

1. It is used for sewerage pipes and other pipe applications where cost or vulnerability to corrosion limit the use of metal.                                                                                                                     2.With the addition of impact modifiers and stabilizers, it has become a popular material for window and door frames.                                                                                                                                 3.By adding plasticizers, it can become flexible enough to be used in cabling applications as a wire insulator.

IMPORTANT QUESTION AND ANSWERS:

1. What is PVC?                                                                                                                                   ANS: PVC stands for poly vinyl chloride which is a polymer of monomer vinyl chloride.

2. Where is PVC used?                                                                                                                       ANS: used in pipes and other household activities.

3.What are plasticizers?
ANS:Plasticizers are generally clear, organic, liquid materials that are added to PVC formulation to obtain a flexible film to enhance both processability and serviceability of the end product

4. What is UPVC?                                                                                                                                ANS: UPVC stands for unplasticised polyvinyl chloride. UPVC is also commonly known as rigid PVC and it is called this because it is hard and does not flex. This material doesn’t not contain any phthalates or BPA, so it is actually quite safe. UPVC is so stable and safe that it is actually used to make dental retainers and mouthguards.

5. Why the process requires cooling?                                                                                                 ANS: The reaction is exothermic hence the process requires cooling.

6. Which type of polymerization takes place in PVC?                                                                          ans: suspension polymerization.

7. What are the initiators is PVC polymerization?                                                                                ANS: dioctanoyl peroxide and diacetyl peroxydicarbonate.

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