PVCPoly Vinyl Chloride.

Accidental miracle…….

IntroductionPVC is the third most used plastic after

polyethylene and poly propylene. Due to its duarability strength and cost effectiveness it has wide applications.

On adding plasticizers it is being used as pthalates which is used in clothing industry, inflatable material and rubber replacement industries.

Pure PVC is a white brittle solid, it is insoluble in alcohol but slightly soluble in Tetra hydro furan.

DiscoveryIt was discovered by two chemists working

independently in the nineteenth century. Surprisingly it was accidental.

The polymer appeared as a white solid inside flasks of vinyl chloride that had been left exposed to sunlight.

It was more flexible and more easily processed material and hence is widespread in its applications.

ProductionPVC is produced by polymerisation of

monomer vinyl chloride.The production involves suspension and

emulsion polymerization where suspension has a major share.

The structure of polymer is linear.

Polymerisation of PVC takes place by addition polymerisation mainly by free radical mechanism.

The monomers are mostly arranged head to tail, that is chlorides on alternating carbon centres.

PVC has mainly atactic stereo chemistry, which means that the relative spatial arrangements of the chloride centres are random.

Suspension polymerisationVinyl chloride monomer and water along with

polymerisation initiator and other additives are taken into a reactor.

The reactor is pressurized and the contents are continually mixed to maintain the suspension and to ensure the uniform size of formed PVC.

The reaction is exothermic and thus requires cooling

As the volume is continually reduced water is added to maintain the suspension.

AdditivesPTHALATE PLASTICIZERS- Plasticizers are

compounds that improve the performance characteristic quotient of PVC. They must have less volatility and less toxicity. The following is Bis(2-ethyl hexyl)pthalate.

HEAT STABILIZERS - These are one of the most important additives. These agents minimise loss of HCl which is a degradation process that starts at 70 degree celsius.

Once dehydrochlorination starts the process is autocatalytic and hence it must be minimised. Derivatives of heavy metals and Calcium stearate are traditional heat stabilizers.

PHYSICAL PROPERTIESGlass Temperature - 82 degree celsius

Melting Temperature – 100 to 260 degree celsius

Effective Heat of Combustion – 17.95 MJ/Kg

Specific Heat – 0.9 KJ/(kg.K)

Density – 1.1 to 1.45 g/c.c

PropertiesMechanical- PVC has high hardness. These

properties increases with increasing molecular weights and decreases with increasing temperatures.

Thermal- As the heat stability of PVC is very poor we are adding the heat stabilizers. It starts to decompose at 140 degrees Celsius and melts at 160 degree Celsius.

Electrical- PVC is a polymer with good insulation properties and generally suitable for medium or low voltage and low frequency insulations.

Chlorinated PVCPVC can be usefully modified by chlorination,

which increases its chlorine content .The new material has higher heat resistance so it is primarily used for hot water pipes and fittings.

CPVC is produced by chlorination of aqueous solution of suspension PVC particles followed by exposure to UV light which initiates the free radical chlorination.

ApplicationsPVC is relatively low cost, biological, chemical

resistance and workability of it resulted in it being used in many applications.

PIPES- It is used for sewage pipes and other pipe applications where cost or vulnerability to corrosion limit the use of metal.

Electrical cables- PVC is an insulator and hence used for insulation of electric cables. For this purpose it must be plasticized

Other applicationsIt is used in ConstructionClothingFurnitureSportsHealth careFlooring The image is of a black PVC pants.

DisadvantagesRecycling difficultyIt is not recommended for use above 70

degrees Celsius. Sensitive to UV and oxidative degradation.Limited thermal capability.Thermal decomposition evolves HCl.Higher density than many plastics.

REFERENCESwww.australianresearch.comwww.google.comwww.sciencedirectory.comWikipedia

THANK YOUA presentation by P S V Sai Teja. D Pramod Reddy. K Vishnu Teja Reddy. Nazeem. B Laxmidhar .