Organic And Inorganic Polymers

Organic and Inorganic Polymers

Organic Polymers

All the covalent macromolecules which have carbon ib their backbones are called organic polymers.They are formed by the combination of inorganic species.Example:polythene,polyvinylchloride,nylon-6,6,etc.

Inorganic Polymers

All the covalent macromolecules which do not have carbon in their backbones are called inorganic polymers.Inorganic polymers are polymers with a skeletal structure that does not include carbon atoms. They are formed by the combination or addition of organic species. One of the best known examples is polydimethylsiloxane, otherwise known commonly as silicone rubber. It has a repeat unit based on silicon and oxygen:

—[O-Si(CH₃)₂]_n—

Rubber

Rubber is a naturally occurring polymer.Rubber consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds plus water. Malaysia is one of the leading producers of rubber. Forms of polyisoprene that are used as natural rubbers are classified as elastomers. Natural rubber is used by many manufacturing companies for the production of rubber products. Currently, rubber is harvested mainly in the form of the latex from the para rubber tree or others. The latex is a sticky, milky colloid drawn off by making incisions into the bark and collecting the fluid in vessels in a process called "tapping". The latex then is refined into rubber ready for commercial processing. Natural rubber is used extensively in many applications and products, either alone or in combination with other materials. In major areas latex is allowed to coagulate in the collection cup. The coagulated lumps are collected and processed into dry forms for marketing. In most of its useful forms, it has a large stretch ratio and high resilience, and is extremely waterproof.

Vulcanization of rubber

Natural rubber is a thermoplastic.There are no cross links between the polymer chain.It becomes soft and sticky in presence of heat.The property of natural rubber can be modified by a process of vulcanization.To improve its properties,it is heated with sulphur at a temperature 373 K to 415 K.

The process of heating natural rubber with sulphur to improve its properties is called vulcanization of rubber.It is a slow process but nowadays it is accelerated by adding zinc oxide with rubber.During vulcanization,sulphur cross links are formed which makes the rubber hard and tough.

A variety of methods exist for vulcanization. The economically most important method (vulcanization of tires) uses high pressure and temperature after the curative has been added to the rubber. A typical vulcanization temperature for a passenger tire is 10 minutes at 177°C. This process employs the technique known as compression molding, where the rubber article is intended to adopt the shape of the mold. Other methods, for instance to make door profiles for cars, use hot air vulcanization or microwave heated vulcanization (both continuous processes).

Five types of curing systems are in common use. They are:

1. Sulfur systems
2. Peroxides
3. Metallic oxides
4. Acetoxysilane
5. Urethane crosslinkers

Plastics

Plastics are formed from the group of high polymers which have a fair range of deformability and mouldability particularly at a high temperature.These synthetic polymers are used in the form of sheets,pipes,films and moulded objects.

Resin

Resin is a clear sticky substance produced by a plant or similar substance produced chemically for the use in the industry.Resins are used in polymer,medicine,and paint industry.Resins can be grouped as natural and synthetic resins.

i)Natural resin:

It is produced by a plant.For example:pine sap.

ii)Synthetic resin:

Synthetic resins are liquid monomers of thermosetting polymers.These are much more stable and uniform than that of natural resins.They are produced in the industry.For example:artificial paints.

Fibres

The polymers in which the molecular chains are held together through a strong intermolecular force is known as fibres.They possesses a very high tensile strength.For example:nylon-6,6,polyester,etc.

References

(c.Prutton, 1992)

(K.L.Kapoor, 1999)