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Plastics & Rubbers

Plastics are made up of polymers, but some polymers like biopolymers are not plastics. Plastic materials are being used in day to day life like computers, pen, mobile phones, compact discs, pen drive, and toothbrushes, etc.

Plastic is defined as any synthetic or semi-synthetic organic material that can be shaped or molded into any form. The chemical composition of plastics includes chains of carbon, oxygen, sulfur or nitrogen.

Rubber is considered as an elastic substance, which is obtained from the exudations of certain tropical plants (natural rubber) or derived from petroleum and natural gas. Rubber also termed as an elastomer, a type of polymer. In 1770 Joseph Priestley coined the term rubber.

Rubber is divided into two groups based on its origin

Natural rubber – used in racing car tires, bus tires, truck tires

Synthetic rubber – examples butadiene rubber, styrene butadiene rubber, neoprene

Physical & Chemical properties of rubber

Did you ever wonder how rubber will stretch?

Before you want to know the reason one should know the physical and chemicals properties of rubber

Physical properties

In a relaxed state, rubber is in the form of long, coiled-up chains. By stretching of rubber all chains will come very close as result, the kinetic energy exerted in the form of heat. In chain elongation process entropy and temperatures required during this process are increased. When chain in relaxed state both entropy and temperatures decrease.

Relaxation of a stretched rubber band is thus driven by a decrease in entropy and temperature, and the force experienced is a result of the cooling of the material being converted to potential energy. The material undergoes adiabatic cooling during contraction.

Vulcanization of rubber creates disulfide bonds between chains. The result is that the chains tighten more quickly for a given strain, thereby increasing the elastic force constant and making rubber harder and less extensible.

Chemical properties

Like plastic, rubber is also a type of polymer, made of subunits called monomers. In rubber, the monomer is isoprene. As the latex dries, the isoprene molecules mass together and one isoprene molecule attacks a carbon-carbon double bond of a neighboring molecule. One of the double bonds breaks and the electrons repositioned to form a bond between the two isoprene molecules.

The process continues until long strands of many isoprene molecules linked like a chain. This long chain of strands is called as polyisoprene polymer. As the drying continues, the polyisoprene strands stick together by forming electrostatic bonds. The attraction between these strands holds the rubber fibers together and allows them to stretch and to recover.

Synthetic rubber production

Emulsion polymerization is the widely used method to produce synthetic rubber.

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