Plastics are polymers primarily made of carbon, hydrogen and oxygen.
The structure of polymers is like a chain where repeating units (-mers) are connected many (-poly)times.
Each unit of a polymer is called "monomer" and the chemical process through which monomers are converted to polymer is known as "polymerization" e.g. ethylene and propylene are monomers and polyethylene and polypropylene are polymers.
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The process of manufacturing starts from natural gas or naphtha by a process called "cracking". In this process larger molecules are broken into monomers such as ethylene, propylene, etc. These monomers are then chemically bonded to form a chain called "polymer". If one type of monomer is used it is termed as "homopolymer" while a combination of different monomers results in "copolymers".
Classification of plastics
Plastics are broadly classified in two types: Thermoplastics & Thermosets.
Thermoset materials undergo chemical change (crosslink) with the application
of heat which results in permanent and non-reversible setting of the material.
Urea formaldehyde and melamine are examples of thermosets.
In thermoplastic materials, melting and solidification is a reversible process
which facilitates reuse several times. PE, PP, PVC, and PS are from the family of thermoplastics. Thermoplastics are further classified into three major categories depending on their properties and applications:
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Polymer Characteristics:
While each polymer is unique, the various polymer properties can
broadly be classified as under:
a) Light weight in comparison to metal, glass
b) Good insulator of heat and electricity
c) Good chemical resistance
d) Multiple processing capabilities to produce complicated parts with precision
e) Can often improve wear resistance, part life, and reduce need for lubrication.
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