Q.5 What is plastic. Give the classification of plastic. Also list their application.
Related Questions -
Q. Write short note on plastic. (AKTU. 2010 - 11)
Ans. Plastics: -
In general terms, the word plastic has been used in the past for all those materials which could be readily moulded by heating or pressure or both. But, the modern applications have changed this concept and have limited the area of this word to cover only those synthetic organic materials which become plastic when heated and can be formed into different shapes under pressure. After having been processed and finished, they are observed to be fairly hard and rigid. Various useful articles can be produced from them rapidly, accurately and with excellent surface finish. They are marked by their extreme lightness in weight, high corrosion resistance and good dielectric strength. Also they can be produced in different colors or as transparent. Plastics are also known as ‘synthetic resins’.
In scientific terms these organic compounds are called polymers. The term polymer has its base in Greek terminology, where’ poly’ means ‘many’ and ‘mers’ means ‘parts’. Thus, the term polymer stands to represent a substance built up of several repeating units, each unit being known as a manomer. Thousands of such units or manomers join together in a polymerization reaction to form a polymer. There are some natural polymers like starch, resins, shellac, cellulose, proteins, etc.
Types of Plastics: -
Plastics can be either thermosetting or thermoplastic. The term thermosetting and thermoplastic refer to the material’s response to elevated temperatures.
1. Thermosetting Plastic: -
A thermoset is a polymer that solidifies or “sets” irreversibly when heated. Similar to the relationship between a raw and a cooked egg, once heated, a thermoset polymer can’t be softened again and once cooked, the egg cannot revert back to its original form. Thermosets are based on polymers that have undergone a chemical reaction (induced by the action of heat, catalysts or ultraviolet light) that results in a relatively infusible, intractable and insoluble product. These materials can be “cured” or polymerized using heat and pressure or as with epoxies a chemical reaction started by a chemical initiator. The polymeric component of the product is in a cross-linked state.
Thermosets are values for their durability and strength and are used primarily in automobiles and construction, although applications such as adhesives, inks and coatings are also significant.
2. Thermoplastic: -
A thermoplastic is a polymer in which the molecules are held together by weak secondary bonding forces that soften when exposed to heat and return to its original condition when cooled back down to room temperature. Thermoplastics are based on linear or branched polymers. When a thermoplastic is softened by heat, it can then be shaped by extrusion, moulding or pressing. The “thermoplastic” materials are either crystalline or amorphous.
Thermoplastic offer versatility and a wide range of applications. They make up the greatest share of plastics used in food packaging because they can be rapidly and economically formed into any shape needed to fulfill the packaging function. Examples are milk jugs and soda bottles.
Application: -
1. Shopping : Plastic wrap, plastic bottles and bags.
2. Grocery Cart Vs. Dent-Resistant Body Panel : Portable phones and computers, appliances such as refrigerators or dishwashers, plastic car fenders and body panels.
3. Packaging : Heat-sealed plastic pouches and wraps, resealable containers, plastic bags.
4. Light weighting : Since 1977, the 2-litre plastic soft drink bottle has gone from weighing 68 grams to just 51 grams today, representing a 25 percent reduction per bottle. That saves more than 206 million pounds of packaging each year.
5. Plastics in Home Construction : Vinyl siding and windows help cut energy consumption and lower your heating and cooling bills. Plastic parts and insulation have helped to improve the energy efficiency by 30 to 50 percent since the early 1970s.
6. Industrial Applications :
- Packaging (bottles, films, seals....)
- Shrink wrap
- High-temperature wire insulation
- Electronics
- Automotive components and seals (engine/brake components/pipes/hoses/tank)
- Any plastic parts that wear out from abrasion
- Breaking down waste plastics for use as lubricants.
Q.6 Write short note on composite material and its application.
(AKTU. 2009-10, 10 - 11, 11 - 12)
Ans. Composite Material: - (AKTU. 2012 - 13)
A composite material is obtained when two or more materials are combined together to produce a new material, which possesses much superior properties than any one of the constituent materials. Wood is the most common example of a naturally occuring composite material which consist of long cellulose fibre held together by amorphous lignin. Examples of artificial (or synthetic) composite materials are cement concrete, glass reinforced plastic plywood etc.
Types of Composite Materials: -
Composite materials are of three types. They are
1. Agglomerated Materials: -
The materials, in which the particles are condensed together to form an integral mass, are known as agglomerated materials. A common example of agglomerated materials is cement concrete, which is formed by mixing coarse aggregate, fine aggregate, cement and water in different proportions. Other useful agglomerated material is grinding wheel (abrasive material) which is formed by mixing asphalt, stone and resin of different sizes. Some other useful agglomerated materials are cemented carbide tools and ceramics. The cemented carbide tools are manufactured by agglomerating small particles of hard tungsten carbide with alloys of cobalt and nickel. These alloys act as a binder between the tungsten carbide particles. The cermets are produced by combining a ceramic material and metal through various processes. In this process, the mixture of ceramic material and metal is taken in the form of powder, which is mixed, pressed and finally sintered to produce a composite material. In cermets, the metal provides high toughness and thermal shock resistance. The ceramic materials provide high refractoriness and creep resistance. They have high abrasion resistance, excellent chemical stability and machinability etc. Examples are cement and cement-concrete.
2. Laminated Materials or Laminates: -
The materials, which are produced by bonding two or more layers of different materials completely to each other, are known as laminated materials or laminates. The materials, constituting a laminated material, may be metallic or non-metallic depending upon the type of application.
The common examples of laminated materials are plywood, tufnol, sunmica, linolium etc. In laminated materials, the top most layer provides the desired appearance and workability, while the lower layer contributes to its strength. These days, a variety of techniques are available to manufacture laminated composite materials. The most common techniques are roll bonding, coextrusion, explosive welding and brazing. Examples of laminates are plywood and Tufnol.
3. Reinforced Materials: -
These are produced by combining some suitable material to provide additional strength which does not exist in a single material. The common examples of reinforced materials are reinforced cement concrete (R.C.C.), glass-fibre reinforced plastic etc.
