Definition Of Plastics :
i) Plastics: Plastics are basically, the synthetic organic materials of high molecular weight, which can be moulded into any desired shape by the application of heat and pressure in the presence of catalyst.
ii) Polymers: Many units or monomers joined together to form a long chain structure called polymers.
Properties of plastics.
Following are the properties of plastics-
1. Impact strength
2. Abrasion resistance.
3. Heat resistance
4. Mechanical strength.
6. Chemical stability
7. Fire resistance
8. Flow property at elevated tempt.
9. Dielectric strength
13. Vicat hardness
14. Tensile strength
Types of Plastics :
Two types of polymeric materials are :
A) Thermoplastic and B) Thermosetting plastic
A) Thermoplastics are-
7. Acrylonitrile butadiene styrene
B) Thermosetting plastic:
Plastics using thermosetting resins
(i) Phenol-formaldehyde resins
(ii) Urea-formaldehyde resins
(iii) Melamine-formaldehyde resins
(iv) Polyester resins
(v) Epoxy resins
(vi) Silicone resins
- These have three-dimensional networks of molecules and will not soften when heated and thereby it can not be reused again. Alternatively, these plastic materials acquire a permanent shape when heated and pressed and thus cannot be easily softened by reheating.
- Those plastics which are hardened by heat, affecting a non-reversible chemical change are called thermosetting. In other words, we can say that they acquire a permanent shape when heated and pressed and cannot be softened by reheating. They are also known as heat-setting or thermosets.
- Thermosetting plastics are made from chains that have been linked together, referred to as cross-linked. These have a three-dimensional network of molecules and will not soften when heated. They are particularly insoluble, fireproof, and usually hard and brittle. These plastics cannot be reused. E.g. epoxy resins, amino resins, phenolics, silicon.
Types of Thermosetting Plastics
The following are the various types of thermosetting plastics :
1. Phenolic resins:
- The most important of the phenolic resins is phenol formaldehyde.
- It is obtained by condensing the phenol with formaldehyde in the presence of a catalyst.
- It is popularly known by its trade name of Bakelite
- It is a hard, rigid, and scratch-resistant material.
- It is highly resistant to heat, water, non-oxidizing acids, salts, and many organic solvents.
- It possesses excellent electrical insulating properties.
- It is one of the cheapest materials of all the thermosetting resins.
- It is used in manufacturing handles for cooking pots, knobs, toilet seats, bottle caps, dials, telephone parts, cabinets for radio and television, electrical components like switches, plugs, switchboards, etc.
- It is also used as a binder in paints and varnishes and as an adhesive for grinding wheels.
2. Amino resins:
- The two important amino resins are urea formaldehyde and melamine formaldehyde.
- These are condensation products obtained by the reaction of urea or melamine with formaldehyde.
- The amino resins can be produced in a wide range of colors and are hard, rigid, and durable.
- They possess good electrical properties and are heat and scratch-resistant.
- The urea-formaldehyde is widely used in domestic electrical fittings such as switch covers, plug tops, socket bases, and lamp sockets.
- It is also used for cabinets, toilet seats, buttons, and clock cases.
- The melamine-formaldehyde, due to the good flowability of melamine, is principally used for molded cups, plates, saucers, bowls, etc. Both the resins are used as coatings and adhesives.
3. Furane resins:
- The furane resins are obtained when waste farm products such as cottonseeds, rice hulls, corncobs are processed with certain acids.
- These resins are dark in color, water-resistant, and have good electrical properties.
- These are used as core sand binders and as hardening additives for gypsum plaster.
4. Silicon resins:
- The silicon resins differ from most other resins which are based on the carbon atom.
- The silicone resins have silicon and oxygen chains which are linked to various organic groups such as methyl side groups.
- The silicon resins may be in the form of liquids, semi-solids (like greases), rubbers, and solids.
- The liquid silicones or silicon oils possess great wetting power for metals, low surface tension, and show very small changes in viscosity with temperature.
- These are used as high-temperature lubricants, anti-foaming agents, water-repellent finishes for leather and textiles heat transfer media, damping, and hydraulic fluids. They are also used in cosmetics and polishes.
- The silicones in the semi-solid form (i.e., silicon greases) are modified silicon oils and are obtained by adding fillers like silica, carbon black, etc.
- The silicones in the rubber form have high abrasion resistance, stability at high temperatures and remain flexible even at very low temperatures. They are mostly used in gaskets, insulations, and as additives in other rubbers.
- Solid silicones possess good electrical insulating properties and outstanding heat resistance. They are mostly used in high voltage insulators, high-temperature insulating foams, and moldings that require high thermal stability.
5. Epoxy resins:
The epoxy resins are obtained from certain special types of organic chemicals, specifically epichlorohydrin and bisphenol (double phenol).
- These are cured or cross-linked by the addition of a hardener.
- The cured epoxy resins have low shrinkage, good flexibility, excellent chemical resistance, and electrical insulating properties.
- These are used for surface coatings, adhesives for glass and metals, and laminating materials used in electrical equipment
- The molds made from epoxy resins are employed for the production of components for aircraft and automobiles.
6. Polyester resins:
The polyester resins are obtained by the reaction between a dihydric alcohol and a dibasic acid.
They are divided into the following three groups:
(a) Saturated polyesters,
(b) Unsaturated polyesters, and
- The saturated polyesters are obtained by reacting glycol with saturated dibasic acid.
- They are good fiber-forming materials and are converted into commercial fibers.
- Such fibers have high scratch resistance, high crease, and wrinkle resistance.
- They are mostly used for making synthetic fibers like terylene, dacron, etc. The unsaturated polyesters are made by reacting glycol with unsaturated dibasic acid (like maleic anhydride).
- They have good flexural strength and can withstand temperatures up to 1450C.
- They are good resistance to water but possess low resistance to acids and alkalis.
- These are generally used in safety helmets, air-craft battery boxes, motor car body components, etc.
- The alkyds are produced by reacting polyhydric alcohol (like glycerol) with polybasic acid (like phthalic anhydride) in correct proportions in the presence of heat and catalyst (CO2 gas).
- The alkyd resins are modified either by oil (drying or non-drying) or fatty acids.
- The drying oil-modified alkyds are used as a coating material in numerous formulations.
- The acid or oil-modified alkyds are hard, dimensionally stable and resistance to corrosion and acids.
- They are used for making good insulators, aircraft, and automobile parts, sheets, rods, tubes, switches, gears, circuit-break insulators, etc.
The polyurethanes are obtained, commercially, by treating di-isocynate and diol.
-They have excellent resistance to abrasion and solvents.
– These are used as coatings, films, foams, adhesives, and elastomers.
Applications of thermosetting plastic materials:
1. It is used in foundry and in transformers as an insulating material
2. Radio cabinets
3. Knife handles
4. Vacuum cleaner parts
These are composed of linear and long-chain straight or slightly branched molecules. They can be re-softened and re-melted by the application of heat and pressure. The materials which can be re-melted to manufacture fresh new products are called thermoplastics.
Different Thermoplastics Materials
4) POLYVINYL CHLORIDE
7) ABS POLYMERS
8) ALPHATE POLYAMIDE HOMOPOLYMERS (NYLONS)
9) POLYVINYL ACETATE (PVA)
Alternative Names: Polythene, Polyurethane, Polymethylene
Principal Variants: LDPE, HDPE, LLDPE, MDPE, UHMWPE
Key application Properties of Polyethylene :
- Easy process ability, toughness & Flexibility, Reasonable clarity of thin films. Excellent electrical insulation characteristics, low cost
- Lower softening point, susceptibility to environmental stress cracking, susceptibility to oxidation, opacity in bulk, low hardness, rigidity and tensile strength, high gas permeability
- Excellent chemical resistance, no solvent at room temperature.
- Will dissolve in hydrocarbon and other solvents of similar solubility parameters as the melting point is approached.
Key Processing Properties of Polyethylene :
- Does not absorb water
- Usual molding creates are easy flow
- Good stability to processing temp provided oxygen is absent
- Shrinkage is high and depends on the type, cooling gate, and part thickness.
Few Typical Applications of Polyethylene :
- LDPE main market is film but is widely used for piping, wire covering. and roto-molded products
- MDPE’s important application is the electrical and chemical industry.
- LLDPE is mainly used in film applications.
Alternative Name: Polypropylene
Principal Variants: Available in isotactic form (a regular crystalline structure ) used in injection & extrusion applications. The other variant, static (an irregular amorphous form) used in bituminous compositions and for carpet backing).
Key Application Properties of Polypropylene:
- Low specific gravity and high softening point.
- Virtual freedom from stress cracking.
- Higher brittle point.
- Very low water absorption, very good electrical insulation characteristics.
- Excellent chemical & solvent resistance.
- No solvent at room temperature.
Key Processing Properties of Polypropylene:
- Does not absorb water
- Flow path to wall thickness ratio 175:1 are possible on 1mm wall thickness section (For easy flow grades, 350:1)
- Good thermal stability in the absence of oxygen. No intermediate purging material is required.
- High molding shrinkage
Few Typical Applications of Polypropylene:
- Household goods, car components, Toys, Medical equipment, luggage, integral hinges.
- Used as packaging material in film & fiber form
Alternative Names: Polyphenyl ethane, Polyphenyl ethylene
Key Application properties of Polystyrene :
- Rigidity, transparency, low moisture absorption, low density
- Excellent electrical insulation characteristics
- Dissolved in a wide range of solvents like hydrocarbons, chlorinated hydrocarbons, ketones (but not acetones), some esters, and oils.
Key Processing Properties of Polystyrene :
- Melts are of medium viscosity but highly pseudoplastic
- Flow path-ratio; for GPPS-150:1. For HIPS-130:1
- Good thermal stability of processing temp.
Few typical applications of Polystyrene :
- For GPPS: Toys, containers, Tape cassettes, disposable tumblers, display Products
- For HIPS: Appliance housing, furniture components, egg box, dairy product containers, refrigerator liners
- For EPS: for insulation & packaging.
4) POLYVINYL CHLORIDE
Alternative Names: PVC, Poly-1-Chlorethylene, Polychloroethane, Vinyl
UPVC unplasticized PVC-a rigid material, PVC Plasticized PVC contains plasticizers & flexible or rubbery.
Key Application Properties of Polyvinyl Chloride:
- (For UPVC): Rigid & good hydrocarbon resistance, low water absorption
- Good weathering resistance & low flammability
- Very good chemical resistance and dissolved by cyclohexanone, dichloroethanes nitrobenzene.
Key Processing Properties of Polyvinyl Chloride:
- Does not absorb water
- UPVC melts are vicious, flow path ratio 60:1
- Viscosity of PPVC depends on plasticizer level
- Degradation rapid at elevated temp lacks thermal stability.
- Never allow the polymer to mix with polyacetals since combinations are at elevated temp. may lead to explosions.
- Low shrinkage.
Few Typical Applications of Polyvinyl Chloride:
- (For UPVC) : Used in building like window frames, gutters, piping, wall
- Cladding: Used in chemical plants and for blow molded bottles
- (For PPVC): Used for wire covering, vinyl leather cloth and upholstery Wall/paper finishers, play balls & toys, garden hose clotting mine belting
- Vinyl chloride: vinyl acetate copolymers used for flooring compositions and, for gramophone records.
Alternative Names: Acrylic, PMMA
Key Application Properties of Acrylic :
- High transparency and high transition properties.
- Excellent weathering resistance.
- Hard and rigid with low moisture absorption
- Good electrical resistance at low frequencies
- Attached by mineral acids but resist to alkalis, water, and most aqueous inorganic salt solutions.
Key Processing Properties of Acrylic:
- To be stored in a dry place.
- High melt viscosity, flow path ratio 100-150:1
- Limited thermal stability
Few typical applications of Acrylic:
- Used where high weather ability and high optical clarity are required
- Car lamp covers, dashboard fittings, street light fittings
- Batch tubs and other sanitary fittings
- Sign boards and lighting fittings
- Dentures, spare part surgery, contact lenses
Alternative Names: Polycarbonate of bis-phenol A
Key Application Properties of Polycarbonate :
- Toughness, rigidity, transparency, heat resistance, self-extinguishing, notch Sensitive
- Good electrical insulation characteristics, limited resistance to electrical tracking & arching.
- Limited resistance to hydrolyzing agents but – good resistance to oxygen
- Not resistant to caustic soda, caustic potash, ammonia & many aromatic amines.
Key Processing Properties of Polycarbonate :
- Should be stored in a dry area
- Good thermal stability
- High melt viscosities. Flow path ratio 30-70: 1
- Moulding shrinkage is slightly higher than amorphous materials.
Few Typical Applications of Polycarbonate:
- Widely used in electronics – electrical engineering, medical side, glazing & tough glazing applications.
- Used in Cameras, domestic mixers & other kitchen equipment, Audio compact discs.
- Blends (with PBT) used for Car bumpers, front ends, using & other components
7) ABS POLYMERS
Alternative Names: Acrylonitrile-butadiene-styrene, ABS Copolymer, ABS Terpolymer
Key Application Properties:
- Toughness, rigidity, and good surface appearance.
- Resistance to alkalis and acids but not concentrated oxidizing acids
- Can be dissolved by many aromatic and chlorinated hydrocarbons, esters, and ketones.
Key Processing Properties:
- Tendency to absorb water (0-3%), must be stored under dry condition
- Avoid excessive screw rotation speed and backpressure during molding.
- Flow path to wall thickness ratio 80-150:1
- Low molding shrinkage due to the amorphous nature of the polymer.
Few typical Applications:
- Like instrumental panels, armrests grills
- Business machine housings
- Luggage, Garden equipment
8) ALPHATE POLYAMIDE HOMOPOLYMERS
Alternative Names: Nylons, Polyamides
Key Applications Properties:
- Toughness with rigidity, abrasion resistance
- Good hydrocarbon resistance, fair good heat resistance, high water absorption tendency
- Electrical insulation properties fair or high frequencies
- Good resistance to hydrocarbons
- Formic acid, glacial acetic acid, phenols, and cresols are solvents.
9) ACETAL POLYMERS
Alternative Names: Polyacetal, Polytormaldehyde, Polyoxymethylene
Key Application Properties of Acetal Polymers :
- Better fatigue endurance, stiffness, creep resistance, and water resistance
- Inferior Impact toughness, abrasion resistance
- Low co-efficient of friction
- Very good resistance to organic chemicals with no solvents below 700 C
Key Processing Properties:
- Hygroscopic in nature, so essential to thoroughly dry when using.
- Melts are very fluid, because of low melt viscosity and melt elasticity, it is difficult to handle extrudates.
- At high processing, temp oxidation can occur.
- Molding shrinkage is much high.
Few Typical Applications:
- Widely used for high engineering applications,
- Particularly valuable where toughness and abrasion resistance are important.
Applications of thermoplastic materials:
1. Copper wire insulation
2. Water tubes
6. Copper wire insulation,
7. Water tubes,
8. Nursing bottles,
9. Ice cube trays,
12. Photographic films,
13. Hose etc.
Difference between thermoplastic and thermosetting plastics.
|Sr. No.||ThermoPlastic / Thermo softening plastics||Thermosetting plastics|
|1.||The plastics who possess linear long-chain structures without cross-linkages are called Thermo softening plastics. It is also called as Thermoplastic .||The plastics that possess a three-dimensional complicated structure with cross-linkages are called as thermosetting plastics.|
|2.||They are formed by additional polymerization.||They are formed by condensation polymerization.|
|3.||They consist of polymers of smaller molecular weight.||They consist of polymers of higher molecular weight.|
|4.||They are softer, weaker & less brittle.||They are harder, stronger & more brittle.|
|5.||They have low tensile strength.||They have high tensile strength.|
|6.||Their intermolecular bonds are weak.||Their inter molecular bonds are strong covalent bonds|
|7.||They soften on heating.||They do not soften on heating.|
|8.||They are soluble in an organic solvent.||They are insoluble in organic solvent.|
|9.||They can be reshaped and reused.||They cannot be reshaped and reused.|
|10.||They can be reclaimed from the waste.||They cannot be reclaimed from the waste.|
|11.||Examples- Polythene, Polystyrene, PVC, Teflon||Examples- Bakelite, Polyester, Nylon66, Urea-formaldehyde, Silicon plastic.|
Question and Answers :
1. What is thermoplastic? State its two properties.
Plastics can be easily softened again and again by heating. They can be reprocessed safely. They retain their plasticity at high temperatures. They can be heated and reshaped by pressing many times. On cooling they become hard. They can be easily shaped into tubes, sheets, films, and many other shapes as per the need.
Following are the properties of Thermoplastics:
i. They are highly plastic
ii. They are easily molded or shaped.
iii. They have a low melting point
iv. As they can be repeatedly used so they have good resale value.
v. Soluble in some organic solvent
vi. Softer and less strong
2. What is thermosetting plastic? write properties and use of Epoxy resins.
i) Once hardened and set they do not soften with the application of heat
ii) They are formed by condensation polymerization.
iii) They have a three-dimensional network structure.
iv) They are usually hard, strong, and more brittle.
v) They are insoluble in almost all organic solvents.
vi) They cannot be reused and do not have resale value
vii) They can be used at a comparatively higher temperature without damage.
Properties of Epoxy
i. It is very tough
ii. Chemical resistant
iii. Electrical resistant
iv. Low shrinkage
v. Good adhesion to metal and glass
vi. Good resistance to wear and impact
vii. Dimensionally stable
viii. Transparent with creamy color
Applications of Epoxy
i. Electrical molding
iii. Laminated tooling
v. Protective coatings
vi. Housing for electrical parts
vii. In transformer as an insulating material
3. What are the basic types of plastics? Give two applications of each
Applications:– electrical parts, knobs, toys, bearings, gears, machine slides, rope, bowls, plates,
dishpans, flexible tubing, squeeze bottles, bottles, hospital equipment, etc.
ii) Thermosetting Plastics
Applications:– aircraft and automobile parts, boat bodies, electrical insulators, furniture, shoe, glass
and silver polishes.
4. What are the properties of ABS?
Properties of ABS
Acrylonitrile Butadiene Styrene (ABS) is a type of Thermoplastic type of plastic. This is made up of chain molecules. ABS can be molded and remolded in any shape. This plastic is comparatively soft and less strong and chemically less inert. The heat resistance is low and cannot be used at higher temperatures. It has Good impact resistance, Rigidity, strength and toughness, and moderate heat resistance.
Applications of ABS
- Refrigerator Linning material
- Lawn and Garden equipment
- Highway Safety devices
- Automobile Parts
- Moulded parts
5. Give two properties and related applications of plastics.
|1.||Low specific gravity & high tensile strength.||In aircraft, motorcars & structural industries.|
|2.||Combination with metals.||Wheels of automobiles plastics cover dashboards.|
|3.||Resistance to wear & tear & abrasion resistance.||For making machinery parts such as gears pulleys.|
|4.||Poor electrical conductivity.||In the electronic industry.|
|5.||High Chemical resistance & corrosion resistance.||In Chemical industries, PVC plastic is used in place of stainless steel.|
|6.||Bad conductor of Heat.||Handles of electric irons, kettles, pressure cookers, frying pan, etc.|
|7.||Hard & shock-absorbing capacity.||In machinery to reduce noise & vibrations.|
|8.||Clear, transparent, translucent, opaque nature.||Decorative knobs for radio, automobile & household appliances, windscreens for automobiles, aircraft, optical lenses, etc.|
|9.||Waterproof||Water bottles, raincoats, buckets,|
water tanks etc.
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