UNIT 2 C
4 marks questions
1. Explain the
properties and application of the PVC and PE materials.
A. the
properties of the PVC
- Properties
- Applications
- Pipes
- Electric cables
- Unplasticized poly(vinyl chloride) (uPVC) for construction
- Signs
- Clothing and furniture
- Healthcare
- Flooring
- Other applications
- Chlorinated PVC
- Health and safety
The properties of the PE
2. What is
polymerization? Describe addition polymerization and condensation
polymerization.
A. polymerization
is a process of reacting monomer molecules together in a chemical reaction to
form polymer chains or three-dimensional networks.There are many forms of
polymerization and different systems exist to categorize them.
Refer
Question No. 4 of 2 marks
3. How plastic
materials are classified? Explain each classification.
A. Internet
4. What properties
make carbon fiber important for reinforced plastics?
A.Carbon
Fiber Properties
·
High Strength to weight ratio
·
Rigidity
·
Corrosion resistance
·
Electrical Conductivity
·
Fatigue Resistance
·
Good tensile strength but Brittle
·
Fire Resistance/Not flammable
·
High Thermal Conductivity in some forms
·
Low coefficient of thermal expansion
·
Non poisonous
·
Biologically inert
·
X-Ray Permeable
·
Self Lubricating
·
Excellent EMI (Electromagnetic Interference)
Shielding Property
·
Relatively Expensive
5. State physical and
mechanical properties of plastics.
A. Mechanical Properties
·
Stress/Strain relationships; tensile, flexural, compressive,
shear; impact, creep, stress relaxation; temperature and strain rate effects;
orientation, environmental effects; crystallinity, residual stress effects;
polymer blends; composites; fracture and failure analysis; dynamic mechanical
modulus
Physical Properties
·
Glass transition temperature; melting and degree of
crystallinity; chemical resistance, permeability; thermal properties;
electrical properties; flammability; miscibility/compatibility of blends;
degradation; characterization and identification of plastics
6. State chemical
properties of plastics. State drawbacks of plastics.
A.
Chemical is used generally to describe the resistance of materials to the effects of chemicals.
In most cases, inadequate chemical resistance is manifested in swelling or softening of the material, which can result in loss of serviceability. The molecules of the medium diffuse into the space between the polymer chains and push them apart. As diffusion processes are temperature dependent, the specifications about chemical resistance only ever apply to the specified temperature. Primarily in the case of amorphous thermoplastic polymers, the influence of chemicals can also lead to stress crack formation. In this case, they initially form microcracks which can grow under the influence of mechanical stress to large crack networks. Consequently, temperature, the concentration of agents, exposure periods and mechanical load are all important criteria when testing for chemical resistance.
In most cases, inadequate chemical resistance is manifested in swelling or softening of the material, which can result in loss of serviceability. The molecules of the medium diffuse into the space between the polymer chains and push them apart. As diffusion processes are temperature dependent, the specifications about chemical resistance only ever apply to the specified temperature. Primarily in the case of amorphous thermoplastic polymers, the influence of chemicals can also lead to stress crack formation. In this case, they initially form microcracks which can grow under the influence of mechanical stress to large crack networks. Consequently, temperature, the concentration of agents, exposure periods and mechanical load are all important criteria when testing for chemical resistance.
Here are some of the drawbacks of plastic:
Durability Environmental Harm
Chemical Risk
Choking Hazard
7. Explain glass in
detail.
A.
Glass is one of the oldest and most versatile materials
known to man. The term ‘glass’ in its widest sense is used to describe a
particular state of matter, known as glassy or vitreous state, which is obtained
when a liquid cools without crystallisation taking place. Therefore, glass
is defined as a super-cooled liquid. Glasses do not show changes like
metals, ceramics or even plastics on cooling from the molten condition.
Therefore, glass is considered as a very viscous liquid when it is a solid. It
has apparent physical properties of a solid, such as, brittleness, hardness,
transparency and chemical inertness.
Glass is manufactured by mixing the raw materials in proper
proportions. The glass raw materials include sand, soda ash, limestone,
dolomite, feldspar, sodium sulphate, broken glass, etc. The mixture is
melted by heating upto 1500 °C. Some modifiers and refining agents are added to
the melt. The melt can be cast, draWn or rolled to produce different
shapes. Tubing is made by extrusion; bottles are made by a technique
similar to the blowmolding techniques used to make plastic containers. Glasses
are cast and ground to make precision shapes such as lenses. Sheet glass
is made by casting in flat plate-type molds. The flat window glass is
made by drawing a sheet out of a molten pool.
8. Explain refractory
material in detail.
A.
Refractory materials withstand high temperatures, possess
sufficient mechanical strength heat resistance and retain a constant volume.
They also possess reversible thermal expansion and resistance to thermal shock.
These materials are used in furnaces either to support the heating elements or
to form the linings of the inner parts of the furnace. Refractory materials which
can be used at temperatures greater than 900 'C include Alundum (bonded
aluminium oxide) Alumina, corundum, Al2 O3
Refractory materials are available in different shapes and
sizes, some of the common shapes are dense refractory bricks, lightweight bricks,
refractory tubes, protection tubes, melting crucibles, and powder form. Light weight
bricks and refractory powder are used as Insulation materials.
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