01 plastics
TRANSCRIPT
-
7/30/2019 01 Plastics
1/14
PLASTIC MATERIALS
-
7/30/2019 01 Plastics
2/14
PLASTIC MATERIALS
Large and varied group
Consists of wholly or in part combination of carbonwith oxygen,hydrogen,nitrogen
and other organic or inorganic elements
Solid in finished stage or moulded stage
Liquid in manufacturing stage
Moulded by application of heat / pressure
Generally flexible
But can be made rigid,stiff,strong,weatherresistant,heat resistant,electrical resistant and if
required can be made electrically conductive also
Basic material of all Plastics is HYDRO CARBON(CH)
-
7/30/2019 01 Plastics
3/14
PLASTIC MATERIALS
Two types of plastics are Thermo plastic and
Thermo set plastics
THERMOPLASTICS are either AMORPHOUS or
CRYSTALLINE in structure
They form a Linear or Branched Molecular Chain
Formulated by Addition Polymerization
Available in Granules of 3x4mm
Undergoes Physical change only, on Heating
Recyclable
-
7/30/2019 01 Plastics
4/14
MOLECULAR
CHAIN (LINEAR)
MOLECULARCHAIN(BRANCHED)
POLYMER
-
7/30/2019 01 Plastics
5/14
CROSS LINKED POLYMERS
WEAKLY CROSS LINKED eg. RUBBER
-
7/30/2019 01 Plastics
6/14
They are having molecules going in
all different directions and normally
transparent. They willundergo small
volumetric change when processing.
They are tougher and more flexible.
AMORPHOUS THERMO PLASTICS
Eg. PolyStyrene,PolyCarbonate,
PolyMethaMethacrylate
CelluloseAcetate,
AcrylonitryleButadine
Styrene,PVC
MoleculesRandomly
arranged
-
7/30/2019 01 Plastics
7/14
Since commercially perfect crystalline polymers are not
produced they are identified technically as semi- crystallinethermoplastics. A crystalline area is stiffer and stronger. It is
difficult to process crystalline materials due to high melt
temperature,melt viscosity & shrinkage.
SEMI-CRYSTALLINE PLASTICS
CRYSTALLINE
(Orderly)
eg. Polypropylene
Polyethylene
PolyAmide, Poly Oxy
Methylene,
AMORPHOUS
(Random)
-
7/30/2019 01 Plastics
8/14
PLASTIC MATERIALS
By adding different modifiers,additives,fillers and
Reinforcements many formulationsof Plastics are
derived (Approx.40,000)
Classification of Thermo Plastics:-
1.Commodity Plastics eg.PE,PS,PP,PVC
2.Engineering Plastics eg.ABS,PA,PC,POM, (has to
work under constant loaded condition over long period
of life)
3.Speciality Plastics eg.Liquid Crystral Polymer,
( even in the liquid state structure is Crystalline)
Super Nylon, PEEK
-
7/30/2019 01 Plastics
9/14
THERMOSETS
Formulated by Condensation Polymerization. Available in Fine Powder form.
A compound partially polymerized.
Undergoes irreversable chemical change by
application of HEAT & PRESSURE.
Tightly Cross linked between molecules by the
Reactive portion of Compound.
Not reusable or recyclable. Difficult to dispose off.
-
7/30/2019 01 Plastics
10/14
CROSS LINKED POLYMERS
DENSLY CROSS LINKED
eg. THERMOSET
Chain
CROSS
LINK
-
7/30/2019 01 Plastics
11/14
Cross-linked
Giant macromolecule Structurally set
Shape cannot be altered once moulded
THERMOSET PLASTICS
-
7/30/2019 01 Plastics
12/14
Forms a Hard, Dense and Polished Shiny
molded component.
Brittle, Highly Heat & Electrical Resistant Has a Shelf life.
Eg. Phenol Formaldehyde
Melamine Formaldehyde
Urea Formaldehyde
Alkyds, Diallys, Polyurethane, Silicones,
Unsaturated Polyesters.
Thermosets are normally moulded by1. Compression moulding.
2. Transfer moulding
3. Injection moulding
-
7/30/2019 01 Plastics
13/14
A
D
V
A
NT
A
G
E
S
O
F
P
LA
S
T
I
CS
1. Less weight
2. Ease of fabrication
3. Properties can be Customized4. Thermal insulation
5. Electrical insulation
6. Corrosion resistant7. Available in Opaque to Transparent
8. Low Coefficient of Friction
9. Suitable for High Volume production
10.Self Lubrication
11.Less Costly
12.Elastic
-
7/30/2019 01 Plastics
14/14
D
I
S
A
D
V
A
N
T
A
G
E
S
O
F
P
L
A
S
I
CS
1. Difficult to develop Product
2. Unpredictable Shrinkage
3. Flammable
4. Poor Weather ability
5. Failure in Creep and Stress Relaxation
6. Environmentally unfriendly
7. High Coefficient of Thermal Expansion
8. Enbrittlement at Low Temperatures
9. High Moisture Absorption
10.Flex and Deform under load
11.Softer than Metal- Wear more ,Less life