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