engineering polymers and elastomers

8/12/2019 Engineering Polymers and Elastomers

1/24

ENGINEERING

POLYMERS ANDELASTOMERS


2/24

Engineering plastics

Used in the manufacture of premium plasticsproducts where

high temperature resistance high impact strength

chemical resistance or other special propertiesare required.

E.g.

ABS,nylon,polycarbonates etc


3/24

Engineering plastics

1-Polyamides

may be aliphatic or aromatic chain backbone.

Particularly nylon-6 and nylon-6,6 are most widely used

aliphatics Excellent resistance to wear and abrasion

Good resilience

High impact strength

Water sensitive Which acts as plasticizer reduces tensile strength and

modulus while increasing elongation to break and toughness

Different grades used in:

Manufacture of fuel lines


4/24

2-ABS

Acrylonitrile+butadiene+styrene(15-35%,5-30%,40-60%).

Excellent resistance (no attack) to Glycerine, Inorganic Salts,

Alkalis, Many Acids, Most Alcohols and Hydrocarbons.

It can be thermo-formed, pressure formed, blow molded, sheared,sawed, drilled.

Joints can be ultrasonic welded, thermo-welded, and chemically

bonded

Impact resistant Commonly used for telephone bodies, safety helmets, piping,

furniture, car components, TV casings, radios, control panels, and

similar Valve bodies, material handling equipment.

ABS is suitable for outdoor applications.


5/24

3-Polycarbonates

It is the 2ndlargest sales volume engg.Thermoplastics.

Amorphous

High impact strength Low moisture absorption

Low combustibility

Good dimensional stability

Used in,

Impact resistance substitute for window glass.

Molding compact disks


6/24

Disadvantage

Polycarbonate does have its disadvantages.

It has only fair chemical resistance and is

attacked by many organic solvents.

It is also fairly expensive compared to other

plastics.

It has been as much as double the price of

ABS. In applications where lower heat and impact

are needed, ABS can be quite a bargain

compared to polycarbonate.


7/24


8/24

4-Polysulfones

High thermal ,oxidative and hydrolytic stability

Good resistance to aqueous mineral acids,salt

solns,oils and greases.

Their high biocompatibility and ability to be

sterilized by a variety of techniques make them

highly suitable for medical applications.

High permeability particularly make themattractive as membrane polymers in gas

seperation.


9/24

Polysulfone has the highest service temperature of all

melt-processable thermoplastics.

Its resistance to high temperatures gives it a role of

a flame retardant, without compromising its strength that

usually results from addition of flame retardants.

Its high hydrolysis stability allows its use in medical

applications requiring autoclave and steam sterilization.

However, it has low resistance to some solvents and

undergoes weathering; this weathering instability can be

offset by adding other materials into the polymer.
http://en.wikipedia.org/wiki/Flame_retardanthttp://en.wikipedia.org/wiki/Weatheringhttp://en.wikipedia.org/wiki/Weatheringhttp://en.wikipedia.org/wiki/Flame_retardanthttp://en.wikipedia.org/wiki/Flame_retardanthttp://en.wikipedia.org/wiki/Flame_retardant


10/24

5-Fluoropolymers

The most imp. one is PTFE which is obtainedby emulsion free radical polymerization of

tetrafluoroethylene.

It is highly dense with high temp. stability Low temp. flexibility

Extremely low coefficient of friction.

Chemical inertness But due to high crystallinity and high crystalline

melting temp.,,it is difficult to process


11/24

ELASTOMERS

A material which can be elastically deformed alarge amount and when the force is released, itcomes back to its original position is known aselastomer

Examples: Natural Rubber, SBR, Polyisoprene etc Chains in elastomers cant slide over each other

which do not causes permanent set up.

Elastomers are cross-linked like thermosets but

cross links are not as much. Moreover the helical type structure of an

elastomer uncoils when stress is applied and thenreturns to its original state as applied stress isremoved.


12/24

APPLICATION OF ELASTOMERS

Many components do not require good

strength but they need flexibility, softness and

reversible elongation. For such applications

elastomers are the best choice. e.g.1. Resilient floor covering

2. Weather stripping

3. Foot wears4. Vehicle tyre

5. Joints seals etc


13/24

RUBBER AS ELASTOMER

A soft elastomer can be turned as rigid andbrittle thermoset e.g. SBR is soft and flexible,but after vulcanization with sulfur it turns rigid

and brittle Fully vulcanized Natural Rubber is called

Ebonite Three major application systems are

1. Vibration insulation and isolation

2. For distortional systems

3. Protective systems


14/24

COMMERCIAL ELASTOMERS

1. Acrylic rubbers2. Butyl rubber

3. Nitrile rubber

4. Neoprene

5. Polyisoprene (natural rubber)6. Polysulfide rubber

7. Polyurethane rubber

8. Rubber hydrochloride

9. Silicon rubbers10. SBR


15/24

1: Acrylic Rubber

Derived from the same family of polymericmaterials as Perspex

But they are not heavily cross linked to give

them properties of elastomers

Excellent resistance to oils, oxygen, ozone and

ultraviolet radiation

Basis for latex paints developed for motor

vehicles


16/24

2: Butyl Rubber

This is impervious to gases and is used as a

vapor barrier and for hose lining.

Highly resistant to outdoor weathering and

ultraviolet radiation

Mainly used for construction industry sealants


17/24

3: NITRILE RUBBER

Excellent resistance to oils and solvents and

can be readily bonded to metals

Used for petrol and fuel oil hoses, hose linings

and air craft fuel tank linings.

Resistant to refrigerant gases


18/24

4: POLYCHLOROPRENE

RUBBER Called as neoprene Synthetic rubber developed after 2ndworld war

Good resistance against oxidation, ageing andweathering

Resistant to oils , solvents, abrasion andelevated temperatures.

Fire resistance due to presence of chlorinecontents

Used as flexible electrical insulator, gaskets,hoses, engine mounts, sealants and protectiveclothing.


19/24

5: POLYISOPRENE

Derived from the sap of tree HerveaBrasiliensis

Low hysteresis, a relatively high tensile strengthand a very low processing temperature.

readily attacked by solvents, petrol, mineral oilsand ozones which causes its degradation

Modification by additives gives improved mech.Properties & wear resistance e.g. NR is used for

vehicle tyres as it has excellent anti skidproperties.


20/24

6:POLYSULPHIDE RUBBER

Excellent resistance to solvents, very good

weathering characteristics and excellent

impermeability to gases

High bonding properties due to which widelyused in construction industries as a sealants

Disadvantage:low mechanical strength


21/24

7: PU RUBBER

May be elastic may be plasticAlthough high strength and good abrasion

resistance, it cant be used in tyres due tolesser skid resistance

Used in shoe heels, painting rollers, oil seals,pump impellors etc


22/24

8: RUBBER

HYDROCHLORIDE

Known as Pilofilm

Used to form a transparent film for the vacuum

packaging of foods

Very high tensile strength and tear resistance


23/24

9: SILICON RUBBERS

Very wide temperature range -80 to 253oC

Relatively low tensile strength

It often outperforms other rubbers which are

superior at room temperature

Can be used for mould linings and high

temperature seals

Used in Space vehicles and artificial seals


24/24

10: SBR

Styrene butadiene rubber

Commercially Used for tyres, floor tiles and

latex paints.

It is superior to NR in skid resistance, solventresistance and weathering

engineering polymers and elastomers

Documents