Natural and synthetic rubber

1. NATURALAND
SYNTHETIC RUBBER

2. What is Rubber
■ Rubberis a material, which can stretch and shrink.
■ It is a polymer.
■ It can be produced from natural sources (e.g. natural rubber) or can be synthesised on an
industrial scale.

3. Natural Rubber
■ Natural rubber is a naturallyoccurringpolymer obtainedfrom the latex of rubber trees.
■ Latex, a milky liquid present in either the latex vessels (ducts) or in the cells of rubber-
producingplants
■ The liquid is 30-40% rubber particles, 55-65% water, and small amounts of protein,
sterol glycosides, resins, ash, and sugars.

4. Rubber tapping
■ Rubber tapping is the process by which latex is collected from a rubber
tree.
■ The latex is harvested by slicing a groove into the bark of the tree at a
depth of one-quarter inch with a hooked knife and peeling back the bark.
■ It is collected in a cup mounted on each tree.

5. Processing of natural rubber
■ Production of rubber is followed by processing into final products
consists of:
1. Compounding
2. Mixing
3. Shaping
4. Vulcanizing
■ Processing techniques for natural and synthetic rubbers are virtually the
same, differences being in the chemicals used to effect vulcanization.

6. Compounding
■ Compounding adds chemicals and other additives to raw rubber in order
to obtain desired properties.
■ Chemicals added during compounding react with the rubber during the
vulcanizing process to stabilize the rubber polymers.
■ Mainly used reinforcing filler is carbon black. Carbon black increases
rubber’s tensile strength and resistance to abrasion and tearing.
■ Other additives include antioxidants , antiozonants colouring pigments,
plasticizers and softening oils.

7. Mixing
■ The additives must be thoroughly mixed with the base rubber to achieve
uniform dispersion of the ingredients.
■ The high viscosity (resistance to flow) of the rubber makes mixing
difficult to accomplish without raising the temperature of the rubber high
enough (up to 300 degrees Fahrenheit) to cause vulcanization.
■ To prevent premature vulcanization, the mixing usually takes place in two
stages.

8. ■ During the first stage, additives like carbon black are mixed into the
rubber. This mixture is referred to as a masterbatch.
■ Once the rubber has cooled, the chemicals for vulcanization are added
and mixed into the rubber.
■ Equipment for mixing includes the Two-roll mill and internal mixers such
as the Banbury mixer.

9. Shaping
■ Shaping processes for rubber products can be divided into four basic categories
1. Extrusion: Extrusion consists of forcing highly plastic rubber through a series
of screw extruders.
2. Calendering: Calendering passes the rubber through a series of increasingly
smaller gaps between rollers.
3. Coating: Coating uses the calendering process to apply a coat of rubber or to
force rubber into fabric or other material.
4. Molding and Casting: Molding is also a step in making tires. Three primary
methods of molding rubber are compression molding, transfer molding and
injection molding.

10. Vulcanization
■ Vulcanization completes the rubber-production process. It is a chemical
process in which the rubber is heated with sulphur.
■ Vulcanization creates the cross-connections between the polymers of
rubber.
■ Increasing cross-connections decreases elasticity, Without vulcanization,
rubber would remain sticky

11. Application of Natural rubber
■ The main use of natural rubber is in automobiles tyres and tubes about 60
% of the total natural rubber production.
■ In heavy duty tyres, the major portion of the rubber used is NR
■ Uses of NR in hoses, footwear, battery boxes, foam mattresses, balloons,
toys etc., are well known.
■ NR now finds extensive use in soil stabilization, in vibration absorption
and in road making.

12. ■ Articles for use in the medical and health sector.
■ Consumer products (like golf or football balls and other recreational and
sports goods, erasers, footwear and other apparel)

13. Synthetic Rubber
■ Synthetic rubbers are complex chemical compounds formed through the
polymerization of monomers.
■ Typical monomers used for production feed material include butadiene,
styrene, isoprene, chloroprene, acrylonitrile, ethylene or propylene.
■ Synthetic rubber production starts with the refining process of oil, coal or
other hydrocarbons with naphtha as one of the desired products.

14. Styrene Butadiene Rubber (SBR)
■ Styrene-Butadiene rubber (SBR) derived from the copolymerization of
styrene and 1,3-butadiene.
■ Styrene content in the range of 10-25% and butadiene unit is composed
approximately 60 to 70% .

15. ■ There are two major types of SBR with different properties based on
their manufacturing process.
■ Emulsion SBR (e-SBR) – Hot SBR or Cold SBR. It can be produced by
free-radical emulsion polymerization of styrene and butadiene either at 50
to 60 C (hot emulsion SBR) or at about 5 C (cold emulsion SBR).
■ Solution SBR (s-SBR). Solution SBR is produced by termination-free*,
anionic solution polymerization of styrene and butadiene with alkyl
lithium initiator (e.g., butyllithium) in a hydrocarbon solvent, usually
hexane or cyclohexane.

16. Uses of SBR
■ The major use of SBR is in the production of tires, particularly car and
lightweight vehicles tires.
■ Cold emulsion SBR is especially used in lighter duty tires.
■ SBR can also be found in industrial applications as belting, insulation for
wire and cabling, haul-off pads, roll coverings, hoses, gaskets, seals.
■ SBR is included in shoe soles, carpet backing adhesive, and in molded
rubber goods.

17. Nitrile Butadiene Rubber – NBR
■ Nitrile Rubber (NBR) is a co-polymer of 75% butadiene and 25%
acrylonitrile monomer.
■ Are emulsified in water and then polymerized (their single-unit molecules
linked into large, multiple-unit molecules) through the action of free-
radical initiators.
■ Nitrile rubber, also known as Buna-N, Perbunan, acrylonitrile butadiene
rubber.

18. Application of NBR
■ Nitrile rubber is popular in applications requiring oil resistance,
performance under extreme temperatures, and personal protection.
■ Used in automotive industry, useful for gaskets, oil seals, o-rings, engine
hoses.
■ Used to make the rolls in the printing industry that spread inks.
■ Used in textiles to waterproof fabric and improve the finish.
■ Nitrile gloves can range from heavy-duty gloves, footwear, floor mats,
sponges, and a host of molded goods.

19. Silicone rubber
■ Silicone rubber (or Si Rubber) is the most commonly used synthetic ruuberor polymer
■ similar bond structure as found in glass, sand and quartz.
■ Composed of silicone- which is itself a polymer- together with hydrogen, carbon, and
oxygen.
■ Made from a cross-linked polymer that is reinforced with silica.

20. Application of silicon rubber
■ Electronics insulating tape, sealant, varnish, lubricants, keyboards, and
housings.
■ Aerospace silicone rubber is used in spacesuit fabrics, tooling materials,
seals and gaskets.
■ Construction uses silicone rubber for adhesives, sealants, and coatings
■ In consumer material include anti-stick bakeware, food containers,
utensils, toys, and jewelry
■ Medical silicone rubber can be found in tubing, adhesives, and
defoamers.

21. Draw back of synthetic rubber
■ During the vulcinization of synthetic rubber, soot is produced. Soot is a
carbon particle that contributes to climate change.