Rubber is a polymer material consisting of Hydrogen (H) and Carbon (C). It is highly elastic, well absorbing and exhausting energy, high abrasion resistance, good elongation, high tear resistance, flexibility and high corrosion resistance.
Moreover, it is resilient to heat, and electricity and resistant to chemicals. Natural Rubber is originated naturally from the white liquid as white milk from the gum tree. It is the water based small molecules of colloid, called “rubber latex”.
Types of Rubbers and Applications
What is difference between Synthetic Rubber (SR) and Natural Rubber (NR)?
SR is artificially made by artificial elastomer in order to replace NR. It is a good resilience over the wider temperature range and still retains its shape without permanent deformation. It is made by polymerisation of petroleum based substances known as “Monomer”. Each SR has different monomer; some consist of one monomer and others do a few types of monomers as various proportionally, depending on purposes of uses of physical, mechanical and chemical properties, for example, Polyisoprene (IR) – is made by only monomer, Isoprene (2 Methyl-1, 3-Butadiene).
Styrene Butadiene Rubber (SBR) and Butyl Rubber (IIR) are made by two types of monomers; Styrene and Butadiene (1,3-butadiene), and Isobutylene (2-methylpropene) and Isoprene, consecutively.
But, NR is harvested by slicing a groove into bark and “rubber latex” consisting of polymers-Isoprene which is collected from a rubber tree (Hevea Brasiliensis) in order to keep it longer. This latex is required to be processed. Two kinds of rubber latex are processed.
- “Concentrated Latex” for producing rubber products such as, rubber gloves, medical equipments, electronic components and balloons.
- “Dried Rubbers” such as, Rubber Smoked Sheet (RSS), Air Dried Sheet (ADS), Blocked Rubbers (STR) and Crepe Rubbers.
Even though, NR has several good properties in uses – high tensile property, good resistance to heat, light, and ozone at the medium level and high to resilience; however, wherever compared to SR, NR has overall properties inferior than SR due to the fact that SR has better properties in abrasion resistance, thermal stability which makes SR more a-life-long-standing than NR.
Several types of SR are also more elastic in low temperature conditions. They are resistant to oil, grease and flame, and good for making as electronic equipment insulator.
Moreover, NR is naturally produced from tropical plants with limited planting area so it is basically insufficient for industry needs; while, SR is more widely used and for substitution of NR in various purposes of uses such as vehicle tyres, medical equipments, molding parts, and machine conveyors.
Synthetic Rubber (SR)
All of Synthetic Rubbers which are made from artificial elastomer(s) are mainly synthesised from chemical reaction which is similar to that of NR (cis-1,4-polyisoprene). SR manufacturing processes can be divided into 2 steps: monomer production and polymerisation reaction.
Each SR is different one by one due to nature of its monomer properties.. In case, SR is composed of and polymerised from one monomer, called “homopolymer” such as, Polybutadiene Rubber (BR) or Polyisoprene Rubber (IR); while, two or more different monomers are polymerised together, this product is called “copolymer”; such Styrene Butadiene Rubber (SBR).
Polybutadiene Rubber (BR)
BR is a polymer formed in solution polymerisation of a monomer called “1,3-butadiene (BD)”. In term of connectivity of polymer chain, 1,3-butadiene can be polymerised in three different ways that are cis-1,4, tran-1,4 and vinyl-1,2. Its average molecular weight is about 250,000 – 300,000.
General Properties of BR
- High Elasticity: highest in rebound, compared to other SRs
- Low tensile strength: reinforced filler is required.
- Excellent abrasion resistance.
- Good in low temperature flexibility due to having very low Tg -112 Degree C
- Short aging property under oxygen, ozone or light conditions. Anti-aging additive is required to add to improve aging property.
- Temperature for services/operations in range of -70 to 75 degree C
- Excellent characteristics in elasticity, abrasion resistance, low heat build-up and resistance to oil or non-polarity solutions.
Butadiene Structure Formula
Superior property of BR is excellent abrasion resistance, but low tensile strength. To blend BR with NR or SBR helps improve shape retention of the blended rubbers which has better dynamic properties.
For getting better quality, a few properties of NR and/or SBR also gain higher abrasion resistance, higher elasticity and good low temperature flexibility.
As such reasons above, more than 90% of BR is used by blending with NR and SBR for tread of vehicle tyre production because of higher abrasion resistance, lower heat build up and better resistance to groove cracking. Furthermore, BR blended rubbers also have better reversion resistance on overcure during production and reduce rolling resistance, then help energy savings during operations. An important point of consideration, the more BR blended in tread, the less wet grip property of tyres, BR is also considered to be applied in other tyre parts such as, carcass, sidewall and bead compound.
More than 90% of BR are used in productions of tyres, conveyors, transmission belts, bumpers, shock absorber rubber pads.
75% of BR is applied in production of sidewall and tread due to its high abrasion resistance and low rolling resistance making less abrasive in tyres, and better energy savings.
Another 25% of BR is consumed as a reinforced additive in production process for specialty plastics such as Acrylonitrile Butadiene Styrene, ABS.
BR is also compounded in other products requiring high rebound and better abrasion resistance such as shoe soles, conveyors, transmission belts, bumpers and shock absorber pads.
It is also blended to produce core of golf ball for better bouncing effect and to produce electronic equipments for its high electricity resistance.
Another SR which is also widely used in various industries like BR is Styrene Butadiene Rubber, SBR.
This SR is made by two monomers: 1,3-Butadiene and Styrene with good anti-aging property and high abrasion resistance. SBR is categorised into 2 types of its production process that are Emulsion Polymerisation, titled as “E-SBR” and Solution Polymerisation, as “S-SBR”.
SBR is one of the mostly widely used Synthetic Rubber; half of all vehicles tyres are made from SBR. It is also used in productions of shoe soles, gaskets, even chewing gum.
A RECOGNISED PRODUCTION PROCESS FOR SYNTHETIC RUBBERS