Why Recycle or reuse rubber goods? Rubber Recovery can be a difficult process. There are many reasons, however why rubber should be reclaimed or recovered? Recovered rubber can cost half that of natural or synthetic rubber. Recovered rubber has some properties that are better than those of virgin rubber. Producing rubber from reclaim requires less energy in the total production process than does virgin material. It is an excellent way to dispose of unwanted rubber products, which is often difficult. It conserves non-renewable petroleum products, which are used to produce synthetic rubbers. Recycling activities can generate work in developing countries. Many useful products are derived from reused tires and other rubber products. If tires are incinerated to reclaim embodied energy then they can yield substantial quantities of useful power. For example, some cement factories use waste tires as a fuel source.

1. RECYCLING RUBBER
Luis Antonio Tormento

2. What is rubber?
• Rubber is produced from natural or synthetic sources.
Natural Rubber
• Natural rubber is extracted from rubber producing plants, most notably the tree Hevea brasiliensis, which
originates from South America. Nowadays, more than 90% of all natural rubber comes from these trees in the
rubber plantations of Indonesia, the Malay Peninsula and Sri Lanka.
• The rubber is extracted from the trees in the form of latex. The tree is ‘tapped’; that is, a diagonal incision is
made in the bark of the tree and as the latex exudes from the cut it is collected in a small cup.
• The gathered latex is strained, diluted with water, and treated with acid to cause the suspended rubber
particles within the latex to coagulate. After being pressed between rollers to form thin sheets, the rubber is air
(or smoke) dried and is then ready for shipment.

3. What is rubber?
Synthetic Rubber
• There are several synthetic rubbers in production. These are produced in a similar way to plastics, by a
chemical process known as polymerization. They include neoprene, Buna rubbers, and butyl rubber. Synthetic
rubbers have usually been properties for specialist applications. The synthetic rubbers commonly used for tire
manufacture are styrene-butadiene rubber and butadiene rubber. Butyl rubber, since it is gas-impermeable, is
commonly used for inner tubes.
Type of rubber Application
Natural rubber Commercial vehicles suach as trucks,
busses and trailers
Styrene-butadiene rubber (SBR) and
Butadiene rubber (BR)
Small trucks, motorcycles, private cars,
bycicles
Butyl rubber IIR) Inner tubes

4. What is rubber?
• The unique property of rubber is that it is elastic. When rubber is stretched, the molecular bonds
can be extended out. When released, the molecules coil back to their original shape
• In its raw state rubber consists of long randomly kinked hydrocarbon chains which can slide past
each other. Raw rubber is therefore plastic, weak and permanently deformable. The purpose of
vulcanization (also called curing) is to chemically link the rubber chains together by "crosslinks" to
form a three-dimensional network.
• The process of vulcanization can improve the quality of rubber. Raw rubber is heated
during vulcanization. This makes the rubber hard, more elastic and strong.
• During the process of vulcanization, some atoms attach themselves to extra loose bonds in
the rubber molecule and also cross-link the molecules. The cross-linking locks the
molecules in place and prevents slipping. Thus making the vulcanized rubber more
strong. Vulcanized rubber is non-sticky and has higher elasticity. It does not loose its
properties easily and can be used in a temperature range of - 40 °C to 100 °C.

5. What is rubber?
• Vulcanized rubber will have the following characteristics :
• the vulcanizate undergoes deformation upon stretching and when released
can recover almost completely its original dimension over time
• the vulcanizate does not dissolve in a good solvent for uncrosslinked rubber
but shows swelling
• the properties of a vulcanizate are less sensitive to temperature.

6. Is only vulcanization sufficient?
• The answer for the question is not, vulcanization will improve some
properties but other deficiencies could by improved by a process
called Rubber Compounding.

7. Rubber Compounding
• In any molded rubber product, we have three major influences on the
quality of the part, that we can control:
• Mold
• Process
• Rubber formulation.
• The last has the major influence on rubber properties.

8. Rubber Compounding
• In plastics, designers can use material suppliers’ specification data to
determine what material will work best in their application, but in
rubber, that information is not readily available.
• The reason is the plastic molder purchases their materials ready to
process and the resulting physical and environmental resistance
properties are controlled by that supplier.
• In contrast, the rubber molder purchases ingredients from many
suppliers and mixes them to form the material that is processed in
the mold, therefore, each molder controls the material's and resulting
end product's properties.

9. Rubber Compounding
• What the designer doesn't realize is that rubber compounders have
over 180 different commercial grades of nitrile from which to select!
• These vary by acrylonitrile (ACN) content, viscosity, chemistry, and supplier
("equivalent" grades usually are not) among other parameters.
• On top of that, we will combine the base polymer (often two or more grades)
with approximately 10 - 20 other ingredients.
• These other ingredients enable us to achieve the desired physical,
environmental resistance and processing properties required to mold the end
product.
• In addition, we have literally thousands of chemicals to choose from when
selecting those other ingredients. As you can see the possible combinations
and resulting material variations are infinite.

10. Rubber Compounding
• In the majority of materials, just adding vulcanizing chemicals will
produce a product so weak, in its mechanical and environmental
resistance characteristics that it is almost unusable.
• Not only can we improve an elastomer’s physical strengths by
compounding other ingredients into the mixture of elastomer and
sulfur, but also we can improve other characteristics and even create
some that do not naturally occur.

11. Rubber Compounding
• For to make a compound we could divide it on five main system, as
follows:
• Elastomer system
• Filler system
• Protection system
• Process aids
• Cure system

12. Rubber Compounding
• An important detail to note is that nearly all compounders us the unit
of measure of "parts per hundred" (PHR) for their formula. This is a
unit of weight for the relationship between the elastomer system and
the other systems. If we always utilize 100 parts of elastomer for all
formulas then it is much simpler to change the other systems to
create changes and different formulas.
• The reason this is so important is that the cure system reacts only
with the elastomer system. Thus, as we change all the other systems,
the relationship between the elastomer system and the cure system
remain constant with a few exceptions that we won’t address here.

13. Rubber Compounding
• Elastomer system
• One or more elastomers blended, to enhance or achieve desired properties.
• Elastomer selection for improved processing

14. Rubber Compounding
• NATURAL RUBBER
• The raw material to make natural rubber actually does come from trees
• Produces compounds with high tensile strength, tear strength, tear and abrasion resistance
• Can be used at lower temperatures, low compression set, and high resilience
• Not recommended for severe applications with oil and solvent exposure; subject to aging by sun, ozone, and
heat
• Also not good for applications in contact with concentrated acids or alkalis
• Maximum continuous operating temperature is about 225°F
• NEOPRENE (CHLOROPRENE)
• Good general purpose rubber with properties close to natural rubber, but is synthetically produced
• Better resistance to oils and solvents compared to natural rubber but similar low compression set
• Can be compounded for flame resistance
• Good weathering resistance
• Poorer low temperature performance compared to natural rubber
• Not good in applications with concentrated acids or alkalis
• Maximum continuous operating temperature is about 275°F

15. Rubber Compounding
• NITRILE (BUNA)
• Much better oil and solvent resistance compared to either natural rubber or Neoprene
• Recommended for most oil field applications
• Can be formulated for use at low temperatures
• Good compression set and abrasion resistance, but poor weathering resistance
• Can be used with concentrated acids and alkalis but there are better alternatives
• Maximum continuous operating temperature is about 275°F
• HNBR (HYDROGENATED NITRILE)
• Similar to Nitrile but with improvements in heat and ozone resistance
• Can be formulated for low temperature applications
• Excellent for oil field service
• Usually not recommended in applications with concentrated acids or alkalis
• Very high cost
• Maximum continuous operating temperature is about 350°F

16. Rubber Compounding
• STYRENE BUTADIENE (SBR)
• Originally developed as a low cost substitute for natural rubber
• Good water resistance and abrasion resistance
• Poor weathering resistance, but can overcome with specific raw materials
• Not recommended for contact with oils and solvents
• Not used with concentrated acids or alkalis
• Maximum continuous operating temperature is about 225°F
• BUTYL
• Very good resistance to most gases including air
• highly resistant to ozone and weathering
• Abrasion resistance close to natural rubber and good for concentrated acids and alkalis
• Not recommended for petroleum product exposure
• Maximum continuous operating temperature is about 300°F

17. Rubber Compounding
• EPDM
• Exceptional resistance to weathering and ozone
• Excellent resistance to water, most gases, steam, and heat aging
• Good for exposure to concentrated acids and alkalies, but not recommended for
exposure to oils and solvents
• Maximum continuous operating temperature is about 350°F
• FKM (VITON®)
• High cost, but high performance material
• Outstanding resistance to most chemicals, oils and solvents
• Good oxidation and ozone resistance
• Maximum continuous operating temperature is about 650°F
• "Viton" is a trademark of DuPont and signifies material produced by DuPont

18. Rubber Compounding
• Filler System
• They are composed of:
• Reinforcing filler
• Semi and non-reinforcing filers
• Plasticizers

19. Rubber Compounding
• Filler System
• Reinforcing filler – typically are:
• Carbon black
• Precipitated silica
• Fumed silica

20. Rubber Compounding
• Filler System
• Semi and non-reinforcing filers
• Typically are used to:
• Reduce cost
• Improve processing
• Increase hardness
• Tensile strength
• Tear resistance
• Abrasion resistance

21. Rubber Compounding
• Filler System
• Plasticizers
• Plasticizers (UK: plasticisers) or dispersants are additives that increase the plasticity or
fluidity of a material. The plasticizers also control the hardness. The dominant applications are
for plastics, especially PVC, and rubbers. The properties of other materials are also improved
when blended with plasticizers including silica, carbon black, clays, and related products

22. Rubber Compounding
• Protection system
• All polymers & products based on them are subject to degradation on
exposure to the degradative environments such as: - Storage aging - Oxygen -
Heat - UV Light & Weathering - Catalytic degradation due to the presence of
heavy metal Ions (Cu, Mn, Fe etc.) - Dynamic Flex - Fatigue - Ozone (Static /
Dynamic / Intermittent exposure) These factors degrade rubbers / rubber
products causing substantial changes in their technical properties and
ultimately lead to their failure during service or shorten the expected service
life in the absence of Antioxidants.

23. Rubber Compounding
• Protection system
• Antioxidants
• Antiozonants
• Initiators/promoters

24. Rubber Compounding
• Process Aids
• High productivity is very important to the rubber industry because it is usual
to encounter large variations of raw materials.
• Processing aids are used mostly to improve the production process, i.e. flow
rate, homogeneity, tackiness etc.; This product range includes lubricants,
tackifiers, homogenizers, chemicals dispersing agents, peptizers, plasticizers,
flow promoter and oil.

25. Rubber Compounding
• Process Aids
• Mixing Aids
• Molding Aids

26. Rubber Compounding
• Cure system
• Vulcanizing Agents
• Activators
• Accelerators
• Scorch Retarders

27. Rubber Compounding
• Cure system
• To vulcanize, you will have to bring the following conditions :
• Energy : mostly thermal energy
• Vulcanization agents:
• Sulfur
• Organic peroxides
• Metallic oxides
• Diamines...
• Active sites on the polymer
• Halogen atom (Br, Cl...)
• Insaturation ( -C=C- )
• Chemical function ( -COOH or epoxy groups )
• Accelerators are chemicals which accelerate the cross-linking reactions.

28. Rubber Compounding
• Cure system

29. Rubber Compounding
• Cure system
• Two factors are very important in the vulcanization of rubber:
• The density of crosslinking (the frequency with which a rubber chain is linked to others)
• The nature of the crosslink.
• There is a clear maximum in strength properties at a certain level of
crosslinking but it is often advantageous to exceed this level to increase
resilience and resistance to set. These latter properties improve with
increasing hardness (or modulus), brought about by increasing crosslinking.
However, increasing the hardness by means of raising the filler loading has a
harmful effect on set and resilience.

30. Rubber Compounding
• Cure system
• Vulcanization with sulfur
• Elemental sulfur is the predominant vulcanizing agent for general-purpose rubbers. It is
used in combination with one or more accelerators and an activator system comprising
zinc oxide and a fatty acid (normally stearic acid). The most popular accelerators are
delayed-action sulphenamides, thiazoles, thiuram sulphides, dithocarbamates and
guanidines. Part or all of the sulfur may be replaced by a sulfur donor such as a thiuram
disulphide.
• The accelerator determines the rate of vulcanization, whereas the accelerator to sulfur
ratio dictates the efficiency of vulcanization and, in turn, the thermal stability of the
resulting vulcanizate.

31. Rubber Compounding
• Cure system
• Vulcanization with sulfur
• In rubber an accelerator to sulfur ratio typically of 1 : 5 is called a conventional vulcanizing system and it gives a
network in which about 20 sulfur atoms are combined with the rubber for each inserted chemical crosslink. The term
'chemical crosslink' is used because chain entanglements can behave as physical crosslinks once 'locked in' by
chemically inserted crosslinks. Most of the crosslinks are polysulphidic (ie with a bridge of not less than three sulfur
atoms) and a high proportion of the sulfur is in the form of cyclic sulphide main chain modifications. This
combination provides good mechanical properties and excellent low temperature resistance, but polysulphidic
crosslinks are thermally unstable and reversion can occur at high vulcanizing temperatures and high service
temperatures.
• An accelerator to sulfur ratio of 5 : 1 is typical of an efficient vulcanizing (EV) system where no more than 4 - 5 sulfur
atoms are combined with the rubber for each chemical crosslink. Most of the crosslinks at optimum cure are
monosulphidic or disulphidic and only a relatively small proportion of the sulfur is wasted in main chain
modifications. This combination provides very much enhanced thermal stability, both under aerobic and anaerobic
conditions, but some mechanical properties may be impaired.

32. Rubber Compounding
• Cure system
• Vulcanization with sulfur
• It is not possible to list all the chemicals used as accelerators, but some of the main
groups used in association with natural rubber are: thiazoles; sulphenamides and
guanidines.
• Vulcanization using sulfur alone is sluggish, but, when the sulfur level is increased to
make the vulcanization faster, a problem of sulfur blooming arises. Organic accelerators
were developed to overcome the sluggishness of sulfur vulcanization and to prevent
blooming of unreacted sulfur.
• You can choose one (or mostly) a combination of the following accelerators.

33. Rubber Compounding
• Cure system

34. Rubber Compounding
• Summary of sulfur crosslink

35. Rubber Compounding
• Cure system
• Vulcanization with peroxide
• Elastomer crosslinking can be carried out by means of peroxides as well. The procedure
can be applied in the case of both diene and saturated (silicone, urethane, ethylene-
propylene, etc.) rubbers.
• Dicumyl peroxide performs crosslinking of NR, SBR, nitrile rubber, resulting in
vulcanizates with good cold and aging resistance.
• Higher tensile strength of the vulcanizates obtained with peroxides as vulcanizing agents,
can be obtained by the addition of small amounts of sulfur, amines or unsaturated
compounds.
• By comparison with the vulcanization with sulfur and accelerators, peroxides produce a
lower reaction rate and the resulting vulcanizates have a lower tensile strength,
scorching tendency and unpleasant smell.

36. Rubber Compounding
• 1. Set specific objectives (properties, price, etc.)
• 2. Select base elastomer(s).
• 3. Study test data of existing compounds.
• 4. Survey compound formulations and properties data presented by material
suppliers in their literature.
• 5. Choose a starting formulation
• 6. Develop compounds in laboratory to meet objectives.
• 7. Estimate cost of compound selected for further evaluation.
• 8. Evaluate processability of compound in the factory.
• 9. Use compound to make a product sample.
• 10. Test product sample against performance specification.

37. Rubber Compounding
• Rubber compounding is one of, if not the most difficult and complex subjects to master
in the field of rubber technology. Compounding is not really a science. It is part art, part
science. In compounding, one must cope with literally hundreds of variables in material
and equipment. There is no infallible mathematical formulation to help the compounder.
That is why compounding is so difficult a task.

38. Why Reclaim or Recycle Rubber Goods
Rubber Recovery can be a difficult process. There are many reasons, however why rubber
should be reclaimed or recovered?
• Recovered rubber can cost half that of natural or synthetic rubber.
• Recovered rubber has some properties that are better than those of virgin rubber.
• Producing rubber from reclaim requires less energy in the total production process than does virgin
material.
• It is an excellent way to dispose of unwanted rubber products, which is often difficult.
• It conserves non-renewable petroleum products, which are used to produce synthetic rubbers.
• Recycling activities can generate work in developing countries.
• Many useful products are derived from reused tires and other rubber products.
• If tires are incinerated to reclaim embodied energy then they can yield substantial quantities of
useful power. For example, some cement factories use waste tires as a fuel source.

39. Tire reuse and recovery
There is an enormous potential for reclamation and reuse of rubber in developing countries.
There is a large wastage of rubber tires in many countries and the aim of this brief is to give
some ideas for what can be done with this valuable resource. Whether rubber tires are
reused, reprocessed or hand crafted into new products, the end result is that there is less
waste and less environmental degradation as a result.
In many countries, there is a culture of reuse and recycling. Waste collectors roam residential areas in
large towns and cities in search of reusable articles. Some of the products that result from the
reprocessing of waste are particularly impressive and the levels of skill and ingenuity are high.
Recycling artisans have integrated themselves into the traditional market place and have created a
viable livelihood for themselves in this sector. The process of tyre collection and reuse is a task
carried out primarily by the informal sector. Tires are seen as being too valuable to enter the waste
stream and are collected and put to use.

40. Recovery of rubber
• Recovery Alternatives
• There are many ways in which tyres and inner tubes can be reused or reclaimed. The waste
management hierarchy dictates that re-use, recycling and energy recovery, in that order, are
superior to disposal and waste management options.

41. Recovery of rubber
Kind of recovery Recovery Process
Product Reuse Repair • Retreading
• Regrooving
Physical Reuse • Use as a fiuller
• Use of form
• Use of Properties
• Use of Volume
Material Reuse Physical • Tearing apart
• Cutting
• Processing to crumb
Chemical • Reclamation
Thermal • Pyrolisis
• Combustion
Energy Reuse • INcineration

42. Recovery of rubber
• Chemical and thermal recovery
• This type of recovery is not only lower in the waste management hierarchy, but is also a higher
technology requiring sophisticated equipment. The applicability of such technologies for small-scale
applications in developing countries is very limited. We will therefore look only very briefly at a
couple of processes. Chemical recovery is the process of heating waste rubber reclaim, treating it
with chemicals and then processing the rubber mechanically.
• Acid reclamation – uses hot sulphuric acid to destroy the fabric incorporated in the tyre and heat
treatment to render the scrap rubber sufficiently plastic to allow its use as a filler with batches of
crude rubber.
• Alkali recovery - Reclaimed rubber, treated by heating with alkali for 12 to 30 hours, can be used as
an adulterant of crude rubber to lower the price of the finished article. The amounts of reclaimed
rubber that are used depend on the quality of the article to be manufactured.

43. Recovery of rubber
References and further reading
• Ahmed, R., Klundert, Arnold van de, Lardinois, I., Rubber Waste, Options for Small-scale Resource
Recovery, TOOL Publications and WASTE, 1996. A book aimed at small-scale rubber recyclers in
developing countries.
• Scrap Tire and Rubber Recycling Terminology Booklet developed by the ITRA Tire and Rubber
Recycling Advisory Council (TRRAC) (See address in following section). It is a valuable resource to
understanding the tire industry and tire recycling issues.
• Recycling Rubber – Practical action

44. Obrigado a todos
Luis Antonio Tormento
E-Mail: luis.tormento@outlook.com
Cel: +55 (11) 98899-0267