BY Ing. Hysen Blloshmi & Master Degree Kastriot Blloshmi/
Scrapped tire are produced in U.S. at an annual rate of 300 million, approximately one tire per year for each person in the country. Les than 30% of these tires are utilized for resource and energy recovery. The remaining tire are either land filled, added to the tire pile, discarded or
destroyed in an environmentally unecceptable maner. At the present time , landfilling is the major technique for scrap tire disposal in the country. Natural rubber consist of polymer of organic compound Isopren, with minor impurity of other organic compound. Rubber has approximately the fallowing composition: water 50-70%, resin 1,5-2%, protein 1,5-2 % ash 0,5% sugar 1-2%.
Natural rubber contain 6-8 % naturally occurring non-rubber materials. Goodyear discovered that heating the rubber and sulfur together, a process called Vulcanization, gave the rubber increased strength and elasticity and reduced its sensitivity to temperature. Natural rubber, when compared to synthetic, provides slightly better properties in tensil strength, teare resistance,and fatigue resistance.
Carbon black discovered in 1915 and added to the rubber compound a tenfold increase in wear resistance of tires. It represents 30% the compound and gives tires their distinctive color.
The first step in the tire manufacturing is mixing of raw material to form the rubber compound natural and synthetic rubber with carbon black, silica, sulfur and other chemical and oil.
Carbon black and Silica flllers can serve to improve the hardness, abrasion resistance, tensile properties and tear strength. Rubber without filler has very low physical strength and no practical use.
Carbon Black may be recovered for reuse and the de-vulcanized rubber may be subjected to revulcanization without separation of the polymer from the solvent by addition appropriate curing composition. Different types of carbon black have a wide range of primary particle size, large surface areas per unit mass, low ash, and solvent extractable materials and varying degrees of particle aggregation. Carbon Black is economically the most important active filler for technical product made from natural rubber, its wide range of application, is very very interesting topic in material science. The filler-rubber interaction are both physical and chemical.
Found that carbon black acted as a catalyst speeding up the cure reaction reducing the induction time composed with the unfilled system. Not all carbon black have the acceleration effect on the vulcanization. Carbon atoms in the rubber are still bound to sulfur atoms, and this bonds prevent them from forming covalent bonds with surrounding materials. Carbon Black generally increases the state of vulcanization and improve the reversion resistance.
In the process of vulcanization, sulfur atoms are chemically bonded to the carbon molecules of the rubber molecules and serve as cross-links between the sulfidic rubber molecules. There are many cross-linking agent but most use sulfur together with accelerators to speed up the process.
The sulfur on the surface of carbon black possibly plays an important role in the cross-linking process.
The chemical bonding of rubber with carbon black increases the degree of chemical cross-linking. Sulfur on the surface of carbon black most probably improved the vulcanization.
Vulcanization is the process by which plastic rubber is converted into the elastic rubber or hard rubber state. The process, which is brought about by the linking of macromolecules at their reactive sites, is also known as crosslinking.
Vulcanizing agents are substances that bring about the actual crosslinking process. Other properties, such as tensil strength, gas permeability, low temperature,flexibility and electrical resistanse change with the degree of vulcanization.
Each cross-linking releases a quantum of energy , making it an exothermal reaction. During this process, the catalyst creates a three dimensional matrix. The energy released in the exothermal reaction is proportional to the cross-linked bonds formed and it is proportional to the cross-linked bonds and it is assumed that each bond releases the same energy.
Vulcanization reaction is an irreversible process. There chain are chemically bounded to one another converting a plastic material into an elastic one.
Vulcanization is a chemical process in which polymer molecules are linked to other polymer molecules by atomic bridges, composed of sulfur atoms or carbon to carbon bonds Elevated temperatures is a driving factor for the degradation of rubber by causing the reversion of the cross-link sulfur network back to the gum state.
As it was first invented by Goodyear vulcanization used “S ” at 140 g/c for about 5 hr Vulcanization with “S” alone is no longer used today.
This heavily cross-linked polymer has strong forces between the chain and is therefore an insoluble and infusible thermosetting polymer. Vulcanization is a chemical by which the physical properties of natural or synthetic rubber are improved. Finished rubber has higher tensil strength, increased resistance to swelling and abrasion and a elastic over rang of temperature of the amount of sulfur.
In the process of vulcanization, the added sulfur allow some C – H bonds to be broken and replaced by C – S or S – S bonds.The cross-linked molecules create a three-dimensional network of rubber.
The accelerated sulfur cure system forms the various cross-links structure: mono, di and polysulfidic network, depending an the accelerator type, ratio of accelerator to sulfur, vulcanization temperature and time as well as the carbon black loading. However, little attention has been made on the effect of the carbon black loading and type of cure system on the cure kinetics of rubber compound.
In the Oxford Dictionary, the word “recycle ” is defined as ” return ” material to a previous stage of a cyclic process, esp. convert (waste ) to reusable material.
Although the rubber industry has more than 170 years of experience, it has still not found the perfect disposal and recycling method for rubber product.
There remain a number of unresolved methodological problems.The advent of industrial rubber production raised the question of what to do with the scrap rubber.The purpose of the devulcanization process is to restore the virgin rubber to its original state.Nevertheless the quest to devulcanize rubber effectively remain on of the primary goal of the tire recyclin industry.
” The idea of devulcanizing rubber back to its original form has an elegant simplicity, but the reality is complex ” say Mar Shays.Until recently the process of vulcanization was irreversible, and nobody in the industry as been able to figure out how to reverse the process.
No technology at present allows complete devulcanization of rubber. Therefore 100% sol will be never reached even if all cross-links are broken because of the carbon black.
Sulfidic cross-linking represents a significant problem in recycling of the rubber vulcanizate and in recovery of the staring material rubber polymer from vulcanized rubber.
” De-vulcanization consist of the cleavage of intermolecular bonds of chemical network, such as carbon – sulfur and sulfur – sulfur bonds, rather than C -C bonds appears to take shortening of chain also occurring”( Rader 1995 )
It is seem that S – S bonds energy is lowest among the various bonds present in the vulcanized natural rubber.
During chemical devulcanization of the amount of energy generated is utilized for breaking S – S bonds instead of C- C especially at shorter time and lower temperature. However, few C – C and C- S bonds may break along with S – S linkages, instead of other linkages. However, to the present time, no devulcanization technique has proven to be cmmercially viable on a large scale.
Devulcanization involves the removal of sulfur from the longer polysulfidic cross-links and eventually leads to the formation of more stable di- and monosulfidic, where the sulfur that is removed from cross-links is reused in the vulcanization process to produce additional cross-links.
Polysulfidic cross-links degrade to dead-ends and main-chain modification, leading to a net lossof cross-links i.e. reversion.
Indeed, the energy required to break monosulfidic bonds, is approximately 20% higher than what is needed to break the polysulfidic bonds
The vulcanization of rubber by sulfur in presence of organic accelerator is a complicated process. But actually devulcanization should be the reverse process of vulcanization.
Recovered rubber has some properties that are better than virgin rubber with common properties.Although vulcanization is not completely reversible.
Devulcanized rubber can be revulcanized with or without the addition of natural or synthetic rubber or binders.
By utilizing the process of this invention rubber crumb can be de-vulcanized using a simple technique without the need for Microwaves treatment, Ultrasonic Waves treatment, Under Pressure treatment with 2-butanol, or an Alkaly Metal, these approaches to de-vulcanization of the rubber tire have, however proved difficult and inefficient.
The employment of the process of this invention preserves the original microstructure of the rubber and allows for it to maintain an relatively high molecular weight.
The partially de-vulcanized rubber can be reprocessed, shaped and re-vulcanized in the same as the virgin rubber.
The de-vulcanized ground tire rubber was blended with natural rubber without interfacial modification. The de-vulcanized rubber can be re-vulcanized by the same type of sulfur accelerator vulcanizing system as it used to the original rubber.
In the process of my invention is formed and carbon black. Centrifuge technology has been used in many applications to separate suspended solids from a fluids. The design of a centrifuge to achieve a desired degree of separating depends on many factors including the type of centrifuge, the properties of the particle to be separated and the properties
of the surrounding fluids.
Carbon Black particles used in the reinforcement of rubber tend to be quite small compared to the size of particle that typical industrial centrifuge are designed to capture.
In practice it is not simple matter to separate the small size carbon black particle from the polymer solution in a cost effective manner with centrifuge technology.
Another method used to remove suspended solids from a solution glycerol is filtration. This is also not ideal in the present application.
Glycerol that is fine enough to be suitable for the filtration of carbon black also tend to result in a slow separation process if gravity is employed to pushed the solution through the filter. If pressure or vaccume is applied to increase the rate of filtration, then carbon black may be pushed such filters.
Another problem with filtration is binding wherein the filtration rate is reduced by build-up of material on the filter. The problem is by increasing polymer weight and the presence of both carbon black and glycerin in the mixture to be filtered. The glycerol tends to become bound-up with carbon black deposited on the filter creating an impenetrable layer.
1-Having a short term of active life, the proton penetrate into material, rubber, only to a small depth, up to 0,4 mm and less. This results in a need for the grinding of the cured rubber 20 – 30 mesh, and correspondingly reduced cost efficiency of this method. High
efficient techniques such as the use grinders can produce crumb rubber ranging from 20-30 mesh, which currently sells at price 0,15 – 0,17 cent per pound.
2- We use in this process crude glycerol 80% with catalyst and heating at temperature 175- 210 gr/celsius for 1,3 – 2 hr without pressure.
” A new phenomenon of alcohol de-vulcanization was announced earlier this year by Goodyear Co. but it currently seems to be a chemical curiosity” say D.A. Brown and W.F. Watson.
But this is not anymore a ” curiosity” because I use Glycerol (sugar alcohol ) for de-vulcanization rubber tire.
The presence of filler entails many difficulties in the chemical characterization of the de-vulcanized rubber while ensuring a closure resemblance with the real-life rubber product.With the separating of the slurry we make de-vulcanization more easy.
3—Recovered from partial de-vulcanized rubber and glycerol ,solid residue as carbon black, silica clay and ect. by centrifugation or filtration.
The carbon particle size is mostly in the nano-meter. Today, nano-particle are not directly use in factories producing tire. But carbon black and amorphous silica aggregates, at nano-sized the particle, are generated inside the rubber during the mixing and are chemically linked the rubber by covalent links.
The carbon black and silica particle further agglomerate into spheres or beads of 1-50 micron in diameter. Carbon black is initially formed as roughly spherical primary particle, which in most cases, rapidly form aggregates. An aggregate is a chain of primary carbon black particle that are permanently fused together in a random branching structure.
The aggregate may consist of a few hundreds of spherical particle. The chain are open structure and are used to absorb fluids and reinforce material such as rubber.
The aggregates can bind together by van-der waals forces in more loosely associated agglomerates.
Aggregates, on the other hand, may occasionally fracture but in essence represent the units of carbon found within a vulcanizate.
The type of aggregate indicates the structure of the black which may be considered to reflect to ratio of the surface area exposed to the rubber molecules.
Elementary particle of carbon black is very short life, aggregation is less then 1/100 second by covalent links, aggregates agglomerate in 1/10 second by electrostatic links.
These particle, however, immediately cluster to form aggregates ( from 100-500 nm in size ) based on covalent bonds. Because of nature of these bonds these aggregates cannot disaggregate under standard conditions.
The aggregate subsequently bind together to form agglomerates from 1-40 micron. Electrostatic bonds, weaker than covalent bonds, cannot be broken from normal use.
4-Continue heating of grinding rubber with crude Glycerol 80% with catalizator and 4-6 hr. After this heating de-vulcanization has been completed.
Sulfur from rubber can replace one of oxygen atoms of glycerol to form a series of sulfur analoges the thio-glycerol. The sulfydric groups in this comound are more reactive than the corresponding hydroxyl groups.
it is very easy and simple method.
1–Grinding rubber to 20-30 mesh.
2-Mixing rubber with crude Glycerol 80 %with catalizator, and heating for 1,3-2 hr. Carbon black is producing.
3-Filtration of Carbon Black from rubber and Glycerol.
4- Continue heating for 4 – 6 hr more, and de-vulcanization has bee completed.