Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Process of treating scrap or waste product containing solid...
Reexamination Certificate
2000-04-04
2002-11-12
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Process of treating scrap or waste product containing solid...
C521S040000, C521S040500
Reexamination Certificate
active
06479558
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates broadly to the treatment and recycle of rubber products and still more particularly to the use of recycled crumb rubber. The United States Government has rights to this invention pursuant to contract number DE-AC09-96-SR18500 between the U.S. Department of Energy and Westinghouse Savannah River Company.
2. Discussion of Background
Existing efforts to recycle used rubber, in particular used tires, into new rubber articles, especially tires, have met with only limited commercial success. In the United States alone, there are currently billions of tires stock-piled in long term storage with additional millions being added annually to such stock piles. Because of the large volume involved with tires, this discussion will be directed to tires although many of these comments are applicable to other new and used rubber products.
Because used rubber is usually processed in the form of crumb rubber, references herein will be to rubber in that form. However, crumb rubber is merely one example of a used rubber product suitable for processing as described herein. An existing limitation in the recycling of used tire material is that the used tire rubber cannot be readily mixed in economical proportions to form suitable new tire polymer mixes having acceptable cured properties.
During the vulcanization process of new tires, chemical accelerators, promoters, and/or initiators, are used and large numbers of sulfur-sulfur and sulfur-carbon cross-links are produced in the vulcanized tire rubber. It is generally believed in the art that the sulfur compounds which are present in used tire rubber are detrimental in the curing process when used tire material is mixed with new tire polymer. Formulations having significant levels of used tire rubber particles with new polymer materials result in a brittle compound unsuitable for many uses such as automobile or truck tires. Heretofore, efforts to reclaim scrap rubber have frequently included a physical sheering process which is suitable for a rubber which can be mixed with asphalt, forming asphalt rubber. Such use is taught in U.S. Pat. No. 5,304,576.
It is also known to take used rubber and depolymerize the vulcanized rubber in an organic solvent and then recover various polymerized fractions as taught in U.S. Pat. No. 5,438,078. Similarly, U.S. Pat. No. 5,264,640 teaches taking scrap rubber from used tires and regenerating the monomeric chemicals which are subsequently recovered. This method uses gaseous ozone to break down the crosslinked structure of the rubber followed by thermal depolymerization in a reaction chamber. U.S. Pat. No. 5,369,215 teaches a similar process in which used tire material may be depolymerized under elevated temperatures and at a reduced pressure to recover the monomeric compounds.
U.S. Pat. No. 4,104,205 teaches a microwave method to devulcanize rubber from hose end trim and butyl tire bladders. While tire tread material was also treated, difficulties in exothermic reactions and physical properties of the microwaved materials were noted.
U.S. Pat. No. 4,341,667 teaches that the green strength of elastomers reclaimed through heat, microwave, chemical treatments, or physical shearing can be improved by the addition of butene polymers.
U.S. Pat. No. 5,275,948, incorporated herein by reference, teaches the use of chemolithotrophic microorganisms to remove sulfur from the surface of finely ground scrap rubber. Preferred organisms include Thiobacillus species which oxidize elemental sulfur to sulfuric acid and which are released into the suspension culture.
U.S. Pat. No. 5,597,851, incorporated herein by reference, teaches the use of microorganisms to desulfurize finely ground rubber particles. Thiobacillus sp. and
Sulfolobus acidocaldarius
are used to bioprocess rubber particles for at least 24 hours but prior to complete oxidation of surface sulfur.
The present application relates to commonly assigned U.S. Application having Ser. No. 09/542,394, filed Apr. 4, 2000, entitled “Combination Biological and Microwave Treatments of Used Rubber” and having Attorney Docket No. WSR-14, and which is incorporated herein by reference. The present application also relates to commonly assigned U.S. patent application Ser. No. 09/542,201, filed Apr. 4, 2000, entitled “Microwave Treatment of Vulcanized Rubber”, and which is incorporated herein by reference.
There remains a strong need for a practical, economical system for processing used rubber into a material which can be incorporated at a substantial loading level into new rubber compounding mixtures. Further, there is room for improvement with respect to bioprocessing of used rubber, particularly in the selection of microorganisms, the selection of starting material, and overall process conditions and parameters.
SUMMARY OF THE INVENTION
The present invention is a process and the resulting product of the process in which previously vulcanized (used) rubber may be incorporated into polymer mixes for new rubber products, including tires, at much greater levels than used heretofore.
The present invention also provides a process and a resulting product of the process wherein previously vulcanized, used crumb rubber has the surface chemistry altered to provide a treated crumb rubber product. When compared to untreated crumb rubber, the treated crumb rubber has generally improved properties useful for incorporation with new tire or virgin rubber into automobile and truck tire polymer formulations. The improved properties for the composite polymer formulation include plasticity, elongation @ break, and energy @ break. The properties listed above are typically better than the combination of untreated crumb and new tire rubber mix control values when the combination of biologically treated crumb rubber and new tire rubber are analyzed and evaluated in Banbury tests.
In accordance with this invention, it has been demonstrated that particles of used crumb rubber can be reacted with active cultures of a bacillus-like bacterium isolated from a natural hot sulfur spring. The preferred isolate shows most favorable growth at 65° C. and has been found to react with S—S, and S—C bonds and provide an improved reaction surface on the rubber. In particular, the bacterium interacts with the surface sulfur constituents and alters the surface chemistry and reactivity of the so treated vulcanized crumb tire rubber. It has been found that the biotreatment of the crumb rubber particle changes the surface reactivity of the crumb rubber particles to an extent that the rubber particles can be integrated into a new tire polymer mix at much higher levels than previously accomplished. The biotreatment of the crumb rubber provides a treated rubber product which is compatible with the new rubber polymer component of a tire mix.
The use of the biotreatment to modify select chemical species provides a process which can be carried out on. an economical basis. The process is thought to be particularly useful in that the biotreatment is believed to alter a wide variety of chemical additives used by tire manufacturers and which are present within the used rubber. The ability to alter these chemical constituents, further enhances the usefulness and compatibility of the treated used rubber with new polymer. The biological treatment provides a more standardized crumb rubber for use in recycling operations, including the incorporation of significant quantities and sizes of treated crumb rubber into polymer formulations for automobile and truck tires. Further, the biological organism is itself a renewable, regenerating resource.
The biological treatment process also facilitates the use of used tire rubber as a renewable resource. Accordingly, the biotreatment process enables the use of a heretofore difficult to recycle waste product into a component for high quality, high end cured rubber products.
The use of the biotreatment provides a process and product which can be operated on an economical basis at a commercial scale and does not
Cain Edward J.
Dority & Manning PA
Lee Katarzyna W.
Westinghouse Savannah River Company
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