WO1999048960A1

WO1999048960A1 - Process for the manufacture of quality reclaimed rubber

Info

Publication number: WO1999048960A1
Application number: PCT/IB1999/000787
Authority: WO
Inventors: Chandrasekaran Pillai; C. Hari Chandra
Original assignee: Chandrasekaran Pillai; Chandra C Hari
Priority date: 1998-03-23
Filing date: 1999-03-17
Publication date: 1999-09-30
Also published as: AU3341699A

Abstract

A process for the manufacture of devulcanized rubbers from a base material of rubber crumbs derived from tire scraps and other high filler loaded rubber products, post industrial wastes, rubber rejects, and use-exhausted rubber articles. The process comprises mixing the rubber crumbs with a particular polymeric additive composition at elevated temperature until devulcanization to the desired viscosity is obtained. The process can be carried out in one stage using conventional rubber processing equipment. The resulting devulcanized rubber is of exceptionally high quality and can be used in products demanding dynamic physical properties such as tire and tire retreads formulations in blends with virgin rubbers.

Description

PROCESS FOR THE MANUFACTURE OF QUALITY RECLAIMED RUBBER

RELATED APPLICATION

The present application is an improvement of the invention described in U.S. Patent application 08/692,628, filed August 6,

1996 by C.R. Pillai, one of the inventors of the present application and entitled "Process For The Manufacture Of High

Grade Devulcanized Rubbers From Scrap and Reject Rubber Items".

FIELD OF INVENTION

The present invention relates to a process for converting rubber crumbs from waste materials such as scrap tires and other highly loaded rubber product scraps, rejects and wastes for reuse in the manufacture of new rubber products. More particularly, the present invention relates to a process for reclaiming vulcanized natural and synthetic rubber crumbs in a single stage wherein a reagent composed of a blend of polymers is added to the rubber crumb and mixed in at elevated temperatures.

BACKGROUND OF THE INVENTION

The process of vulcanization which converts rubber from its plastic state to its elastic state was discovered by Charles Goodyear in 1839. This exceptional discovery has led to the growth of an international rubber industry ranging from rubber plantations to extensive manufacturing operations, including the production of synthetic rubbers. Synthetic rubbers initially were produced as a substitute for natural rubber and later for specialized applications. Today, annual rubber production and consumption of both synthetic rubbers and natural rubbers is in of excess 20 million tons, about 35% of this amount being in the form of natural rubber.

This massive volume of rubber production gives rise to substantial amounts of scraps and rejects most of which constitutes tires and products with high levels of fillers such as carbon black and calcium carbonate. The enormous quantity of used rubber products has created a serious disposal problem, particularly in the United States where in excess of 250 million tires are discarded annually. Due to environmental pressures and the decreasing availability of landfills, demand for recycling scrap and reject rubber products has grown substantially.

Reclaiming of scrap rubber to its original plastic state from its vulcanized elastic state enables the rubber to be recycled for use in new rubber articles. However, most attempts to recycle reclaimed rubber have resulted in only a minor proportion of the reclaimed rubber being used in blends with virgin rubbers. Moreover, the properties of reclaimed rubber are affected by the presence of large amounts of mineral fillers and aromatic oils which are an essential part of the conventional rubber reclaiming process. Recently developed processes for reclaiming rubber include an ultrasonic method of devulcanization and mixing of chemical additives on mills at ambient room temperatures without the use of vulcanizing agents. However, both methods fail to produce a product which meets the quality specifications of tire and tire retread materials demanded by the industry and the products produced from these methods cannot be used as an extender to lower cost or to partially replace the virgin polymer base in tire compound formulations. As a result, automobile tire and tire retread manufacture is one area where reclaimed rubber typically is not used. Further, a majority of the reclaim rubbers generally available contain about 5% oil and

-2- higher levels of conventional fillers deliberately introduced during the reclaiming process to facilitate chemical reaction and handling. These reclaim rubbers are not always used by manufacturers of products of high quality or those requiring dynamic properties due to the level of these contaminants.

Despite the development of rubber reclamation, a need still exists for a new rubber reclamation process which reduces costs and improves the quality of reclaimed rubber, in particular for reclaiming rubber crumbs from scrap tires and similar materials having large amounts of carbon blacks and other fillers. Such a process should produce more consistent reclaimed rubber and should enable the manufacturer to control the viscosity of the devulcanized rubber without the addition of plasticizers or mineral oil that adversely effect the physical properties of the rubber. In addition, a need still exists for a process capable of producing a high grade rubber polymer that closely resembles the virgin natural or synthetic rubbers in its vulcanization characteristics in order that it can be incorporated easily into a new rubber product formulation containing virgin rubbers.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a process for the manufacture of devulcanized rubbers from rubber crumbs which produces high quality, high grade rubbers.

It also is an object of the present invention to provide a process for the manufacture of high grade devulcanized rubbers from rubber crumbs and other highly loaded rubber scraps in a single stage process. It is a further object of the present invention to provide a process for the manufacture of high grade devulcanized rubbers

^■3- from rubber crumbs and other highly loaded rubber scraps which produces a higher yield of high quality, re-usable reclaimed rubber.

It is an additional object of the present invention to provide a process for the manufacture of high grade devulcanized rubbers from rubber crumbs and highly loaded rubber scraps which enables the manufacturer to control the viscosity of the devulcanized rubber.

It is another object of the present invention to provide a process for the manufacture of high grade devulcanized rubbers from scrap rubbers which does not use undesirable contaminants such as oils and peptisers.

Additional objects, advantages and novel features of the invention will be set forth in part of the description which follows, and in part will become apparent to those skilled in the art upon examination of the following specification or may be learned by practice of the invention.

These objects are achieved by providing a process for the production of high grade devulcanized rubber comprising introducing into a pre-heated blending apparatus a base material of rubber crumbs and a polymeric additive composition, mixing said rubber crumbs and polymeric additive composition at elevated temperature until devulcanization of the rubber crumbs has been attained, transferring the blended mixture to a two roll mill and cooling the mixture.

DETAILED DESCRIPTION

The present invention relates to a process for the production of high grade devulcanized rubber from tire crumbs and other highly loaded rubber scraps in a single stage process. The tire crumbs or crumbs from other highly loaded rubber scraps are

-4- mixed with several polymeric additives (hereinafter sometimes referred to the polymeric blend) at a pre-established temperature range for a specific period of time. The composition of the polymeric blend, the processing temperature and the duration of the mixing of these additives with the rubber crumbs is dependent upon the type of crumbs to be devulcanized and the final degree of devulcanization as indicated by the viscosity/plasticity of the final product. Included among the types of crumbs of vulcanized rubber scrap materials contemplated for use in the present invention are those derived from products such as tires and other highly loaded articles based on natural rubber, styrene-butadiene rubber, nitrile rubber, polybutadiene, neoprene and EPDM rubber, for example, post industrial rejects and use- exhausted rubber articles. However, it is to be understood that these types of rubbers are meant to be illustrative only and that scrap crumb rubbers derived from other types of rubber may be devulcanized using the present invention.

The process of the present invention constitutes introducing the rubber crumb to be devulcanized and the blend of polymeric additives into a blending/mixing apparatus provided with heating means to attain chamber temperatures of up to 250°C. Polymeric additives suitable for use in the present invention are listed in Table I . The level or dosage amount of the polymeric additives is dependent upon the type of rubber scrap and filler loading from which the crumbs were derived. Preferably, the polymeric additive dosage ranges from 13 parts to 18 parts per 100 parts of the crumb to be reclaimed. There is a critical maximum dosage level of the polymeric blend for each type of rubber crumb, beyond which the devulcanizing effect of the additive drops dramatically, as provided in Table II. In addition, the size of the rubber crumbs to be reclaimed should be as uniform as possible, for example, within a mesh size of about 40 mesh, preferably within a mesh size of about 30 mesh and more preferably within a mesh size of about 20 mesh, in order to yield a final product having excellent physical properties hitherto not attained in reclaimed crumbs .

The mixture of the crumb and the polymeric additives, except natural rubber based additives, namely chemically modified epoxidized natural rubber (ENR) and natural rubber (SMRL) , are mixed continuously in a blending apparatus at a temperature starting at about 150 °C. In those instances where ENR and SMRL form part of the polymeric additive component, they are added to the mixture after about 5 minutes of mixing, and the mixing and heating is continued until the temperature reaches from about 200 to about 220°C, depending on the type of crumb used. The mixture is continuously mixed at this peak temperature range of about 200 to about 220 °C. for a period of from about 5 to about 30 minutes before being discharged onto a Rubber Two Roll Mill having cooling means to keep the rolls at ambient room temperature. The duration of the entire mixing and heating process can range from about 10 minutes to about 30 minutes depending on the type of rubber crumb being reclaimed. One indication that the rubber crumb has reached the stage of devulcanization is the power load drop on the motor of the blending apparatus. As most conventional mixers are provided with ampere meters showing the load of the machine's motor, a drop in ampere usage is evidence of devulcanization.

It is important to note that caution should be exercised to control the temperature of the mixture as excess temperature may result in the burning of the rubber crumb. In some rubbers with high level "nerve", the process of mixing is exothermic if the mixing equipment is fully enclosed due to friction against the wall of the mixing chamber. Therefore, the heat conducting coils also should have the provision to carry cooling water or other cooling medium when needed in order to maintain a temperature under 250 °C.

Once the mixture is discharged onto the Two Roll Mill, the material forms a continuous band, an indication of the level of devulcanization and plasticity. When the material cools to about 70 to 80°C, it can be cut off from the Mill and pressed into bales or blocks of desired dimension.

Table I lists the several types of polymeric additives suitable for use in the polymeric blend of the present invention. The level or dosage of each additive in the polymeric blend is listed is provided in parts per 100 parts of rubber crumb.

Table I: Types, Grades & Parts of Polymeric Additives

Polymer Type Grade Part

Chemically modified epoxidized ENR 50 1 to 5 natural rubber (ER)

Ethylene vinyl acetate (VA40E) VA content 1 to 5 <50

Styrene-butadiene rubber (SBR) SMR L 1 to 5

Natural Rubber (SMRL) SMR L 3 to 13

Maleic anhydride (MaHd) as required *

Polypropylene (PP) copolymer 1.5 to 3.5

* level is based on the PP and VA40E content of the polymeric additive for any given type of crumbs, typically 0.1 to about 0.5 %/wt . Table II provides examples of specific polymeric blends for devulcanizing particular types of rubber crumbs.

Table II: Additive compositions for different types of rubber scraps

Scrap Mesh Additive Additive Parts

Composition Size composition per 100 Parts of Scrap Crumb

NR tire crumb 20 to ER 1.0 13 to 18 40 SMRL 7.0

VA40E 5.0

MaHd **

PP 1.5

SBR tire 20 to VA40E 4.0 13 to 18 crumb 30 SBR 3.0

ER 1.0

SMRL 5.0

MaHd **

PP 2.0

SBR/BR tire 20 to VA40E 5.0 13 to 18 crumb 30 SMRL 8.0

MaHd **

PP 2.0

EPDM crumb 10 to ER 5.0 10 to 15

40 SBR 5.0

MaHd **

PP 1.5

Neoprene 10 to ER 8.0 13 to 15 crumb 30 VA40W 5.0

MaHd **

PP 1.5

Nitrile crumb 10 to ER 10.0 13 to 15

30 VA40E 3.0

MaHd **

PP 1.5

SKOR crumb*** 30 to ER 8.0 13 to 18 60 SMRL 5.0

VA40E 5.0

SBR 3.0

MaHd **

PP 2.0

** MaHd dosage is dependent on the level of PP and VA40E in the composition of the polymer additive, and is typically 0.1 to 0.5 %/wt.

*** SKOR = Some Kind Of Rubber crumbs from recycled rubber parts of unknown grades and types of polymers .

It is important to note that the above range and compositions are recommended levels. However, as the type of rubber crumb can vary widely, some adjustments may be necessary in order to produce reclaimed devulcanized rubbers of very good quality.

The following example is provided merely to illustrate the present invention, and it is to be understood the invention is not limited thereto. All amounts of the various ingredients in the examples and elsewhere in the specification are by weight unless otherwise specified.

Example: Devulcanized/Reclaimed Rubber from Scrap Tire Crumbs

An excellent high grade devulcanized material was produced from natural rubber (NR) tire crumb using the additive composition set forth in Table II (ER 1, SMRL 7 and VA40E 4, polypropylene 1) Thirteen (13) parts of the additive composition was used per 100 parts of 30 mesh crumb.

Crumb: The rubber crumb employed was whole tire crumb free of fiber and metal and sieved through 30 mesh secured from commercially available sources in Malaysia where most tires are made from natural rubber comprising 70 to 100% base polymer in the compound formulations.

Equipment : A Two Roll Mill, a Blending apparatus having an enclosed chamber (capacity 30L with heating coils) and Hydraulic Baling Press were used. Process : The blending chamber was preheated to a temperature of 150°C, followed by the introduction of the NR tire crumbs and all of the polymeric additives except for ENR and SMRL. The mixture was blended while the temperature of the chamber was controlled to not exceed 200 °C. After 5 minutes of mixing, the ENR and SMRL were added to the blending chamber and the mixing continued until the power load on the blending machine's motor began to peak (about 15 minutes) . The mixture, a resinous mass, was discharged and transferred to the Two Roll Mill having a nip setting of about 3/8". The discharged material's temperature, as it was dumped from the blender chamber, was 210 °C. Once on the mill with cooling water circulating inside the rolls and a fan blowing over the rolls, it took about 10 minutes for the resinous mass to cool down sufficiently (about 70°C.) to be removed and laid out on a table. The resulting reclaimed mass was allowed to cool further for about an hour before being baled into a block weighing 30Kg.

The final product had a mooney viscosity (ML1+4 100°C.) of 35 and unlike devulcanized reclaims produced by conventional methods, had good green strength. Other physical properties of the final product follow:

Tensile strength 15MPa

Modulus 100% 4 MPa

Modulus 300% Ultimate Elongation % 280

While particular embodiments of the invention have been described, it will be understood, of course, that the invention is not limited thereto, and that many obvious modifications and variations can be made, and that such modifications and variations are intended to fall within the scope of the appended claims .

^■10-

Claims

What is claimed is: 1. A process for the manufacture of devulcanized rubber from a base material composed of rubber crumbs comprising the steps of : (a) introducing into a blending apparatus pre-heated to a temperature of about 150 ┬░C. said base material and a polymeric additive composition comprising at least one additive selected from the group consisting of polypropylene, ethylene vinyl acetate, styrene-butadiene rubber and maleic anhydride and mixing said base material and said polymeric additive composition for about 5 minutes; (b) introducing into said blending apparatus at least one natural rubber based additive component selected from the group consisting of natural rubber and epoxidized natural rubber and mixing said base material, said polymeric additive composition and said natural rubber based additive component at a temperature in the range of from about 200 to about 220 ┬░C. for a period of from about 5 to about 30 minutes until the load on the blending apparatus' motor peaks to form a blended mixture; and (c) transferring said blended mixture to a two roll mill having cooling means and milling said mixture for a sufficient period for the mix to band and cool to a temperature in the range of about 70 to about 80 ┬░C; (d) removing said material from said mill and cooling it at ambient temperature.

2. The process in accordance with claim 1, wherein said rubber crumbs are selected from the group consisting of scrap tires and other highly loaded rubber scrap, post industrial rejects and exhausted rubber articles.

-11-

3. The process in accordance with claim 1, wherein said base material is derived from crumbs of natural rubber and said polymeric additive composition consists essentially of ethylene vinyl acetate, maleic anhydride and polypropylene and said natural rubber based additive component consists essentially of epoxidized natural rubber and natural rubber.

4. The process in accordance with claim 1, wherein said base material is derived from crumbs of styrene-butadiene rubber and said polymeric additive composition consists essentially of styrene-butadiene rubber, ethylene vinyl acetate, maleic anhydride and polypropylene and said natural rubber based additive component consists essentially of epoxidized natural rubber and natural rubber.

5. The process in accordance with claim 1, wherein said base material is derived from crumbs of styrene- butadiene/butadiene rubber and said polymeric additive composition consists essentially of ethylene vinyl acetate, maleic anhydride and polypropylene and said natural rubber based additive component consists essentially of natural rubber.

6. The process in accordance with claim 1, wherein said base material is derived from crumbs of EPDM rubber and said polymeric additive composition consists essentially of maleic anhydride and polypropylene and said natural rubber based additive component consists essentially of epoxidized natural rubber and natural rubber.

ΓÇó12-

7. The process in accordance with claim 1, wherein said base material is derived from crumbs of neoprene rubber and said polymeric additive composition consists essentially of ethylene vinyl acetate, maleic anhydride and polypropylene and said natural rubber based additive component consists essentially of epoxidized natural rubber.

8. The process in accordance with claim 1, wherein said base material is derived from crumbs of nitrile rubber and said polymeric additive composition consists essentially of ethylene vinyl acetate, maleic anhydride and polypropylene and said natural rubber based additive component consists essentially of epoxidized natural rubber.

9. The process in accordance with claim 1, wherein said rubber crumbs are derived from rubbers selected from the group consisting of natural rubber, styrene-butadiene, polybutadiene, neoprene, nitrile rubber, EPDM rubber and mixtures thereof.

10. The process in accordance with claim 1, wherein said base material is derived from mixed rubber of unknown composition, said polymeric additive composition consists essentially of styrene-butadiene, ethylene vinyl acetate, maleic anhydride and polypropylene and said natural rubber based additive component consists essentially of epoxidized natural rubber and natural rubber.

11. The process in accordance with claim 1, wherein the dosage amount of said polymeric additive composition and said natural rubber based additive is from about 10 to about 18 parts per 100 parts of said base material.

ΓÇó13-