ELASTOMERIC COMPOSITIONS COMPRISING RECLAIMED VULCANIZED ELASTOMER PARTICLES AND IMPROVED METHODS OF MANUFACTURE THEREOF

Methods for making elastomer compounds are described. The compounds include reclaimed vulcanized elastomer materials such as micronized rubber powders (MRP). The elastomeric compositions exhibit lower tensile strength variability. As described herein, shorter mixing times can be used to achieve the same minimum tensile strength as composition containing no reclaimed material. The elastomeric compositions may include various proportions of reclaimed vulcanized elastomer materials. A rubber compound is also described which comprises reclaimed material and which has a minimum tensile strength equal to or higher than a predetermined minimum tensile strength associated with a compound containing no reclaimed material. The rubber compound is manufactured with a reduced mixing time compared to that of the compound with no MRP.

DETAILED DESCRIPTION

For the purpose of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the tables and attached exhibits, and specific language will be used to describe the same. It will, nevertheless, be understood that no limitation of the scope of the disclosure is thereby intended; any alterations and further modifications of the described or illustrated embodiments, and any further applications of the principles of the disclosure as illustrated therein are contemplated as would normally occur to one skilled in the art to which the disclosure relates. All limitations of scope should be determined in accordance with and as expressed in the claims.

Various tables are included herein which help to explain the present subject matter and set forth experimental results relating to the same. These tables include experimental results relating to tensile strength testing of cured elastomer composition samples and an exemplary formulation of a control elastomer composition comprising no MRP.

According to an embodiment, aspects of the present disclosure generally relate to elastomeric compositions comprising reclaimed vulcanized elastomer materials (micronized rubber powders or MRP), wherein the elastomeric compositions comprising MRP exhibit a lower tensile strength variability during testing. For example, elastomeric compositions described herein may comprise reclaimed vulcanized elastomer materials (micronized rubber powders) comprising various proportions of MRP. According to one embodiment, these reclaimed vulcanized elastomer materials are used within standard rubber compounds (such as those used for vehicle tires) as replacements for conventional reclaimed vulcanized elastomer materials with relatively uniform particle size distributions that conform to ASTM standards. As described herein, experiments have determined that elastomeric compositions (e.g., tread rubber compounds) that include reclaimed vulcanized elastomer materials maintained a lower mean tensile strength, but demonstrated a lower tensile strength variability.

According to another embodiment, aspects of the present disclosure also relate to testing of different elastomeric compositions comprising a ratio of reclaimed vulcanized elastomer materials (micronized rubber particles) comprising one uniform particle size distribution per sample. For example, elastomeric compositions described herein may comprise 10% of reclaimed vulcanized elastomer material wherein the size distribution may comprise 140 mesh. As will be understood, when reclaimed vulcanized elastomer material is added to elastomeric compounds, an equal amount of virgin compound material is removed from the overall composition.

According to a further embodiment of the present disclosure, findings related to improved tensile strength variability also decrease the mixing time associated with mixing the various ingredients comprising the elastomeric compositions, thereby reducing the overall mixing costs. As described herein, experiments have determined that elastomeric compositions comprising various ratios of reclaimed vulcanized elastomer demonstrated lower tensile strength variability and raised the minimum tensile strength of the elastomer compositions. As will be understood and appreciated by one skilled in the art, using an elastomer composition comprising MRP, which raises the minimum tensile strength, may make specific applications more affordable when a minimum strength or durability threshold is required for that application.

As used herein and recited in the enclosed figures and tables, the term “PolyDyne” or “PD” refers to a brand name of vulcanized elastomer particles (e.g., cured rubber particles, recycled rubber particles, micronized rubber powder, or MRP) produced by Lehigh Technologies, Inc. of Tucker, Ga. According to one embodiment, the particles described herein are produced via a cryogenic grinding system described by U.S. Pat. No. 7,445,170, entitled Process and Apparatus for Manufacturing Crumb and Powder Rubber, and an impact mill as described by U.S. Pat. No. 7,861,958, entitled Conical-Shaped Impact Mill. In other embodiments of the present disclosure, these micronized rubber powders are produced via a variety of other known processes and techniques as will occur to one of ordinary skill in the art, and the powders used herein are not limited to the specific cryogenic grinding processes described herein.

As also used herein and recited in incorporated figures and tables, “PD80” generally refers to a reclaimed elastomer material composition (i.e., micronized rubber powder) conforming to conventional 80 mesh standards, “PD40” generally refers to MRP conforming to conventional 40 mesh standards, and so on. The term “PD84” generally refers to a reclaimed elastomer material composition having a broad distribution of particle sizes (and not conforming to any specific ASTM standards). Thus, PD40, PD80, PD84, PD140, etc. are proprietary brand names used to describe specific reclaimed elastomer material compositions (micronized rubber powders) produced by Lehigh Technologies, Inc., which have predetermined particle size distributions. PD84 corresponds to a proprietary composition of particles having a broad particle size distribution. As will be understood and appreciated, the specific formulations and particle size distributions associated with PD40, PD80, PD84, or PD140 (or any other formulation) are presented purely for illustrative purposes, and elastomeric compositions, reclaimed elastomer material compositions, or other elastomer formulations contemplated by the present disclosure are not limited to the specific characteristics or features recited herein.

As noted previously, it heretofore was assumed that elastomer compositions comprising MRP (e.g., PD80 or PD84) would exhibit poor performance characteristics as compared to similar compositions including no MRP and would, therefore, be less-desirable for many elastomer compositions (e.g., tire tread compositions). To confirm this assumption and to identify and collect statistical measures relating to strength and other durability characteristics of elastomer compositions, sample elastomer formulations comprising various percentages of MRP were produced such that their performance characteristics could be tested and compared to each other and to control samples comprising no MRP, such as the exemplary control formulation shown in Table 1. During experimentation, the elastomer composition samples that were produced for testing were prepared from a standard tire tread formulation using a 2-3 pass mix procedure, batch replication, and randomization (e.g., mixing, curing, and testing). Further, a t-test was used to ensure the statistical differences between the sets of test specimens were consistent and the results of the t-test confirmed the statistical differences between the sets were within a greater than 99 percent confidence.

The experimental parameters, testing criteria, and results of the tests are described herein. Further, Table 1 illustrates an exemplary elastomer composition that was used for testing purposes. The formulation shown in Table 1 includes no MRP. When MRP was added to the composition of Table 1 according to the “over batch weight” addition method (as will be understood by one of ordinary skill in the art), the percentage of other composition materials was reduced accordingly in a conventional manner. For example, if the compound batch weight without the reclaimed material is 20 kg and if 5% by weight of reclaimed material is used, the batch weight would then be 21 kg (i.e., 20+1 kg of reclaimed material) for the batch containing the reclaimed material using the over batch weight addition method. As will be understood by one of ordinary skill in the art, the sample control formulation described in Table 1 and the resulting formulations wherein MRP is added to the control compound, are used purely for illustrative purposes, and are not intended to be limiting of the elastomer compositions or formulations that could be used in connection with aspects of the present disclosure.

FIG. 1is a bar chart showing tensile strength data and variation in tensile strength for the control composition and for compositions containing 3%, 6% and 10% by weight of two different MRPs (PD84 and PD80). Tensile strength was measured as per test method ASTM D 412 in MPa. As would generally be expected, the control sample comprising no reclaimed material displayed greater mean tensile strength than the samples comprising various percentages of MRP. For example, the sample comprising 3% of PD84 had a mean tensile strength of 15.9 MPa, and the sample comprising 6% PD80 had a mean tensile strength of 16.0 MPa, as compared to the control sample, which was shown to have a mean tensile strength of 17.4 MPa. Surprisingly, however, the samples comprising MRP demonstrated a lower tensile strength variability.

FIG. 2is a bar chart showing average within batch tensile strength variability for elastomeric compositions comprising 3%, 6%, and 10% MRP. As can be seen fromFIG. 2, the compositions containing reclaimed material have a lower tensile strength variability than the control sample. For example, and as shown in Table 2, batches (i.e., samples of elastomeric compositions) comprising 3% MRP had an average tensile strength variability (measured at two standard deviations) of 0.69 MPa, while the control samples containing no MRP had an average tensile strength variability (measured at two standard deviations) of 1.27 MPa.

As shown in the embodiment described in Table 3, similar results were achieved for compositions containing 6% MRP.

TABLE 3Test results of 6% MRP vs. control sample.6%ControlMRPMean (Tensile 2SD in MPa)1.270.75Variance0.250.04Observations199Hypothesized Mean Difference0Degrees of Freedom26p0.01t Stat3.86P(T <= t) two-tail0.00067T Critical two-tail2.78
In particular, the elastomeric compositions containing 6% MRP had an average tensile strength variability of 0.75 MPa in contrast with the control samples comprising an average tensile strength variability of 1.27 MPa.

Similar results were observed for compositions containing 10% MRP. In particular, as can be seen from the data in Table 4, elastomeric compositions containing 10% MRP had an average tensile strength variability of 0.65 MPa whereas the control had an average tensile strength variability of 1.27 MPa. Generally, it was observed that elastomer compositions containing MRP exhibit an approximately 45% decrease in tensile strength variability.

A significant takeaway from these results is that although compositions with MRP exhibited lower average tensile strength characteristics, certain of these compositions actually exhibited higher minimum tensile strength properties. In certain applications (e.g., the tire industry), an elastomer composition's tensile strength is evaluated not based on its mean tensile strength but instead based on its minimum tensile strength. Therefore, including MRP in elastomer compositions is advantageous in certain applications as it is shown to yield lower average tensile strength variability, which in turn yields higher overall minimum tensile strength (assuming other composition properties, such as the materials used in the composition, mix times, etc., are held constant).

FIG. 3is a bar chart showing the minimum tensile strength for various elastomer compositions containing 0% (control), 3%, 6% and 10% by weight reclaimed material. As can be seen fromFIG. 3, because of lower average tensile strength variability certain elastomer compositions containing MRP have higher overall minimum tensile strength than elastomer compositions with no reclaimed material. Minimum tensile strength is defined inFIG. 3as three standard deviations below the mean tensile strength for the sample. As shown inFIG. 3, batches containing, for example, 3% PD140, had a minimum tensile strength of 16.77 MPa, whereas the control sample (with no MRP) had a minimum tensile strength of 15.50 MPa. As noted, this unexpected result is advantageous as it was previously assumed that elastomer compositions incorporating reclaimed material exhibited poor performance characteristics (i.e., exhibited performance characteristics inferior to elastomer compositions with no reclaimed material). Further, as previously noted, inclusion of reclaimed material in elastomer compositions can lead to reduced production costs.

The testing of the sample elastomer compositions comprising various percentages of MRP, the results of which are shown inFIG. 3, further indicated that incorporating MRP into elastomer compositions yielded improved batch quality as compared to elastomer compositions with no reclaimed material. While not wishing to be bound by theory, it is believed that incorporating reclaimed material into the formulation promoted shear in the mixing process, thus resulting in better dispersion throughout the batch. Put differently, it is believed that the MRP acted as a process aid and assisted in homogenizing the elastomer composition mix. As will be understood by those of ordinary skill in the art, a more homogenous mix is significant as uniform distribution of all ingredients is important in manufacturing elastomer compositions.

The findings relating to improved minimum tensile strength characteristics and improved homogeneity of elastomer compositions including MRP are unexpected and advantageous for several reasons. Specifically, one aspect of manufacturing elastomer compositions that affects production time and overall cost is the mixing time associated with mixing the various ingredients in a given composition (such as the composition illustrated in Table 1). Because elastomer compositions with MRP tend to produce a more homogeneous and thorough batch mix, it is possible to reduce the mix time of a given elastomer composition (as compared to a conventional mix time for a similar elastomer composition with no MRP) and still arrive at a predetermined minimum tensile strength threshold. For example, if a given virgin elastomer composition requires a mix time of six minutes to produce an elastomer compound batch having a predetermined minimum tensile strength, the mix time for a similar elastomer composition having MRP may only be five minutes to produce a batch with the same minimum tensile strength value for the compound.

Alternatively, if mix times in the production of elastomer compositions are held constant, incorporating MRP of certain particle sizes (for example, in one embodiment, MRP of size PD140 and smaller) into a given composition should result in an increased minimum tensile strength over virgin elastomer compositions. This result enables the use of certain (perhaps less expensive) compositions in applications that were previously considered unsuitable for such compositions.

According to some embodiments, a method for producing a rubber compound having a prescribed minimum tensile strength is provided. The method comprises including the use of MRP in the compound and employing a shorter mixing time than would have been used if the MRP were not incorporated. According to some embodiments, a rubber compound comprising MRP is provided wherein the compound has reduced tensile strength variability and/or improved minimum tensile strength compared to a composition without MRP. According to some embodiments, the MRP used in the composition comprises 100 mesh or finer particles. According to some embodiments, the MRP used in the composition comprises 140 mesh or finer particles.

The embodiments were chosen and described in order to explain the principles of the inventions and their practical application so as to enable others skilled in the art to utilize the inventions and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present inventions pertain without departing from their spirit and scope. Accordingly, the scope of the present inventions is defined by the appended claims rather than the foregoing description and the exemplary embodiments described therein.