Rubber World August 2012 : Page 16
Optimizing the use of micronized rubber powder made from end-of-life tire material by F.P. Papp, Lehigh Technologies The incorporation of materials derived from end-of-life tires back into new rubber articles has significant positive impact on the North American economy and environment, including: cost savings for consumers, reduced dependence on petroleum imports, lower energy consumption and fewer greenhouse gas emissions. With 300 million tires annually in the U.S. becom-ing end-of-life, 36 million end-of-life tires are still sent to land-fills (ref. 1). Over half of this end-of-life rubber is still directed at low value end uses such as tire derived fuel. On a global ba-sis each year, approximately one billion tires become unusable and are classified as end-of-life. In the European Union, land filling whole tires was banned in July 2003, and land filling shredded tires in July 2006 (ref. 2). This article will describe ways to incorporate end-of-life rubber into new rubber products through the optimal use of micronized rubber powder (MRP), helping to contain costs and Figure 2 -cure behavior of a typical tire tread compound produce more sustainable products. when 3% to 12% 177 m m MRP has been incorporated The need for the optimization work de-scribed here arose out of two situations con-MDR rheometer at 160 ° C tread with 177 micron MRP cerning MRP. The first situation is the most Normalized time to stated property critical and that is the impact on rubber rheo-120.0 logical and physical properties when MRP 100.0 is added to the rubber mix/compound. The 80.0 second is the realization that many users do not optimize their base recipes when incor-60.0 porating MRP, thus limiting the usage levels 40.0 and potential cost savings. The goal of these 20.0 studies was to establish recommendations on formula modifications when using MRP in 0.0 new rubber compounds to meet target per-Control 3% 6% 9% 12% Control formance specifications. Scorch Ts1 ASTM D 5289 The impact on rubber rheological and T10 physical properties when MRP is added to T90 the mix has been investigated and reported Figure 1 -physical properties of a typical tread compound when 3% to 12% 177 m m MRP has been incorporated Normalized physical properties of tread with 177 m m MRP 140 120 100 Percent 80 60 40 20 0 Control 3% 6% 9% 12% Higher is better Control T.S. 300 M Elong. @ break HBU Comp set Reb. 60 ° C ARI Tear Percent in published literature. Many researchers, including the au-thor, have reported losses in rheological and physical proper-ties when incorporating MRP into new rubber (refs. 3-9). In a typical replacement tire tread compound, figures 1 and 2 show some of the key properties of new rubber when 177 µm MRP has been incorporated in increasing levels from 3% to 12% by weight (ref. 9). Figure 1, with normalized values to the con-trol, is set up such that a higher bar means better performance, so the tests providing higher numbers for worse performance have been inverted. In figure 2, also with normalized values to the control, no test results are inverted. Compared to a control tread compound without MRP, add-ing 3% to 12% 177 µm MRP causes a gradual decline in basic physical properties, tensile strength, T.S., 300% modulus and elongation at break. Heat build-up, compression set, rebound at 60°C and abrasion resistance index also are all reduced. The 16 RUBBER WORLD
Optimizing the use of micronized rubber powder made from end-of-life tire material
The incorporation of materials derived from end-of-life tires back into new rubber articles has significant positive impact on the North American economy and environment, including: cost savings for consumers, reduced dependence on petroleum imports, lower energy consumption and fewer greenhouse gas emissions. With 300 million tires annually in the U.S. becoming end-of-life, 36 million end-of-life tires are still sent to landfills (ref. 1). Over half of this end-of-life rubber is still directed at low value end uses such as tire derived fuel. On a global basis each year, approximately one billion tires become unusable and are classified as end-of-life. In the European Union, land filling whole tires was banned in July 2003, and land filling shredded tires in July 2006 (ref. 2). This article will describe ways to incorporate end-of-life rubber into new rubber products through the optimal use of micronized rubber powder (MRP), helping to contain costs and produce more sustainable products.
The need for the optimization work described here arose out of two situations concerning MRP. The first situation is the most critical and that is the impact on rubber rheological and physical properties when MRP is added to the rubber mix/compound. The second is the realization that many users do not optimize their base recipes when incorporating MRP, thus limiting the usage levels and potential cost savings. The goal of these studies was to establish recommendations on formula modifications when using MRP in new rubber compounds to meet target performance specifications.
The impact on rubber rheological and physical properties when MRP is added to the mix has been investigated and reported in published literature. Many researchers, including the author, have reported losses in rheological and physical properties when incorporating MRP into new rubber (refs. 3-9). In a typical replacement tire tread compound, figures 1 and 2 show some of the key properties of new rubber when 177 µm MRP has been incorporated in increasing levels from 3% to 12% by weight (ref. 9). Figure 1, with normalized values to the control, is set up such that a higher bar means better performance, so the tests providing higher numbers for worse performance have been inverted. In figure 2, also with normalized values to the control, no test results are inverted.
Compared to a control tread compound without MRP, adding 3% to 12% 177 µm MRP causes a gradual decline in basic physical properties, tensile strength, T.S., 300% modulus and elongation at break. Heat build-up, compression set, rebound at 60°C and abrasion resistance index also are all reduced. The previously mentioned literature references offer explanations for most of these property losses. Gibala, Thomas and Hamed (ref. 6) postulated that MRP particles in new cured rubber are discontinuities and act like stress-raising flaws. Phadke, Chakraborty and De (ref. 8) published scanning electron microscope (SEM) photographs showing improper bonding of MRP to the new rubber matrix. From these references, we can say there is a poor attraction of MRP to the new rubber matrix, causing the reduction in tensile, elongation at break, rebound, abrasion resistance and increases in heat build-up and compression set. The decreased modulus is caused by sulfur in the new rubber matrix migrating into the MRP causing a lower crosslink density in the final product (refs. 5, 6 and 10). However, we can see that trouser tear resistance actually improves slightly and this effect was explained by Gibala, Thomas, and Hamed (ref. 6) with the theory of crack tip blunting. Figure 2 shows shorter scorch times and faster cure rates which are explained by the migration of accelerator fragments from the MRP into the new rubber matrix (ref. 5).
Over the years, the author has seen the mixing of MRP in various ways such as incorporating MRP in the master pass and in the finish pass (ref. 11). This makes one wonder which procedure provides the optimum physical properties. If there are unsaturation sites, or allylic hydrogens remaining in the MRP, then these bonding sites should be available for crosslinking during vulcanization if the MRP was mixed in the finish pass due to the lower mix temperature. If the MRP was added in the master pass, the remaining unsaturation sites, or allylic hydrogens, would be rendered useless to crosslink with new rubber, because any sulfur remaining in the MRP would simply increase the crosslink density within the MRP particle and increase its hardness. On the other hand, if there are no unsaturation sites, or allylic hydrogens remaining in the MRP, 18 which would then be a non-reinforcing filler, we should simply see the effects of better dispersion on the basic physical properties from incorporating the MRP in the master pass.
There are a number of references that mention the aging resistant benefits of using reclaimed rubber. For example, Crane, et al. (ref. 12), show the stability of solution SBR upon aging when depolymerized scrap rubber is used. Noordermeer, et al., (ref. 13), describe a process in which reclaimed sulfur cured EPDM is incorporated into virgin EPDM roofing compound for better aging resistance. The questions then are, does MRP in new rubber provide any resistance against ozone and oxidation attack in outdoor exposure, and does MRP in new rubber provide any physical property stability upon aging?
Finally, when using MRP in demanding rubber applications, such as tires and belting, what are the optimum particle sizes to provide the best performance? A review of published literature will be provided along with a study of basic performance of a rubber compound with MRP using different particle sizes.
All experiments were planned and mixed in Lehigh Technologies’ Application & Development Center in Tucker, GA. All rubber mixes were performed in a 1.6L Farrel Banbury internal mixer. Milling was performed on a KSB two-roll mill 33 cm x 15 cm. Both machines are connected to two identical Sterlco temperature control units. Mixing was conducted either as a two or three pass mix as indicated in the results section on the separate studies. In master mixing, carbon black, oil and chemical additions were incorporated using low melt polyethylene bags of the type used in production factory mixing. The first master mix times were 7’ for mixes using all free carbon black and oil, and 6’ for mixes using black masterbatch. For mixes using three passes, the second pass was simply a re-mill mix for 5’. All finish mixes were 2’ long in the internal mixer and used the after mixing milling method recommended in ASTM D 3182 Section 7.2.8 and 7.2.9. In all studies for each step of the operation, weighing, mixing, curing and testing, a unique randomized sequence was employed to reduce or eliminate bias scatter of the data. The experimental designs used replication of batches as discussed in the results section on the separate studies. Some of the designs with replicated batches used a procedure of blending the masterbatches for reducing variation. A basic recipe representing an ESBR/BR all carbon black replacement passenger car tire tread compound is shown in table 1a. Any modifications to this recipe are discussed in the results section on the separate studies. The particle size distribution and the properties of the PolyDyne micronized rubber powder used in the studies are shown in table 1b. The mixing procedures are provided in table 2.
Molding and curing were performed using a Wabash compression molding press. Standard curing was performed as per table 3. Uncured specimens for the drum abrader, flexometer and Zwick rebound tests were prepared by cutting disks from flat sheets and plying up sufficient layers to fill the cavities in multi-cavity molds for curing.
Per each test plan, as discussed in the results section on the separate studies, rubber specimens were tested according to the following methods. Cured test specimens for tensile, elongation, modulus, trouser tear and outdoor exposure were cut from flat sheets using the respective dumbbell Die C, Die T and rectangular shaped die cutters on a hydraulic clicker press. Tests 1 to 8 below were performed in Lehigh Technologies’ Application & Development Center.
1. MDR2000 rheometer ASTM D 5289 @ 160°C.
2. Tensile, elongation, modulus ASTM D 412, unaged and oven aged.
3. Trouser tear resistance, ASTM D 624 T, unaged and oven aged.
4. Hardness tested with Rex digital durometer, ASTM D 2240 Type A on rebound specimens.
5. BF Goodrich flexometer ASTM D 623, Method A.
6. Zwick rebound ASTM D 7121.
7. Zwick rotary drum abrader ASTM D 5963, Method A.
8. Static outdoor exposure (20% Strain) ASTM D 518, Method A.
Results and discussion
The first study to be discussed is the addition sequence for the MRP. We performed the study in two parts; the first a simple study investigating the addition of 177 µm MRP with the carbon black in the first master pass of a three pass mix versus adding the MRP in the finish pass with the curatives. The second part investigated at what point in the master it is best to add the MRP. The recipes, shown in table 4, used a black masterbatch version of the recipe discussed previously. The first part used the 177 µm MRP, and the second part used 300 µm MRP, both at 10% by weight loading. Table 5 displays the details of the mixing procedure with the MRP addition points.
We decided to use the basic physical properties of tensile strength, elongation at break and modulus to measure the impact of MRP into the new rubber matrix. From the simple tests run, adding the MRP in the master with the carbon black as opposed to adding in the finish pass provides the higher tensile and modulus values. When mixing MRP in the first master pass with the polymers, or carbon black, or with the chemicals, the optimum tensile and modulus properties are achieved mixing with either the polymers or the carbon black. The better tensile and modulus achieved by mixing the MRP in the first pass can most likely be explained by better dispersion of the MRP material, no doubt aided by the extra mixing in the second pass. Certainly a simple dispersion test, not performed here, would be able to confirm this explanation. The higher values that occur on the tensile and modulus tests when the MRP is added in the first pass appear to support this mixing procedure over adding the material in the finish pass.
The next study to review is based on the phenomenon discussed earlier with the migration of sulfur into and migration of accelerator fragments out of the MRP material. The goal of the study was to provide rubber chemists with specific guidelines on formula modifications based on actual laboratory data to help the chemist achieve the optimum performance when using MRP. The study design used the basic recipe without the black masterbatch shown earlier in a two pass mix version. The experimental design selected was the central composite design, response surface method with the aid of Design Expert software published by Stat-Ease. The 177 µm MRP was used from 2% to 14% by weight loading, the sulfur loading was from 1.5 phr to 4.0 phr, and the TBBS (BBTS) accelerator loading was from 0.2 phr to 1.4 phr. A three-dimensional graphical representation of the experimental design is presented in figure 3, which shows a 20 batch experimental design. Curing of the test specimens used the cure times set by rheometer T90+5’. Specimens from each group were tested for the basic physical properties of tensile strength, modulus and elongation at break. The results were entered into the Design Expert software for generation of contour plots, of which the key ones are shown in figures 4a and 4b.
For the rheometer scorch Ts1, T10 and T90 times contour plots, the sulfur level was fixed at 2.00 phr, while the TBBS (BBTS) accelerator levels were plotted against the 177 µm 80 mesh MRP weight percent. An example plot for the rheometer scorch Ts1 is shown in figure 4a. From these plots we can see the effects of the accelerator levels on the various scorch and cure times and can arrive at a level of accelerator reduction to achieve similar cure performance to a control compound, data which are included in the example plots. The change in accelerator appears to have a bigger impact on times to T10 and much less so on the scorch and T90 times. Users of MRP can then decide which property to focus on for modification of the accelerator level when using MRP. For example, the situation was simplified and assumed a linear relationship of the accelerator levels with MRP levels. The following relationship was established, equation (1), using rheometer scorch Ts1 for chemists to arrive at a reasonably close approximation to achieve similar scorch properties to the control compound when using MRP.
Nal = Oal - (Oal x 0.0167 x Lmrp x 100) (1)
Where: Nal = new primary accelerator level in phr;
Oal = original primary accelerator level in phr; and
Lmrp = level of MRP by weight in decimal.
As an example calculation, consider the following:
Oal = 1.50 phr of TBBS;
Lmrp = 0.10 for a 10% by weight loading of MRP;
Nal = 1.50 – (1.50 x 0.0167 x 0.1 x 100); thus
Nal = 1.25 phr TBBS.
Consider now the remaining physical properties in the designed experiment. In these contour plots, the TBBS accelerator remains fixed at 1.0 phr, while the sulfur levels were plotted against the 177 µm MRP. The contour plot for tensile strength showed that the property can be improved somewhat with increasing sulfur levels, but this does not imply there is an improved attraction of the MRP to the new polymers due to the increasing sulfur. A possible explanation is that as a tensile specimen is being pulled to ever increasing elongations, the higher crosslink density from the higher sulfur loading is providing greater resistance to the deformation, a higher modulus, as exhibited in the graph in figure 4b, which displays a linear relationship of the increasing sulfur with increasing MRP weight percent to the modulus level. A relationship was then established for increasing the sulfur level to match the modulus of the control compound based on the percent loading of MRP as shown below.
Nsl = Osl + (Osl x 0.025 x Lmrp x 100) (2)
Where: Nsl = new sulfur level in phr;
Osl = original sulfur level in phr; and
Lmrp = level of MRP by weight in decimal.
As an example calculation, consider the following:
Osl = 2.00 phr of sulfur;
Lmrp = 0.10 for a 10% by weight loading of MRP;
Nsl = 2.00 + (2.00 x 0.025 x 0.1 x 100); thus
Nsl = 2.50 phr sulfur
By focusing on maintaining the modulus with increasing MRP loading, many of the other modulus dependent properties, such as hardness, heat build-up, compression set and rebound, should respond in a similar way. The Design Expert software was then set to provide two predictions, one tread compound with no MRP and one with 10% by weight loading of the previously tested 177 µm MRP, for a set of typical tread compound physical test properties. The normalized predictions are shown in a radar chart in figure 5. The recipe differences are shown in table 6 and the base recipe is shown in table 1a. The predictions show that when incorporating MRP and focusing on maintaining the modulus by increasing the sulfur content, many of the modulus dependent test results are at least improved or even made equivalent to the control compound.
To confirm these predictions, a follow-up study was performed which used the basic recipe without the black masterbatch in a two pass mix version. The 177 µm MRP was used at a 10% by weight loading and introduced into the first pass with the carbon black. Specimens from each group were tested per the test plan discussed earlier, with the exception of the outdoor exposure test. The normalized test results are shown in a radar chart in figure 6 comparing the results. The recipe differences are shown in table 7. As can be seen in the radar chart based on actual test data, when the sulfur is increased per the recommendation, the key modulus dependent tests are made closer to, and in some cases equal to, the control compound without MRP.
The next study investigated the impact of MRP on normal weathering resistance as measured by the static outdoor exposure test using a constant 20% strain. The first part of the study was to determine if any antidegradants were migrating from MRP made from end-of-life tires. The second part of the study was to determine if there were any MRP particle size effects on outdoor exposure. Finally, the third part of the study was to determine if the dilution of antidegradants by adding a high loading of MRP, 12% by weight, adversely affected the weathering resistance. The test guidelines offered in ASTM D 518 Method A Exposure of Straight Specimens were used. Three test rigs were built to mount 150 mm x 25 mm straight specimens with a 20% fixed extension and fixed to a platform and placed outdoors on the grounds of the facility of Lehigh Technologies in Tucker, GA. This area usually receives abundant heat and sunshine during the summer months, and has considerable truck and automobile traffic to generate ozone, as would any major metropolitan region (ref. 14).
The outdoor exposure study used the basic recipe in a three pass mix version without the black masterbatch shown earlier. Three different MRP particle sizes, 400 µm, 177 µm and 75 µm, were used, all at 12% by weight loading. The changes from the basic recipe are shown in table 8, which shows all three particle sizes of MRP and includes three sets of experimental features, 1) without antidegradants, 2) with the control compound antidegradant phr level, (dilution effect), and 3) the same weight percent of antidegradants to match the control compound. The MRP containing compounds also employed a modified cure system to target the same modulus level as the control compound.
The test rigs with the mounted specimens were placed out- doors on May 4, 2011, facing south at a 45° angle with the horizon. The specimens were inspected daily, using a 7x magnifying glass, and the dates were recorded of any appearance of cracks according to the ASTM D 518 Method A test procedure. The extent of cracking was also noted. The results are presented in table 9, which shows that after just two days of outdoor weathering exposure, all the specimens without any added antidegradants, including the control compound, had numerous cracks on the entire surface, but only observable with the 7x magnifying glass. One week later, the cracks became large enough to be observed with the unaided eye. Specimen photographs, taken on May 17, 2011, are shown in figure 7. From these results, one can conclude that there were no antidegradants migrating from the MRPs used in this study, which were made from end-of-life tires. Also, the different MRP particle sizes show no differences in weathering resistance performance in compounds without added antidegradants. It appeared that all the antidegradants in end-of-life tires which were used to make the MRP had completely or nearly completely dissipated and were no longer available.
The two sets of compounds remaining contain different particle sizes of 12% by weight of MRPs and include one set with the control standard phr antidegradant levels, but lower weight percent due to dilution, and one set with the same weight percent antidegradant levels. The data in table 9 show that cracking occurred in most of the specimens with the MRPs, but are only observed with the magnifying glass. Other than one small edge crack on a 400 µm 12% compound specimen with the standard antidegradant levels, all the remaining cracks were located either below or above the aluminum shield, suggesting some localized strains higher than the 20% imposed stretch across the specimens. It is speculated that the higher strains in the region of the shield could be caused by the differences in the specimen mounting, or by the MRP particles near the surface, or both. It appeared that using a higher level of antidegradants to compensate for the dilution effect of adding MRPs, helped to delay the onset of the localized cracking. It also appeared that the lower particle sized MRPs may have provided a slight advantage to delay the localized cracking, possibly by imparting lowers strains at the rubber surface, or by better dispersion. More work is needed in this area.
It is important to mention that from the first appearance of the cracks in the specimens containing the MRPs with both the standard and higher antidegradant loadings until the last inspection, no growth in the cracks appeared to occur. From the first appearance of these localized cracks to the last inspection, the magnifying glass was needed to view the cracks during the entire exposure duration. Nevertheless, six specimens of control compounds, subject to the same mounting conditions as the MRP containing compounds, had not shown any cracking. Additional studies of MRP in rubber compounds are needed to better understand the impact on weathering resistance.
Heat aging resistance is an important property for many demanding rubber manufactured articles. In particular, heat aging resistance data are important for compounds with elevated levels of sulfur, such as optimized MRP compounds. This study was an evaluation of the heat aging resistance of the optimized recipe based on the above studies. The standard recipe was used with the modifications of an SBR black masterbatch, three pass mix, two batches for each feature, including the control batches, and blended masters for mixing the second and finish passes. For each step of the operation, weighing, mixing, curing and testing, a unique randomized sequence was employed. Table 10 shows the details of the recipe, with the MRP at 3%, 6% and 10% by weight in the first master with the carbon black, and optimized sulfur, accelerator and antidegradants, as shown earlier. Mixing and curing were performed according to tables 2 and 3, respectively. Test plaque heat aging conditions were 48 hours @ 100°C and two weeks @ 70°C, and accomplished under aerobic conditions in a Lunaire Limited Oven, Model # CE210. Dumbbell test specimens were cut from the aged test plaques and tensile testing was performed as previously discussed in the experimental section. The heat aging resistance was measured by evaluating the changes in tensile strength, elongation at break and, in this case, the 100% modulus based on the work of Ahagon (ref. 15), who had reported the modulus of a rubber compound is proportional to the crosslink density, but only at strains near 100%.
First we will look at the change in tensile strength with heat aging. Figure 8a shows the actual tensile strength values of the control and the optimized compounds with the MRP, and figure 8b shows the percent change in the tensile values. From these graphs we can see that the changes in tensile strength due to heat aging of the compounds with the 3% to 10% MRP with optimized recipes are essentially the same as the control compound under the same conditions. For evaluating the effects of heat aging on the elongation at break and 100% modulus, we will use plots of the log of the elongation at break and the log of the 100% modulus, as discussed by Ahagon, et al. (refs. 16 and 17), who showed these to be useful in evaluating rubber compound aging, paying particular attention to the slope of the line. Plots were prepared of the log of the elongation at break, and the log of the 100% modulus for all four test compounds, and both aging conditions. These results are shown in figures 9a and 9b. The charts show that the slopes of the lines are essentially equal and therefore the aging characteristics of the compounds with the MRP at 3%, 6% and 10% by weight, using the optimization protocol described, are essentially equivalent to the control compound.
Particle size and loading study
The final study to be reported is an evaluation of four production MRP products representing four particle size distributions, as shown in table 1b. 400 µm, 300 µm, 177 µm and 105 µm MRP products from whole tire were each evaluated at 3%, 6% and 10% by weight loading. The standard recipe was used with the modifications of an SBR black masterbatch, three pass mix, two batches for control compound and single batches for the MRP containing compounds. The control batches had the masters blended for mixing the second and finish passes. For each step of the operation, weighing, mixing, curing and testing, a unique randomized sequence was employed, as discussed previously. Table 11 shows the details of the recipe, with the MRP at 3%, 6% and 10% by weight in the first master with the carbon black, and optimized sulfur and accelerator. The antidegradants were kept to the control phr level. Mixing and curing were performed according to tables 2 and 3, respectively.
Tensile strength, elongation at break and 300% modulus were measured and the data are shown in figures 10a-c using scatter plots to graphically display the tensile strength vs. elongation at break, 300% modulus vs. elongation at break and tensile strength vs. 300% modulus. The scatter plots show that while the larger particle sizes of MRP, such as the 400 µm, 300 µm and the 177 µm MRPs, delivered physical properties within 90% of the control compound, especially at the lower loading levels, only the 105 µm MRP consistently delivered physical properties within the 95% target zone or better. This is consistent with the findings of a group of researchers in the U.K., Kumar, Fukahori, Thomas and Busfield (ref. 18), who estimated the intrinsic flaw size of carbon black filled SBR, without MRP, to be 130 µm. This study and the referenced work support our recommendation that for the most demanding applications, such as tires and conveyor belts, the MRP of choice up to 10% loading is the 105 µm MRP with the optimization protocol described earlier.
Summary of findings and recommendations
This article discussed how the use of MRP up to 10% load ing can be successful in achieving equal or nearly equal physical properties to a base all synthetic rubber control compound without MRP. In the face of rising and unpredictable raw material prices and difficult to obtain raw materials, using a substantial quantity of MRP can go a long way in reducing compound costs and extending raw material supplies, while helping the environment by finding a high value, productive use for end-of-life tires. The key findings and recommendations are given below.
• For optimum tensile and modulus, maximum dispersion is the most important, so mix MRPs into the first pass, either with the polymers or the carbon black. For optimum elongation at break, mix MRPs later in the first pass with the chemicals.
• Increasing the sulfur and slightly decreasing the accelerator levels can recover many of the physical properties to match, or nearly match the physical properties in the same compound without MRP.
• There appear to be no antidegradants migrating from MRPs into the new rubber matrix when the MRPs have been made from end-of-life tires.
• Increasing the antidegradant levels to the same percent by weight as the starting compound will help ensure satisfactory weathering performance.
• The aging resistance of rubber compounds with MRP up to 10% by weight loading, and the adjustments in sulfur, accelerator and antidegradants, are essentially equivalent to the control rubber compound without MRP.
• For products with demanding performance requirements, such as tires, the largest particle size MRP to use at 10% loading while maintaining basic physical properties is the 105 µm product.
This article was originally presented at the Tire Technology Expo 2012 in Cologne, Germany.
Read the full article at http://digitaleditions.walsworthprintgroup.com/article/Optimizing+the+use+of+micronized+rubber+powder+made+from+end-of-life+tire+material/1155000/123767/article.html.
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