Advances in tire innerliner technologies.

Improvements in tire performance over the last 15 years have been dramatic. Significant enhancements in tire tread wear and traction, reductions in rolling resistance and improvements in durability have enabled development of products of the highest quality. Though design changes have been made and new reinforcement materials have been introduced, many of the major improvements can be attributed to developments such as the introduction of the silica tread compound, functionalized and coupled solution SBR and improvements in compound aging and reversion resistance.

Since the introduction of bromobutyl rubber, however, there have been very few significant changes to the composition and form of the tire innerliner. With improvements in other tire components, the innerliner now offers many more opportunities to improve performance parameters, such as air retention and tire casing durability that is of particular importance for commercial tires. Innerliners based on nanocomposites and other new materials may allow gauge adjustments and permeability reductions with potential improvements in tire casing durability and, for example, reductions in truck fleet tire casing attrition rates. Nanocomposites based on brominated isobutylene p-methylstyrene copolymers with organically modified layered silicates enable permeability reductions not possible with conventional halobutyl elastomers and filler systems. The use of nanocomposites may require reformulation of compounds and modification of processing specifications. This article discusses potential innerliner permeability reduction, as well as the impact of formulation and compounding parameters on the properties of model nanocomposite based innerliners.

The modern radial tire was in many respects made possible through the introduction and use of halobutyl rubber innerliners. Use of this polymer in the innerliner compound enabled improvements in air retention performance, improvements in liner-to-tire casing adhesion and improvements in tire durability. This second generation technology represented a major advance over the use of first generation liner technologies using regular butyl robber found in tubes and liners of bias tires and early radial tire constructions. Since the introduction of halobutyl rubber, there has been no significant advance in the composition of innerliner formulas used in the industry. Some of this might be due to the tolerances in properties that innerliner compounds must meet. For example, small increases in liner compound 300% modulus could lead to reduction in fatigue resistance and cracks with consequent loss in tire durability. In this context, the industry has therefore focused on five strategic areas for development of new inner-liner technologies:

* Tire constructions: Examples would be non-pneumatic structures such as the polyurethane tire or self-supporting structures such as the Michelin 'Tweel' (refs. 1 and 2).

* Compounding: The use of general purpose elastomers or special purpose elastomers in place of halobutyl rubber, combined with large particle size fillers such as medium thermal carbon blacks have been studied (ref. 3).

* Sprays: The application of a butyl rubber coating inside the tire that may serve as an air barrier has been explored (ref. 4).

* Films: Dynamically vulcanized alloys (DVA) are being introduced as liners and are highly effective at maintaining air pressure, are durable and have demonstrated other benefits such as rolling resistance improvements (refs. 5 and 6).

* Nanocomposites: Use of organically modified layered silicates or nanoclays in compounded isobutylene polymers can reduce permeability by up to 50% compared to bromobutyl compounds or compounds containing halobutyl-natural rubber blends found in many automobile tires (ref. 7).

Compared to many other technologies, the use of nanocomposites, which is the primary focus of this discussion, offers an advantage in that the tire manufacturer has no capital requirements, the compounds can be processed on existing production equipment and formulas would use conventional compounding materials. A nanocomposite is a polymer containing a nano sized dispersed phase. In this work, nano-composites are based on isobutylene elastomers and clay, whose particles display large aspect ratios, i.e., where the clay plate thickness is in the order of 1.0 nm, but the plate width can be over 50 nm. Such clays, when treated with a surfactant, are frequently referred to as nanoclays due to an apparent ability to form nano dispersions in a polymer matrix.

There are several potential applications for nanoclays in tire compounds. For example, inclusion of low amounts of nanoclay in the tread compound will lead to an increase in the storage modulus, G'. Optimum storage moduli will enable tread wear improvements, and more important, improvement in tread wear uniformity. An increase in the stiffness of the shoulder wedge may enable improvement in the pressure uniformity of the footprint of the tire in service, again allowing improved wear performance and ultimate miles to tire removal, without loss in other compound properties, such as hysteresis or tear strength.

Nanoclays may also be added to the bead filler or apex compound and associated secondary components above the bead area to control modulus, thereby enabling creation of a stiffness gradient up the tire sidewall and minimization of stress concentrations at ply endings or endings of other stiff components. Minimization of stress concentrations will reduce the potential for cracks forming in the tire's sidewall. Such concerns become more important in ultra low aspect ratio tires, where sidewall deflection might be more severe than that found in larger tires.

The focus of this work is the tire innerliner. The reported improvement in air retention qualities can allow improved maintenance of tire rolling resistance performance through the service life of the tire, improved durability and lower tire operating temperatures (refs. 4 and 7). Therefore, the objective of the work centers on a number of items, including:

* Benchmarking of current industry innerliner compounds;

* identification of property targets innerliner compounds must meet, and;

* properties of nanocomposite innerliner compounds.

Experimental methods

The bromobutyl model tire innerliner compound illustrated in table 1 was used for benchmarking purposes (ref. 8). Bromobutyl grade 2222 (Mooney viscosity MLI+8 specification 32) and bromobutyl grade 2255 (Mooney viscosity MLI+8 specification 46) were used in the study. Struktol 40MS is commonly used in innerliners to improve factory processing, compound adhesion and fatigue resistance. The phenolic tackifying resin typically used is SP-1068. As an alternative, the hydrocarbon Escorez 1102 can be substituted with no modification in the compound formula. Zinc oxide, stearic acid, benzothiazole disulfide (MBTS) and sulfur were used in the cure system.

Though grades 2222 and 2255 were used interchangeably, 2255 was primarily selected for the study, as it is typically the preferred polymer for innerliners of larger tires, such as those for heavy-duty trucks. Tire innerliner compounds containing higher viscosity bromobutyl have good green strength for ease of processing and offer improved resistance to ply cord strike-through.

Mooney viscosity and Mooney scorch resistance were determined, as described in ASTM D 1646. The MDR rheometer was used for determination of compound cure kinetics. Tensile strength and tear strength were measured using test samples described in ASTM D412 and D624, respectively. Test samples were vulcanized at 160[degrees]C and cure times were set by adding two minutes to the rheometer [t.sub.90] time.

Permeability was measured using a Model 2/61 oxygen transmission rate test apparatus. There are six cells per instrument, where gas transmission through each test sample in a cell is measured individually. The compression molded compound sample disks with 5.0 centimeter diameter and about 0.5 mm thickness are mounted in the cells and sealed with vacuum grease. Nitrogen (0.7 kg/cm) is kept on one side of the disk, while oxygen (0.7 kg/cm) is placed on the other side. Measurement is typically conducted at 40[degrees]C or 60[degrees]C, and an oxygen sensor is used to measure the increase of oxygen concentration on the nitrogen side. The time required for oxygen concentration on the nitrogen side to reach content value is recorded and used to determine the oxygen permeability. Data are reported as a permeation coefficient in cc*mm/([m.sup.2]-day) or permeability coefficient in cc*mm/([m.sup.2]-day-mmHg). Permeability is then expressed as a rating relative to the control compound. The model compound illustrated in table 1 has a rating of 100. This control compound has a nominal permeation coefficient at 40[degrees]C of 200 to 220 cc*mm/([m.sup.2]-day)

To elaborate, the permeation coefficient is the transmission rate normalized for sample thickness and is expressed as volume (cc) of gas at one (mm) per unit area of sample ([m.sup.2]) in a discreet unit of time (24 hours). The term permeance frequently cited is the ratio of the barrier's transmission rate to the partial vapor pressure differential across the barrier.

Results

The composition of a typical tire innerliner compound has changed little since the introduction of bromobutyl in 1981. Even though innerliner compound formulations are well established, in this work it would be appropriate to determine the basic properties a nanocomposite innerliner must meet.

Benchmarking of bromobutyl innerliner compounds

Tire innerliner compounds in many instances can contain natural rubber. Depending on the tire manufacturer, this can serve several functions, such as improved processability and potential improvement in liner to tire casing adhesion. Using the model formula illustrated in table 1, five compounds were prepared by varying natural rubber content in 10 phr increments to illustrate what properties might be expected in liner compounds, and the results are listed in table 2. A more complete set of mechanical properties for such compounds can be found on the web site, www.butylrubber.com (ref. 8). A number of points can be noted here:

* Viewing compounds 1 to 5 of table 2, decreasing natural rubber content resulted in a decrease in compound Moonev viscosity (ML1+4) at 100[degrees]C, but had little effect on Mooney scorch minimum viscosity at 125[degrees]C.

* Scorch time increased with a decrease in natural rubber, but cure time (t90) was only slightly affected. Cure state measured from rheometer [DELTA]torque (MH-ML) was not affected, and cure rate did not change.

* Tensile strength, elongation at break, 300% modulus and tear strength for compounds containing up to 30 phr natural rubber all fell within a narrow range.

* Permeability coefficient decreased rapidly with a decrease in natural rubber. Dropping natural rubber content from 40 phr to 10 phr, the permeability coefficient decreased from 1.740 to 0.92 cc*mm/([m.sup.2]-day-mmHg).

Comparison of bromobutyl and chlorobutyl polymer grades

Table 3 illustrates typical properties that might be expected when bromobutyl grade 2222, with a nominal Mooney viscosity of 32, is replaced by higher viscosity bromobutyl or chlorobutyl rubbers. It can be seen that cure kinetics (from the rheometer test), tensile strength and tear strength are within the range of values that might be expected after viewing the data in table 2 (compounds 2 to 5). It is also noted that the permeability coefficients for the four elastomers are within a narrow range. Considering the effect of natural rubber on permeability, halobutyl elastomers are clearly superior, but within the commercial halobutyl elastomer grades considered here, there is little effect on impermeability.

The most significant difference in the compounds is the Mooney viscosity, which increases with an increase in viscosity of the elastomer. For example, replacing bromobutyl 2222 (nominal polymer viscosity of 32) with bromobutyl 2255 (viscosity of 46), used primarily in the liner of larger truck tires, resulted in an increase in compounded Mooney viscosity from 56 to 64.

Innerliner properties in tires

Mechanical properties of an innerliner, such as that found in a truck tire, should fall within a given range. For example, if the compound's 300% modulus is too high and elongation at break is low, the innerliner in the tire might be susceptible to poor fatigue resistance. If the compound hardness is too high, the liner compound in the tire might crack. At the opposite end, if tensile strength is too low, liner durability in the tire might not be adequate, tear resistance would be low and the tire might not be capable of being retreaded, with consequent loss in casing service fife.

Forty two truck tire innerliners were analyzed and the liner compound tensile strength and hardness were tabulated. The data have been summarized in table 4.

This now allows a set of property targets to be defined that a nanocomposite innerliner should meet. Thus, regardless of the polymer used, tire compound tensile strength, elongation at break and 300% modulus would be in the order of 10 MPa, 700% and 4.0 MPa, respectively. Considering the data in table 2. compounds with high tensile strength (i.e., greater than 11.5 MPa) and elongations at break below 650% may contain high levels of natural rubber, are more permeable, and therefore might be discarded when attempting to define a set of compound property targets.

Viewing tables 2 and 3 illustrating the effect of natural rubber and other halobutyl elastomers on compound properties. tensile strength, elongation at break and 300% modulus are also in the range of 10 MPa. 745% to 800% and 3.1 to 3.9 MPa, respectively. These results allow an assessment of how a nanocomposite innerliner might perform in a tire relative to more conventional halobutyl compounds.

Nanocomposite innerliner

A polymer-filler nanocomposite was compounded using the model formula in table 1. The results are illustrated in table 5. It can be seen that the naphthenic oil level was reduced to compensate for surfactant and other additives that might be added in the preparation of the nanocomposite. No other changes were made to the formula.

A number of observations may be noted, including:

* The model tire innerliner compound containing bromobutyl 2255 had a Mooney viscosity of 65. Replacement of bromobutyl with a nanocomposite resulted in the compound viscosity increasing to 70. This is likely due to association between the surfactant and polymer chain functional groups in the nanocomposite. The association is thought to be weak and can be readily broken by addition of a mastication step in a compound mix cycle stage.

* Cure time, [t.sub.90], increased from 10 to 15 minutes for the nanocomposite compound. Such changes can be expected when a silicate or silica is added to a compound. In this case cure time can be readily adjusted by a change in stearic acid content.

* Compound tensile strength, elongation at break, and tear strength are within the range of values identified in preliminary studies (tables 2, 3 and 4) and therefore no concerns would be anticipated regarding durability of the compound in a tire.

Of particular note is the significant reduction in permeability, with a rating of 61 compared to the bromobutyl control compound (rating 100) or the compounds containing 10 phr or 20 phr of natural rubber (rating 118 and 154, respectively).

The reduction in permeability is further illustrated in figure 1. Such differentials between the reference bromobutyl compound and the nanocomposite are not attainable via traditional compounding methods, while still meeting other compound property requirements.

Tire evaluation of nanocomposite innerliner

To assess the comparative performance of the nanocomposite compound formula as a tire innerliner, a collaborative program was run with Cheng Shin Rubber Industries in Taiwan. The radial truck tire design, UR188, was selected. This tire has a rib tread pattern and the fire size selected, 275/80R22.5, is typical of that used on United States line haul trucks. The load range selected was -H, and 110 radial medium truck fires were built, 55 with a bromobutyl 2222 innerliner and 55 with the nanocomposite innerliner. On completion of the build, the tires were visually inspected, a cut tire analysis was conducted and the tires were tested for uniformity, which included balance, run out, conicity and force variation. All tires were x-rayed and inspected for internal separations using shearography.

The compound formulas were based on those illustrated in table 5. Because of the improved impermeability of the nano-composite compound, the gauge (thickness) of the innerliner was reduced by 35% compared to the control tire. This had a number of benefits:

* The nanocomposite innerliner gauge reduction resulted in an average fire weight savings of over 1.0 kg.

* Viewing the quality of the nanocomposite tire by x-ray showed no detriment in parameters such as ply wire spacing, and shearography did not show any internal separations in the casing.

* Liner splice integrity and adhesion for both the bromobutyl innefliner and nanocomposite liner were equivalent. Green tires were also aged in the factory before curing. No liner or liner splice concerns were noted.

* To maintain equal output rates at the innerliner extrusion line, extruder RPM speed for the nanocomposite innerliner was reduced 40%, with resulting energy savings.

* The reduced nanocomposite innerliner gauge allowed a tire cure time reduction of 2%.

The tires were tested for uniformity, inflation pressure retention and durability. Tire uniformity, such as balance, run out, force variation and conicity for the two sets of tires was equivalent. Even though there was a reduction in the liner gauge, at 94 days the average inflation pressure retention of the nanocomposite tire (expressed as a percent loss) is superior to the bromobutyl innerliner tire (figure 2). This correlates directly with tire durability. After 85 days, the intracarcass pressure for the bromobutyl tire was 113 KPa, compared to 108 KPa for the nanocomposite innerliner.

Durability was assessed by conducting a simple dynamometer test to FMVSS 119. Rather than stopping at 47 hours, the test continued running at 50 kph and the load on the tire was increased by 10% at eight-hour increments until the tires failed. Tire temperature was measured at the tread centerline and shoulder at each load step increase. The following observations were noted:

* At 47 hours, the running temperature of the nanocomposite tire, measured by a needle probe, was 13[degrees]C cooler than the tire with the bromobutyl innerliner.

* Tire test duration for the bromobutyl control and nanocomposite tires, in ratings relative to the control at 100, were 100 and 125, respectively. The ratings for mileage to failure were 100 and 123, respectively (higher ratings are better).

* The tire load at failure, in ratings, was 100 and 116 for the bromobutyl and nanocomposite tires, respectively.

The potential benefits in truck tire retreadability by the use of nanocomposites could be extrapolated from this initial durability data and thus would merit further study. Furthermore, the benefits of nanocomposite innerliners may be more extensive than this preliminary data suggest. For example, the effect on tire rolling resistance, field durability that would be assessed from market trials, tread wear and overall in-service miles-to-removal, merit investigation and are the subject of more research.

Discussion and conclusions

Truck tire innerliner technology and the role of halobutyl was reviewed by Jones and later by Waddell and Rodgers highlighting the importance of the innerliner composition for air pressure retention (IPR), intracarcass pressure (ICP), adhesion to the casing and resistance to fatigue (refs. 9 and 10). However, there has been little advance in innerliner compound technology since the 1980s. This work has focused on the technological aspects of using nanocomposites as a basis for an innerliner in a tire and is applicable to the range of tires used in automobiles, light trucks, heavy duty trucks, agricultural equipment and large off-road vehicles. There is a number of observations that may be noted from this study, summarized as follows:

* Decrease in the natural rubber content of an innerliner will improve impermeability, and in turn improve tire inflation pressure retention and reduce intracarcass pressure.

* Tire innerliner compounds have a series of property targets that must be met to ensure adequate durability. From tables 2, 3 and 4, this could be summarized in table 6. A nano-composite compound is included for comparison.

* Table 5, illustrating a comparison of nanocomposite with bromobutyl rubber in a truck tire innerliner compound, has shown that nanocomposites can meet these general property targets, but also have the potential to significantly improve impermeability (table 6).

Figure 3 shows the improvements in impermeability by reducing natural rubber content in the innerliner, and then replacing halobutyl with this nanocomposite material. The use of butyl or halobutyl rubber containing a nanoclay will not achieve comparable performance.

Improvement in innerliner performance, in the order of magnitude demonstrated here, presents a number of opportunities in further improving tire performance. As noted earlier, reduction in permeability leads to improved tire inflation pressure retention (IPR). In many instances, this parallels improvement in intracarcass pressure (ICP), which correlates favorably with improved tire dynamometer durability (ref. 9).

Alternatively, improved impermeability may allow a corresponding reduction in the tire innerliner gauge and a reduction in tire weight. Reduced gauges will favorably influence tire operating temperatures. Reduced innerliner gauge may also afford improvements in factory mixing equipment utilization and efficiency, offer a potential increase in liner compound calendering or extruder output rates (due to thinner gauges) and potential cure time savings. Such improvements would not be possible by other compounding means. The data displayed in this study can therefore provide a foundation for further work to not only improve tire factory productivity, but also improve performance of the final product.

References

(1.) www.michelin.com.

(2.) www.goodyear.com.

(3.) R.R. Juengel, D.C. Novakoski and S.G. Laube, "Effect of carbon black loading, surface area and polymer type on the permeability of innerliner compounds," International Tire Exhibition & Conference, 1994.

(4.) WO 98/56598, "Barrier coating of an elastomer and dispersed layered filler in a liquid carrier and coated compositions, particularly tires," Herberts GMBH, Michelin Recherche et Technique SA, C.E. Feeney and R.J. Balzer, 1998.

(5.) H. Kaidou and Y. Hatano, "Tire testing evaluation of a novel very high impermeability innerliner, "International Tire Exhibition & Conference, 2004.

(6.) K.F. Lin, D.W. Klosiewicz and G.I. Brodsky, "Tire innerliner," U.S. 5,292,590, 1994.

(7.) S.S. Ray and M. Okamoto, "Polymer/layered silicate nanocomposites: A review from preparation to processing," Prog. Polym. Sci. 28. pp. 1,539-1,641, 2003.

(8.) www.butylrubber.com.

(9.) G.E. Jones, "Innerliners for truck and off-the-road tires: A review," paper 35, presented at a meeting of The Rubber Division, ACS, April 2003.

(10.) W.H. Waddell and M.B. Rodgers, "Tire applications of elastomers 3. Tire innerliners, "presented at a meeting of the Rubber Division, ACS, May 2004.

Brendan Rodgers, Robert N. Webb and Weiqing Weng, ExxonMobil Chemical

Table 1--model innerliner compound/

Compound                      PHR

Bromobutyl                  100.0
Carbon black N660            60.0
Naphthenic oil                8.0
Struktol 40MS                 7.0
Phenolic tackifying resin     4.0
Stearic acid                  1.0
Zinc oxide                   1.00
MBTS                         1.25
Sulfur                       0.50

Table 2--typical properties of bromobutyl
innerliner compounds with increasing
natural rubber content

Compound                            1      2      3      4       5

Bromobutyl                       60.0   70.0   80.0   90.0   100.0
Natural rubber                   40.0   30.0   20.0   10.0
Carbon black N660                60.0   60.0   60.0   60.0    60.0
Naphthenic oil                    8.0    8.0    8.0    8.0     8.0
Struktol40MS                      7.0    7.0    7.0    7.0     7.0
Phenolic tackifying resin         4.0    4.0    4.0    4.0     4.0
Stearic acid                      1.0    1.0    1.0    1.0     1.0
Zinc oxide                        1.0    1.0    1.0    1.0     1.0
MBTS                             1.25   1.25   1.25   1.25    1.25
Sulfur                           0.50   0.50   0.50   0.50    0.50
Mooney viscosity                 56.0   57.0   50.0     --    51.0
(ML 1+4) at 100[degrees]C
Mooney scorch at 125[degrees]C
Minimum viscosity                22.0   17.0   22.0   23.0    22.9
Time to 5 pt. rise               13.0   23.0   25.0   18.0    34.0
MDR rheometer at 160[degrees]C
t10%                              2.2    2.6    2.5    2.8     2.2
t90%                             16.9   14.0   14.6   16.1    12.8
Cure rate                         0.5    0.4    0.4    0.4     0.5
[DELTA] Torque (MH-ML)            4.1    3.3    3.8    4.5     3.5
Tensile strength, MPa            11.8   10.2   10.4   10.0     9.6
Elongation, %                     676    768    745    796     837
300% modulus, MPa                 3.8    3.1    3.9    3.3     3.3
Tear resistance, KN/m            57.9   55.6   54.2   50.6    53.8
Permeability coefficient,        1.74   1.35    1.2   0.92    0.78
cc*mm/([m.sup.2]-day-mmHg)
Rating                            223    173    154    118     100

Table 3--comparison of bromobutyl and chlorobutyl elastomer grades

Compound                                       6       7       8      9

Bromobutyl 2222                            100.0
Bromobutyl 2235                                    100.0
Bromobutyl 2255                                            100.0
Chlorobutyl 1066                                                  100.0
Carbon black N660                           60.0    60.0    60.0   60.0
Naphthenic oil                               8.0     8.0     8.0    8.0
Struktol 40MS                                7.0     7.0     7.0    7.0
Phenolic tackifying resin                    4.0     4.0     4.0    4.0
Stearic acid                                 2.0     2.0     2.0    2.0
MgO                                         0.15    0.15    0.15   0.15
Zinc oxide                                  1.00    3.00    1.00   1.00
MBTS                                        1.20    1.50    1.20   1.50
Sulfur                                      0.50    0.50    0.50   0.50
Nominal polymer viscosity                   32.0    39.0    46.0   38.0
(ML 1+4 at 125[degrees]C)
Mooney viscosity (ML 1+4)                   56.0    59.3    63.6   55.1
at 100[degrees]C
Mooney scorch at 125[degrees]C
Minimum viscosity                           22.9    25.1    28.6   30.8
Time to 5 pt. rise                          34.0    22.3    24.6   35.7
MDR rheometer at 160[degrees]C
t10%                                         2.2     1.7     2.0    1.7
t90%                                        12.8    13.3    11.9    8.9
Cure rate                                    0.5     0.5     0.6    0.9
[DELTA] torque (MH-ML)                       3.5     3.7     3.5    3.6
Tensile strength, MPa                        9.6    11.1    10.1    9.4
Elongation, %                                837     827     784    950
300% modulus, MPa                            3.3     3.2     3.7    2.6
Tear resistance, KN/m                       53.8    56.0    59.4    487
Permeability coefficient (60[degrees]C),   0.744   0.703   0.710  0.706
cc*mm/([m.sup.2]-day-mmHg)

Table 4--summary of basic properties of truck
tire innerliner

Manufacturer            A      B      C      D       E      F   Aver-
Tire analyses           8      5      4      8      11      6   age

Tensile (MPa)        9.81   8.73   11.6   9.71   11.68   9.47      42
Elongation (%)        681    736    533    748     734    663   10.17
300% modulus (MPa)   4.23   3.17   6.36   3.33    3.70   4.21     683
Hardness (duro A)      58     59     64     58      56     58    4.17

Table 5--comparison of bromobutyl 2255
truck tire innerliner compound with a
nanocomposite innerliner

Compound                                        10      11

BIIR 2255                                    100.0
Nanocomposite                                        100.0
N660                                          60.0    60.0
Naphthenic oil                                 8.0     3.5
Struktol40MS                                   7.0     7.0
SP-1068                                        4.0     4.0
Stearic acid                                   1.0     1.0
Zinc oxide                                    1.00    1.00
M BTS                                         1.25    1.25
Sulfur                                        0.50     0.5
Mooney viscosity (ML 1+4) of 100[degrees]C    65.3    70.3
MDR rheometer at 160[degrees]C
[DELTA] torque (Mh-Ml), dNm                   2.98    3.16
t10%, min.                                    1.31    1.36
t90%, min.                                   10.13   15.79
Peak rate, dNm/min.                           0.78    0.43
Tensile strength, MPa                        11.63   10.33
Elongation, %                                  742     836
Tear resistance, KN/m                         59.1    58.4
Permeation coefficient,                        198     121
cc*mm/([m.sup.2]-day)
Rating                                         100      61

Table 6--nanocomposite compound properties

                                            Target    Target  Nano-com-
                                           minimum   maximum   posite
Compound viscosity                                            (summary)

(ML 1+4 at 100[degrees]C)                     50.0      70.0      70.0
Tensile strength (MPa)
Elongation at break (%)                        9.0      11.0      10.3
Tear strength (KN/m)                           700       900       836
Permeation coefficient  (40[degrees]C),       50.0        --      58.0
(cc*mm/([m.sup.2]-day)                          --       220     120.0
Permeability coefficient (40[degrees]C),
(cc*mm/([m.sup.7]-day-mmHg)                     --      0.27      0.16

Figure 1--comparison of bromobutyl 2255
and nanocomposite in a model truck
innerliner compound

Bromobutyl Innerliner      100
Nanocomposite innerliner    61

Note: Table made from bar graph

Figure 3--reduction in permeability due to
reduction and elimination of natural
rubber and then use of nanocomposites

Polymer             Permeability
composition         coefficient (rating)

BIIR 60 NR 40             223
BIIR 70 NR 30             173
BIIR 80 NR 20             154
BIIR 90 NR 10             118
BIIR 100                  100
Nanocomposite 100          61

Note: table made from bar graph.