Effect of Functionalization of Carbon Black on Rubber Properties

<strong>Effect</strong> <strong>of</strong> <strong>Functionalization</strong> <strong>of</strong> <strong>Carbon</strong> <strong>Black</strong> on Rubber Properties
- Using CSDPF 2000 and CSDPF 4000 to Improve Global Compromise between
Rolling Resistance, Wear Resistance and Wet Skid Resistance for Tires
Meng-Jiao Wang, Yakov Kutsovsky, Ping Zhang,
Greg Mehos, Lawrence J. Murphy and Khaled Mahmud
Cabot Corporation, Business & Technology Center
157 Concord Road, Billerica, Massachusetts 01821-7001, USA
Presented at “Functional Tire Fillers 2001”,
Fort Lauderdale, Florida, January 29-31, 2001

Introduction
The tire industry requires continuous development in the areas <strong>of</strong>
• Increased durability;
• Better fuel economy; and
• Improved safety.
2
CRX4XXX-012-FTF’01-Simp.doc
These requirements can only be met by improvement <strong>of</strong> wear resistance, rolling
resistance and skid resistance, especially in wet conditions. From the compounding point
<strong>of</strong> view, it has been recognized that the filler and polymer play an equally important role
in governing the compound properties, thus tire performance. In fact, the term filler is
misleading as it implies a material that increases the volume and reduces the compound
cost. Additionally, the filler cannot only be considered to be what is commonly referred
to as a “reinforcing agent” in the sense <strong>of</strong> a material that increases modulus and improves
the tensile strength <strong>of</strong> the compound. What is commonly referred to as “filler” is actually
a functional material or component which has a significant effect on tire performances.
It has been well established that the wear resistance <strong>of</strong> filled rubber is essentially
determined by the polymer-filler interaction. For fillers having similar morphologies, the
increase in polymer-filler interaction, either through enhancement <strong>of</strong> physical adsorption
<strong>of</strong> polymer chains on the filler surface or via creation <strong>of</strong> chemical linkages between filler
and polymer, is crucial to the enhancement <strong>of</strong> wear resistance.
It has also been established that there is a good correlation between the rolling resistance
<strong>of</strong> tires and the hysteresis <strong>of</strong> the tread compound, characterized by the loss factor, tan δ,
at high temperature. The hysteresis is in turn determined by the filler networking which is
governed by polymer-filler, and especially filler-filler interactions. 1 The stronger the
filler-filler interaction, the more developed is the filler network, hence the higher the
rolling resistance <strong>of</strong> tires.
In the last few years, in response to ever more demanding requirements from the tire
industry, a great effort has been made by Cabot Corporation to develop functionalized

carbon blacks to improve the trade<strong>of</strong>f between wear resistance and rolling resistance.
These include chemically modified carbon blacks with different functional groups and
carbon-metal oxide-multiphase composites produced by the c<strong>of</strong>uming process. Among
others a new material, carbon-silica dual phase filler (CSDPF), has been commercialized
under the trade name <strong>of</strong> ECOBLACK CRX TM 2XXX 2,3 group which are also referred to
as CSDPF 2000 family. With this material, the filler-filler interaction is substantially
reduced due to the surface modification, and the polymer-filler interaction is enhanced by
increasing the surface energy <strong>of</strong> the carbon domain <strong>of</strong> the filler and creating chemical
bonding via coupling reaction between polymer chains and silanols on the silica domain. 2
Consequently, the trade<strong>of</strong>f between rolling resistance and wear resistance is greatly
improved, significantly enhancing one without sacrificing the other.
With regard to wet skid resistance, the mechanism is more complicated. Based on the
comprehensive studies carried out in the laboratories <strong>of</strong> Cabot Corporation, it has been
recognized that for wet skid resistance, while the dynamic hysteresis at low temperature
due to the high-frequency nature <strong>of</strong> the dynamic strain involved in the skid process, is <strong>of</strong>
importance, the elasto-hydrodynamic lubrication (EHL) and boundary lubrication (BL),
especially in the micro scale, are also critical. 4 It was also found that besides dynamic
properties, namely dynamic hysteresis and modulus, the test conditions, such as vehicles
type (passenger vs. truck), braking system (locked wheel vs. anti-lock brake system
140
130
120
110
100
90
80
Relative friction force
on wet surface, %
Passenger tire Truck tire
3°C , 1.44 km/hr, 25° slip angle
0 50 100 150
Figure 1. wet skid resistances measured by GAFT as a function <strong>of</strong> load for passeger tire tread compounds with a variety <strong>of</strong> fillers
ECOBLACK and CRX are the trademarks <strong>of</strong> Cabot Corporation.
3
SSBR/BR 75/25,
filler 80 phr,
oil 32.5 phr
CSDPF
<strong>Carbon</strong> black
Silica
Load, N

(ABS)), speeds, temperature, road surface, and load have a great impact on micro-elastohydrodynamic
lubrication (MEHL) and BL. The relative role <strong>of</strong> MEHL is also
determined by the composition <strong>of</strong> the tread compound, such as the nature <strong>of</strong> the polymer
and filler, and their interaction. Whereas the silica compound is favorable for reducing
MEHL, carbon black is good for boundary and dry friction. 4 Shown in Figure 1 is a
comparison <strong>of</strong> the wet skid resistance measured by the Grosch abrasion and friction tester
(GAFT) under different loads for carbon black-, silica- and ECOBLACK filler-filled
tread compounds, taking a smooth sandblasted glass as the friction substrate. As can be
seen, under lower load, corresponding to passenger tire where micro-elastohydrodynamic
lubrication plays an important part, silica shows a significant advantage
over carbon black and the ECOBLACK filler. However, with increasing load, the
advantage <strong>of</strong> silica diminishes. At high load corresponding to that applied to the truck tire
where the boundary lubrication is relatively dominant, the wet friction coefficient
eventually turns in favor <strong>of</strong> the CSDPF 2000 materials, due to its better-balance between
dynamic properties and hydrodynamic lubrication. Consequently, the trade<strong>of</strong>f between
wear resistance, rolling resistance and wet skid resistance for truck tires can potentially
be significantly improved with the ECOBLACK filler, while for passenger tires this
product has a deficiency in wet skid resistance compared to silica.
With a series <strong>of</strong> silica-containing fillers and carbon black, it has been found that the wet
skid resistance measured by means <strong>of</strong> an improved British portable skid tester (BPST) on
a wet and smooth glass surface is closely related to the silica-polymer interfacial area in
the passenger tread compounds. A higher interfacial area gives better wet skid resistance.
On the other hand, it has been reported that the BPST number is well correlated with
peak friction coefficients obtained from the skid test <strong>of</strong> passenger tires on a wet road. 5
Accordingly, in order to be able to improve wet skid resistance for passenger tires, a new
carbon-silica dual phase filler with substantially increased silica-surface coverage has
been developed. This is achieved by increasing silicon content and, most importantly, by
optimizing the morphology and distribution <strong>of</strong> the silica domain in the filler aggregates,
using a unique multi-stage-c<strong>of</strong>uming technology developed by Cabot Corporation. 6 In
order to differentiate this new material from the CSDPF 2000 family introduced before, it
4

Table I. Analytical properties <strong>of</strong> the fillers
Si content % BET-SA, m2 /g STSA, m2/g CDBP I2 No.
Silica
coveragea TMCS
uptake
Filler As is HF As is HF As is HF mL/100g mg/g % #/nm 2
N134 N/A N/A 146 N/A 134 N/A 104 143 N/A N/A
N234 N/A N/A 122 122 118 118 100 120 N/A 0.02
CSDPF CRX2124 4.1 0.85 171 251 133 146 115 120 9 0.32
CSDPF CRX4210 10.0 0.01 154 167 123 155 108 62 55 1.04
Silica Z1165 46.7 N/A 168 N/A 132 N/A N/A NA 100 2.02
a. The silica-surface coverage <strong>of</strong> CRX2124 was estimated from silicon content and that <strong>of</strong> CRX4000
was from iodine number and surface area which was the averaged value <strong>of</strong> BET-SA and STSA.
b. Number <strong>of</strong> TMCS uptake per nm 2 estimated using averaged surface areas from BET-SA and STSA
is referred to as CSDPF 4000 family corresponding to CRX4XXX group. In this paper,
we will first describe the features <strong>of</strong> CSDPF 2000 and 4000 with regard to their analytical
characteristics and in-rubber properties, and then discuss the applications <strong>of</strong> CSDPF 4000
to passenger tire tread compounds and CSDPF 2000 to truck tire tread compounds, taking
CRX4210 and CRX2124 as examples, respectively.
The features <strong>of</strong> CSDPF 2000 and CSDPF 4000 Series
Shown in Table I are the basic properties <strong>of</strong> CSDPF 2000 and 4000 compared with those
<strong>of</strong> conventional fillers. While both new materials contain silica, some <strong>of</strong> the differences
between CSDPF 2000 and 4000 include their distribution <strong>of</strong> silica, silica-surface
coverage and silicon content. CSDPF 4000 has much higher silica-surface coverage
relative to CSDPF 2000 which is due to the silica domain distribution and high silicon
content. This can be seen from the changes in silica content and surface area upon
hydr<strong>of</strong>luoric acid (HF) extraction. During HF extraction, the silica will be dissolved with
the carbon domain remaining unchanged. The fact that significant portions <strong>of</strong> silica still
remains, and surface areas drastically increase upon HF treatment <strong>of</strong> CSDPF 2000,
suggest that the silica <strong>of</strong> CSDPF 2000 is distributed throughout the aggregates. By
contrast, in the case <strong>of</strong> CSDPF 4000, the small change in surface areas and the fact that
there is almost no silica left after HF extraction indicate that the silica in the CSDPF 4000
aggregates is located on the surface. This observation is supported by the images and the
6
b

Bright field image <strong>Carbon</strong> map Silicon map
Figure 2. Bright field and compositional images (carbon and silicon) <strong>of</strong> a CSDPF 4000 aggregate
carbon- and silicon-maps obtained by means <strong>of</strong> STEM/EDX. In the aggregate <strong>of</strong> CSDPF
4000 shown in Figure 2, the silica is obviously concentrated on the aggregate surface. In
the case <strong>of</strong> CSDPF 2000, the silica domains are distributed within the aggregates (Figure
3). The silica distributions can be also visualized from the TEM images <strong>of</strong> the filler
aggregates/agglomerates and those <strong>of</strong> ashed aggregates/agglomerates. Figure 4 contains a
TEM image <strong>of</strong> a CSDPF 2000 aggregate and an image <strong>of</strong> the same aggregate that was
ashed leaving behind the silica phase. Obviously, the silica domains can be envisaged as
having been finely distributed throughout the aggregate. However, ashing <strong>of</strong> the CSDPF
4000 aggregates resulted in a quite different picture (Figure 5). Upon ashing, silica is left
as a shell-like structure whose shape is similar to the contour <strong>of</strong> the unashed particles/
Bright field image <strong>Carbon</strong> map Silicon map
Figure 3. Bright field and compositional images (carbon and silicon) <strong>of</strong> a CSDPF 2000 aggregate
7

Before ashing After ashing
Figure 4. TEM images <strong>of</strong> CSDPF 2000 aggregate, before and after ashing
aggregates. It is apparent that the silica domain is intimately attached on the carbon black
surface with a high surface coverage. According to the information obtained from
different techniques, the pictures can be drawn for CSDPF 2000 and 4000, as presented
in Figure 6.
When incorporated in hydrocarbon polymers, both CSDPF 2000 and 4000 are
characterized by higher filler-polymer interaction in relation to a physical blend <strong>of</strong> carbon
black and silica, and lower filler-filler interaction compared to both traditional fillers.
Evidence <strong>of</strong> the higher filler-polymer interaction <strong>of</strong> the silica-containing fillers in
Before ashing After ashing
Figure 5. TEM images <strong>of</strong> CSDPF 4000 aggregate, before and after ashing
8

hydrocarbon polymers can be obtained by comparing the adsorption energies <strong>of</strong> polymer
analogs on the filler surfaces. Shown in Figure 7 are the adsorption free energies <strong>of</strong>
heptane, a model compound for hydrocarbon polymers, measured by inverse gas
chromatography (IGC).
The results for both CSDPF 2000 and 4000 are presented along with those <strong>of</strong> blends <strong>of</strong>
carbon black N234 and silica. Regardless <strong>of</strong> the difference in surface areas, at the same
silica contents, the silica-containing fillers give significantly higher adsorption energies.
The lower filler-filler interaction <strong>of</strong> CSDPF 2000 and 4000 can be demonstrated by the
Silica
N234
60
50
40
30
20
10
0
-∆ G°, kJ/mol
9
Section A-A
Figure 6. General views <strong>of</strong> CSDPF 2000 and CSDPF 4000
CSDPF 2000
CSDPF 4000
Heptane, 180°C
CB+Silica
CSDPF 4000
CSDPF 2000
0 20 40 60 80 100
100 80 60 40 20 0
Figure 7. adsorption energies <strong>of</strong> heptane at 180°C on a variety <strong>of</strong> fillers
%

12.0
10.0
8.0
6.0
4.0
2.0
0.0
Strain, %
0.0
Strain, %
0.1 1 10 100 0.1 1 10 100
Figure 8. Strain dependence <strong>of</strong> G' at 70°C and 10 Hz for OESSBR/BR and NR compounds filled with a variety <strong>of</strong> fillers
strain dependence <strong>of</strong> the elastic modulus, G’(Figure 8). For filled rubber, the elastic
modulus decreases with strain amplitude, which has been termed the “Payne effect”. 7
This effect is generally used as a measure <strong>of</strong> filler networking, controlled mainly by
filler-filler interaction. 8 Although from the chemical composition point <strong>of</strong> view, both
CSDPF 2000 and 4000 are between carbon black and silica, what is actually observed
here is that the two new fillers give the lowest Payne effect. This unique behavior <strong>of</strong> the
two new materials is readily explained by the low filler-filler interaction due to their
hybrid surfaces. It has been established that from the point <strong>of</strong> view <strong>of</strong> surface energies,
interaction between unlike surfaces is lower than that between the same category
surfaces. 1
G', MPa
Silica
N234
CRX4210
CRX4210/TESPT 2.7 phr
OESSBR/BR 70/30,
Filler: equal volume
70°C, 10 Hz
Due to the higher surface activity on the surface <strong>of</strong> carbon domains and lower filler-filler
interaction, it is evident that these fillers will require significantly lower silane coupling
agent compared to silica.
Application <strong>of</strong> CSDPF 2000 and CSDPF 4000 in Tire Tread Compounds
Following the discussion on the filler parameters that control the tire performance, the
higher polymer-filler interaction and lower filler-filler interaction <strong>of</strong> CSDPF 2000 and
4000 will allow a better compromise between abrasion resistance and dynamic hysteresis
at high temperature. This will result in a good wear resistance and rolling resistance
compromise for the tires. With regard to wet skid resistance, the increased friction
10
12.0
10.0
8.0
6.0
4.0
2.0
G', MPa
Silica
N134
CRX2124
CRX2124/TESPT 1.0 phr
NR, Filler: 50 phr
70°C, 10 Hz

coefficient at high load by CSDPF 2000 suggests the potential for using this material in
truck tire tread compounds to improve wet skid resistance. In contrast, the high-silicacoverage
<strong>of</strong> CRX 4000 should reduce the micro-elasto-hydrodynamic lubrication, which
is favorable for wet skid resistance <strong>of</strong> passenger tire. Therefore, in order to improve the
global compromise in tire tread performance, the CSDPF 4000 type <strong>of</strong> material is
recommended for passenger tires, and the CSDPF 2000 type for truck tire tread
formulations.
Application <strong>of</strong> CSDPF CRX4210 to tread compounds for passenger tires
CRX4210 was evaluated using typical passenger tire tread formulations which are based
on a polymer blend <strong>of</strong> oil-extended solution SBR and BR (Table II). Besides CRX4210,
two conventional fillers were included as controls: carbon black N234 and precipitated
silica Z1165MP. The filler loading was adjusted to have an equal volume fraction, and
the coupling agent TESPT and curatives were also adjusted for CRX4210 and silica
compounds to optimize the polymer-filler interaction and filler-filler interaction as well
as cure characteristics. Since the stress-strain properties <strong>of</strong> all compounds fall in the
practical range, the discussion will be focused on the dynamic properties, abrasion
resistance and skid behavior.
Table II. Formulations for Passenger Tire Tread Compounds
OE-SSBR (Buna VSL 5025-1) 96.3 96.3 96.3
BR 30 30 30
Silica Z1165 80 - -
<strong>Carbon</strong> black N234 - 72 -
CSDPF CRX4210 - - 72
Coupling agent TESPT 6.4 - 2.7
Aromatic Processing Oil 1.8 1.8 1.8
Zinc Oxide 3.0 3.0 3.0
Stearic Acid 2.0 2.0 2.0
Antioxidant (Sant<strong>of</strong>lex 13) a 1.0 1.0 1.0
Antioxidant (Wingstay 100) b 1.0 1.0 1.0
Wax (Sunpro<strong>of</strong> Imp) 3.5 3.5 3.5
CBS c 2.0 1.1 1.6
DPG d 2.1 0.3 0.7
Sulfur 1.4 1.4 1.4
a. N-1,3-dimethyl-butyl-N’-phenyl –p- phenylenediamine. b. Diaryl-p-phenylenediamine.
c. N-cyclohexyl-2-benzothiazolesulfenamide. d. 1,3-diphenylguanidine
11

1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
T, °C
0.1
-100 -80 -60 -40 -20 0 20 40 60 80 100
Figure 9. Temperature dependences <strong>of</strong> tan δ at strain amplitude 2.5% and 10 Hz for OE-SSBR/BR compounds with a variety <strong>of</strong> fillers
Dynamic properties (rolling resistance):
As mentioned before, due to the lower filler-filler interaction and higher polymer-filler
interaction, the filler networking is substantially depressed in CSDPF 4000-filled
compounds. The much less developed filler networking in CRX4210 compounds would
show a great impact on the temperature dependence <strong>of</strong> hysteresis for filled vulcanizates.
As can be seen in Figure 9, where the temperature dependencies <strong>of</strong> tan δ measured at
2.5% strain amplitude and 10 Hz are presented, relative to carbon black, CRX4210 gives
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
tan δ OESSBR/BR 70/30,
Filler: equal volume
Strain 2.5%, 10 Hz
tan δ max
N234
12
Silica/TESPT 6.4 phr
Silica +
TESPT 6.4 phr
N234
CRX4210/
TESPT 2.7 phr
OESSBR/BR 70/30,
Filler: equal volume
70°C, 10 Hz
CRX4210
TESPT 2.7 phr
Figure 10. Comparison <strong>of</strong> tan δ max <strong>of</strong> OE-SSBR/BR compounds filled with a variety <strong>of</strong> fillers

very low tan δ at high temperature and very high hysteresis at lower temperature, similar
to silica. The same results were also obtained in the strain sweep test (Figure 10). At
70°C, the maximum tan δ is 0.323 for the carbon black compound. This value is reduced
by 48% and 50% with CRX4210 and silica, respectively. Based on the well-known
correlation between rolling resistance and tan δ at high temperature, it can be expected
that the rolling resistance <strong>of</strong> CRX4210 tire is comparable to that <strong>of</strong> silica tires and much
lower than that <strong>of</strong> carbon black tires.
Abrasion resistance:
Due to the weak polymer-filler interaction between silica and hydrocarbon rubber, even
with a high dosage <strong>of</strong> coupling agent TESPT, the abrasion resistance <strong>of</strong> the silica
compound is still significantly poor relative to carbon black compound. This could also
be applicable for the silica domain in CRX4210 aggregates. However, this deficiency
would be partially compensated for by the high surface activity <strong>of</strong> the carbon domain <strong>of</strong>
the silica-containing fillers. Presented in Figure 11 are the abrasion resistance indexes
measured with the Cabot Abrader at a slip ratio <strong>of</strong> 14%. Although the abrasion resistance
<strong>of</strong> a compound filled with CRX4210 and 2.7 phr TESPT does not fully reach the level <strong>of</strong>
the carbon black compound, it is significantly better than the silica compound.
140
120
100
80
60
40
20
0
Abrasion index, %
N234
Silica +
TESPT 6.4 phr
13
OESSBR/BR 70/30,
Filler: equal volume
14% slip
CRX4210 +
TESPT 2.7 phr
Figure 11. Comparison <strong>of</strong> abrasion resistance <strong>of</strong> OE-SSBR/BR compounds filled with a variety <strong>of</strong> fillers

Wet skid resistance:
The results <strong>of</strong> wet skid resistance measured with BPST are illustrated in Figure 12 as a
function <strong>of</strong> silica surface area per unit mass <strong>of</strong> the filler. This silica surface area is
proportional to the silica-polymer interfacial area per unit volume <strong>of</strong> the compound at the
same filler loading. The test was performed at room temperature, using a wet sandblasted
glass plate as a path surface. It was found that the skid resistance increases linearly with
the silica interfacial area in the compounds, regardless <strong>of</strong> the dynamic properties.
Compared with carbon black and CSDPF 2000, due to the high silica-surface-coverage,
CRX4210 gives significantly higher wet skid resistance. As mentioned previously, the
EHL and BL are essential for wet skid resistance. Under the test condition <strong>of</strong> BPST, due
to a very small contact length <strong>of</strong> the test pad with smooth glass in the sliding direction,
the MEHL plays a dominant role in skid resistance. 4 It has also been recognized that for
the SSBR/BR compound, while silica is very effective to reduce MEHL, carbon black is
favorable to friction under BL condition. Therefore compared with carbon black and
CSDPF, the higher BPST number <strong>of</strong> CRX4210 should be expected from its improved
silica-coverage. Moreover, there is a good correlation <strong>of</strong> BPST numbers with peak
friction values from road tests for passenger tire. 5 Thus, an improved wet skid resistance
can be expected from CRX4210 for passenger tires equipped on the vehicle having ABS.
This is because ABS operates near the peak. It should be pointed out that, the relative
roles <strong>of</strong> the EHL and BL in wet skid resistance vary with test conditions. With increasing
115
110
105
100
95
BPST index, %
OESSBR/BR 70/30, Filler: equal volume
0 20 40 60 80 100 120
14
CRX 4210
N234
CSDPF CRX 2214
CSDPF 4000
Silica Surface Area, m 2/g filler
Figure 12. effect <strong>of</strong> silica surface area in fillers on wet skid resistance

oad surface roughness, decreasing vehicle speed, decreasing water film thickness,
increasing load, and raising temperature, the importance <strong>of</strong> BL will increase. Therefore a
better-balanced result would be expected in the road test for CRX4210 due to its hybrid
surface and dynamic properties.
In conclusion, when CRX4210 is used in passenger tire tread compounds to replace
carbon black, the rolling resistance and wet skid resistance compromise will be
significantly improved without significant trade-<strong>of</strong>f in treadwear, as in the case with
silica.
Application <strong>of</strong> CSDPF CRX2124 to tread compounds for truck tires
Although silica has been successfully used with solution SBR and coupling agent in
passenger tread compounds to improve rolling resistance and wet traction, the application
<strong>of</strong> silica to truck tire compounds has not been successful. 9 This is mainly due to the poor
treadwear which is related to its lower filler-polymer interaction. For heavy radial truck
tire, NR is essentially the principle polymer in tread compounds. 10,11 Due to the high nonrubber
content <strong>of</strong> the natural rubber and high polarity <strong>of</strong> the silica surface, the weak
polymer-filler interaction is not well compensated for by the coupling agent, so that there is
a significant deficiency in abrasion resistance. 12 Accordingly, CSDPF 2000, especially its
higher surface area grade CRX2124, should be the best filler for NR-based truck tire
Table III. Formulations for truck tire tread compounds
NR (SIR-20) 100 100 100
<strong>Carbon</strong> black N134 50 - -
CRX2124 - 50
50
TESPT - 1.0 -
Oil (CircoLite) 2.5 2.5 2.5
Zinc Oxide 5.0 5.0 5.0
Stearic Acid 3.0 3.0 3.0
Antioxidant (AgeRite resin D) a 1.5 1.5 1.5
Antioxidant (Sant<strong>of</strong>lex 13) 1.5 1.5 1.5
Wax (Sunpro<strong>of</strong> Imp) 1.5 1.5 1.5
TBBS b 1.2 1.2 1.2
Sulfur 1.0 1.4 1.7
a. Polymerized 2,2,4,-trimethyl-1,2-dihydroquinoline.b. N-tert-butyl-benzothazole-2-sulfenamide.
15

compounds. With this filler, the high polymer-filler interaction will ensure abrasion
resistance and the lower filler-filler interaction resulting in lower hysteresis, hence lower
rolling resistance.
The impact <strong>of</strong> the characteristics <strong>of</strong> CRX2124 on truck tire tread compounds was
investigated experimentally, taking carbon black N134, a currently used highly reinforcing
filler in truck tread compounds, as a reference. Morphologically, CRX2124 is similar to
carbon black N134 but contains 4.1% silicon. The formulations used for the investigation
are typical for truck tire tread compounds (Table III). In the case <strong>of</strong> CRX2124, the dosages
<strong>of</strong> curatives were adjusted according to their cure characteristics. Additionally, one <strong>of</strong> the
compounds contains 1.0 phr coupling agent TESPT.
Dynamic properties (rolling resistance):
As shown in Figure 13, over the temperature range from 50 to 80°C, the CRX2124
compound gives substantially lower hysteresis than the carbon black compound, and
further reduction in tan δ can be obtained by the addition <strong>of</strong> TESPT. At lower
temperatures, the compounds filled with CRX2124 give significantly higher hysteresis.
However, the reduction in tan δ due to the silane is <strong>of</strong> a much smaller degree compared to
the OE-SSBR/BR formulation. This observation is also supported by strain sweeps. Shown
in Figure 14 are the maximum loss factors, tan δmax, obtained from strain sweeps at 70°C.
Similar to the results obtained at high temperature from the temperature sweep
2.0
1.0
0.8
0.7
0.6
0.5
0.4
0.3
0.2
tan δ
CRX 2124
0.1
0.08
0.07
0.06
0.05
T, °C
CRX2124/
TESPT 1.0 phr
-100 -80 -60 -40 -20 0 20 40 60 80 100
Figure 13. Temperature dependences <strong>of</strong> tan δ at strain amplitude 2.5% and 10 Hz for NR compounds with CRX2124 and N134
17
NR, Filler: 50 phr
Strain 2.5%, 10 Hz
N134

0.24
0.21
0.18
0.15
0.12
0.09
0.06
0.03
0.00
measurement, CRX2124 shows a 24% reduction in tan δmax relative to the carbon black
control and this difference is further increased to 33% by the addition <strong>of</strong> 1.0 phr TESPT.
Both results from strain and temperature sweeps suggest that owing to its lower hysteresis
at high temperature, CRX2124 will give substantially lower rolling resistance in relation to
carbon black.
Abrasion resistance
tan δ max
N110
CRX2124 +
TESPT 1.0 phr
As discussed earlier, with regard to abrasion resistance, silica has a significant deficiency in
polymer-filler interaction. In NR, the deficiency cannot be effectively compensated for by
chemical linkages between polymer molecules and the silica surface via the coupling agent
as the reactive groups, i.e., silanols may be blocked by adsorbed non-rubbers. 12 This could
also be applied to the silica domain on CSDPF. However, as indicated in Figure 15, the
abrasion index <strong>of</strong> the CRX2124-filled compound measured at 7% slip ratio is only about
17% lower than its carbon black counterpart. The negative impact <strong>of</strong> the silica domain on
the abrasion resistance seems to be partially <strong>of</strong>fset by the high surface activity <strong>of</strong> carbon
domain on the aggregates. By addition <strong>of</strong> 1.0 phr TESPT, the abrasion resistance <strong>of</strong>
CRX2124 can be further improved, making it closer to that <strong>of</strong> carbon black N134, one <strong>of</strong>
the preferred reinforcing fillers for truck tire tread.
18
NR, Filler: 50 phr
70°C, 10 Hz
CRX2124
Figure 14. Comparison <strong>of</strong> tan δ max <strong>of</strong> NR compounds filled with a variety <strong>of</strong> fillers

140
120
100
80
60
40
20
0
Wet skid resistance
Abrasion index, %
N110
CRX2124 +
TESPT 1.0 phr
Illustrated in Figure 16 are the BPST indexes <strong>of</strong> CRX4210-filled vulcanizates referenced
to the skid resistance <strong>of</strong> the compound filled with carbon black N134. As can be seen, the
CRX2124-based compounds show higher wet skid resistance, and additional TESPT does
not show a significant effect. Of course, these observations need to be verified via actual
tire testing.
19
NR, Filler: 50 phr
7% slip
CRX2124
Figure 15. Comparison <strong>of</strong> abrasion resistance <strong>of</strong> NR compounds filled with a variety <strong>of</strong> fillers
106
104
102
100
98
96
94
92
BPST index, % NR, Filler- 50 phr
N134
CRX2124 +
TESPT 1.0 phr
CRX2124
Figure 16. Comparison <strong>of</strong> wet skid resistance <strong>of</strong> NR compounds filled with a variety <strong>of</strong> fillers

Conclusions
Two different types <strong>of</strong> silica modified materials, CSDPF 2000 and CSDPF 4000 have
been discussed. Their applications in tread compounds have been investigated. Based on
the performance in the laboratory, the global compromise between rolling resistance,
wear resistance and wet skid resistance for the tread compounds can be significantly
improved by replacing the conventional fillers with the CSDPF 4000 type <strong>of</strong> product
(CRX4210) for passenger tire tread and with CSDPF 2000 type <strong>of</strong> product (CRX2124)
for truck tire tread.
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