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Use of resol-modified bentonite clay nanocomposites in CB N660 filled SBR.

For a filler to behave as a good reinforcing agent, the three main factors to consider are particle size, structure and surface characteristics. It was only recently that researchers succeeded in intercalating polymers into the clay layers and thereby prepared polymer clay nanocomposite (PCN) which not only exhibit outstanding mechanical properties, but also very good barrier and thermal properties. PCNs can be prepared by solution blending (refs. 1-12) or direct intercalation or sol/gel technique or in situ polymerization or by latex blending.

Most of the robbers are available in the form of latex, which is nothing but an aqueous dispersion of rubber particles in the submicron-micron range (the particle size distribution depending on the manufacturing conditions). The layered silicates are easily dispersed in water, as water acts as a swelling agent owing to the hydration of the intergallery cations usually [Na.sup.+] or [K.sup.+]. The water swelling capability of the natural clays is not the same, but depends upon the type of clay and its cation exchange capacity (ref. 13), and, hence, the mixing of the latex with the layered silicates (having high cation exchange capacity) followed by co-precipitation (coagulation) is a promising route for producing rubber nanocomposites (ref. 14). Varghese and Karger-Kocsis prepared NR based nanocomposites with 10 wt. % natural (sodium bentonite) and synthetic (sodium fluorohectorite) layered silicates by the latex compounding method (ref. 15). Wang et al. prepared NR-MMT and chloroprene rubber (CR)-MMT clay nanocomposites by co-coagulating the rubber latex and the aqueous clay suspension (ref. 16). Potential application areas suggested by Wang et al. for these nanocomposites were as inner tubes, inner liners and dumpers.

U.S. Patent 20030144401 refers to the preparation of clay/ rubber nanocomposites by the latex route, and such materials have been suggested for use in tire components like tire tread, sidewall and/or inner liner (ref. 17). Another U.S. Patent (U.S. 2005065266) reports the preparation of nanocomposites comprised of water swellable clay particles in aqueous emulsions like anionic SBR or NR containing a novel amine for aiding in intercalation and partial exfoliation of the clay particles (ref. 18).

Apart from fillers, certain resin systems impart reinforcement when added to elastomers. Le Bras and Piccini (ref. 19) and Piccini (ref. 20) reported significant reinforcing action of resorcinol- formaldehyde (RF) resins formed in situ (by the condensation of resorcinol and formaldehyde in alkaline medium) by the addition to natural rubber (NR) latex. Further, Uzina and Dostian (ref. 21) reported the usage of bentonite clay for reinforcement of NR latex. They showed that the strength of bentonite clay loaded NR latex film was minimum at 5-15 parts by weight bentonite loading and the maximum strength was reached when the filler loading was 50 parts by weight. To the best of our knowledge, the usage of RF resins for modification of layered silicate and subsequent addition of SBR latex to this modified clay has not been reported so far.

In the present study, the authors have used naturally occurring unfractionated bentonite clay, which is very cheap and abundantly available in India. Further, an attempt has been made to organically modify the unfractionated bentonite clay using in situ formation of RF resin (an attempt to intercalate the clay gallery gaps by the RF resin) followed by addition of SBR latex to the RF modified unfractionated bentonite clay suspension in water. The mixture was acid coagulated, dried and finally melt compounded with the usual conventional rubber compounding ingredients. The nano composites master was examined by FTIR, WAXD and TEM. The mechanical and physical properties of the RF-modified unfractionated bentonite clay/SBR vulcanizates were compared with low structure (N660) carbon black filled compound. Partial replacements (up to 5 phr) and addition (up to 5 phr) were also carried out.

Experimental

Materials

The SBR latex (Encord 205) with 25% bound styrene and 40% solids content was supplied by M/S Jubilant Organosys, Borada, India. The Mooney viscosity (ML [1+4] at 100[degrees]C) of the coagulated SBR latex was 51. Apart from SBR latex, SBR 1502 (emulsion grade) from BST Elastomers, Bankok, Thailand (bound styrene 24%, Mooney viscosity 50 (ML [1 +4] at 100[degrees]C), volatile matter 0.02%, specific gravity 0.94) was also used in the compound formulations. Unpublished work in our laboratory indicates that the gum properties of both those SBRs are similar, and thus SBR 1502 was used for dose adjustment during compound formulation as reported later. The clay used in this work is unfractionated bentonite clay. The physical and chemical characteristics of this clay are summarized in table 1

The rubber compounding ingredients used in this work were of commercial grade, viz. zinc oxide, stearic acid, sulfur, N-tbutylbenzothiazole-2-sulfenamide (TBBS) and N660 carbon black. Resorcinol (commercial grade) and 37% formaldehyde solution (laboratory reagent grade) were procured from Deepak Nitrite, India and Ranbaxy Labs, India, respectively.

Synthesis of the SBR/RF modified bentonite clay nanocomposite masterbatch

About 10 gm of the unfractionated pristine bentonite clay was dispersed in 300 ml of distilled water using a Remi, India stirrer for one hour at 300-400 rpm. Next, 0.82 gm of resorcinol and 1.22 gm of 37% formaldehyde solution (molar ratio of resorcinol/formaldehyde = 1/2) were added to the clay slurry. 100 ml of distilled water was further added to this mixture, the pH maintained at 8-9 by adding a small amount of sodium hydroxide and the mixture was stirred for six hours at room temperature. This gives ~10% of RF resin with respect to clay. Diluted SBR latex (20% total solid) was then added to the aqueous slurry. The amount of latex was adjusted to make 20 parts of clay in 100 parts of rubber (i.e., 20 phr clay loading) on a dry basis. The pH of the solution was adjusted to 8. The solids content of the slurry was finally maintained around 20-25%. The mixture was further stirred for another six hours. The resultant solution was coagulated with 10% sulfuric solution, washed several times with tap water and dried at 70[degrees]C in a hot air oven.

[FIGURE 1 OMITTED]

Compound mixing

The single stage mixing was done in a Brabender Plasticorder Model PL 2000-3 having a chamber volume of 80 [cm.sup.3], cam rotors, ram pressure weight of 5 kg and batch weight of 70 g. Single stage mixing was carried out for 10 minutes using 60 rpm rotor speed at 70[degrees]C. Initially, one minute mastication time was allowed for the rubber. Then clay or clay masterbatch was added and mixed for six minutes. Then, the other ingredients were added and the batch dumped after three minutes.

Two-stage mixing was carried out in the same machine in two steps, master and final. The masterbatch mixing was carried out for seven minutes using 60 rpm rotor speed at 90[degrees]C. Initially, one minute mastication time was allowed for the rubber. Then clay or clay masterbatch or carbon black and oil was added and mixed for six minutes. In final stage, one minute mastication was allowed, followed by the addition of the curatives and further mixing for three minutes.

[FIGURE 2 OMITTED]

The mixed batches were further milled on a laboratory two-roll mill. The respective compound formulations are shown in table 2. The SBR dose was adjusted by adding SBR 1502 from outside during mixing.

Characterization of the SBR/bentonite clay nanocomposites

The Fourier Transform Infrared (FTIR) of the samples in the form of thin films (~100 [micro]m thick) and of the powders (bentonite clay and RF resin modified bentonite clay) was carried out on a System 2000 FTIR of Perkin Elmer, with a scan range of 400-4,000 [cm.sup.-1] at a resolution of 4 cm. The FTIR spectra are shown in figures 1 and 2.

Wide angle x-ray diffraction (WAXD) measurements were carried out in a Philips 1710 x-ray diffractometer using a scan rate of 0.5[degrees]/min. with Cu K[alpha] target at 40 kV and 25 mA (wavelength = 0.154 nm) with 2[theta] scan range from 2 to 10[degrees]. The x-ray diffractograms are represented in figures 3 and 4.

For transmission electron microscopy (TEM) measurements, 100 nm sections were microtomed at -120[degrees]C using Ultracut E ultramicrotome (Reichert and Jung) with a diamond knife. Measurements were carried out with a Philips CM200 TEM at an acceleration voltage of 120 kV. The TEM images are shown in figures 5 and 6.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

The rheometric properties were determined in a moving die rheometer at 160[degrees]C for 60 minutes keeping the rotor arc at 0.5[degrees] in accordance with ASTM D 5289. Rheometric properties are reported in table 3.

Curing of tensile slabs was done using a compression molding technique in an electrically heated curing press at 160[degrees]C for 60 minutes. The tensile samples were died out in accordance with ASTM D412 type C die.

The stress-strain properties were determined using a universal testing machine, Zwick UTM 1445, in accordance with ASTM D412. The hardness was determined in a durometer in accordance with ASTM D2240.

The tear properties were measured according to ASTM D 624. The Mooney viscosity was measured using an MV2000E from Alpha Technologies in accordance with ISO 289-1.

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

The fatigue to failure properties (FTFT) at 100% extension ratio were measured in a Monsanto FTFT machine (ASTM D 4482). The fatigue life was calculated using the Japanese Industrial Standard (JIS) average method.

Cure rate index (CRI) was measured according to ASTM D5289. The following formula was used for the CRI in the study:

where,

CRI = 100 / [tc.sub.90] - [t.sub.s2] (1)

The swelling index of the cured samples was measured using the following formula in accordance with ASTM D3616.

Swelling index = Swollen weight / Initial weight (2)

Volume fraction was also performed to get an indication of apparent crosslink density. Weighed sample of cured rubber vulcanizate was immersed in toluene solvent for 48 hours at room temperature. Excess solvent was then blotted from the sample and the swollen weight was measured. The swollen sample was dried in an oven at 100[degrees]C until constant weight. Dried weight of the sample was taken after cooling the sample in the desiccator. The volume fraction, [V.sub.r], of the vulcanizate rubber was calculated using the following formula:

[V.sub.r] = ([(D-FT)/ [[rho].sub.r]] / [(D-FT)/[[rho].sub.r]]+ [[A.sub.0]/[[rho].sub.s]] (3)

where D is the weight of the unswollen sample; F is the weight fraction of the insoluble non-rubber ingredients; T is the original dry weight of the sample; [A.sub.0] is the weight of solvent absorbed; Or is the density of the rubber (density value is 910 kg/[m.sup.3]); and [[rho].sub.s] is the density of the solvent (density value is 870 kg/[m.sup.3]).

Bound rubber content was also measured by using the following formula:

Bound rubber = [([M.sub.B] - [M.sub.F] - [M.sub.D)] / [M.sub.B]] x 100% (4)

where [M.sub.B] - weight of the uncured mix before immersing; [M.sub.F] = weight of the filler in the uncured mix; and [M.sub.D] = weight of the rubber dissolved in the solvent.

The physical properties are summarized in tables 4 and 5.

An air permeability test was carried out according to ISO 2782.

Results and discussion

From the chemical analysis data of the bentonite clay, it is clear that the bentonite clay sample was impure in nature. The presence of transition metals also indicated the impurity of the clay. The atomic percentage of different metals, as reported in table 1, supports the above fact. The bentonite clay was basically a mixture of calcium and sodium montmorillonite. The cation exchange capacity of this unfractionated bentonite clay was low compared to commercially available synthetic montmorillonite (ref. 22).

FTIR analysis

The FTIR spectra shown in figure 1 compares the bentonite clay with the RF resin modified bentonite clay. The bentonite clay shows the following characteristic bands: ~3,700-3,400 [cm.sup.-1] (OH stretching of Si-OH groups), ~1,640 [cm.sup.-1] (deformation vibrations of the interlayer water in the clay) and ~1,030 [cm.sup.-1] (asymmetric Si-O-Si stretching) (ref. 23). The FTIR study for both the samples is almost the same except for the presence of extra peaks for the modified clay ~2,925 and 2,854 [cm.sup.-1] due to the methylene ([CH.sub.2]) linkages present in the RF resin. Since the amount of RF resin used is very low (10% with respect to clay), the band due to the phenolic OH stretch overlaps with the OH stretch of the silanol (Si-OH) groups of the bentonite clay. Figure 2 compares the spectra of compounds B and D. The presence of phenolic groups in D is not detectable due to the overlapping of the characteristic bands with those of SBR and bentonite clay. For the detection of resol in the composites, acetone extraction of SBR/RF modified bentonite clay masterbatch was carried out for 24 hours and then the extract was concentrated by drying, poured over a KBr pellet and then the FTIR spectrum was recorded and shown in figure 2. The extracted RF resin showed all the characteristic phenolic bands: ~3,250 [cm.sup.-1] (OH stretching), ~1,390-1,320 [cm.sup.-1] (interaction of O-H deformation and C-O stretching) and ~1,110 [cm.sup.-1] (aromatic C-H deformation) (ref. 24), thereby providing evidence for the presence of resol resin in the resin modified batches.

Dispersion morphology of SBR/clay nanocomposite

WAXD

Figure 3 shows the x-ray diffraction patterns of bentonite clay and compounds B and D, respectively. Bentonite clay shows a characteristic diffraction peak at 20 ~ 7.2[degrees] corresponding to an inter-gallery distance of 1.23 nm. Compound B, on the other hand, does not exhibit any shift in the diffraction peak, and thus the inter-gallery distance in compound B remains the same as that in bentonite clay. The XRD of RF-modified bentonite clay shown in figure 4 shows a peak at 6.1[degrees] and this corresponds to the inter-gallery spacing of 1.4 nm. The peak shift from 7.2 to 6.1[degrees] definitely indicates intercalation of the clay layers by the RF resin. However, the double peaks observed in the intensity curve for compound D probably represent two populations of intercalated bentonite - one coming from the RF modified clay and the other from SBR intercalated bentonite. The two diffraction peaks observed in compound D at 6.3[degrees] and 4.2[degrees] correspond to the inter-gallery spacing of 1.4 and 2.1 nm, respectively. This is clearly an indication of intercalated nanocomposite (ref. 25). Thus, the RF resin modification of the bentonite clay is responsible for the swelling of the bentonite clay galleries.

TEM

The TEM photomicrograph of compound D shown in figure 5 points out the exfoliated as well as the intercalated nature of the SBR/RF resin modified bentonite clay nanocomposite. Most of the clay platelets are observed to be uniformly dispersed throughout the polymeric matrix with some intercalated clay platelets, which have thickness ranging from ~0.1-0.15 [micro]m. Figure 6 shows clearly the SBR/resol intercalated clay particle, coagulated resol particle, mechanically bound robber chain with intercalated resol chain and several resol particles scattered in the SBR matrix.

Effect of clay on cure kinetics

The cure properties of the compounds are compiled in table 3. The extent of curing (given by the [DELTA]torque values) is higher in the case of compounds D and F compared to compound B. This may be explained due to intercalation of the SBR rubber chains into the galleries of the bentonite clay resulting in higher rubber-to-filler interaction. The [t.sub.s2] (scorch time) for the compound B was lower compared to that of compounds D and F, and this was probably due to the presence of different free transition metals in the bentonite clay. It is known that transition metals reduce the scorch safety of rubber compounds. In the case of compounds D and F, scorch safety remained comparable. However, the [t.sub.c90] (optimum cure time) was higher in the case of compounds D and F. This trend is also shown by the decrease in cure rate index (CRI) values. This behavior is in contrast to that exhibited by organo-modified montmorillonite, which increased the cure rate and reduced the scorch safety of the rubber vulcanizates (refs. 26 and 27). This was due to the presence of the amine moiety in the organo-modified montmorillonite. However, in the present work, no such amine has been used and hence no such increase in cure rate was observed. The lower cure rate can be explained based on the increased interaction of the curative with the intercalated clay layers. It has been reported that fillers like silica reduce the cure rate due to interaction of the polar -OH groups with the accelerator molecules (ref. 28). Probably, exfoliation of the clay layers results in a higher amount of silica being available for the accelerator fragments.

In the case of compounds [N5.sub.660] and [N10.sub.660], extent of curing (A torque) value was higher compared to B, D and F. This was due to the absence of any curative deactivating (like silanol-OH) group in the compounds. The trend of extent of curing (given by the [DELTA]torque values), [t.sub.s2] (scorch time), [t.sub.c90] (optimum cure time) and cure rate index (CRI) of compounds [N40.sub.660], [N35D5.sub.660] and [N40D5.sub.660] can be explained as above.

Physical properties

The unaged and aged tensile properties of the compounds are compared in tables 4 and 5. The data represented in the figures are the mean of five measurements. Regarding the unaged mechanical properties, viz., 50 and 300% modulus, tensile strength of D and F was found to be better compared to compound B. The intercalation and/or exfoliation of the SBR chains in the resol-modified clay are probably responsible for the increase in tensile properties. Both B and D contain the same phr of bentonite filler, but the sole difference between them is that bentonite is resol-modified in D. As a result the corresponding increase in the unaged 50% modulus, 300% modulus, tensile strength and EB are ~12, 45, 90, 28 and 110%, respectively, over compound B. The TEM micrograph (figure 5) corroborates the partial exfoliation of the clay platelets in D, and this was responsible for the increase in mechanical properties. Similarly, the corresponding increase in the unaged 50% modulus, 300% modulus, tensile strength and EB are ~59, 182, 214 and 14%, respectively, for compound F over compound B, and this trend can also be ascribed to the intercalation of the rubber chains in the clay and/or exfoliation of the clay platelets in the SBR matrix. The aged tensile property trends are in line with those observed for their unaged counterparts. The increase in the aged modulus values over the unaged specimens can be ascribed due to the increase in crosslink density as a result of aging. The aged tensile strength of the resol-modified nanocomposites shows improvement, and this may be due to the presence of phenolic moieties in the resol which are known to exhibit antioxidant behavior, thus retarding polymer chain degradation which gets facilitated during high temperature aging. The aged EB was lower than the unaged values, and this was due to the increased crosslink density of the samples on aging. The same reason can explain the higher tear strength of compounds D and F.

The durometer A, as reported in table 4, echoes the modulus trends of the nanocomposites containing RF modified bentonite clay. In the SBR/bentonite clay nanocomposites, the swelling index decreases with an increase in bentonite clay loading, and this was not only due to intercalation and/or partial exfoliation of the SBR chains in the gallery gap of the bentonite clay, but also due to the presence of resol in the matrix. Very high amounts of bound rubber and Mooney viscosity also support the fact. The resol resin is probably forming semi-crosslinked gel in the matrix.

The rebound resilience of the compounds D and F was found to be lower compared to compound B. This was probably due to restricted mobility of the SBR chains within the bentonite layers, thereby increasing the relaxation time of the SBR chains and hence decreasing the storage energy of the compound. It was also observed that the set property was better in the case of compounds D and F.

The FTFT of compounds D and F was better compared to compound B. Compound D was relatively better than compound F. This was probably due to the higher hardness of compound F. It indicated that at a fixed strain, the durability of the compounds were better.

It was found that at equivalent loading of carbon black (compound D, [N5.sub.660] and F, [N10.sub.660]), the strength property of the resol-modified nano-clay filled compounds was better in comparison to black filled compound. The retention of the strength property after aging was also better in the case of clay filled compound due to the presence of phenolic compound in the matrix. Hardness and the bound rubber was also higher in compounds D and F. Higher Mooney viscosity of the compounds D and F compared to [N5.sub.660] and [N10.sub.660] can be explained based on the presence of resol in the clay-filled compounds. Rebound resilience of compounds D and F was inferior compared to [N5.sub.660] and [N10.sub.660]. The compression set of the nano-clay filled compounds was comparable with corresponding black filled compounds. Fatigue life of the compounds D and F was inferior in comparison to the black-filledcounter parts.

The replacement of 5 phr of N660 carbon black by resol modified clay exhibited low modulus and low tensile strength and hardness. This may be due to low extent of curing (given by the [DELTA]torque values). This was also supported by the high swelling index and high volume fraction. Higher elongation was also supported by the above fact. Tear strength was higher in the [N35D5.sub.660] compound. Higher Mooney viscosity was observed in the [N35D5.sub.660] compound due to the presence of resol. However, the rebound resilience was slightly lower in comparison to [N40.sub.660]. Compression set and fatigue life were comparable. The air permeability was much better in the [N35D5.sub.660] compound due to the presence of nano-structure clay in the matrix. The same observation was noticed in the case of compounds D and F. Addition of 5 phr of resol modified clay ([N40D5.sub.660]) exhibited comparable stress-strain and tear properties. Bound rubber and Mooney viscosity were higher. As expected, the rebound resilience and fatigue life was lower in comparison to compound [N40.sub.660]. However, compression set was better in the case of [N40D5.sub.660]. The air permeability of the compound was much better than the control compound, i.e., [N40.sub.660]. It was also observed that the retention of the physical properties after aging was much better in the case of [N35D5.sub.660] and [N40D5.sub.660].

Mechanism of reinforcement

From the above results, a mechanism can be proposed for explaining the superior mechanical and physical properties of resol-modified bentonite clay reinforced SBR nanocomposites. The reinforcement is due to partial exfoliation and intercalation of the SBR rubber into the bentonite clay, which is probably facilitated by the initial intercalation of the clay galleries by the resol resin during synthesis. In water suspension, the clay forms the house of cards structure and swells up. AS the sizes of the resorcinol and formaldehyde molecules are small, they can easily penetrate into the interlayer spacing of the clay particles. On polymerization, the resorcinol and formaldehyde interact to form the RF resin, which would not only be formed within the gallery gap of the clay particles, but some might also be adsorbed on the clay surface due to polar-polar interactions and thus prevent the individual clay particles from coming closer in the solution. However, the SBR latex particles are stabilized by an anionic surfactant. Under this condition, the SBR latex can also penetrate the interlayer of the clay due to strong polar or hydrogen bonding with the resol-modified clay particle. Further, the intercalated RF resin also has some synergism with the SBR rubber chains. Moreover, the resin also mechanically anchors the rubber chain on coagulation and this is evident from the increase of bound robber for D and F. A substantial increase in Mooney viscosity of D and F also reinforces this mechanical anchoring concept. The TEM image of compound D also gave some pictorial support of the above mechanism. The reinforcement mechanism is summarized in figure 7.

It was found that the fatigue life of modified clay containing compounds was inferior in comparison to black-filled compounds. This was surprising, as the compounds D and F exhibited higher fatigue life compared to compound B. The reason was the better rubber-to-filler interaction. But, in the carbon black filled compound, it was not reflected. The reason may be due to the plate-like nature of the clay. The carbon black consists of nano particles with a nearly spherical shape. The interaction of the carbon black with rubber is a strong physico-chemical interaction, whereas, the interaction of the clay with rubber is due to the van der Walls force of interaction. The interaction at the edge of the clay particles is the weakest. Therefore, during the cyclic deformation, the stress concentration is highest at the edge of the clay particles. Thus, the flaws can generate easily at these points compared to the strongly attached nearly spherical carbon black particles. Thus, the clay-containing compounds exhibited low fatigue life compared to black-filled compounds. A pictorial presentation of the above mechanism is represented in figure 8.

Conclusions

Unfractionated bentonite clay suspension was modified with in-situ generated resol resin formed by the reaction of resorcinol and formaldehyde. SBR latex and the resol-modified clay were mixed to prepare SBR/bentonite clay nanocomposites by the latex blending technique. An FTIR study proved the presence of the resol in the resol-modified bentonite. Incorporation of this modified clay in the SBR matrix resulted in intercalation and/or exfoliation as observed from the XRD and TEM results. At equivalent carbon black loading (low phr level), resol-modified clay was found to exhibit better properties. Thus, total replacement of the carbon black (low structure) can be done by the resol-modified clay. Fatigue life and the air permeability of the resol modified clay compounds were much better in comparison to the carbon black loaded (10-15 phr) compound. Partial replacement and addition of the resol-modified clay exhibited more or less equivalent results. This method of co-coagulating rubber latex and resol-modified pristine clay is very promising from the industrial viewpoint due to the low cost of the pristine clay, simplicity of the preparation technique, environmental friendliness and good cost/performance ratio.

[FIGURE 7 OMITTED]

[FIGURE 8 OMITTED]

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by Sugata Chakraborty, Saikat Dasgupta and Rabindra Mukhopadhyay, Hari Shankar Singhania Elastomer and Tyre Research Institute; Samar Bandyopadhyay, J.K. Tyre; Mangala Joshi, Indian Institute of Technology; and Suresh C. Ameta, Mohanlal Sukhadia University
Table 1--typical physical and chemical
characteristics of unfractionated
bentonite clay

Parameter Average values
 (based on five
 individual
 measurements)

Moisture @ 105[degrees]C by 10.14
 infrared moisture balance
pH @ 25[degrees]C, 5% aqueous solution 9.04
Nitrogen surface area, [m.sup.2]/g 76.60
Specific gravity @ 26[degrees]C 2.18
325 mesh (45 gym) sieve residue (%) <0.50
Cation exchange capacity, CEC (meq/ 59.0
 100 g of sample)
Concentration of elements using energy
 dispersive x-ray spectrophotometer, EDS
 (Weight, %):
 Sodium (Na) 0.88
 Calcium (Ca) 0.29
 Aluminum (AI) 8.33
 Silicon (Si) 14.84
 Potassium (K) 0.16
 Magnesium (Mg) 0.36
 Iron (Fe) 4.78
 Titanium (Ti) 0.89
 Carbon (C) 3.31
 Oxygen (O) 66.17

Table 2--compound formulations

Material [N5. [N10. B D F
 sub.660] sub.660]

SBR 1502 100 100 100 100 100
ZnO 3 3 3 3 3
Stearic acid 1 1 1 1 1
TBBS 1 1 1 1 1
Sulfur 1.75 1.75 1.75 1.75 1.75
Aromatic oil -- -- -- -- --
Clay from resol-modified -- -- -- 5 10
 nanocomposite master
 batch
Bentonite clay -- -- 5 -- --
Carbon black (N660) 5 10 -- -- --

Material [N40 N35[D5 N40[D5
 .sub.660] .sub.660] .sub.660]

SBR 1502 100 100 100
ZnO 3 3 3
Stearic acid 1 1 1
TBBS 1 1 1
Sulfur 1.75 1.75 1.75
Aromatic oil 5 5 5
Clay from resol-modified -- 5 5
 nanocomposite master
 batch
Bentonite clay -- -- --
Carbon black (N660) 40 35 40

Table 3--cure characteristics of the studied compounds

Material B D F [N5.
 sub.660]

Maximum 6.3 7.3 7.7 10.6
 torque ([T.sub.max.]),
 (dN-m)
Minimum 1.6 1.4 1.4 0.8
 torque ([T.sub.min.]),
 (dN-m)
[DELTA] torque = 4.7 5.9 6.3 9.8
 [T.sub.max.] - [T.sub.min.]
 (dN-m)
[t.sub.s2] (min.) 13.3 16.0 15.7 9.5
[t.sub.c90] (min.) 24.3 31.6 34.9 16.6
CRI ([min.sup.-1]) 9.03 6.39 5.21 14.0

Material [N10. [N40. N35[D5.
 sub.660] sub.660] sub.660]

Maximum 10.2 14.7 10.9
 torque ([T.sub.max.]),
 (dN-m)
Minimum 0.9 1.4 1.7
 torque ([T.sub.min.]),
 (dN-m)
[DELTA] torque = 9.3 13.2 9.3
 [T.sub.max.] - [T.sub.min.]
 (dN-m)
[t.sub.s2] (min.) 8.0 6.0 7.3
[t.sub.c90] (min.) 14.9 13.2 24.6
CRI ([min.sup.-1]) 14.5 13.9 5.8

Material N40[D5.
 sub.660]

Maximum 10.3
 torque ([T.sub.max.]),
 (dN-m)
Minimum 1.6
 torque ([T.sub.min.]),
 (dN-m)
[DELTA] torque = 8.8
 [T.sub.max.] - [T.sub.min.]
 (dN-m)
[t.sub.s2] (min.) 7.2
[t.sub.c90] (min.) 23.2
CRI ([min.sup.-1]) 6.2

Table 4--physical properties of the compounds at
equivalent carbon black loading

Parameter B D F

50% modulus 0.58 0.65 0.92
 (MPa) (0.61) (0.69) (0.94)
300% modulus 1.75 2.54 4.94
 (MPa) (1.74) (2.70) (5.52)
TS (MPa) 2.10 4.10 6.60
 (1.90) (4.00) (7.84)
EB (%) 361 461 410
 (350) (403) (378)
Hardness (duro. A) 45 46 53
 (44) (44) (51)
Swelling index 5.94 5.30 4.33
Vr 0.140 0.159 0.190
Tear (N/mm) 12.90 20.15 26.52
Bound rubber (%) 8.2 33.9 41.4
Mooney ML 46.7 58.4 72.4
 (1+4) @ 100[degrees]C
Rebound 67.8 41.5 24.2
 resilience
Compression set 24.7 10.2 13.6
 (%), (@70[degrees]C,
 72 hrs.)
FTFT (KCys) 4.84 27.0 24.2
Air permeability
 ([m.sup.2]/Pa-sec) 2.34x 1.64x 1.15x
 [10.sup.-16] [10.sup.-16] [10.sup.-16]

Parameter [N5. [N10.
 sub.660] sub.660]

50% modulus 0.91 1.02
 (MPa) (0.94) (1.1)
300% modulus 3.4 3.6
 (MPa) (-) (-)
TS (MPa) 4.9 5.8
 (2.7) (4.0)
EB (%) 387 405
 (242) (280)
Hardness (duro. A) 44 48
 (48) (50)
Swelling index 4.45 4.35
Vr 0.191 0.188
Tear (N/mm) 22.0 25.0
Bound rubber (%) 14.02 18.20
Mooney ML 48.8 48.4
 (1+4) @ 100[degrees]C
Rebound 68.4 68.0
 resilience
Compression set 9.0 11.0
 (%), (@70[degrees]C,
 72 hrs.)
FTFT (KCys) 29.4 29.4
Air permeability
 ([m.sup.2]/Pa-sec) 2.20x 2.11x
 [10.sup.-16] [10.sup.-16]

(The result in parenthesis represents the aged property.)

(Mixing was done in a single stage.)

Table 5--physical properties of the
black-filled compounds

Parameter [N40. N35[D5. N40[D5.
 sub.660] sub.660] sub.660]

50% modulus 1.12 1.0 1.14
 (MPa) (1.3) (1.2) (1.5)
300% modulus 7.71 6.00 7.20
 (MPa) (12.7) (9.2) (10.7)
TS (MPa) 16.2 13.5 14.2
 (13.2) (14.6) (14.0)
EB(%) 498 551 525
 (305) (414) (366)
Hardness (duro. A) 58 56 59
 (59) (60) (63)
Swelling index 3.38 3.62 3.48
Vr 0.164 0.154 0.283
Tear (N/mm) 50.4 53.4 49.9
Bound rubber (%) 20.2 24.3 26.0
Mooney ML 55.2 62.4 65.2
 (1+4) @ 100[degrees]C
Rebound 57.1 54.6 53.8
 resilience
Compression set 32.7 36.6 27.5
 (%), (@105[degrees]C,
 72 hrs.)
FTFT (KCys) 26.0 23.3 19.8
Air permeability
 ([m.sup.2]/Pa-sec) 1.74x 1.57x 1.45x
 [10.sup.-16] [10.sup.-16] [10.sup.-16]

(The result in parenthesis represents the aged property.)

(Mixing was done in two stages, master and final.)
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Author:Chakraborty, Sugata; Dasgupta, Saikat; Mukhopadhyay, Rabindra; Elastomer, Hari Shankar Singhania; Ba
Publication:Rubber World
Date:Aug 1, 2010
Words:6003
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