Silica in rubber

Polyacetylene-, Thiophene- and Pyrrole-Coated Silica in Rubber. 197... 

Figure 18.6. Torque vs. mixing time of silica in rubber. [Adapted, by permission, from Bomo F, Meeting of the Rubber Division, ACS, Montreal, May 5-8, 1996, paper E.]...

Following the preparation of this paper, the author s attention was drawn to a paper presented by D. C. Edwards at the 1978 A.C.S. Rubber Division meeting in Boston. The evidence presented supports the mechanism developed here, and indicates that his work was planned and successfully concluded with these speculations in mind. Later discussions with S. Wolff make it appear likely that the function of the silane (produced commercially as Si69) in increasing the reinforcing activity of silica in rubber is to provide a mechanism similar to the one described... 

The use of silica in rubber mixes cannot be considered as new at all, because this filler has been used in rubber formulations since the beginning of the 20th century (Voet et al., 1977). Silicas are not reinforcing fillers in the proper sense, because silica-reinforced mixes exhibit much lower mechanical properties, particularly considering modulus at break and abrasion resistance. So silicas weren t used as reinforcing fillers but mainly in association with carbon black. 

In very recent years, tiller dispersion characterization has been brought again into light because of the difficulties encountered to disperse silica in rubber (Bomal etal., 1998,1993). 

TESPT, a bifunctional polysulfidic organosilane, was introduced as a coupling agent to improve the reinforcement properties of silicas in rubbers. Use of coupling agents offers the following advantages ... 

The properties of the synthetic silicas are related to the BET surface area, particle size, and particle shape, as is the case with carbon black, but also to silanol group density. Table 1.8 summarizes the characteristics of synthetic silicas. In rubber processing applications, the degree of reinforcement obtained with silicas is related, like carbon black, to the external surface area. The internal surface area is not conducive to reinforcement it is believed that the internal surface is inaccessible to large polymer molecules and thus excluded from reinforcement. 

The most common fillers used in rubber base formulations will be briefly described. On the basis of their chemical structure, these fillers may be classified in five broad groups silicates, silicas, metal oxides, calcium carbonate, and carbon blacks. 

Although natural quartz, cristobalite and opal are used as fillers, only synthetic products (fumed and precipitated silicas) find use as fillers in rubber base adhesives. 

Fine silica network is visible in the in situ silica-filled rubber composite synthesized from 50 wt% of TEOS, producing almost 15 wt% of sdica. On the other hand, addition of only 10 wt% of precipitated silica externally gives distinct aggregations. 

Finer dispersion of silica in THF provides higher surface area to interact with the rubber molecules and the resultant nanocomposites show better mechanical properties than their macrocounterparts. Figure 3.13 illustrates these results. 

FIGURE 3.16 Morphology and visual appearance of acrylic rubber (ACM)-silica and epoxidized natural rubber (ENR)-silica hybrid composites prepared from different pH ranges (a) transmission electron microscopic (TEM) picture of ACM-siUca in pH 1.0-2.0, (b) scanning electron microscopic (SEM) picture of ACM-siUca in pH 5.0-6.0, (c) SEM image of ACM-siUca in pH 9.0-10.0, (d) TEM picture of ENR-silica in pH... 

FIGURE 3.20 Occurrence of silica in (a) less interactive and (b) more interactive rubber matrices. (From Bandyopadhyay, A., De Sarkar, M., and Bhowmick, A.K., J. Polym. Set, Part B Polym. Phys., 43, 2399, 2005. Courtesy of Wiley InterScience.)... 

Effects of nanoclay and silica in mbber matrices have been discussed in earlier chapters. Recently, several other nanofillers have been investigated and have shown a lot of promise. All these fillers have not been investigated on rubbers extensively, although they have great potential to do so in the days to come. In this chapter, we have compiled the current research on mbber nanocomposites having nanofillers other than nanoclay and nanosilica. Further, this chapter provides a snapshot of the current experimental and theoretical tools being used to advance our understanding of mbber nanocomposites. 

Recently, several metal oxides apart from silica have been investigated and reported for mbber-based nanocomposites. Some important and commercially meaningful oxides used in rubber are zinc oxide (ZnO), magnesium hydroxide (MH), calcium carbonate, zirconate, iron oxide, etc. 

FIGURE 12.10 Tapping mode atomic force microscopy (AFM) images of the section analyzes of ethylene-propylene-diene monomer (EPDM) rubber-melamine fiber composites. A, composite containing no dry bonding system B, composite containing resorcinol, hexamine, and silica in the concentrations 5, 3, and 15 phr, respectively. 

FIGURE 12.18 Stress-strain curves of rubber-fiber composites developed for solid rocket motor insulator A, ethylene-propylene-diene monomer (EPDM) rubber-carbon fiber composites B, EPDM mbber-melamine fiber composites C, EPDM mbber-aramid fiber composites and D, EPDM rubber-aramid pulp composites. 1 and 2 stands for unaged and aged composites respectively. Carbon fiber- and melamine fiber-reinforced composites contain resorcinol, hexamine, and silica in the concentrations 10, 6 and 15, respectively and aramid fiber- and aramid pulp-based composites contain resorcinol, hexamine, and silica in the concentrations 5, 3 and 15, respectively. (From Rajeev, R.S., Bhowmick, A.K., De, S.K., and John, B., Internal communication. Rubber Technology Center, Indian Institute of Technology, Kharagpur, India, 2002.)... 

It is demonstrated in Figure 22.11 that the quasi-static stress-strain cycles at different prestrains of silica-filled rubbers can be well described in the scope of the above-mentioned dynamic flocculation model of stress softening and filler-induced hysteresis up to large strain. Thereby, the size distribution < ( ) has been chosen as an isotropic logarithmic normal distribution (< ( i) = 4> ) = A( 3)) ... 

Phenolic antioxidants in rubber extracts were determined indirectly photometrically after reaction with Fe(III) salts which form a red Fe(II)-dipyridyl compound. The method was applicable to Vulkanox BKF and Vulkanox KB [52]. Similarly, aromatic amines (Vulkanox PBN, 4020, DDA, 4010 NA) were determined photometrically after coupling with Echtrotsalz GG (4-nitrobenzdiazonium fluoroborate). For qualitative analysis of vulcanisation accelerators in extracts of rubbers and elastomers colour reactions with dithio-carbamates (for Vulkacit P, ZP, L, LDA, LDB, WL), thiuram derivatives (for Vulkacit I), zinc 2-mercaptobenzthiazol (for Vulkacit ZM, DM, F, AZ, CZ, MOZ, DZ) and hexamethylene tetramine (for Vulkacit H30), were mentioned as well as PC and TLC analyses (according to DIN 53622) followed by IR identification [52]. 8-Hydroquinoline extraction of interference ions and alizarin-La3+ complexation were utilised for the spectrophotometric determination of fluorine in silica used as an antistatic agent in PE [74], Also Polygard (trisnonylphenylphosphite) in styrene-butadienes has been determined by colorimetric methods [75,76], Most procedures are fairly dated for more detailed descriptions see references [25,42,44],... 

Diatomaceous earth, a fairly pure silica, formed from the skeletons of minute organisms, known as diatoms. In rubber compounding it is used as an inert filler. 

Silica reinforced rubber, 22 703 Silica sheets, 22 383-385 Silica-silane system, 22 377-378 Silica sol-gel fiber processing, 23 80 Silica sols, 22 383, 473-474 applications of, 22 394 modification of, 22 393-394 preparation of, 22 392-393 properties of, 22 391-392 purification of, 22 393 Silica, solubility in steam, 23 212-213 Silica-supported activated manganese dioxide, 76 568... 

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