Silica reinforcement

The incorporation of silica into epoxy resins has little effect on tensile strength. The tensile strength of reinforced epoxy resin is 30-84 MPa, compared to values of 68-72 MPa for silica-reinforced polymer. The flexnral modulus falls from 80 GPa for the unreinforced polymer to 15 GPa for the reinforced polymerm while elongation at break remains virtually unchanged. 

Pasquel-Sanchez and Martinez [157] studied the effect on mechanical properties of incorporating silica nanoparticles into an epoxy resin based on the diglycidyl ether of bisphenol A. 

Choudhary et al. [158] determined the mechanical properties of polymers produced by the mixing of two incompatible components nanoclay polypropylene and rice husk silica. 

An analysis of the composite mechanical performance indicated that the state of mixing influenced the filler-matrix interaction and the composite tensile modulus. Results showed that an increase in composite crystallinity was related to the increase in tensile modulus. It was also found that reducing the particle size of the filler has 

Ethylene diamine and maleic anhydride-grafted PP Medi cal 161 

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Similar types of lamellar morphologies were observed for triblock copolymers of diphenylsiloxane and dimethylsiloxane having 40 wt% polydiphenylsiloxane, using electron microscopy, 47-148>. The lamellae thickness was approximately equal to the chain length of the rigid polydiphenylsiloxane blocks. These copolymers showed elastomeric properties comparable to those of conventional silica-reinforced, chemically crosslinked silicone rubbers. Tensile tests yielded an initial modulus of 0.5-1 MPa, tensile strength of 6-7 MPa and ultimate elongation between 400 and 800 %. 

Currently, breast cancer is the most frequently diagnosed cancer in both white and African-American women. According to latest reports, of the 662,870 cancer cases reported for women in 2005, 32% were breast cancer. The incidence of breast cancer increased from 1 in 20 in 1960 to 1 in 8 today. More than 100,000 women per year require mastectomy for treatment, and every year 75% decide to have reconstmction. About half the number of these women select prostheses made of silica-reinforced silicone-rubber shell filled with silicone gel, while the other half have the same shell filled with physiological saline. Reportedly, gel-fiUed prostheses feel more natural, but are associated with true or perceived health problems and remain highly controversial. 

Recent work has focused on a variety of thermoplastic elastomers and modified thermoplastic polyimides based on the aminopropyl end functionality present in suitably equilibrated polydimethylsiloxanes. Characteristic of these are the urea linked materials described in references 22-25. The chemistry is summarized in Scheme 7. A characteristic stress-strain curve and dynamic mechanical behavior for the urea linked systems in provided in Figures 3 and 4. It was of interest to note that the ultimate properties of the soluble, processible, urea linked copolymers were equivalent to some of the best silica reinforced, chemically crosslinked, silicone rubber... 

The addition of a coupling agent can dramatically improve the abrasion resistance of compounds containing silica reinforcement. The effect is dependant on the surface area of the silica. 

Silica fillers also react with the rubber causing an increase in viscosity and dry and unmanageable processing behaviour. Filler activators need to be added to silica-reinforced compounds to overcome these problems. The usual filler activators used are diethylene glycol, polyethylene glycol and amines such as triethanolamine. Some of these activators not only overcome the problems of processing and accelerator absorption, but depending on the cure system used, will also act as vulcanisation activators. 

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... 

Mihara S (2009) Reactive processing of silica-reinforced tire rubber. Enschede, The Netherlands, Ph.D. thesis. ISBN 978-90-365-2839-9... 

Introduction by Michelin et Cie. of the "Green Tyre", with a silica-reinforced tread, rather than with carbon black, and using solution-polymerised rather than emulsion-polymerised SBR, for 30% reduced rolling resistance and corresponding energy saving... 

Many effects can be produced by the pores in filler particles. One is that pores in silica reinforce rubber. During mixing, rubber chains migrate into the pores which increase the adhesion between the phases. The selective absorption of low molecular weight components affects the performance of paints and other materials. Microporous membranes and fibers are produced to clean water and selectively absorb certain solutes. 

Methods of filler pretreatment thermal treatment at 800°C and hexadecanol treatment were performed to study the effect that hydroxyl groups have on silica reinforcement ... 

The technology is still not problem-lree. Carbon black is a conductive filler therefore it does not cause an accumulation of static electricity formed because of fi ictional contact with the road. In a silica reinforced tire, static charge is a problem. Remedial actions have already been taken by the introduction of neoalkoxy zirconates and titanates which are capable of dissipating electrostatic charges. The future of the tire is not yet clear but it is expected that silica s share of this market will be 150,000 tons. This will be supplied to make full silica and silica/carbon black tires. 

Akrochem RubberSil. [Akrochem] Precipitated amcxphous silica reinforcement for rubber mech. goods, tires, footwear. 

Hubersil . [J.M. Huber] Hydrated silica reinforcing filler, carrier for rubber parts incl. hose, belting, molded and extruded parts, tires, footwear, wire and cable, thermqilastic elastomers, caulks and sealants. 

In another study, the ground reclaim rubber was blended with stirene-butadiene rubber and cured under pressure at 160°C. The cured sheets were silica-reinforced by soaking in tetraethyl ortho silicate, then in an aqueous solution of n-butyl amine catalyst, followed by heat treatment at 50°C. The tensile properties of the blends containing conventionally incorporated silica, with no coupling agent, were superior to those containing silica incorporated by the sol-gel reaction [21]. 

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. 

The use of silica has given a new light to this domain, because, contrary to carbon black, dispersibility is one of the key properties for achieving silica-reinforced mixes (EP0157703 et al., 1984 Chevallier and Morawski, 1986 Evans and Waddell, 1995 Cochet et al., 1993,1994). 

Compared to morphology, filler chemistry has been only slightly studied, partly because of the difficulty of such characterizations and more probably because since the 1970s reinforcement is broadly considered as a physical interaction between elastomer and filler. So carbon black chemical characterizations mainly date from the 1960s, and few new technical methods have been applied to carbon black surface characterization since then. The situation is somewhat different for silicas, because silica reinforcement is the consequence of a chemical reaction of silane with silica surface. Few studies have been published in the elastomer reinforcement area, probably because silica surface was already well characterized for other applications. 

Silanol surface content cannot reasonably be considered an indicator for silica reinforcement ability indeed, because of its size, the coupling agent used to bond silica surface and elastomer cannot react with more than two or three... 

Obviously, if any coupling agent is used, polymer adsorption will naturally occur (Bomo, 1989 Killian etal., 1987) in addition, because of the high polarity of silica, some direct interaction between silica aggregates will also take place and constitute an additional filler-filler network. These effects will not happen in silica-reinforced systems when an appropriate amount of coupling agent is used. 

High-tensile-strength butyl compounds generally use FEF- or GPF-grade carbon blacks. Vulcanization systems tend to be based on thiazole accelerators such as mercaptobenzothiazole disulfide (MBTS) and thiuram accelerators such as tetramethylthiuram disulfide (TMTD). Low-tensile-sfrengfh compounds will use a clay or silica reinforcing filler in place of carbon black. 

In silica reinforcement systems containing TESPT, Wolff has suggested that the reaction is similar when the TESPT/silica intermediate is present instead of sulfur, in which case the crosslinking agent is the polysulfidic sulfur chain. Wolff showed that mercaptobenzothiazyl disulfide (MBTS) reacts with the tetrasulfane group, thus forming 2 mol of the polysulfide ... 

Reynaud, E., Jouen, T., Gauthier, C., Vigier, G., and Varlet, J., NanoflUers in polymeric matrix a study on silica reinforced PA6, Polymer, 42, 8759-8768 (2001). 

The ablative characteristics of the carbon fabric RP composites were significantly different from that containing silica reinforcement. The carbon reinforced composites had higher heats of ablation, poorer... 

Hui, S., Chaki, T. K., Chattopadhyay, S., Exploring the simultaneous effect of nano-silica reinforcement and electron-beam irradiation on a model LDPE/ EVA-based TPE system. Polymer International 2009,58,680-690. 

Lin Lin, J.-C. Investigation of impact behavior of various silica-reinforced polymeric matrix nanocomposites. Compos. Struct. 84 (2008) 125-131. 

Fig. 5.4 Crack initiation value A of silica-reinforced NR vulcanizates for different specimen thicknesses.

Values of fJf vs. E/Eq for a series of silica-reinforced silicone elastomers are shown in Figure 10.19. The most surprising feature is the relatively large value of fjf, which approaches 0.6 for fully reinforced materials. This means... 

Tschoegl s result is especially interesting in the light of a recent proposal by Shuttleworth (1968, 1969) that equilibrium polymer-filler debonding is responsible for decreased tensile strength at elevated temperatures. This is contrary to the viscoelastic mechanism of high-temperature failure of Halpin and Bueche (1964), which was developed in an earlier section. A possible resolution of the relative importance of the two proposed mechanisms could lie in the application of Tschoegl s experiment to carbon black- or silica-reinforced materials. 

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