Epoxy/silica system

The ability of organically modified ceramics based on alumina, zirconia, titania, or silica (and mixtures of each) to function as abrasion-resistant coatings has also been studied (62). For example, polycarbonate, when coated with an epoxy—aluminosilicate system, experiences a significant reduction in the degree of hazing induced by an abrader, as compared to uncoated polycarbonate. 

The particle size and distribution are important for maximizing the shelf fife of epoxy-DICY systems. Generally optimum properties are produced when the particle size of the DICY is less than 10 im. Usually fumed silica is used to keep the DICY particles in suspension and evenly distributed in the epoxy resin. 

Comparative sag resistance properties of various commercial types of fumed silica are shown in Table 9.7. In most liquid epoxy resin systems, fumed silica is only employed at a 1 to 3 wt percent basis to provide thixotropic characteristics. 

Conn, R. C., How Silane Fumed Silica Influences Adhesion Properties of a Model Epoxy Adhesive System after Water Immersion, Adhesives Age, February 2002. 

Covers a two-part epoxy-resin system in the form of a bisphenol "A" epoxy resin filled with fumed silica and carbon microspheres and a separate aromatic diamine curing agent. 

The filler effects on the chemoviscosity of thermosetting resins have not been studied extensively, but are vital to understanding the rheology of filled thermosets. For example, the effects of filler concentration on viscosity can be used in process control to monitor batch-to-batch variations or to provide essential information for research into alternative filler/resin batches. Ng and Manas-Zloczower (1993) examined an epoxy-resin system with silica filler and established that the elastic modulus of the resin can be expressed in terms of... 

Dutta and Ryan (1979) examined the effects of fillers (carbon black and silane-surface-treated silica) on the cure of DGEBA/MPDA epoxy-amine systems. They found that the rate constants of the cure reaction are affected by the presence of the fillers in an unusual fashion (a function of temperature and concentration) with respect to concentrations up to 10%. This was postulated to be due to the reactive surface groups on the fillers. The reaction order, however, is not affected. 

Kogan et al. (1988) examined the chemorheology of silica- and carbon-fibre-filled epoxyresin systems. They found unusual effects of carbon fibre on the uncured rheology and chemorheology of filled epoxy-resin systems, and related these to the anisotropic namre of the filler shape and the effect of filler surfaces on the kinetics. 

De Miranda et al. (1997) showed the effects of silica flour on the cure of DGEBA/DDM epoxy-resin systems. They noted that there were appreciable decreases in reaction rates for systems with higher filler concentrations than 10 wt.% at high temperatures and conversions above 50%. 

Typical systems are epoxy resins (typically epoxy-novolac systems) with silica fillers, hardeners, catalyst and rubber modifiers used in integrated chip packaging. This process is well illustrated by Figure 6.14. 

Fillers. In practice most epoxy resin systems have fillers incorporated, often simply to reduce cost although they may also assist in gap filling, reduction of creep, reduction of exotherm, corrosion inhibition and fire retardation. Their incorporation will also alter the physical and mechanical properties of the adhesive. Construction resins in particular often include a large volume fraction of sand or silica. 

Figure 24.4 TEM micrographs of systems containing 15 wt% SiOi, both produced from a bisphenol-A epoxy resin grafted with an amine alkoxysilane-coupling agent (a) epoxy/silica hybrid (cocontinuous domains) and (b) epoxy/silica nanocomposite (particulate silica domains).

The theoretical curves of the EBM model in Fig.9 were calculated using the critical exponent t = 2.0 (16) and various values of parameter K corresponding to systems with very strong epoxy-silica interaction (curve 3) and without interaction (curve 2). Lower continuity of the one-stage ETl network was assumed by taking vsicr = 0.02 (curve 4). 

Structure and morphology of the epoxy-silica hybrid systems is determined by (a) reaction mechanism of the sol-gel process in formation of the silica structure,... 

Epoxies are adhesive systems made by a complex chemical reaction. Various resins are made synthetically by reacting two or more chemicals. The resultant resin can then be reacted or cured by the addition of another chemical called a hardener or catalyst. The basic epoxy resin systems are further modified to change their physical properties by the addition of such things as flexihilizers for impact resistance and flexibility, diluents or solvents to reduce the viscosity fillers, and reinforcements hke glass fiber, alumina, silica sand, clay, metal powders, and flakes to change properties such as heat and electrical resistance, fire retardance, strength, and adhesion to certain substrates or materials. 

Microcapsule Induced Toughening. Brown and co-workers have demonstrated that the incorporation of microcapsules into an epoxy matrix do not adversely affect the mechanical properties of the matrix. On the contrary, the fracture toughness measurements of samples cast from an EPON 828 epoxy resin system were observed to increase with concentration up to an optimal concentration that is dependent on the average diameter of the microcapsules. Overall, the incorporation of microcapsules containing DCPD into epoxy samples yielded up to a 127% increase in fracture toughness, outperforming samples containing similar concentrations of silica microspheres, or solid urea-formaldehyde particles (31). 

Chem. Descrip. 77% Salt of unsat. polyamine amides and acidic polyesters with 20% 2-butoxyethanol, 2% xylene, 0.5% ethylbenzene Uses Wetting agent, dispersant, vise, reducer for filled, unsat. polyester and epoxy resin systems, esp. those with alumina trihydrate or calcium carbonate fillers and silica-filled epoxy flooring compds. 

L. Mascia and T. Tang, Ceramers based on crosslinked epoxy resins-silica hybrids low surface energy systems, J. Sol-Gel Sci. Technol., 1998, 13, 405. 

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