Epoxy resins filler content

Owing to relatively low viscosity, these resins offer advantages for 100% soHds (solvent-free) systems. Higher filler levels are possible because of the low viscosity. Faster bubble release is also achieved. Higher epoxy content and functionaHty of bisphenol F epoxy resins can provide improved chemical resistance compared to conventional epoxies. 

As soon as the Ar s were determined and the values of r s are found, the values of the adhesion coefficient A may be readily defined by using relation (27). The values of A s for the different fiber-volume contents studied are given in Table II for E-glass fiber-epoxy resin composites with different amounts of fillers, up to 70 percent 22 >. 

The effective area modd predicts that the stress concentration factor 7 should be independent of composition in conqmsites containing well-bonded rigid filler paitides. This prediction is supported by the compressive yield data for silica-loaded epoxy resins presented in Fig. 8 yield stress is linear with log (strain rate) for eadi material, and the dopes are identical in each case. The increase of yield stress with silica content must therefore be interpreted as a decrease in the pre-exponential factor rather than in 7. Young and Beaumont observed a similar large increase in the yidd stress of silica-loaded epoxy resins, and suggested an analc with precipi-taticm-hardening in metals ... 

F . 10. Relationsh between filler content in epoxy resin composition containing 70 pm silica particles (42) and alumina trihydrate particles of differing sizes (51)... 

The effects of ceramic particles and filler content on the thermal shock behavior of toughened epoxy resins have been studied. Resins filled with stiff and strong particles, such as silicon nitride and silicon carbide, show high thermal shock resistance, and the effect of filler content is remarkable. At higher volume fractions (Vf > 40%), the thermal shock resistance of these composites reaches 140 K, whereas that of neat resin is about 90 K. The highest thermal shock resistance is obtained with silicon nitride. The thermal shock resistance of silica-filled composites also increases with increasing filler content, but above 30% of volume fraction it comes close to a certain value. On the contrary, in alumina-filled resin, the thermal shock resistance shows a decrease with increasing filler content. 

Figure 3.17 Effect of filler content on the expansion coefficient of an epoxy resin,...

Figure 12.42. Effect of glass beads on loss modulus E" of an epoxy resin (Manson and Chiu, 1973n). The shift to higher temperatures at higher filler content indicates an increase in 7 —in this case, of about 10°C for a volume fraction of 0.3 (50 wt %).

Furthermore, the introduction of organo-modified clays in an epoxy resin was found to lead to the formation of a stronger interface with E-glass fibers, with an increase of the interfacial shear strength of around of 30% for a filler content of 5 wt% [11]. 

A typical thermally conductive epoxy system used as an adhesive, as well as for other purposes, has a thermal conductivity of 0.0026 cal/cm/sec/°C and a volume resistivity of 1.5 x 10 ohm.cm (1.5 x 10 ohm.m). Fillers include alumina (aluminum oxide), beryllia (beryllium oxide), other unspecified inorganic oxides, boron nitride, and silica. Boron nitride is an excellent choice as a thermally conductive filler except that its content reaches a maximum at about 40% by weight in epoxy resins. The resultant products are always thixotropic pastes. BerylUa powder has excellent thermal conductivity by itself, but when mixed with a resin binder its conductivity drops drastically. It is also highly toxic and high in cost. Alumina is a commonly used filler to impart thermal conductivity in resins. ... 

The use of organic nanofillers allows the reduction of the filler content required to achieve high thermal conductivity. In particular, multi-walled carbon nanotubes (MWCNTs), with their one-dimensional structure, high aspect ratio and superior thermal conductivity (3000 W/mK for an individual MWCNT and 200 W/mK for bulk MWCNTs at room temperature (Yang et al., 1991)) have recently attracted great attention in the scientific world. The influence of different carbon nanotube types, particle content, interfacial area, surface functionalization and aspect ratio on the electrical and thermal conductivity of epoxy resins has been investigated (Gojny et al., 2006). 

Carbon nanotubes decorated with silver nanoparticles (Ag-CNTs) have been used as conducting fillers in epoxy resin to fabricate electrically conducting polymer (Ma et al., 2008). The experimental results have shown that the electrical conductivity of composites containing 0.1 % in weight of Ag-CNTs was more than four orders of magnitude higher than those containing the same content of functionalized CNTs, and this improvement was not at the expense of thermal or mechanical properties. 

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