Thermal properties silica/clay composites

More recently nanoscale fillers such as clay platelets, silica, nano-calcium carbonate, titanium dioxide, and carbon nanotube nanoparticles have been used extensively to achieve reinforcement, improve barrier properties, flame retardancy and thermal stability, as well as synthesize electrically conductive composites. In contrast to micron-size fillers, the desired effects can be usually achieved through addihon of very small amounts (a few weight percent) of nanofillers [4]. For example, it has been reported that the addition of 5 wt% of nanoclays to a thermoplastic matrix provides the same degree of reinforcement as 20 wt% of talc [5]. The dispersion and/or exfoliahon of nanofillers have been identified as a critical factor in order to reach optimum performance. Techniques such as filler modification and matrix functionalization have been employed to facilitate the breakup of filler agglomerates and to improve their interactions with the polymeric matrix. 

In many cases several different fillers are used in a composite material. The use of a clay with fiber glass is one typical combination. The clay is used to add bulk and improve primarily the compression properties while the fiber glass is used to improve the tensile and compression properties. The relatively inert extender also reduces the coefficient of thermal expansion and improves the thermal conductivity which is advantageous in many cases. Colloidal silica is also frequently added to glass reinforced materials to improve the tensile properties by stiffening the resin phase. Beryllium fillers greatly increase the thermal conductivity. 

The properties of rubber-rubber blend composites depend on the size and shape and concentration of nano particles and their interactions with the individual mbber matrix. The interaction between the filler and the matrix are improved by surface modification. In the mbber industry the uniform distribution of nano particles is considered to be important as it affects the mechanical properties and performance of the composite. For mbber-mbber blend composites fillers like carbon black prefer to migrate to less polar, less viscous mbber phase whereas silica and clay particles migrate to more polar mbber phase. CNTs mainly reside in the highly polar and non-polar mbbers but not in weakly polar ones. The Tg remain unaltered for a completely incompatible blend. In the case of partially compatible blends, the Tgs of the blend components are expected to shift towards each other as compared with the pure components. Shifting of Tg of polymers to lower or higher values in a blend depends on the polarity difference and the difference in the thermal expansion coefficient of the respective polymers in the blend. 

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