Adhesion filler/matrix material

We have outlined factors which affect particle distribution in a matrix. This distribution depends partly on filler properties but predominantly on the combination of properties of the pair filler-matrix. Filler distribution in a matrix depends on intended application. Some, such as applications which use fillers for reinforcement, require a homogeneous distribution of particles. In others, such as mentioned above electrical conductive materials, adhesives), a uniform distribution of filler particles may decrease their effectiveness. 

Several characteristics of the matrix and filler-matrix interphase are involved in material toughening. These include the particle size of filler, interfacial adhesion, filler concentration (already discussed), filler surface composition, the crystallization of the matrix, shell thickness, stress whitening, and strain hardening. 

ESR has been used to investigate the role of the filler-matrix Interaction in filled rubbers at cryogenic temperatures (10). The breakdown In adhesion between filler and matrix results In vacuoles or voids in the material. Figures 3 and 4 show a contrast In behavior for Sp glass spheres In rubber with and without a silicone coupling agent treatment. In the first case strength Is low and very few free radicals are produced... 

Composites, where a matrix material is "filled" with fibers, platelets or particulates [3], as illustrated schematically in Figure 19.1. The strength of the adhesion between the phases is a major factor in determining the mechanical properties of composites, since it determines the effectiveness of the interface in transferring an applied load from the matrix to the filler phase. 

Young s modulus values of 2.7 GPa. Plasma-enhanced chemical vapour deposition (PECVD) was successfully used to produce a PMMA conformal coating (using methyl methacrylate monomers) on MWNTs. This increased the Young s modulus to 2.85 GPa at 3 wt% which corresponds to dT/dFf of 28.4 GPa. The overall set of mechanical properties indicates that the polymer coating had a significant effect on the mechanical properties at a 1 wt% concentration of tubes, suggesting improved interfacial adhesion between the filler and the matrix material. 

Dispersion of inorganic particles gives rise to filled polymers. A wide variety of properties can be achieved, depending on the filler and its adhesion to the matrix. See Filler-matrix adhesion. The scope of application of rubbers is enormously extended by use of fillers that can give increased strength, stiffness and abrasion resistance to the material (see Rubber fillers). 

Thermosets also benefit from the foam structure, as evidenced by improved thermal insulation, sound dampening and mechanical stress absorption responses to temperature changes or impact. Hollow spheres with an already set volume are normally used, that is, pre-expanded microspheres. The reason is that the curing reactions often interfere with any expansion before a sufficient volume increase has been obtained. Hollow organic spheres are found in products such as sealants, adhesives, putties, pipes, cultured marble, body fillers, model-making materials, and pastes [2, 3, 19]. Common suitable matrix materials are epoxies, PUR, and polyesters. 

Application of the coupling agent causes considerable reduction in the Izod impact strength of the composites. Improved filler-matrix adhesion does not favour the impact resistance of the RHA-polypropylene composites. The tradeoff in impact strength (lower value) for modulus (higher value) seems to be inevitable. The probable reason is the inability of the resin material to slip over the surface of filler particles when the composite is subjected to the impact force. 

Electromagnetic/radio-frequency interference shielding materials have to meet much lower demands in terms of overall electrical conductivity (typically 4-5 orders of magnitude lower than a silver-flake-filled adhesive). This means that cheaper conductive fillers can be employed, for example, silver-coated copper flake, nickel flake, and carbon black. Typically the adhesive has to form a compliant joint between two mating surfaces, and hence room temperature vulcanizing or heat-cure silicone is often a convenient choice of matrix material. 

These adhesives consist of a polymerizable liquid matrix and large volume fractions -of electrically insulating thermally conductive filler. Typical matrix materials are epoxies, silicones, urethanes, and acrylates, although solvent-based systems, hot-melt adhesives, and pressure-sensitive adhesive tapes are also available. Aluminum oxide, boron nitride, zinc oxide, and increasingly aluminum nitride are used as fillers for these types of adhesives. The filler loading can be as high as 70 - 80 wt %, and the fillers raise the thermal conductivity of the base matrix from 0.17-0.3 up to about... 

It is most logical to add equally degradable fillers to biodegradable thermoplastic starch. Natural fibers may be added to biopolymers at amounts of 1% or even up to 20-45%, depending on the kind of fibers used The most common fibers have proven to be flax, hemp, coconut, jute, or cotton fibers. To achieve better adhesion between the fiber and the matrix material, the fibers are often modified in acid solutions or in acetone for degreasing and to produce structural changes in the fiber surface [5-9]. 

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