Filler-Matrix adhesion

Biopolymers have diverse roles to play in the advancement of green nanotechnology. Nanosized derivatives of polysaccharides like starch and cellulose can be synthesized in bulk and can be used for the development of bionanocomposites. They can be promising substitutes of environment pollutant carbon black for reinforcement of rubbers even at higher loadings (upto SOphr) via commercially viable process. The combined effect of size reduction and organic modification improves filler-matrix adhesion and in turn the performance of polysaccharides. The study opens up a new and green alternative for reinforcement of rubbers. 

Special considerations dewetting angles can be calculated which represent filler-matrix adhesion carbon black is a compatibilizer of PVDF/PS blends " the thickness of a silane layer coating was estimated to be -16 nm ... 

Polymer blends and alloys have more complex behavior in the presence of fillers than the binary mixtures of polymer and filler. The same factors, such as filler distribution, filler-matrix interaction, filler-matrix adhesion, particle orientation, nucleation, chemical reactivity, etc. have influence on properties, but this influence is complicated by the fact that there are two or more polymers present which compete for the same filler particles. These complex interactions result in many interesting phenomena discussed below. 

Adhesion, filler/matrix adhesion, dimensional stability, reinforcement, and wear resistance are the most important concerns in the development of dental compos-ites. These requirements are shared with composites used for many other purposes. So much as the methods of testing, mathematical models, methods of interpretation, and remedies developed in other applications may be applied to dental composites. 

With regard to particle size effects contradictory results have been published (11,12). Assuming that the filler particles change the properties of the resin In the Immediate neighbourhood (13), an Influence of particle size should be expected. A reduction of particle radius from 25 to 1 means a 1600 fold number of particles and a 300 fold surface area. Even if actually Important aspects like agglomeration of filler particles and filler/matrix adhesion are neglected it seems almost impossible to deduce effective mechanical properties from constituent properties without knowing more about bondary layers. 

Trachte and DiBenedetto, 1971 Wambach et ai, 1968). Since PPO is much more ductile at 25 C than the epoxy resins mentioned, the effects of filler and adhesion promoter on PPO should tend to resemble the effects on an epoxy resin in a ductile state (e.g., at 130°C). Indeed this is the case. The point is that a filler tends to increase surface roughness and hence y in an otherwise brittle matrix, especially if the filler-matrix adhesion is poor, but tends to inhibit plastic deformation (by constraints or by simple volume replacement) in an otherwise ductile matrix. Such effects are not accounted for in Nielsen s simple treatment (Section 12.1.2.3) and conceivably may occur as competitive mechanisms (see Figure 12.20). A useful summary of such competitive factors is given in Table 12.3 for the glass-bead-epoxy systems (DiBenedetto and Wambach, 1972) the discussion should be relevant to other cases as well. 

Tensile measurements were taken in most cases to determine the mechanical properties of NR/CNT nanocomposites. Initial modulus, determined from stress-strain curves, was observed to remarkably increase with the filler content. At 1 wt%, the increase was 25.9%, compared to pure NR, ° at 3, 5, 7 and 10 wt% the increase % was 142, 306, 680 and 850, respectively.It was commented that the modulus increase is due to the hydrodynamic effect, further increased by the filler anisotropy, and by the presence of occluded rub-ber.i° For composites with 37 wt% of CNT, the storage modulus was about three orders of magnitude higher than that of the pure rubber. CNT modification with resorcinol caused an increase in modulus at all CNT loadings, indicating improved filler-matrix adhesion. 

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). 

This theory allows the design of adhesive joints with resistance to internal stress. The most important objective is to minimize shrinkage by appropriate choice of polymer. An alternative approach is to add filler to the polymer to reduce shrinkage (see Filler-matrix adhesion). Use of a compliant or rubbery adhesive reduces the internal stress. Weakening of the joint is minimized by using the smallest possible volume of adhesive when making the joint. 

A way of significantly altering the properties of a polymer is to incorporate fillers or fibres (see Filler-matrix adhesion, Fibre composites - introduction). The stiffness and often the toughness of the polymers are increased. 

Filler-matrix adhesion V KOVACEVIC, S LUCiO BLAGOJEVIC and M LESKOVAC Surface treatment of fillers and composite properties... 

Thus, their final expression for the ultimate strength of the composite (o, .), for the case of no filler-matrix adhesion, is ... 

When the filler loading is small they argue that the extra load placed on the matrix, when the matrix-filler bond fails, is small and so Oj, approximates to the case for no filler-matrix adhesion. At high filler loadings the authors derive the following expression... 

The Effect of Filler-Matrix Adhesion on Dynamic Fatigue... 

More work is being done on metallic fillers to investigate the filler/matrix adhesion, as other workers have found that additions of copper, zinc and aluminium produce quite varied results when tested in tension. Indeed the authors have also found that zinc will react readily with dicyandiamide, which is commonly used as a hardener in epoxies. The reaction can cause severe foaming and a change in the structure of the cured epoxy at the interface with the zinc. 

Evrard et al. [195] evaluated powdered polyamides of different types as sani-reinfoicing fillers in carboxylated nitrile rubber. They evaluated the filler vulcanizates for tensile properties, tear strength, coefficient of friction, filler matrix adhesion, and swelling in various fluids. 

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. 

Figure 3 Effects of an aminosilane on filler/matrix adhesion in a glass sphere/ polyamide 6 composite (a) untreated (b) with aminosilicate treatment (reprinted by permission of OSi Specialities).

The static moduli failure stresses and dynamic moduli of both filled and unfilled polyurethanes are measured over a range of equihbrium water contents and these results are compared with those obtained from dry controls. The degradation of mechanical properties in the presence of water, and the hydrolytic disruption of filler/matrix adhesion is assessed. A quantitative relationship between the water content and mechanical properties is established and the mechanics of the water/polymer/filler interaction are considered. 4 refs. 

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