Unmodified filler surfaces

The interaction between the surface of particulate and fibrous fillers and a polymer matrix plays a key role in deterrnining the processability and properties of filled composites. Unmodified filler surfaces often give poor interactions and this has led to the growth of an industry based on the use of additives to modify filler surfaces and improve their interactions with polymers. Several types of additives have been evolved for this purpose. Two of these, organofunctional silanes and titanates, have been described in Chapters 4 and 5. This chapter covers other approaches that have been studied, although only a few of these, notably fatty and unsaturated carboxylic acids and functionalized polymers, have achieved much commercial importance. 

The lowering of die swell values has a direct consequence on the improvement of processability. It is apparent that the processability improves with the incorporation of the unmodified and the modified nanofillers. Figure lOa-c show the SEM micrographs of the surface of the extrudates at a particular shear rate of 61.2 s 1 for the unfilled and the nanoclay-filled 23SBR systems. The surface smoothness increases on addition of the unmodified filler, and further improves with the incorporation of the modified filler. This has been again attributed to the improved rubber-clay interaction in the exfoliated nanocomposites. 

Any silane surface modification needs to prove its value through a practical test. Proper selection of mineral, silane, and production parameters will lead to optimum properties of the composite [21]. But still, there exists a desire to see the silane on the filler surface, to visualize the silane layers or, at least, to see the difference between a silane-modified and an unmodified mineral surface [22, 23]. In general, surface analysis depends on the type of organofimctional group of the silane. To avoid the analysis of physiosorbed instead of chemically bound silanes, the treated mineral can be eluted with an excess of solvent in which the respective silane is soluble. 

The effects of modifying particulate surfaces are illustrated in terms of the mechanical properties of the filled LDPE. In Fig. 30 are given the values of Young s modulus vs CaC03 concentrations (wt%) for different particulate surface treatments. Addition of unmodified filler raises the modulus (Fig. 30, curve 1) as may be expected. Modifications of the acid-base interaction characteristics and of the surface energies yield major changes in the effect of filler on modulus. Treatments in Ar, CH4 and both Ar and CH4 plasma are most effective in increasing the modulus of the compounds (curves 2 and 3, Fig. 30), while the treat-... 

For a number of purposes the unmodified epoxide resins may be considered to have certain disadvantages. These disadvantages include high viscosity, high cost and too great a rigidity for specific applications. The resins are therefore often modified by incorporation of diluents, fillers, and flexibilisers and sometimes, particularly for surface coating applications, blended with other resins. 

Disperse oxides unmodified or modified by organics (OC) or OSC are used as fillers, adsorbents, or additives [1-11]. OSCs are used as promoters of adhesion, inhibitors of corrosion, for the stabilization of monodisperse oxides and the formation of the nanoscaled particles. Oxide modification by alcohols or other OC is of interest for synthesis of polymer fillers, as such modification leads to plasticization and reinforcement of the filled coating, but in this case a question arises about hydrolyz-ability of the =M—O—C bonds between oxide surface and alkoxy groups, as those are less stable than =M—O— M= formed, for example, upon the silica modification by silanes or siloxanes. The high dispersity, high specific surface area, and high adsorption ability of fumed oxides have an influence on their efficiency as fillers of polymer systems. 

Although epoxy resin and hardener may be used in unmodified form in adhesive systems, most systems will consist of components that have been modified by incorporation of various additives to achieve specific effects. Formulators will add catalysts or blend hardeners to obtain a specific usable life of the mix and to control the curing temperature. Reactive diluents may be added to modify viscosity or flexibility. Fillers impart improved compression strength and reduce shrinkage and cost. Solvents may be used to reduce viscosity or improve adhesion. Various additives may be added, usually at a low percentage, to reduce aeration, improve adhesion to difficult surfaces, or minimize settlement of fillers. Depending on the application, particular properties such as flame retardency. 

Many factors such as adhesion between components, fiber topography, and kinetic parameters of crystallization of semicrystalline matrix have been reported to influence transciystallinity. The transcrystallinity phenomenon in the natural fibers/polypropylene system is affected by the different type of chemical treatment of lignocellulosic materials. Moreover, the ability of natural filler to induce nucleation in polypropylene matrix is also dependent on the kind of chemical modification of surface fibers. Predominant nucleation ability was found for unmodified fibers. However, chemical modification of fiber surface slightly depressed the nucleation of polypropylene matrixes. 

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