Modification of the filler surface

The modification of the filler surface reacts with a similar group on another filler particle... 

The chemical modification of the filler surface is frequently used to increase the affinity of the dispersed phase with the polymeric phase or with the solvent used to prepare the casting solution. The nature of the chemical moieties grafted depends on the features of the polymer or the solvent considered for the particular membrane preparation procedure, and either covalent or noncovalent bonds can be considered. 

The polar nature of wood-based fillers also simplifies the chemical modification of the filler surface. Grafting is one of the most widely studied methods of improving adhesion at the fibre-matrix interface. By attaching a suitable polymer segment to wood fibres having a solubility parameter similar to that of the polymer matrix, the compatability between the polymer and fibre can be improved. Kokta and co-workers reported an improvement in the mechanical properties of PS filled with styrene-grafted hard wood fibres [54]. 

As noted above, poor results have generally been obtained when wood flour is added to non-polar thermoplastics. While commercial wood flour has a low aspect ratio, the primary cause of the reduction in strength properties of wood flour filled thermoplastics appears to be incompatibility of the wood flour and the plastic due to the polar character of the surface of the wood flour. To determine if modification of the filler surface would improve composite properties, three types of wood-based fillers were investigated by molding into composites with polypropylene. One was a commercial grade wood flour with low aspect ratio. A second was pulp mill residue described elsewherell. 

Optical or electron microscopy studies of ciystalline polymers fiUed with mineral fillers show that fdlers have a great influence on the size and morphology of the sphendites. There is an optimum fdler concentration above which the influence of filler on the size of the sphendites becomes insignificant. This influence of filler depends not only on its nature but also on the size and shape of its particles. The influence of filler particles on the formation of supermolecular structures is affected by modification of the filler surface to increase the affinity for the polymer. 

The processes of polymer grafting to the surface are not considered here, since these problems traditionally refer to the modification of the filler surface (see Chapter 2). 

It was also shown that rheological properties of filled melts may be changed when some modification of the filler surface takes place. This effect is... 

It should be noted that for polymerization-modified perlite the strength parameters of the composition algo go up with the increasing initial particle size. [164]. In some studies it has been shown that the filler modification effect on the mechanical properties of composites is maximum when only a portion of the filler surface is given the polymerophilic properties (cf., e.g. [166-168]). The reason lies in the specifics of the boundary layer formation in the polymer-filler systems and formation of a secondary filler network . In principle, the patchy polymerophilic behavior of the filler in relation to the matrix should also have place in the failing polymerization-modified perlite. 

Surface modification of the fillers and curing agents in order to increase their wettability and interaction with the polymers... 

By chemical modification of the silica surface it has become possible to design new highly-selective adsorbents and catalysts, active polymer fillers, efficient thickeners of dispersive media. Interest in the modified silicas, in particular, in the activated matrices based on functional organosilicas has quickened in the past few years as a result of the favorable prospects for their application for various kinds of chromatographic separation, preparation of grafted metal complex catalysts, immobilized enzymes and other biologically active compounds [1]. 

The modification of a filler surface with isocyanates is a simple process which involves the reaction of hydroxyl groups on the filler surface with monomeric isocyanate. 2,4-toluene diisocyanate or hexamethylene diisocyanate are commonly used. Since isocyanates are bifunctional they can be further reacted with polyols to form a coating on the surface or they can be used for the reinforcement of polyurethane. A strong covalent bonding can be verified by controlled extraction with the solvent. Bound material will not be removed from the fillefs surface. 

The effect of the modification of the fibre surface consists in the shift of the sound absorption maximum towards higher frequency range and is accompanied by the decrease of the sound absorption coefficient a. The reduction of the coefficient a is not large. It amounts 2.5 % in the case of composites with pine wood and rapeseed straw Californium. For the samples with beech wood filler the coefficient a remains unaffected after modification. The exception is the composite containing the rapeseed straw Kaszub as a filler that shows the decreasing in the sound absorption of 7%. The reduction of the a coefficient value at the frequency related to the maximum of the sound absorption can be associated with the increase in the density of the composite after modification (Table 1) due to better adhesion between filler particles and polypropylene matrix. The fact implies that the specific acoustic impedance of... 

In in-situ polymerization, nanoscale particles are dispersed in the monomer or monomer solution, and the resulting mixture is polymerized by standard polymerization methods. This method provides the opportunity to graft the polymer onto the particle surface. Many different types of nanocomposites have been processed by in-situ polymerization. Some examples for in-situ polymerization are polypyrrole nanoparticle/amphiphilic elastomer composites magnetite coated multi-walled carbon nanotube/polypyrrole nanocomposites and polypyrrole/ silver nanocomposites. The key to in-situ polymerization is appropriate dispersion of the filler in the monomer. This often requires modification of the particle surface because, although dispersion is easier in a liquid than in a viscous melt, the settling process is also more rapid. 

However, owing to better interfacial interactions due to the elimination of the thermal degradation of the filler surface modification to a large extent (thus eliminating the unwanted side reactions) and the effect of shearing forces, a decrease in the tac-toid thickness and, hence, an increase in the aspect ratio can still be expected. Figure... 

Much research has been done over foe years in these laboratories with regard to property enhancement of composite materials by surface modification of the filler material, either by corona or by low pressure plasma pretreatment... 

For modification of polymer/filler surfaces to improve properties like adhesion, fluid absorbancy and wetting properties "exposure of the surfaces to proper electrical glow discharge method is usually and succesfully employed. This technique can also be employed in polymer composite systems to modify interfaces and interphases to improve properties. 

In their function as fillers, the organic spheres share the performances and benefits of the spherical form, similar to glass and ceramic spheres. However, their effect on a polymer matrix is normally not the enhancement of mechanical strength, such as tensile strength and abrasion resistance. Instead, they can impart new features to thermoplastics and thermosets, such as reduced density, improved resilience and ductility, mechanical and thermal stress absorption, or enhanced thermal and electrical insulating properties. When added to binders and plastisols for coatings, the function of the spheres can be surface modification of the coated surface this may include the creation of a visual effect or antislip properties, or to make a protective coating [2, 3]. 

The surface modification can aim at different goals for example, the purpose could be the achievement of a superior chemical compatibility between the two phases through the addition of bridging agents [82]. The modification of the CNTs surface is frequently reported to increase their affinity with polymer solution. One example has been reported in the literature to obtain MMMs of multiwalled carbon nanotubes (MWNTs) in hydrophilic polymer blends for the synthesis of gas separation membranes. Acidification [62] and amino functionalization [56] of the fillers have been performed to increase their dispersability in an aqueous-based casting solution and to offer a reactive moiety for further crosslinking with polymer chains. 

Many factors influence the microstructure and hence the properties of the nanocomposites. The first of such factors is the surface modification of the filler and its interaction with the polymer. The modification is required to make the filler organophilic and to push the filler interlayers apart, thus providing possibilities for polymer intercalation. Table 1.1 details the various kinds of surface... 

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