Silane filler treatment

If such fillers are to be used, they should have a neutral or slightly alkaline pH, otherwise additives such as ethylene glycol and triethanolamine, which are preferentially adsorbed on the surface of the filler, should be used, preventing any undesirable interference reactions between the filler and the crosslinking peroxide. These additives must, however, always be added to the mix before the peroxide. With some mineral fillers, such as some types of clay, the polymer may be bound to the filler by means of silane treatment, and the surface of the filler becomes completely non-polar. Consequently, the interaction with the polymer matrix increases, while the adsorption of the crosslinking peroxide by the filler is severely suppressed. 

While organo-silane treatments are extensively used in both thermoset and elastomer applications, their use in thermoplastics has so far been somewhat restricted. This is because they do not react with the surface of calcium carbonate, one of the principal fillers used in this type of polymer and because of the lack of a suitable reactive functionality for most of the thermoplastic polymers. Today they are principally used in conjunction with glass fibres, calcined clays, aluminium and magnesium hydroxides, micas and wollastonite. The main thermo-... 

Methods of filler pretreatment silane treatment of wollastonite polyamide has ability to wet carbon fiber, polyamide behaves like a melt at 180°C even though its melting temperature is 225°C 5... 

Methods of filler pretreatment silane treatment of carbon black during mixing with rubber co-precipitation of cellulose xanthate and NBR latex" ... 

The most frequently used fillers are glass powder, lithium aminosilicate, and glass-ceramic. Figure 19.14 shows that properties of dental composites are enhanced by the use of silanes. Treatment with silane also improves water resistance. ... 

The effect of fillers on creep phenomena (essentially the inverse of stress relaxation) is also of interest a detailed study by Nielsen (1969b) of creep in filled polyethylene is illuminating. Kaolin and wollastonite were used as fillers, both treated with a silane coupling agent and untreated. A major aim was to discover whether the major effect of a filler is due to its effect on elastic modulus, or whether a filler also changes the viscoelastic nature of the system. As reported in previous work by others, the presence of a filler did in fact reduce the creep, the relative effect being nearly independent of the applied stress. The nature of the filler and the surface treatment were also found to be important. In experiments at a constant volume fraction (0.2), kaolin was more effective than wollastonite. Silane treatment of the filler surface tended to decrease creep, especially if the specimens had been soaked in water. 

Fig. 9. Reducing the aqueous dispersion viscosity of fillers by silane treatment.

Silanes are well recognized and very efficient coupling agents extensively used in composites and adhesive formulations. They have been successfully applied in inorganic filler reinforced polymer composites for years and extensively used for glass fibre reinforced polymer composites.In this chapter, only silane treatment is discussed in short which is as follows ... 

Both the ground and precipitated calcium carbonates can by treated with stearic acid to control water absorption, improve dispersabUity, and promote better wetting of the flUer by rubber. Silane treatment of these fillers is not effective. However, there is an ultra-fine grade coated with carboxylated polybutadiene, which reactively links to the particle surfaces. Such treated ultra-fine products can give reinforcement of about the same level of the semireinforcing thermal carbon blacks. 

Surface treatment is another value-added step that can improve the performance of kaolin. Since the filler is naturally very hydrophilic due to its hydroxyl groups, a treatment can be applied to render its surface hydrophobic or organophilic. These surface-modified kaolins are useful especially in plastics and rubber industries, where they improve adhesion and dispersion and hence act more effectively as functional fillers. Silanes, titanates, and fatty adds as discussed in Chapters 4-6, respectively, may be used to modify the surface charaderistics of either hydrous or calcined kaolins, promoting dea lomeration, often lower viscosities, and improved mechanical and eledrical properties. 

The beneficial effects of surface treatments of filler particles, including silane treatments, are generally attributed to improved adhesion of the polymer to the filler surface. However, it should be realised that in many cases the changes in the degree of agglomeration brought about by the surface treatments are equally, or more, important [83]. 

Although frequently used with organo-silane treatments, these fillers have not traditionally been pre-coated, the in situ method of addition being preferred (see Chapter 4). Largely due to developments in tyre technology, some pre-coated products are now becoming available. 

Similar solution coating procedures have been widely used in much of the scientific work on silane treatment of particulate fillers. Unfortunately such procedures do not lend themselves readily to most commercial filler production processes, where some form of direct reaction between the silane and filler powder is frequently used. In many instances the filler coating is actually carried out in situ during the compounding process, essentially utilising the polymer matrix as the solvent. These distinctions must be borne in mind when trying to relate laboratory studies to results achieved with commercial products. 

BMI-based composites with exceptional mechanical properties were obtained using glass hollow microspheres that were previously submitted to a silane treatment (Koopman et al. 2006). All data indicated that interface adhesion between BMl and filler is strongly affected by the silylation reaction at the glass surface, which enhanced the compatibility. 

Figure 25.8 Silane treatment of fillers in a styrene-butadiene casting.

At least a monolayer of silane is needed on the filler surface. In practice, about 1% silane is applied to a filler with a particle size of 1 mp, enough for several monolayers. Higher surface-area fillers require higher levels of the coupling agent. Fig. 25.8 shows the effect of the level of silane treatment with several different fillers on the flexural strength of a styrene-butadiene casting. 

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