Coupling agents coverage

Fig. 18. Yield strengths in three-point bend tests of highly filled composites of polyfvinyl butyral) and silica particles treated with methylsilane and octylsilane coupling agents to varying degrees of surface coverage vs. work of adhesion measured independently using IGC. Redrawn from ref. [90].

Spectroscopic techniques are extremely useful for the characterization of filler surfaces treated with surfactants or coupling agents in order to modify interactions in composites. Such an analysis makes possible the study of the chemical composition of the interlayer, the determination of surface coverage and possible coupling of the filler and the polymer. This is especially important in the case of reactive coupling, since, for example, the application of organofunctional silanes may lead to a complicated polysiloxane interlayer of chemically and physically bonded molecules [65]. The description of the principles of the techniques can be found elsewhere [15,66-68], only their application possibilities are discussed here. 

The addition of MAPP at around 1-2% ensures perfect coverage of the wood fibres by polypropylene or polyethylene. The micrographs in Figure 5.25 clearly show the lack of adhesion between the fibres (in dark colour) and the PP matrix (in light colour). The mechanical properties are increased by at least 30% when a coupling agent is used. 

The molecular coverage and molecular orientation of the coupling agent... 

Contrary to the trialkoxysilane, the MPDES coupling agent, cannot condense in solution and forms a monolayer coverage lying flat on the border of the clay plates. Synthesis of the nanocomposite latexes in the presence of grafted Laponite was carried out using 1 g of the organicaUy-... 

The ability of tri-alkoxy silanes to condense with themselves to produce various three-dimensional networks makes the concept of monolayer coverage based on simple surface reaction of restricted value when considering this type of molecule. This is especially true of the silane coupling agents, where the picture is often further complicated by the tendency of some of the functional groups present to also interact with the surface. As will be discussed later, it has also been demonstrated that optimmn results are sometimes obtained with coating levels well in excess of a notional monolayer. 

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