Preparation of Filled Polymer Systems

In context with the preparation of filled polymer systems, there are three terms, namely, compounding, blending and mixing, which are often synonymously or interchangeably used and though various researchers have defined these terms, one is at times faced with the dilemma of terminology [1]. In the present case, definitions of the terms are given as applicable to the subject matter and hence exclude any other connotations of the terms. 

Poslinski et al. [72] undertook the study of the influence of a bimodal size distribution of glass spheres on the rheology of filled polymer systems as already discussed in section 6.4. The bimodal size distribution was prepared by mixing together various vol% of tiie smaller 15 )un spheres with the larger 78 pm spheres given in Table 6.3. Various bimodal mixtures were compounded into a polybutene grade 24 polymer obtained from Petrochemical Division of the Chevron Company, at total solids concentrations up to 60% by volume. 

The actual industrial practice is similar to that used in the filled polymer system and it is preferable to prepare the concentrate or master batch of the polymer with more nanomaterial than is required. This is subsequently incorporated into the base polymer with the required dose of nanomaterial. It should be noted that the final state of dispersion of nanomaterial in the polymer matrix ultimately depends on favourable thermodynamic factors, whichever technique is used to prepare it. 

Filled polymer systems of industrial importance, e.g., filled rubber compounds, filled thermoplastics are thus meso or microcomposites, possibly with a structuration (of the dispersed phase) at the nano or meso scale. Whilst no sizeable commercial application yet exist for nanocomposites rubbers or thermoplastics (to the author s knowledge), considerable research has been made since 1984 with so-called ex-foliated layered silicate "nano-clays." Exfoliation means that individual clay sheets, of around 1 nm thickness, have been separated and adequately dispersed in the matrix. Some reinforcement has indeed been demonstrated with such exfoliated nanoparticles but, generally with very specific rubber systems and/or at a cost of preparation that is hardly compatible with reasonable chances of commercialization. 

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