Fillers reactive groups

Figure 6.3 Filler reactive groups introduced into polymer backbones by maleic anhydride and acrylic acid grafting.

Adhesion is usually controlled by means of various finishing agents. Mikhalsky noted in [260] that reactions between such agents and thermoplastics are hindered for a number of reasons, one reason being that the chemical structure of the polymer is formed before the treated filler is added. In the majority of cases thermoplastics do not contain reactive groups, if perhaps only at the ends of macromolecules where they enjoy little mobility. The probability of contact between the reactive groups of the agent and the plastic. 

The amount that is theoretically needed to completely cover the surface of a filler can be calculated in many instances if the specific surface area of the filler (or better the spacing of coating reactive groups on the surface) and the area oc-... 

This technology was first commercially applied to polyurethane blend [121] and patented as Rimplast (for Reactive Injection Molding), but many polymers have since been blended with polysiloxane thanks to this method polyethylene [122], polypropylene [122,123], polyamide [124-130], polyesters [128,131-133], poly(phenylene ether) [134], fluorocarbons [135] and many more. Many of them include reinforcing fillers such as fumed silica. The silicone base involved can moreover contain reactive groups such as the epoxy group [136,137]. A typical silicone base useful for these blends was de-... 

The properties of filled materials are eritieally dependent on the interphase between the filler and the matrix polymer. The type of interphase depends on the character of the interaction which may be either a physical force or a chemical reaction. Both types of interaction contribute to the reinforcement of polymeric materials. Formation of chemical bonds in filled materials generates much of their physical properties. An interfacial bond improves interlaminar adhesion, delamination resistance, fatigue resistance, and corrosion resistance. These properties must be considered in the design of filled materials, composites, and in tailoring the properties of the final product. Other consequences of filler reactivity can be explained based on the properties of monodisperse inorganic materials having small particle sizes. The controlled shape, size and functional group distribution of these materials develop a controlled, ordered structure in the material. The filler surface acts as a template for interface formation which allows the reactivity of the filler surface to come into play. Here are examples ... 

Fillers play an important role in powder coating of polyamide to form articles with a metal-like look (e.g., handles, mountings for radiators and pipes). For a material to be powder coated, it must withstand the stoving temperatures (170°C or more). It must also be electrically conductive, be chargeable and its reactive groups must be able to link with the coating system. Fillers such as metal and metal coated ceramic spheres and carbon fibers are added to polyamide for its strength and paintability. 

Because the chemical composition of crosslinked plastics cannot be given with any accuracy, this table lists starting materials and reactive groups but does not describe the products or give the trade names of the many available thermosets that differ in composition as well as content of additives, e.g., fillers. 

Incompatibility problems with organic and inorganic spherical fillers in plastics may be overcome by grafting reactive groups on their surface or adding coupling agents. 

It can be seen that modification of filler snrfaces both to aid processing and improve composite properties is an important and active area of research. While there are a considerable number of treatments proposed, they all follow the principle of a filler surface reactive group linked to an organic backbone, which may carry further functionality. The main variation is in the group used to achieve surface reaction. As we have seen this may be an acid or acid precursor, an aluminate, borate, phosphate, silane, titanate or zirconate. 

Glass transition temperature, crystallinity, cross-linking, fiber fillers, plasticizers Molecular weight, chain orientation, reinforcement, rubber additions Molecular motion, reactive groups Free motion of electrons... 

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