CHEMICAL PROPERTIES OF FILLERS AND FILLED MATERIALS

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  

The first example refers to the creation of functional groups on the fillef s surface during controlled synthesis of the filler. Silica-gel, prepared from tetraethyl orthosilicate under acidic conditions, has OH groups on its surface. A similar synthesis under basic conditions deposits alkoxy groups (OCH2CH3) due to an incomplete hydrolysis of the substrate. This simple example shows the numerous 

100% but because there are no active sites available for grafting, no grafting of polymer 

Chemical reaction depends on the presence of reactive substrates and on the probability of their encounters. Thus, the possibilities of reactions can be numerous. The literature describes reactions of OH groups on the surface of kaolin with isocyanates, vulcanization of nitrile rubber by ZnO, reactions of carboxyl groups on the filler surface with amines and epoxy groups, reactions of carboxyl groups with diols, and many others.The presence of a reactant on the surface of a material particle increases the probability of chemical reaction. Other factors include statistical probabilities, surface barriers which affect contact, dilution factors, molecular mobility, and viscosity changes in the system. These are discussed in other sections of this book. 

---