General Principles of Surface Modification

Virtually all treatments in commercial use are chosen to chemically bond an organic species to the filler surface, thus improving compatibility with organic polymers. The most common functionalities used for this are acids or acid precursors, such as anhydrides (for basic or amphoteric fillers) and alkoxy-silanes (for fillers with metal hydroxyls present, especially siliceous fillers). Organo-titanates and related compounds are also proposed for nse with a wide variety of fillers. 

Two distinct types of surface modifier can be recognised non-coupling and coupling. The non-coupling types have a chemical bond to the filler surface, but no strong bonding to the polymer matrix. The widely used saturated fatty acids are typical of this class. 

Where the matrix polymer undergoes a polymerisation, or crosslinking process, during composite formation then it is fairly simple to choose a suitable polymer reactive group (e.g., a carbon=carbon double bond). However, with polymers such as the polyolefins, this can be difficult. Highly reactive functionalities, such as azides, are sometimes used in this case. It is also possible to pre-functionalise a part of the polymer matrix, by grafting on a species such as an acid, anhydride or alkoxy-silane, in a separate process. 

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