Modification of fibrous silicates surfaces with organic derivatives: an infrared spectroscopic study

This contribution explores the interaction of the fibrous silicates, palygorskite, sepiolite and chrysotile with a wide range of organic agents. Infrared spectroscopy (IR) methods are essential for the characterization of solid surfaces and for the investigation of the kind of bonds formed between the surface of these silicates and the organic moieties. Thus, when sepiolite or palygorskite are treated, e.g., with polyurethanes, alcohols, isocyanates, amines or pyridines, specific SiNHC or SiOC bonds are derived from the linkage of the differently located OH groups in these fibrous silicates with the organic moieties. On the other hand, more stable, covalent SiOSiC bondings are formed when the fibrous silicates, especially chrysotile, are reacted with heterofunctional silylating agents like chlorosilanes or ethoxysilanes carrying, alkyl, alkenyl or aryl groups. Such reactions may occur in the presence or absence of HCl. An absorption band at 960 cm(-1)--which we assigned to SiOH groups--is detected only in the presence of HCl. The evolution of this band is related to the degree of grafting of the organic radicals with the silanol groups of the silicates. HCl-generated silanol groups are the main bridges for the coupling of organosilyl groups on chrysotile and other silicates by covalent bonding, leading the way to the preparation of interesting new materials, including fibrous sheet polymers.