Influence of Mechanical Activation on the Structure and Sorption Properties of Hydrolytic Lignin, Kaolin, and Composites Based Thereon

Abstract

An express method of solvent-free dry mechanochemistry using fine grinding in air for 3 and 6 minutes in a mill (0.94 kW; 26 000 rpm) is employed to targetedly change the structure of kaolin and increase its sorption capacity. During the same process, kaolin is modified together with hydrolytic lignin to hydrophobize its surface and improve its sorption properties. The influence of the mechanical activation on the structure and properties of kaolin, hydrolytic lignin, and their composites with different component ratios is studied using electronic microscopy, X-ray diffraction, infrared spectroscopy, low-temperature nitrogen adsorption, and UV absorption spectroscopy. The dense structure of kaolinite remains preserved, hydrogen bonds in hydrolytic lignin are ruptured, and the number of carbonyl groups increases, while fragments of the natural polymer are grafted to kaolinite. It has been found that an agglomeration–aggregative microstructure is formed in the composites. Kaolin and the kaolin–hydrolytic lignin composite (10 : 1, weight/weight) treated at a mechanical energy dose of 0.83 kJ g^–1 undergo significant structural changes and exhibit rather high sorption characteristics. The Brunauer−Emmett−Teller specific surface area of these sorbents is ∼16 m² g^–1, while their adsorption capacities for bovine serum albumin are 83.63 and 44.10 mg g^–1, respectively. Thus, the dry mechanical activation in air under “mild” conditions makes it possible to increase the sorption of bovine serum albumin on kaolin by 104%.