Microwave carbonization of cotton fiber for the production of carbon materials
This article presents the results of comparative studies of the structural and physico-chemical features of cotton lint samples carbonized by the microwave method and the standard (thermal) method. The dependences of the temperature change of the samples during the microwave carbonization process are obtained. The heterogeneity of the morphology of the fiber surface along the cross-section of the microwave carbonized sample was revealed. It is shown that the structure of the surface layers is characterized by two mechanisms of fiber destruction: numerous brittle transverse fractures and coloring of the fibers in places of swellings (a sharp increase in their diameter) and fluffing of the surface into convoluted fibrils with a transverse size of 50 - 300 nm due to the destruction of the outer layers of the secondary fiber wall. In the central region, the destruction of fibers occurs by the formation of longitudinal interfibrillary slits and the delamination of the secondary fiber wall, which leads to the formation of pores with dimensions of 50 - 200 nm. It is established that during the microwave carbonization process, the central part ofthe sample is almost completely freed from impurities that are deposited on the fibers of the surface layers. It is shown that the integral adsorption capacity of the microwave carbonized sample is higher than the adsorption capacity of the sample carbonized by the thermal method (126 mg/g and 47 mg/g, respectively). It was found that during microwave exposure more than 10 minutes, regions with an adsorption capacity of ~ 350 - 450 mg/g appear in the carbonized material, that is comparable to the capacity of samples activated by the standard method.