Transformation of Specific Dispersion Interactions between Cellulose and Polyacrylonitrile in Solutions into Covalent Interactions in Fibers

Morphological transformations in emulsions of cellulose and polyacrylonitrile (PAN) ternary copolymers containing acrylonitrile, methyl acrylate, and methylsulfonate comonomers in N-methylmorpholine-N-oxide were studied over the entire range of concentrations depending on temperature and intensity of the deformation action. Based on the morphological and rheological features of the system, the temperature-concentration range of spinnability of mixed solutions was determined, and composite fibers were spun. The fibers are characterized by a heterogeneous fibrillar texture. Studies of the structure of the fibers, carried out using X-ray diffraction analysis, revealed a decrease in cellulose crystallinity with an increase in the content of PAN. The study of the thermal properties of the obtained fibers, carried out using DSC, and chemical transformations in them in a wide temperature range by high-temperature diffuse reflection IR spectroscopy made it possible to reveal a new intense exothermic peak on the thermograms at 360 °C, which according to the IR spectra corresponds to the transformation of intermacromolecular physical interactions of the PAN and cellulose into covalent bonds between polymers. In addition, the ester groups found during the thermal treatment of the PAN part of the composite fibers in the pyrolysis zone can have a key effect on the process of their further carbonization.