Comparative analysis of the effect of solvent on the structural and dynamic characteristics of film and nonwoven fiber materials prepared from polyurethane and styrene acrylonitrile

Abstract

Structural and dynamic analysis, combining thermophysical measurements by differential scanning calorimetry and measurements of segmental mobility by the EPR microprobe technique, is performed for films and nonwoven fiber materials prepared from polyurethane (PU) and a styrene-acrylonitrile copolymer (SAN), as well as mixed compositions thereof. The effect of the tetrahydrofuran, ethyl acetate, and acetone solvents on the structure and molecular dynamics of films and matrices based on ultrathin PU and SAN fibers is examined. A weak effect of solvent on the molecular dynamics of chains in the PU film and nonwoven materials and a strong influence on the molecular mobility in SAN films and films of mixed compositions with a high SAN content are observed. For fibers, such influence is negligible. In PU and PU/SAN mixed formulations, mesomorphic structures are formed in both the film and nonwoven materials. The temperature dependence of the rotational correlation time τ of the probe exhibits a kink at temperatures close to the melting point of the mesomorphic structures in the PU/SAN mixtures. All the studied dependences for both the films and fibers feature a kink at PU/SAN = 50/50, which is associated with phase inversion in the compositions. The probe measurements show the impact of an oxidant (ozone) on the amorphous phase in these polymers. Measuring the rotational dynamics of the probe before and after exposure to ozone of the film and ultrafine fiber materials showed that, for both the PU films and fibers, ozonation produces practically no effect on the molecular dynamics, while for PU/SAN compositions and pure SAN, τ changes significantly.