Some experiments on viscose rayon “stabilized” by heat treatment

Making use of very dilute aqueous acetic acid solutions instead of sulfuric acid solutions as the swelling agent, we have confirmed the experimental fact previously observed that, when viscose rayon, after being preswollen in a bath of the pH range optimal for its maximal hydration, is heattreated at the temperature near or just above the glass transition temperature of regenerated cellulose, i.e., at 60–70°C., the effects of the heat treatment in stabilizing viscose rayon, as exhibited by various mechanical properties, are most marked. By means of infrared spectroscopy by the deuteration method of Mann and Marrinan, a qualitative study was made of the change caused by the heat treatment. That is, infrared spectra in the region of absorption by OD groups at 2700–2400 cm.−1 were observed on deuterated viscose films obtained by various conditions of pretreatment and subsequent hydrogenation. It was concluded that the crystallization effect shown by regenerated cellulose which was heat-treated after being preswollen in acid bath (pH = 3.0), makes its most marked appearance at heat-treatment temperatures just above 55–70°C. Also x-ray diffraction curves of viscose rayon fiber heat-treated at various conditions were resolved according to the method of Hermans and Weidinger into amorphous, background, and crystalline peaks. It was found that the preparation obtained at the best condition for stabilizing viscose rayon (preswollen at pH = 3.0 and heat-treated at 70°C.) shows about 3% higher crystallinity than the untreated sample or as the sample which was heat-treated without preswelling.