ON DETERMINING THE CRYSTALLINITY OF CELLULOSE FIBERS OF WHICH COHESIVE STRUCTURES ARE NOT SET IN STABLE STATE

Abstract

(1) For the purpose of determining cellulose structure (crystallinity) of moist or wet cellulose fibres, such as freshly spun rayon, the modified iodine absorption method, that is based upon Hessler & Power's technique, is presented.(2) Using some regenerated cellulose fibres, which differ in stability of cohesive structure, comparison of the results obtained by iodine absorption method with those of hydrolysis method for determining crystallinity was carried out. And iodine absorption before and after depolymerizing treatment (acid hydrolysis) was taken as a measure of recrystallization of cellulose.(3) Degree of recrystallization which occurs in acid solution is conclusively determined by degree of order or stability of cohesive structure present in original fibre; the extent of recrystallization during hydrolysis (1% H2SO4, 95°C, 5 hrs) was estimated at 30% for high tenacity rayon (after first drying), 40% for ordinary rayon (after first drying), and 65% for freshly spun ordinary rayon (before first drying).(4) For cellulose fibres of which cohesive structures are set in stable state, such as rayon after first drying, iodine absorption and hydrolysis methods show good agreement in placing the fibres according to their relative crystallinity in order. But for fibres having unstable cohesive structure, such as freshly spun rayon, hydrolysis method gives very high values for the reason of a remarkable recrystallization effect, and shows opposite results to indine absorption method in placing the fibres according to their relative crystallinity in order.(5) The iodine absorption method is useful in detecting changes in cellulose structure occurred during first drying of freshly spun rayon or in alkali-treatment of rayon.