Kinetic study on the alkaline degradation of cotton hydrocellulose

Abstract

SynopsisThe kinetics of alkaline degradation of cotton hydrocellulose were determined in 5% NaOH at various temperatures. An activation energy of 24 kcal./mole was found for the endwise degradation reaction, while that of termination to a stable m-saccharinic acid endunit is 32 kcal./mole. Consequently, the DP, of the degradable chain length is highly dependent on the reaction temperature, being 1000 at 65°C. and 140 a t 132°C. A t lower temperatures, the majority of degrading chains terminate to a normal reducing endgroup a t the crystallineamorphous transition region. From the data, the DP, of cellulose chain segments participating in the amorphous regions of the original cotton fibril was calculated to be 143. This result strongly supports the classical micellar fibril structure over the folded model proposed by Manley.

A systematic approach for determination of optimal conditions for Lo-Solids™ kraft pulping of Eucalyptus nitens

“…The results indicate that the dissolution rate of pentosans is proportional to [OH − ] 0.27 and the activation energy is 92.2 ± 8.9 kJ/mol. This activation energy is in the same order of magnitude of previous results obtained for different types of hemicelluloses [8,15,16].…”

“…The degradation in alkaline solutions of the major cellulose and hemicelluloses in softwood and hardwood were presented in several studies [8][9][10][11]. Hemicelluloses (including pentosans) in major wood species appeared to be readily soluble in alkaline solutions in the initial stage of kraft pulping.…”

Prediction of alkaline pulping yield: equation derivation and validation

“…This also suggests that the length of the amorphous region of cellulose in cotton is about twice this value since alkaline hydrolysis is a random process, and termination of peeling occurs mostly by physical stopping, i.e. by inaccessibility of caustic in the crystalline region (Haas et al 1967;Van Loon and Glaus 1997).…”

“…The alkaline degradation chemistry and kinetics of cellulose have been described in a number of studies (Franzon and Samuelson 1957;Lai and Sarkanen 1967;Haas et al 1967;Van Loon andGlaus 1997 andNieminen et al 2014). The latter paper, and in particular the information given in the Supporting Information, quantifies most of the knowledge gathered by the Sixta's research group on the topic of carbohydrate degradation and dissolution during Kraft cooking.…”

“…The glucose removal has been termed secondary peeling to distinguish from peeling of reducing ends in native cellulose during heat-up at alkaline cooking conditions. The latter process is called primary peeling, and takes place fully before secondary peeling because the rate of alkaline hydrolysis is about six orders of magnitude smaller than alkaline peeling (Lai and Sarkanen 1967;Haas et al 1967). The number of glucose units removed before a stopping reaction by primary and secondary peeling, (DDP) P and (DDP) S respectively, depends of the relative rate of reaction of peeling and stopping.…”