Crystallinity of Cellulose Fibers as Determined by Acid Hydrolysis

Abstract

A study of the kinetics of the heterogeneous hydrolysis of cellulose indicates that there are two distinct rates which have been attributed to the rapid hydrolysis of the loose amorphous regions and to the slow hydrolysis of the dense crystalline portions of the fiber. Based on this interpretation, a simple method for the determination of the relative proportions of crystalline and amorphous cellulose has been developed. The method was applied to a series of natural and regenerated cellulose fibers and the resulting "degree of crystallinity," defined as the amount of crystalline cellulose in a sample expressed as a decimal fraction of the total cellulose, was tabulated. Results obtained on four samples of rayon are very well correlated with crystal linity data derived from x-ray diffraction patterns. There is apparently no correlation between the degree of crystallinity and the tenacity of five samples of rayon. In six samples of Stone , ville cotton there appeared to be no relationship between the degree of crystallinity and crystal lite orientation. There are indications that the ultimate elongation and the moisture absorption of the rayon samples are proportional to the content of amorphous cellulose.

Carbon-13 solid state NMR investigation and modeling of the morphological reorganization in regenerated cellulose fibres induced by controlled acid hydrolysis

“…Hydrolytic treatment of cellulose is widely used on a commercial scale, for pulp refining (Maloney and Chapman 1985), for sugar and biofuel production (Iranmahboob et al 2002), to manufacture microcrystalline cellulose for food and health-care products (Battista and Smith 1962;Levis and Deasy 2001), and for production of micro and nanofibrillated cellulose (Hubbe et al 2008). Acid hydrolysis reactions of both regenerated and native cellulose in the water swollen state are known to follow two distinct rate constants (Phillip et al 1947). The faster of these reactions is believed to result from random chain scission in disordered polymer regions, between crystals, with the slower reaction resulting from the step-wise scission of glucose monomers from crystallite ends (Sharples 1954).…”

The hydrolysis and recrystallisation of lyocell and comparative cellulosic fibres in solutions of mineral acid

“…Typically an initial fast rate is observed, accounting for a highly accessible non-crystalline fraction, superimposed over a slower rate, which is associated with the hydrolysis of a less accessible crystalline fraction. The slow reaction extends past the formation of microscrystaline cellulose, to the point of complete dissolution of the material as low molecular weight sugars (Phillip et al 1947). The onset of this slower reaction is associated with the observation of a nearly constant average molecular weight, referred to as the levelling-off-degree-ofpolymerisation (LDP) (Nelson et al 1953).…”

The Degree of Disorder in Hardwood Kraft Pulps Studied by Means of LODP

“…The LODP observed in the hydrolysis process is assumed to be a result of the arrangement of cellulose in microfibrils with crystalline regions interrupted by amorphous ones. The loss of weight during hydrolysis was previously used as a means of determining the crystallinity of the cellulose (Phillipp et al 1947;Scallan 1971). This method gives much higher values for the crystallinity than physical methods such as X-ray diffraction and NMR measurements.…”