Effects of chemical treatments and heating on the crystallinity of celluloses and their implications for evaluating the effect of crystallinity on cellulose biodegradation

Abstract

Chemical treatments similar to those routinely used to extract cellulose from plant biomass caused significant increases in the relative crystallinity index (RCI) of Sig-macell 100 (a commercial cellulose of moderate crystallinity), as measured by x-ray powder diffraction in both the reflectance and transmittance modes. In general, the largest increases in RCI were observed following higher (rather than lower) temperature treatments. Substantial increases in crystalliity were also observed upon resuspension in water prior to drying, with higher temperatures again resulting in the greatest increases in RCI. Measurement of the RCIs of wetted Sigmacell 100 samples by acid hydrolysis kinetics revealed that most of the increased crystallinity occurred rapidly upon contact with water. In contrast to Sigmacell 100, a cellulose of higher initial crystallinity (the microcrystalline cellulose Sigmacell 50) showed little change in crystallinity following the above treatments. The results provide a partial explanation for the inconsistent relationships reported between cellulose crystallinity and cellulose biodegradation. (c) 1995 John Wiley & Sons, Inc.

Acidic activation of cellulose and its esterification by long-chain fatty acid

“…CA was a highly crystalline type I cellulose, whereas the cellulose from wheat bran residues was highly amorphous even after acidic pretreatment. Generally, chemical treatment and high temperature increased the crystallinity of cellulose 21 ; however, in our conditions, the temperature of drying was low (40°C), and only a slight decrease in crystallinity was observed.…”

Microbial Cellulose Utilization: Fundamentals and Biotechnology

“…The unavoidable consequence of this fact is that it is difficult to alter (e.g., by physical or chemical treatments) one fine-structure feature without simultaneously altering others. Thus, as noted by several workers (202,730), studies purporting to identify structural features that determine the rate of hydrolysis or utilization often have been overinterpreted, due to a failure to measure or consider changes in other structural determinants. Moreover, correlation is often interpreted as causation, which in at least some cases appears to be unfounded.…”

“…The disparity in the results from these studies may be partially explained by artifacts in the measurement of RCI. These measurements are typically performed by powder X-ray diffraction on dried material and can change greatly during recovery and drying of cellulose from biodegradation experiments or on suspension of dried cellulosic substrates in aqueous media (730). Since cellulose hydrolysis is a surface phenomenon, available surface area is a potential determinant of hydrolytic rate, although there remains some debate about what constitutes the "available" surface area.…”

“…If this difference were due to crystallinity, then cellulose crystallinity should increase over the course of reaction. However, relatively constant crystallinity over the course of enzymatic hydrolysis has been observed in studies involving a variety of cellulase systems (149,178,201,374,381,547), although such crystallinity measurements may be due to artifacts (730).…”

Toward an aggregated understanding of enzymatic hydrolysis of cellulose: Noncomplexed cellulase systems

“…Typical values of CrI for various model cellulosic substrates are presented in Table I. The CrI value of cellulose increases after a period of water swelling due to recrystallization Lee et al, 1983;Fengel and Wegener, 1984), and the variations in drying condition prior to measurement of CrI may cause differences between substrates arising from the method of substrate preparation rather than properties of the substrate per se (Lenze et al, 1990;Weimer et al, 1995). The presence of residual cells and proteins can also result in artifacts in the CrI assay (Converse, 1993).…”