Changes In Cellulose Crystallinity Research Articles

Influence of ultrasound treatment on accessibility and regioselective oxidation reactivity of cellulose

Cellulose fibers were treated with ultrasound in order to improve the accessibility and the reactivity of cellulose. The influence of ultrasound treatment on changes of morphology structure, accessibility and oxidation reactivity of cellulose with sodium periodate were discussed. The results revealed an increase in cellulose’s accessibility in terms of water retention value (WRV) with increasing ultrasound treatment time, corresponding to 73.0%, 75.6%, 80.8%, 98.7% and 119.0% after treated for 0, 90, 180, 360 and 720 s, respectively. Furthermore, the regioselective oxidation reactivity of cellulose with sodium periodate was also successfully improved by the ultrasound treatment. However, no significant changes in crystallinity of cellulose were noted after ultrasound treatment. The oxidized products dialdehyde cellulose (DAC) was further characterized by means of FTIR, X-ray diffraction and SEM.

NMR processing techniques based on multivariate data analysis and orthogonal signal correction. 13C CP/MAS NMR spectroscopic characterization of softwood kraft pulp

AbstractThis paper presents a novel way of extracting information from a series of severely overlapped NMR spectra using multivariate data analysis techniques. A number of softwood pulps were prepared from wood chips that were subjected to kraft cooking conditions in laboratory digesters. In addition to measurements of traditional physical parameters, the pulps were characterized using standard 13C CP/MAS NMR spectroscopy. The relationship between the kappa number and both the NMR time domain and frequency domain data was modeled using multivariate data analysis techniques. The variation in the NMR spectra that was not correlated with the kappa number was removed using a new preprocessing tool, orthogonal signal correction (OSC). The resulting OSC‐treated NMR spectra were used as descriptors to generate partial least‐squares projections to latent structures (PLS) models for the variation of the kappa number. PLS weights were used to generate NMR ‘sub‐spectra’ which correspond to changes in the pulps that occur as the pulping process proceeds from high to low values of the kappa number. The sub‐spectra were used to gain insight into the changes in the pulps occurring at the molecular level. Concomitant changes in cellulose crystallinity and the amounts of hemicellulose and lignin were observed in these sub‐spectra. Copyright © 2001 John Wiley & Sons, Ltd.

Changes in Cellulose Crystallinity During Kraft Pulping. Comparison of Infrared, X-ray Diffraction and Solid State NMR Results

Changes in cellulose crystallinity during kraft pulping were investigated by analysing a series of kraft pulps with yields between 96 and 47% using X-ray diffraction and infrared (IR) spectroscopy. The results were compared with those obtained for the same set of samples using solid state 13 C nuclear magnetic resonance (NMR) spectroscopy. All three methods indicated that the degree of crystallinity of the cellulose increased as kraft pulping proceeded due to preferential removal of the less ordered carbohydrates. Both X-ray and IR analyses indicated that the amount of crystalline cellulose remaining in the fibre stayed nearly constant as pulping proceeded. NMR spectroscopy, on the other hand, showed some increase in the amount of crystal interior cellulose in the early stages of pulping and evidence for damaged cellulose at yields below 57 %. The differences between the results obtained using the three methods are discussed.

Studies on Chemically Modified Cotton

This study describes the effects of chemical treatments with varying concentrations of ethylamine, ethylenediamine (EDA), potassium hydroxide (KOH), and lithium hydroxide (LiOH) on various properties of cotton fiber, such as crystallinity, moisture regain, DP, and tensile, mechanical, and optical properties. Concentrations of 70–90% EDA, 70% and higher ethylamine, 20% and higher KOH, and 7–10% LiOH showed marked changes in cellulose crystallinity and some other properties. Maximum change was produced by KOH and ethylamine, while EDA produced the least effect. Most of the treatments also reduced the DP, tensile strength at 0 gauge and birefringence values, but increased moisture regain, percent elongation and fiber toughness considerably.

Studies of Chemically Modified Cotton

High crystallinity of cellulose is the cause of undue stiffness and brittleness as well as low absorptioh and chemical reactivity. With a view to overcome these drawbacks and bring about changes in the elastic and other properties of cotton fibers, two cottons, Gaorani and 170-Co.2, were treated with anhydrous ethylamine, diethylamine, pyridine, and aqueous solutions of sodium hydroxide (30%) and potassium hydroxide (40%) for 15 min to 50 hr. Modified lint samples showed interesting changes in cellulose crystallinity and moisture regain, on treatment with ethylamine, sodium hydroxide, and potassium hydroxide after certain periods. Some of the treatments also showed a marked effect on the degree of polymerization and the tensile, mechanical, swelling, and optical properties of the fiber. Moisture regain and degree of swelling were found to be higher in the case of samples treated with alkali, compared with those treated with amines.

Changes in Crystallinity of Cellulose During Dehydration

SUMMARY—Samples of onions and bell peppers were taken during various stages of high‐ and low‐temperature dehydration and lyophilization to ascertain the step‐wise changes that occur in the crystallinity of cellulose. Cellulose crystallizes mainly during the later stages of drying in all three processes, and freezing produces only a minor amount of crystallization. Most of the water loss and loss of rehydration capacity occurs at the start of dehydration. The latter is ascribed to cell death and loss of differential permeability in protoplasmic membranes. Rehydration volume is related to crystallinity of cellulose in these materials within each method of dehydration.