Kirsi Leppänen

Changes in Submicrometer Structure of Enzymatically Hydrolyzed Microcrystalline Cellulose

To understand the limitations occurring during enzymatic hydrolysis of cellulosic materials in renewable energy production, we used wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), X-ray microtomography, and transmission electron microscopy (TEM) to characterize submicrometer changes in the structure of microcrystalline cellulose (Avicel) digested with the Trichoderma reesei enzyme system. The microtomography measurements showed a clear decrease in particle size in scale of tens of micrometers. In all the TEM pictures, similar elongated and partly ramified structures were observed, independent of the hydrolysis time. The SAXS results of rewetted samples suggested a slight change in the structure in scale of 10-20 nm, whereas the WAXS results confirmed that the degree of crystallinity and the crystal sizes remained unchanged. This indicates that the enzymes act on the surface of cellulose bundles and are unable to penetrate into the nanopores of wet cellulose.

X-ray scattering and microtomography study on the structural changes of never-dried silver birch, European aspen and hybrid aspen during drying

Abstract The impact of drying on the structure of the never-dried hardwood cell wall was studied at nanometer level by means of wide- and small-angle X-ray scattering (WAXS, SAXS), and at micrometer level by X-ray microtomography (μCT). Never-dried silver birch, European aspen and hybrid aspen samples were measured by WAXS in situ during drying in air. The samples included juvenile and mature wood, as well as normal and tension wood to allow comparison of the effects of different matrix compositions and microfibril angles. The deformations of cellulose crystallites and amorphous components of the cell wall were detected as changes in the cellulose reflections 200 and 004 and amorphous halo in the WAXS patterns. Especially, the width of the reflection 004, corresponding to the cellulose chain direction, increased due to drying in all the samples, indicating an increase of strain and disorder of the chains. Also, the cellulose unit cell shrank 0.2–0.3% during drying in this direction in all the samples except in hybrid aspen tension wood. According to the SAXS results of silver birch, the distance between micro-fibrils decreased during drying. It was detected by μCT that the mean cross-sectional maximum width of the parenchymatous rays decreased from that of never-dried to air-dried birch by roughly 16%.

Simultaneous X-ray diffraction and X-ray fluorescence microanalysis on secondary xylem of Norway spruce

Secondary xylem of Norway spruce was studied by X-ray microanalysis. Average dimensions of cellulose crystallites, fraction of oriented cellulose, mean microfibril angle, and nutrient element concentrations of K, Ca, Mn, and Zn were simultaneously determined using microfocused synchrotron radiation and a combination of X-ray diffraction and X-ray fluorescence spectroscopy techniques. The variation of these quantities in the microscopic size scale was noticeable, and similar between samples taken from the same annual ring. The mean microfibril angle and the nutrient concentrations of Ca, Mn, and Zn showed a correlation. The mean values of the structural parameters and their variation as a function of the annual ring were similar as reported in previous studies on Norway spruce.

Small-angle x-ray scattering study on the structure of microcrystalline and nanofibrillated cellulose

The effects of different solvents on the structure of microcrystalline and nanofibrillated cellulose (MCC, NFC) were studied using small-angle x-ray scattering (SAXS). MCC was immersed in water, ethanol, and acetone, and NFC was immersed only in water and ethanol, but studied also in the form of foam-like water-NFC-gel in wet, air-dried and re-wet states. The solvent affected the average chord length, which reveals the typical length scale of the structure of the sample: 2.4 ± 0.1 nm was obtained for MCC-water, 2.5 ± 0.1 nm for re-wet NFC-gel, 1.6 ± 0.1 nm for MCC-ethanol, 1.2 ± 0.1 nm for NFC-ethanol, and 1.3 ± 0.1 nm for MCC-acetone. The specific surface of cellulose increased strongly when MCC and NFC were immersed in the solvents compared to dry cellulose. The specific surface of cellulose was determined to be larger for NFC-water than MCC-water, and slightly larger for dry NFC powder than for dry MCC, which can be explained by the fact that the width of cellulose crystallites perpendicular to the cellulose chain direction was slightly larger in MCC than in NFC on the basis of wide-angle x-ray scattering results.