Helena Lennholm

The influence of hemicellulose on fibril aggregation of kraft pulp fibres as revealed by FE-SEM and CP/MAS 13C-NMR

Three Norway spruce pulps were produced using different kraft pulping methods, in order to obtain large differences in cellulose and hemicellulose proportions at a similar lignin content. The hemicellulose content in the three pulps varied between 10% and 22%. The aim of the study was to evaluate the influence of cellulose and hemicellulose on fibre ultrastructure and correlate this with the differences observed in the mechanical properties between the pulps. The ultrastructure of the pulp fibres were studied using Field Emission Scanning Electron Microscopy (FE-SEM) and Solid-State Cross Polarisation Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance (CP/MAS 13C-NMR) in combination with spectral fitting. CP/MAS 13C-NMR measured the average bulk properties of the pulp fibres, while FE-SEM allowed for observations on the ultrastructure of fibre surfaces. The ultrastructure of the fibres varied with varying hemicellulose content. The pulp with a high hemicellulose content had a porous surface structure. In fibres with a low hemicellulose content, the fibril aggregates (macrofibrils) formed a much more compact surface structure. With CP/MAS 13C-NMR this change was reflected by an increase in average fibril aggregate width with decreasing hemicellulose content. Results from FE-SEM and CP/MAS 13C-NMR correlated well. The changes recorded in ultrastructure may explain the very different mechanical properties reported previously for pulps with different hemicellulose content.

Comparison of solid-state NMR and isothermal microcalorimetry in the assessment of the amorphous component of lactose

Abstract The aim of this study was to evaluate the use of solid-state nuclear magnetic resonance (NMR) in the assessment of the degree of disorder of processed lactose. The results obtained from 13 C cross-polarisation/magic angle spinning NMR were compared with those obtained from isothermal heat-conductive microcalorimetry, in which the heat flow during crystallisation of the amorphous lactose in the samples was recorded. A series of lactose mixtures was prepared and studied. In agreement with earlier studies, the microcalorimetric analyses resulted in a linear relationship between heat flow and the nominal crystallinity of the lactose mixtures. Mathematical models established from NMR spectra accurately predicted results even when the lactose mixture contained an additional component, acetylsalicylic acid. The results obtained by microcalorimetry and solid-state NMR were in agreement. Both methods were very sensitive and could detect as low as 0.5% amorphous lactose in a mixture. In addition, solid-state NMR has the advantage of being able to provide structural information about a sample containing several different components.

Determination of cellulose Iα and Iβ in lignocellulosic materials

Abstract A novel method to estimate the relative amounts of cellulose I α and I β in lignocellulosic materials has been developed. 13 C-CP/MAS NMR spectra were recorded on 12 calibration samples containing cellulose of various degrees of crystallinity. Principal component analysis of the NMR data extracted qualitative information about the relative amounts of amorphous cellulose, cellulose I α , and cellulose I β in the calibration samples. A quantitative partial least-squares (PLS) model was established between estimates of amorphicity index, cellulose I α -content, and cellulose I β -content and the 13 C-CP/MAS NMR data of the calibration samples. The cellulose I α and I β content in some chemical and high-yield pulps was predicted from their NMR spectra by use of the PLS model. The existence of substantial amounts of cellulose I α in the pulp samples was demonstrated with the PLS model.

Characterisation of particle properties and compaction behaviour of hydroxypropyl methylcellulose with different degrees of methoxy/ hydroxypropyl substitution

The particle characteristics and compaction behaviour of hydroxypropyl methylcellulose (HPMC) powders from two different suppliers were studied regarding effects of methoxy/hydroxypropyl substitution. Samples included Methocel K4M (low substitution ratio), E4M (medium) and F4M (high) and the corresponding substitution ratios from Metolose: 90 SH 4000, 60 SH 4000, and 65 SH 4000. Characterisation of the particle properties and compaction behaviour of the pure polymers suggested that reported differences in drug release behaviour of Methocel E4M compared with the other two powders may be related to the lower powder surface area, differing particle morphology and lower fragmentation propensity during compaction. In addition, compacts of Methocel E4M were weaker when tested in both axial and radial directions and had different porosity and elastic recovery properties. There were no differences between the polymers in degree of disorder, as evaluated by solid-state nuclear magnetic resonance spectroscopy. The different behaviour of Methocel E4M could, however, be related to the overall higher total degree of substitution of this polymer and in particular the high content of methoxy groups compared to the other polymers. The methoxy substituent is hydrophobic and may, when present in sufficiently high concentrations, change the particulate and mechanical properties of the powder, thus potentially affecting the compactability. The high content of methoxy groups might also decrease the development of inter- and intraparticulate hydrogen bonds during compaction, and suppress the actions of the hydrophilic hydroxypropyl groups, both of which could affect drug release.

Steam explosion of aspen wood. Characterisation of reaction products

Summary The steam explosion process was used to separate the components of aspen wood. The main goal was to obtain a material with a molecular weight distribution similar to that of dissolving pulp. To achieve variations in fibre structure and molecular weight, two series of steam explosions were made in which the time and temperature were varied according to factorial designs. The resulting pulps were very dark and were therefore bleached with hydrogen peroxide. The bleaching was sufficient to increase the brightness of the exploded material significantly. The resulting lignocellulosic materials as well as the washing water were characterised by carbohydrate analysis, lignin analysis and size-exclusion chromatography. A large variation in the pulp composition as well as in cellulose and hemicellulose molecular weight was obtained merely by varying the time and temperature of the explosions. The results showed that pulps with properties ranging from a high xylan content (7%) and high molecular weight cellulose (900 000) to a low xylose content (< 1%)and low molecular weight cellulose (<40 000) were produced. The exploded material consisted mainly of cellulose, hemicellulose and degraded polysaccharides. The degraded polysaccharides showed up as lignin in the Klason lignin analysis and in measurements of kappa number.

Quantification of cellulose forms in complex cellulose materials: a chemometric model

In this paper, we present a chemometric model for quantifying the cellulose forms with different states of order found within cellulose I fibrils. The relative amounts of the different cellulose forms, that is crystalline cellulose I, para-crystalline cellulose and cellulose at accessible and inaccessible cellulose surfaces, were determined by non-linear least squares fitting of the C4-region in CP/MAS 13C-NMR (Cross-Polarisation Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance) spectra. By correlating these results from the C4-region with the full spectral data we obtained a model which is able to provide an assessment of the relative amounts of the different cellulose forms directly from NMR-spectra of complex lignocellulosic samples. Furthermore, this model enabled new assignments to be made in the C1-region for signals from cellulose at accessible fibril surfaces.

Changes in cellulose supramolecular structure and molecular weight distribution during steam explosion of aspen wood

We have studied the cellulose supramolecular structure in pulps obtainedby steam explosion of aspen wood. The pulps were bleached with hydrogenperoxidein an OQP-sequence and characterised by size exclusion chromatography and13C cross polarisation magic angle spinning (CP/MAS)NMR-spectroscopy. With CP/MAS-NMR-spectroscopy and chemometrics we were able toseparate the supramolecular structural changes taking place during steamexplosion into two independent processes. One process was related to the extentof processing and showed degradation and dissolution of cellulose,hemicelluloseand lignin accompanied by an increase in cellulose content. The second processwas displayed by pulps having molecular weights below approximately 100000 andwas interpreted as showing the removal of dislocations and an increase incrystalline and/or paracrystalline cellulose in the cellulose fibrils.

Pore swelling in beads made of cellulose fibres and fibre fragments

Abstract The swelling of a new pharmaceutical excipient consisting of highly porous cellulose beads has been studied. Different degrees of swelling were produced by absorption of water and cyclohexane, two liquids with different ‘swelling capacity’. The pore size in cellulose beads with different porosities was investigated using the spin echo NMR technique and found to increase due to swelling. The crystallinity of dry and wet cellulose fibres was investigated using 13 C CP/MAS NMR. A basic application of the beads is to use them as well-defined drug carrier particles. The beads can be loaded with drugs by a sorption process from water or organic solvents. It was concluded that it is beneficial to load the beads using drug solutions containing a cellulose swelling liquid.

Estimation of Cellulose I and II in Cellulosic Samples by Principal Component Analysis of 13C-CP/MAS-NMR-Spectra

This work presents a principal component analysis (PCA) model constructed from 13 C-CP/MAS-NMR-data of cellulosic samples derived from different species and different manufacturing processes. Some of the samples were also subjected to additional chemical or mechanical treatments. The relative amounts of the cellulose I, cellulose II and amorphous polysaccharides in the cellulosic samples could be estimated by PCA of the NMR-spectra. The effects of various treatments of the samples (decrystallisation, regeneration, mercerisation, drying, hydrolysis) could be monitored. Samples commonly thought to consist exclusively of cellulose I, such as pulps, were found to contain small amounts of cellulose II

Evaluation of Surface and Bulk Characteristics of Cellulose I Powders in Relation to Compaction Behavior and Tablet Properties

Abstract The particle properties and solid-state characteristics of two celluloses, Avicel PH101 and cellulose obtained from the alga Cladophora sp., were evaluated and related to the compaction behavior and the properties of the tablets made from them. The surface area of the celluloses was measured at different levels of penetration capacity, ranging from external surface area of particles to molecular texture with Blaine permeametry, Kr-gasadsorption, and solid-state NMR. The important cellulose fibril surface area was best reflected by solid-state NMR, although for the Cladophora cellulose, Kr-gas adsorption also resulted in a surface area of the order of what has been suggested earlier on the basis of the cellulose fibril dimensions. The difference in fibril dimension and, thereby, the fibril surface area of the two celluloses was shown to be the primary factor in determining their properties and behavior. Properties such as the crystallinity and the tablet disintegration could be related to the fibril dimensions. The Cladophora cellulose resulted in rather strong compacts that still disintegrated rapidly. The irregular surface morphology of the particles and the fragmenting behavior of Cladophora probably contributed to the strength of the tablets.