Ian D. Suckling

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.

Mild hydrogenolysis of in-situ and isolated Pinus radiata lignins.

The Pd/C-catalysed hydrogenolysis of in-situ and isolated lignins from Pinus radiata wood was investigated to gain a more complete understanding of the factors affecting yield and composition of the hydrogenolysis products. Such hydrogenolysis products could potentially be refined into aromatic feedstock chemicals providing sustainable alternatives to petroleum-derived phenols. Lignins were converted into solvent-soluble oils composed of monomeric, dimeric and oligomeric products in high yields, up to 89% of the original lignin. The main monomer products were dihydroconiferyl alcohol and 4-n-propyl guaiacol. Dimeric and oligomeric compounds constituted 75% of the hydrogenolysis oils and were mainly composed of dihydroconiferyl alcohol and 4-n-propyl guaiacol units linked by β-5, 5-5, 4-O-5 and β-1 linkages. Hydrogenolysis of steam exploded wood gave lower yields of lignin hydrogenolysis products compared to unmodified wood due to fewer reactive aryl-ether linkages in the lignin.

Quantitative chemical indicators to assess the gradation of compression wood

Abstract A chemistry-based parameter has been sought for determining the gradation of compression wood (CW), i.e., the severity, in tissues of Pinus radiata wood. Fluorescence microscopy was the reference for characterisation of the tissues containing CW. The collected material contained CW of varying severity, beginning with normal wood (NW containing no CW), continuing with material with some features of CW (CW of mild severity, MCW) and ending up with a material with pronounced features of CW (CW of high severity, SCW). Matching opposite wood (OW) was also included in the study. The chemical analyses included lignin determination, sugar analysis in the acid hydrolysate, thioacidolysis, 31P-NMR spectroscopic analysis and steric exclusion chromatography of thioacidolysis products. As the severity of CW changed progressively from NW through MCW to SCW, all chemical parameters changed concurrently. In particular, levels of galactose and lignin increased, while those of glucose and mannose decreased. The amounts of p-hydroxyphenyl β-ethers released by chemical degradation and uncondensed p-hydroxyphenyl C-9 units also increased at elevated CW severity levels. The amounts of galactose and the p-hydroxyphenyl content of the lignin correlated linearly with lignin for CW samples. The chemical differences between CW and OW in the stem, branch and seedling were similar, i.e., they are independent of the morphological origin of the sample. Parameters based on the p-hydroxyphenyl unit content appear the most suitable chemical indicators of CW severity, as they are least sensitive to the samples morphological origin and their response to CW severity is high.

Micromorphological changes and mechanism associated with wet ball milling of Pinus radiata substrate and consequences for saccharification at low enzyme loading.

In this work, substrates prepared from thermo-mechanical treatment of Pinus radiata chips were vibratory ball milled for different times. In subsequent enzymatic hydrolysis, percent glucan conversion passed through a maximum value at a milling time of around 120min and then declined. Scanning electron microscopy revealed breakage of fibers to porous fragments in which lamellae and fibrils were exposed during ball milling. Over-milling caused compression of the porous fragments to compact globular particles with a granular texture, decreasing accessibility to enzymes. Carbon-13 NMR spectroscopy showed partial loss of interior cellulose in crystallites, leveling off once fiber breakage was complete. A mathematical model based on observed micromorphological changes supports ball milling mechanism. At a low enzyme loading of 2FPU/g of substrate and milling time of 120min gave a total monomeric sugar yield of 306g/kg of pulp which is higher than conventional pretreatment method such as steam exploded wood.

Lignin and carbohydrate variation with earlywood, latewood, and compression wood content of bent and straight ramets of a radiata pine clone.

Abstract Changes in lignin and carbohydrate content with radial direction, growth-layer number, compression wood (CW) severity, and earlywood (EW) and latewood (LW) origin are described for one near-ground position in each of a severely bent and a nominally straight ramet (tree) of a clone (genotype) of Pinus radiata. Bark-to-bark strips were taken through the pith and the longest radial dimension of the CW side of the discs. Separate EW and LW samples were obtained for most growth layers, yielding a total of 95 samples. Differences in lignin and carbohydrate content between EW and LW were large where CW formation was moderate and small where it was severe. Mannose content was consistently different in the EW and LW of opposite wood (OW) and CW. Results suggested that the inner juvenile wood of OW rings might contain either a galactose-rich galactoglucomannan or a β-1,4-galactan. Consideration of all 95 samples showed that although the contents of galactose, lignin, glucose, and mannose were linearly and strongly correlated with one another, their relationship with xylose and arabinose content was non-linear.

Citric acid crosslinking of paper products for improved high-humidity performance

Fibre crosslinking with polycarboxylic acids can be used to improve certain properties of paper products, including wet tensile and compressive strength. In the present work it was proposed that citric acid (CA) crosslinks the cellulosic fibres of linerboard by self-catalysed esterification of cellulosic hydroxyl groups, which makes an additional catalyst unnecessary. An increase in CA dose or curing temperature increased linerboard compressive strength. In CA-treated corrugated board most of the applied CA was esterified with fibres while some CA thermolysis products were also present. A significant portion of the applied CA was unaccounted for. The deficit was attributed to thermolysis to give volatile anhydrides of unsaturated acids. Under cyclic humidity and static compressive loading, CA-treated corrugated boxes showed a greater than three-fold increase in resistance to compressive creep, showing that CA treatment can be used to extend the lifetime of corrugated boxes used for horticultural produce storage.

Comparison of hydrogenolysis with thioacidolysis for lignin structural analysis

Abstract Mild hydrogenolysis has been compared with thioacidolysis as a method for degrading lignins in situ and in isolated form before analysis by gas chromatography/mass spectrometry and quantitative 31P nuclear magnetic resonance (NMR) spectroscopy. Both degradation methods gave similar levels of β-aryl ether-linked phenylpropane units that were released as monomers. Degradation by hydrogenolysis generally gave lower levels of total phenylpropane units when analyzed by 31P NMR, especially in the case of lignins with high levels of condensed units. Overall, these results indicate that mild hydrogenolysis could offer an alternative to thioacidolysis for probing lignin structure.

Understanding the degree of condensation of phenolic and etherified C-9 units of in situ lignins.

A novel approach for the quantification of the degree of condensation at the C(5) position of etherified and phenolic phenylpropane (C-9) units of in situ lignin is described. This is achieved by degrading unmethylated and methylated wood by thioacidolysis and analyzing the resultant product mixtures by quantitative (31)P NMR spectroscopy. Applying this new method to compression wood and normal wood from Pinus radiata showed that, whereas 41-47% of etherified guaiacyl C-9 units are condensed at the C(5) position, almost all phenolic guaiacyl C-9 units exist as uncondensed moieties. Analysis of milled wood lignin (MWL) isolated from the same wood by (31)P NMR spectroscopy before and after thioacidolysis showed that the phenolic guaiacyl C-9 units were more condensed than those in the in situ lignin. This is likely due to partial cleavage of the more condensed etherified linkages during the lignin isolation, leading to a relative increase in condensed phenolic guaiacyl C-9 units.