Two-dimensional proton nuclear magnetic resonance (2D 1H NMR) relaxometry is increasingly used in the field of wood sciences due to its great potential in detecting and quantifying water states at the level of wood constituents. More precisely, in this study, this technique is used to investigate the changes induced by “natural” and “artificial” aging methods on modern and historical oak woods. Two bound water components are detected and present differences in terms of association to the different wood polymers in cell walls: one is more strongly associated with wood polymers than the other. The evolution of the two bound water types is discussed in regard to aging methods and is related to the structure of the cell wall, especially with the S2 layer and the evolution of wood chemical composition (cellulose, hemicelluloses and lignin). The evolution of hydric strains is also discussed taking into account the effect of aging methods on the two bound water components. The obtained results confirm the ability of 2D 1H NMR relaxometry to evaluate the effect of aging at the molecular level and on hydric deformation. Furthermore, this method shows that it is possible to determine the moisture content of wood without the necessity to oven-dry the wood material.
For the mechanical properties of paper, tensile testing has been widely used. Among the tensile properties, the tensile stiffness has been used to determine the softness of low-density paper. The lower tensile stiffness, the greater softness of paper. Because the elastic region may not be clearly defined in a load-elongation curve, it is suggested to use the tensile modulus which is defined as the slope between the two points in the curve. The two points which provide the best correlation with subjective softness evaluation should be selected. Low-density paper has a much lower tensile strength, but much larger elongation at the break. It undergoes a continuous structural change during mechanical testing. The degree of the structural change should depend on tensile conditions such as the sample size, the gauge length, and the rate of elongation. For low-density paper, the tensile modulus and the tensile strength should be independent of each other. The structure efficiency factor (SEF) is defined as a ratio of the tensile strength to the tensile modulus and it may be used a guideline in developing superior low-density paper products.
Heat treatment (HT) is a well-known means to reduce the equilibrium wood moisture content (EMC) at a specified relative humidity (RH). EMC is profoundly decreased by the loss of accessible hydroxyl groups (OHacc) in the wood matrix by thermochemical reactions. However, the obtained EMC reduction after HT can be partly reversible, depending on the ability of the wood matrix polymers to fully mechanically relax during HT. We discuss the results of our earlier experimental study on the OHacc content and the associated EMC decrease at 93% RH by a relaxation inhibiting dry-HT vs. a relaxation enabling wet-HT. New experimental results, showing that OHacc does not significantly change during reversible EMC changes, are added to the discussion. This study quantitatively supports a molecular explanation of the reversible EMC, in which wood moisture is principally bound at sorption sites, composed of two functional groups, constituting a hydrogen-donor/acceptor pair, involving at least one OHacc group. The irreversible part of EMC reduction is assigned to the thermochemical removal of OHacc from the wood matrix. The reversible part is attributed to a process of wood polymer conformal rearrangements, bringing an isolated OHacc group in proximity of another free hydrogen-bonding functional group, creating a site for water sorption.
This paper is a review of the development of the mechanical pulping process with focus on refiner-based processes. The intention is to provide an overview of the trends and the major advances in the development of the mechanical pulping (MP) process. The focus is on the development of the entire MP process, rather than the refiner as such. However, when discussing the MP process development, it is inevitable to consider the development of the refiner unit operation briefly. Processes for printing papers based on softwood is mainly discussed, but board processes are discussed briefly as well.
Circular economy may play a key role in the future success of modified wood products. The European Union (EU) aims toward a circular economy, i.e. increasing resource efficiency by waste minimization in production processes, cascade uses of materials, elimination of landfill wastes, and maximizing the value of raw materials. The policy has great expected impact across all sectors, and will influence countries with strong wood modification industries, such as Finland, Germany, Norway, and the Netherlands. It also means considerable economic efforts and sets transformation challenges to the societies and industries. Challenges have country-wise differences depending on production structure, environmental circumstances, local policies and regulations, as well as economic resources. This paper is an outlook of the renewed waste legislation in the EU, based on which it assesses the possible impacts of circular economy development on the future of wood modification. One of the key indicators for resource efficiency is € kg−1, which allows pursuing increased efficiency by minimizing material input (and waste) and/or by maximizing the value. In the case of modified wood, both of these approaches may be considered market opportunities, while the key challenge and the consequent need for action relate to improved waste management.
This study aimed to investigate the oxalate formation mechanism during chlorine dioxide () bleaching of bamboo kraft pulp, and thus explore favourable bleaching conditions to better control oxalate formation. The amount of oxalate formed varied linearly with dosage within the whole research range, while it rose exponentially within the first 90 mins of pulp bleaching. Then the actual bleaching process was simulated by reacting with three representative lignin model compounds and comparatively studied. The rule of oxalate formation in the simulated reaction system was identical to that in pulp bleaching by , except for oxalate production by veratraldehyde with prolonged reaction time. Under identical conditions, vanillin formed the highest amount of oxalate, while veratraldehyde formed the least. Furthermore, the amount of oxalate formed increased by 19.59 mg/kg when the kappa number of the delignified pulp was reduced by one unit. Considering the satisfactory pulp brightness and decreased oxalate formation, the recommended conditions for bleaching of bamboo kraft pulp were a dosage of 4 %, 60 °C and 70 mins.
In this study we have evaluated the suitability of laboratory testing methods to predict inkjet printing results. We have developed and used testing liquids that are spanning the operational window of industrial High Speed Inkjet (HSI) printers while still covering the maximum possible range of viscosity and surface tension. First we correlated liquid penetration measured with ultrasound (ULP) and direct absorption (ASA) to print through from HSI prints. The best correlation () was found for the sized paper. For papers with increasing liquid penetration speed we found a decreasing ability of both testing methods to predict print through, for the strong absorbing paper the correlation drops to . Second we correlated contact angle and drop diameter to the dot area from HSI prints. Contact angle turned out to be a better predictor for printed dot area than drop diameter. Evaluating the change in contact angle over time we found the highest correlation to the dot area in the print when measuring the contact angle as soon as possible, in our case 1 ms after deposition of the drop on the paper. We also compared contact angle with microliter drops to picoliter drops, which are in the size scale of the actual inkjet droplet. To our great surprise correlations for microliter drops were equal or better than for picoliter drops, particularly for highly absorbing papers. Thus in order to predict dot spreading on paper our results suggest to measure the contact angle with microliter drops. Overall we found that, using laboratory testing methods, print through and dot spreading for HSI printing can be quite well predicted for slow absorbing papers but not very well for fast absorbing papers.
The contribution of structural changes of softwood bleached kraft pulp (SBKP) fibers and partly dried SBKP handsheets to their water retention values (WRVs) was studied. Two factors related to mesopores and macropores, which were determined for super critical point (SCP)-dried SBKP sheet samples, should participate in the WRVs determined for wet SBKP sheet samples. The mesopores are formed during pulping/bleaching to remove lignin and a part of hemicelluloses that are present originally in wood cell walls. The combined volumes of mesopores and macropores (totally < ∼0.6 g g−1) in SBKP fibers after SCP drying were significantly lower than the entire WRV (∼1.6 g g−1) of the original never-dried SBKP. We hypothesize that external fibrils of SBKP fibers are formed during pulping, bleaching, washing, pressure-screening, and pressing processes at high and low solid contents in water under high shear forces. The WRV can be used as an indicator to evaluate such structural changes of external fibrils in pulp fibers and paper sheets during drying/wetting in papermaking process as well as in use under various conditions. In contrast, changes in mesopore and macropore volumes determined for SCP-dried sheets cannot properly detect such structural changes of external fibrils.
The efficacy of chemical wood modification is closely related to the permeability of the wood species and the cell wall deposition of the reagent, causing a permanent swelling (“bulking effect”). This study aimed to analyze how rubberwood (Hevea brasiliensis Müll. Arg.) and English oak (Quercus robur L.) may be affected by chemical wood modification, although they are known to show either variations in permeability or being less permeable. Thin clear veneers were treated with 1,3-dimethylol-4,5- dihydroxyethyleneurea (DMDHEU) which resulted in significantly reduced moisture-induced swelling and increased the resistance to static and dynamic indentation loads. The results evidenced significantly lower liquid uptakes in English oak compared to rubberwood, which directly affected the weight percent gains (WPGs) and restricted the range for potential improvements of the material properties. Surprisingly, rubberwood showed a lower cell wall bulking, which, in comparison with English oak, indicated less DMDHEU monomers entering the cell walls and rather being located in the cell lumens. Atypical for treatments with cell wall penetration chemicals, no further decrease in maximum swelling (SM) was detected with increasing bulking in rubberwood specimens. English oak showed higher variations in DMDHEU distribution within treated veneers and between earlywood and latewood areas, effecting a less homogeneous performance.
The goal of this study was to assess the suitability of a single mono-aromatic for substitution of petroleum-based phenol for phenol-formaldehyde (PF) resin synthesis and the usage of a new resin for wood treatment. After proper thermal decomposition of wood-based lignin, pyrolysis oil can be obtained. Due to the heterogeneity of the lignin macromolecule, oil contains large variety of organic-based compounds, mainly mono-aromatics, which are proposed to be used for replacement of phenol during PF resin synthesis. Therefore, for this purpose, nine of the most abundant mono-aromatic compounds in bio-oil were selected: ortho-, meta-, para-cresol, guaiacol, catechol, 4-methylcatechol, resorcinol, syringol, 4-ethylphenol and resol-type resin from each mono-aromatic were synthesized. Relevant features of the resin such as pH, viscosity, average molecular weight and curing behavior of resins using differential scanning calorimetry (DSC) were analyzed. Scots pine (Pinus sylvestris L.) sapwood samples were used to evaluate the suitability of resin for wood treatment in terms of dimensional stability and were compared with the PF resin-treated wood. From all tested resins, those made of guaiacol or ortho-, or meta-, or para-cresol and/or 4-ethylphenol proved to be suitable for wood treatment, whereas resins made of catechol or 4-methylguaiacol and syringol did not. Suitability of mono-aromatics for synthesis of resol-type resin depends on chemical structure, where the reactivity of the mono-aromatic (derivative of hydroxybenzene) is defined by the type, location and number of substituents.