Volume 72, Issue 8

Kraft cooking kinetics of three different lignocellulosic substrates have been investigated, namely fibers from unbleached kraft pulp (UBKP from Pinus radiata), fibers from softwood unbleached thermomechanical pulp (TMP), and wood chips for TMP production. UBKP and TMP were considered to be representative of a fiber mixture obtained after the pulping and cleaning of old corrugated cardboards (OCC). The characteristic parameters for fitting a mathematical model for kraft pulping were estimated. Based on the results, a “fiber mixture cooking model” was developed to predict the cooking kinetics of TMP/UBKP mixes, accounting for the proportion of each component. The aim was to tailor OCC upcycling in terms of high quality products, which can be used for various purposes including paper and non-paper applications.

Autohydrolysis (AH) prior to the kraft process is one way to valorize hemicelluloses. The presented results show that AH also has a beneficial effect insofar as kraft cooking can be substituted by soda cooking, and higher brightness levels can be achieved under the same bleaching conditions. The lignin has more free phenolic groups after AH, which is attributable to depolymerization, and which could partly explain the better pulping and bleaching results. Another explanation could be the lower amount of lignin involved in lignin carbohydrate complexes after an AH step.

A novel lignin-based slow release fertilizer with low environmental impact has been developed. More precisely, a granulated simple superphosphate fertilizer, consisting of calcium phosphate monobasic [Ca(H 2 PO 4 ) 2 ·H 2 O] and gypsum (CaSO 4 ·2H 2 O) was coated with modified kraft lignins and the diffusion of phosphorus was observed as a function of time. The lignin was hydroxymethylated with formaldehyde and subsequently cross-linked with phenol-formaldehyde resin resulting in HML-PF as coating. Moreover, coating films were prepared from a mixture of acetylated lignin (L ac ) and acetylated cellulose (Cell ac ). Both coatings show similar permeability to calcium phosphate and controlled effectively the P-release, particularly at the initial stages of the experiment. The P-release was linear in the decay phase but there is no lag time in the process. A significant P amount was not released from the particles coated with HML-PF, i.e. 80–50% remained irreversible bound, depending on the coating formulation. The maximum fractional P-release varied among the different coatings tested. Phosphorus is partly retained inside the slightly soluble calcium sulfate matrix.

A new and robust high performance thin-layer chromatography (HPTLC) method has been developed for carbohydrate analysis in biorefinery streams. The samples can be applied directly from industrial streams without any purification or pretreatment, saving time and resources and avoiding potential alterations to the samples’ composition. The main neutral monosaccharides found in wood-based lignocellulosic biomass – glucose, xylose, mannose, arabinose and galactose – can be separated and quantified using acetonitrile:1-pentanol:water (4:1:1, v/v/v) on silica impregnated with a phosphate buffer. Common minor compounds – glucuronic acid, galacturonic acid, rhamnose, cellobiose and hydroxymethylfurfural (HMF) – can also be detected qualitatively. Matrix compounds, which are a major part of biomass, do not interfere with the analysis. Validation showed that the method is selective, has good repeatability and has limits of detection and quantification in the nanogram range. The visual fingerprint offers information on the samples’ constituents in the case of unknown samples. Also, incomplete hydrolysis is indicated by the visibility of oligosaccharides.

Particleboard (PB), medium density fibreboard (MDF), oriented strand board (OSB) and plywood (PW), the most common products of wood panel industry, are produced by means of synthetic adhesives (resins). From the wide range of adhesives employed, amino resins as combination of formaldehyde (F) and urea (U), and melamine (M) are the most important ones, which include the most popular UF and MUF resins. This review is an introduction to the UF and MUF synthesis processes, and also addresses the key parameters for the performance of these adhesives and gives an overview about the final characteristics of PB and MDF prepared with amino resins. The characterization methods for amino resins and panels are outlined. The strategies for the optimization of resin properties and pressing conditions are discussed in terms of their good performance also under conditions of low formaldehyde emission.

Thick poplar veneers (4–8 mm) have been finely fluffed to manufacture novel scrimbers by two paving ways, namely by random and laminated mat formations. The following properties of the scrimbers were evaluated: modulus of rupture (MOR) via static bending, modulus of elasticity (MOE), compression strength (CS), shear strength (SS), water absorption rate, thickness swelling rate (TSR) and width swelling rate. The results show that utilization of fluffed thicker veneers reduced the mechanical properties to a certain extent. The TSR of the scrimber was first improved and then weakened by increasing the thickness of the veneers. The scrimber prepared from 6-mm-thick veneers showed the best waterproof performance. The random and laminated mat formations affected the surface texture significantly but the mechanical properties and dimensional stability to a lesser extent. With increasing resin content, the waterproof performance of the scrimbers was improved, which was not otherwise expected. The mechanical properties remained essentially unchanged except for the shear strength.

Profiled hollow core sandwich panels (SPs) and their components (outer layers and core) were manufactured with ponderosa and lodgepole pine wood strands to determine the effects of low-velocity impact forces and to observe their energy absorption (EA) capacities and failure modes. An instrumented drop weight impact system was applied and the tests were performed by releasing the impact head from 500 mm for all the specimens while the impactors (IMPs) were equipped with hemispherical and flat head cylindrical heads. SPs with cavities filled with a rigid foam insulation material (SP foam ) were also tested to understand the change in EA behavior and failure mode. Failure modes induced by both IMPs to SPs were found to be splitting, perforating, penetrating, core crushing and debonding between the core and the outer layers. SP foam s absorbed 26% more energy than unfilled SPs. SP foam s with urethane foam suffer less severe failure modes than SPs. SPs in a ridge-loading configuration absorbed more impact energy than those in a valley-loading configuration, especially when impacted by a hemispherical IMP. Based on the results, it is evident that sandwich structure is more efficient than a solid panel concerning impact energy absorption, primarily due to a larger elastic section modulus of the core’s corrugated geometry.

The differences in hydrophilicity are a main drawback for wood polymer composites (WPCs). This work aims at compatibilizing bio-derived poly(lactic acid) (PLA), high density polyethylene (PE) and wood fibers (WFs) with either functional PEs [PE-graft-maleic anhydride (MA) (Polybond 3029) or random copolymer of ethylene and glycidyl methacrylate (PE-g-GMA) (Lotader AX8840)] or trihexyl(tetradecyl)phosphonium bistriflamide ionic liquid (IL). The interactions and possible chemical reactions between PLA and functional PE or IL were studied including their mechanical properties. PE-g-GMA significantly increased elongation at break of PLA. According to scanning electron microscopy (SEM), the latter also displays good compatibility with WF. Addition of IL plastifies PLA without degrading it and improves the thermal stability of WF.

The study aimed at treating metil ( Sterculia appendiculata K. Schum) and neem ( Azadirachta indica A. Juss) timber from Mozambique under industrial conditions by steam [Thermowood ® (TW)] and vacuum [Termovuoto (TV)] thermal modifications (TM). Matched boards were treated identically and wood alterations in chemistry, colour, mass loss (ML), mechanical properties and durability were compared. The applied vacuum partly removed the acetic acid that causes carbohydrate degradation, i.e. heat applied under vacuum was less destructive. TM under vacuum generated a lighter colour than that caused by steam treatment. ML was significantly higher after the TW process namely, 14.1 vs. 9.9% after thermo-vacuum treatment for metil and 14.2 and 12.1% for neem. Colour and ML changes correlated with the decrease in shear strength, rupture and elasticity moduli and increase in wood decay resistance. Metil wood is more permeable and demonstrated significant differences between the treatments; the thermo-vacuum process was less destructive but led to less improvement of durability compared to TW treatment.

Aiming at a better leaching resistance of borate-treated wood, the quaternary ammonium compounds (QACs), didecyl dimethyl ammonium chloride (DDAC) and benzalkonium chloride (BAC) were reacted with sodium tetrafluoroborate (NaBF 4 ). The anti-fungal properties of the resulting didecyl dimethyl ammonium tetrafluoroborate (DBF) and benzalkonium tetrafluoroborate (BBF) were tested by the Petri dish method. Poplar ( Populus tomentosa Carr.) and Southern pine ( Pinus spp.) blocks were treated through a two-step method at three molar ratios of NaBF 4 to the QACs. The retentions of the reactive components were determined by inductively coupled plasma atomic emission (ICP-AE) spectroscopy and the distribution of boron in wood was observed by scanning electron microscopy/energy-dispersive X-ray analyses (SEM-EDXA). Fourteen-day leaching and water absorption tests were also performed. DBF and BBF both exhibited moderate fungicidal activity against Trametes versicolor and Gloeophyllum trabeum in Petri dishes. The boron remaining in samples after leaching increased with increasing QACs concentration in the second step impregnation. SEM-EDXA showed no obvious morphological changes in the wood surface and DBF and BBF were only found in the cell walls. The water absorption of the treated samples were lower than the controls.