The broad applicability of the wood modification protocol recently published by Kaufmann et al. allows to improve the fire resistance of renewable materials, too. In this study organophosphorus and organoboron compounds have been synthesized, characterized and subsequently applied for enhanced flame retardancy of wood. Wood hydroxyl groups of Scots pine (Pinus sylvestris L.) sapwood veneer chips were covalently modified upon esterification with benzotriazolyl-activated P- and B-substituted benz-amides. The efficacy of this synthetic strategy was demonstrated by the weight percent gain (WPG) of up to 32% and the corresponding quantities of covalently bonded organicmaterial (QCO) of up to 1.1 mmol/g, respectively. The successful covalent attachment of the functional precursors was proven by attenuated total reflection infrared spectroscopy (ATR-IR). The effect of the flame retardants on the properties of the modified sapwood samples was shown by a significant decrease of the temperature of mass loss from about 346–248 °C in the thermogravimetric analysis (TGA).
“Non-Fickian” diffusion of wood moisture refers to the unexplained anomalous behaviour of water vapour sorption in wood. The depression of moisture diffusion rates in thin sections of wood tissue during moisture content change at high relative humidity is one of the least-understood aspects of “non-Fickian” diffusion. In a previous work, a rate-limiting effect by two cooperative couplings of moisture and heat transfer, was shown to generate some signature features of “non-Fickian” diffusion. The present work aims to heuristically study the simultaneous action of this thermal rate-limiting effect and intrinsic slow relaxation processes in wood. Using an analytical non-geometrical model, exact solutions are obtained which show that the thermal rate-limiting effect acts directly and equally on diffusion and all relaxation processes, effectively time-stretching the entire dynamic wood moisture response. The magnitude of the time-scaling effect is proportional to the coupling strength between heat and mass transfer, which increases progressively with the relative humidity.
Adhesives based on vegetable tannins are already a reality in the market. However, their use is still limited due to their low mechanical resistance and weak humidity resistance. Cellulose nanofibrils (CNFs) are being used as reinforcing materials in various composites, resulting in an improvement of mechanical proprieties in general. The objective of this work was to evaluate the incorporation of CNFs in adhesives made of tannins obtained from the Angico tree (Anadenanthera peregrine). Concentrations of nanofibrils at 1, 5, and 10% were added to the adhesives on a dry basis. Tests of viscosity, pH, solids content, and gel time were performed to determine the physical proprieties of the adhesives. The Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Raman spectra measurements were also determined to understand the interaction between tannins and CNFs. Thermogravimetric analyses (TGA) were carried out to determine the thermal resistance of the composite. The FTIR and Raman characterization identified some differences in the peaks in the chemical composition of the adhesives with different percentages of CNFs. The adhesives showed no different decomposition in the thermogravimetric analyses. The shear strength in the glue line of the adhesive with 5% of CNFs in Toona ciliata woods was determined. Among all the adhesives analyzed, the one with 5% of CNFs produced an improvement in the mechanical resistance and humidity resistance on the glue line.
This study presents a novel application of the Wilhelmy plate method on welded joints of Scots pine sapwood and beech. Welding resulted in an increase in the contact angle (increased hydrophobicity) as well as a decrease in the water uptake and swelling of the welded pine-joint compared to non-welded pine. When the welding time was extended from 4 to 5 s, these properties were further pronounced. Welding of beech, on the other hand, led to an increase in the contact angle and a decrease in the water uptake, but an increase in the swelling.
Fourier Transform Infrared spectroscopy showed that welding increased the aliphatic C–H and unsaturated C=C stretching absorption bands in pine and beech. Scanning electron microscopy showed a dense structure at the welded joints of the both species, giving evidence of a lower porosity that leads to a lower permeability as a result of the welding.
Forests are under great pressure due to climate changes. It is forecast that the importance of Mediterranean type forests will significantly increase. Among various types of oak species, pubescent oak (Quercus pubescens) will likely gain ecological and economic importance in the region south of Alps. Although this wood species is well known, there are not much data available about chemical properties and durability. A comprehensive analysis of extractives and durability against wood decay fungi was therefore performed. The results of the chemical analysis revealed that heartwood contains up to 20% of the extractives, with considerable amounts of phenols, including a fairly high concentration of Gallic acid (GAc). Anatomical structure, with high frequency of tylosis, resulted in good water exclusion efficacy. The presence of biologically active extractives and superior water exclusion efficacy resulted in good durability, as shown by basidiomycetes tests. Based on the laboratory data, factors that determine the service life of wood were calculated. Data indicate superior performance in above-ground applications.
The forest policies of new Congo basin countries have increased the wood timber industry output since the year 2000. Thus, a high content of underutilized wood waste from sawmill, furniture and plywood industries is generated. Among them, Khaya ivorensis A. Chev bark, sapwood and heartwood account for the less valorized wood wastes. Therefore, an attempt was made to study the chemical variability and thermal stability of tannins extracted from the sapwood and heartwood by the acetone/water method (7:3, v:v); the potential recovery of these polyphenols for industrial applications was also aimed. Quantitative analysis pointed out that the heartwood was the most abundant in phenolic units, and a significant difference (P < 0.05) was found in condensed tannin content between the bark, sapwood and heartwood. This result indicated an intra-tree variability while no significant difference was found for inter-tree tannin contents (P > 0.05). These tannins were characterized by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS) and Fourier transform infrared (FTIR) spectroscopy. Their chemical structures were fisitinidin- and gallocatechin-type units. No evidence of free cathechin moiety was found in these extracts. Moreover, oligomers up to seven tannin monomers free from glycosyl structures were found in the K. ivorensis condensed tannins. Moreover, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) pointed out good thermal stability of these hardwood species’ tannin. These findings could be useful for future valorizations of African mahogany wood wastes as source of tannins for chemistry or composite materials.