Wood Furfurylation Research Articles

Effect of Tannins Addition on Thermal Stability of Furfurylated Wood.

This article presents the effect of the addition of condensed tannins, used as a reticulation agent, on the polymerization of furfuryl alcohol during wood furfurylation, as well as the effect of these condensed tannins on the thermal stability of modified wood. Three kinds of dicarboxylic acids (adipic acid, succinic acid, and tartaric acid), as well as glyoxal, used as model of a wood reticulation agent, were used to catalyze the polymerization of furfuryl alcohol or tannin-furfuryl alcohol solutions. Impregnation of furfuryl alcohol or tannin-furfuryl alcohol solution into the wood, followed by curing at 103 °C for a specific duration, was performed for the wood modification. The thermal stability of the obtained tannin-furfuryl alcohol polymers and their corresponding modified woods was investigated. The leaching resistance and dimensional stability of the modified woods were also evaluated. Results indicated that the partial substitution of furfuryl alcohol by the tannins improved the polymerization reactivity in conditions where furfuryl alcohol alone did not lead to the formation of a solid polymeric material. The thermal stability and leaching resistance of the furfurylated wood in the presence of tannins were improved. Dimensional stability was also improved for furfurylated samples, but the effect of tannin addition was not so obvious, depending on the acidic catalyst used.

Modification of Wood by Tannin-Furfuryl Alcohol Resins–Effect on Dimensional Stability, Mechanical Properties and Decay Durability

Furfurylation is a well-known wood modification technology. This paper studied the effect of tannin addition on the wood furfurylation. Three kinds of dicarboxylic acids, adipic acid, succinic acid, and tartaric acid, as well as glyoxal as a comparing agent, were used to catalyse the polymerisation of furanic or tannin-furanic solutions during wood modification. Impregnation of furanic or tannin-furanic solution at a certain concentration into the wood followed with curing at 103°C for a specific duration was performed for the wood modification. Different properties of the modified woods like dimensional stability, resistance of treatment to leaching, mechanical properties, decay durability against white-rot (Coriolus versicolor, Pycnoporus sanguineus) and brown-rot (Coniophora puteana) as well as their chemical and anatomical characteristics were evaluated. Results revealed that the partial substitution of FA by the tannins improved the fixation of the chemicals impregnated in wood. Further, dimensional stability, leaching resistance, Brinell hardness, modulus of elasticity/modulus of rupture, and decay durability properties of the furfurylated wood were also improved in the presence of tannins. Scanning electron microscopy revealed the deposition of the polymer in the wood lumen cells and in the wood cell walls.

Performance improvement of poplar wood based on the synergies of furfurylation and polyethylene glycol impregnation

Abstract Fast-growing wood usually exhibits dimensional instability and inferior mechanical strength, which severely obstructs its wide application. To improve the dimensional stability and mechanical strength, biomass-derived furfuryl alcohol combined with polyethylene glycol (PEG) was vacuum-impregnated into wood hierarchical structures, causing cell wall bulking and porosity reduction. Furfural resin and PEG distributed in cell lumina, cell walls and middle lamella regions indicated by analyses of scanning electron microscope and fourier transform infrared spectroscopy. Wood porosity was generally reduced and the specific surface area decreased by over 65% analyzed by the nitrogen absorption. Consequently, wood hydrophobicity and dimensional stability were highly improved, and the water absorption and volumetric change decreased by over 55% and 78%. The flexural strength and modulus elasticity were improved by over 49% and 46%. Furfural resin helped the fixation of PEG in wood and significantly reduced PEG leaching. PEG with flexible linear molecular structure formed interpenetrating polymer network in wood hierarchical structures with furfural resin and reduced self-crosslinking of furfural resin. Accordingly, the impact toughness of compound modified wood increased by 39% compared with solely furfurylated wood. This study provided efficient and sustainable concepts to facilitate better industrialized application of wood furfurylation and improve service value of fast-growing wood.

Application of polyvinyl alcohol (PVA) as a toughening agent in wood furfurylation

Abstract In order to explore the application of furfurylated wood as engineering material, polyvinyl alcohol (PVA) was proposed as a toughening agent to incorporate with furfuryl alcohol (FA) to form FA/PVA precursor and impregnate wood in a one-step method. After in situ polymerization upon heating, a hydrophobic network composed of polyfurfuryl alcohol (PFA) and PVA was formed within the wood scaffold. The impact toughness, as well as some water-related properties of modified wood including the contact angle, water absorption, moisture adsorption, and dimensional stability were investigated in this study. The results showed that the impact toughness of wood significantly decreased after furfurylation. The incorporation of PVA could alleviate the reduction, and this effect was more obvious for highly furfurylated wood. PVA could penetrate and bulk the wood cell wall to a certain degree, but increased concentration of PVA may negatively influence the penetration of FA in wood cell wall. PVA showed only slight influence on water-related properties of FA modified wood, and it depended on both concentrations of PVA and FA. All results indicate that incorporation of PVA in FA system is a promising approach to enhance the toughness of FA modified wood.

Furfurylation of wood from fast-growing tropical species to enhance their resistance to subterranean termite

The purpose of this study was to use furfurylation to enhance the resistance of wood to subterranean termite attack. Wood samples were obtained from four fast-growing tropical wood species, namely sengon (Falcataria moluccana), jabon (Anthocephalus cadamba), mangium (Acacia mangium), and pine (Pinus merkusii), felled at a short cutting rotation. Specimens were impregnated with furfuryl alcohol (FA) solution and tartaric acid as a catalyst and then heated at 100 °C for 24 h. After conditioning, the specimens were exposed to subterranean termite attack in the laboratory according to the Indonesian standard. Furfurylated samples were found to have a higher density presumably because poly-FA filled the void space. It also had a lower moisture content because of the presence of poly-FA bulking in the wood cell wall, making it more hydrophobic. Furfurylation greatly enhanced subterranean termite attack resistance of wood, as shown by remarkably higher termite mortality, higher wood resistance class, lower wood weight percent loss, and reduced termite feeding rate. Based on the Indonesian standard, in which class I indicates very resistant wood and class V indicates very poorly resistant wood, untreated wood was class IV, but all furfurylated wood specimens were rated as class I.

Furfurylation protects timber from degradation by marine wood boring crustaceans

We fed furfurylated and control wood to gribble. Our results imply that furfurylation of wood protects against degradation by gribble without the reliance on broad spectrum biocides and can reduce costs associated with damaged wooden structures.

Comparison of physical-mechanical and mould-proof properties of furfurylated and DMDHEU-modified wood

In this study, 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) and furfuryl alcohol (FA) modification catalyzed by acrylic acid were comparatively studied. The effects on physical-mechanical properties and durability against mould of Masson pine and Camphor pine wood were investigated, including weight gain rate (WPG), moisture uptake, equilibrium moisture content (EMC), anti-swelling efficiency (ASE), parallel-to-grain compressive strength (CS), modulus of rupture (MOR), and mould resistance. The wood samples modified with DMDHEU closely retained their original color and texture, whereas the color of furfurylated wood became dark brown and the texture became clearer. The WPG of DMDHEU-treated wood ranged from 17.9% to 29.3%, which was lower than that of furfurylated wood that ranged from 36.7% to 39.3%. The equilibrium moisture content of DMDHEU-modified wood was slightly higher than the untreated wood, while furfurylation decreased the EMC of wood by approximately 50% compared with the untreated wood. The dimensional stability, parallel-to-grain compressive strength, and mildew resistance of Masson pine and Camphor pine improved after both modifications noticeably. It was concluded that acrylic acid can be utilized as a catalyst to perform wood furfurylation and DMDHEU modification.

How does delignification influence the furfurylation of wood?

To investigate the influence of delignification on wood furfurylation, poplar wood (Populus euramericana Cv.) was partly delignified prior to the impregnation of furfuryl alcohol (FA) at concentration of 25%. The observation by using scanning electron microscope (SEM) and confocal laser scanning microscopy (CLSM) showed that many intercellular spaces appeared in middle lamella and cell corners in the wood with 8.86% lignin loss (LL), after further furfurylation, these spaces were filled with polymerized furfural resin, which contributed to the more uniform distribution of modifier and larger bulking of cell wall in furfurylated wood with low lignin (LF) than furfurylated control (CF). The size distribution of mesopores increased after delignification but decreased after furfurylation, and the specific surface area was reduced over 20% for LF with about 50% total pore volume decrease compared with the control from the analysis of nitrogen adsorption. Lignin loss and chemical polymerization of furfural resin were confirmed but without chemical reaction between FA and cell wall components by both results of Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). Delignification resulted in increased equilibrium moisture content (EMC) and dimensional instability, after further furfurylation, the EMC and dimensional changes of LF decreased and were lower than those of control by 16.3% on average, suggesting the availability of furfurylation in reducing moisture sorption and improving dimensional stability of low lignin content wood. The number of accessible hydroxyl groups in wood calculated by using Hailwood-Horrobin theory exhibited in the following order: LL > control > LF > CF. The results can potentially help with understanding the action of delignification in wood furfurylation, as well as providing information on the possibility of make sustainable use of wood products with degraded lignin by furfurylation.

Lignin-based catalysts for Chinese fir furfurylation to improve dimensional stability and mechanical properties

In order to valorize lignin from spent liquor of pulping mills, a novel catalyzing system for wood furfurylation which composed of lignin-derived acids (LDAs, i.e. lignosulfonic acid and sulfomethylated lignin acid) and buffer sodium borate was developed, and was applied to Chinese fir furfurylation for improved dimensional stability and mechanical properties. LDAs were prepared by protonating of sulfomethylated lignin and lignosulfonate through cation exchange resin. The catalyzing system was optimized by the storage duration of FA formulas with respective catalyzing system at room temperature and the curing time at elevated temperature. Then, three formulas were selected out to treat Chinese fir and their performance was evaluated by weight percentage gain, dimensional stability, and compressive strength. The results showed that LDAs, especially sulfomethylated lignin acid, penetrated into cell walls and catalyzed furfurylation reaction quite well. The best performance achieved in this study by Formula III was with weight percentage gain of 66.4%, equilibrium moisture content 12.9%, anti-swelling efficiency 61.9% and 70.6% for the conditions of high humidity and water-soaking, respectively; its parallel-to-grain compressive strength was improved by 45.4%. It hints lignin-derived acids combined with borate would be a promising catalyst system for wood furfurylation since it valorizes both the waste lignin and low-valued wood.

Chemical Modification of Wood by Acetylation or Furfurylation: A Review of the Present Scaled-up Technologies

Significant developments in the area of wood modification have been achieved during the last three decades. These developments can be attributed to increased environmental concerns, the escalating demand for a high and constant quality of wood products, and the rising prices of the durable tropical timber as well as its very limited availability, as affected by illegal logging. As a consequence, a number of wood modification techniques such as chemical and impregnation modifications or heat treatments have been introduced, and some of these technologies have reached the industrial level. This review paper deals with two successful technologies, that is, wood acetylation and wood furfurylation. It briefly discusses the advantages of the new modified products and presents in short their improved properties. Published findings indicate that chemical modification of wood, to a full or partial degree, by means of acetylation or furfurylation, offers a way to transform low durability wood species to new ‘green’ wood materials having advanced qualities and properties.

Melamine Formaldehyde Modified Furfurylation to Improve Chinese Fir’s Dimensional Stability and Mechanical Properties

Melamine formaldehyde modified furfurylation (MFMF) was developed in this investigation to overcome the issues encountered by traditional wood furfurylation, the strong acidic reaction condition and the high cost of furfuryl alcohol. In this study, the optimum ratio of melamine, formaldehyde, and furfuryl alcohol constituents and the optimum curing conditions were explored. Then, MFMF was applied to Chinese fir modification and its performance was evaluated by the weight gain rate (WGR), equilibrium moisture content (EMC), dimensional stability (anti-swelling efficiency [ASE]), and parallel-to-grain compressive strength. The results showed that MFMF took place at a pH close to neutral (6.8) and the formulas had good penetration of cell walls. The best stability and improvement to mechanical properties achieved by MFMF were: a WGR of 158.9%; a low EMC of 11.5% under 96% relative humidity conditions; an ASE in high humidity and water-soaked conditions of 58.5% and 64.2%, respectively; and an increase in parallel-to-grain compressive strength by 81.9%, when compared with the control.

Tartaric acid catalyzed furfurylation of beech wood

European beech (Fagus sylvatica L.) is a major tree species of European forest which is underexploited because of its low dimensional stability and durability. Similarly to what has been developed with radiata pine, furfurylation might be the answer to optimize the utilization of local beech wood. Beech wood furfurylation process was studied using five different catalysts: maleic anhydride, maleic acid, citric acid, itaconic acid, and tartaric acid. Optimization of the furfurylation process was investigated for different catalyst and furfuryl alcohol (FA) contents, and different duration of polymerization. The following properties were studied: weight percent gain (WPG), leachability, anti-swelling efficiency (ASE), wettability, modulus of elasticity, modulus of rupture, Brinell hardness, and decay durability. Tartaric acid, never investigated up to now, was retained as catalyst to perform furfurylation due to its efficacy compared to other catalysts and its novelty. Wood modification with FA and tartaric acid as catalyst led to samples with high WPG even after leaching, improved ASE, and lower wettability with water. Increasing the polymerization duration increased the fixation of FA in treated wood. Most of all, treatment gave a significant improvement in mechanical properties and resistance to wood decaying fungi.

Determining the curing parameters of furfuryl alcohol for wood modification by nanoindentation

Wood furfurylation is a very promising modification process, which can greatly improve several important properties of wood simultaneously. The polymerization degree of furfuryl alcohol (FA) in wood significantly influences the performances of modified wood. However, it is normally time-consuming and expensive to determine the curing parameters of a new FA solution formula for a target wood species, as the process requires lots of lab-scale experiments. To address this challenge, nanoindentation was used to determine the hardness and elastic modulus of FA resin which are cured with different catalyst content, curing time and curing temperature, assuming that these mechanical properties should closely relate to the polymerization degree of cured FA (resin). Single-factor experiments were designed to obtain preliminary curing parameters. Three key curing parameters were selected, namely the catalyst content of maleic anhydride (1.5, 3, 5 %), curing time (2, 3, 4, 5, 6 h) and curing temperature (95, 105, 115, 125 °C). The proposed set of curing parameters based on the nanoindentation results are 3 % maleic anhydride, 3 h curing time and 105 °C curing temperature. This set of parameters was slightly modified and then used as the starting process parameters for Masson pine modification, which resulted in greatly improved wood properties. Therefore, the method proposed in this study offers an effective and time-saving means of developing new processes of wood furfurylation.

The Furfurylation of Wood: A Nanomechanical Study of Modified Wood Cells

Furfurylation of wood is of interest worldwide as an environmentally friendly modification process. It is widely assumed that low-molecular weight furfuryl alcohol (FA) can penetrate into wood cells and polymerize in-situ during the process, resulting in substantial improvement in the physical-mechanical properties and durability of wood. In this study, confocal laser scanning microscopy (CLSM) was used to visualize the microscopic distribution of polymerized FA resin in the Masson pine wood cavities, and a Nanoindenter was used to probe the mechanical properties of modified wood cells. The effects of catalysts (maleic anhydride and a mixed organic acid catalyst), FA concentration, curing time, and curing temperature on the nanomechanical properties of wood cell walls were investigated. An improvement in the indentation modulus and hardness of modified wood cells demonstrated indirectly but strongly that FA indeed penetrated wood cells during the modification process. Based on the results of the cell wall nanoindentation test, a combination of 50% furfuryl alcohol, 8 h curing time, and 95 °C curing temperature were proposed as the starting processing parameters for the development of a more practical and effective wood furfurylation process using a mixed organic acid catalyst.

Macroscopic and microscopic monitoring of swelling of beech wood after impregnation with furfuryl alcohol

Wood furfurylation is a modification method that improves several wood properties. Thereby wood is impregnated with a solution of furfuryl alcohol, catalysts and water, in general. The objective of this study was to understand the penetration of furfuryl alcohol into wood. Furthermore, a possible relationship between the substance amount and the swelling behaviour should be determined. To this end microscopic investigations were conducted to describe the temporal process of penetration and swelling. It was found that the swelling coefficients differ at the microscopic and macroscopic level. The microscopic swelling can reach twice the values of macroscopic swelling.

The fluorescence characteristics of furfurylated wood studied by fluorescence spectroscopy and confocal laser scanning microscopy

The fluorescence of furfurylated wood was studied. Furfurylation of wood introduced fluorescent curing products into the cell walls. Fluorescent products were also found in the lumina if high loadings were used and/or if the wood contained cells with small radii. More intense fluorescence was obtained from lignin-rich parts of the compound cell wall (i.e., the middle lamella and the cell corners) than from the secondary cell wall if the wood was impregnated using furfuryl alcohol (FA), while impregnation using small poly(FA) oligomers showed no or only minor differences between different regions. The study also showed that when higher amounts of catalyst were added to the impregnation liquid, a red-shift in the fluorescence from the furfurylated wood was seen, corresponding to an increased conjugation length of conjugated poly(FA) formed within the wood cell wall. Longer conjugation length than within the cell wall was observed for the poly(FA) formed within the lumina. This indicates that the cell wall polymers restrict poly(FA) formation.

Poly(furfuryl alcohol) formation in neat furfuryl alcohol and in cymene studied by ATR-IR spectroscopy and density functional theory (B3LYP) prediction of vibrational bands

Poly(FA) formation was studied using Attenuated Total Reflectance (ATR)-IR spectroscopy and theoretical predictions of the vibrational bands of appropriate poly(FA) model structures. This combination of methods allowed different reaction phases and product types to be identified. Aliphatically linked furan units explained most of the dominant bands with an average frequency prediction error of 6 cm −1. Changes in IR band positions and shapes, e.g. the furanic ring CH wag bands at ∼730–800 and 1010–1020 cm −1, reflect the degree of polymerization and the overall reaction progress. The predictions allowed to correct previous misassignments of bands of the aliphatically linked polymer, and furthermore the present work is the first to consider the vibrations of conjugated poly(FA) chains and Diels–Alder cross-links. Based on predicted and observed vibrations, these product types are suggested to be present throughout the reaction. The results show an unexplored potential of gaining insight into poly(FA) formation and wood furfurylation from vibrational spectroscopy and theoretical predictions.

Development of Modified Wood Products Based on Furan Chemistry

The first processes for “furfurylation” of wood (wood modification with furfuryl alcohol) were developed several decades ago. Furfuryl alcohol is a renewable chemical since it is derived from furfural, produced from hydrolysed biomass waste. Over the last decade modernised processes for furfurylation of wood have been developed. These new processes are based on completely new catalytic systems and process additives. The properties of furfurylated wood depend on the retention of grafted/polymerised furfuryl alcohol (PFA) in the wood. At high modification levels (high retention of PFA) the enhancement of a wide variety of properties are achieved: an exceptional hardness increase, exceptional resistance to microbial decay and insect attack, high resistance to chemical degradation, increase in MOR and MOE, and high dimensional stability. At lower modification levels many property enhancements also occur, however to slightly lower extent. Notable are resistance to microbial decay and insect attack, increase in MOR and MOE, and relatively high dimensional stability. Two main processes for production of furfurylated wood have been developed for Kebony ASA (Former Wood Polymer Technology ASA) by the authors. Kebony TM for hardwood modification and VisorWood TM for soft wood modification, where the name reflects the colour of the material produced by the process. Commercial production according to the Kebony process has been running since October 2003, mainly for flooring. A small Kebony production plant is now in operation in Lithuania. A Kebony/VisorWood production plant was started during of 2003 in Porsgrunn, Norway. There are now planed for an expansion of this plant, and plans for a large Visorwood plant is ongoing. Further commercialisation of the technology will be done through licences issued by Kebony ASA.

Chemistry and ecotoxicology of furfurylated wood

Over the past decade modernized processes for furfurylation of wood have been developed. These new processes are based on completely new catalytic systems and process additives. These new systems do not add metals or halogens to the product, which is important for an environmentally acceptable product. However, little is known about the ecotoxicity of furfurylated wood or other environmental impacts that may result from the modification method. The study shows that concentrations of non-reacted furfuryl alcohol in the final products are low and do not contribute to any fungicidal effect. Environmental tests show no significant level of increased ecotoxicity, and degradation through combustion does not release any volatile organic compounds or polyaromatic hydrocarbons above normal levels for wood combustion. Hence, furfurylation of wood to enhance wood properties is not believed to be harmful to the environment.

Properties of furfurylated wood

The first processes of wood modification with furfuryl alcohol (FA) (furfurylation) were developed several decades ago. FA is a renewable chemical, produced from hydrolysed biomass waste. Over the past decade modernized processes for furfurylation of wood have been developed. This study presents decay properties of furfurylated wood. Laboratory methods and field tests were performed on fungi, termite and marine borer attack. Tests on physical and mechanical properties are also presented. The properties of furfurylated wood depend on the retention of grafted/polymerized poly-FA in the wood. At high modification levels (high retention of poly-FA) the enhancement of a wide variety of properties is achieved: an exceptional increase in hardness, exceptional resistance to microbial decay and insect attack, increase in modulus of rupture (MOR) and modulus of elasticity, and high dimensional stability. At lower modification levels property enhancements also occur. Notable are resistance to microbial decay and insect attack, and relatively high dimensional stability.