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Wood Modification: Optimisation and Characterisation of Modified Timbers

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A special issue of Forests (ISSN 1999-4907). This special issue belongs to the section "Wood Science and Forest Products".

Deadline for manuscript submissions: closed (8 March 2024) | Viewed by 16843

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Dr. Morwenna Spear

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Guest Editor

The BioComposites Centre, Bangor University, Bangor, UK
Interests: wood chemistry; wood decay; wood modification; wood protection; viscoelasticity; macromolecular effects in the cell wall; wood anatomy; mechanical properties; fluid flow
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Dr. Miklós Bak

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Guest Editor

Faculty of Wood Engineering and Creative Industries, University of Sopron, Sopron, Hungary
Interests: wood modification; wood structure and properties; hygroscopic properties; nanotechnology; durability; biopolymers
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Wood modification techniques such as thermal modification, acetylation, and furfurylation have been well studied and commercially available. Many other modification systems for wood are still under development, using resins, bio-based chemicals, biopolymers, and novel combinations of heat, pressure, steam, or other active components. Most wood modification systems seek to enhance dimensional stability, while many also extend service life and provide durability and resistance to fungal decay, weathering, or insect and marine borer attacks. In recent years, innovation in wood modification has focused on three main themes: combining modifications to increase the range of benefits offered; seeking bio-based or green chemistry modifications; and introducing nanotechnologies to provide innovative functional materials. Papers relating to all of these aspects are welcomed for this Special Issue of Forests.

Potential topics include, but are not limited to:

Thermal modification;
Chemical modification;
Passive chemical modification;
Bio-based polymers, resins, and reagents for modification;
Novel combined modification systems;
Nanotechnology in wood modifications;
Sustainability in wood modification;
Service life and durability of modified wood;
Properties of modified wood.

Dr. Morwenna Spear
Dr. Miklós Bak
Guest Editors

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Keywords

wood modification
thermal modification
chemical modification
impregnation
hygroscopic properties
mechanical properties
surface properties
service life
durability
sustainability

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Published Papers (11 papers)

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Editorial

Jump to: Research

4 pages, 665 KiB

Open AccessEditorial

Wood Modification—Trends and Combinations

by Morwenna J. Spear and Miklós Bak

Forests 2024, 15(7), 1268; https://doi.org/10.3390/f15071268 - 20 Jul 2024

Viewed by 707

Abstract

Wood modification is a field that has enjoyed sustained interest over the past two decades, although its history can be tracked back significantly further, to the pioneering work of Alfred Stamm and co-workers at the Forest Products Laboratory in the USA in the [...] Read more.

(This article belongs to the Special Issue Wood Modification: Optimisation and Characterisation of Modified Timbers)

Research

Jump to: Editorial

20 pages, 5753 KiB

Open AccessArticle

Moisture and Temperature Profiles of Heartwood Pinus pinaster Ait. Wood Specimens during Microwave Drying

by Fernando Júnior Resende Mascarenhas, Rogério Manuel dos Santos Simões, Alfredo Manuel Pereira Geraldes Dias, André Luis Christoforo and André Eduardo Palos Cunha

Forests 2024, 15(6), 944; https://doi.org/10.3390/f15060944 - 30 May 2024

Cited by 1 | Viewed by 763

Abstract

Microwave (MW) drying of wood has gained popularity in the field of wood modification. The rise in temperature during MW drying leads to increased steam pressure, enhancing wood permeability but potentially decreasing mechanical properties. Understanding temperature and moisture behaviors during MW drying is crucial for its industrial application in wood drying. Therefore, this study aimed to characterize the temperature and moisture behaviors during MW drying of small Portuguese maritime pine (Pinus pinaster Aiton.) wood samples to support a wider use of this technology. The effects on water uptake and the compressive strength parallel to the grain were also investigated. The results indicated three distinct phases in the MW drying rates, with an average of 0.085% of water removed per second. Moreover, the temperature underwent three distinct stages: an initial rapid increase, a period of constant temperature, and a slight decrease until drying was complete. At the beginning of MW drying, the temperatures were below 100 °C, with average temperatures ranging from 126 to 145 °C. Specimens with lower initial moisture content had higher temperatures, and a positive correlation was found between initial moisture content and drying time. In contrast, negative correlations were found between the initial moisture content and average temperature, as well as average temperature and MW drying time. Additionally, the operating condition parameters used in MW drying of pine samples enhanced water impregnability by 65%, generating a slight reduction of 11% in compressive strength. It was also noticed that the initial moisture content did not impact MW-dried samples’ water uptake or compressive strength. Finally, although small clear wood samples of maritime pine were utilized, the temperature and moisture patterns observed closely matched real-scale specimens. Thus, the findings corroborate a wide utilization of MW technology for wood drying, mainly demonstrating positive possibilities for structural-sized wood specimens. Full article

(This article belongs to the Special Issue Wood Modification: Optimisation and Characterisation of Modified Timbers)

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14 pages, 3228 KiB

Open AccessArticle

Chemical Composition of Larch Oleoresin before and during Thermal Modification

by Morwenna J. Spear, Athanasios Dimitriou and Ray Marriott

Forests 2024, 15(6), 904; https://doi.org/10.3390/f15060904 - 23 May 2024

Cited by 2 | Viewed by 931

Abstract

Larch is a strong timber, which grows rapidly in the UK climate, but can contain abundant resin pockets. To address the resin exudation issue, a mild thermal modification process has been developed, promoting the curing of the resin. This paper reports a series of studies which characterised the chemical profile of larch oleoresin before and after the mild thermal treatment, explaining the changes which occur when resin is dried. Further experiments were used to simulate specific points in time during the mild treatment process. The non-polar components of the fresh (untreated) and treated larch oleoresin were profiled using gas chromatography mass spectrometry (GC-MS). Fresh larch oleoresin was also subjected to isothermal experiments at different temperatures in a thermogravimetric analyser–differential scanning calorimeter (TGA/DSC), followed by re-analysing the resin composition. This demonstrated the loss of monoterpenes at temperatures of 120 °C and above, with complete loss by isothermal conditions of 150 °C and 60 min. The partial loss of sesquiterpene alkanes and alkenes were also observed at all temperatures, although completeness of this loss was achieved at isothermal temperatures of 150 °C and above. The diterpene composition was seen to change for isothermal experiments conducted at 150 °C and above, with a dehydration of terpenols to form the equivalent terpene alkenes. The observed physical changes in the TGA/DSC experiment were in good agreement with observations of the oleoresin sampled from thermally modified larch planks. Full article

(This article belongs to the Special Issue Wood Modification: Optimisation and Characterisation of Modified Timbers)

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12 pages, 1752 KiB

Open AccessArticle

Densification of Delignified Wood: Influence of Chemical Composition on Wood Density, Compressive Strength, and Hardness of Eurasian Aspen and Scots Pine

by Przemysław Mania, Carlo Kupfernagel and Simon Curling

Forests 2024, 15(6), 892; https://doi.org/10.3390/f15060892 - 21 May 2024

Cited by 2 | Viewed by 1369

Abstract

The densification of solid wood is a well-studied technique that aims to increase the strength and hardness of the material by permanently compressing the wood tissue. To optimise the densification process in this study, a pre-treatment with sodium sulphite was used (delignification). With delignification prior to densification, one achieves higher compression ratios and better mechanical properties compared to densification without pre-treatment. The reactivity of syringyl (dominant in hardwoods) and guaiacyl (dominant in softwoods) lignin towards delignification is different. The influences of this difference on the delignification and densification of softwoods and hardwoods need to be investigated. This study aimed to densify wood after delignification and investigate how variations in chemical composition between coniferous and deciduous species affect the densification process. Scots pine and Eurasian aspen specimens with a similar initial density were investigated to study the influence of the different lignin chemistry in softwoods and hardwoods on the densification process. Both timbers were delignified with sodium sulphite and sodium hydroxide and subsequently densified. While the delignification was twice as efficient in aspen than in pine, the compression ratios were almost identical in both species. The Brinell hardness and compressive strength showed a more significant increase in aspen than in Scots pine; however, one exception was the compressive strength in a radial direction, which increased more effectively in Scots pine. Scanning electron microscopy (SEM) revealed the microstructure of densified aspen and Scots pine, showing the crushing and collapse of the cells. Full article

(This article belongs to the Special Issue Wood Modification: Optimisation and Characterisation of Modified Timbers)

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19 pages, 4524 KiB

Open AccessArticle

Silver Nanoparticles and Chitosan Oligomers Composites as Poplar Wood Protective Treatments against Wood-Decay Fungi and Termites

by Eleana Spavento, María Teresa de Troya-Franco, Luis Acuña-Rello, Mónica Murace, Sara M. Santos, Milagros Casado-Sanz, Roberto D. Martínez-López, Jesús Martín-Gil, Javier Álvarez-Martínez and Pablo Martín-Ramos

Forests 2023, 14(12), 2316; https://doi.org/10.3390/f14122316 - 25 Nov 2023

Cited by 3 | Viewed by 1432

Abstract

This study focuses on Populus ×euramericana (Dode) Guinier, a globally distributed fast-growing tree. Despite its valuable wood, it exhibits low durability. The aim of this study was to assess the efficacy of a binary composite comprising silver nanoparticles (AgNPs) and chitosan oligomers (COS) in protecting P. ×euramericana ‘I-214’ wood against degradation caused by xylophagous fungi and termites through vacuum-pressure impregnation. The test material was carefully selected and conditioned following the guidelines of EN 350:2016, and impregnation was carried out in accordance with EN 113-1:2021. Five concentrations of AgNPs–COS composites were utilized. Biodeterioration resistance was evaluated based on EN 350:2016 for white (Trametes versicolor (L.) Lloyd) and brown (Coniophora puteana (Schumach.) P.Karst.) rot fungi, and EN 117:2012 for subterranean termites (Reticulitermis grassei Clément). The durability class and use class were assigned following EN 350:2016 and EN 335:2013, respectively. In comparison to the untreated control, the binary solution at its highest concentration (AgNPs 4 ppm + COS 20 g·L⁻¹) demonstrated a notable reduction in weight loss, decreasing from 41.96 ± 4.49% to 30.15 ± 3.08% for white-rot fungi and from 41.93 ± 4.33% to 27.22 ± 0.66% for brown rot fungi. Furthermore, the observed termite infestation shifted from “heavy” to “attempted attack”, resulting in a decrease in the survival rate from 53.98 ± 10.40% to 26.62 ± 8.63%. Consequently, the durability classification of P. ×euramericana I-214 witnessed an enhancement from “Not durable” to “Slightly” and “Moderately durable” concerning decay fungi and termites, respectively. These findings expand the potential applications of this wood and substantiate the advantages of employing this environmentally friendly treatment. Full article

(This article belongs to the Special Issue Wood Modification: Optimisation and Characterisation of Modified Timbers)

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14 pages, 3491 KiB

Open AccessFeature PaperArticle

Wood Modification Using Imidazole and Succinimide: Effects on Dimensional Stability and Bending Properties

by Alexander Scharf, Henric Dernegård, Johan Oja, Dick Sandberg and Dennis Jones

Forests 2023, 14(10), 1976; https://doi.org/10.3390/f14101976 - 29 Sep 2023

Cited by 3 | Viewed by 1385

Abstract

The modification of Scots pine sapwood (Pinus sylvestris L.) with the heterocyclic compounds imidazole and succinimide was investigated. Pressure-impregnation with aqueous solutions containing imidazole, imidazole + citric acid, succinimide, succinimide + citric acid, and citric acid + sorbitol (CIOL^®) with solid contents of 5%, 10%, and 15% was followed by oven-curing at 220 °C for 1 h. During the treatment steps, the changes in mass, bending properties, and anti-swelling efficiency (ASE) were examined. The results indicate that solid concentrations within the range of 5% to 10% were optimal. The results seem to show that there are two differing mechanisms in the modification of imidazole and succinimide, respectively. Mass loss due to heat treatment was highest in the imidazole-treated specimens, whereas it remained low and concentration-independent in the succinimide-treated specimens. After three cycles, the ASE reached 31% for the imidazole-treated specimens and improved to 38% with the addition of citric acid. For succinimide, the ASE increased from 17% to 41%. The bending properties generally showed improvement, except for succinimide + citric acid and CIOL^®, which displayed a reduced modulus of rupture. Chemical analyses are warranted to fully understand the reaction mechanisms of these treatments. The positive effects of imidazole treatment are suggested to stem from a thermal reaction between the chemical and the wood, indicated by substantial mass loss during leaching and specimen darkening. Succinimide and citric acid might exhibit polymerization with each other and with wood components, which is akin to the CIOL^® process. Further research should delve into the reaction mechanisms and the impact of imidazole and succinimide on biological durability. Full article

(This article belongs to the Special Issue Wood Modification: Optimisation and Characterisation of Modified Timbers)

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14 pages, 4418 KiB

Open AccessArticle

Effect of Citric Acid on the Properties of Sapwood of Pinus sylvestris Submitted to Thermomechanical Treatment

by Matheus Crisostomo, Cláudio Del Menezzi, Holger Militz, Katarzyna Kurkowiak, Aaron Mayer, Luisa Carvalho and Jorge Martins

Forests 2023, 14(9), 1839; https://doi.org/10.3390/f14091839 - 9 Sep 2023

Cited by 3 | Viewed by 1075

Abstract

The present study aimed to evaluate the effect of citric acid on the properties of solid pine wood, which were submitted to thermomechanical treatment. A preliminary test was performed in a previous study to evaluate the influence of different temperatures of pressing and concentrations of citric acid on the physical properties of wood. After choosing the best treatments (170 °C and 5% and 10% of citric acid), the effect of these on the chemical properties (SEM, FTIR and pH); on the density profile using an X-ray microtomography and on the resistance to aging through an abrasion test were evaluated. The result of the chemical analysis showed an increase of the presence of ester functional groups, as well as better coverage and higher acidity of the surface. The density profile technique allowed us to observe the formation of peaks of density on the surface where the acid was applied. Lastly, it was also possible to verify an increase in the resistance to abrasions because of the application of citric acid. Full article

(This article belongs to the Special Issue Wood Modification: Optimisation and Characterisation of Modified Timbers)

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15 pages, 3894 KiB

Open AccessArticle

Improvement of the Dimensional Stability of Rubber Wood Based on the Synergies of Sucrose and Tung Oil Impregnation

by Chunwang Yang, Susu Yang, Huanxin Yang, Buapan Puangsin and Jian Qiu

Forests 2023, 14(9), 1831; https://doi.org/10.3390/f14091831 - 8 Sep 2023

Cited by 2 | Viewed by 1417

Abstract

Rubber wood often exhibits dimensional instability during use, which seriously hinders its widespread application. In order to enhance the dimensional stability of rubber wood, a two-step method was employed in this study to modify rubber wood using two plant-derived compounds, namely sucrose and tung oil. Samples treated alone with sucrose or tung oil were also prepared. The water absorption, dimensional stability, and thermal stability of modified and untreated wood were evaluated. The results show that wood samples treated with 30% sucrose and tung oil had excellent water resistance and dimensional stability based on the synergistic effect of sucrose and tung oil. After 384 h of immersion, the 30% sucrose and tung oil group presented a reduction in water absorption by 76.7% compared to the control group, and the anti-swelling efficiency was 57.85%, which was 66.81% higher than that of the tung oil treatment alone. Additionally, the leaching rate of the 30% sucrose and tung oil group decreased by 81.27% compared to the sample modified with the 30% sucrose solution alone. Simultaneously, the 30% sucrose and tung oil group showed better thermal stability. Therefore, this study demonstrates that the synergistic treatment of modified rubber wood by sucrose and tung oil is an eco-friendly, economical, and highly efficient approach with the potential to expand the range of applications of rubber wood products. Full article

(This article belongs to the Special Issue Wood Modification: Optimisation and Characterisation of Modified Timbers)

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12 pages, 2949 KiB

Open AccessArticle

Prediction of Thermally Modified Wood Color Change after Artificial Weathering Based on IPSO-SVM Model

by Juncheng Li, Ning Li, Jinze Li, Wei Wang and Haolin Wang

Forests 2023, 14(5), 948; https://doi.org/10.3390/f14050948 - 4 May 2023

Cited by 3 | Viewed by 1396

Abstract

The support vector machine (SVM) model was applied to predict the color change of heat-modified wood after artificial weathering. In order to improve the prediction performance, the improved particle swarm optimization (IPSO) algorithm was used to optimize the parameters of the SVM model, and an improved particle swarm optimized support vector machine (IPSO-SVM) model was established on the basis of the nonlinear descending weight strategy to improve the particle swarm optimization. To verify the performance of the established model, the MAE, RMSE, and R² of the test set and training set were compared with the PSO-SVM model and the SVM model. Analysis of the results showed that compared to the PSO-SVM model and the SVM model, the IPSO-SVM model reduced the RMSE of the training set data by 49% and 72%, the MAE by 52% and 78%, the STD by 14% and 68%, the test set data by 6% and 24%, the MAE by 2% and 25%, and the STD by 22% and 29%, respectively. The results show that modeling studies using the IPSO-SVM model provide results showing that color changes in heat-modified wood after artificial weathering can be successfully predicted without expensive and time-consuming experimental studies. Full article

(This article belongs to the Special Issue Wood Modification: Optimisation and Characterisation of Modified Timbers)

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29 pages, 4818 KiB

Open AccessArticle

Predicting the Mechanical Properties of Heat-Treated Woods Using Optimization-Algorithm-Based BPNN

by Runze Zhang and Yujie Zhu

Forests 2023, 14(5), 935; https://doi.org/10.3390/f14050935 - 2 May 2023

Cited by 31 | Viewed by 2619

Abstract

This paper aims to enhance the accuracy of predicting the mechanical behavior of wood subjected to thermal modification using an improved dung beetle optimization (IDBO) model. The IDBO algorithm improves the original DBO algorithm via three main steps: (1) using piece-wise linear chaotic mapping (PWLCM) to generate the initial dung beetle species and increase its heterogeneity; (2) adopting an adaptive nonlinear decreasing producer ratio model to control the number of producers and boost the algorithm’s convergence rate; and (3) applying a dimensional learning-enhanced foraging (DLF) search strategy that optimizes the algorithm’s ability to explore and exploit the search space. The IDBO algorithm is evaluated on 14 benchmark functions and outperforms other algorithms. The IDBO algorithm is then applied to optimize a back-propagation (BP) neural network for predicting five mechanical property parameters of heat-treated larch-sawn timber. The results indicate that the IDBO-BP model significantly reduces the error compared with the BP, tent-sparrow search algorithm (TSSA)-BP, grey wolf optimizer (GWO)-BP, nonlinear adaptive grouping grey wolf optimizer (IGWO)-BP and DBO-BP models, demonstrating its superiority in predicting the physical characteristics of lumber after heat treatment. Full article

(This article belongs to the Special Issue Wood Modification: Optimisation and Characterisation of Modified Timbers)

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16 pages, 2124 KiB

Open AccessArticle

Phase-Change-Material-Impregnated Wood for Potential Energy-Saving Building Materials

by Ahmet Can, Seng Hua Lee, Petar Antov and Muhammad Aizat Abd Ghani

Forests 2023, 14(3), 514; https://doi.org/10.3390/f14030514 - 6 Mar 2023

Cited by 12 | Viewed by 2460

Abstract

PCMs (phase change materials) are ideal for thermal management solutions in buildings. This is because they release and store thermal energy during melting and freezing. When this material freezes, it releases a lot of energy in the form of latent heat of fusion or crystallization energy. Conversely, when the material melts, it absorbs the same amount of energy from its surroundings as it changes from a solid to a liquid state. In this study, Oriental spruce (Picea orientalis L.) sapwood was impregnated with three different commercial PCMs. The biological properties and the hygroscopic and thermal performance of the PCM-impregnated wood were studied. The morphology of PCM-impregnated wood was characterized through the use of scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). PCM-impregnated wood demonstrated low performance in terms of storing and releasing heat during phase change processes, as confirmed by DSC. The results show that PCMs possess excellent thermal stability at working temperatures, and the most satisfying sample is PCM1W, with a phase change enthalpy of 40.34 J/g and a phase change temperature of 21.49 °C. This study revealed that PCMs are resistant to wood-destroying fungi. After the 96 h water absorption test, the water absorption of the wood samples decreased by 28%, and the tangential swelling decreased by 75%. In addition, it has been proven on a laboratory scale that the PCM material used is highly resistant to biological attacks. However, large-scale pilot studies are still needed. Full article

(This article belongs to the Special Issue Wood Modification: Optimisation and Characterisation of Modified Timbers)

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