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Frontiers in Modification of Wood and Wood-Based Composites

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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 (30 June 2023) | Viewed by 22196

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Dr. Seng Hua Lee

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Guest Editor

Department of Wood Industry, Faculty of Applied Sciences, Universiti Teknologi MARA Pahang Branch Campus Jengka, Bandar Tun Razak 26400, Pahang, Malaysia
Interests: wood composites; wood treatments; wood adhesives; wood modification; polymers
Special Issues, Collections and Topics in MDPI journals

Dr. Wei Chen Lum

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Institute for Infrastructure Engineering and Sustainable Management (IIESM), Universiti Teknologi MARA, Shah Alam 40450, Selangor, Malaysia
Interests: materials science; formaldehyde; physical properties

Dr. Manfred Dunky

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Guest Editor

University Lecturer, St. Poelten, Austria
Interests: materials engineering; computed tomography; composites; polymeric materials; chemistry; medical imaging physics

Special Issue Information

Dear Colleagues,

Dimensional stability and biological durability are very critical criteria for different types of wood, particularly those types that are used structurally. The hydroscopic nature of wood and wood-based composites is responsible for the dimensional instability and decay of wooden structures, which in turn negatively impact its functionality and pose serious risks to its users. Suitable modification methods to reduce the hygroscopic behaviour of wood are highly sought after. Wood modification is an all-encompassing term that refers to the process of altering the properties of a material through the use of chemical, mechanical, physical, or biological methods. In the interest of environmental protection, more environmentally friendly treatments utilizing non-toxic chemicals are strongly encouraged. As a result, advancements in the modification of wood and wood-based composites are critical. This Special Issue aimed to collect high-quality original research and systematic review articles on the most recent advancements in wood and wood-based composites modification technologies. Additionally, this Special Issue will feature selected contributions on the modification of non-wood materials such as bamboo and palm, as well as the procedure for the modification, characterization, and applications of modified wood and wood-based composites.

Dr. Seng Hua Lee
Dr. Wei Chen Lum
Dr. Manfred Dunky
Guest Editors

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Keywords

wood science
wood composite
wood treatment
bioadhesive
bamboo

Published Papers (10 papers)

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Research

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14 pages, 1709 KiB

Open AccessArticle

Chemical, Crystallinity and Morphological Changes of Rubberwood (Hevea brasiliensis (Willd. ex A. Juss.) Müll. Arg.) Hydrothermally Treated in Different Buffered Media

by Md. Rowson Ali, Ummi Hani Abdullah, Philippe Gerardin, Zaidon Ashaari, Norul Hisham Hamid and Siti Hasnah Kamarudin

Forests 2023, 14(2), 203; https://doi.org/10.3390/f14020203 - 20 Jan 2023

Cited by 1 | Viewed by 1313

Abstract

Hydrothermal treatment is an efficient and environmentally friendly method of enhancing the dimensional stability and durability of wood. The destructive effects of formic and acetic acids generated during thermal treatment, on the other hand, are known to have a negative impact on wood strength. As a result, hydrothermal treatment in different buffered media (acidic, neutral, and alkaline buffer) was performed in this study to mitigate the effects of the acids. As heating media, acidic buffer (pH 4 and 6), alkaline buffer (pH 8 and 10), and tap water (pH 7.43) were used to treat rubberwood at three different temperatures (160 °C, 180 °C, and 200 °C). The effects of different buffered media and treatment temperatures on the chemical components, crystallinity, and morphological changes in treated and untreated rubberwood were studied. The results of the experiments revealed that the chemical constituents of rubberwood changed along with the pH of the buffered media and treatment temperature. Rubberwood treated in alkaline media showed the least degradation, whereas water medium caused the most severe degradation. The crystallinity of wood increased initially (from 160 to 180 °C) and then decreased further at 200 °C. In addition, minimal damage to the wood cell was observed in an alkaline medium. Full article

(This article belongs to the Special Issue Frontiers in Modification of Wood and Wood-Based Composites)

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17 pages, 6867 KiB

Open AccessArticle

European Yield Model Exponential Decay Constant Modification for Glulam after Fire Exposure

by Mohd Nizam Shakimon, Rohana Hassan, Nor Jihan Abd Malek, Azman Zainal, Ali Awaludin, Nor Hayati Abdul Hamid, Wei Chen Lum and Mohd Sapuan Salit

Forests 2022, 13(12), 2012; https://doi.org/10.3390/f13122012 - 28 Nov 2022

Cited by 1 | Viewed by 1346

Abstract

Many real-scale fire tests have been performed on timber connections to analyze the mechanical behavior of timber connections in previous years. However, little research focused on the bending performance of glued laminated (glulam) timber beam bolted connections after fire exposure. In this paper, the three-dimensional numerical model of the glulam timber beam bolted connections was developed and validated by experimental results. The model can simulate temperature evolution in the connections and their mechanical behavior. In the real-scale test, three (3) samples were prepared for a four-point bending test at normal temperature, while another three (3) samples were tested after exposure to a 30-min standard fire and cooled down to normal temperature. The results show the reduction of the load-carrying capacity before and after exposure to the standard fire by 23.9 kN (71.8%), 8.3 kN (26.1%), and 20.2 kN (47.6%) for bolt diameters of 12 mm, 16 mm, and 20 mm, respectively. The numerical model aims to conduct a parametric study and propose the modification of the exponential decay constant, k, for tropical glulam timber to predict the load-carrying capacity of the glulam timber beam bolted connections after exposure to standard fire. Full article

(This article belongs to the Special Issue Frontiers in Modification of Wood and Wood-Based Composites)

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24 pages, 18916 KiB

Open AccessArticle

Improvement of Thermal Behavior of Rattan by Lignosulphonate Impregnation Treatment

by Elvara Windra Madyaratri, Apri Heri Iswanto, Deded Sarip Nawawi, Seng Hua Lee and Widya Fatriasari

Forests 2022, 13(11), 1773; https://doi.org/10.3390/f13111773 - 27 Oct 2022

Cited by 6 | Viewed by 1392

Abstract

Lignin derived from black liquor has a lot of potentials, particularly in its thermal stability, for making value-added chemicals. The purpose of this study was to determine the effect of washing frequency during hydrochloric acid lignin isolation on the properties of eucalyptus kraft lignin. To improve its thermal characteristics and enable its usage as an additive flame retardant, the isolated lignin was synthesized into lignosulphonate. The lignin produced by 3× and 5× washing treatments had a purity of 85.88 and 92.85%, respectively. An FTIR analysis indicated that lignosulphonate was successfully synthesized from isolated lignin after 3× and 5× washing treatments, as the S=O bond was detected at around 627 cm⁻¹. The lignosulphonate exhibited a purity of 71.89 and 67.21%, respectively. Thermal gravimetry and differential scanning calorimetry analysis revealed that the lignin and lignosulphonate after 3× and 5× washing treatments had a char residue of 44, 42, 32, and 48%, respectively. Glass transition temperatures (Tg) of 141, 147, 129, and 174 °C were observed. According to the findings, washing frequency increases lignin purity and Tg, thereby improving the thermal properties of lignosulphonate. Furthermore, the flammability of rattan impregnated with lignosulphonate was V-0 in the UL-94 vertical burning test. Full article

(This article belongs to the Special Issue Frontiers in Modification of Wood and Wood-Based Composites)

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14 pages, 3417 KiB

Open AccessArticle

Cross-Laminated Timber and Glulam from Low-Density Paraserianthes falcataria: A Look into Densification and Shear Strength

by Kang Chiang Liew, Yu Feng Tan, Charles Michael Albert and Vinodini Raman

Forests 2022, 13(10), 1540; https://doi.org/10.3390/f13101540 - 21 Sep 2022

Cited by 3 | Viewed by 1525

Abstract

The aim of this study was to investigate the shear performance of cross-laminated timber (CLT) and glulam made from densified Paraserianthes falcataria laminas. The densification process involved pre-treatment, compression with heat (105 °C, 6 MPa), and a cooling phase. CLT was manufactured from densified laminas of different thicknesses (24–60 mm), while glulam was produced from densified laminas that underwent pre-treatments of (1) pre-steaming (0–30 min) and (2) alkaline pre-treatment (sodium hydroxide (NaOH) concentrations: 0%–9%). Both CLT and glulam were cut into a pre-determined size before being subjected to a block shear test. The findings showed that the presence of pre-steaming (20 min) exhibited the highest shearing strength value. In contrast, alkaline pre-treatment reduced the shear performance of glulam. Here, 24 mm and 30 mm CLT were found to have the highest shearing strength among the parameters. Pre-steamed laminas showed better wettability, but no statistically significant correlation between the contact angle and shear strength of glulam. The densification process reduced the fiber pore areas of the laminas. The fiber pore areas with a shear strength of glulam, with or without alkaline pre-treatment, revealed a weak correlation. The correlation between fiber pore areas and the shear strength of CLT show no statistical significance. Here, 30 mm CLT with lowest moisture content and highest wood failure percentage exhibited a better bonding performance. Full article

(This article belongs to the Special Issue Frontiers in Modification of Wood and Wood-Based Composites)

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16 pages, 3670 KiB

Open AccessFeature PaperArticle

Compressive Strength Characteristic Values of Nine Structural Sized Malaysian Tropical Hardwoods

by Anis Azmi, Zakiah Ahmad, Wei Chen Lum, Adnie Baharin, Nurul Izzatul Lydia Za’ba, Norshariza Mohamad Bhkari and Seng Hua Lee

Forests 2022, 13(8), 1172; https://doi.org/10.3390/f13081172 - 24 Jul 2022

Cited by 3 | Viewed by 1687

Abstract

The design practice of timber structures in Malaysia is still based on permissible stress codes as stated in Malaysian Standard (MS) 544: Part 2 and MS 544: Part 3, which was adopted from the British Standard (BS) 5268. The British Standard was later completely replaced by Eurocode 5 (EC5) in 2009. Therefore, to preserve the continuity of design concepts specified in the British code of practice, local designers should adopt an EC5 limit state design to generate safe and economical designs. However, new strength data based on characteristic values which comply with EC5 for Malaysian tropical hardwoods are still lacking. The aim of this study was to investigate the compressive strength properties of nine structural-sized Malaysian tropical hardwood species namely Balau, Kempas, Kelat, Resak, Kapur, Keruing, Mengkulang, Light Red Meranti and Geronggang tested according to European Standard (EN) 408. A compression test was performed to measure the compressive strength and modulus of elasticity of the timbers and were used to derive characteristic values. The equation for determining characteristic compressive strength given in EN 384 was also assessed to verify that whether it is suitable for high density Malaysian hardwoods, as this equation was derived from softwood and European hardwoods. The results revealed that the derived characteristic values are higher than the values given in EN 338 for the relevant strength classes, particularly for heavy and medium hardwood with densities greater than 700 kg/m³. A verification of the equation used in EN 384 to determine compressive strength characteristic value yields a different equation,

f_{c, 0, k} = 2.2 {(f_{m, k})}^{0.7}

. This shows that the EN 384 equation is not suitable to be used with hardwood timber with a density more than 700 kg/m³, since it will underestimate the strength value. Full article

(This article belongs to the Special Issue Frontiers in Modification of Wood and Wood-Based Composites)

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16 pages, 2463 KiB

Open AccessArticle

Comparative Study of Plywood Boards Produced with Castor Oil-Based Polyurethane and Phenol-Formaldehyde Using Pinus taeda L. Veneers Treated with Chromated Copper Arsenate

by Estefani Sugahara, Bruno Casagrande, Felipe Arroyo, Victor De Araujo, Herisson Santos, Emerson Faustino, Andre Christoforo and Cristiane Campos

Forests 2022, 13(7), 1144; https://doi.org/10.3390/f13071144 - 20 Jul 2022

Cited by 5 | Viewed by 2217

Abstract

Plywood is widely used in civil construction. Due to the importance of preservation and gluing in bio-composites, this study compares the influence of a chemical treatment with CCA (chromated-copper-arsenate) on Pinus taeda L. wood veneers to produce two plywood types using phenol-formaldehyde (PF) and castor oil-based polyurethane (PU). Four different treatments were performed to analyze both varieties’ physical and mechanical properties. As a result, an improvement in the properties of the treated panels was observed. Lower moisture contents and better interactions caused by less thickness swelling and water absorption were identified in the PU-based plywoods. The treatment with CCA was efficient, improving these properties when they were compared to the reference panels. Most treatments evidenced increases in the modulus of elasticity and modulus of rupture for both adhesives when the CCA treatment was applied to the veneers. Comparing the resins, the PF showed the best values of modulus of elasticity. All treatments met the requirements defined by the Brazilian standard document for the glue line shear. Full article

(This article belongs to the Special Issue Frontiers in Modification of Wood and Wood-Based Composites)

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7 pages, 989 KiB

Open AccessArticle

Compression of Acetylated Beech (Fagus sylvatica L.) Laminated Veneer Lumber (LVL)

by Maik Slabohm, Aaron Kilian Mayer and Holger Militz

Forests 2022, 13(7), 1122; https://doi.org/10.3390/f13071122 - 16 Jul 2022

Cited by 8 | Viewed by 1475

Abstract

Acetylation with acetic anhydride is well known to improve the dimensional stability and durability of wood. Veneer is appealing for acetylation because of its thin thickness, which supports a complete and even impregnation of difficult-to-treat wood species, such as beech (Fagus sylvatica L.). Unlike resin-based veneer impregnation, acetylated veneer does not require any additional curing. As a result, veneer properties are already altered prior to bonding. The compression thickness reduction in acetylated beech veneer during the manufacturing of laminated veneer lumber (LVL) utilizing 1, 3, and 6 MPa at 150 °C for 30 min is investigated in this study. The results show that acetylated beech veneer is considerably less compressible than the references. Moreover, the density of acetylated LVL at low pressure (1 MPa) is similar to the one of references, even though the compressibility is much lower. This is due to the added acetyl groups after acetylation. The reduction in compressibility is most likely caused due to a decrease in moisture content (MC) and its accompanied mechanisms. Full article

(This article belongs to the Special Issue Frontiers in Modification of Wood and Wood-Based Composites)

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14 pages, 2380 KiB

Open AccessArticle

Physical Properties of Hydrothermally Treated Rubberwood [Hevea brasiliensis (Willd. ex A. Juss.) Müll. Arg.] in Different Buffered Media

by Md. Rowson Ali, Ummi Hani Abdullah, Zaidon Ashaari, Lee Seng Hua, Norul Hisham Hamid and Siti Hasnah Kamarudin

Forests 2022, 13(7), 1052; https://doi.org/10.3390/f13071052 - 04 Jul 2022

Cited by 2 | Viewed by 1863

Abstract

The dimensional instability of rubberwood [Hevea brasiliensis (Willd. ex A. Juss.) Müll. Arg.] is one of the major drawbacks that limits its utilization. Therefore, treatment is needed to improve these properties. Hydrothermal treatment in different buffered media is one of the techniques that improve its dimensional stability. The physical properties of hydrothermally treated rubberwood in different buffered media (pH 4, 6, 8, 10) and tap water (pH 7.43) with different temperatures (160 °C, 180 °C and 200 °C) were studied. In this study, physical properties such as equilibrium moisture content (EMC), density (ρ), mass loss (ML), water absorption (WA), volumetric swelling coefficient (VSC), thickness swelling (TS) and anti-swelling efficiency (ASE) were investigated for both treated and untreated specimens. Both the buffered media and temperature significantly affected the physical properties. The results indicated that the EMC (%), ρ (kg/m³), ML (%), VSC (%), TS (%) of treated rubberwood samples reduced as the treatment temperature increased. With the exception of WA (%), as WA increased when the treatment temperature increased from 160 °C to 180 °C but started to decrease when the temperature was further increased to 200 °C. The research study also exhibited that hydrothermal treatment using buffered media at different temperatures enhanced the dimensional stability of the treated samples. Alkaline media gave the best results on the physical properties compared to other treatment medias. Full article

(This article belongs to the Special Issue Frontiers in Modification of Wood and Wood-Based Composites)

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20 pages, 3046 KiB

Open AccessArticle

Potential of Using Natural and Synthetic Binder in Wood Composites

by Kangchiang Liew, Yufeng Tan, Charles Michael Albert, Vinodini Raman and Michelle Boyou

Forests 2022, 13(6), 844; https://doi.org/10.3390/f13060844 - 28 May 2022

Cited by 2 | Viewed by 3029

Abstract

The physical and mechanical properties of particleboard bonded with different cooking percentages of seaweed (Kappaphycus alvarezii), with different percentages of starch and different percentages of adhesives, and wood plastic composite (WPC) from High-Density Polyethlene (HDPE) with Acacia mangium wood powder were determined in this study. Seaweed mixed with different percentages of sulfuric acid (30%, 50%, 70%) and Sodium Hydroxide (70%, 50%, 30%) were prepared as a binder for particleboard. For a starch-based binder, different percentages of starch (10%, 15%, 20%) were prepared, before producing particleboard with different amounts of binder (20%, 25%, 30%). As for WPC, wood powders were bonded with different percentages of HDPE content (70%, 80%, 90%). Results indicated that WPC at 90% HDPE shows the best performance in the water absorption (0.07%) and thickness swelling test (2.54%). Starch-based particleboard recorded the highest Modulus of Elasticity (MOE) value (1115.07 N/mm² at 15% starch with 30% amount of binder), while WPC (90% HDPE) and starch-based particleboard (10% starch with 20% amount of binder) both recorded the highest Modulus of Rupture (MOR) at the same value, which is 7.84 N/mm². Starch-based particleboard has a better internal bond, which is 0.05 N/mm². However, seaweed-based particleboard has a higher density value, which is 0.6 g/cm³. Full article

(This article belongs to the Special Issue Frontiers in Modification of Wood and Wood-Based Composites)

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Review

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28 pages, 7986 KiB

Open AccessEditor’s ChoiceReview

Adhesive-and Metal-Free Assembly Techniques for Prefabricated Multi-Layer Engineered Wood Products: A Review on Wooden Connectors

by Lei Han, Andreja Kutnar, Jakub Sandak, Iztok Šušteršič and Dick Sandberg

Forests 2023, 14(2), 311; https://doi.org/10.3390/f14020311 - 05 Feb 2023

Cited by 8 | Viewed by 5091

Abstract

Engineered wood products (EWPs) are being increasingly used as construction materials. EWPs are currently being made using synthetic adhesives or metal fasteners, which lead to poor recyclability and reusability. Therefore, this review paper focused on emerging adhesive- and metal-free assembling techniques including wood dowels, rotary-dowel welding, wooden nails, and dovetail joining as alternative ways of making prefabricated EWPs. This will contribute towards green construction and optimising the building process to minimise its negative impact on the environment and its inhabitants, while maximising the positive aspects of the finished structure. The respective advantages and shortcomings will be compared with those of equivalent EWPs. In general, the dowel-laminated timber (DLT) provides sufficient load-bearing capacity and even better ductility than EWPs of equivalent size, but its relatively low stiffness under a bending load limits its application as a structural element. Optimised manufacturing parameters such as dowel species, dowel spacing, dowel diameter, dowel insertion angle, dowel shape, etc. could be studied to improve the stiffness. The improved mechanical properties and tight fitting due to set-recovery of densified wood support its use as sustainable alternatives to hardwood dowels in DLT to overcome problems such as the loosening of connections over time and dimensional instability. The rotary welding technology could also enhance the strength and long-term performance of dowel-type joints, but its poor water resistance needs further investigation. The main obstacles to implementing DLT products in the market are missing technical information and design guidelines based on national codes. Full article

(This article belongs to the Special Issue Frontiers in Modification of Wood and Wood-Based Composites)

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