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11 pages, 7349 KiB

Open AccessArticle

A Small-Scale Test to Examine Heat Delamination in Cross Laminated Timber (CLT)

by Byrne Miyamoto, Nathan J. Bechle, Douglas R. Rammer and Samuel L. Zelinka

Forests 2021, 12(2), 232; https://doi.org/10.3390/f12020232 - 17 Feb 2021

Cited by 8 | Viewed by 2803

This paper examines the strength of wood adhesive bonds at high temperatures. The goal of this research is to better understand the conditions of heat delamination in cross laminated timber (CLT) that is exposed to fire. Heat delamination in CLT occurs when one [...] Read more.

This paper examines the strength of wood adhesive bonds at high temperatures. The goal of this research is to better understand the conditions of heat delamination in cross laminated timber (CLT) that is exposed to fire. Heat delamination in CLT occurs when one lamination detaches from the composite panel before the char front reaches the bondline. Timber that falls from the panel, as a result of delamination, contributes additional fuel to the fire, which can cause fire regrowth, while the loss of a lamination causes a sudden loss in strength. Currently, to demonstrate that an adhesive does not delaminate, it must pass a full scale (6 m by 3 m) compartment fire test as prescribed in the PRG-320 product standard. In this work, we scaled down the mechanical loads and temperatures to 300 mm lap shear specimens. Seven different adhesives were tested and compared against solid wood controls with the same geometry as the lap shear specimens. Quasi-static tests were run where the specimens were loaded to failure at 25 °C and 260 °C, when the samples were at thermal equilibrium. Additionally, creep tests were performed where the load and temperature ramp was matched to the adhesive bondline temperatures measured in the large scale PRG-320 tests. With the exception of some of the polyurethane formulations, all adhesives passed the scaled-down creep test that resembles the PRG-320 standard. Of the polyurethane adhesives tested, only one formulation remained intact for the duration of the test. These results can be used to help better predict which adhesives may pass the PRG-320 test prior to full scale testing. Full article

(This article belongs to the Special Issue Performance of Wood and Wood-Based Materials)

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12 pages, 1500 KiB

Open AccessArticle

The Influence of Thickness on the Tensile Strength of Finnish Birch Veneers under Varying Load Angles

by Maximilian Pramreiter, Alexander Stadlmann, Christian Huber, Johannes Konnerth, Peter Halbauer, Georg Baumann and Ulrich Müller

Forests 2021, 12(1), 87; https://doi.org/10.3390/f12010087 - 15 Jan 2021

Cited by 13 | Viewed by 2639

Abstract

The development of high-performance, veneer-based wood composites is a topic of increasing importance due to the high design flexibility and the comparable mechanical performance to solid wood. Part of this improved mechanical performance can be contributed to the size effect present in wood. [...] Read more.

The development of high-performance, veneer-based wood composites is a topic of increasing importance due to the high design flexibility and the comparable mechanical performance to solid wood. Part of this improved mechanical performance can be contributed to the size effect present in wood. Based on previous findings in the literature, this size effect can be either strengthening or weakening. The presented study investigates the influence of thickness and load angle on the tensile strength and tensile stiffness of peeled veneers compared to thin sawn timber. Veneers with thicknesses of 0.5 ± 0.05 mm, 1.0 ± 0.05 mm and 1.5 ± 0.05 mm as well as sawn wood with thicknesses of 1.5 ± 0.1 mm, 3.0 ± 0.1 mm and 5.0 ± 0.1 mm were tested in tension under different load angles (0°, 45° and 90°). The results only partly confirm a size effect for strength parallel to the grain. The strength perpendicular to the grain increased significantly between 0.5 mm and 1.5 mm, with a significant decrease between 1.5 mm and 5.0 mm. The presence of lathe checks diminished the strength perpendicular to the grain of the veneers by about 70% compared to solid wood, partly overshadowing a possible strengthening effect. It was concluded that a transition from a strengthening to a weakening behaviour lies in the range of multiple millimetres, but further investigations are needed to quantify this zone more precisely. The presented results provide a useful basis for the development of veneer-based wood composites with a performance driven layer-thickness. Full article

(This article belongs to the Special Issue Performance of Wood and Wood-Based Materials)

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21 pages, 5086 KiB

Open AccessArticle

Determination of Elastic Properties of Beech Plywood by Analytical, Experimental and Numerical Methods

by Miran Merhar

Forests 2020, 11(11), 1221; https://doi.org/10.3390/f11111221 - 20 Nov 2020

Cited by 8 | Viewed by 3139

Abstract

This research article examines the application of various methods to determine the effective elastic properties of beech veneer-wood composites. Using laminate theory, the theoretically calculated effective values of the in-plane and out-of-plane modulus of elasticity as well as shear modulus are compared with [...] Read more.

This research article examines the application of various methods to determine the effective elastic properties of beech veneer-wood composites. Using laminate theory, the theoretically calculated effective values of the in-plane and out-of-plane modulus of elasticity as well as shear modulus are compared with the values determined from the natural frequencies of flexural, torsional and longitudinal vibrations of samples having different orientations and numbers of composite layers. The samples are also modelled using the finite element method, and their natural frequencies are calculated by the modal analysis. Research has shown that the laminate theory, which is well established and applied in the world of synthetic composites, can also be applied to beech plywood composites, where the theoretically calculated effective values can be up to 15% higher. Similarly, due to the higher calculated effective elastic properties, higher natural frequencies of flexural, torsional and longitudinal vibrations are also calculated by the finite element method. Full article

(This article belongs to the Special Issue Performance of Wood and Wood-Based Materials)

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14 pages, 3345 KiB

Open AccessArticle

Properties of Wood Ceramics Prepared from Thermo-Modified Poplar

by Hongyan Chen, Mohsen Bahmani, Miha Humar and Dali Cheng

Forests 2020, 11(11), 1204; https://doi.org/10.3390/f11111204 - 16 Nov 2020

Cited by 7 | Viewed by 2541

Abstract

Wood ceramics (WCS) were prepared from thermo-modified poplar wood residues and untreated poplar wood. At 1000 °C sintering temperature, the ratios of wood powder and phenolic resin at 10:3, 10:6 and 10:9 were tested. The effects of materials on the properties of WCS, [...] Read more.

Wood ceramics (WCS) were prepared from thermo-modified poplar wood residues and untreated poplar wood. At 1000 °C sintering temperature, the ratios of wood powder and phenolic resin at 10:3, 10:6 and 10:9 were tested. The effects of materials on the properties of WCS, carbon yield and volume shrinkage were studied. With the increase in resin content, the carbon yield increased; however, the volume shrinkage decreased. Carbon yield of WCS made from 220 °C thermo-modified poplar wood was 40.45%, as the ratio of wood powder/phenolic resins was 10:6. The microstructure, chemical structure and crystallinity of WCS were analysed by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) and X-ray diffraction (XRD), respectively. The results showed that WCS had a porous structure. WCS prepared from thermo-modified materials, amorphous carbon and hard glass carbon melted more evenly; meanwhile, there were more pores on glass carbon. The FTIR spectra showed that the stretching vibration of C-O-C weakened at ceramics made of thermo-modified poplar. The XRD pattern indicated that the raw material has no apparent influence on the graphitization degree of WCS. Full article

(This article belongs to the Special Issue Performance of Wood and Wood-Based Materials)

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17 pages, 7232 KiB

Open AccessArticle

The Development of Pneumatic Fatigue Test Rig for Wood-Based Specimens

by Gorazd Fajdiga, Denis Rajh, Drago Vidic and Bojan Gospodarič

Forests 2020, 11(11), 1187; https://doi.org/10.3390/f11111187 - 10 Nov 2020

Cited by 3 | Viewed by 2584

Abstract

In product design, the focus is increasingly shifting towards optimizing and increasing the efficiency of the development process. This can be achieved with advanced numerical tools, but these methods require precise knowledge of material properties. One of the desired properties is the dynamic [...] Read more.

In product design, the focus is increasingly shifting towards optimizing and increasing the efficiency of the development process. This can be achieved with advanced numerical tools, but these methods require precise knowledge of material properties. One of the desired properties is the dynamic load behavior of the material. The research is directly related with the company that developed the slender wooden beams used in industry to produce windows of larger dimensions (height over 3 m). For the testing of wooden beams, the pneumatic four-point bending fatigue test rig was developed. In this paper, the whole structure of the test rig is described in detail. Based on the performed experiments of dynamic strength, the Woehler curve was determined, which serves as a necessary input for further numerical simulation of the fatigue process of wood-based beams. Knowledge of the response of wood to dynamic loads is very important to predict its life expectancy in various products. Full article

(This article belongs to the Special Issue Performance of Wood and Wood-Based Materials)

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23 pages, 10013 KiB

Open AccessArticle

Improving Fungal Decay Resistance of Less Durable Sapwood by Impregnation with Scots Pine Knotwood and Black Locust Heartwood Hydrophilic Extractives with Antifungal or Antioxidant Properties

by Viljem Vek, Angela Balzano, Ida Poljanšek, Miha Humar and Primož Oven

Forests 2020, 11(9), 1024; https://doi.org/10.3390/f11091024 - 22 Sep 2020

Cited by 29 | Viewed by 3337

Abstract

Research Highlights: The antifungal assay confirmed that knotwood extractives of Scots pine inhibit the growth of wood decay fungi. Heartwood extracts of black locust were found to be much stronger free radical scavengers than the extracts of Scots pine. The extracts were deposited [...] Read more.

Research Highlights: The antifungal assay confirmed that knotwood extractives of Scots pine inhibit the growth of wood decay fungi. Heartwood extracts of black locust were found to be much stronger free radical scavengers than the extracts of Scots pine. The extracts were deposited in the lumina and on the wall surface of cells in the impregnated sapwood. Impregnation of the sapwood blocks with Scots pine and black locust extracts reduced the fungal decay of wood. Objectives: Hydrophilic extracts of Scots pine knotwood and black locust heartwood were chemically analyzed, tested for antifungal and antioxidant properties and used for impregnation of beech and Scots pine sapwood. Materials and Methods: Scots pine knotwood and black locust heartwood were extracted, and obtained hydrophilic extractives were chemically analyzed. Extracts were analyzed for antifungal properties with the in vitro well-diffusion method. The free radical scavenging activity of wood extracts was measured colorimetrically. The retention of the extracts in the impregnated sapwood blocks was evaluated with microscopy and gravimetry. A decay test was performed with the mini block test. Results: Almost half of both Scots pine knotwood and black locust heartwood hydrophilic extracts obtained were described by phenolic compounds. The extracts were deposited in the lumina of cells and on the cell wall surface. Extractives of Scots pine knotwood had good inhibitory properties against white- and brown-rot fungi. On the other hand, extractives of black locust heartwood were found to be good radical scavengers, better than knotwood extractives of Scots pine. The extracts of Scots pine knotwood and black locust reduced the fungal decay of the tested sapwood blocks. Conclusions: The results of this research show that the less-valued knotwood of Scots pine and heartwood of black locust are a potential source of antifungal and antioxidant agents for bio-based wood preservatives. Full article

(This article belongs to the Special Issue Performance of Wood and Wood-Based Materials)

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13 pages, 2465 KiB

Open AccessArticle

Durability of Wood Exposed to Alternating Climate Test and Natural Weathering

by Alexander Stadlmann, Maximilian Pramreiter, Robert Stingl, Christian Kurzböck, Thomas Jost and Ulrich Müller

Forests 2020, 11(9), 953; https://doi.org/10.3390/f11090953 - 31 Aug 2020

Cited by 7 | Viewed by 2967

Abstract

The use of wood-based materials in the automotive industry is currently under discussion and investigation. One of the major material requirements for such applications is sufficient weathering stability. This can be demonstrated by an accelerated aging process in which the samples are exposed [...] Read more.

The use of wood-based materials in the automotive industry is currently under discussion and investigation. One of the major material requirements for such applications is sufficient weathering stability. This can be demonstrated by an accelerated aging process in which the samples are exposed to changing climatic conditions and a spray mist of an aqueous NaCl solution. The effects of media salt (NaCl) on the mechanical and physical properties of wood have scarcely been investigated. The presented study investigated the changes in bending strength (MOR), modulus of elasticity (MOE), and impact bending strength (α) of naturally and artificially weathered oak (Quercus spp.) and birch (Betula pendula Roth) wood. The tests provided comparable results. The decrease under natural weathering of oak was 3.73%, 4.69%, and 6.45% for MOR, MOE, and α. Under artificial weathering the decrease observed for oak was 7.33%, 10.87%, and 16.29% and 3.2%, 8.21%, and 4.03% for birch respectively. It is remarkable that α increased for birch wood at the beginning of the artificial weathering cycles. The penetration of the aqueous NaCl solution into the wood substance resulted in an increase in the wood’s equilibrium moisture content (EMC), which can be explained by the stronger hygroscopic properties of NaCl compared to wood. The higher impact strength at the beginning of artificial weathering can be partly explained by this increase in EMC. In order to investigate the penetration behavior of salt into the wood substrate, the artificially weathered samples were examined by means of energy dispersive X-ray analysis (EDX) and it was shown that the salt concentration changes significantly over the weathering cycles and sample cross-section. Full article

(This article belongs to the Special Issue Performance of Wood and Wood-Based Materials)

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13 pages, 3397 KiB

Open AccessArticle

The Brinell Method for Determining Hardness of Wood Flooring Materials

by Maciej Sydor, Grzegorz Pinkowski and Anna Jasińska

Forests 2020, 11(8), 878; https://doi.org/10.3390/f11080878 - 12 Aug 2020

Cited by 14 | Viewed by 4803

Abstract

We hypothesize that the ability to recovery the depth of the indentation increases with increasing the hardness of the flooring material. The research was carried out for ten lignocellulosic flooring materials: merbau, oak, maple, red oak, laminated HDF (high-density fiberboard), innovative plywood, beech, [...] Read more.

We hypothesize that the ability to recovery the depth of the indentation increases with increasing the hardness of the flooring material. The research was carried out for ten lignocellulosic flooring materials: merbau, oak, maple, red oak, laminated HDF (high-density fiberboard), innovative plywood, beech, pine, peasantry, iroko. The hardness was examined using the Brinell method, and additionally, the elastic indentation of the indenter was measured during the hardness test. On this basis, the permanent (plastic) and temporary (elastic) component of total deformation was determined. Different ability to recovery was found. The harder materials were the higher percentage of elastic indentation in total indentation depth. Moreover, it was found that the measurement of the indentation diameter in wood materials is characterized by high uncertainty and measurements based on the depth of the indentation are more unambiguous and of greater practical importance, especially when testing hard lignocellulosic flooring materials. Full article

(This article belongs to the Special Issue Performance of Wood and Wood-Based Materials)

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13 pages, 3822 KiB

Open AccessArticle

Machinability Research of the Most Common Invasive Tree Species in Slovenia

by Miran Merhar, Dominika Gornik Bučar and Maks Merela

Forests 2020, 11(7), 752; https://doi.org/10.3390/f11070752 - 12 Jul 2020

Cited by 8 | Viewed by 2651

Abstract

This article investigates the quality of the machining surface of the five most common invasive tree species in Slovenia, i.e., black locust (Robinia pseudoacacia L.), boxelder maple (Acer negundo L.), horse chestnut (Aesculus hippocastanum), honey locust (Gleditsia triacanthos [...] Read more.

This article investigates the quality of the machining surface of the five most common invasive tree species in Slovenia, i.e., black locust (Robinia pseudoacacia L.), boxelder maple (Acer negundo L.), horse chestnut (Aesculus hippocastanum), honey locust (Gleditsia triacanthos) and tree of heaven (Ailanthus altissima). The machining tests were made according to the American Society for Testing and Materials (ASTM) D1666-17 standard, where the quality of the surfaces after planing, routing and turning were evaluated with visual assessment, and the area and profile roughness parameters were also determined on selected specimens. The results showed that boxelder maple, horse chestnut and honey locust can be machined very well in all the studied operations, with the best results in routing and a little less good by turning, whereas the tree of heaven had the best quality in planing, and the worst by turning. Among all studied tree species, the black locust had the worst quality in planing, but the quality at routing was very similar to other tested species. The research also showed that there is little or no significant relationship between the qualities of the various types of machining for tested tree species. Full article

(This article belongs to the Special Issue Performance of Wood and Wood-Based Materials)

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12 pages, 1765 KiB

Open AccessArticle

Influence of Copper and Biopolymer/Saqez Resin on the Properties of Poplar Wood

by Huijun Dong, Mohsen Bahmani, Sohrab Rahimi and Miha Humar

Forests 2020, 11(6), 667; https://doi.org/10.3390/f11060667 - 11 Jun 2020

Cited by 13 | Viewed by 2560

Abstract

There is an increasing trend in the use of environmentally-friendly materials in wood protection. This includes the use of less toxic active ingredients, as well as better fixation. This study investigates the formulation based on the combination of copper and Saqez resin on [...] Read more.

There is an increasing trend in the use of environmentally-friendly materials in wood protection. This includes the use of less toxic active ingredients, as well as better fixation. This study investigates the formulation based on the combination of copper and Saqez resin on the physical and biological resistance properties of poplar wood. Samples were treated by either copper-ethanolamine (Cu/MEA) and/or Saqez resin at various treatment levels. A vacuum pressure procedure was applied. The retention, weight percent gain, water absorption, volumetric swelling, and decay resistance of the samples were then determined. The highest retention and weight percent gain were obtained in the samples treated with the combination of copper-based system and Saqez resin. Additionally, the combination of the copper and Saqez improved the physical properties and decay-resistance against white-rot fungus Trametes versicolor. Full article

(This article belongs to the Special Issue Performance of Wood and Wood-Based Materials)

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12 pages, 1905 KiB

Open AccessArticle

Quality Control of Thermally Modified Timber Using Dynamic Vapor Sorption (DVS) Analysis

by Miha Humar, Rožle Repič, Davor Kržišnik, Boštjan Lesar, Romana Cerc Korošec, Christian Brischke, Lukas Emmerich and Gregor Rep

Forests 2020, 11(6), 666; https://doi.org/10.3390/f11060666 - 11 Jun 2020

Cited by 19 | Viewed by 3281

Abstract

The importance of thermal modification is increasing worldwide. Increased use of thermally modified timber (TMT) has resulted in a need for reliable quality control, comprising control of variation of the production within defined limits, allowing third-party control in the case of certification and [...] Read more.

The importance of thermal modification is increasing worldwide. Increased use of thermally modified timber (TMT) has resulted in a need for reliable quality control, comprising control of variation of the production within defined limits, allowing third-party control in the case of certification and the regulation of customer complaints and claims. Techniques are thus needed to characterise the modification of quality in terms of improved target properties of TMT during industrial production, and of TMT products that have been in service for an arbitrary time. In this study, we aimed to utilise dynamic vapor sorption (DVS) for this purpose. Norway spruce (Picea abies) and European beech (Fagus sylvatica) samples were thermally modified at different temperatures according to different heat treatment techniques: (1) the Silvapro process based on an initial vacuum; (2) an air heat treatment, whereby samples were wrapped in aluminium foil; (3) thermal modification of wood samples in the ambient atmosphere in a laboratory oven. Wood samples from closed processes were analysed for validation. TMT was characterised with respect to mass loss, colour and density. Mass loss of wood due to modification (ML_TM) was correlated with factors derived from DVS analysis. The present DVS measurements suggest that the equilibrium wood moisture content (EMC_{95% RH}), the time to reach 10% wood moisture content (t_{10% MC}), and the elongation factor, c, derived from a logarithmic function, can serve as alternative parameters to characterise the quality of several thermal modification processes. Further studies are recommended using other wood species, different modification processes and further parameters gained from DVS measurements to understand the robustness and the predictive power of the applied technique. Full article

(This article belongs to the Special Issue Performance of Wood and Wood-Based Materials)

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11 pages, 2209 KiB

Open AccessArticle

Cell Wall Saturation Limit and Selected Properties of Thermally Modified Oak Wood and Cellulose

by Richard Hrčka, Viera Kučerová, Tatiana Hýrošová and Vladimír Hönig

Forests 2020, 11(6), 640; https://doi.org/10.3390/f11060640 - 5 Jun 2020

Cited by 7 | Viewed by 2171

Abstract

The interaction of water and oak wood is common in outdoor expositions and will remain a probable occurrence in the future. New insights into the recognition of a cell wall saturation limit are presented by a double-weighing method at 20 °C. The cell [...] Read more.

The interaction of water and oak wood is common in outdoor expositions and will remain a probable occurrence in the future. New insights into the recognition of a cell wall saturation limit are presented by a double-weighing method at 20 °C. The cell wall saturation limit, as the property of thermally modified oak wood, is significantly influenced by different treatment temperatures (20, 160, 180, 210 and 240 °C) on a 5% alpha level. A significantly higher equilibrium moisture content was reached by thermally modified oak wood at a temperature of 20 °C and relative humidity of 65% after its equilibrium in the water-in-reservoir. Moreover, the results are used in the treatment of woodchips to produce cellulose or decomposition of thermally modified wood to its basic chemical components. The investigated properties of cellulose revealed its relationship with water. The number of water molecules bonded to a cellulose chain was correlated with other measured compositions: average molecular weight, total crystalline index, lateral order index and polydispersity index. Analyses showed that there was a strong negative correlation between lateral order index and average molecular weight. The same was true between total crystalline index and average molecular weight. The rest of the properties were positively correlated with the number of water molecules bonded to glucopyranose. The results revealed the possible regeneration of a wood sorption ability after heat treatment and the stability of cellulose in such process. Full article

(This article belongs to the Special Issue Performance of Wood and Wood-Based Materials)

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12 pages, 3966 KiB

Open AccessArticle

Properties of Cement-Bonded Particleboards Made from Canary Islands Palm (Phoenix canariensis Ch.) Trunks and Different Amounts of Potato Starch

by Manuel Ferrandez-Villena, Clara Eugenia Ferrandez-Garcia, Teresa Garcia-Ortuño, Antonio Ferrandez-Garcia and Maria Teresa Ferrandez-Garcia

Forests 2020, 11(5), 560; https://doi.org/10.3390/f11050560 - 15 May 2020

Cited by 10 | Viewed by 2548

Abstract

Wood-cement panels are becoming increasingly widely used as prefabricated building materials. In order to increase the use of renewable resources as materials for industrial applications, the use of alternative plant fibres has been gaining interest. Additionally, it is assumed that new or better [...] Read more.

Wood-cement panels are becoming increasingly widely used as prefabricated building materials. In order to increase the use of renewable resources as materials for industrial applications, the use of alternative plant fibres has been gaining interest. Additionally, it is assumed that new or better board properties can be achieved due to the different chemical and mechanical properties of such alternative sources of fibres. In south-eastern Spain, the Canary Islands palm (Phoenix canariensis) is widely used in urban landscaping. Plantations attacked by red palm weevils generate abundant plant waste that must be shredded and taken to authorised landfills. This paper discusses the use of particles of Canary Islands palm for manufacturing fibre panels containing 20% cement in relation to the weight of the particles, using different proportions of starch as a plasticiser. A pressure of 2.6 MPa and a temperature of 100 °C were used in their production. Density, thickness swelling, water absorption, internal bonding strength, modulus of rupture (MOR), modulus of elasticity (MOE), and thermal conductivity were studied. The mechanical tests showed that the MOR and MOE values increased with longer setting times, meaning that the palm particles were able to tolerate the alkalinity of the cement. The board with 5% starch had a MOR of 15.76 N·mm⁻² and a MOE of 1.872 N·mm⁻² after 28 days. The boards with thicknesses of 6.7 mm had a mean thermal conductivity of 0.054 W·m⁻¹·K⁻¹. These boards achieved good mechanical properties and could be used for general use and as a thermal insulation material in building construction. Full article

(This article belongs to the Special Issue Performance of Wood and Wood-Based Materials)

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