Published by De Gruyter

Volume 75 Issue 7

Issue of Holzforschung

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Contents
Journal Overview

Publicly Available July 2, 2021

Original articles

Open Access November 13, 2020

Wood identification of two anatomically similar Cupressaceae species based on two-dimensional microfibril angle mapping

Yusuke Kita, Junji Sugiyama

Page range: 591-602

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Abstract

Identifying two anatomically similar species of Cupressaceae, Chamaecyparis obtusa and Thujopsis spp., is important to better understand the culture of wood use in Japan. However, the conventional method, which involves observing their cross-field pitting, cannot identify them in many cases. This study solves the above problem by introducing an anatomical criterion based on the micro fibril angle (MFA). MFA values were obtained through two-dimensional MFA images using the uniaxial optical anisotropy of cellulose microfibrils. A combination of the preprocessed MFA images and a convolutional neural network (CNN) yielded an accuracy nearly of 90% in classifying these species in cases of present and old wood specimens. Our feature extraction and classification techniques provide a new way for describing the anatomical features of wood and identifying featureless softwoods. Using the model interpretation-related methodologies of the CNN, distinct features of the two wood species were partly explained by MFA anisotropy in the S 2 wall induced by the existence of pits.

Open Access December 10, 2020

Treatment of wood with atmospheric plasma discharge: study of the treatment process, dynamic wettability and interactions with a waterborne coating

Jure Žigon, Matjaž Pavlič, Pierre Kibleur, Jan Van den Bulcke, Marko Petrič, Joris Van Acker, Sebastian Dahle

Page range: 603-613

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Abstract

Plasma treatment is becoming a mature technique for modification of surfaces of various materials, including wood. A better insight in the treatment process and the impact of the plasma on properties of wood bulk are still needed. The study was performed on Norway spruce and common beech wood, as well as their thermally modified variations. The formations of the airborne discharge, as well as mass changes of the treated wood, were monitored. The impact of such treatment on wood-coating interaction was investigated by evaluating the dynamic wettability and penetration into wood. At the wood surface, plasma streamers were observed more intense on denser latewood regions. Wood mass loss was higher with increasing number of passes through the plasma discharge and was lower for thermally modified wood than for unmodified wood. Plasma treatment increased the surface free energy of all wood species and lowered the contact angles of a waterborne coating, these together indicating enhanced wettability after treatment. Finally, the distribution and penetration depth of the coating were studied with X-ray microtomography. It was found that the coating penetrated deeper into beech than into spruce wood. However, the treatment with plasma increased the penetration of the coating only into spruce wood.

November 19, 2020

Impact of hygrothermal treatment on the physical properties and chemical composition of Moso bamboo (Phyllostachys edulis)

Qiming Feng, Yanhui Huang, Cuiyin Ye, Benhua Fei, Shumin Yang

Page range: 614-625

Abstract

Natural bamboo is rapidly replacing wood, but it is highly hygroscopic and has poor dimensional stability. Herein, Moso bamboo was subjected to hygrothermal treatment at different temperatures. The hydrophobicity and dimensional stability of bamboo increased, as indicated by the 16.5% decrease in volumetric swelling and three-fold increase in the contact angle at 220 °C. The fibers and parenchyma cells delaminated, and pores appeared after treatment at 200 °C. These changes were attributed to the significant degradation of hemicelluloses. The acetyl groups of hemicelluloses decomposed into acetic acid. The apparent crystallinity of cellulose increased mainly due to the reduced hemicellulose content. Furthermore, a breakage of xylan and β-O-4 bonds was observed, and S units were condensed after treatment at 220 °C. In addition, the syringyl/guaiacyl ratio showed more than a five-fold increase, while associated ferulic acid decreased after hygrothermal treatment, indicating that the dense structure of the cell walls was broken. These data were used to propose a mechanism for changes in the bamboo cell walls during hygrothermal treatment. This simple and environmentally-friendly approach holds great potential for use in high-humidity environments.

December 4, 2020

Inverse characterisation of gradient distribution of the modulus of bamboo using a four-point bending test

Xianzhi Gao, Guangyan Liu, Lu Wang, Yanan Yi, Guang Lin, Shaopeng Ma

Page range: 626-634

Abstract

As a natural graded material, bamboo has gradually increasing elastic modulus along the radial direction from the inner to the outer skin. Accurate measurement of the modulus distribution plays an important role in bamboo-based structural design. However, it is difficult to characterise this modulus distribution by using conventional testing approaches on bamboo slices. A more effective method was developed in this study for the inverse identification of gradually varying material properties. The method is based on the digital image correlation and finite element model updating techniques. The radial distribution of the elastic modulus of bamboo was obtained through only one four-point bending test. The inversely identified modulus distribution was verified through uniaxial tensile tests on sliced bamboo strips and microscopic observation of the volume fraction distribution of its vascular bundle. The results showed that the elastic modulus of the bamboo material decreased from the outer skin (20 GPa) to the inner skin (2 GPa), which is in good consistence with the tensile test results on sliced specimens.

Open Access November 23, 2020

Correlation between bacterial decay and chemical changes in waterlogged archaeological wood analysed by light microscopy and Py-GC/MS

Nanna Bjerregaard Pedersen, Jeannette Jacqueline Łucejko, Francesca Modugno, Charlotte Björdal

Page range: 635-645

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Abstract

Erosion bacteria are the main degraders of archaeological wood excavated from waterlogged environments. Light microscopy and analytical pyrolysis coupled with gas chromatography/mass spectrometry (Py-GC/MS) were exploited to study waterlogged archaeological wood ( Pinus sylvestris L.) at different stages of bacterial decay. The research explored the biochemical changes related to erosion bacteria degradation of the secondary cell wall in the wood cells and the chemical changes related to abiotic processes induced by the long-term waterlogged burial environment. Erosion bacteria were demonstrated by chemical analysis to cause significant holocellulose depletion. Detailed analysis of the holocellulose and lignin pyrolysis products revealed only minor chemical changes in the residual structure even after heavy erosion bacteria decay. Chemical changes in the lignin polymer is associated to enzymatic unlocking of the lignocellulose to gain access to the holocellulose fraction of the cell wall. Chemical changes in the holocellulose fraction are suggested to stem from depolymerisation and from alterations in the polymer matrix of the residual wood cell wall structure. Interestingly, a difference was observed between the sound reference wood and the waterlogged archaeological wood without erosion bacteria decay, indicating that long-term exposure in waterlogged environments results in partial decay of the holocellulose even in absence of bacterial activity.

November 23, 2020

Artificial neural networks modelling based on visual analysis of coated cross laminated timber (CLT) to predict color change during outdoor exposure

Gabrielly S. Bobadilha, C. Elizabeth Stokes, Dercilio Junior Verly Lopes

Page range: 646-654

Abstract

In this study, an artificial neural network (ANN) model was designed to predict color change based on visual assessment of coated cross laminated timber (CLT) exposed outdoors. Coatings and stains were investigated based on ASTM protocols to assess wood surface visual rating, against checking, flaking, erosion, and mildew growth in the State of Mississippi (USA) during one year (2019–2020). It was hypothesized that accurate ratings would promote precise color prediction by the ANN model. Visual assessment inputs were used to develop the model for predicting total color change (Δ E ). The training and validation splits of the network were based on a 10-fold cross-validation technique, and the ANN model performance was assessed on the validation set using mean squared error (MSE), mean average precision (MAE), and coefficient of determination ( R 2 ) after permutation feature importance analysis (PFI). Results indicated that coating was the most important feature in color change model. Erosion, checking and flaking achieved similar importance with an approximate difference of 6%. The ANN model was able to effectively predict color change values based on visual ratings with overall accuracy of 95% on truly unseen data. These findings revealed that coating properties, visual appearance, time of exposure, are associated with discoloration. Accurate visual assessment and a well-trained ANN can successfully provide the desired values of Δ E with a smaller number of complex test procedures.

Open Access December 18, 2020

Wood-adhesive bond loaded in mode II: experimental and numerical analysis using elasto-plastic and fracture mechanics models

Václav Sebera, Jaka Gašper Pečnik, Boris Azinović, Jaromír Milch, Sabina Huč

Page range: 655-667

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Abstract

The goal of the study was to analyze fracture properties of adhesive bond using a three-point end-notched flexure test and the compliance-based beam method. Critical strain energy release rates ( G IIc ) and cohesive laws were obtained for adhesive bonds made of European beech ( Fagus sylvatica L . ) and adhesives such as EPI, MUF, PRF and PUR. The experiments were assisted with FE analyses employing three different material models of wood: elastic (Elas), symmetric elasto-plastic (EP) and elasto-plastic with different compressive and tensile yield stresses parallel to fiber (EP+). The highest mean G IIc was achieved for PUR (5.40 Nmm −1 ) and then decreased as follows: 2.33, 1.80, 1.59 Nmm −1 for MUF, EPI, and PRF, respectively. The failure of bondline was brittle and occurred at bondline for EPI, MUF and PRF, and ductile and commonly occurring in wood for PUR adhesive. The FE simulations employing cohesive models agreed well with the experimental findings for all adhesives. FE model with Elas material was found accurate enough for EPI, MUF and PRF adhesives. For PUR adhesive, the model EP+ was found to be the most accurate in prediction of maximal force. The impact of friction between lamellas may be up to 4.2% when varying friction coefficient from 0 to 1. The impact of the grain angle distortion ( α ) with respect to longitudinal specimen axis showed its high influence on resulting stiffness and maximal force. It was found that three-point end-notched test is suitable for EPI, MUF, and PRF, while it is less appropriate for a bond with PUR adhesive due to notable plastic behavior.

Open Access December 23, 2020

Influences of liquefied lignin content on the properties of waterborne polyurethane prepared with different chain extenders

Wen-Jau Lee, Ming-Shan Hu, Chao-Yun Yu, Yi-Chun Chen

Page range: 668-676

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Abstract

Waterborne polyurethane resins (WPUs) were prepared from polytetramethylene ether glycol (PTMG) and PTMG/polyhydric alcohol liquefied lignin (LL) with isophorone diisocyanate (IPDI), and ethylenediamine (EDA) and 1,4-butanediol (1,4-BD) were used as chain extenders. The effects of LL and the kind of chain extender on the properties of the WPU suspensions and dried films were studied. WPU suspensions prepared with PTMG/LL as the polyol had higher viscosity and larger average particle dimension than those with PTMG alone. WPU films prepared with EDA as the chain extender had higher tensile strength with less tensile deformation. LL can enhance the stiffness of WPU films, but the breaking deformation decreases. Dynamic mechanical analyzer (DMA) results showed that the main effect of LL was reduced thermal activity of the soft segment. Thermogravimetric analyzer (TGA) results showed WPU films prepared with EDA as the chain extender had better heat-resistance than those with 1,4-BD.

January 7, 2021

Composition and antioxidant properties of extracts from Douglas fir bark

Isabel Miranda, Joana Ferreira, Sofia Cardoso, Helena Pereira

Page range: 677-687

Abstract

This study aimed to investigate the antioxidant ability and the chemical composition of apolar and polar extractives from Douglas-fir bark, cork and phloem, establishing a possible correlation with the structural variation along the tree stem and geographic location. Douglas-fir bark extractives’ composition were analyzed at three stem heights in trees from two locations. Cork and phloem extracts’ composition were analyzed in samples collected at stem base. Extractives content in Douglas-fir bark varied between 14 and 31% and polar extractives (11–29%) were dominant over non-polar. Lipophilic extracts were mainly composed of terpenoids, representing 27–77% of all compounds, highlighted by callitrisic acid (11–34%). Sterols were also abundant (6–45%), with β-sitosterol representing 7–33% of all compounds. Alkanoic acids were present in smaller amounts. Ethanol–water extracts showed high phenolic (562–762 mg GAE/g extract), flavonoid and condensed tannins contents (399–683 mg CE/g extract and 120–262 mg CE/g of extract), high scavenging (IC 50 2.8 µg extract/mL) and reducing (12 mM Fe 2+ /g extract) abilities. Cork had high phenolic (819 mg GAE/g extract) and flavonoid contents (524 mg CE/g extract) and high antioxidant capacity (1080 mg TEAC/g extract). Detailed knowledge of Douglas-fir extracts demonstrates their potential as a source of fine chemicals towards different applications.

About this journal

Objective
Holzforschung (HF) is an international scholarly journal that publishes cutting-edge research on the biology, chemistry, physics and technology of wood and wood components. High quality papers about biotechnology and tree genetics are also welcome. Rated year after year as one of the top scientific journals in the category of Pulp and Paper (ISI Journal Citation Index), Holzforschung represents innovative, high quality basic and applied research. The German title reflects the journal's origins in a long scientific tradition, but all articles are published in English to stimulate and promote cooperation between experts all over the world. Ahead-of-print publishing ensures fastest possible knowledge transfer.

Topics

Biology, chemistry, physics and technology of wood and wood components
Biotechnology and tree genetics

Article formats
Original articles, Reviews, Short notes

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Volume 75 Issue 7

Issue of Holzforschung

Frontmatter

Wood identification of two anatomically similar Cupressaceae species based on two-dimensional microfibril angle mapping

Abstract

Treatment of wood with atmospheric plasma discharge: study of the treatment process, dynamic wettability and interactions with a waterborne coating

Abstract

Impact of hygrothermal treatment on the physical properties and chemical composition of Moso bamboo (Phyllostachys edulis)

Abstract

Inverse characterisation of gradient distribution of the modulus of bamboo using a four-point bending test

Abstract

Correlation between bacterial decay and chemical changes in waterlogged archaeological wood analysed by light microscopy and Py-GC/MS

Abstract

Artificial neural networks modelling based on visual analysis of coated cross laminated timber (CLT) to predict color change during outdoor exposure

Abstract

Wood-adhesive bond loaded in mode II: experimental and numerical analysis using elasto-plastic and fracture mechanics models

Abstract

Influences of liquefied lignin content on the properties of waterborne polyurethane prepared with different chain extenders

Abstract

Composition and antioxidant properties of extracts from Douglas fir bark

Abstract