WOOD RESEARCH Volume 67, Number 6, 2022
Peter Godovčin, Jozef Martinka, Peter Rantuch, Martina Hladová, Juraj Kopúnek, Mária Otajovičová, and Mária Zuzana Bednáriková

Impact of temperature and ultraviolet radiation on changes of colour of fir and spruce wood

This study deals with the investigation of impact of temperature and ultraviolet (UV) radiation on spruce wood (Picea abies (L.) H. Karst.) and fir wood (Abies alba Mill.) colour changes. Samples of investigated woods species were loaded by temperatures of 110, 130, and 150°C and UV radiation (with 253.7 nm wavelength and 40 W m-2 intensity) during 72, 168, 336 and 672 hours. Colour changes were evaluated in the CIE Lab colour space. The neural network for prediction of both colour coordinates and total colour difference of spruce and fir wood was trained by data regarding exposure conditions (temperature, UV radiation and time) and by obtained results. Coefficient of determination (R2) of the neural network was above 0.99 for training, validation and testing. Average colour coordinates (± standard deviation) of the spruce and fir wood before exposure were L* = 80.08 ± 3.70, a* = 7.55 ± 2.13, b* = 21.56 ± 1.79, L* = 80.46 ± 1.91, a* = 6.84 ± 0.97, and b* = 18.90 ± 1.26, resp. Total colour differences after thermal loading were in the interval from ΔEab* = 3.76 ± 1.95 (spruce wood at 110°C) to ΔEab* = 45.37±1.46 (fir wood at 150°C). Total colour differences of both wood species exposed by UV radiation were approximately in intervals from ΔEab* = 12 to 13 (after 72 h) up to ΔEab* = 16 to 20 (after 168 to 672 h). Obtained results proven that both temperature and UV radiation have significant impact on the colour changes of the investigated woods.

WOOD RESEARCH Volume 67, Number 6, 2022
Honghai Liu, Xiaokai Zhang, and Jingwen Zhang

Study of dewatering characteristics of eucalyptus wood by supercritical CO2

Wood collapse is a major defect for their applications in solid wood production. Supercritical CO2 (ScCO2) dewatering can quickly remove water in wood and effectively reduce the capillary tension leading to collapse of wood structure. In this study, Eucalyptus exserta F.V. Muell wood was dewatered using ScCO2 at 35, 45, 55°C and 15, 20, 25 MPa, separately. The dewatering characteristics and wood deformation were statistically analyzed and compared after dewatering. The results show that the dewatering rate of ScCO2 is affected by moisture content (MC) of wood, showing the higher the MC, the faster the dewatering. It is also affected significantly by pressure, indicating increased dewatering rate with the pressure. The effect of temperature on dewatering rate is not apparent as the pressure is less than 25 MPa, but it becomes significant at 25 MPa condition, showing an increased dewatering rate with temperature. In this experiment, the greatest dewatering rate was 19.8%·h-1 at 55°C and 25 MPa. The transversal shrinkage of all specimens after 5 cycles dewatering was lower than 1.5%, indicating the ScCO2 dewatering could effectively inhibit collapse of eucalyptus wood structure. The transversal shrinkage decreases with the pressure, and is not affected significantly by temperature.

WOOD RESEARCH Volume 67, Number 6, 2022
Endre Magoss, Richárd Rozs, and Sándor Tatai

Evaluation of wood surface roughness by confocal microscopy

The main aim of this study is to define the usability of the confocal scanning optical microscope (CSOM) to evaluate the wood surface roughness. Therefore, systematic investigation was carried out to define the influences of CSOM on the acquisition of 2D surface roughness parameters. Mahr Perthometer was applied to get reference data to estimate the applicability of the CSOM. Because wood roughness parameters measured with stylus and optical methods are not always comparable a calibration method was conducted on a metal calibration etalon. After the calibration process, the roughness profiles taken with the optical and stylus units were much closer to each other and only the optical Rpk parameter was definitely higher due to artificial peaks generated by the optical system. In order to eliminate this measuring failure, the morphological filter option of the optical apparatus may be activated. The surface roughness parameters were measured on planed Scotch pine samples. The planed surface plains were produced with 0.2 mm parallel offset to investigate the structural influence of the single cutting plains. The obtained results show that the average values for Ra, Rq, Rz, Rk, and Rvk are close to each other for both measuring systems, only the optically measured Rpk values must be corrected. The standard deviations, however, are systematically slightly higher for optical system. This may be explained by the higher resolution of the optical system giving more fine profile details. The earlier developed and introduced dimensionless quantities, such as Abbott ratio, are also fully comparable for both systems provided that the optically measured Rpk values are also correct.

WOOD RESEARCH Volume 67, Number 6, 2022
Nduduzo Khumalo, Samson Mohomane, Setumo V. Motloung, Lehlohonolo Koao, Malevu D. Thembinkosi, and Tshwafo E. Motaung

Effect of H2SO4/HCLO4 mixture on properties of sugarcane bagasse cellulose crystals

The main objective of the study was to investigate the effect of mixed acid concentration on the morphology, crystallinity and thermal properties of cellulose nanocrystals (CNCs). Acid hydrolysis using mixture of sulphuric (H2SO4) acid and perchloric (HClO4) acid was used to extract CNCs from sugarcane bagasse (SCB). The properties of the raw SCB, extracted cellulose, 45% H2SO4 hydrolysed CNCs, 45% H2SO4/HClO4 hydrolysed CNCs, 55% H2SO4/HClO4 hydrolysed CNCs and 65% H2SO4/HClO4 hydrolysed CNCs were analysed using Fourier transmission infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The crystallinity of SCB was significantly increased after bleaching and acid hydrolysis. Acid hydrolysis using 55% H2SO4/HClO4 showed the highest crystallinity. The TGA results showed significant increase in thermal stability of 55% H2SO4/HClO4. The lowest thermal stability was observed with 45% H2SO4 hydrolysed CNCs. The order of thermal stability was raw SCB < extracted cellulose < 45% H2SO4 hydrolysed CNCs < 65% H2SO4/HClO4 hydrolysed CNCs < 45% H2SO4/HClO4 hydrolysed CNCs < 55% H2SO4/HClO4 hydrolysed CNCs. The SEM results showed fibre breakage for 65% H2SO4/HClO4 hydrolysed CNCs. The fibre breakage seemed to be acid concentration dependent.

WOOD RESEARCH Volume 67, Number 6, 2022
Chao Deng, Yang Liu, Junxian Xu, Xiangyu Li, Mingyu Wen, Xixin Duan, and Heejun Park

Fire retardant performance of sugi and hinoki treated with phosphorus and nitrogen fire retardant

In this paper, ammonium phosphate polymer (APP), guanidinium phosphate urea (GUP), phosphonic acid, and a small number of additives that confer flame retardant properties were prepared as a new composite flame retardant. Cedar (Cryptomeria japonica) and hinoki (Chamaecyparis obtuse) penetrate and absorb the solution into the inner wall of the wood by vacuum pressurization, thus obtaining fire-retardant woods. The flame retardant effects at different absorption amounts were investigated by thermogravimetric analysis and cone calorimetry. The absorption amounts of both kinds of wood above 0.095 g.cm-3 and 0.085 g.cm-3 respectively, met the flame retardant standard ISO-5660-1: 2015. Thermogravimetric analysis showed that the fire-retardant-treated wood increased thermal stability, accelerated carbonization, and lower the decomposition temperature to below 300°C.

WOOD RESEARCH Volume 67, Number 6, 2022
Boháček Štefan, Pažitný Andrej, and Michaela Handlovská

Intensification of the freeze-thaw pretreatment of disintegrated poplar wood

This research was focused on the effect of water content in the cells of disintegrated Populus nigra L. on a freeze-thaw pretreatment method before an enzymatic hydrolysis. Two chipped and sieved fractions 2.5 mm and 0.7 mm and two milled fractions, characterized as 18°SR (Shopper–Riegler index) and 37°SR, of the disintegrated 5 years old poplar tree were used for our experiment. Glucose and xylose yields were measured after 24 and 48 hours of enzymatic hydrolysis with a 15% load of the enzyme measured to a total cellulose content. The influence of nine freeze-thaw cycles under -20°C and +20°C was considered. The results showed that an increase in moisture content positively affects yields in all fractions but a desirable result was achieved mainly for the 0.7 mm fraction where the total yield increased by about 16%. More effective way is a finer wet beating of wood mass, while wood fibre receives moisture already in the technological process. The highest glucan conversion 51,74% and the total hemicelluloses conversion 47,72% was achieved for the finest fraction 37°SR. The higher moisture content has a positive effect on the increase in the conversion of oligosaccharides, especially glucan, in chipped fractions.

WOOD RESEARCH Volume 67, Number 6, 2022
Gezhou Qin, Ming Li, Saiyin Fang, Tingting Deng, Changlin Huang, Zhouling Yang, Feilong Mao, and Yue Zhao

Study on the dispersion characteristics of wood acoustic emission signal based on wavelet decomposition

Artificial AE sources were generated on the surfaces of Ulmus pumila, Zelkova schneideriana, Cunninghamia lanceolata, and Pinus sylvestris var. mongolica Litv. specimens. The AE transverse wave signal was decomposed into 3-layers detail signals by wavelet decomposition and reconstructed, and it was calculated based on correlation analysis. Then the longitudinal wave speed was calculated according to the time-difference-of-arrival (TDOA) method, and the wood dispersion phenomenon was studied. The results showed that the dispersion phenomenon of Ulmus pumila was obvious. The propagation speed of high-frequency signal was 2.38 times that of low-frequency signal. The ratio of high and low frequency propagation speed of soft wood was 1.72 and 1.73. The dispersion degree of Zelkova schneideriana was the weakest, and the propagation speed of the high frequency was 1.25 times of the low one. The ratios of longitudinal and transverse wave speeds of the four specimens were 4.59, 4.07, 4.24 and 4.2, respectively.

WOOD RESEARCH Volume 67, Number 6, 2022
Guan Shili, Liang Youzhen, Wang Jun, Lu Lixin, and Hou Xue

Modelling for single-wall corrugated fibreboard with a trapezoidal core under the quasi-static edgewise crushing load

In this paper, the energy absorption of single-wall corrugated fibreboard with a trapezoidal core under edgewise crushing load was studied experimentally and analytically, and a physical surface bonding was assumed to represent the interaction between the fluted board and the linerboard based on the production process of corrugated fibreboards. A new folding element was proposed, including two boards and two trapezoidal corrugated cores with central symmetry. Moreover, three folding modes of the fluted board were proposed based on experimental phenomena, and a plateau stress model was characterized by the geometry parameters of the corrugated fibreboard. It was found that the plateau stress predicted by the developed model compared well with the experimental results, from which one can conclude that the proposed model was effective and helpful for corrugated structures design and parameters selection to meet different strength requirements.

WOOD RESEARCH Volume 67, Number 6, 2022
Ondřej Dvořák, Miloš Pánek, Monika Sarvašová Kvietková, Filip Pastierovič, Irena Štěrbová, Kryštof Kubista, and Lukáš Sahula

Influence of wood species on quality of exterior transparent acrylic coating during outdoor exposure

Coating systems are a popular way to protect wood against the effects of weathering when used outdoors. This study evaluates the impact of the basic wood species on the overall durability and color fastness of the selected water-based acrylic exterior paint. Spruce (Picea abies L.) and oak (Quercus robur L.) wood samples were subjected to external weathering according to EN 927-3 (2000) for 6 and 12 months. The evaluation by instrumental methods related to co changes in color, gloss, surface wettability contact angle, at which paint damage was also visually evaluated. The results showed that the durability of the tested coating was higher for spruce. Still, on the other hand, thanks to its lighter shade, a significant color change caused by the base wood’s photodegradation was detected, showing that oak wood has a negative effect on the overall life of the tested coating.

WOOD RESEARCH Volume 67, Number 6, 2022
Matúš Neusch, Jaroslav Sandanus, and Klara Freudenberger

Experimental verification of the modern semi-rigid timber connections

The paper deals with theoretical and experimental research of the timber connections using modern timber connectors Rothoblaas Alumidi. These connectors allow for semi-rigid behaviour of the connections. The paper describes the theoretical background of semi-rigid connections, explains the methods used in the numerical analysis and the design of test connections. The thesis continues with the experimental verification of the designed specimens. The experimental results are compared with the numerical analysis. The findings obtained from the experiment and recommendations for practice are summarized in the conclusion.

WOOD RESEARCH Volume 67, Number 6, 2022
Jamaludin Malik, Erlina Nurul Aini, Deazy Rachmi Trisatya, Sona Suhartana, Imam Wahyudi, and Sarah Augustina

Dimensional stability and durability of hybrid sandwich panel made from oil palm lumber, sengon and gmelina with boron-alum impregnation

In this study, sandwich panels made from oil palm lumber, sengon, and gmelina wood were impregnated with a boron-alum solution to improve their water and termite resistance. Water resistance testing was evaluated using a thickness swelling test following the method in SNI 03-2105. The sandwich panel was also tested for its durability against dry wood termites, according to SNI 01-7207. The weight loss, mortality, and attack degree were used as the parameters for evaluating termite durability. The results showed that the treatment with a boron-alum solution can increase the stability, water resistance, and weight loss properties up to 73%, 41%, and 100%, respectively. The best properties of the sandwich panel were obtained by the sengon-isocyanate panel with 8% boric acid-borax and 5% alum treatment which has thickness swelling of 2.37%, water absorption of 49.04%, weight loss of 0.0124%, termite mortality of 100%, and attack degree of 0.

WOOD RESEARCH Volume 67, Number 6, 2022
Aokai Cheng, Dengyun Tu, Zhipeng Zhu, Qiaofang Zhou, Wei Wei, Chuanshuang Hu, and Xianghao Liu

Study on machining properties and surface coating properties of heat treated densified poplar wood

In this study, a modification combining densification and heat treatment of poplar wood (Populus tomentosa Carr.) was carried out, and the machining properties of the unmodified poplar wood (control) and the heat treated densified wood (HTD) were tested and evaluated. In addition, the water-based UV paint was covered on the control and HTD respectively, and the surface coating properties of them were evaluated. The results showed that: (1) The machining properties of poplar wood were improved after the heat treatmentdensification modification. The score of comprehensive machining properties of the HTD was 45 (excellent grade), while the score of the control was 36 (good grade). (2) The abrasion resistance, hydrophobicity and adhesion were improved after heat treatment-densification modification. Therefore, the modification combining densification and heat treatment played a significant role in enhancing the value of wood.

WOOD RESEARCH Volume 67, Number 6, 2022
Yang Wu, Jiangang Zhu, Qian Qi, and Lina Cui

Research progress of solid wood bending softening technology. Review

The softening process of wood bending has a very important influence on the performance, forming shape, and yield of bentwood. The paper reviewed the typical softening processes in solid wood bending by analyzing the various softening mechanism and softening processes. The main influencing factors of the softening technology on the bending properties were summarized based on the comparative analysis of the related research progress of wood softening. In view of the lack of systematic analyses of the cost and environmental factors associated with the softening process, this paper goes in detail analyzing the major softening technologies with comprehensive comparison of the economic and environmental advantages and disadvantages. The paper also draws light on the development trends of softening technology that can be implemented in wood industry which can hence improve the added value of wood. Under the background of green development, the authors believe that the softening technology should not only benefit the economic efficiency but also meet the social needs of low-carbon and environment-friendly.

WOOD RESEARCH Volume 67, Number 6, 2022
Manish Ranjan, Anand Nandanwar, and Pradeep Kumar Kushwaha

Comparative study on physical-mechanical properties of plywood produced from eucalyptus grandis and populus deltoids veneers. Short notes

Nine-ply plywood panels were produced from Eucalyptus grandis and Populus deltoids using urea-formaldehyde (UF) and phenol-formaldehyde (PF) adhesives. The physical and mechanical properties, such as moisture content, density, modulus of rupture (MOR) and modulus of elasticity (MOE) of the eucalyptus and poplar boards, were compared in this study. Samples were tested on both, along and across the grain. Higher values of MOR and MOE were observed for eucalyptus as compare to poplar. Density of ply board was observed as 500-560 kg.m-3 in plywood from poplar and 700-720 kg.m-3 in plywood from eucalyptus species. These differences were attributed to the variation in properties of veneer wood species. The effect of veneer wood species on some physical and mechanical properties of plywood was found statistically different.