Manufacture of oriented board using mild steam treatment of plant fiber bundles

This study investigated the effects of mild steam treatment (0.1 MPa for 2 h) of natural bio-based fibers and orientation (0° and 90°) of those fibers in various fiberboards. Ramie bast, pineapple leaf, and sansevieria fiber bundles were used as materials. The composite fiberboards were prepared using phenol-formaldehyde (PF) resin. To investigate the effect of mild steam treatment on wettability, contact angles of PF resin to the fiber were measured. The mechanical properties of the boards were examined as well as their dimensional stability. The contact angle data showed that mild steam treatment was effective in improving the wettability of fibers. Unioriented steam-treated boards showed better performance of internal bond (IB), moduli of rupture (MOR) and elasticity (MOE), thickness swelling (TS), and water absorption (WA) than other boards. Unioriented steam-treated sansevieria board with longitudinal fiber direction showed higher average values of MOR (403 MPa), MOE (39.2 GPa), and IB (1.33 MPa) and lower values of TS (5.15%) and WA (8.68%) than other boards. The differences in the mechanical properties and dimensional stability of boards were found mainly due to the differences in the ratios of fiber fraction of the boards to the density of the fiber bundles.     

Monitoring fiber orientation in OSB during production using filtered image analysis

The orientation of oriented strand board (OSB) mats has been practically measured on a commercial factory production line to demonstrate the practical capabilities of the filtered image analysis (FIA) technique. Samples have been cut from OSB panels at a range of angles to the panel axis and these samples have been tested in bending. The factory data and the experimental data have been compared in order to investigate the relationship between the practical condition of fiber orientation in the factory and the bending properties as a function of orientation. The following conclusions can be drawn. Fiber orientation in the production line is good and stable irrespective of position across the width of the production line, time of day and changing line speed. The average value for the orientation angle of the forming mat on the production line is approximately 25°. The general shape of the fiber orientation distribution is similar to a normal distribution, however, at the centre of the fiber mat the sharpness of the distribution is greater than a normal distribution. The average orientations of fibers in commercial board lie at 25° and 60° to the longitudinal and perpendicular directions, respectively. The results suggest that there is potential to improve the mean fiber orientation angle of commercial OSB to improve longitudinal values of MOR and MOE, especially where perpendicular properties are not critical. Received 31 March 2000     

Mechanical fiber separation under torsional stress

Summary Spruce wood (Picea abies) samples were pretreated at different temperatures and, in some cases, with sodium sulfite solution under normal conditions for the chemimechanical pulping of wood chips. The pretreated samples were simultaneously subjected to torsion and compression stresses at temperatures ranging from 20 to 90 °C. The load-deformation relationship was analyzed at each temperature. The failure zones were studied using the scanning electron microscope technique. The results showed that the maximum torque decreased with increasing temperature under the deformation conditions applied. Sulfonation of the samples gave a similar effect, although to a smaller extent. The elastoplasticity of the samples, as viewed in terms of the twist angle at failure, was also affected by the pretreatment. While axial compression had a major effect, sulfonation only caused a marginal change. Microscopic studies of the failure zone showed that when the temperature increased, the fracture plane traveled around fibers instead of through them, thus causing less fiber damage. Sulfonation improved fiber separation and decreased fiber damage. The separation of ray cells from the fiber tracheids was improved, particularly by sulfonation. Increasing temperature and sulfonation changed the fracture plane from the secondary wall of fibers towards the more lignin enriched primary wall and middle lamella. Received 29 January 1997     

A morphological study on the behavior of bamboo pulp fibers in the beating process

Summary Bamboo pulp fibers respond to beating more rapidly than do wood fibers. This is probably due to the difference in secondary wall structure between the fibers. In the present paper, the behavior on beating of pulp fibers from Bambusa polymorpha Munro was investigated from a morphological point of view. The secondary wall of bamboo fibers consists of alternately arranged broad and narrow layers. During the beating process, a number of transverse and concentric cracks are generated in the broad layers, which causes an internal fibrillation. The outer broad layers with their numerous cracks separate from the inner layers and swell highly toward the outside. The outer secondary wall layer of bamboo fibers has a microfibril angle of about 20° with respect to the fiber axis which is much smaller than that of the S1 layer of wood fibers. As a result this layer appears to offer little resistance to prevent the external swelling of the broad layers.Part of this work was financially supported by a Grand-in Aid for Scientific Research, Ministry of Education, Japan, 57470095Currently with the Japan Pulp and Paper Research Institute, Inc., Tsukaba, Japan     

Effects of temperature on the growth of a Japanese willow (Salix gilgiana Seemen)

The effects of temperature on the growth characteristics of a Japanese willow (Salix gilgiana Seemen) were studied with respect to dry matter production, wood anatomy and the net photosynthetic rates of leaves. Clonal materials were grown in natural-light rooms (phytotrons) at 30°C/25°C, at 25°C/20°C or at 20°C/15°C (day/night: 12 h/12 h), respectively. The elongation rate of shoots from the beginning of June to the end of July was approximately 22 cm per week under the three different sets of conditions. The shoots reached approximately 3 m in height after 4 months of growth. Total dry matter production and dry weights of stems did not differ very much among the three sets of temperature conditions after 9 months of growth. The dry weight of leaves increased at high temperatures while that of roots decreased. The number of vessels increased significantly at 30°C/25°C and 25°C/20°C, whereas the diameters of vessels and fibers, and the double wall thickness of fibers did not vary markedly under all three temperature regimes. The net photosynthetic rate and the respiration rate in mature leaves were highest at 30°C/25°C, and both activities increased with increases in growth temperature. The increase in the photosynthetic rate was much smaller than that in the respiration rate. Individual plants had been completely adapted to the respective growth temperatures, as judged from the decrease in the photosynthetic rate after the transfer to different temperatures. Part of this work was reported at the 102nd Annual Meeting of the Japanese Forestry Society (Nagoya, Japan, 1991). This work was supported by Grants-in-Aid (Integrated Research Program for Effective Use of Biological Activities to Create New Demand) from the Ministry of Agriculture, forestry and Fisheries of Japan (BRP 97-IV-B-10).     

Morphological changes of ramie fiber during mercerization

Morphological changes of ramie fibers due to swelling in alkali solution were investigated. The observed twisting and changes in the cross-sectional shape of the fibers could be explained as a geometrical alteration caused by lateral expansion of coiling fibrils, as the unmercerized ramie fiber showed an S-helix structure. The fibril angle of ramie fibers was estimated to be 3°. Although the swollen fiber untwisted to some extent on washing with water, the shape of the twisted ribbons as observed by scanning electron microscopy was retained even after drying. Concentrated 8N NaOH produced only a moderate change in morphology, whereas swelling with 3.5N NaOH at 0°C expanded the cross sections about 30 times over the initial ones accompanied by a drastic change in the shape of the fiber.Part of this paper was presented at the annual meeting of the Wood Research Society of Japan in Kumamoto, April 1996     

Characterization of raffia palm fiber for use in polymer composites

Raffia palm fibers are potential reinforcement materials for making cost-effective polymer-based composite. This paper presents the results obtained from a study of physical, chemical, thermal and mechanical properties of raffia palm fibers (RPFs) derived from the raffia palm tree (Raphia farinifera). The as-received RPFs had their remnant binders manually removed and was subsequently cleaned in a 2% detergent solution before drying in an air oven at 70 °C for 24 h. Evaluation of the properties of the dried samples was carried out using a combination of characterization techniques including chemical composition determination, density measurement, moisture adsorption and water absorption measurements, tensile testing, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Raman spectroscopy, X-ray diffractometry, and Fourier transform infrared spectromicroscopy. The main constituents of RPFs were found to be cellulose, hemicellulose and lignin. The average diameter and average density were 1.53?±?0.29 mm and 1.50?±?0.01 g/cm³, respectively. The average breaking strength of the fibers ranged from 152?±?22 to 270?±?39 MPa; it did not vary significantly with fiber length and cross-head speed during tensile testing. The results of scanning electron microscopic investigation of the fibers showed that they comprise several elemental fibers which are tightly packed together with each having its own lumen. Synchrotron-based Fourier-transform infrared spectromicroscopy of a cross-section of the fiber showed that lignin is concentrated mostly on the outside while cellulose and pectin are concentrated in the mid-section. A two-stage water sorption behavior was observed for the fibers.     

杨树微纤丝角的变异及其与木材性质的相关关系

微纤丝角为细胞次生壁S2层微纤丝排列方向与细胞主轴所形成的夹角,与木材的物理性质、力学性质和化学性质都有着直接的关系。应用x射线衍射法测定了7个杨树无性系(14株样木)胸径处各年轮的微纤丝角,并对应分析和测定了各年轮的木材基本密度、纤维长度、纤维宽度和纤维素含量。研究结果表明,杨树微纤丝角在年轮间存在显著差异,其径向变异规律为从髓心向外以微纤丝角逐渐降低,年轮间的平均微纤丝角在7.8旱?8褐洌荒静幕久芏取⑾宋ざ取⑾宋矶群拖宋睾吭谀曷旨湟泊嬖谙灾钜臁O喙胤治霰砻鳎⑾怂拷怯肽静幕久芏取⑾宋ざ取⑾宋矶群拖宋睾看嬖谙灾母合喙毓叵??0.01),相关系数分别为-0.450、-0.586、-0.516和-0.660。回归分析结果表明,多项式方程可较好地描述杨树微纤丝角与所测定的木材性质的关系,相关系数均在-0.45以上(n=125)。本文的研究结果认为,在今后针对杨树材性改良的育种计划中,微纤丝角是一个重要的选育和改良指标。图3表3参34。     

Tensile strength of softwood butt end joints. Part 1: Effect of grain angle on adhesive bond strength

Abstract

To study the effect of grain angle on the adhesive bond strength in wood, three-part Norway spruce wood specimens were bonded and tested in tension. The two axially orientated outer parts of the specimens were joined with the middle part by means of three adhesives typically used for load-bearing constructions, i.e. one-component polyurethane (PUR), melamine–urea–formaldehyde (MUF) and phenol–resorcinol–formaldehyde (PRF). The grain angle of the middle part was varied from 0° (end grain to end grain) to 90° (flat grain to end grain) in incremental steps of 10°. In general, PRF- and MUF-bonded samples exhibited highest tensile strength at end grain to end grain orientation of the three parts, while specimens bonded with PUR showed only 25% of the strength measured for PRF and MUF, respectively. At high grain angles (90°) all specimens showed similar strength values in the range of 30% of maximum strength of MUF- and PRF-bonded specimens. To explain the changing strength levels at different grain angle a composite failure criterion was applied.     

Study on drying rate in contact drying with flexible screen

IntroductionA new type contact dryer with non-metal flexibleplaten was patented in 1998 in China, which specialstructure and material solved the problem of low productivity in platen drying. The machine was similar tohot press. Direct contact betWeen wood and heatedplaten allows rapid heat transfer by conduction (Sandoe 1983). Though the flexible screen conducts heatslower than metal platen does, it transfers massmuch fast6r. So water removing rate decides veneerdrying rate in the new machin…     

Intercalation of wood charcoal with sulfuric acid

Intercalation of wood charcoal with sulfuric acid (H₂SO₄) was investigated. Carbonized sugi (Japanese cedar) samples were prepared by heating at various temperatures in the range 1700°–2700°C. Electrochemical oxidization was carried out in H₂SO₄ and the feasibility of intercalation was determined. In potentiometric analysis, plateaus appeared for samples carbonized at temperatures above 2300°C. In their X-ray diffraction profiles, the peak at around 26° was shifted to a smaller angle of about 22.4°. These results can be considered as signs of intercalation with acid molecules. Fourier transform infrared analysis of charcoal heated at 2700°C, following washing with water and drying of the sample, showed a band at 1220 cm⁻¹ that was assigned to a sulfonate group. This band was not observed for samples heated at 1900°C. These observations suggest the occurrence of intercalation in the former charcoal, but not in the latter. It is concluded that wood charcoal can undergo intercalation when it has ordered stacking of hexagonal carbon layers. Part of this article was presented at the 55th, 56th, and 57th Annual Meetings of the Japan Wood Research Society, Akita, Hiroshima, and Tsukuba, August 2006, August 2007, and March 2008, respectively, and at the International Conference on Carbon “CARBON 2008,” Nagano, July 2008     

Ultrasonic treatment to improve the quality of recycled pulp fiber

The effect of ultrasound on the quality of recycled fibers was investigated. Ultrasound was applied to recycled pulp fiber suspension before ink removal by conventional flotation. The ultrasonic treatment induced an increase in the sedimentation volume of the fiber, which implies that the flexibility and bulkiness of the fiber increase. The water retention value of the ultrasonically treated fiber recovered from the loss caused by the recycling. These facts are due to a beating effect of the treatment. The paper sheets prepared from the ultrasonically treated fiber suspension showed higher sheet density, tensile strength, and brightness than that from an untreated fiber suspension. The process, which consists of ultrasonic treatment for 1 min following flotation deinking, requires about 1.4 times as much energy as the conventional flotation deinking process, but it induced 20% improvement in brightness. The results indicate that the ultrasonic treatment is effective in improving recycled fiber quality.This report was presented in part at the 48th Annual Meeting of the Japan Wood Research Society, Shizuoka, April 1998; and at the 5th Annual Meeting of the Japan Cellulose Society, Kyoto, July 1998     

Microscopic structure and properties of wood-based foaming composites

In order to reduce the density of wood-based composites without causing a deterioration of their mechanical properties, we studied the process of manufacturing wood-based composites. A combination of polymer foaming technology and flat hot-pressing technology was used. The microscopic structure of the various wood-based composites was analyzed with a scanning electron microscope (SEM). Modulus of rupture (MOR), modulus of elasticity (MOE), impact strength, and thickness expansion rate of water sorption (TS) were all measured. The results showed that fibers loosely interweave, and fibers had been connected by micropore. They also showed that spaces between fibers had big micropore structure. MOR, MOE and impact strength were the highest among three levels of ratio. When the total content of resin and foaming agent were 20% by weight, TS was higher. A hot-pressing temperature of 120°C was optimal. At the low temperatures of 80°C, the foaming process was uncompleted. At a higher temperature, micropores burst at a certain pressure. Based on the variance analysis and maximum difference analysis, a significance test shows that the optimum conditions for the total content of resin and foaming agent is 20% by weight, with a hot pressing temperature of 120°C for 15 min. Under these conditions, the properties of wood-based foaming composites all achieved the industry standard. __________ Translated from Journal of Beijing Forestry University, 2007, 29(3): 154–158 [译自: 北京林业大学学报]     

Influence of heating history on dynamic viscoelastic properties and dimensions of dry wood

To obtain new information about the mechanical and physical properties of dry wood in unstable states, the influence of heating history on viscoelastic properties and dimensional changes of dry wood in the radial, tangential, and longitudinal directions was studied between 100° and 200°C. Unstable states of dry wood still existed after heating at 105°C for 30 min and were modified by activated molecular motion in the first heating process to temperatures above 105°C. This phenomenon is thought to be caused by the unstable states reappearing after wetting and drying again. Dry wood components did not completely approach the stable state in the temperature range tested, because they did not entirely surpass the glass transition temperatures in most of the temperature range. In constant temperature processes at 135° and 165°C, E′ increased and E″ decreased with time regardless of the direction. This indicated that the unstable states of dry wood components were gradually modified with time at constant temperatures. On the other hand, anisotropy of dimensional change existed and dimension increased in the longitudinal direction, was unchanged in the radial direction, and decreased in the tangential direction with time at constant temperatures. Part of this report was presented at the 13th Annual Meeting of the Chubu Branch of the Japan Wood Research Society, Shizuoka, August 2003     

Mechanical properties of kenaf fiber–cement composites containing kenaf gamma-ray grafted with acrylamide

Kenaf fibers have excellent properties and possess the potential to be outstanding reinforcing fillers in cement. The grafting of acrylamide to kenaf fibers is important in improving the compatibility between the fibers and the cement. Acrylamide was grafted onto kenaf fibers using gamma-ray radiation. The radiation dose ranged from 20 to 100 kGy, and the dose rate was 10 kGy/h. The degree of grafting increased with increased radiation doses. FT-IR analysis revealed an increase in amide content after gamma-ray-radiation-induced grafting, further evincing the attachment of acrylamide to the kenaf fibers. SEM images showed evidence of acrylamide grafting to the fiber surface. Contact angle measurements on individual fibers taken before and after grafting demonstrated changes in wettability. The mechanical properties of the gamma-ray-grafted kenaf fiber–cement composites were superior to those of the ungrafted kenaf fiber–cement specimens.     

Relaxation mechanism of residual stress inside logs by heat treatment: choosing the heating time and temperature

 Some methods to reduce residual stress inside logs have been reported, although the conditions for stress relaxation are not yet clarified. Our study using precise experiments revealed that residual stress relaxation occurs only when both heat and moisture exist inside the logs. We then determined the heating time and temperature required to relax the residual stress inside the logs. Short air-drying treatments did not relax residual stress even though free water in the logs was greatly reduced. The residual stress of the 33-h 80°C-heated bolts was relaxed, whereas that of the 48-h 70°C-heated bolts was not. As for the influence of treatment time, bolts heated at 100°C were relaxed after 18 h of treatment. The 13-h heated bolts did not show any relaxation. Therefore, residual stress relaxation occurred rapidly owing to the thermomechanical change of the individual wood components comprising the cell wall. The moisture content inside all the bolts was much higher than the fiber saturation point. This is because relaxation occurs only when the heating temperature is maintained above 80°C for a particular duration of treatment. Received: December 12, 2001 / Accepted: February 18, 2002 Present address: Institute for Structural and Engineering Materials, National Institute of Advanced Industrial Sciences and Technology, Independent Administrative Institution, Nagoya 463-8560, Japan Tel. +81-52-736-7320; Fax +81-52-736-7419 e-mail: m.nogi@aist.go.jp Part of this report was presented at the 50th Annual Meeting of the Japan Wood Research Society, Kyoto, April 2000 Correspondence to:M. Nogi     

Effect of tool angles on the chips generated during milling of wood by straight router-bits

 The effect of tool angles on the shapes of chips generated by parallel-to-grain and end-grain milling was explored for China fir and maple under fixed spindle and feed speeds and cutting depth. The milling path was up-milling by straight router-bits with a diameter of 12 mm. The chip shapes could be distinguished as five types: spiral, splinter, flow, thin, and granules or powder. The flow and thin chips were generated most often (on a weight percentage basis) for all tool angles investigated for parallel-to-grain and end-grain milling of China fir and maple. More granule chips were produced with parallel-to-grain milling than with end-grain milling for both woods. The measured chip thickness (t′) was thicker than the calculated thickness (t _max). Thicker and longer maple chips were produced by end-grain milling than by parallel-to-grain milling. The tool geometries of 40°/15° (sharpness of the angle–rake angle), 50°/15°, and 60°/15° for China fir and 40°/25°, 50°/5°, and 60°/5° for maple produced relatively more flow chips with parallel-to-grain milling. Furthermore, the tool geometries of 40°/5°, 50°/15° and 60°/25° produced more flow chips (weight percentage) by end-grain milling of China fir and maple. Received: May 23, 2001 / Accepted: June 28, 2002 Acknowledgment This study was supported by a grant from the National Council of Science, Taiwan (NSC89-2313-B-415-011).     

Nondestructive test and prediction of modulus of elasticity of veneer-overlaid particleboard composite

The effects of grain angle, thickness of face veneer, and shelling ratio on dynamic modulus of elasticity (E) of veneer-overlaid particleboard composite (VOP) were examined by using nondestructive test. In this study, the possibility that E of VOP can be predicted by means of some empirical formula was also discussed. This study has shown that grain angle, thickness of face veneer, and shelling ratio have substantial effects on E of VOP. The E at 0° of grain angle of face veneer was the largest, decreasing rapidly with increase in the grain angle. The lowest value of E occurred at 90° of grain angle of face veneer. The relationship between grain angle of face veneer and E of VOP can be expressed in the form of Jenkin’s and Hankinson’s equations. The orthotropic properties of wood and VOP defined as the ratio E ₀/ E ₉₀ were 25.7 for wood and 4.7 for VOP. When the grain direction of face veneer was parallel to the length of the specimens, the E of VOP increased with increasing shelling ratio. VOP increased E from 125 to 179% over that of the particleboard and veneer thickness from 2.1 upto 3.6 mm. However, when the grain direction of face veneer was perpendicular to the length of the specimens, the E of VOP decreased with increasing shelling ratio. VOP decreased E from 23 to 41% over that of the particleboard and veneer thickness from 2.1 upto 3.6 mm. The relationship between E of VOP and face veneer thickness can be expressed in the form of a second-order parabolic equation. Rule of Mixture (ROM) can be used to predict E of VOP from the E of wood element and particleboard element.     

Comparative studies on microstructures and chemical compositions of cell walls of two solid wood floorings

Two common wood flooring materials, taun (Pometia spp.) and cumaru (Dipteryx odorata), were used as investigated objects and comparison was made between the two wood species for their density, microstructure, microfibril angle (MFA), cellulose crystallinity and the main chemical composition. Results showed that the density of cumaru was 0.941 g·cm^?3, significantly larger than that of taun, 0.737 g·cm^?3. The biggest difference of two wood species in microstructures was fiber cells. Fiber cells of cumaru had dense cell walls, almost no cell lumens; while fiber cells of taun had relatively thin cell walls, with apparent cell lumens. The thickness of fiber cell wall of cumaru and taun were 6.80 and 2.82 µm, respectively, and the former is about 2.5 times thicker than the latter. Measured data of MFA indicated that the average MFA of cumaru was 11.7°, smaller than that of taun, 13.4°. The relative crystallinity of cumaru and taun were 54.0 and 50.8%, respectively. The two wood species had the similar holocellulose contents, but the lignin content of cumaru was higher than that of taun, especially that the content of extractive of cumaru was as twice as that of taun.     

Micromorphological characteristics of bamboo (<Emphasis Type="Italic">Phyllostachys pubescens</Emphasis>) fibers degraded by a brown rot fungus (<Emphasis Type="Italic">Gloeophyllum trabeum</Emphasis>)

The decay pattern in bamboo fibers caused by a brown rot fungus, Gloeophyllum trabeum, was examined by microscopy. The inner part of the polylaminate secondary wall was degraded, while the outer part of the secondary wall remained essentially intact. Degradation in bamboo fiber walls without direct contact with the fungal hyphae was similar to wood decay caused by brown rot fungi. Degradation in polylaminate walls was almost confined to the broad layers whereas the narrow layers appeared resistant. The p-hydroxylphenyl unit lignin in middle lamella, particularly in the cell corner regions, was also degraded. The degradation of lignin in bamboo fibers was evidenced by Fourier transform infrared spectra. The present work suggests that the decay of bamboo fiber walls by G. trabeum was influenced by lignin distribution in the fiber walls as well as the polylaminate structures.