Chemical changes of kenaf core binderless boards during hot pressing (I): influence of the pressing temperature condition

Self-bonding is the main factor of the performance expression of binderless boards, and therefore its clarification is considered to be an important issue. For this purpose, a series of chemical analyses were conducted on kenaf core binderless boards and their chemical changes during the hot-pressing process are discussed in this article. First of all, binderless boards were prepared from kenaf core powder at different pressing temperatures (without steam-explosion process) and were used for chemical analyses after they were reduced into powders and extracted with methanol. To investigate their chemical changes, lignin, holocellulose, and neutral sugar contents were determined, Fourier transform infrared (FTIR) spectra were recorded, and the nitrobenzene oxidation procedure was applied. As a result, it was found that parts of lignin and hemicelullose were decomposed during the hot-pressing process; however, the contribution of the resulting fractions to selfbonding was not observed. In addition, progress of condensation reactions in lignin and the formation of chemical bonds by low molecular weight conjugated carbonyl compounds in methanol extractives were observed. Thermal softening of lignin is also suggested to play an important role in the expression of board performance.     

Manufacture and properties of binderless particleboard from bagasse I: effects of raw material type, storage methods, and manufacturing process

Binderless particleboards were manufactured from sugarcane (Saccharum officinarum L.) bagasse by steam-injection pressing and by using hot pressing as a reference method. The inner layer (core/pith) and the outer hard fibrous layer (face/rind) of bagasse were used as raw materials. The effects of bagasse type, manufacturing process, and storage method on the mechanical properties of binderless particleboards were investigated. The results showed that the bagasse pith particles provided better board properties than bagasse rind particles. It seemed that bagasse pith particles were more easily deformed than bagasse rind particles, enlarging the bonding contact area. The severe conditions of steam-injection pressing caused delamination on the bagasse pith binderless boards with densities of 0.6 g/cm³ or higher, and gave poor bonding quality. However, steam-pressed boards showed relatively higher board properties than hot-pressed boards. The storage method of sugarcane bagasse affected the chemical composition and the board properties. It was shown that the extent of self-bonding formation depends on the chemical and morphological properties of lignocellulosic materials, as well as on the manufacturing conditions. Part of this paper was presented at the 5th International Wood Science Symposium, Kyoto, Japan, September 2004     

Chemical changes in steam-pressed kenaf core binderless particleboard

The effects of chemical changes in kenaf core binderless particleboards on the bonding performance and thickness swelling of boards were investigated by chemical and spectroscopic analyses. Mild steam-injection treatments (0.6–1.0MPa) caused significant degradation of hemicelluloses, lignin, and cellulose. Conventional hot pressing caused a lower degree of degradation of the chemical components. The hot-pressed kenaf core board without any binders showed poor bonding performance. Thus, it was found that partial degradation of the three major chemical components of the kenaf core by mild steam-injection treatment increased the bonding performance and dimensional stability of the binderless boards, and gave better quality binderless boards than those made by hot-pressing treatments.Part of this report was presented at the 4th International Wood Science Symposium, Serpong, Indonesia, September 2002; and at the 53rd Annual Meeting of The Japan Wood Research Society, Fukuoka, March 2003     

The suitable harvesting season and the part of moso bamboo (Phyllostachys pubescens) for producing binderless boards

The properties of the binderless boards of moso bamboo depending on the harvest seasons and the parts of the height were reported and the optimum harvesting conditions investigated. The binderless boards were prepared from the powdered bamboo harvested each month from June to May, and the parts in height. The hot water extract (HWE), lignin, α-cellulose, and hemicelluloses contents were examined. The board properties were evaluated with internal bonding (IB), water absorption (WA), and thickness swelling (TS). From the experiment, the boards prepared between March and October had higher HWE content and higher IB and lower WA and TS than the ones prepared in other months. The board from the top part showed lower IB and higher WA and TS than the bottom and the middle. The boards prepared from the residue after extraction of HWE showed lower IB than the unextracted samples. These results indicated that for producing board from bamboo, the suitable harvesting season is when HWE contents are higher and that the suitable parts in height for harvesting are the bottom and the middle where lignin contents are not low.     

Self-bonding characteristics of binderless kenaf core composites

We investigated optimum self-bonding conditions of kenaf core composites manufactured by steam treatment, and discussed on the roles of cinnamic acids in the self-bonding mechanism. The presence of cinnamic acids in the kenaf core and its composites were analyzed by pyrolysis gas chromatography-mass spectrophotometry in the presence of tetramethyl ammonium hydroxide (TMAH/Py-GC-MS). The results showed that the optimum bonding properties of kenaf core composites were achieved under these conditions: steam pressure of 0.8–1.0 MPa and pressing time of 10–15 min were able to provide shear strength of 0.40–0.42 MPa while having 2–5% of weight loss. Lignin analysis showed that steam-treated kenaf core composites had a lower proportion of syringyl- to guaiacyl-derived moieties and also cinnamic acids to guaiacyl-derived moieties than its native counterpart. The results indicated that some parts of the ester-linked cinnamic acids were also cleaved due to the degradation of hemicelluloses and lignin during steam treatment. Based on these results, it was concluded that in addition to three main components, the cinnamic acid was also suggested to participate in the self-bonding mechanism of non-wood lignocellulosic binderless boards.     

Characterization of bagasse binderless particleboard manufactured in high-temperature range

This paper describes the features of binderless particleboard manufactured from sugarcane bagasse, under a high pressing temperature of 200–280 °C. Mechanical properties [i.e., modulus of rupture (MOR) and elasticity (MOE) in dry and wet conditions, internal bonding strength (IB)] and dimensional stability [i.e., thickness swelling (TS)] of the board were evaluated to investigate the effect of high pressing temperature. Recycled chip binderless particleboards were manufactured under the same conditions for comparison, and particleboards bonded with polymeric methylene diphenyl diisocyanate (PMDI) resin were manufactured as reference material. The target density was 0.8 g/cm³ for all of the boards. The results showed that the mechanical properties and dimensional stability of both types of binderless boards were improved by increasing the pressing temperature. Bagasse showed better performance than that of recycled chip as a raw material in all evaluations. Bagasse binderless particleboard manufactured at 260 °C had an MOE value of 3.5 GPa, which was equivalent to the PMDI particleboard, and a lower TS value of 3.7 % than that of PMDI particleboard. The MOR retention ratio under the dry and wet conditions was 87.0 %, while the ratio for the PMDI particleboard was only 54.6 %. The obtained results showed the possibility of manufacturing high-durability binderless particleboard, with good dimensional stability and water resistance, which previously were points of weakness for binderless boards. Manufacturing binderless boards under high temperature was effective even when using particles with poor contact area, and it was possible to express acceptable properties to allow the manufacture of particleboards. Further chemical analysis indicated a contribution of a saccharide in the bagasse to the improvement of the board properties.     

The effects of chemical components and particle size on the mechanical properties of binderless boards made from oak (<Emphasis Type="Italic">Quercus</Emphasis> spp.) logs degraded by shiitake fungi <Emphasis Type="Italic">(Lentinula edodes</Emphasis>)

Binderless boards are composite boards that rely on self-bonding mechanisms for inter-fibre bonding. Quercus acutissima and Quercus serrata logs degraded by Lentinula edodes (shiitake fungi) were used in this study to investigate whether physical and chemical changes induced by shiitake fungi can enhance board mechanical properties. Binderless boards were manufactured with 0.8 g/cm³ target density, 220 °C pressing temperature, 5 MPa pressure, and pressing duration of 10 min. Boards made from logs degraded for ≥?26 months were stronger than control boards and met modulus of rupture (MOR) and internal bonding (IB) requirements for fibreboards. Chemical composition and particle size distribution of the wood powder used to make the boards were determined to elucidate the drivers of board mechanical properties. The proportion of small particles (<?150 µm) showed a strong positive correlation with MOR for both species and hot water extractives showed a strong positive correlation with IB for Q. acutissima boards. Introduction of shiitake fungi pre-treatment to the production process may enhance the mechanical strength of binderless boards.     

Water resistance properties of kenaf core binderless boards

Abstract Binderless boards were prepared from kenaf core under various manufacturing conditions and their water resistance properties were evaluated. The board properties evaluated were retention ratios of modulus of rupture (MOR) and modulus of elasticity (MOE), internal bonding strength after water treatment (IB), thickness swelling (TS), water absorption (WA), and linear expansion (LE). These values were then compared with those of boards bonded with urea-formaldehyde (UF), urea melamine formaldehyde (UMF), and phenol-formaldehyde (PF) resins, and their water resistance properties were assessed. We found that pressing temperature was one of the most important conditions for the improvement of water resistance properties. The retention ratios of MOR, MOE, and IB of kenaf core chip binderless boards (pressing temperature 200°C, target density 0.8g/cm³, and the three-step pressing of 6MPa for 10min, then 4MPa for 3min, and 2MPa for 3min) were 37.1%, 49.9%, and 55.7%, respectively, compared with values for UMF-bonded boards of 22.5%, 27.1%, and 40.7%, and values for PF-bonded boards of 42.8%, 41.8%, and 54.1%, respectively. The results showed that the water resistance properties of binderless boards were higher than those of UMF-bonded boards and almost as high as those of PF-bonded boards. Part of this article was presented at the 53rd Annual Meeting of the Japan Wood Research Society, Fukuoka, March 2003     

Development of boards made from oil palm frond II: properties of binderless boards from steam-exploded fibers of oil palm frond

Binderless boards were prepared from steam-exploded fiber of oil palm(Elaeis guineensis Jacq.) frond at six levels of explosion conditions. Their properties were investigated and evaluated. The mechanical properties (i.e., modulus of rupture, modulus of elasticity, and internal bonding strength) of the boards increased linearly with increasing board density as the usual hardboard. The boards made from fibers treated under a steam explosion condition of 25 kgf/cm² (steam pressure) and 5 min (digestion period) exhibited the maximum strength. These boards at a density of 1.2 g/cm³ met the requirement of S-20 grade of JIS A 5905 — 1994 (fiberboard). Thickness swelling of the boards ranged from 6% to 14% under the JIS A 5908 — 1994 (particleboard) test condition and showed no significant changes with increasing board density. The main bonding strength of the board is believed to be due to a ligninfurfural linkage. Considering the chemical components of oil palm frond, which is rich in hemicellulose, there seems to be a good possibility for producing binderless boards using steam-exploded fibers of oil palm frond.This study was presented in part at the 2nd International Wood Science Seminar, Serpong, Indonesia, November 1998     

Bond durability of kenaf core binderless boards II: outdoor exposure test

An outdoor exposure test was conducted on kenaf core binderless boards (pressing temperatures 200°, 180°, and 160°C; pressing pressure 3.0 MPa, time 10 min, target board thickness 5 mm, target board density 0.8 g/cm³) to estimate their bond durability. Modulus of rupture (MOR), modulus of elasticity (MOE), internal bonding strength (IB), thickness change, weight loss, Fourier transform infrared (FTIR) spectra, and color difference (ΔE*) by the CIE L^*a^*b^* system were measured at various outdoor exposure periods up to 19 months. These values were then compared with those of a commercial medium-density fiberboard (MDF; melamine-urea-formaldehyde resin; thickness 9.0 mm, density 0.75 g/cm³). Generally, dimensional stability and the retention ratios of MOR, MOE, and IB after the outdoor exposure test increased with increased pressing temperature of binderless boards. The MOR retention ratio of the kenaf core binderless boards with a pressing temperature of 200°C was 59.5% after 12 months of outdoor exposure, which was slightly lower than that of the MDF (75.6% after 11 months of outdoor exposure). Despite this, the bond durability of the kenaf core binderless boards should be viewed as favorable, especially when considering the fact that the retention ratio of 59.5% was achieved without binder and without obvious element loss. Part of this report was presented at the International Symposium on Wood Science and Technology, IAWPS2005, November 27-30, 2005, Yokohama, Japan     

Development of binderless fiberboard from kenaf core

Binderless fiberboards with densities of 0.3 and 0.5 g/cm³ were developed from kenaf core material using the conventional dry-manufacturing process. The effects of steam pressure (0.4–0.8 MPa) and cooking time (10–30 min) in the refining process, fiber moisture content (MC) (10%, 30%), and hot-pressing time (3–10 min) on the board properties were investigated. The results showed that kenaf core binderless fiberboards manufactured with high steam pressure and long cooking time during the refining process had high internal bond (IB) strength, low thickness swelling (TS), but low bending strength values. The binderless fiberboards made from 30% MC fibers showed better mechanical and dimensional properties than those from air-dried fibers. Hot-pressing time was found to have little effect on the IB value of the binderless board at the refining conditions of 0.8 MPa/20 min, but longer pressing time resulted in lower TS. At a density of 0.5 g/cm³, binderless fiberboard with the refining conditions of 0.8 MPa/20 min recorded a modulus of rupture (MOR) of 12 MPa, modulus of elasticity (MOE) of 1.7 GPa, IB of 0.43 MPa, and 12% TS under the optimum board manufacturing conditions. Part of this article was presented at the 54th Annual Meeting of the Japan Wood Research Society, Hokkaido, August 3–5, 2004     

Manufacture and mechanical properties of binderless boards from kenaf core

Binderless boards were prepared from finely ground powders of kenaf (Hibiscus cannabinus L.) core under varying manufacturing conditions. This research was designed to investigate their mechanical properties and evaluate the various manufacturing conditions: pressing temperature and time, pressing pressure, board density, board thickness, grain size of raw materials, and addition of furfural. The mechanical properties (i.e., modulus of rupture and elasticity, internal bonding strength) of boards increased with increasing board density and met the requirement for 15 type medium-density fiberboard (MDF) by JIS A 5905-1994. Thickness swelling and water absorption of boards exceeded the maximum permitted levels for 15 type MDF and S20 grade hardboard by JIS A 5905-1994, which indicates the low water-resistant property of binderless boards. In contrast to that in usual wood-based materials, internal bonding strength showed significant correlations with other board properties: modulus of rupture and elasticity, thickness swelling, and water absorption. We confirmed experimentally that the best manufacturing conditions proved to be as follows: pressing temperature 180°C, time 10min; pressing pressure 5.3MPa; board thickness 5mm; board density 1.0g/cm³; average grain size 53µm; and powder with no furfural content.Part of this paper was presented at the 52nd Annual Meeting of the Japan Wood Research Society, Gifu, April 2002     

Thermo characteristics of steam-exploded bamboo (Phyllostachys pubescens) lignin

Bamboo (Phyllostachys pubescens) internode was subjected to steam explosion treatment to produce an excellent fiber for binderless boards. Lignin was isolated from extract-free bamboo meal with Björkman’s procedure and steam-exploded pulp. The self binding-mechanism was discussed by scanning electron microscopy (SEM), thermo-gravimetry (TG), differential scanning calorimetry (DSC) and analytical ozonation. It is well-known that steam explosion treatment liberates lignin from the cell wall to the fiber surface, which is the most important component relevant to binderless board production. Results of TG and DSC analyses showed that steam-exploded bamboo pulp started mass loss at lower temperature compared to bamboo internode meal. The thermal softening temperature of lignin prepared from steam-exploded pulp was much lower than that of lignin prepared from extract-free bamboo meal. This suggests that intermonomer linkages of lignin, especially β-aryl-ether linkage which is the major intermonomer linkage of lignin, were cleaved during steam explosion treatment resulting in low molecular weight phenolic compounds. The cleavage of β-aryl-ether intermonomer linkage of lignin was also confirmed by ozonation analysis.     

Manufacture and properties of low-density binderless particleboard from kenaf core

Low-density binderless particleboards from kenaf core were successfully developed using steam injection pressing. The target board density ranged from 0.10 to 0.30g/cm³, the steam pressure used was 1.0MPa, and the steam treatment times were 7 and 10min. The mechanical properties, dimensional stability, and thermal and sound insulation performances of the boards were investigated. The results showed that the low-density kenaf binderless particleboards had good mechanical properties and dimensional stability relative to their low board densities. The board of 0.20g/cm³ density with a 10-min treatment time produced the following values: modulus of rupture 1.1MPa, modulus of elasticity 0.3GPa, internal bond strength 0.10MPa, thickness swelling in 24h water immersion 6.6%, and water absorption 355%. The thermal conductivity of the low-density kenaf binderless particleboards showed values similar to those of insulation material (i.e., rock wool), and the sound absorption coefficient was high. In addition, the boards are free from formaldehyde emission. Kenaf core appears to be a potential raw material for low-density binderless panels suitable for sound absorption and thermally resistant interior products.Part of this report was presented at the 52th Annual Meeting of the Japan Wood Research Society, Gifu, Japan, April 2002     

Bond durability of kenaf core binderless boards I: two-cycle accelerated aging boil test

A two-cycle accelerated aging boil test was conducted on kenaf core binderless boards to estimate their bond durability. This is one of the methods to estimate the bond quality of kenaf core binderless boards, as stipulated by Notification 1539 of the Ministry of Land, Infrastructure, and Transport, October 15, 2001, for the Building Standard Law of Japan. Generally, retention ratios of modulus of rupture (MOR), modulus of elasticity (MOE), and internal bond (IB) strength after the boil test increased with increased pressing temperature. In particular, the MOR retention ratio of boards with a pressing temperature of 200°C (average 106.4%) was higher than that of a commercial medium-density fiberboard (MDF) (melamine-urea-formaldehyde resin) (average 72.7%), and the value sometimes exceeded 100%. The durability of kenaf core binderless boards with a pressing temperature of 200°C compared favorably with that of the commercial MDF (melamine-urea-formaldehyde resin), having almost the same retained strength values after the boil test. Part of this article was presented at the International Symposium on Wood Science and Technology, IAWPS2005, November 27–30, 2005, Yokohama, Japan     

Lignin Characteristics of Steam Exploded Bamboo Residue during Hot Pressing

bamboo(Phyllostachys edulis) residue was subjected to steam explosion treatment to produce superior fibers for binderless boards.Then,lignin was isolated from extract-free bamboo meal,steam exploded pulp,and binderless boards with characteristics being determined by thermo-gravimetry (TG),differential scanning calorimetry (DSC),and fourier transform infrared spectroscopy (FTIR).Results showed that:1) the yield of lignin directly extracted with dioxane-water from steam exploded bamboo pulp(SEBPL) and binderless board (SEBBL) was higher than that of milled bamboo lignin (MBL).Also,the yield of SEBBL was lower than that of SEBPL.2) FTIR results showed cleavage of ester and ether bonds between lignin and p-coumaric acid during steam explosion treatment.3) SEBBL showed two glass transitions at 115℃and 200℃, while MBL gave one glass transitions at 155℃.And 4) the modulus of rupture(MOR) and modulus of elasticity(MOE) decreased with an increase in steaming time;whereas internal bonding(IB) increased.In all cases the dimensional stability of boards did not exceed the maximum requirements for type GB/T 11718- 1999.     

Evaluation of the self-bonding ability of sugi and application of sugi powder as a binder for plywood

Binderless particleboards were manufactured from sugi (Cryptomeria japonica D. Don) heartwood and sapwood by hot-pressing (pressure: 5 MPa; temperatures: 180°, 200°, and 220°C; times: 10, 20, and 30 min), and the board properties [internal bonding (IB), thickness swelling (TS), water absorption (WA)] were investigated to evaluate the self-bonding ability. The IB, TS, and WA of the boards from sugi heartwood were better than those of the boards from sugi sapwood at any hot-pressing condition. Therefore, it was suggested that the self-bonding ability of sugi heartwood was superior to that of sugi sapwood. Then, sugi heartwood and sapwood powder with grain size 10 βm were used as a binder for plywoods. Four kinds of plywood were manufactured from the combination of powder and veneer, both of which were prepared from sugi heartwood and sapwood under the same hot-pressing conditions as the binderless particleboard, and the adhesive shear strength and wood failure of the plywood were investigated. As a result, the plywood composed of sugi heartwood veneer met the second grade of JAS for plywood, when either powder was used as a binder, when they were pressed at 200°C for 20–30 min and 220°C for 10 min.     

干法无胶纤维板粘合机理的研究Ⅲ．木材主要化学成分的影响

分别用氢氧化钾和亚氯酸钠处理木材原料，以移去木材原料中的一部分半纤维素和木素。用这些特制浆料压制的无胶纤维板，无论是板的强度性能还是板的耐水性能都比未处理木材原料制造的无胶纤维板的性能有明显的下降。这一结果表明，木材原料中的半纤维素和木素都对纤维间自生胶粘因素的形成具有重要的影响     

Development of binderless particleboard from kenaf core using steam-injection pressing

Binderless particleboards were successfully developed from kenaf core using the steam-injection press. The effects of board density, steam pressure, and treatment time on the properties of the board were evaluated. The target board densities were relatively low, ranging from 0.40 to 0.70g/cm³. The properties [i.e., moduli of rupture (MOR) and elasticity (MOE) in both dry and wet conditions, internal bonding strength (IB), and water absorption (WA)] of the boards increased linearly with increasing board density. Steam pressure and treatment time also affected the board properties. The bending strength and IB were improved with increased steam pressure. A long steam treatment time contributed to low thickness swelling (TS) values and thus better dimensional stability. The appropriate steam pressure was 1.0MPa, and the treatment time was 10–15min. The properties for 0.55g/cm³ density boards under optimum conditions were MOR 12.6MPa, MOE 2.5GPa, IB 0.49MPa, TS 7.5%, and wet MOR 2.4MPa. Compared with the requirement of JIS 5908, 1994 for particleboard, kenaf binderless boards showed excellent IB strength but relatively poor durability.Part of this report was presented at the 19th Annual Meeting of the Japan Wood Technological Association, Tokyo, October 2001     

汽爆压力对无胶棉秆纤维板性能的影响

不添加任何化学助剂,在不同汽爆压力下进行棉秆解纤,将解纤后的纤维热压制成无胶纤维板.分析了汽爆压力对棉秆纤维形态、化学成分以及无胶纤维板产品性能的影响.结果表明,随着汽爆压力的增大,纤维分离程度提高,纤维中游离酸、游离糖及游离醇的质量分数含量增加,试板的内结合强度增大,但静曲强度和弹性模量则减小.