Measurement of urea-formaldehyde resin distribution as a function of MDF fiber size by laser scanning microscopy

A technique has been developed to show the extent of the distribution of the adhesive on the fiber surface. This involves treatment of the resinated fibers with the dye Toluidine blue O, to quench the autofluorescence of the wood materials, to show only the fluorescence of the UF resin in the presence of the dye. The results indicate that this method is a simple and practical way to understand UF resin coverage on wood fibers. With image analysis, the adhesive has been shown to cover a small percentage (3.5%) of the fiber surface, although the percent by weight (based on wood fiber) of resin is much more (13%). The fiber size strongly affects the resin coverage ratio and the chance to collect resin droplets, but it is not significant in the resin-droplets size distribution. Decreasing the proportion of shorter fibers is beneficial in improving resin coverage uniformity. A model for calculating the resin-coverage ratio was developed. The resin coverage is about 4.8% for the resin content of 13% by the model.     

Effects of surface laminate type and recycled fiber content on properties of three-layer medium density fiberboard

ABSTRACT

High global production of medium-density fiberboard (MDF) in recent years could generate an equal quantity of waste MDF at the end of its service life, requiring recycling of waste MDF instead of landfilling or incineration. This study investigated effects of the addition of recycled fiber (RF) obtained from surface laminated MDFs with three different materials to the properties of three-layer recycled MDF (rMDF). Three types of surface laminates such as low-pressure laminate, polyethylene terephthalate, and polyester coating were hammer milled, and then went through a patent-pending fiber recovery system to obtain the resultant RFs that were added to the core layer of rMDF. These RFs at three contents (10, 20, and 30%) were blended with 12% of urea-formaldehyde (UF) resin prior to hot-pressing. Statistical analysis showed that the best internal bonding strength, modulus of rupture, and modulus of elasticity of rMDF panels were obtained for LPL-rMDF with a 20% RF content. Thickness swelling, water absorption, and formaldehyde emission of rMDF were reduced by increasing the RF content. These findings suggest that a minimum RF content of 20% can be replaced with virgin fibers for the rMDF manufacture, indicating the feasibility of recycling waste laminated MDF into three-layer rMDF.     

Influence of pulping variables on the properties of Elaeis guineensis soda pulp as evaluated by response surface methodology

Response surface methodology with central composite design was used to investigate the influence of pulping conditions, viz. cooking temperature, time-at-temperature and alkali charge for alkaline pulping of oil palm empty fruit bunch fibres, on the properties of the pulp and paper obtained (screened yield, Kappa number, tensile and tear indices). Quadratic models consisting of the three independent variables were found to accurately describe the pulping of this material with correlation between the actual and predicted values of the response variables having a relatively good degree of R². The delignification of oil palm empty fruit bunch fibre can be achieved with ease using sodium hydroxide as the sole cooking agent to about 30–45% yield with the process greatly enhanced by an increase in temperature. Although, a relatively low temperature (about 160°C) within the limits of pulping time (60–120 min) and of alkali charge between 20 and 30% is generally sufficient.     

The ambient aging of wood fiber and its effect on mechanical properties of MDF panels

Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) were used to study ambient-aged wood fibers and their effects on the mechanical properties of medium-density fiberboard (MDF). It was found that MDF made with ambient-aged fibers had poorer mechanical properties than MDF made with fresh fibers; this difference resulted from the alterations of surface characteristics of wood fibers after ambient aging, which led to poor wettability of the urea–formaldehyde (UF) resin applied to the aged wood fibers. After 6 months of ambient aging, the concentration of carbonyl groups in the fibers increased by 144%, while the pH value of wood fiber decreased from 5.2 to 4.7. SEM showed that much more UF resin agglomerated on the surface of ambient-aged fibers and the breakage of MDF made with aged fiber frequently occurred at the resin-fiber interfaces, indicated the poorer wettability of UF resin to fibers due to the decrease in surface energy after aging.     

静电粉末喷涂的特点及在MDF板材表面装饰上的应用

静电粉末喷涂工艺出现于 2 0世纪 6 0年代 ,主要是应用于金属表面涂装。进入 2 0世纪 90年代末 ,随着粉末涂料和喷涂设备的发展 ,使静电粉末喷涂工艺应用于非金属表面成为可能。1　静电粉末喷涂的特点自从粉末涂料喷涂技术进入涂装业后 ,粉末涂料在一般工业用涂料中所占有的市场比例逐年持续增长 ,其原因是粉末喷涂技术具有独特的优势。1 1　降低对环境的污染程度随着环保法对在大气中有机挥发物 (VOC)含量越来越严格的规定 ,涂装业一直试图开发对环境较温和的涂装技术 ,经过长期的研究与实验后 ,发现“静电粉末喷涂”是目前能够达到的最…     

Veneer strand flanged I-beam with MDF or particleboard as web material II: effect of resin type,application rate,strand dimension,and pressing time on the basic properties

Optimization of the manufacturing conditions of the veneer strand flanged I-beam invented in the previous study was investigated using different combinations of strand dimensions, resin types between web and flange, different pressing times, and different wood–resin moisture contents under conventional hot pressing conditions. The main results revealed that the strand dimensions have no effect on the bending properties of the flange part and the dimensional stability of the I-beam. Increasing the resin application rate between strands was found to improve the dimensional stability of the I-beams. The use of isocyanate (MDI) resin between web and flange significantly improved the bond strength between web and flange, the modulus of rupture of the I-beam, and the modulus of rupture of the flange part. Dimensional stability was also improved. Shortening the pressing time from 20 to 12min was found to be feasible. Using low wood-resin moisture content was found to interfere with the curing of the phenol–formaldehyde (PF) resin at the flange part resulting in poor quality beams. Of the three moisture content levels tested, 12% was found to be the optimal level for producing I-beams with balanced mechanical properties and dimensional stability.Part of this work was presented at the 53rd Annual Meeting of the Japan Wood Research Society, Fukuoka, March 2003     

Veneer strand flanged I-beam with MDF or particleboard as web material IV: Effect of web material types and flange density on the basic properties

The balance of strength between the flange and web parts of veneer strand flanged I-beam was investigated by the following methods: (1) use of different web material types, such as plywood, oriented strand board (OSB), particleboard (PB), and medium density fiberboard (MDF), that have different strength properties; and (2) fabrication of I-beams with low-density flanges using low-density strands with PB web material. Replacing PB or MDF with plywood showed slight significant improvement in the modulus of rupture but not in the modulus of elasticity of the entire I-beam. However, PB and MDF showed competent performance in comparison with OSB, thus strengthening the promising future of the use of PB or MDF as web material to fabricate I-beams. Hot-pressing conditions used for I-beam production exerted slightly adverse effects on the bending properties of PB, but not on MDF, OSB, and plywood web materials. The flange density of 0.60 g/cm³ was considered to be the lower limit that provides I-beams with balanced mechanical properties and dimensional stability.     

刨花形态,树皮含量及石膏质量与石膏刨花板性能的关系

对刨花形态、树皮含量及石膏粉质量与石膏刨花板性能之间关系的研究结果表明:保持一定的刨花长度有利于提高石膏刨花板的静曲强度;石膏刨花板的静曲强度随着木刨花中树皮含量的增加而下降,但把树皮作为填料加入石密刨花板能使板子强度得以提高,不同产地的石膏粉制成的石膏刨花板性能差异很大,按建筑石膏粉标准测定的性能指标及相组成与石膏刨花板的性能之间无显著的相关关系。     

Veneer strand flanged I-beam with MDF or particleboard as web material III: effect of strand density and preparation method on the basic properties

Optimizing the manufacturing conditions of veneer strand-flanged I-beams was continued in this study and focused on the strand density and preparation method. Three levels of strand density were used, while the strands were prepared by either saw or roll-press splitter. The main results indicated that: within the compaction ratios (1.4–2.3) investigated in this study, the strand with lower density showed slight improvement in the dimensional stability and the bond strength between web and flange, but not in bending properties of the I-beams. The strand preparation method was concluded to be dependent on species for akamatsu, sugi, and bamboo strands; roll-press splitter-prepared strands tended to negatively affect dimensional stability and mechanical properties of the I-beams. When using akamatsu or sugi strands, low density allowed the possibility of using lower resin application rates between strands. Part of this paper was presented at the 54th Annual Meeting of the Japan Wood Research Society in Sapporo, August 2004     

Control by ATR-FTIR of surface treatment of cork stoppers and its effect on their mechanical performance

Fourier transform infrared (FTIR) spectroscopy was applied to determine the type of surface treatment and dose used on cork stoppers and to predict the friction between stopper and bottleneck. Agglomerated cork stoppers were finished with two different doses and using two surface treatments: P (paraffin and silicone), 15 and 25?mg/stopper, and S (only silicone), 10 and 15?mg/stopper. FTIR spectra were recorded at five points for each stopper by attenuated total reflectance (ATR). Absorbances at 1,010, 2,916, and 2,963?cm^?1 were obtained in each spectrum. Discriminant analysis techniques allowed the treatment, and dose applied to each stopper to be identified from the absorbance values. 91.2% success rates were obtained from individual values and 96.0% from the mean values of each stopper. Spectrometric data also allowed treatment homogeneity to be determined on the stopper surface, and a multiple regression model was used to predict the friction index (If?=?Fe/Fc) (R ²?=?0.93).     

Effect of two relative humidity environments on the performance properties of MDF, OSB and chipboard

The static strength, stiffness and fatigue life of MDF, OSB and chipboard have been measured in a 65%RH environment and a 85%RH environment. Chipboard is commonly utilised as a flooring material and OSB is also used in structural applications, for example floor decking and webs of I-beams. The mean static strengths of MDF, OSB and chipboard at 65%RH were 47.9 MPa, 27.9 MPa and 21.0Mpa, respectively, compared with 34.59 MPa, 21.70 MPa and 10.61 MPa at 85%RH. However, MDF has mostly been used in non-structural applications, such as furniture, so its resistance to fatigue loads as a structural panel is of considerable interest. In a 65%RH environment dynamic modulus values showed that whilst MDF and chipboard exhibit similar stiffness values (4 GPa), OSB is approximately 50% stiffer. However, at 85%RH MDF was the stiffest of the three materials, followed by OSB and chipboard. The fatigue life performance of all three panel products was markedly lower at 85%RH compared with 65%RH. Overall, the high RH environment had a noticeably detrimental effect on the MOE (modulus of elasticity), MOR (modulus of rupture) and fatigue lives of OSB and chipboard. This is attributed to these panels retaining more of the original characteristics of the original wood, i.e. larger particle sizes (flakes/chips) compared with the homogeneous fibrous composition of MDF. Received 5 November 1999     

The effect of the physical state of the surface of organic soil material on its wettability

The water repellency of different forms and types of forest floors was studied, using two methods: (1) measurement of the contact angle θ, and (2) measurement of the rate of the initial phase of water absorption in an Enslin device. Measurements were made on samples with their natural degree of disintegration and roughness, and on the same samples pressed into tablets to give a smooth contact interface between the water and the organic material. The contact angle θ, of organic material from an epihumus subhorizon AoH, with a rough surface, is about 145°, whereas for the same material with a smooth contact interface it is about 60°. Pressed samples exhibited much higher rates of water absorption than samples of the same materials in their natural state. The present studies demonstrate that, because of its chemical nature, organic material is hydrophilic. Its water repellency is closely related to the degree of dispersion and roughness of its structural elements. A theoretical explanation of the effect of the surface state of organic material on its wettability is attempted.     

Effect of two relative humidity environments on the performance properties of MDF, OSB and chipboard.

The fatigue and creep performance of MDF, OSB and chipboard have been examined in two environments, namely 65%RH (standard environment) and 85%RH (high humidity). Parallel fatigue and creep tests have been performed in four-point bending on the three wood-based panel products in the two environments. The constant 65%RH environment is service class 1 and the constant 85% RH environment is indicative of a service class 2 environment as detailed in Eurocode 5. The non-interruptive technique of stress-strain hysteresis loop capture has been utilised to follow property changes of the fatigue samples during cyclic loading at a stress ratio of R equal to 0.1. Loop parameters such as loop area, dynamic modulus, and fatigue modulus have been used to characterise the response of these materials to fatigue loads in the two environments. Creep microstrains for the creep samples were recorded in parallel with the fatigue parameters. Fatigue and creep results at 85%RH were more variable than those reported at 65%RH for MDF, OSB and chipboard. In general, at R=0.1 and 85%RH, fatigue and creep microstrains were higher, dynamic stiffnesses were lower and hysteresis loop areas were higher than corresponding properties measured at 65%RH. MDF and chipboard were less moisture tolerant than OSB, this is reflected in the large changes in fatigue and creep parameters.     

Optimization of the selective preparation of 20(R)-ginsenoside Rg3 catalyzed by d,l-tartaric acid using response surface methodology

The optimization of the selective preparation of 20(R)-ginsenoside Rg3 converting protopanaxadiol type saponins (PPD saponins) by the commercially available d, l-tartaric acid was carried out using response surface methodology (RSM) based on a three-factor and six-level central composite design. The optimal 20(R)-ginsenoside Rg3 de% was predicted to be 94.52% in the combination of the factors (d, l-tartaric acid concentration 1.19 mol/L, temperature 107.9 °C and time 2.79 h) through the canonical analysis with maximum responses. Under the optimum reaction conditions, the actual 20(R)-ginsenoside Rg3 de% was 96.49%. 20(R)-ginsenoside Rg3 (1) and 20(S)-ginsenoside Rg3 (2) were separated and identified by ¹H-NMR and ¹³C-NMR. Therefore, the RSM was effective to optimize the preparation of 20(R)-ginsenoside Rg3 by converting PPD saponins using d, l-tartaric acid.     

银杏生物生态学特性,经济价值及开发利用调查研究

银杏ＧｉｎｋｇｏｂｉｌｏｂａＬ．是我国特有树种。银杏的用途广、经济价值高，尤其叶提取物的医疗保健功能，举世瞩目，倍受青睐。银杏分布广、生态适应性强，亚、欧、美洲的许多国家和地区都有引种栽培。甘肃是我国银杏地理分布的西部适生区，陇南一带有悠久的栽培历史、良好的工作基础和自然优势，具有广阔的发展前景。随着银杏的不断开发利用，发展银杏将是创汇、致富的重要资源和战略措施。在介绍了银杏的生物学和生态学特性、经济价值和国内外开发利用现状的同时，提出了加强发展银杏的建议，包括科研与推广、栽培与加工、组织与技术等方面的问题和意见。     

Influence of the melamine content in melamine-urea-formaldehyde resins on formaldehyde emission and cured resin structure

The effect of melamine content in melamine-urea-formaldehyde (MUF) resins on the formaldehyde emission and resin structure was investigated using six MUF resins synthesized with different F/(M + U) and M/U molar ratios. The formaldehyde emission from the plywood decreased as the F/(M + U) molar ratio decreased and the M/ U molar ratio increased. In addition, the bond performance was enhanced as the M/U molar ratio increased in the MUF resins with a fixed F/(M + U) molar ratio. Quantitative solution¹³C-NMR spectra of MUF resins revealed that the MUF resins with a high melamine content consisted of more highly branched crosslinkage structure and free melamine compared to the resins with low melamine contents. Furthermore, solid-state¹³C CP-MAS NMR spectra of cured MUF resins proved that more methylol groups, dimethylene ether, and branched methylene structures were present in the MUF resins with a higher F/(M + U) molar ratio, leading to increased bond strength and formaldehyde emission. There is no significant difference in the linkage structure of the cured resins with the same F/(M + U) and different M/U molar ratios except the ratios of carbonyl carbon of urea and triazine carbon of melamine. Therefore, the lower formaldehyde emission from cured MUF resins with a higher M/U molar ratio might be ascribed to the stronger linkages between triazine carbons of melamine than those of urea carbons. Consequently, the melamine contributed to strong crosslinking linkages in the cured resin structures, leading to lower formaldehyde emission and better bond performance.Part of this work was presented at the 48th Annual Meeting of the Japan Wood Research Society, Shizuoka, April 1998     

Impregnation of radiata pine wood by vacuum treatment II: effect of pre-steaming on wood structure and resin content

Radiata pine sapwood and heartwood were dried using high-temperature, conventional-temperature, and air drying schedules with and without pre-steaming. They were then impregnated by vacuum treatment with double-distilled water, toluidine blue, and fluorescein dye. For sapwood, there were only minor differences in uptake between drying methods and when pre-steaming was used. Using microscopy, the primary flow pathways in sapwood were found to be the resin canal network and ray parenchyma cells, which provided conduction without large resistance. In heartwood, uptake was strongly influenced by pre-steaming the green lumber. After pre-steaming heart-wood, there was an increase in uptake from all surfaces but especially from the radial surfaces. Lower extractive contents, disruption of epithelial and ray parenchyma cells, and alteration of the condition of bordered pits were also associated with pre-steaming. It was therefore possible to classify flow paths in radiata pine heartwood five ways, according to uptake values and wood anatomical features.This research was presented in part at the 48th annual meeting of the Japan Wood Research Society, Shizuoka, April 1998.     

NyPa草生物学性状观测和耐盐生产性能研究

对最新引人我国的盐草属(Distichlis spicata)植物NyPa草的部分生物学性状和盐碱条件下的生产特性进行了研究。结果表明:NyPa宽叶品种在试验地条件下,2月中旬与冬小麦同时返青生长,12月中旬停止生长,进入休眠,生长期长达10个月,休眠期植株保持绿色。NyPa窄叶品种3月上旬开始返青,11月下旬停止生长,生长期达8个半月,叶片细长、鲜绿、柔软。NyPa草不能进行种子繁殖,可防止成为有害杂草无限扩散。示范田大面积种植2年后使土壤含盐量从4‰~5‰降低为1‰。在含盐量4‰~6‰的土壤上,最大鲜草产量达70435.2kg/hm2,最大干草产量18964.05kg/hm2。在高盐碱地(含盐量5‰~6‰)的鲜草产量分别为高羊茅和獐茅的190.97%和154.04%,干草产量分别为455.06%和427.21%。     

Influence of the chemical composition of kenaf bast and core on the alkaline pulping response

The bast and core of kenaf,Hibiscus cannabinus L., have markedly different chemical components and alkaline cooking responses. The bast had about double the hot-water extractives content and only about half the lignin content of the core. The core contained a large amount of hemicellulose, mostly composed of xylan. The lignin structures of bast and core were also quite different: The former had a significant abundance of syringyl structures. Evidence showed that the bast was much more easily delignified than the core. When the bast and core were cooked together in alkaline condition, the pulp yields at the same kappa number were higher than those of the individual pulpings of bast and core. The bast-core pulping gave a positive effect on the yield of bast pulp in the sodaanthraquinone and kraft pulpings. On the other hand, kenaf was abundant in the hot water extractives. These extractives consumed alkali during cooking to a relatively large extent but acted as a protector of hemicellulose and slightly increased the pulp yields.Part of this paper was presented at the 48th and 49th Annual Meetings of the Japan Wood Research Society, Shizuoka, April 3–5, 1998 and Tokyo, April 3–5, 1999