Durability of isocyanate resin adhesives for wood IV: degradation under constant steam heating

The durability of isocyanate resins consisting of emulsion-type polymeric diphenylmethane diisocyanate (EMDI) was investigated under constant steam heating. Two kinds of resin, water only-added resin and polyol/water-added resin, were used in this study. The degradation of the resins under steam heating was observed using Fourier transform infrared spectroscopy (FT-IR), weight changes, and thermogravimetric analysis (TGA). FT-IR analysis showed that the degradation reaction of the resins scarcely proceeded for a few hours and then increased significantly. The weights of the resins decreased linearly during steam heating. The thermal stability of steam-treated resins was made clear by TGA. The bond strength reductions of the specimens bonded with the resins were also observed. The best fitting regression function for the behavior of bond strength reduction was determined statistically. The apparent activation energy of each resin was calculated from the regression function, for the half-life period. Considering the calculated values, the adhesion durability of using polyol-added resin was superior to that of using water only-added resin. It was clarified that the durability of the isocyanate resins under steam heating was markedly inferior to that under dry heating.Part of this paper was presented at the 50th Annual Meeting of the Japan Wood Research Society, Kyoto, 2000     

Effect of polyol on thermo-oxidative degradation of isocyanate resin for wood adhesives

The thermo-oxidative degradation of various polyol-added isocyanate resins for wood adhesives was studied using differential scanning calorimetry and thermogravimetry. The degradation of the resin cured with water began at 150°C. When a certain polyol was added to the resin at an NCO/OH ratio of 25 in addition to water, the cured resin began to degrade at 200°C. To clarify the cause of the good thermal stability in polyol-added resins, the effect of various polyols on the reactivity of isocyanate was investigated. It was found that the reactivity of isocyanate was enhanced by the addition of a dipropylene glycol and glycerin-type polyols. In addition, the effect of the NCO/ polyol-OH ratio was investigated using dipropylene glycoltype polyol. The reactivity of isocyanate increased with increasing polyol content. The thermal stability of the resin was improved to a certain degree by addition of a small amount of the polyol but deteriorated when a large amount of the polyol was added.Part of this paper was presented at the 48th annual meeting of the Japan Wood Research Society, Shizuoka, April 1998     

Durability of isocyanate resin adhesives for wood I: Thermal properties of isocyanate resin cured with water

The thermal properties of isocyanate (IC) resin cured with water were studied using dynamic mechanical analysis (DMA) and Fourier transform infrared spectroscopy. The thermal properties of cured phenol formaldehyde (PF) resin were also studied for comparison purposes. The DMA specimens were prepared using a unique technique. The relation between the mechanical and chemical changes of the resin during DMA was clarified. The cured PF resin had better thermal stability than the IC resin cured with water. The improvement of thermal stability in cured IC resin by heat treatment was considered to be less effective. The effect of the heating rate on the mechanical properties was also investigated. The apparent activation energy in the thermal degradation of cured IC resin was calculated based on the results obtained.Part of this paper was presented at the 47th Annual Meeting of the Japan Wood Research Society, Kochi, April 1997     

Durability of isocyanate resin adhesives for wood V: changes of color and chemical structure in photodegradation

The effect of ultraviolet (UV) light irradiation on the color and chemical structure of water-cured polymeric diphenylmethane diisocyanate (PMDI) was investigated using a UV long-life fade meter. Control treatment was performed without UV light irradiation using a thermohygrostat for comparison. Two kinds of resin were used in this study: that to which only water had been added, and resin to which a small amount of polyol and water had been added. In addition, lauan (Shorea spp.) wood was used as a reference. The photodegradation of the resins over a period of up to 300 h was observed using a colorimeter and Fourier transform infrared (FT-IR) spectroscopy. When the resins were treated with UV light, the color difference (ΔE ^* ab) of the resins increased signifi cantly in a short time, and then reached a near-constant value. For lightness, L ^* decreased rapidly for a few hours and then decreased gradually. The color darkened compared with that of the wood used. When treatment was performed without UV light irradiation, ΔE ^* ab and ΔL ^* of the resins showed negligible change. Based on the results of FT-IR analysis, severe degradation such as cleavage of the main chemical bond was hardly observed under UV light irradiation irrespective of the type of resin. Part of this report was presented at the 54th Annual Meeting of the Japan Wood Research Society, Sapporo, Japan, and at the 6th International Wood Science Symposium, Bali, Indonesia     

The thermochemical degradation of cork

Summary The thermochemical degradation of cork from Quercus suber L. was studied in the temperature range 150°C–450°C in relation to mass loss, chemical composition and the influence on the cellular structure. The degradation of cork is strongly dependent on temperature and mass losses become significant at 200°C (15% of initial dry weight) and increase rapidly for higher temperatures (27% at 250 °C, 49% at 300 °C, 62% at 350 °C) until ashing at 450 °C. The polysaccharides are the most heat sensitive components: at 200 °C, hemicelluloses disappear and cellulose is degraded to a considerable extent. Suberin is more resistant and degradation starts at approx. 250 °C; 300 °C-treated samples only contain 7% suberin.The cellular structure of cork is also significantly influenced by temperature. Upon heating, cells expand and the cell walls stretch, attaining at 250 °C a maximum cell volume increase corresponding to a factor of approximately 2. Above 300 °C, the structure of cell walls is considerably changed and show profound physical damage; in the later stages of pyrolysis, a cellular structure is no longer observed.We are grateful to Mrs. Joaquina Ferreira for her help with the chemical analysis. The research was financially supported by the Junta Nacional de Investigação Científica e Tecnológica (JNICT) and by the Instituto de Ciência e Tecnologia dos Materiais (ICTM)     

Comparison of protein-based adhesive resins for wood composites

The search for new value-added uses for oilseed and animal proteins led us to develop protein-based wood adhesives. Low-fat soy and peanut flours and blood meal were hydrolyzed in an alkaline state, and PF-cross-linked protein resins were formulated by reacting the protein hydrolyzates with phenol-formaldehyde (PF) in solid-tosolid ratios ranging from 70% to 50% hydrolyzates and 30% to 50% PF. Physical properties of medium density fiberboard (MDF) bonded with protein-based phenolic resins were compared to those of boards bonded with ureaformaldehyde (UF) and PF resins, and flakeboard bonded with soy protein-based phenolic resin was compared to PF-bonded board. As MDF binders, adhesive properties of protein-based phenolic resins depended upon protein content of proteinacious materials. MDF board bonded with blood-based phenolic resin was comparable to PF-bonded board and met the requirements for exterior MDF. Boards bonded with soy-protein-based phenolic resin met requirements for interior MDF, while peanut-based phenolic failed to meet some of the requirements. Flakeboard bonded with soy-protein-based phenolic resins was inferior to PF-bonded board but outperformed PF-bonded board in accelerated aging tests. Although they exhibit a slow curing rate, the cost effectiveness and superior dimensional stability of protein-based phenolic resins may make them attractive for some uses.     

Determination of equilibrium moisture content of yellow-poplar sapwood above 100°C with the aid of an experimental psychrometer

Summary The equilibrium moisture content (EMC) of yellow-poplar sapwood was experimentally determined at dry bulb temperatures from 88 to 116°C and wet bulb temperatures from 77 to 99°C at atmospheric pressure. EMC values were within 1.3 percent moisture content of theoretical values reported in the literature. A high temperature psychrometer, capable of handling humid air at dry bulb temperatures to 177°C, was designed and constructed to accurately measure the humidity during evaluation of EMC's.     

Treatment of timber with water soluble dimethylol resins to improve their dimensional stability and durability

Summary European Beech (Fagus silvatica L.) was impregnated with a dimethylol resin to improve its dimensional stability and durability. Different catalysts were evaluated in combination with the resin. Depending on the range of relative humidity, the resin improved the shrinkage and swelling by approximately 50%. The use of an acid (citric or tartaric) catalyst lead to improved resin curing. A curing temperature of 100 °C is necessary.The reported work has been part of an EEC Research Program (DGXII) and had been carried out by the author at TNO Timber Research Institute     

The modification of wood by treatment with low molecular weight phenol-formaldehyde resin: a properties enhancement with neutralized phenolic-resin and resin penetration into wood cell walls

To enhance dimensional stability and biological properties, low molecular weight phenolic resins of a conventional alkaline type and neutralized type were impregnated into Japanese cedar wood (Cryptomeria japonica D. Don) and heat-cured. The treatment with the neutralized type resin retained the original wood color, whereas the alkaline treatment changed the color of wood to red-brown. The concentrations of the resin solutions and the weight gains due to the resin loading of wood after treatment were highly correlated, and the target resin loading could be assessed from the solution concentration. A high dimensional stability of 60% antiswelling efficiency was attained when both types of resins were impregnated at about 30% resin loading and no significant difference was recognized between the two. To suppress decay attack from brown-rot and white-rot fungi, 15% and 10% resin loading due to treatment was required for the neutralized and alkaline types of phenolic resins, respectively. The penetration of resin into wood cell walls was investigated by means of light microscopy, Scanning Electron Microscopy (SEM), and Electron Probe X-ray Microanalysis (EPMA). A m-Bromophenol-formaldehyde resin of three levels of an average molecular weight was used to detect the presence of resin by bromine signals. The phenolic resins with low and medium molecular weights (290 and 470) were shown to penetrate into the cell walls the furthest, thereby contributing to the enhancement of dimensional stability and decay resistance in the resin-impregnated wood. Also, for phenolic resin with a high molecular weight (820), only the resin components of low molecular weight appeared to be present in the walls, making very little contribution to the dimensional stability.     

Curing behavior and adhesion properties of epoxy resin blended with polyhydric alcohol-liquefied <Emphasis Type="Italic">Cryptomeria japonica</Emphasis> wood

Cryptomeria japonica (Japanese cedar) wood was liquefied using polyethylene glycol (PEG-400 and PEG-600)/glycerol as the solvent with H₂SO₄ as a catalyst. The blended epoxy resins were prepared by mixing the liquefied wood with epoxy resin of various weight ratios and used for wood gluing. The results showed that blended epoxy resins could cure under room temperature with an exothermic reaction. DSC thermoanalysis showed that increasing the blending amount of liquefied wood would shift the peak of curing reaction to a higher temperature but with less heat released. Blended epoxy resins had a good dry bonding strength for wood when cured at room temperature. However, curing with heat treatment could improve the wet bonding strength of blended epoxy resins, especially for those prepared with PEG-400-liquefied wood.     

Effects of high temperature kiln drying on the practical performances of Japanese cedar wood (Cryptomeria japonica) I: changes in hygroscopicity due to heating

The effect of heating on the hygroscopicity of Japanese cedar wood was investigated as a simple evaluation of thermal degradation in large-dimension timber being kiln-dried at high temperatures (>100°C). Small wood pieces were heated at 120°C in the absence of moisture (dry heating) and steamed at 60°, 90°, and 120°C with saturated water vapor over 2 weeks, and their equilibrium moisture contents (M) at 20°C and 60% relative humidity (RH) were compared with those of unheated samples. No significant change was induced by steaming at 60°C, while heating above 90°C caused loss in weight (WL) and reduction in M of wood. The effects of steaming were greater than those of dry heating at the same heating temperature. After extraction in water, the steamed wood showed additional WL and slight increase in M because of the loss of water-soluble decomposition residue. The M of heated wood decreased with increasing WL, and such a correlation became clearer after the extraction in water. On the basis of experimental correlation, the WL of local parts in large-dimension kiln-dried timber was evaluated from their M values. The results indicated that the thermal degradation of inner parts was greater than that of outer parts.     

The effects of a heat treatment on the behaviour of extractives in softwood studied by FTIR spectroscopic methods

Scots pine battens were heat-treated at 100–240º C under saturated steam. Cross-sections of heat-treated battens were analysed using ATR and reflection FTIR microscopies. A typical absorption band of fats and waxes at 1740 cm^-1 was detected on the sapwood edges in the temperature range of 100–160º C, indicating that fats and waxes moved along the axial parenchyma cells to the surface of the sapwood during the heat treatment. At the elevated temperatures (above 180° C) fats and waxes disappeared from the sapwood surface and were no longer detected with FTIR spectroscopy. Resin acids were detected at temperatures between 100 and 180º C in the middle of the battens. IR spectra of these spots showed a characteristic absorption band of resin acids at 1697 cm^-1. At 200º C resin acids were not detected in the middle of the battens; however, resin acids were detected at distances of 500 and 600 mm from the midpoint of the battens and on the edges of battens. At temperatures above 200° C, resin acids had disappeared from the wood.     

Heat damage in boxed white spruce (Picea glauca [Moench.] Voss) seedlings: Its pre-planting detection and effect on field performance

This study investigated the effects of holding 1+0 PSB313a white spruce (Picea glauca (Moench.) Voss) seedlings in storage boxes at air temperatures of 5, 10, 20, 30 and 40°C for 12, 24, 48, 72 and 96 h before planting. The ability to detect physiological damage to seedlings as a result of such treatment, before planting, was also examined. After one growing season, no needle damage or mortality >8% was found for temperature treatments up to 20°C for 4 days. At 30°C and above, seedling damage and mortality increased, while bud flush, shoot height, stem diameter and shoot dry weight decreased with increasing temperature and duration of treatment. Seedling mortality in the field was 100% after the 40°C treatment exposure for 72 h or longer. Pre-planting needle electrolyte leakage was indicative of visible needle damage 14 days after planting, whereas stem electrolyte leakage and root growth potential were more closely related to end of season plantation mortality. Despite the lack of damage observed at 20°C or below, preplanting exposure of white spruce seedlings to temperatures above 5°C, during transportation and field storage, is not recommended.     

Analysis of phenol-resorcinol-formaldehyde resins

A method based on high-performance liquid chromatography (HPLC) and proton magnetic resonance (PMR) spectroscopy for analyzing phenol-resorcinolformaldehyde (PRF) resins is reported. The equations that describe the number-averaged structures of PRF resins in terms of the PMR absorption intensities of acetylated resins have been derived on the basis of the work of Woodbrey et al. and Anderson et al. The P/R molar ratio of the resin calculated from the PMR intensities was in good agreement with the synthetic P/R molar ratio when correction was made for the loss of phenol evaporated during the drying process that preceded the acetylation. The number-averaged molecular weight (M_n) of the acetylated resin calculated from the PMR intensities agreed with the M_n determined by cryoscopy. Unreacted phenol and resorcinol could be determined by analyzing the water-soluble fraction of the resin by use of high-performance liquid chromatography.Part of this paper was presented at the 4th annual meeting of the Kyushu branch of the Japan Wood Research Society, Miyazaki, November 1997, and at the 48th annual meeting of the Japan Wood Research Society, Shizuoka, April 1998     

The influence of curing conditions on the chemical distribution in wood modified with thermosetting resins

Scots pine (Pinus sylvestris L.) sapwood was impregnated with aqueous solutions of phenol formaldehyde and methylated melamine formaldehyde resins and subsequently cured in an oven. One set of specimens was cured in plastic bags to avoid drying (wet curing) while another set of samples was heated and water was allowed to freely evaporate (dry curing). Macroscopic resin distribution was investigated using X-ray densitometry and infrared spectroscopy (FTIR-ATR). During dry curing, the resins migrated to the wood surface resulting in a gradient. Wet curing resulted in even distribution of the resins because it was immobilized due to condensation and precipitation in the wood. Neither densitometry nor FTIR-ATR was found to be generally applicable for investigating resin distribution in modified wood. Wet curing resulted in low cell wall bulking as compared to dry curing, probably because resin precipitated before drying. Storing impregnated wood prior to curing under non-drying conditions (“diffusion phase”) also reduced cell wall penetration and bulking.     

马来海松酸快干醇酸树脂涂料的研制

采用松香和顺酐反应合成的马来海松酸 (MPA)代替苯酐制备醇酸树脂涂料。讨论了合成工艺对涂膜性能的影响 ,发现采用非醇解工艺可以缩短合成改性醇酸树脂的反应时间。应用GPC和FTIR分析了MPA醇酸树脂的结构及分子质量 ,表明MPA醇酸树脂的分子质量比苯酐醇酸树脂的大 ;比较了MPA醇酸树脂和苯酐醇酸树脂的涂膜性能 ,发现MPA醇酸树脂涂膜干燥速度快、硬度高和耐水性好     

阳离子型萜烯基环氧树脂多元醇的合成及其分散稳定性研究

利用二乙醇胺(DEA)、聚乙二醇200(PEG200)对氢化萜烯 - 马来酸酐缩水甘油酯型环氧树脂(HTME)改性,制备了阳离子型环氧树脂基多元醇水分散体.通过对合成反应影响因素分析,确定了制备环氧树脂基多元醇的最佳反应条件:DEA用量为12%(以HTME的质量计,下同),PEG200与HTME(与DEA氨基反应后的量)物质的量比为1: 1 ～ 1.2: 1;催化剂ZnCl_2用量为2%,在100℃下反应6 ～ 7h.通过化学分析和红外光谱分析方法表征了该多元醇的化学结构.随着PEG200用量的增加,所合成多元醇的羟值提高,软化点、玻璃化温度(T_g)及分散体黏度降低.纳米粒度及电位分析表明,在酸性条件下,DEA用量为12%时所合成的环氧树脂基多元醇具有良好的水分散稳定性,水分散体的Z均粒径小于100nm.多元醇水分散体在高固含量时黏度较大,添加适量极性惰性稀释剂丙二醇甲醚醋酸酯可有效降低分散体黏度.     

The effects of temperature and humidity on phenol-formaldehyde resin bonding

Summary The effects of temperature and relative humidity on phenol-formaldehyde resin bonding were evaluated. Two flakes in a lap-shear configuration were bonded under an environment of controlled temperature (110 °C, 120 °C, 130 °C, 140 °C) and relative humidity (41%, 75%, 90%) for a series of time periods (0.25 to 16 min). The lap-shear specimens were then shear-tested on a mechanical testing machine and the results were used to establish a family of bond strength development curves at each temperature and level of relative humidity. At 110°C, the higher relative humidity appeared to retard resin bonding. The effects of relative humidity diminished as temperature increased to 140 °C. Bond strength development was chemical ratecontrolled. The rate of bond strength development at each relative humidity follows a first order reaction mechanism. The activation energy of resin-wood bonding, determined by bonding kinetics, was higher than that of resin alone, determined by differential scanning calorimetry. This comparison indicates that to form a strong resin-wood bond, a higher energy level might be required.This material is based on work supported by the Ministry of International Affairs, Quebec Government, the Natural Sciences and Engineering Research Council of Canada, and Laval University (Quebec City). The work was also supported by the U.S. Department of Agriculture under research joint venture agreement FP-92-1835     

羟基酪醇的热稳定性和分解动力学研究

研究不同升温速率(β=5、10、20、40 K/min)下羟基酪醇的热稳定性、分解动力学和贮存期。利用热重分析得到羟基酪醇在氮气氛围中不同升温速率(β)下的热分解曲线,运用3种多升温速率法Kissinger法、Friedman法和Flynn-Wall-Ozawa法以及2种单升温速率方法 Coats-Redfern法和Achar法进行动力学分析,计算热分解的表观活化能(Ea)和指前因子(A),且根据Ea和A推算羟基酪醇的贮存期。结果显示:羟基酪醇的热分解过程一步完成,在升温速率为10 K/min时,从260~409℃为羟基酪醇的主要失重阶段;TG曲线随着温度的升高而迅速出现陡峭明显的失重台阶,DTG曲线亦出现负值,且随着温度的升高而急剧下降,在305.2℃达到了DTG的峰值,此时达到最大热失重速率为-12.91%/min;升温速率的变化对羟基酪醇的分解有影响,随着速率的升高,羟基酪醇的热分解温度逐渐升高,热分解曲线略微向高温移动,呈现了分解滞后现象。羟基酪醇的热分解机制符合一维扩散(D1)模型。测得平均Ea为122.40 k J/mol,A为3.37×1010min-1。根据Ea和A可推断,在室温25℃下,羟基酪醇在氮气氛围下的理论贮存期为4~5年。     

Buttock temperature in a sedentary posture on plywood flooring of varying thickness over the ONDOL heating system

This study investigated the thermophysiological responses of healthy subjects that sat on the plywood covering of the ONDOL floor heating system. Environmental chambers were constructed for this study, wherein ambient temperature, and wall and ceiling surface temperature were controlled at 24°C, and relative humidity was 50%. The temperature of supply water (t _sw) flowing into the floor coil was altered from 15°C to 40°C at 5°C intervals. The floor covering materials used in this experiment were mortar and three types of plywood with thicknesses of 2.7, 7.5, and 12mm. The floor surface temperatures (t _f) and the skin temperatures of eight subjects were measured while they were sitting on the floor. Buttock temperature, in particular, was monitored. This experiment yielded the following results: (1) t _f was 17.0°–35.2°C on mortar finishing and 19.1°–30.2°C on 12-mm plywood covering; (2) the buttocks skin temperature increased with t _sw higher than 30°C on mortar finishing and for t _sw higher than 30°, 25°, and 20° on 2.7-, 7.5-, and 12-mm plywood finishing, respectively; (3) the differences of buttock temperature when t _sw was varied between 15° and 40°C were 11.4°C on mortar, 7.9°C on 2.7-mm plywood, 6.5°C on 7.5-mm plywood, and 5.0°C on 12-mm plywood; (4) using regression analysis, the neutral point temperature of buttocks was determined to be 32.8°C.Part of this report was presented at the 53rd Annual Meeting of the Japan Wood Research Society, Fukuoka, Japan, March 2003