蒸汽介质热处理对毛白杨木材颜色的影响

以毛白杨木材为研究对象,采用蒸汽介质热处理方法在氧气含量低于2%的密闭容器中以温度170～230℃、时间1～5h的处理条件对其进行热处理。结果表明:随着处理温度的升高和处理时间的延长,色饱和度差ΔC*逐渐减小、色差ΔE*和色相差ΔH*逐渐增大,说明热处理后木材的颜色由原色逐步过渡到深褐色。方差分析和多重比较结果表明:热处理温度比热处理时间对毛白杨木材颜色变化的影响更为重要。此外,进一步得出了色差值与热处理温度、时间三者之间的回归模型。利用此特性,对一些浅色木材进行热处理,可赋予其凝重的颜色,同时还可增强其尺寸稳定性,从而提高其产品附加值,扩大应用领域。     

观光木人工林木材热处理材色变化研究

为探究观光木木材在高温处理下木材材色变化,对0.4 mm、0.6 mm、1.6 mm厚观光木薄木及观光木板材进行热处理,用色差计测定处理前后木材的明度指数(L*)、红绿指数(a*)、黄蓝指数(b*),计算出色饱和度差(ΔC*)、色相差(ΔH*)和总体色差(ΔE*)。结果表明,观光木薄木经干燥处理颜色变化不大,可通过干燥处理烘干观光木薄木的同时保证薄木的颜色特性;观光木板材经高温压缩密实化后材色变化明显,170℃热处理45 min时色饱和度差(ΔC*)为3.02,总体色差(ΔE*)为5.47,总色相差(ΔH*)为7.71,经济价值最高。     

高温热处理对尾叶桉木材颜色的影响

热处理可改变木材的颜色,使其由原来的浅色系逐渐过渡到咖啡色乃至深褐色。以尾叶桉(Eucalyptus urophylla)木材为研究对象,采用完全随机区组设计方法,以180~220℃、处理时间1~5 h的条件对其进行高温热改性处理。结果表明,随着处理时间的延长和处理温度的升高,木材的总体色差ΔE*和色相差ΔH*逐渐增大,而色饱和度差值ΔC*逐渐减小,表明热处理后尾叶桉木材的颜色由原色逐步过渡到深褐色。双因素方差分析结果表明,在0.01水平上,热处理温度和时间均对木材颜色变化有显著影响,热处理温度对桉树木材颜色变化的影响要比热处理时间更为重要。     

3种木材涂饰前后表面视觉性质差异的研究

测定分析了筒状非洲楝Entandrophragma cylindricum,古夷苏木Guibourtia tessmannii和水曲柳Fraxinus mandschurica木材醇酸清漆涂饰前后表面视觉性质的差异。结果表明,涂饰处理降低了3种木材表面的明度(L*)和红绿轴色品指数(a*)值,其中,古夷苏木的L*变化差异最大,明度降低明显;水曲柳的红绿轴色品指数差(Δa*)绝对值最大,相比处理前更偏向绿色;3种木材透明涂饰后的黄蓝轴色品指数(b*)均有所升高,黄蓝轴色品指数差(Δb*)绝对值由大到小分别为水曲柳古夷苏木筒状非洲楝,数值越大越趋于黄色;总体色差(ΔE*)变化差异不大,涂饰对3种木材的总体色差影响不明显。     

温致变色杨木单板浸渍工艺

以杨木单板为基体,以热敏染料、显色剂、十四醇、增感剂为木材温致变色剂,利用超声波浸渍注入木材的方法制备可逆温致变色杨木单板,研究可逆温致变色杨木单板的浸渍工艺。结果表明:影响试件变色色差(ΔE*)的主要试验因子为超声波功率,方差分析其在0.01水平下对试件ΔE*影响显著;其次为浸渍时间和浸渍温度,方差分析二者在0.01水平下对试件ΔE*影响不显著。最佳浸渍工艺为浸渍温度75.0℃、浸渍时间4.0h、超声波功率120.0W。研制成可逆温致变色杨木单板新产品,杨木单板起始变色温度为26℃,终止变色温度为32℃;温度由26℃升至32℃时,试件由蓝色变成木材本色;温度由32℃降至26℃时,试件由木材本色变成蓝色,达到室温可逆变色的效果。     

新西兰辐射松高温热处理颜色变化研究

采用不同热处理温度和时间对新西兰辐射松蓝变材和未蓝变材进行高温热处理,分析热处理温度、时间对试材颜色的影响,结果表明:随着处理温度的升高和处理时间的增长,试材的明度(L~*)逐渐降低,红绿色品指数(a~*)逐渐增大,黄蓝色品指数(b~*)逐渐减小(蓝变材b~*逐渐增大),总体综合色差(△E)增大。蓝变材和未蓝变材的颜色差异逐渐变小,为使蓝变色斑达到肉眼不容易识别的程度,最低的热处理条件为190℃,3h。多元回归分析和方差分析表明,在α=0.05水平上,热处理温度(x_1)和时间(x_2)两因素及其共同作用对L~*、a~*、b~*、△E的变化影响极为显著,其中温度对各颜色指标的影响比时间的影响更显著一些。     

高温热处理对尾叶桉木材颜色的影响*

热处理可改变木材的颜色,使其由原来的浅色系逐渐过渡到咖啡色乃至深褐色。以尾叶桉 （Eucalyptus urophylla）木材为研究对象,采用完全随机区组设计方法,以 180~220 ℃、处理时间 1~5 h 的 条件对其进行高温热改性处理。结果表明,随着处理时间的延长和处理温度的升高,木材的总体色差 ΔE * 和色相差 ΔH * 逐渐增大,而色饱和度差值 ΔC * 逐渐减小,表明热处理后尾叶桉木材的颜色由原色逐步 过渡到深褐色。双因素方差分析结果表明,在 0.01 水平上,热处理温度和时间均对木材颜色变化有显著 影响,热处理温度对桉树木材颜色变化的影响要比热处理时间更为重要。     

真空热处理对家具用奥克榄木材物理力学性能的影响

热处理是提高木材尺寸稳定性的有效方法之一,目前热处理主要针对室外等较恶劣的用材环境,采用高温(200℃)处理。针对家具材装饰性要求高、使用环境变化较温和等特点,以家具常用材奥克榄木材为实验材料,研究真空(≤0.06 MPa)条件处理后奥克榄木材物理力学性能的变化,以确定适用于家具用材的真空低温热处理工艺。将奥克榄木材以0.06 MPa、不同温度(120,140,160,180,200℃)处理5 h,测定不同处理温度下木材的全干密度、湿胀率、干缩率、色差、抗弯弹性模量、抗弯强度、冲击韧性及硬度变化,并比较低温(120,140,160℃)和常规温度(180,200℃)处理及未处理奥克榄木材的物理力学性能。结果表明:物理性质方面,随温度升高,奥克榄材色加深,处理后奥克榄与未处理材相比,色差值ΔE为6.1～25.9;全干密度随处理温度呈波动状态变化,在200℃处理时达最低值,较未处理材下降30.9%;干缩率、湿胀率均明显下降,但在120℃升高至140℃、160℃升高至180℃时变化幅度较小。力学性能方面,随炭化温度升高,抗弯强度、抗弯弹性模量先增大后减小;冲击韧性降低,140℃之后变化幅度趋缓,200℃时降幅最大为52.42%;不同温度热处理后的端面硬度较未处理材均有所上升,径、弦变化不明显。与常规热处理和未处理处理材相比,真空低温热处理可改善木材的尺寸稳定性,降低炭化对于木材材色变化的影响,且不明显降低木材的力学性能。     

加压热处理对表层压缩杨木变形回弹的影响

以水热控制法对人工林毛白杨木材进行间歇式压缩,获得表层密度1.0 g/cm~3、芯部密度基本不变的表层压缩木;再在常压和0.3 MPa压力下,分别对表层压缩木材进行热处理,检测热处理后木材的变形回弹率。结果表明,随着热处理温度升高,表层压缩木材变形回弹率呈降低趋势;加压热处理比常压热处理,对表层压缩木材的变形固定效果更优。200℃、0.3 MPa加压热处理,能够使杨木压缩材的厚度变化率降低67.38%。     

圆盘豆热处理材颜色变化及其变化机理

试验采用过热蒸汽作为传热介质和保护气体,对圆盘豆木材进行热处理,热处理温度为160℃、180℃、200℃、220℃,热处理时间为2h、4h、6h、8h,并采用紫外光谱和气-质联用对圆盘豆木粉抽提物进行分析。结果表明,热处理后圆盘豆木材颜色发生明显变化。随着热处理温度升高,木材明度L*下降,红绿色品指数a*变化不明显,黄蓝色品指数b*下降,色差△E*增大,木材表面颜色加深,其主要原因是木素及木材抽提物发生了氧化、还原反应。     

Effect of Nanocomposites Coatings on Exterior Performance of Bamboo during Aging*

Bamboo deterioration caused by light becomes a significant problem as application of bamboo extends from indoor to outdoor.The color and roughness of bamboo are two important exterior performances.This study focused on UV resistant nano composites coatings for exterior use and what aimed to find a formulation which could enhance the durability of bamboo.Four kinds of film-forming materials and four kinds of nano particles were used to improve bamboo exterior performance.The color and roughness of nano composites coatings were measured during accelerated weathering.Artificial aging time was 174 h at the temperature of 50 ℃.The experiment showed nanocomposites coatings had significant improvement in UV-shielding and nearly all the samples presented a darkening tendency in ΔL* and increasing tendency in Δa*,ΔE* and ΔRa.The orthogonal experiment obtained the least change in color and Ra which could be achieved with nano composites coating made by melamine resin and TiO2 when a* was considered as an important index.Film-forming material was the only factor which had significant influence on color and roughness when a* was not considered as important index,then melamine resin was the best choice.     

Effects of preheating temperatures on the formation of sandwich compression and density distribution in the compressed wood

Sandwich compression of wood that can control the density and position of compressed layer(s) in the compressed wood provides a promising pathway for full valorization of low-density plantation wood. This study aims at investigating the effects of preheating temperatures (60–210 °C) on sandwich compression of wood, with respect to density distribution, position and thickness of the compressed layer(s). Poplar (Populus tomentosa) lumbers with moisture content below 10.0% were first soaked in water for 2 h and stored in a sealed plastic bag for 18 h, the surface-wetted lumbers were preheated on hot plates at 60–210 °C and further compressed from 25 to 20 cm under 6.0 MPa at the same temperature on the radial direction. The compressed lumbers were characterized in terms of density distribution, position and thickness of compressed layer(s). It was found that depending on preheating temperatures, sandwich compressed wood with three structural modes, namely, surface compressed wood, internal compressed wood and central compressed wood can be formed. Density of the compressed layer(s) in wood increased gradually as a result of the elevated preheating temperatures. Higher preheating temperatures gave rise to bigger distance between compressed layer(s) and the surface, and preheating temperature elevation from 90 to 120 °C contributed to a maximal distance increase of 2.71 mm. In addition, higher preheating temperatures resulted in bigger thickness of compressed layer(s) over 60–150 °C and temperature elevation from 120 to 150 °C lead to the layers integration from two into one. Further temperature elevation over 150 °C reduced the thickness of the compressed layer in wood. SEM scanning suggested that cell wall bucking rather than cell wall crack occurred in compressed layer(s) and transition layer(s).     

用物理化学原理研究生态系统

由热力学第一、第二定律而产生的物理化学的主要内容———焓 (H)、熵 (S)、自由能 (G)及其关系ΔG =ΔH -TΔS来模拟生态系统的物质能量流动过程 ,得出结论 :生态系统的熵值随系统能量的增加而增加 ,反之亦然 ,并及时纠正了 5种错误观点 ,与现实进行了科学印证 ,指出生产发展的方向     

Response of colour and hygroscopic properties of Scots pine wood to thermal treatment

The effect of heat treatment on the surface colour and hygroscopic properties of pine wood were investigated in this study. Boards of Scots pine wood (Pinus sylvestris L.) were subjected to thermal treatment at 200°C, for 4, 6, and 8 h. The change of equilibrium moisture content and density values of the specimens in order to facilitate the understanding of the treated material behavior. The colour parameters L*, a* and b*, used to depict the total colour change (Δ E) of wood surface, were shown to change proportionally to the treatment intensity. Moreover, swelling in the tangential and radial directions and absorption of the specimens appeared to be enhanced in great extent by the thermal treatment process. The mean value of swelling percentage in the tangential direction decreased 10.26%, 17.22%, and 19.60% for specimens treated for 4, 6, and 8 h, respectively, referring to the final measurement after 72 h of immersion. In radial direction, mean value of swelling percentage decreased 19.56%, 32.75%, and 34.65% for treated for 4, 6 and 8 h, respectively, after 72 h immersion, which attests the decrease in swelling and improvement in the hygroscopic behavior of Scots pine wood.     

木材真空-浮压干燥特性的试验研究

以马尾松为试验材料 ,首先分别以过热蒸汽和空气作为干燥介质 ,在预热阶段通过对木材内部温度场和含水率变化的测定 ,探讨了木材真空 -浮压干燥预热阶段的特性 ;然后 ,通过对干燥介质条件与干燥速率之间影响关系的研究 ,总结出木材真空 -浮压干燥的特性。结果表明 :真空 -浮压干燥预热阶段进行得非常迅速 ,同时其表面水分的凝结量也较空气干燥大 ;木材的浮压干燥速率随着干燥介质温度的增加、绝对压力的减小和浮动频率的加大而增加。上述因素中对干燥速率影响程度从大到小的排列顺序为 :介质温度 (T) >压力浮动频率 (Hz) >绝对压力 (P)     

Optical performance of finished and unfinished tropical timbers exposed to ultraviolet light in the field in Costa Rica

This study evaluated wood color change (ΔE*) and the surface quality in 10 tropical wood species painted with three finishes (composed of wax and polyurethane). Two weathering conditions were tested: natural weathering (NW) and artificial weathering (AW). The results showed that the application of these finishes, decreased the luminosity (L*), increased the redness (a*) and the yellowness (b*) parameters in all species. ΔE*, after weathering exposure, was affected significantly by L*, a*, and b, whereas for finished or pretreated wood, L* and b* are the main parameters affecting ΔE* in the 10 tropical species studied. ΔE* values found in different finishes and pretreatments are cataloged as total change of color. Other important results were that tropical light colored timber with natural pretreatment produced higher ΔE* than dark colored timber. The stains and fungal development were observed in polyurethane finishes in NW, but not in AW. The irregular and mosaic flaws were not observed in any kind of finish or pretreatment of surface. The values of the quality index created, which considered long and short lines and switch flaws, were lowest in NW and in waxy finish, while the highest value was obtained with the polyurethane finish.     

Moisture-dependent orthotropic viscoelastic properties of Chinese fir wood in low temperature environment

The influence of moisture content (MC) on the orthotropic viscoelasticity of Chinese fir wood (Cunninghamia lanceolata [Lamb.] Hook.) has been examined in low temperature environment. Storage modulus E′ and loss modulus E″ of wood with six different levels of MC ranging from 0.6 to 22.0% were determined from ??120 to 40 °C and at multi-frequency range of 0.5, 1, 2, 5, and 10 Hz using a TA instruments^® Dynamic Mechanical Analyzer (DMA 2980). The results showed that a distinct moisture dependency is exhibited by the orthotropic viscoelastic behaviour of Chinese fir wood. With the exception of some apparent activation energy (ΔE) for β-relaxation process, the E′ decreased and the E″ peak temperatures moved towards lower temperature and the ΔE for α-relaxation process became lower with MC increasing in all orthotropic directions, whereby individual decline of E′ and the E″ peak temperatures were affected by MC to different degrees. Besides, a little E″ peak at around 0 °C was only seen in L direction, which could be attributed to the melting of frozen water. Furthermore, the dynamic viscoelastic behavior of wood is also dependent on the measurement frequency. The findings suggest that the orthotropic structure and moisture content have an important influence on the viscoelastic performance in low temperature environment.     

Study on Wood Drying Properties under Vacuum-floating Pressure

Using Masson pine as specimens, when drying mediums are overheated steam and hot-air respectively, preheating characteristics of wood under vacuum-floating pressure drying are discussed by measurement of internal temperature field and variation of moisture content during period of preheating. The relationship between drying medium conditions and drying rate of wood reveals that, firstly, compared with process of air-drying, time needed to be preheated under vacuum-floating decreased dramatically, meanwhile, the magnitude of condensation on the surface is relatively larger. Secondly, drying rate of wood under vacuum-floating pressure increases coupled with temperature of medium, reduction of absolute pressure, and raise of fluctuation rate of pressure. The sequence of factors contribution to drying rate is listed as following: temperature of medium (t) > fluctuation rate of pressure (f)> absolute pressure (p).