植物油蜡涂饰热改性落叶松的色度学差异性分析

Chromatic variability of larch wood impacted by high-temperature thermal treatment and oil-wax coating

高温热处理-植物油蜡涂饰组合技术在提高人工林落叶松木材尺寸稳定性的同时,能够强化-美化表面纹理特征,提高其产品的综合附加值。鉴于落叶松早晚材在细胞孔隙尺度、胞壁厚度、松脂含量等属性上存在显著性差异,本研究基于计算机图像色度学原理,采用"K-means"聚类分析算法,在L*a*b*色度空间下,对热改性-植物油蜡涂饰落叶松早材-晚材组织的色度学指标进行独立测试、计算和分析,为热改性落叶松植物油蜡透明涂饰研究与应用提供参考。选取兴安落叶松(Larix gmelinii)为试验材料,采用芬兰Thermo-Wood热改性工艺,以常压过热蒸汽为加热保护介质,在温度为160,180和200℃条件下对木材进行热改性处理。随后对落叶松热改性材及常规干燥材分别进行植物油蜡底油l1(方案N1)、植物油蜡底油l1-面油l2(方案N2)的透明涂饰,分析涂饰表面色度学指标,探索高温热改性、植物油蜡透明涂饰对落叶松早材-晚材组织色度学特性的影响规律。木材色度学测试计算显示:以落叶松常规干燥材为对比参考对象,各类试材经过高温热改性-植物油蜡透明涂饰后,其早材与晚材组织的明度指标L*呈阶段式降低趋势,红绿指标a*、饱和度S*呈阶段式升高趋势;早材-晚材总体色差ΔE*随热处理温度升高而增大,而植物油蜡透明涂饰则导致ΔE*降低;在N2透明涂饰处理方案下,180℃热改性木材早材-晚材饱和度差ΔS*较常规室干材提高60.8%,而相应的总体色差则保持不变。红外光谱分析发现:植物油蜡复合体富含以碳碳双键-乙烯基为代表的发色基团与以碳氧单键-酯基为代表的助色基团,在植物油蜡涂饰浸润木材组织过程中,这些化学基团与落叶松半纤维素-木素高温热解的碳水化合物结合而形成发色体,改变了落叶松试材对可见光的吸收,使木材颜色发生变化;因落叶松晚材富含大量松脂成分,在涂饰过程中这些化学成分对植物油蜡在木材组织内的扩散起到了隔离-屏障作用,延缓了植物油蜡浸润木材、干燥过程,对早材-晚材涂饰后色彩差异产生影响。研究结果表明:通过对人工林落叶松木材实施高温热处理-植物油蜡涂饰加工,其表面颜色趋向于暖色调-深色调,早晚材色彩饱和度对比更加鲜明,木材整体装饰质量与效果得到提升。

In terms of aesthetical perception,color is one of the most fundamental physical properties of wood materials,and surface color differences have decisive influences over the customer’s acceptance of solid wood products.This study investigated the effect of thermal treatment and surface oil-wax coating on the chromatic variability of larch wood.Green larch lumber samples were kiln-dried with conventional technology and further high-temperature thermally treated in atmospheric superheated steam conditions.Subsequently,the larch samples were surface-painted with the transparent oil-wax coating,and the colorimetric variables of the earlywood and latewood of specified larch samples were further determined separately by a specially designed image colorimetry method.The colorimetric variable differences between the earlywood and latewood were calculated,aiming at quantitatively analyzing the chromatic variability of larch earlywood and latewood in specified cases.Comparing with the kiln-dried samples,under the circumstance of N2 oil-wax coating option and thermal treatment at 180 for 1 h,the saturation variable difference△S~*between the earlywood and latewood increased by 60.8%,while the general colorimetric variable difference△E~*remained at the same magnitude level.The variability mechanism behind the chromatic alterations of larch samples,induced by the combination of thermal treatment and surface oil-wax coating,was proposed as the interaction between the existing chromogen groups and the newly emerging ones brought about by these technical processes.Due to the inhomogeneous distribution of resin contents inside each annual ring,the latewood tissue,which contains more resin canals than the earlywood,could act as the diffusion barrier for the oil-wax compound and postpone the penetration of plant oils.In the light of this circumstance,the disrupt distribution behaviors of larch resins partially contributed to the chromatic variabilities between these two types of wood tissues.The test results demonstrated that a proper combination of thermal treatment and oil-wax coating could be used for improving softwood colorimetric properties,enhancing the surface characteristics of larch wood,promoting it as a sustainable alternative wood resource.