Effect of thermal treatment with water, H2SO4 and NaOH aqueous solution on color, cell wall and chemical structure of poplar wood
Effect of thermal treatment with water, H2SO4 and NaOH aqueous solution on color, cell wall and chemical structure of poplar wood
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DOI：
10.1038/s41598-018-36086-9
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发表时间：
2018-12-07
影响因子：
4.6
通讯作者：
Shi, Sheldon Q.
中科院分区：
文献类型：
--
作者：
Shi, Jiangtao;Lu, Yu;Shi, Sheldon Q.
用水、稀酸和稀碱水溶液对杨木木块进行热处理，在铁氟龙内衬的高压釜中，在三种温度下进行。采用色度仪、扫描电镜（SEM）和傅里叶变换红外光谱（FTIR）研究了不同液体和温度对木材表面颜色、细胞壁微观结构和化学结构的影响。从色度计观察到，在所有处理条件下，亮度值都随温度的升高而降低。在所有液体处理中，a*值随温度升高而升高。b*值随水热温度和H2SO4处理温度的升高而升高，随NaOH处理温度的升高而降低。总色差（Delta E）在水热处理中变化不大，而在H2SO4和NaOH水热处理中变化较大。扫描电镜显示，不同的试剂和温度对细胞壁结构的破坏程度不同。在热液和氢氧化钠的作用下，中间片层总是破裂。H2SO4处理后，中片层和次生细胞壁均出现损伤，且随温度升高而加剧。这些骨折通常平行于纤维细胞壁的52层微纤维角（MFA）。FTIR分析表明，经过H2SO4和NaOH热处理后，其化学结构发生了明显的变化。C=0吸收峰的缺失或减小表明半纤维素在H2SO4和NaOH的热处理过程中被降解，产生了新的化合物。另一方面，木质素在H2SO4处理下被部分降解，愈创木酰基核在紫丁香基核之前被降解。
Thermal treatments with water, diluted acid, and diluted alkali aqueous solution of poplar wood blocks were carried out in a Teflon-lined autoclave at three temperatures. The effects of different liquids and temperatures on wood surface color, cell wall microstructure, and chemical structures were investigated by the chromameter, scanning electron microscope (SEM), and Fourier transform infrared spectroscopy (FTIR). From the chromameter, it was observed that the lightness value decreased with temperature for all treatment conditions. The a* value increased with temperature in all liquid treatments. The b* value increased with temperature in hydrothermal and thermal with H2SO4 treatment but decreased with temperature in thermal with NaOH treatment. The total color difference (Delta E) was slightly changed in the hydrothermal treatment, but dramatically changed in the thermal with H2SO4 and NaOH aqueous treatments. SEM showed that the cell wall structure was damaged differently with different reagents and temperature. Middle lamella layers were always fractured in hydrothermal and NaOH treatments. However, both middle lamella and secondary cell wall were damaged after the H2SO4 treatment and intensified with temperature. These fractures usually parallel with the 52 layer microfibril angle (MFA) in the fiber cell wall. The FTIR analysis suggested that the chemical structure was obviously changed after the thermal with H2SO4 and NaOH treatments. And the missing or decreasing C=0 absorption peak indicated hemicellulose is degraded and new compounds produced during thermal with H2SO4 and NaOH treatment. On the other hand, lignin was partly degraded in the H2SO4 treatment and guaiacyl nuclei was degraded before syringyl nuclei.