响应面法优化木材NaOH-冻融循环预处理条件

Optimization of NaOH extraction combined with freeze-thaw cycle pretreatment process of Chinese fir plantation wood using response surface methodology

对人工林杉木木材进行NaOH-冻融循环预处理,以处理后木材的上染率、纵向和横向染透率作为预处理效果的评价指标,利用模糊综合评判模型对各指标进行综合评判,并以综合评判值为响应值,运用响应面法探讨NaOH质量分数、抽提时间、冷冻时间和循环次数对响应值的影响,优化NaOH-冻融循环预处理条件,通过扫描电镜和压汞法分析预处理后木材微观结构和孔隙的变化。结果表明,随NaOH质量分数增大、抽提时间延长、冷冻时间和循环次数增加,综合评判值均先增大后减小,各因素对综合评判值的影响顺序为NaOH质量分数>冷冻时间>抽提时间>循环次数;优化的预处理条件是NaOH质量分数0.42%、抽提时间24.25 h、冷冻时间18.67 h、循环2次,此条件下处理材的综合评判值为0.956,与理论预测值的相对误差为2.60%,差异较小;NaOH抽提再冻融循环处理后,封闭的纹孔被打开,部分纹孔膜破裂以及射线薄壁细胞与轴向管胞层间有裂隙,使大孔孔径和总孔体积均进一步增大,比表面积增加,染液在木材内的渗透特别是横向渗透显著增大。

Chinese fir plantation wood(Cunninghamia lanceolata)was pretreated using NaOH extraction combined with freeze-thaw cycles to improve the permeability of dye liquor in wood.Dye-uptake and dye penetration rate in the longitudinal and transverse direction of pretreated wood were used as the evaluation indexes in response surface methodology.The system of fuzzy comprehensive evaluation was establishied,and the values of fuzzy comprehensive evaluation,which was set as the response,was calculated.Optimal pretreatment conditions,such as NaOH mass fraction,extraction time,freezing time,and number of cycles,were evaluated.The change in the microstructure and pore size of the wood before and after pretreatment were examined using field emission scanning electron microscope(SEM)and mercury intrusion porosimetry(MIP),respectively.The results showed that the values of fuzzy comprehensive evaluation increased at first and then decreased with increased NaOH mass fraction,extraction time,freezing time,and number of cycles.The effects of the four factors on the values of fuzzy comprehensive evaluation were in the order:NaOH mass fraction>freezing time>extraction time>number of cycles.Optimal pretreatment conditions were as follows:0.42%NaOH mass fraction,24.25 h extraction time,18.67 h freezing time,and double cycle.Under these conditions,the values of fuzzy comprehensive evaluation was 0.956,which was in accordance with the theoretical value.Phenonmena such as opened and ruptured pit membrane and crack in the longitudinal tracheids cell wall and ray parenchyma cells were observed in pretreated wood.MIP test results showed that macropore diameter,total pore volume,and pore surface area increased after NaOH extraction and freeze-thaw cycle treatment,consequently enhancing the penetration of dye liquor in wood;particularly,the permeability in the tranverse direction was enhanced significantly.