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毛竹Phyllostachys edulis物理力学性能优异,原竹可代替建筑物中的钢承载结构[1],但竹壁厚度较小,不利于直接利用,将原竹进行碾压、机械疏解制成横向不断裂纵向松散的竹束,后对竹束进行胶合压制可得一定尺寸规格的材料——重组竹,重组竹的出现在一定程度上解决了竹材尺寸限制所带来的应用障碍。但由于重组竹压制过程压力较高,导致其密度较高,这在一定程度上限制了它的应用。对竹材进行浸泡处理,一方面可以使竹材软化,便于压制胶合;另一方面也可起到润胀的作用,这两者对重组竹的压制都有积极作用。对竹材的软化[2-3],可采用氢氧化钠水溶液、氨水、尿素水溶液、或直接水煮,都可取得较好的效果,但对竹材润胀化学试剂的选择,依然是一个待解决的问题。润胀是所有弹性材料都具有的特性,但由于材料与溶剂的不同,润胀效果往往具有较大差异。KEYLWERTH[4]用水浸泡木材后观察其润胀效果,发现温度的升高、抽提物的减少均有助于促进木材在水中的润胀,并首次提出了木材润胀激活能的概念;MANTANIS等[5]研究了木材在有机水溶液中的润胀效果,结果表明有机水溶液的pH值、摩尔质量与木材体积增大率的对数呈负相关;NAYER等[6]也验证了润胀激活能的高低、木材润胀效果的大小与氢键有着密不可分的关系。木材和竹材[7-9]同属木质纤维素材料,两者在化学成分、显微结构上相近,对木材的润胀研究可以为竹材提供借鉴。润胀的原因是纤维素和半纤维素分子中的羟基与水分子产生极性吸引,水分子进入纤维素的无定形区,使纤维素分子链之间距离增大,引起纤维变形[10]。研究竹材的润胀,介质的选择是关键。WEN等[11]利用碱性水溶液分离竹材中的碱溶性半纤维素,发现水溶液pH值是消除半纤维素与木质素间连接的关键因素,碱性水溶液是半纤维素与木质素分离的理想水溶液;KULA等[12]发现氯化锌具有良好的吸附作用,在纳米结构[13-16]中能够得到有效的分散,这意味着氯化锌水溶液对竹材的润胀效果较好。鉴于此,本研究使用碱性水溶液(碳酸钠、氢氧化钠)、弱酸性水溶液(氯化锌)以及去离子水分别对毛竹进行润胀,研究竹材在不同介质中的润胀效果,以期为竹材改性技术开发提供更多的理论支撑。
Swelling of Phyllostachys edulis with different treatments
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摘要: 以毛竹Phyllostachys edulis为研究对象,采用不同浓度无水碳酸钠(Na2CO3),氢氧化钠(NaOH),氯化锌(ZnCl2)水溶液(结合硝酸蒸煮)及去离子水对毛竹材进行润胀处理,以体积、面积变化率作为润胀效果的影响指标,观察毛竹宏观、微观构造的变化,探究在不同水溶液中毛竹材的润胀效果。结果表明:氢氧化钠水溶液与碳酸钠水溶液对毛竹的润胀效果较好;润胀效果随水溶液浓度的变化而变化,氢氧化钠水溶液浓度越低,润胀效果越好,而碳酸钠水溶液则相反,其中0.5 mol·L-1氢氧化钠水溶液和1.0 mol·L-1碳酸钠水溶液对毛竹的润胀效果最佳,体积增大率分别为9.69%和10.57%;直接使用氯化锌水溶液对毛竹进行润胀,润胀效果较差,但低浓度硝酸水溶液预处理可提高氯化锌水溶液对毛竹的润胀效果,其中500 g·L-1氯化锌水溶液浸泡后(100 g·L-1硝酸水溶液预处理)体积增大率为7.98%。同时,通过对润胀前后毛竹横切面不同区域面积的计算,显示在润胀过程中,纤维鞘区域面积变化幅度明显大于薄壁细胞区域面积变化幅度,说明毛竹润胀后体积变化的因素主要来源于纤维鞘分布面积的变化。Abstract: To determine the degree of swelling for bamboo (Phyllostachys edulis) in different aqueous solutions, bamboo samples were soaked in different concentrations of Na2CO3, NaOH, ZnCl2 (combined with HNO3 hydrothermal treatment), and deionized water. Changes in macro-and micro-structure were observed with the volume and area expansion rates used as evaluation indexes for the degree of swelling. Results indicated that NaOH and Na2CO3 both showed a good effect on the swelling of bamboo, meanwhile, the swelling effect of bamboo was proportional to concentration of Na2CO3, but inversely proportional to concentration of NaOH. Among the treatments, optimal volume increase rate were found with 0.5 mol·L-1 NaOH (9.69%) and with 1.0 mol·L-1 Na2CO3 (10.57%). Unsatisfactory swelling effect for swelling occurred when ZnCl2 was used alone, but pretreatment with a low concentration of HNO3 solution (500 g·L-1 ZnCl2 with 100 g·L-1 HNO3) improved swelling effect. Meanwhile, area of the bamboo in transverse sections before and after swelling showed that the area of fiber sheath distribution increased, but the area for parenchyma cell distribution after swelling was increased relatively small. Thus, changes in volume of bamboo after swelling was mainly due to changes in the fiber sheath distribution area.
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Key words:
- wood science /
- swelling effect /
- alkaline solution /
- cell wall /
- microstructure /
- Phyllostachys edulis
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链接本文:
https://zlxb.zafu.edu.cn/article/doi/10.11833/j.issn.2095-0756.2019.01.021