化学处理对竹笋壳润湿性的影响

竹笋壳疏水性好,润湿性差,影响自身及与其他材料的复合,该文旨在通过化学处理提高竹笋壳表面润湿性。分别采用不同浓度的HCl、Na OH溶液对竹笋壳进行不同时间的处理,测定处理前后竹笋壳内外表面的接触角,分析处理后内外表面的表面自由能,并用扫描电镜(scanning electron microscope,SEM)分析处理前后表面微观结构的变化。结果表明:HCl、Na OH对竹笋壳表面处理效果较好的分别为质量分数5%HCl处理6 h和质量分数2%Na OH处理6 h。水和酚醛胶作为接触试剂时,竹笋壳内外表面接触角的排列顺序均为:未处理组质量分数5%HCl处理6 h组质量分数5%Na OH处理6 h组。质量分数5%HCl处理6 h的竹笋壳内外表面的表面自由能分别提高了1%、77.68%,质量分数2%Na OH处理6 h的竹笋壳内外表面的表面自由能分别升高58.33%、79.17%。SEM表面微观结构分析表明质量分数5%HCl处理6 h的竹笋壳内表面可明显看到气孔,外表面微乳突数量增多;质量分数2%Na OH处理6 h的竹笋壳内表面纤维方向更加清晰,外表面微乳突数量增多。综上所述,质量分数2%Na OH处理6 h的竹笋壳内外表面润湿性改善效果最好,质量分数5%HCl处理6 h和质量分数2%Na OH处理6 h对竹笋壳外面表的润湿性改进的效果相近。

Wettability of bamboo shoot shell under chemical treatment

Bamboo shoot shell is a kind of natural biomaterial waste from bamboo shoot growing and processing in China. With more than 40% cellulose and strong vascular bundle fiber, it is a good raw material for biomaterial composites. Its main functions are water blockage and tissue protection. The wax coat on the inner surface prevents loss of water from the shoot, the micropapillae and trichome on outer surface also hinder liquids entry. Therefore, poor wettability of bamboo shoot shell blocks adhesive application in making it into biomaterial composites. This study aimed to understand the wettability of bamboo shoot shell and improve the wettability of bamboo shoot shell by chemical treatment methods. The bamboo shoot shell of Pleioblastus amarus (keng) was treated with HCl and NaOH solution of 3 different concentrations by 3 kinds of time. Bamboo shoot shell samples with 30 mm × 30 mm × t mm (t is thickness) were dipped in 1%, 2% and 5% HCl solution and 0.5%, 1% and 2% NaOH solution respectively and dipping time was controlled as 2, 4 and 6 h correspondingly. After treatment, the contact angle of the inner surface and outer surface of bamboo shoot shell was analyzed by 4 reagents, i.e., water, phenolic formaldehyde resin (solid content was 42.6%, and viscosity was 200 cps), 2 methyl iodide, and ethylene glycol. The surface free energy was also calculated based on the function of Lifshitz - van der Waals. Scanning electron microscope (SEM) was used to characterize microstructure of the surface of bamboo shoot shell after treatment. The results showed that when water and phenolic formaldehyde resin adhesive were taken as contact reagent, the contact angle values of the inner surface of bamboo shoot shell were bigger than those of the outer surface of bamboo shoot shell under different treatment conditions. The contact angle values of 3 groups were as follows: Control > HCl group > NaOH group. While, there was not similar trend when ethylene glycol and 2 methyl iodide were taken as contact reagent. When the concentration of HCl solution was the same, the contact angle of water and phenol formaldehyde resin adhesive on the inner and outer surface of bamboo shoot shell decreased with the treatment time increasing. When water was as contact reagent, under the treatment of 5% HCl solution for 6 h, the decrease amplitude of contact angle values of the inner and outer surface of bamboo shoot shell was 3.53% and 22.82% respectively compared with Control group. When the concentration of NaOH solution was the same, the contact angle of water and phenol formaldehyde resin adhesive on the inner and outer surface of bamboo shoot shell also decreased with the treatment time increasing. Under the treatment of 2% NaOH solution for 6 h, the decrease amplitude of contact angle values of the inner and outer surface of bamboo shoot shell was 29.85% and 35.69% respectively compared with Control group. The surface free energy of the inner and outer surface of bamboo shoot shell was calculated according to the initial contact angle values of the water, ethylene glycol and 2 methyl iodide as contact reagent. The surface free energy of the inner and outer surface of bamboo shoot shell ranged from 26 to 50 mJ/m2, and was ranked as 2% NaOH solution for 6 h > 5% HCl solution for 6 h > Control group. Compared with Control group, the surface free energy of the inner and the outer surface of bamboo shoot shell increased by 1% and 77.68% respectively after 5% HCl solution treatment for 6 h, while those after 2% NaOH solution treatment for 6 h increased by 58.33% and 79.68% respectively. It was obvious that the similar effect occurred between 5% HCl solution and 2% NaOH solution treatment on wettability of the outer surface. While, 2% NaOH solution has better effect on wettability of the inner surface of bamboo shoot shell. SEM analysis showed that the inner surface of Control group was covered with smooth waxy coat on its vascular bundles fiber, and uneven trichomes and micropapillae were distributed on the outer surface of bamboo shoot shell; after treatment of 5% HCl solution for 6 h, stomata were seen on the inner surface of bamboo shoot shell and wax coat became smoother compared with those of control group, and more micropapillaes appeared on the outer surface of bamboo shoot. Under the treatment of 2% NaOH solution for 6 h, vascular bundle fibers stood out and wax coating hardly existed, only a small amount of wax particle residues existed on the inner surface of bamboo shoot shell, and fiber grain became clear and more micropapillaes appeared on the outer surface of bamboo shoot. This SEM result also showed that 2% NaOH solution for 6 h had better effect on improving the wettability of the inner surface of bamboo shoot shell and had similar effect on the outer surface of bamboo shoot shell with 5% HCl solution for 6 h.