竹龄、粒径配比和含水率对毛竹无胶板材物理力学性能的影响

Effects of age, particle size and moisture content on physical and mechanical properties of moso bamboo non-glue bonded composites

采用1,3,5年生毛竹,经过机械粉碎1,3,5次后,处理成含水率为10%,60%和饱水的原料,通过竹材无胶成型技术,即将竹材机械粉碎后,不添加任何胶黏剂及助剂,直接铺装热压,通过其自身化学成分及微观结构形成结合,制备竹粉无胶板材。以竹龄、粒径配比和含水率为正交试验的影响因素,采用L_(9)(3^(4))的正交试验研究3种因素对竹粉无胶板材的吸水率、吸水厚度膨胀率、静曲强度、弹性模量和内结合强度的影响,确定最佳的原料组合。结果表明:随着粉碎次数增加,原料中60目(0.250 mm)以下的颗粒占比减少,200目(0.075 mm)以上小粒径颗粒增加;竹龄为3 a、粒径在60目以上、含水率为60%的原料制备的竹粉无胶板综合物理力学性能最佳,相对于综合物理力学性能最差的无胶板材,吸水率、吸水厚度膨胀率、静曲强度和内结合强度分别提升了46%,74.3%,56.8%和340%,但弹性模量下降了60.6%。通过对两组板材微观形貌及化学成分的对比分析可得,原料粒径在60目以上且含水率为60%时有利于竹粉的自结合成型。

As an abundant natural resource in China, the bamboo forest area in China accounts for one-quarter of the global bamboo forest area. Bamboo processing and utilization have long record history worldwide. However, bamboo non-glue self-bonding technology is an emerging immature technology in the modern bamboo processing industry. Traditionally, bamboo is usually processed into a variety of forms such as bamboo fibers, bamboo powder, bamboo shavings and bamboo scraps, and then the reduced-size bamboo materials were pretreated with acid, alkali, enzyme, or other additives followed by hot-pressing to manufacture different bamboo products. However, the traditional process methods are not only time-consuming during the board-making preproduction process, but also do not allow for the utilization of the whole bamboo. In this study, 1-, 3-, and 5-year-old moso bamboos were mechanically grounded 1, 3, and 5 times, respectively, and processed into bamboo powder with three moisture contents(MCs) of 10%, 60%, and water-saturated. Bamboo non-glue bonded panels were prepared with bamboo powder without any adhesives and additives. The effects of age, particle size, and MC on the water absorption, water absorption thickness swelling rate, modulus of rupture(MOR), modulus of elasticity(MOE), and internal bonding(IB) strength of bamboo self-bonded panels were studied by orthogonal tests. The results showed that the proportion of larger than 60 mesh(0.250 mm) particles decreased and the proportion of small particles increased as the ground times increased. The bamboo non-glue bonded panels with high physical and mechanical properties were prepared using 3-year-old bamboo powder with a MC of 60%, of which the particle size was mainly above 60 mesh. Bamboo non-glue bonded panels had the water absorption rate of 45.0%, thickness swelling of 14.5%, MOR of 6.9 MPa, IB strength of 0.44 MPa and MOE of 1 446 MPa. The board’s water absorption thickness swelling rate met the MDF-GP MR performance requirements in accor-dance with the Chinese national standards. The water absorption rate, water absorption thickness swelling rate, MOR, and IB strength were improved by 46%, 74.3%, 56.8% and 340%, respectively, while the MOE decreased by 60.6% compared with those of self-bonded panels with the worst physical and mechanical properties. The particle size smaller than 60 mesh and the MC of 60% were beneficial for forming a compact structure, thus generating the self-bonded panels with the best mechanical and physical performances.