竹材多尺度下强韧性及水热影响研究进展

Advances in strength and toughness of hierarchical bamboo under humidity and heat

高强韧性是竹材最重要的材性特征和加工利用优势之一,这种强韧性与竹材独特的多尺度结构有着密切关系。作为天然生物质复合材料,水分与温度的变化对其强韧性有着直接影响:含水率增加,有利于提升竹材抵抗塑性变形的能力;温度升高,则使其材性变脆;在水-热协同效应下,具有维管束梯度结构的竹材通过微纳结构和化学组分的变化影响强韧性。笔者着重从材料学角度分析了竹材的增韧机制,介绍了竹材的多尺度结构,综述了竹材如何在不同尺度下通过梯度结构、细胞协同变形、多细胞壁层结构和分子链滑移体现增韧机制。水分主要增大竹材细胞变形和分子链滑移空间,从而使竹材在相同外力作用下能发生更大的位移,增加韧性。分析了湿热处理时,竹材纤维素、木质素和半纤维素的位置、构象及其比例可能在较低温度下发生变化,进而调控其强韧性能的变化。在此基础上,按照传统竹制品和现代竹材加工工艺,列举了竹材强韧性的典型应用案例和强韧性新材料发展方向。最后,提出了竹材在湿热作用下强韧性机理可进一步研究的方向。

High strength and toughness are the most important properties for the utilization of bamboo,which are closely related to the unique hierarchical structure of bamboo.As a natural biomass composite material,the changes of moisture and temperature have a direct impact on its strength and toughness.The increase of moisture content is beneficial to improve the ability of bamboo to resist plastic deformation,and the increase of temperature makes the bamboo properties to become brittle.Under the hydro-thermal synergistic effect,the mechanism of the changes of micro-nano structure and chemical composition on strength and toughness of bamboo with typical vascular bundle-parenchyma cell gradient structure has not been explored.This study focused on the analysis of the toughening mechanism of bamboo from the perspective of materials and summarized the toughening mechanism of bamboo reflected at different scales,the change of strength and toughness of bamboo after the hygrothermal treatment and the action mechanism.In addition,several typical application cases of bamboo strength and toughness were reported.At last,some suggestions on the future research regarding the effect of hierarchical structure on the relevant mechanical properties of bamboo under the action of environmental temperature and humidity were put forward:(1)under the action of water and moisture,the effects of vascular bundle-parenchyma cell cooperative deformation,cell wall filament slip and multi-stage weak interface swelling on the strength and toughness;(2)the inherent relationship between the lignin cross-linking,hemicellulose degradation,cellulose aggregation and relevant mechanical properties of cell wall lignin cross-linking,hemicellulose degradation,cellulose aggregation and relevant mechanical properties of bamboo vascular bundle cell gradient structure under temperature effect;(3)under the synergistic effect of water and heat,the action mechanism of cell gradient structure and chemical components of bamboo vascular bundles on flexibility on multi-scale(tissue-cell-nano).A strength and toughness gray correlation model was developed,which considered the effects of bamboo structure factors,component factors and water-thermal environment factors.It can provide a scientific theoretical basis for the optimal design of high-performance bamboo winding,braiding and depth molded composites of curved surface with the integration of structure and function.