竹材结构的防腐

由于在露天环境中遭遇生物腐蚀,竹秆的持久性差,所以需要采取化学手段增强其耐力.但是它的解剖构造使化学物质难以像木材那样容易进入竹材.竹秆的外部由其表皮保护防水,不像木材那样有径向渗透的途径.而其内部腔隙也有保护性纤维.化学物质的主要渗透途径位于竹秆根部微管束的后生木质部.这些渗透途径分布于横剖面,很不均匀,且少,只占总面积的8～10%,而且在通过竹节时改变方向.由于在采伐时砍伤竹秆,通向导管的细胞腔被堵塞,渗透途径也受影响.周围的薄壁细胞是竹秆组织的主要部分,它们通过微小的纹孔互相连接,只能通过弥散进入.它们所含的淀粉是昆虫和某些真菌的食品.对纤维的保护也有赖于弥散.用化学物质进行保护,对于新鲜的含水量高的竹秆效果最好.就像简单的根部处理,或技术性较强的细胞液改善.新鲜竹秆的薄壁组织和纤维也能通过垂直弥散的方法得到保护.如进行滴渍和浸渍工作,最好在竹材含水分时劈开,因为薄壁组织容易接受弥散.技术措施如竹秆的水分储存和熏蒸的过程,与竹秆的自然结构,尤其是薄壁组织有关.

Preservation of a Bamboo Culm in Relation to its Structure

The low durability of a bamboo culm towards biodeterioration in an exposed environment requires mostly a protection with chemical solutions for long time use. Its anato mical structure, however, makes an efficient treatment difficult as bamboo provides more resistance to penetration than wood. At its outside the culm is protected by an epidermis as a water-tight seal. No pathways for radial penetration exist, like the ray cells in wood. Also on its inner side towards the lacuna a special tissue acts protective. Main avenues for pen- etration are the metaxylem vessels of the vascular bundles at the ends of the culm. They are unevenly distributed over the cross-section with only about 8-10% of the total area. Their strongly axial orientation is distorted at the nodes. Access to the vessels is often reduced soon after harvest due to wound reactions filling their lumen. The surrounding parenchyma cells as main component of the tissue are connected by small pits and can be reached by diffusion only. Their starch content is the main food for insects and some fungi. Also the protection of the fibres depend on diffusion. Preservation with chemical solutions is best achieved by using the water-filled vessels of a fresh culm as transportation channels, like by the butt-end treatment as a simple process or by the sap-replacement method on a technical level. The parenchyma tissue and also fibres of a fresh culm can be protected with the Vertical-Soak-Diffusion method. Dipping and soaking works best with moist split culms where the parenchyma is accessible for diffusion. Technical processes, as water-storage and the smoking of culms are correlated naturally to its structures, especially the parenchyma.