(181a) Evaluation of Decay Resistance and Fixation Ability of Catechu and Boric Acid Based Preservative for D. Strictus Bamboo Species

In view of depleting wood resources and high cost of metal processing, bamboo has emerged as an excellent substitute. Bamboo species has perfect amalgamation of high tensile strength, low weight to height ratio, hollow tube form structure and relatively high shape factors. This has resulted in high bending strength and torsion, making it most desirable material for the structural design. Also, the high growth rate, and earth quake resistant properties make bamboo a prominent material for advanced engineering and civil construction. However, it is vulnerable to extracellular fungal attack, which restricts its applications. This has circumvented the need for preservation and treatment of bamboo culm. At present, conventional preservatives include solution of Copper Chrome Arsenic (CCA), Copper Chrome Boron (CCB), PentaCholoroPhenol (PCP) etc. Use of Chromium and Arsenic in CCA and CCB resulted in the restriction on use of such preservatives. It has been reported that CCA in preserved wood can rub off onto hands when wood structures are touched and leach from the wood into surrounding soil after exposure to rain and water, thus posing severe health hazards. Therefore, it is impetus to look for alternative preservatives with minimum leaching characteristics.

 Natural components extracted from various plant species have been proven to possess antifungal properties. They are used as antimicrobial agents in various traditional medicines. Tannic acid has strong ability to bond with egg proteins, boric acid and form chelates with metal ions. Earlier studies suggest Pinus radiate, Mimosa plant, Poria placenta as a source of tannin with antifungal properties for various wood species. The extract from the heartwood of Acacia catechu has been used in India as a preservative for fabrics and fishing nets. This extract is termed “catechu" and has been found to contain a large proportion of low molecular weight flavonoids, catechin in particular. 

 The bamboo samples were dipped in above mixtures for different duration of time (24, 48 and72 hours). The fixation ability of above solutions, was performed by leaching for 5 days in water using 50 ml water for each specimen, changed each day with a fresh 50 ml volume of water. Folin-Ciocalteau method was used to quantify the tannic acid content in different extracts using Perkin Elmer, Lambda 25, UV-VIS spectrophotometer. Results of leach resistance indicate that leaching efficiency of individual tannic acid, boric acid solution was 44.39%+0.24 and 49.42%+0.12, respectively. Preservative solution based on the cross-linking of condensed tannins complexes with boric acid (5%), Gelatin (1%) and copper oxide (0.1%) was found to markedly slow down the leaching of boron (leaching:3.2%+0.19).

 The bio-efficacy of all treatments was evaluated against Polyporus versicolor white rot fungi, using Soil Block Analysis method, as per guidelines of ASTM D 1413. All the treatments have shown decay resistance effectiveness better than control. They significantly enhanced bamboo durability before and after leaching. The catechu extracts treated unleached samples have shown some antifungal properties, with weight loss to be 26.54% +0.23. However, the solution was found to have poor fixation ability inside the bamboo cells. The leached sample with weight loss: 49.12%+0.15 were found to be comparable to control (55.2%). This might be because of water leaching of all the active ingredients from treated products. This will confine the applicability of treated product to limited applications. Addition of boric acid and gelatin has resulted in positive increase in decay resistance. The bamboo sample treated with solution containing boric acid (5%), Gelatin (1%) and copper oxide (0.1%), weight loss of leached and unleached samples was found to be 9.25+0.23 and 8.25%+ 0.19 respectively. The ability of tannic acid to bond with gelatin and boric acid, might have helped preservative to be bonded to the cells of bamboo culm, resulting in drastic reduction in leaching.

  The above research findings are very encouraging. Results show a strong possibility of alternative treatment technique to synthetic chemical preservatives. Overall, it represents an advanced strategy  capable of imitigating both environmental and health concerns associated with the prevailing trends in bamboo preservatives.