Influence of tannin and cashew nut shell liquid based resins on the performance of bamboobased composite panels

The bamboo plant is light with high mechanical strengths, can produce panel boards by bonding it with synthetic resins or natural resins such as wattle tannin (WT) and cashew nut shell liquid (CNSL). In this work, bamboo species were characterized for physical and chemical properties, while natural resins; WT and CNSL were characterized for chemical and thermal properties. Arundinaria alpina bamboo was selected and made into mats which were grouped into three groups: untreated, water soaked and treated with aqueous NaOH solution at 3%, 5% and 10% NaOH w/w concentrations. The influence of wattle tannin (WT) and cashew nut shell liquid (CNSL) resins on the mechanical, physical and water resistance properties of bamboo panel boards bonded with WT and CNSL resins was determined. The influence of synthetic resins; urea formaldehyde (UF) and phenol formaldehyde (PF) was also investigated for comparison purposes. The effect of the resins on degradation of bamboo panel boards was also investigated both when the panel board is exposed to atmospheric conditions or buried and exposed to termite attack. It was found out that all common Tanzanian bamboo species were similar to bamboo species from other countries in terms of physical and mechanical properties. Treatment of bamboo with NaOH altered the chemical, thermal and water resistance of the panel boards. WT and CNSL bonded panel boards showed lower water resistance than boards bonded with synthetic resins such as UF and PF due to hydrophilic nature of natural resins. Panel boards bonded with WT, CNSL and mixture of WT-CNSL showed low internal bond strength and modulus of elasticity for NaOH treated bamboo, while UF and PF bonded panel boards showed an opposite trend. Subjecting the panel boards to dynamic thermal mechanical analysis enabled confirmation of the panel boards’ stiffness and rigidity magnitude and glass transition temperatures of panels bonded with different resins. Nearly all the boards when subjected under termite containing conditions (buried) as well as open air environment showed a similar response. The water resistance, mechanical, physical and degradation properties show that WT and CNSL bonded bamboo panel boards can be used as general purpose panel boards.