Efficacy Of Selected Preservatives On Bamboo (Gigantochloa Scortechinii) Strips And Laminates

Bamboo can be an alternative for wood as raw material for laminated products. Like wood, bamboo is non-durable. It is susceptible to fungal and termite attacks. Hence, there is a need to treat bamboo to enhance their resistance towards fungal and termite attacks. Chemical treatment is one of the effective ways to preserve bamboo and the choice of preservatives and its concentrations would determine the success of the treatment. The objective of this study was to evaluate the efficacy of some preservatives on bamboo (Gigantochloa scortechinii) strips and laminates in terms of their resistance towards fungal and termite attacks. Other properties such as strength and gluing quality of the strips were also determined. The preservatives used in this study were pyrethroid compounds, i.e., light organic solvent preservatives (LOSP) (a.i tributyltin naphthenate (3.5%), permethrin (0.2%)), water based preservatives (WBP) (a.i disodium octaborate (10%), benzalkonium chloride (2%), permethrin (0.2%), tributyltin-oxide (TBTO, 1%) and borax (5% w/v). Bamboo strips without epidermis, 150 mm x 20 mm x 4 mm were prepared and vacuum-preassure treated with the treating solutions.Untreated and water-boiled strips were served as controls. A batch of the treated and untreated strips were evaluated for colour changes, strength properties (static bending) and resistance towards white rot (Pycnophorous sanguineus Wulfex Fries) and termite (Coptotermus curvignathus Holmgren) attacks. Another batch of the treated and untreated strips were fabricated into laminates using phenol formaldehyde (PF) as binder. The laminates were then tested for their bonding quality which includes buffering capacity, contact angle, shear strength and percentage of wood failure. The laminates were also subjected to white rot and termite tests. All treatments changed the bamboo strips into lighter colour with the colour changes index (ΔE) value ranging from 2.68 to 11.7 and whitish (W) value 0.67 – 8.46%. TBTO-treated strips had the highest ΔE while WBP-treated strips had the highest whitish values, i.e., 9.29 and whitish value of 8.46%. The resistance of bamboo strips and laminates against white rot and termite attacks were evaluated based on their weight loss after exposure to those biodeteriorating agents. The results showed that all preservative treatments increased the resistance of bamboo strips and laminates towards white rot from the original value of 17.6%, i.e., weight loss of untreated strips and 22.9% (untreated laminates). However, boiling in water for 30 minutes was decreased the resistance of the strips against white rot attacks. The weight loss value for this strip was 21.8% while 22.4% for the laminates. TBTO was found to be the best preservative to protect both bamboo strips (10.7%) and laminates (9.71%) against the fungus. The results also revealed that bamboo laminate was more durable than bamboo strips when exposed to termite. The increment in resistance for these materials were 62.5% and 72.9%, respectively. All preservative-treated materials had significantly lower weight loss values compared to untreated and water-boiled bamboo materials. Among the preservatives, WBP gave the best protection against termite and borax-treated materials had the least efficacy in protecting the strips. For the laminates, TBTO gave the best protection while borax gave the least protection against termite. A study on the strength properties of treated bamboo strips revealed that the chemical treatments slightly reduced the modulus of rupture (MOR) and modulus of elasticity (MOE) in static bending. The reduction of MOR for the treated strips was in the range of 1.22% to 19.6% whilst the reduction in MOE ranging from 1.3% to 18.2%. Strips treated with LOSP gave the most effect on the MOE and MOR properties. The strength and stiffness of bamboo strips were markedly reduced when treated with LOSP while for boiled treatment, the properties were slightly reduced. The shear strength and bamboo failure of the laminates were evaluated in dry and wet conditions. For wet condition test, the laminates were exposed to cyclic boil test. In dry test, with the exception of borax treatment, the shear strength and bamboo failure of the treated laminates were significantly reduced. The shear strength values for the treated laminates were in the range of 0.64 Nmm-2 to 2.04 Nmm-2 compared to 2.66 Nmm-2 for the untreated laminates. The same trend was observed when tested in wet condition. The shear strength of the laminates was reduced for all treatments which the shear strength ranged from 0.48 Nmm-2 to 0.65 Nmm-2 compared to 0.79 Nmm-2 for untreated laminates. The wood failure of the treated material did not differ significantly to untreated bamboo laminates. The wood failures ranged from 8 % to 28 % in dry condition test and 2 to 4% in wet condition. The results also showed the bamboo laminates surpass the requirement of the British Standard: Part 8: Specification for Bond Performance of Veneer Plywood.

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