Bond durability of kenaf core binderless boards II: outdoor exposure test

Abstract

An outdoor exposure test was conducted on kenaf core binderless boards (pressing temperatures 200°, 180°, and 160°C; pressing pressure 3.0 MPa, time 10 min, target board thickness 5 mm, target board density 0.8 g/cm3) to estimate their bond durability. Modulus of rupture (MOR), modulus of elasticity (MOE), internal bonding strength (IB), thickness change, weight loss, Fourier transform infrared (FTIR) spectra, and color difference (ΔE*) by the CIE L*a*b* system were measured at various outdoor exposure periods up to 19 months. These values were then compared with those of a commercial medium-density fiberboard (MDF; melamine-urea-formaldehyde resin; thickness 9.0 mm, density 0.75 g/cm3). Generally, dimensional stability and the retention ratios of MOR, MOE, and IB after the outdoor exposure test increased with increased pressing temperature of binderless boards. The MOR retention ratio of the kenaf core binderless boards with a pressing temperature of 200°C was 59.5% after 12 months of outdoor exposure, which was slightly lower than that of the MDF (75.6% after 11 months of outdoor exposure). Despite this, the bond durability of the kenaf core binderless boards should be viewed as favorable, especially when considering the fact that the retention ratio of 59.5% was achieved without binder and without obvious element loss.