Dimensional stability improvement of kenaf panels by post-manufacturing hygrothermal treatments using response surface methodology

• Hygrothermal treatment significantly improves kenaf panel’s dimensional stability.
• First order response surface models fits well to predict the desirable responses.
• Optimum treatment parameters for kenaf MDF panels are 225 °C, 30 min, 85% RH.
• Optimum treatment parameters for kenaf HDF panels are 200 °C, 90 min, 85% RH.
• Hygrothermal treatment makes kenaf panels commercially viable.

The potential of various hygrothermal post manufacturing treatments is evaluated in this study to determine the suitable heat treatment and moisture conditions for relieving the internal residual stresses and improving the dimensional stability characteristics of medium density and high density kenaf fiberboards (MDF and HDF, respectively), generally known to have poor dimensional stability. Furthermore, the effects of these conditions on the density and mechanical properties of the panels have been evaluated. The treatment involves conditioning at normal (65% relative humidity, RH) or high humidity (85% RH) and then heat treating these panels at different combinations of temperature and time. The results are statistically analyzed by using response surface method of Design Expert® software. The desirability function is employed to find the treatment conditions that give suitable dimensional stability with minimum compromise on the mechanical properties of the panels. Within the range of experimental conditions, the parameters with maximum desirability are 225 °C, 30 min, 85% RH and 200 °C, 90 min, 85% RH for MDF and HDF panels, respectively. The panels treated under these conditions result in approximately 25–30% reduction in thickness swelling without any significant reduction in their mechanical properties with respect to those of the non- treated panels. However, with more intensive treatment, the thickness swelling within the limits of experimental study can be decreased by approximately 35%. Although some mechanical properties of the panels are compromised under these conditions, they are still above the requirements of ANSI A208.2-2009 and ANSI A135.4-2012 standards.