Urea-Formaldehyde Resin Removal in Medium-Density Fiberboards by Steam Explosion: Developing Nondestructive Analytical Tools

The cascading recycling of wood waste is currently a hot topic. Medium-density fiberboard (MDF) is a material whose consumption has been increasing worldwide for several decades. However, current wood waste treatment processes do not allow for efficient recycling. The potential of steam explosion (SE) treatment was investigated for stripping off the urea-formaldehyde (UF) resin and producing clean fibers from MDF. Hot liquid water during the hydrothermal stage and water expansion during the decompression stage of SE provoked the (1) hydrolytic breakdown of UF and removal of >80% of resin from the fibers and (2) efficient defibration of MDF producing ≈67% of fibers with similar morphological features when compared with MDF fibers. Near infrared spectroscopy (NIRS), nitrogen quantification, and confocal laser scanning microscopy/scanning electron microscopy-wavelength dispersive spectroscopy were used to evaluate the SE effect on UF removal from MDF fibers. The sample clusters obtained by principal component analysis of NIRS spectra were correlated with the nitrogen content and processing conditions used. This work brings versatile solutions based on hydrothermal treatments, namely SE, for diverse low environmental impact and valorization routes of MDF waste. We showed that MDF processing treatment must be chosen wisely according to the future valorization of the MDF targeted.