Effect of blending L-lysine-modified montmorillonite into urea-formaldehyde resin on formaldehyde emission and physicomechanical properties of medium density fiberboard

Urea-formaldehyde (UF) resin is one of the most common adhesives used in wood-based composites, including medium density fiberboard (MDF). However, the formaldehyde emission from this resin has created limitations for its use. This study investigated the effects of montmorillonite modified with L-lysine (Lys) on the characteristics of UF resin, formaldehyde emission, and MDF’s physical and mechanical properties. The modification of montmorillonite with Lys was confirmed by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and elemental analysis (CHN). The effects of adding modified montmorillonite on UF resin properties were investigated by FTIR, XRD, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Based on the results of FTIR and XRD, the cross-links increased, and the crystalline surface decreased. Also, DSC showed a delay in resin curing temperature. TGA results indicated an increase in the UF resin’s thermal stability by adding modified montmorillonite. Adding modified montmorillonite at three levels of 1.5, 2, and 2.5% reduced formaldehyde emission by 38, 44, and 50% compared to the control sample. At the 2.5% level, formaldehyde emission reached lower than E1 standard. Also, the modulus of rupture (MOR), modulus of elasticity (MOE), and internal bonding (IB), after adding 2.5% modified montmorillonite, increased by 17%, 11%, and 16%. Whereas, the thickness swelling (TS) and water absorption (WA) decreased by 16% and 13%, respectively. Based on the obtained results, adding modified montmorillonite to UF resin can reduce the formaldehyde emission, and improve the properties of resin and the physical and mechanical properties of MDF.