Urea glyoxal and urea melamine glyoxal wood adhesives hardened with acid ionic liquid for particleboard pressing

In wood based panel industry, formaldehyde based adhesives are widely employed for bonding, and formaldehyde released from panels negatively affects the environment and human health. Decreasing formaldehyde emission without compromising mechanical properties is an important challenge. In this study, urea glyoxal (UG) and urea melamine glyoxal (UMG) resins were synthesized as non-formaldehyde adhesive, and the effects of melamine content were investigated. Furthermore, an acid ionic liquid named as N-methyl-2-pyrrolidone hydrogen sulfate, was synthesized and used as hardener for particleboard pressing. The solid content, gel time, and viscosity of the synthesized resins were determined. In addition, the structures of these resins were investigated by means of Fourier transform infrared spectroscopy (FTIR) and solid-state cross-polarization/magic angle spinning nuclear magnetic spectroscopy (CP-MAS ¹³C NMR). Thermal properties of resins were determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The obtained samples were also characterized morphologically by scanning electron microscope (SEM) and scanning electron microscope energy dispersive X-ray analyses (SEM EDEX). The synthesized resins and hardener were employed for particleboard pressing in laboratory scale. All of the pressed particleboards were evaluated as P1 class according to EN 312 standard. The formaldehyde content was determined with the perforator method (EN 12460-5) resulting in E1 classification. Furthermore, as a whole, the particleboards fulfil E0 and F**** criteria according to well-acknowledged approaches in determining formaldehyde emission.