Ecofriendly wood adhesives from date palm fronds lignin for plywood

Abstract

Utilization of lignin phenol glyoxal (LPG) resins was studied as a potential alternative for phenol formaldehyde (PF) resins. Lignin was extracted by alkaline pulping processes (kraft and soda) from date palm fronds (DPF) and was used as an alternative for phenol in LPG resins. The isolated lignin samples were characterized using complementary analyses that included Fourier transform infrared (FTIR) spectroscopy, 13C nuclear magnetic resonance (NMR) spectroscopy, thermal stability, thermogravi-metric analysis (TGA), and differential scanning calorimetry (DSC). Kraft lignin phenol glyoxal (KLPG) and soda lignin phenol glyoxal (SLPG) resins also were characterized in terms of solid content, viscosity, and gel time. Finally, physico-mechanical tests were performed on plywood panels that were treated with different molar ratios of LPG resins. The results revealed that 50% (w/w) KLPG resin resulted in higher tensile strength (65.3 MPa) than PF resin (58.57 MPa), which was potentially attributed to the higher amount of phenolic groups compared to soda lignin. Therefore, the substitution of DPF lignin in LPG resins enhanced the adhesive in terms of its chemical and mechanical properties, enabling it to produce a more environmentally friendly wood adhesive.