Preparation, optimisation and characterisation of lignin phenol formaldehyde resin as wood adhesive

Purpose - The purpose of this paper is to examine the preparation of adhesive by incorporation of kraft lignin as an agricultural waste into phenol formaldehyde (PF) resin structure and to evaluate the mechanical properties of lignin phenol formaldehyde (LPF) as wood adhesive. Design/methodcilogy/approach - PF resin (resole) was prepared using sodium hydroxide as a catalyst. Different concentrations of lignin were incorporated into PF resin structure. The effect of lignin concentration, formaldehyde to phenol molar ratio, catalyst concentration, temperature and time upon solid content, adhesive strength and gel time was studied. The kraft lignin, PF and LPF resins were characterised using FT-IR and thermal analysis. Findings - The incorporation of lignin into PF resin (resole) increases adhesive strength and decreases gel time. The highest adhesive strength and the lowest gel time were achieved at 90 per cent of kraft lignin, formaldehyde to phenol molar ratio, 7.2 and 10 per cent of catalyst, after 4 h and at 80 C. Research limitations/implications - The effect of different concentrations of kraft lignin, formaldehyde/phenol molar ratio, catalyst concentration, temperatures and time upon solid content, gel time and adhesive strength was studied. Practical implications - Incorporation of kraft lignin into resole leads to adhesive with improved mechanical properties. Originality/value - It was found that LPF resin is better than PF resin from the economical point of view and has the better mechanical properties.