Application of Lignin‐Phenolic‐Formaldehyde (LPF) Resole as an Adhesive in Rice Husks (RH) Particle Boards

Herein, we report a lignin–phenol formaldehyde resin (LPF) prepared from lignin fractionated from black liquor after pulping pineapple peels. Hydrochloric acid, methanol, and acetone were subsequently added to the liquor to obtain lignin fractions that were used to prepare the LPF resin using lignin, phenol, and formaldehyde in the ratio of 0.3:0.7:1.5 in 10 % sodium hydroxide. The functional groups, degree of crystallinity, thermal properties, and morphology of the fractions were then studied using infrared spectroscopy, powder diffraction, thermal gravimetry, and scanning electron microscopy. From the results obtained, all the fractions had hydroxyl, methyl, and carbonyl functional groups typical of lignin, though at slightly different vibrational frequencies. However, the three fractions had varying degrees of crystallinities with spherical and cubical particles, while others were amorphous in nature, comprising nanoplatelets. The optimum temperature for the preparation of the resin was found to be 100°C for 2 h, while the curing temperature for the medium‐density particle board was found to be 120°C for 3 h when using a rice husk to resin ratio of 1:2 % w/w. In conclusion, lignin can be used to prepare LPF resin binders to make RH‐PB with good mechanical and water resistance properties.