Synthesis of Lignin-Phenolic-Formaldehyde (LPF) Resin and its Application as a Binder in Rice Husks (RH) Particle Boards

Lignin-phenol-formaldehyde (LPF) resins were synthesized using lignin isolated from spent black liquor obtained after pineapple peals waste pulping. It was first precipitated using hydrochloric acid followed by fractionation in methanol, and acetone before being utilized in the synthesis of LPF resin used as binders in rice husks particle boards (RH-PB). The preparation of LPF resin was accomplished using molar ratios of lignin, phenol, formaldehyde of 0.3:0.7:1.5 in 10 % NaOH solution in 200 ml methanol. The functional groups, degree of crystallinity, thermal properties, and morphology of the fractions were then studied using Fourier Transform Infrared spectroscopy, powder diffraction, thermal gravimetric analysis and scanning electron microscopy. From the results obtained, all the fractions had hydroxyl functional groups, methyl functional groups, and carbonyl functional groups typical of lignin though at slightly different vibrational frequencies. However, the three fractions had varying degrees of crystallinities and morphology with some having sharp distinct peaks typical of soda lignin with spherical and cubicle particles while others were amorphous in nature comprising of nanoplatelets. The optimum temperature for the preparation of the resin was found to be 100 ℃ for 2 hours while the curing temperature for the medium density particle board was found to be 120 ℃ for 3 hours when using a rice husk to resin ratio of 1:2 % w/w. In conclusion, lignin isolated from pineapple peal waste during cellulose isolation can be used to prepare LPF resoles that can be used in the development of RH-PB with good mechanical and water resistance properties when compared to commercial particle boards.