Isolation, Characterization, and Utilization of Coconut Pith Lignin in a Biobased Adhesive

In the study, lignin was extracted from coconut pith (CP) using soda pulping method, utilizing Response Surface Methodology to optimize key process parameters. The dependent variables were the extraction temperature and time, and NaOH concentration, with the yield (g lignin/10 g material) as the response. The statistical results identified ex-traction temperature (ρ = 0.0044) and time (ρ = 0.0035) as significant factors. NaOH con-centration, though not significant individually (ρ = 0.757), exhibited interaction effect with time (ρ = 0.006). The theoretical optimal extraction conditions were 159.0 °C, 169.0 min, and 2.1% NaOH, under which an actual coconut pith lignin (CPL) yield of 1.806 g/10 g CP was achieved. Characterization of CPL showed a composition of 92.96 ± 0.32% ac-id-insoluble lignin. To demonstrate its applicability, CPL was incorporated into a phenol-formaldehyde (PF) adhesive formulation, substituting the phenol component. The Adhesive Shear Strength Test demonstrated that the lignin-formaldehyde (LF) adhesive had a mean failing load of 0.819 kg/cm², nearly half that of the prepared PF adhesive at 1.78 kg/cm². The FT-IR spectra of the CPL and LF adhesives revealed notable differences in the 1750 – 1000 cm⁻¹ region, suggesting distinct structure and bond formations. These findings illustrate the potential of CPL as a sustainable phenol substitute in industrial adhesive formulations and in other applications.