Hydrophobicity and mechanical properties of purified lignin nanoparticles reinforced marine-derived biopolymer composites

Lignin has been considered the main aromatic renewable biopolymer. Besides its availability in large quantities as a major and low-cost side product of several industries as a polysaccharide component of lignocellulosic biomass for industrial applications, it remains underutilized and as such, lignin valorization is highly desirable. This study was focused on the fabrication, purification, and characterization of lignin nanoparticles (LNPs) from black liquor of oil palm (Elaeis guineensis) empty fruit bunch (EFB). The functional properties of the LNPs investigated include the morphology, particle size, zeta potential distribution, elemental composition, functional groups, and gas chromatography-mass spectrometry (GC-MS). The purified LNPs provided smaller particle sizes ranging from 32 to 62 nm while the unpurified sample sizes range between 53 and 88 nm. The zeta potential value of purified LNPs displays relatively good stability to the unpurified LNPs despite the consistency in their particle size spreading as observed from the TEM micrograph. The results of the GC-MS analysis signify that the purification procedure affects the compounds in the LNPs. The kappa-carrageenan (KC) biopolymers reinforced with purified LNPs provided more organized surfaces than the biopolymers reinforced with unpurified LNPs, leading to enhanced hydrophobicity and mechanical properties of the bionanocomposites. This study shows the potential applications of valorized lignin from oil palm residue as a reinforcement agent in renewable packaging.Highlights Lignin nanoparticles (LNPs) were yielded from empty fruit bunch black liquor. Syringyl to guaiacyl ratio of LNPs was increased from 0.83 to 1.26. Biopolymers were prepared by incorporating LNPs into the kappa-carrageenan. Biopolymer with 4% purified LNPs had an optimum contact angle of 106.83 degrees. The optimized biopolymer showed an optimum tensile strength of 38.42 MPa. Isolation, purification, and characterization of lignin nanoparticles (LNPs), and functional properties evaluation of kappa-carrageenan biopolymer composites containing different loading levels of unpurified and purified LNPs. image