The demand for bioplastic material for industrial applications is increasing. However, moisture absorption and low mechanical strength have limited the use of bioplastic in commercial-scale applications. Macroalgae is no exception to these challenges of bioplastics. In this study, Kappaphycus alvarezii macroalgae were reinforced with lignin nanoparticles. Lignin nanoparticles (LNPs) were used as a filler to reduce the brittleness and hydrophilic nature of macroalgae (matrix). Lignin nanofiller was produced using a green approach from black liquor of soda pulping waste and purified. The physical, mechanical, morphological, structural, thermal, and water barrier properties of LNPs with and without the purification process in macroalgae films were studied. The bioplastic films’ functional properties, such as physical, mechanical, thermal, and water barrier properties, were significantly improved by incorporating purified and unpurified LNPs. However, the purified LNPs have a greater reinforcement effect on the macroalgae than unpurified LNPs. In this study, bioplastic film with 5% purified LNPs presented the optimum enhancement on almost all the functional properties. The enhancement is attributed to high compatibility due to strong interfacial interaction between the nanofiller and matrix. The developed LNPs/macroalgae bioplastic films can provide additional benefits and solutions to various industrial applications, especially packaging material.

The development of bioplastic materials that are biobased and/or degradable is commonly presented as an alleviating alternative, offering sustainable and eco-friendly properties over conventional petroleum-derived plastics. However, the hydrophobicity, water barrier, and antimicrobial properties of bioplastics have hindered their utilization in packaging applications. In this study, lignin nanoparticles (LNPs) with a purification process were used in different loadings as enhancements in a Kappaphycus alvarezii matrix to reduce the hydrophilic nature and improve antibacterial properties of the matrix and compared with unpurified LNPs. The influence of the incorporation of LNPs on functional properties of bioplastic films, such as morphology, surface roughness, structure, hydrophobicity, water barrier, antimicrobial, and biodegradability, was studied and found to be remarkably enhanced. Bioplastic film containing 5% purified LNPs showed the optimum enhancement in almost all of the ultimate performances. The enhancement is related to strong interfacial interaction between the LNPs and matrix, resulting in high compatibility of films. Bioplastic films could have additional advantages and provide breakthroughs in packaging materials for a wide range of applications.