Lignin derived from <i>Borassus flabellifer</i> leaves as a nano-filler for polyhydroxybutyrate composites

Deterioration of the environment is occurring at an alarming rate due to the widespread use of plastics. Conventional plastics do not degrade easily and pose severe environmental threats. Hence, it is imperative to devise a sustainable solution to reduce their detrimental impact on our ecosystem. The applications of polyhydroxybutyrate (PHB) are limited due to its shortcomings, such as low tensile strength, poor thermal stability, and inherent brittleness. In the present study, lignin, another natural polymer, was blended with the polymer PHB to address these limitations. Lignin, extracted from the leaves of Borassus flabellifer, is a complex polymer second only to cellulose in abundance. It possesses excellent mechanical properties, good toughening capacity, and disease resistance in plants, making it a promising co-polymer for PHB. Upon blending the polymers PHB and lignin, the composite film was further assessed for structural, mechanical, and thermal analysis. Incorporation of 20% lignin into PHB increased the tensile strength from 0.5 MPa (pure PHB) to 1.05 MPa. Water absorption after 24 h was reduced from 13% in PHB to 10% in the composite, indicating improved hydrophobicity due to effective lignin integration. Enhanced thermal properties were also observed, with the composite film showing a degradation temperature of 300°C, compared to 290°C for PHB alone. These findings affirm the improved thermal stability and durability of the composite film. Furthermore, PHB-lignin composite films hold strong potential for applications in sustainable food packaging systems as the polymers involved are entirely bio-derived and bio-stable. The approach demonstrates a simple yet effective method for enhancing biopolymer performance using plant-derived additives. The developed composite offers a promising alternative to synthetic packaging materials, aligning with global sustainability goals.