Impact of Sulfur Vulcanization and Electron Beam Irradiation on the Properties of Antimicrobial Natural Rubber/Lignin Composite Films

Lignin and sodium lignosulfonate (SLS) are gaining attention as sustainable additives to improve the mechanical and antimicrobial properties of natural rubber (NR) composite films. However, their performance under different vulcanization methods, including sulfur vulcanization and electron beam (EB) irradiation, remains inadequately investigated. This study compares these methods using lignin and SLS at concentrations of 1 and 3 phr (parts per hundred rubber). Sulfur vulcanization with 3 phr lignin achieved superior mechanical properties, including a tensile strength of 27.8 MPa, elongation at break of 840%, and a 100% modulus of 1.18 MPa, compared to EB irradiation, which yielded a tensile strength of 16.3 MPa, elongation at break of 802%, and a 100% modulus of 0.89 MPa at the same concentration. Conversely, SLS at 1 phr enhanced tensile strength and modulus in sulfur-vulcanized films but showed minimal effects in EB-irradiated films. Antimicrobial tests demonstrated that sulfur-vulcanized films and EB-irradiated films with SLS inhibited bacterial growth against <i>Staphylococcus aureus</i> and <i>Escherichia coli</i>. These results highlight the superiority of sulfur vulcanization in enhancing both the mechanical and antimicrobial properties of NR composites while also underscoring the potential of lignin and SLS as sustainable reinforcements.