The effect of pulp type on the performance of microfibrillar lignocellulosic bismuth-based active packaging material

The study aims to investigate the effect of the different lignocellulosic pulp on the composite properties for active packaging application. Microfibrillated cellulose from bleached and unbleached Kraft and thermomechanical pulp (TMP) having different cellulose, hemicellulose, lignin, and extractive content were used as the matrix phase with antimicrobial bis -phosphinato bismuth complex as the dispersed phase. The Kraft pulp has thinner fibres as observed in the SEM images and have higher aspect ratio (EMT 109–157) compared to TMP (EMT 43–51). So, it is more easily fibrillated resulting in a strong close network and therefore resulting in low water vapor transmission rate (WVTR) and high tensile index (20–91 g/m 2 .day and 59–78 Nm/g respectively) compared to the TMP ones (153–261 g/m 2 .day and 35–43 Nm/g respectively). While the physical dimension of the fibres controls the mechanical and barrier properties, the leaching and antibacterial performance is related to the bonding of the complex with the matrix. The high hydrophilicity of the bleached kraft pulp results in a weak bond with the hydrophobic bismuth complex, easing its release to kill the surrounding microbial population and thus resulting in larger zones of inhibition against both Gram-positive and Gram-negative bacteria. Therefore, bleached kraft pulp was found to be the most suitable with promising barrier, mechanical and antibacterial properties.