Functionalized Starch Nanoparticles for Pulp-Based Active Packaging

Abstract

The characterization of functionalized cationic starch nanoparticles (StNPs) was conducted in this study. Three different strategies in the preparation of sustainable and biodegradable active packaging materials were explored. These strategies are: (1) to improve wet and dry strength by optimizing the composition of the pulp paper; (2) to introduce an antimicrobial component to the pulp using silver nanoparticles (AgNP); and (3) to explore paper sizing using hydrophobically modified starch. Firstly, cationic StNPs were used in combination with long or short cellulosic fibers (LCF and SCF) to enhance the dry and wet tensile strength of the pulp hand sheets. It was found that the wet and dry tensile index could be enhanced by 35% and 106%, respectively, over unmodified hardwood pulp. Additionally, it was found that the amount of SCF in the system correlated with the time it took to form the hand sheet in the filtration apparatus. The StNPs alone had no effect on the filtration time, but an increase in filtration time was observed when combined with SCF. It was observed that the hand sheets retained most of their tensile performance after undergoing repulping to reform the hand sheet. Secondly, a method for introducing AgNPs into the pulp matrix to prepare antimicrobial hand sheets was evaluated. A green synthesis route was employed using tannic acid (TA) coated StNPs to reduce and stabilize the AgNPs. The size of the AgNPs could be altered by adjusting the concentration of TA and StNPs. The smallest AgNPs were observed for the highest concentrations of both TA and StNP. AgNPs impregnated hand sheets were prepared via the wet-end (pulp slurry) or dry-end (formed hand sheet) addition of the silver ions. Four different hand sheets were tested and compared with the control sample; namely the wet-end addition, dry-end addition with two different concentrations of AgNO3, and finally hand sheets containing only TA coated StNPs. All the hand sheets displayed enhanced antimicrobial activity for both E. coli and S. aureus, with the hand sheets prepared with AgNPs added in the dry-end step possessed the highest activity. These hand sheets also showed an increased tensile strength over the control for both wet and dry strength. The wet-end addition hand sheets had a reduced water vapour transmission rate (WVTR), while the other hand sheets showed an increased WVTR over the control sample. Lastly, the sizing effect of the wet-end addition of water dispersible amphiphilic StNPs on pulp paper was demonstrated. Hand sheets produced using amphiphilic StNPs were able to temporarily repel water for several seconds and possessed a contact angle greater than 90°; a threshold for hydrophobic system. These hand sheets displayed increased dry tensile strength with no change in the wet strength. Additionally, these hydrophobic forces had no impact on the drying rate of the hand sheets. The use of active packaging components will help reduce the negative influence of food waste on the environment by extending the shelf-life of perishable food products. Moreover, as the world recognizes the negative impact of using non-renewable materials and non-biodegradable plastics that accumulate in landfills and oceans, this work will offer a sustainable solution in the field of advanced packaging materials.