Reinforcement of paper sheets with subcritical water-treated cellulose for improved mechanical strength and resistance to water, oil, and grease

Abstract The excessive use of non-biodegradable plastics has raised serious environmental concerns, indicating the urgent need for biodegradable packaging materials. Thus, paper packaging systems have gained increasing attention. However, their weak mechanical strength and insufficient barrier properties limit their practical applications. To address these limitations, a paper-based packaging system reinforced with subcritical water-treated cellulose (SWT-C) was developed to enhance mechanical and barrier properties in this study. The specimens were prepared by incorporating varying concentrations of SWT-C into softwood and hardwood pulps. Their structural, physical, and chemical characteristics were evaluated using SEM images, FTIR analysis, XRD test, and BET surface area measurements. Mechanical properties were evaluated with tensile test and barrier performance was assessed by Cobb60 water absorption test and oil and grease resistance (OGR) test. As a result, the pore volume of both pulps decreased from 0.9546 cm³/g to 0.04253 cm³/g with increasing SWT-C incorporation, as confirmed by SEM observations and BET analysis. This reduction in porosity may contribute to an increase in tensile strength, reaching a maximum of 35.91 MPa. Both paper sheets reinforced with SWT-C showed a substantial reduction in Cobb60 and OGR tests, indicating enhanced water and oil resistance. In conclusion, SWT-C improved the performance of paper sheets mainly through pore filling, network densification, and hydrogen bonding reinforcement. The findings in this study demonstrate that SWT-C serves as an effective reinforcing agent to improve the mechanical strength and barrier properties of paper packaging system, thereby showing its potential for application in the industry.