High strength polyvinyl alcohol composite films reinforced with lignocellulosic nanofibrils produced from corn stalk with concentrated maleic acid pretreatments

Utilizing corn stalk (CS) as the raw material, lignin-containing cellulose nanofibrils (LCNFs) were prepared through concentrated maleic acid (MA, 60-80 %) pretreatment (30 min) followed by ultrasonic disintegration. As the concentration of MA increased from 60 % to 80 %, the diameter expanded from 22 nm to 34 nm, and the carboxyl content rose from 0.095 mmol/g to 0.131 mmol/g. This phenomenon can be attributed primarily to the esterification reaction between MA and lignocellulosic components in conjunction with the presence of lignin. LCNFs served as reinforcer for fabricating polyvinyl alcohol (PVA)/LCNF composite films, where their mechanical properties were significantly influenced by both type and content of LCNFs used. The composite films reinforced with LCNFs (loading of 14.1 %) derived from a 60 % MA pretreatment exhibited a maximum tensile strength of 25.8 MPa, an elongation at break reaching up to 900.3 %, Young's modulus of 1.9 MPa, and toughness of 150.9 MJ/m3. Conversely, when employing LCNFs (loading of 16.4 %) prepared via an 80 % MA pretreatment, composite films demonstrated enhanced performance metrics including maximum tensile strength of 35.8 MPa, elongation at break of 579.7 %, Young's modulus at 3.5 MPa, and toughness of 150.3 MJ/m3. Furthermore, these composite films exhibited characteristics indicative of closed-loop recyclability. The hydroxyl and carboxyl groups within LCNFs participate in hydrogen bonding with the hydroxyl groups in PVA, thereby significantly improving the mechanical properties of the composite films.