Preparation of tough, antioxidant and antibacterial bioplastic for sustainable packaging through an in situ phenolization strategy†

Abstract

Bioplastic packaging derived from renewable and biodegradable lignocellulose presents a promising alternative to petroleum-based plastics. However, the preparation of bioplastic packaging faces problems related to its inadequate mechanical strength and multifunctionality, stemming from weak interactions between and low chemical activity among its components. Herein, we have reported a facile in situ phenolization strategy to produce highly active components directly from wood in a ternary phenolic-based deep eutectic solvent (ChCl)/oxalic acid/resorcinol), enabling the assembly of high-performance bioplastic. In this process, the ether bond of lignin in wood is protonated to form a benzylic carbocation, which then in situ traps resorcinol to incorporate phenolic active sites into lignin. Consequently, the phenolic hydroxyl content of lignin increases to 10.43 mmol g⁻¹, approximately 14 times higher than that of milled wood lignin. The phenolic lignin can provide multiple binding sites that tightly bond with cellulose, forming a robust network through enhanced hydrogen bond interactions. The resulting bioplastic, denoted as Ph-bioplastic, exhibits a tensile strength of ∼160 MPa and enhanced toughness of ∼20 MJ m⁻³, 3 times greater than that of the non-phenolized bioplastic. Furthermore, the plentiful active sites provided by phenolized lignin enable the reduction of silver nanoparticles within the cellulose–lignin network. The Ph-bioplastic exhibits excellent oxidation resistance, achieving a DPPH radical scavenging rate of ∼100%, and possesses antimicrobial properties. Additionally, the Ph-bioplastic also demonstrates excellent biodegradability and can be recycled through mechanical decomposition. This in situ phenolization strategy provides an efficient, economical and environmentally friendly pathway for sustainable packaging materials from natural resources.