Eco-friendly fabrication of multifunctional lignin-based black films for sustainable agriculture

To address the environmental challenges concerns associated with petroleum-based agricultural films, we developed a sustainable approach for fabricating multifunctional lignin-based black films using a γ-valerolactone (GVL)/water binary system as a green solvent. Industrial alkali lignin was effectively dissolved at low temperatures and subsequently crosslinked with bis-epoxy agents (BDDE or PEGDE) to construct a dense, three-dimensional (3D) polymeric network. The optimized films exhibited robust mechanical properties, with a tensile strength of 23.7 MPa, elongation at break of 21.8 %, and toughness of 4.1 MJ/m³. In addition, they demonstrated moderate oxygen barrier properties (31.6-36.2 cm³/(m²·24h·0.1 MPa)), favorable carbon dioxide permeability (206-217 cm³/(m²·24h·0.1 MPa)), and outstanding water vapor barrier performance (WVTR: 219.8 g/(m²·day)). The films also exhibited high light-blocking efficiency (>99 % opacity) and strong photothermal conversion capabilities. These synergistic properties confer effective moisture retention, temperature regulation, and gas-selective barrier properties, fulfilling critical agricultural requirements. Importantly, the environmentally benign and recyclable solvent system, coupled with the high lignin content (up to 67 wt%), aligns with the principles of the circular economy, offering a viable and sustainable alternative to conventional polyethylene mulch films. This work highlights the significant potential of lignin as a renewable resource for the development of eco-friendly, high-performance agricultural materials.