Freeze–thaw durable, oil-resistant molded pulp via lignin-driven fiber welding and conformal coating for sustainable plastic alternatives

Pulp-molded utensils (PMUs) are gaining attention as biodegradable alternatives to petroleum-based plastics, yet their adoption is hindered by poor freeze–thaw durability and the lack of fluorine-free oil resistance strategies. Here, a bio-based and scalable approach was presented to fabricate robust, oil-resistant PMUs by leveraging lignin-driven fiber welding and conformal coating with poly(3-hydroxybutyrate- co -4-hydroxybutyrate) (PHB). Residual lignin undergoes thermocompression-induced self-fusion and inter-fiber crosslinking, enhancing structural cohesion and network densification. Simultaneously, co-melted lignin and PHB form a continuous surface barrier, imparting superior oil repellency (Grade 12) and effectively blocking hot oil penetration. The resulting PMUs exhibit high density (0.83 g cm −3 ), low porosity (42.49 %), and mechanical strength up to 25 MPa, while maintaining integrity over multiple freeze–thaw cycles. Life cycle analysis confirms full biodegradability and a reduced carbon footprint. This lignin-enabled strategy offers a sustainable and high-performance route for disposable tableware.