High-Performance Multiscale LNPs from Black Liquor as Repulpable Paper Coatings with Enhanced Water, Oil, and Vapor Resistance

Technical lignin in alkaline pulping black liquor is usually combusted for energy in a soda recovery unit. To improve resource utilization, multiscale lignin nanoparticles (LNPs) were acid precipitated from black liquor and combined with gelatinized starch (SS) to produce a series of uniformly mixed surface coating agents to enhance the barrier properties of paper materials including water, oil, and water vapor resistance. The coating with 20%SS and 50%LNPs (based on oven-dried SS) with a diameter of 276 nm could significantly improve the barrier properties of the coated paper. Cobb 60 decreased by 79.6% from 67.98 to 13.86 g/m², Kit rating improved from 0 to 10, and water vapor transmission reduced from ≥3000 to 441.69 g/m²·day. The coated paper presented superior mechanical properties, thermal stability, repulpability, and biodegradability. This work provides an effective strategy for the high-value application of pulping black liquor and holds promise for paper-based packaging.