Paper and molded fiber packaging products feature per- and poly-fluoroalkyl substances (PFAS) that pose severe threat to human health and the ecosystem. In response to the urgent need to migrate away from PFAS coatings and to develop eco-friendly and sustainable single-use packaging, we have developed lignin-based spray coatings. Different chemical functionalization routes of the lignin hydroxyl groups were investigated with the aim of increasing both the oil and water contact angles relative to that of un-coated paper. The chemically modified lignins were blended with water or ethanol, spray coated at 144 ± 2 mg/g of paper, and then air dried prior to contact angle measurements. We also tested the efficacy of lignin micro- and nano-particles, generated using eco-friendly ultrafine grinding and modified using in-situ aqueous chemical means, for further increasing the oil contact angle. The best-performing chemical modification scheme was optimized for variable pH (1, 4, 9) of the spray coating formulation and the particle size of lignin (100 to 500 nm). The test results indicated that a water contact angle of ≥ 110° and an oil contact angle of ≥ 56° could be achieved using the lignin coatings on paper. Additional characterizations using atomic force microscopy and X-ray photoelectron spectroscopy provided insights on lignin interactions with cellulose fibers and self-assembly of modified lignin coatings. Thus, through comprehensive evaluation of surface chemistry and morphology of lignin-coated-fibers, this study provides a pathway for improving the barrier performance of bio-based coatings to be on par with PFAS.

Developing amphiphobic nanolignin coatings for paper packaging

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