A pathway to large-scale surface modification of CNF-coated food serving containers made from lignocellulosic materials, Advanced Coating Symposium (TAPPICon26)

Molded fiber is regaining popularity for food service applications attributed to growing concerns about plastic pollution and environmental sustainability. However, to make molded fiber products water and grease resistant, per- and polyfluoroalkyl substances (PFAS) have been traditionally added to the system. With widespread bans on PFAS in food contact applications and limitations of current available chemistries, there is a need for robust biobased coatings for these products. Previously, we mixed various types of raw materials with cellulose nanofibrils (CNFs) as a binder to develop an environmentally safe composite system for food serving containers to get rid of PFAS. The lignocellulosic materials used to make paper plates were wood fiber (WF) or thermomechanical pulp (TMP) and bleached Kraft pulp (BKP). The molded paper plates were laminated with CNFs to impart grease resistance. Although the CNF coating by itelf also reduced water absorption, this reduction is still not enough for food serving containers. The laminated samples then underwent surface modification under gas phase with reactants such as hexamethyldisilazane (HMDZ), methyltrimethoxysilane (MTMS), and trimethylmethoxysilane (TMMS) with pyridine as a catalyst, as silanes can form 2D polymers by reacting with adsorbed water on the surface. In this work, we investigated a pathway to scale up our reaction for commercial use. CNF films and paper plate specimens were treated with the reactant (MTMS) using wet air to ensure sufficient water on the surface of the paper plate for 2D polymerization, thereby improving the reaction rate. To optimize the setup, wet air was mixed with dry air to control humidity and ultimately equilibrate the reaction. The CNF coated paper plate, treated under controlled humidity with wet air to ensure sufficient surface moisture, showed improvements in Cobb value (g/m2) and contact angle (o) by 43% and 52%, respectively, compared to treatment with no water addition. The Cobb value increased by 50% and 70% after 5 minutes and 120 minutes of treatment time, respectively, compared to untreated specimens. The contact angle improved to 99 ± 9o after 5 minutes of treatment and 30 seconds of contact curing in a hot press.

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