Wrinkling and de-wrinkling of renewable barrier-enhanced polymer thin films on paper through a roll-to-roll system

Paper has been an advantageous material in various applications, including renewable food packaging, particularly barrier packaging with the use of coatings. However, due to swelling and capillary forces during the coating process, coating defects can occur, such as wrinkling, a permanent deformation that arises after drying. Such defects can impact the performance of the barrier coating. In this study, the onset and mechanisms of millimeter-scale wrinkling of paper coated with newly developed renewable barrier biopolymers (cellulose nanocrystals (CNCs) and UCARE™ JR-125) are investigated through scalable slot die and Mayer rod coating techniques. Modifications to process conditions of edge-constraint control and vacuum assistance are applied to mitigate the wrinkling instability and accommodate stable and consistent coating results in both the wet and dry states. Results show machine directional edge-taping can effectively de-wrinkle the coated sheets due to reduced constraints, allowing greater relaxation during swelling and deswelling. Wrinkling orientations are also found to be adjustable through vacuum assistance by alternating the dominant localized compressive strain. Further, the de-wrinkled coated papers obtained enhanced oxygen barrier performance with high uniformity. This work establishes a pathway to innovative, high-performance paper coating with biodegradable materials, suitable for food packaging, bioelectronics, and other sustainable applications. • Correlated millimeter-scale wrinkling in renewable polymer films on papers to barrier performance. • Introduced a scaling model relating edge constraints, coating thickness, and material properties to predict wrinkle behavior. • Developed edge-taping and vacuum-assist for roll-to-roll coating to enhance film uniformity and barrier performance. • Provided mechanistic understanding of how wet film wrinkle formation affects final functional performance. • Applied viable renewable-polymer coating strategies for high-performance, sustainable packaging.