Polymer protective coatings find use in a manufacturing setting as either weak temporary protective coatings used during multi-step industrial processes, or robust coatings aiming for prolonged, or if possible, permanent protection of surfaces. Such coatings are also utilized within the Swiss watch industry. Known for its precision manufacturing, yet relying on manual application of these resins, the watch industry can significantly benefit from applying polymeric resins through automated processing, and if possible, stronger yet easily and cleanly removable polymer coatings.
The main objective of this thesis was to investigate alternative materials for protective coatings and their relevant coating and printing processes. The ideal solution was defined based on being photo-curable, printable on metal surfaces without pre-treatment, providing mechanical protection for its substrate, on-demand and cleanly removable under mild conditions. The thesis focused on themes such as nanoparticle reinforcement of photo-cured soft polymers for hardness and wear resistance improvement, structural changes in photo-cleavable polymers when subjected to light, adhesion of hydrogels on metal surfaces, grafting functionalities onto nanoparticles and their quantification, and solvent-based polymer removal.
Rapidly photo-curing but weak thiol-ene resins were chosen as the base polymer for reinforcing with nanocellulose particles. The mechanical performance of the polymer could be improved significantly by adding surface-modified nanocellulose as evidenced by 3.4x surface hardness and prevention of wear at the same testing conditions. Moreover, these shear-thinning resins were utilized in preparing superhydrophobic surfaces using UV nanoimprint lithography by replicating morphology of lotus leaves.
Adhesion of hydrogels with nanocellulose was investigated by a rheometer via pull-out tests. In swollen gels with more nanocellulose, the force at break and fracture energy were improved. Moreover, incorporating a polyethyleneimine adhesion promoter into photo-cleavable hydrogels increased fracture energy by 3.25x and changed the fracture mode from adhesive to cohesive.
Nanocellulose was additionally surface-modified with cinnamates. Before embedding these particles in cinnamate-based thiol-ene resins, the grafted particles were assessed for their grafting density. This was achieved by a UV-visible spectroscopic approach, which involved a Beer-Lambert law-derived absorbance calculation methodology. Lastly, the grafting of cinnamate-functionalized nanocellulose was calculated as 40.3 % and 1.49 cinnamate per nm2.
Lastly, cinnamate-based thiol-ene resins and their composites with methacrylate-functionalized nanosilica and cinnamate-functionalized nanocellulose were assessed for photo-curing, mechanical protection, printability and removal by environmental stress cracking. The mechanical performances were outstanding, resulting with a 211.8 MPa hardness for the base poly
