UV-curable waterborne polyurethane coatings: A state-of-the-art and recent advances review

Waterborne polyurethane coatings prepared by UV-induced photoreactions (UV-WPU) are becoming very attractive due to the increasingly stringent environmental demands. They were developed to replace solvent-based polyurethanes in the coatings of wood, paper, plastics, metal, and glass, mainly because of their good physicochemical, rheological, and optical properties. Several UV-WPU formulations have been tested over the years, making their research substantial. However, no valuable review of this literature, focusing on the significant influencing factors in UV-WPU's manufacture, is available to date. This work aims to answer specific questions about the state of these materials' art, such as: "which monomers have been used most in UV-WPU synthesis?", "what type of photo-initiator has promoted the most efficient curing of the material?", "what additives or particles have been tested for composite UV-WPUs?", "which applications have UV-WPUs been directed to?", "what adaptations and technologies have already been tested to overcome the challenges of the process?", among others. As a result of a systematized bibliographic search in four databases, considering the period from January 2000 to July 2020, a total of one hundred and thirty-eight distinct and relevant articles on UV-WPUs were found. From this study, we hope to present a scientific source on the current state-of-the-art of UV-WPU synthesis, providing new combinations of raw materials and intelligent solutions, thus making material and industrial engineers able to mitigate the inconveniences of the process.