Enhanced Fluorescence Emission and Thermomechanical Properties of Cardanol Polyol-Modified Waterborne Polyurethanes

Waterborne polyurethane dispersions (WPUs) based on renewable polyols have attracted significant attention due to their design versatility in structure and properties. Polyols based on cardanol, a byproduct of the cashew processing industry, have assumed significance as a nonedible renewable feedstock oil, owing to their plentiful availability and structural diversity. In this article, we report the fluorescence emission and thermomechanical properties of WPUs with Glycard, a renewable cardanol polyol. The segmented structure of the PU is influenced by the incorporation of Glycard into the polyurethane backbone, imparting tunable fluorescence, apart from controlling the thermomechanical and film formation properties, as probed using particle size data and FTIR, XPS, TEM, XRD, and AFM techniques. The incorporation of Glycard markedly enhances the propensity for crystallization, microphase separation, and film properties, such as gel content increasing from 0 to 20.3%, water contact angle rising from 53 to 73°, and Shore A hardness increasing from 59 to 83, as the Glycard concentration is increased from 0 to 20 wt %. Detailed photophysical studies revealed enhanced microphase separation and tunable blue fluorescence emission due to clusterization-triggered emission (CTE) of aggregated fluorophores in waterborne polyurethanes. PUG with 20 wt % Glycard displayed a 7-fold increment in emission intensity as compared to the bare PU. Studies confirm that the utilization of biobased cardanol polyol improves performance and yields fluorescent waterborne polyurethanes with enhanced processability and low water absorption, demonstrating their potential for textile, leather coatings, and other applications.