Fast Curing of a Biobased Polyhydroxyurethane Thermoset Using Near-Infrared Photothermal Effect

Polyhydroxyurethanes (PHU), which are obtained by the reaction of cyclocarbonates and amines, represent an eco-friendly alternative to conventional polyurethanes because their synthesis relies on CO₂-based precursors, avoids the use of toxic isocyanates, and allows introducing additional functionalities (“hydroxy”) in the polymer backbone. However, the low reactivity of the cyclocarbonates’ aminolysis to form polyhydroxyurethane represents a major drawback, particularly for industrialization. To overcome this lack of reactivity, through this study we propose the use of the photothermal effect generated by the organic heater 2-chloro-3-[2-(1,1,3-trimethylbenz[e]indolin-2-ylidene)ethylidene]-1-[2-(1,1,3-trimethylbenz[e]indolium-2-yl)vinyl]cyclohexene p-toluenesulfonate (IR-813 p-toluenesulfonate) absorbing in the near-infrared (NIR) region. IR-813 was chosen because of its commercial availability and its good solubility in organic resins and REACH-registered behavior. It was added to a formulation composed of trimethylolpropane tricarbonate (TMPTC) and 1,5-pentanediamine, the curing of which under NIR light (850 nm) was subsequently studied. Various parameters were varied, such as the amount of IR-813 “heater” and the irradiance of the light-emitting diode (LED) source, and their influence on gel time and maximum reached temperature were evaluated. The best system allowed reaching a temperature of 150 °C, a gel time of 3 min, and a gel content of 94%, using only the light generated by the NIR light-emitting diode (LED) as external energy source. Finally, the energetic costs associated with LED curing were compared with those of conventional thermal curing. By providing an energy savings of 36%, photothermal curing using LED proved to be a more sustainable alternative than conventional thermal curing using ovens.