Performance of Polyurethane Formulations With Partially Bio‐Based Isocyanate Trimer and Aliphatic Diisocyanate as Reactive Diluent

ABSTRACT Following a trend for enhancing bio‐based content in polyurethane coatings in parallel with better performance, isocyanates (i.e., 1,5‐pentamethylene‐diisocyanate trimer (PDI; partially bio‐based), 1,6‐hexamethylene diisocyanate trimer (HDI; fossil‐based), and a partially bio‐based reactive diluent) were blended and crosslinked with a branched fatty‐acid‐based polyol. The intrinsic properties such as viscosity, reactivity, and thermo‐mechanical properties of PDI‐based and HDI‐based polyurethanes were compared with microhardness, scratching resistance, gloss, hydrophobicity, and abrasive wear of the coatings. The PDI‐based formulations exhibited higher viscosity, enhanced reactivity, and better compatibility with the reactive diluent, resulting in superior processing. The PDI‐based coatings possess lower thermal stability, but higher glass transition temperatures, greater storage modulus, and lower tan δ values, in parallel with a higher crosslink density. While adding a reactive diluent introduces flexibility and reduces crosslink density, the progressive weakening was less significant for PDI‐based coatings. Mechanical testing confirmed improved microhardness, hydrophobicity, gloss, and abrasive wear resistance for PDI‐based coatings. The specific wear rates were directly related to the microhardness. Scratch resistance and surface morphology analyses further demonstrated ductile behavior in PDI‐based coatings versus brittle fracture in HDI‐based systems. Based on infrared spectroscopy, free isocyanates were identified in HDI‐based coatings, and good homogeneity was detected in PDI‐based coatings.