Effects of monomer type and oligomer-to-monomer ratio on UV-curable coating performance on paper substrates

Sustainable ultraviolet-curable coatings were developed from jatropha-oil-based epoxy acrylate (EJOLA) for paper substrate applications, with the objective of evaluating the combined influence of monomer type and oligomer–monomer ratio on coating performance. Three monomers with different functionalities, 1,6-hexanediol diacrylate (HDDA), tripropylene glycol diacrylate (TPGDA), and trimethylolpropane triacrylate (TMPTA), were incorporated, while the EJOLA content was varied from 10 to 90 wt% to establish structure–property relationships. An intermediate composition of approximately 50 wt% EJOLA provided the most balanced formulation, where viscosity was sufficiently controlled to maintain flowability while preserving adequate chain mobility for uniform network formation on the porous paper substrate. FTIR analysis confirmed the progressive consumption of reactive double bonds and the formation of crosslinked networks during ultraviolet irradiation, with conversion exceeding 90% within approximately 16 s, indicating efficient photopolymerization. Coating performance was strongly dependent on monomer functionality, where TMPTA formulations exhibited faster curing and produced smooth, high-gloss surfaces, whereas HDDA and TRGDA formulations demonstrated superior wetting, penetration, and adhesion due to their greater flexibility and enhanced interaction with the fibrous paper matrix. This study highlights the coupled role of oligomer–monomer ratio and monomer functionality in governing rheology, curing behavior, and interfacial coating performance, demonstrating the potential of EJOLA as a tunable sustainable platform for paper-based coating applications.