Interaction of porous substrate and vegetable oil-based hydrophobic thermoset coatings during UV-polymerization

In the current study, we report the progress in developing new UV polymerizable hydrophobic biobased coatings from modified vegetable oil for porous substrates like paper and wood. The aim was to produce novel hydrophobic coatings on porous substrates and investigate how the porous nature of the substrates will be affected by different chemical formulations that penetrate into the interior of the substrate during the exposure to different intensities of UV light, and what hydrophobic properties that interaction will result in. The curing formulations were based on acrylated epoxidized linseed oil (AELO) as a prepolymer. For the UV polymerization, 1-hydroxycyclohexyl phenyl ketone (Irgacure 184) was used as a photoinitiator; isobornyl acrylate (IBA) and isosorbide methacrylate (IM) were used as bio-based diluents; hexadecyltrimethoxysilane (HDTMS), vinyl-polydimethylsiloxane (v-PDMS), triethoxyoctylsilane (TEOS) were used as hydrophobic additives and they were added in different concentrations to the AELO curing formulations. The formulations were then cured under UV light on wood and paper substrates. FT-IR analysis showed that the AELO resin was successfully polymerized on both paper and wood substrates, and by contact angle measurements it was found that the highest hydrophobicity was achieved for the coatings that contain HDTMS (108° in average). The layer thickness on wood substrates was in between 9 and 20 µm, and on paper substrates between 8 and 24 µm. Only about a 5° difference in contact angle was observed between the coatings with respect to change in diluents and different UV light intensity. All cured samples showed a good chemical resistance to acetic acid, citric acid and ethyl alcohol after 1 hour exposure; to acetone and ethylbutyl acetate after 10 s, and to benzine after 2 minutes. Outstanding hydrophobic behavior was observed for the HDTMS coatings, however, better physical properties were determined for the coatings containing v-PDMS and TEOS, on which the scratching was observed after the applied force of 1.5 and 0.6 N in comparison to HDTMS coatings (0.4 N). The resulting properties achieved for the AELO coatings indicated that it has a potential to be used for wood coating and packaging application.