(590g) Incorporation of Unmodified Technical Kraft Lignin Particles in Anticorrosive Epoxy Novolac Coatings

To protect steel structures from corrosion in harsh environments, high-performance anticorrosive coatings are commonly used. However, due to an increasing demand for environmentally friendly alternatives, there is a need to incorporate renewable raw materials in coating formulations.

The present study aims at replacing pigments and fillers with technical Kraft lignin particles in epoxy novolac coatings. Furthermore, the influence of Kraft lignin particles on the anticorrosive properties of the coating were evaluated and compared with an epoxy novolac coating containing iron oxide pigment (IO-EN), a commercial coating and a neat (particle-free) epoxy novolac coating (neat EN), using salt spray exposure, rust creep assessment (ISO 12944-9), and chemical resistance test. Methods, such as scanning electron microscopy (SEM), size exclusion chromatography (SEC), differential scanning calorimetry (DSC), pull-off adhesion, and König pendulum hardness, were used to study the thermal and mechanical properties of lignin-based epoxy novolac coatings.

Compared to the IO-EN coating and commercial coating, the lignin-based EN (L-EN) coating showed about 6% and 8% lower rust creep after 70 days of salt spray exposure. However, no surface defects or chemical degradation were observed on any of the coatings.

The L-EN coating showed an excellent adhesion strength (23 MPa) and impact resistance (0.49 N), exceeding the values for both commercial (17 MPa and 0.41 N) and lignin-based diglycidyl ether bisphenol F (L-DGEBF) coatings (13 MPa and 0.07 N). Furthermore, the addition of lignin particles did not influence the chemical resistance, hardness, or glass transition temperature of the epoxy novolac coatings.

This study highlights the potential physical and chemical interactions between lignin particles and epoxy novolac, and elaborates the orientation of lignin particles within the coating matrix. Finally, Kraft lignin particles, without solvent fractionation and/or chemical modification, can be incorporated into heavy-duty coatings as a bio-based alternative to pigments and fillers, thereby presenting an opportunity to reduce the use of fossil-based ingredients in anticorrosive coatings.