Comparative study of fire-resistant coatings based on high and low molecular weight tannins

In order to provide adequate fire resistance to construction materials, such as steel and wood, the use of high and low molecular weight tannins (TMw-H and TMw-L), extracted from the bark of Pinus radiata , as carbonaceous agents, was studied. The extracts were fully characterized by GPC, HPLC, and UV to determine the total amount of phenols, percentage of the monomers, and total yield. The molecular weights of both extracts varied between 2986 and 5573 Da, and they were mainly composed of catechin and taxifolin. Eco-friendly water-based formulations were obtained, without producing volatile organic compounds (VOCs), by varying the extract content between 15.5 and 37.8% w/w. The coatings, varying in thickness and substrates, were evaluated for their film-forming properties, covering power, mechanical properties, such as adhesion, embossing, abrasion, and flexibility, as well as their resistance to fire. The results indicated that good mechanical properties were obtained when using coatings containing TMw-L compared with those obtained when using TMw-H. The carbonization index (28%) and the mass loss percentage (9.35%) of the coatings containing TMw-L compared well to commercial coatings, indicating that they have excellent fire-retardant properties. However, the behavior of the TMw-H containing coatings was rather intumescent.