Different
formulations of phenolic resins based on two natural
products, namely, lignin and tannins, were implemented as biobased
fireproofing coatings for wood. Moreover, inorganic nanoparticles
were included as additives for improving the thermal resistance of
the coatings. The biobased coating formulations were first characterized
for their structure and thermal properties via Fourier transformed
infrared (FTIR) and thermogravimetric analyses (TGA). Then, their
fireproofing performance was assessed over a softwood and a hardwood
species. Various parameters were studied, such as the heat released
during combustion, the integrity of the samples, and the flames’
propagation. Furthermore, their performance regarding the mentioned
parameters was evaluated with respect to two different commercial
formulations (top-ranked fireproofing coatings). It was confirmed
that the risks derived from the exposure of wood to fire were significantly
reduced after the application of the biobased coatings: the heat release
during combustion was reduced, a protective effect was achieved concerning
wood integrity, and the propagation of the flames was significantly
delayed. Besides, these parameters displayed a better performance
on beechwood compared to maritime pinewood. Finally, it was observed
that the results obtained by the biobased coating formulations RA and RB were comparable to those achieved with
the used commercial fireproofing coatings.
Biosourced phenolic foams (BPFs) based on lignin alkaline liquor and tannins were successfully synthesized without using formaldehyde and any blowing agent. The influence of three sorts of catalysis (acid, alkaline, and thermal) and different curing temperatures (80, 100, and 120 °C) on the final properties of the foams was investigated. Concerning foam morphology, scanning electron microscopy observations showed that a low-curing temperature could significantly reduce the cell size and improve the structural homogeneity of phenolic foams. It was also proved by Fourier transform infrared spectroscopy analysis that alkaline catalysis promotes aromatic functions, whereas the polycondensation reaction and ether linkages were dominant under acid catalysis. Thermogravimetric analysis, cone calorimetry, and Bunsen burner test revealed that the foams prepared under alkaline catalysis displayed the best thermal stability and fire resistance. The obtained BPFs exhibited a high compressive strength (0.11−1.65 MPa) and good thermal conductivity (41.5−50.55 mW/m•K), which are linearly proportional to the foam densities. Accordingly, they could be used as a thermal insulator for the construction or retrofitting of buildings.
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