Effect of Catalysts and Curing Temperature on the Properties of Biosourced Phenolic Foams

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.