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

Abstract

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.

Nanocellulose Removes the Need for Chemical Crosslinking in Tannin-Based Rigid Foams and Enhances Their Strength and Fire Retardancy

“…In tannin-FA rigid foams, the pores and overall foam structure are formed from bubbling a blowing agent that is added to the precursor. Here, we use diethyl ether, but we point out that several other greener molecules have been used efficiently as well. , As far as foam growth, one should consider the viscosity of the precursor medium, that is, solvent bubbling and its removal by evaporation cannot lead to pore formation at high viscosity. CNF suspensions are known to form highly viscous gels at low mass fractions (∼1.5 wt %) because of the entanglement and interconnectivity of the nanofiber network .…”

“… 7 Therefore, many efforts have been directed to produce efficient thermal insulating and fire-resistant foams from eco-friendly and nonhazardous components. 13 , 14 In this area, plant-based phenolic molecules, such as lignins 14 and tannins, 15 have been shown to potentially replace isocyanate PF. For instance, tannin-based rigid foams, built from the copolymerization of condensed tannins and furfuryl alcohol under acidic conditions, 16 have been reported along with major advances in the optimization of foam synthesis 17 , 18 and properties.…”

“…They are usually combined with flame retardants (e.g., halogenated compounds) given the PF flammability and the highly toxic and combustible gases it generates. − Hence, despite PF’s excellent thermal insulation, , there are major concerns related to safety and environmental impact . Therefore, many efforts have been directed to produce efficient thermal insulating and fire-resistant foams from eco-friendly and nonhazardous components. , In this area, plant-based phenolic molecules, such as lignins and tannins, have been shown to potentially replace isocyanate PF. For instance, tannin-based rigid foams, built from the copolymerization of condensed tannins and furfuryl alcohol under acidic conditions, have been reported along with major advances in the optimization of foam synthesis , and properties. , However, these materials are still heavily dependent on chemical crosslinkers, , such as formaldehyde and glutaraldehyde.…”

Progress in Bio‐Based Phenolic Foams: Synthesis, Properties, and Applications

“…Recent research has focused on bio-sourced foams prepared by completely replacing petroleum-derived phenol and formal-dehyde. Issaoui et al [106] reported lignin alkaline liquor-and tannins-based bio-sourced phenolic foam synthesized without the use of formaldehyde or any blowing agent. The foams were prepared using three types of catalysis (acid, alkaline, and thermal) and at different curing temperatures (80, 100, and 120 °C).…”

Phenolic Foams Toughened with Triethylene Glycol by In Situ Polymerization and Prepolymerization Processes

“…26 The compressive strength of biosourced PF based on lignin in alkaline liquor and tannins has reached 1.65 MPa. 27 The pulverization rate of the lignin-based PF that has been prepared using lignin instead of phenol to react with formaldehyde has been reduced by 43.5%. 28 The bending strength of PF that has been prepared using bio-oil to replace part of phenol has been increased by 50.5%.…”