Preparation of Lignin-Based Phenolic Foam with Excellent Performance Based on Hydroxymethylation of Lignosulfonate...

In this paper, a novel biobased phenol formaldehyde resin foam was fabricated. Specifically, lignosulfonate, a byproduct of paper and pulping, is hydroxymethylated with paraformaldehyde and then condensed with phenol to form lignosulfonate-based phenol formaldehyde (LPF) resin, subsequently undergoing foam technology to prepare LPF foam. The structures and properties of the intermediate and target products were characterized by ¹H nuclear magnetic resonance (¹H NMR) spectroscopy, gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry derivative thermogravimetry (TGA-DTG), scanning electron microscopy (SEM), compression performance test, limiting oxygen index test and thermal conductivity measurement. It was found that the prepared foam exhibited excellent mechanical and thermal properties. At a lignin substitution degree of 10%, the optimal thermal stability (at 800 °C), compressive strength (0.14 MPa) and thermal conductivity (0.0294 W/m·K) were achieved. As the lignosulfonate content gradually increases, the limit oxygen index initially showed a significant increase and then decreased. It is worth noting that when the LS substitution degree is increased to 30%, the limiting oxygen index of foam is up to 32.6%. These results underscore the application potential of industrial lignin as a promising biobased substitute in the synthesizing PF foam with excellent thermal insulation and flame-retardant properties.