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

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.