Using lignin degraded to synthesize phenolic foams with excellent flame retardant property

Lignin had similarity with phenol in properties and it was renewable, so the phenol was partly replaced by lignin to synthesize safer resin. Lignin had fewer high active sites, which was not conducive to the combination of lignin and phenolic resin, so lignin was modified by degradation. In this paper, the auxiliary agent sodium thiosulfate and sodium hydroxide are selected to degrade lignin on the basis of the hydrothermal method. Then the resin was foamed to obtain the cellular insulant, which could improve the environment and reduce costs. The effects of various conditions on foaming were explored to reduce the time of curing and improve the safety of foams. The flame retardant and mechanical properties of the prepared phenolic foam samples were characterized. In terms of flame retardant performance, the oxygen indices of all foams exceeded 32%. The foam obtained had excellent flame retardant property. All foams met the requirements of the compressive strength in the national standard.