Abstract:

Sodium lignosulfonate was used to modify polyurethane foam and improve its flame retardant performance. First, hydroxymethylated sodium lignosulfonate(HSL) was obtained by methylation of sodium lignosulfonate. Then, some polyether polyol was replaced by hydroxymethylated sodium lignosulfonate and mixed with polymerized 4, 4'-diphenyl-methane-diisocyanate(MDI) to prepare hydroxymethylated sodium lignosulfonate modified polyurethane foam, and then added aluminum hypophosphite(AHP) and expanded graphite(EG) to further improve the flame retardancy of polyurethane foam. The limit oxygen index(LOI), thermogravimetry(TGA) and scanning electron microscopy(SEM) were used to test the samples. The flame-retardant properties of polyurethane foam samples were analyzed by limiting oxygen index test. The results showed that when the amount of hydroxymethylated sodium lignosulfonate instead of polyether polyols was 60% calculated by the percentage of HSL mass in the total mass of HSL and polyether polyol, the LOI index of polyurethane foam reached 21.6%, the maximum thermal degradation rate reduced by 1.53 %/min, the carbon residue increased by 15.04 percent points, and the number and area of foam pores decreased. When adding a mixture of flame retardants(mass ratio of expanded graphite and aluminum hypophosphite 3:1), the LOI index of polyurethane foam reached 26.3%, the maximum thermal degradation rate reduced by 1.52 %/min, the carbon residue increased by 23.52 percent points, and the number and area of foam pores decreased further. Therefore, a polyurethane foam with excellent flame retardancy is prepared in this experiment. It has broad application prospects in the field of architecture, transportation and food insulation.

Key words: hydroxymethylated sodium lignosulfonate, polyurethane foam, expanded graphite, aluminum hypophosphite, flame retardancy