Waste liquors from cellulosic industries. III.. Lignin from soda‐spent liquor as a component in phenol‐formaldehyde resin

Lignin separated from soda‐spent liquor of rice straw pulping was used to replace some of the phenol condensed with formaldehyde to form phenol‐formaldehyde resins (PF). The phenol‐lignin‐formaldehyde resin was obtained through two stages, namely adduct and polymerization stage. In the adduct stage, lignin: phenol ratio, time and temperature were studied. The produced phenol‐lignin was condensed with formaldehyde to produce phenol‐lignin‐formaldehyde resins. The ratio of phenol‐lignin to formaldehyde during the condensation, temperature and time of polymerization were also studied. In each case the yield, viscosity, solubility, and the softening point of the resins were determined. Lignin can replace up to 25% of the phenol without affecting the physical properties of the produced phenol‐lignin‐formaldehyde resins. IR‐spectra showed a structural similarity of phenol formaldehyde and phenol‐lignin‐formaldehyde resins.