NEW MATERIAL: Lignin containing at least 7% by wt. of a lignin substance of N and at least 3.1% of S and containing a waterinsoluble lignin substance having an IR absorption band having peak width of at least 60 cm-1 in the vicinity of 1550-1670 cm-1 and not containing thiourea and an isothiuronium salt and having good chelating characteristics and capable of absorbing a metal and containing least 4.5 wt.% of N if P is present.

USE: A flame retardant and a thermoplastic additive.

PROCESS: A lignin-containing substance is heated in a basic or neutral medium along with thiourea and NH2-C(S)NH2 at temp. equal to or lower than the decomposition temp. of thiourea to form N and Scontaining insoluble reaction product which is, in turn, purified to remove unreacted thiourea to obtain the objective lignin.