Abstract: The invention relates to a method for producing a crosslinked lignin in particle form using a hydrothermal treatment of a liquid, which is made of black liquor, contains lignin and a crosslinker or a precursor thereof, and has an electrical activity ranging from more than 15 mS/cm, preferably more than 25 mS/cm, to 400 mS/cm, and to the crosslinked lignin produced using the aforementioned method. The invention additionally relates to crosslinked lignin particles which have a glass transition temperature Tg of at least 160° C. or no glass transition temperature and an STSA surface area of at least 10 m2/g and to rubber articles, in particular technical rubber articles or tires, which comprise crosslinked lignin particles as a filler.