A process for making a hydrogel forming material from a kraft or sulfite pulping process cellulosic pulp slurry by extracting hemicellulose heteropolymers from the cellulosic pulp slurry as a hemicaustic extract by treating the cellulosic pulp slurry with a cold caustic solution, then isolating the hemicaustic extract and preparing a mixture of the hemicellulose extract and a derivatizing agent comprised of a monofunctional etherifying agent and/or a polyfunctional organic cross-linking agent, and reacting the mixture to produce the hydrogel forming material. A polyvalent metal cross-linking agent can optionally be reacted with the hydrogel forming material to enhance its gel strength.