Abstract: The present invention relates to a process for crosslinking polysaccharides from macroalgae to yield a polymer material in a processing chamber. The process includes the steps of producing a mixture comprising a solid containing polysaccharide from macroalgae and a water-containing liquid, with a ratio of liquid to solid of between 3:1 and 1:9, adjusting a pressure acting on the mixture to at least the vapour pressure of water at a first temperature, the first temperature being greater than/equal to 100° Celsius, and heating the mixture to the first temperature, wherein the solid comprises as polysaccharide at least one of alginate, alginic acid, agar and/or Carrageenan. The invention further relates to a process for producing a biopolymer product from such a polymer material in an apparatus comprising a processing chamber and a shaping apparatus. The invention also relates to a biopolymer product obtained by such a process.