Complex sentence: Viscose is both a semi-synthetic fabric formerly called "viscose rayon" or "rayon" and a solution of cellulose xanthate produced by treating dissolving pulp with aqueous sodium hydroxide and carbon disulfide used to spin the viscose rayon fiber.
Split into simpler sentences: Viscose is both a semi-synthetic fabric, formerly called "viscose rayon," or "rayon" and a solution of cellulose xanthate. The latter is produced by treating dissolving pulp with aqueous sodium hydroxide and carbon disulfide which is used to spin the viscose rayon fiber.