The present invention relates to novel thermoplastic, water-insoluble cellulose hydroxyalkyl hydroxycarboxylic acid esters of the general structureCell--O--Rwhere Cell--O is the substituted OH group of a polymeric cellulose unit and R is either a monomeric and/or polymeric hydroxyalkylether hydroxycarboxylic acid ester of the structure X:X=--A--B--in which A is a linear polyether chain:A=(--D--O--).sub.nin which D signifies a linear aliphatic branched or unbranched chain with 2 to 11 C atoms and n is a whole number equal to or greater than 1, and B is a linear polyester chain: ##STR1## in which E signifies a linear aliphatic branched or unbranched chain with 2 to 5 C atoms and m is a whole number equal to or greater than 1, or R is equal to A or B or X and a combination thereof in any ratio, or R is equal to H (hydrogen) according to the degree of substitution per anhydroglucose unit (max. 3) with A, B or X, and a process for their production and use of these cellulose derivatives as biodegradable mouldings.