Membranes, composed of either regenerated cellulose or cellulose esters, are manufactured through distinct processes of modifying and cross-linking cellulose fibers (derived from wood pulp or cotton fibers) to form films with differing properties and pore sizes. Variations in the manufacturing process significantly change the properties and pore sizes of the films; depending on the cross-linkages introduced in cellulose, the size of pores can be modulated. While similar in composition, most of the cellulose-based membranes currently manufactured are not necessarily useful for dialysis. Cellulose-based membranes are also widely used for applications ranging from food wrapping, film stock, or “plastic” wrap.
For dialysis applications, regenerated cellulose-based membranes are extruded as tubing or sheets and then dried. Glycerol is frequently added as a humectant to prevent cracking during drying and to help maintain the desired pore structure. Regenerated cellulose membranes are very hydrophilic and hydrate rapidly when introduced to water. Due to their additional crosslinking, regenerated cellulose membranes have better chemical compatibility and heat stability than membranes made from cellulose esters. Regenerated cellulose membranes are more resistant to organic solvents and to the weak or dilute acids and bases that are commonly used in protein and molecular biology applications. Membranes based on cellulose esters are typically supplied wet and come in a greater range of MWCOs. Pore sizes are typically more consistent across cellulose acetate membranes.