Supermolecular structure and orientation of blown cellulosic films

N-Methylmorpholine-N-oxide (NMMO) technology provides new possibilities for shaping fibers and films from cellulose. We discuss a blow-extrusion techn ique can be applied to a cellulose-amine oxide dope, yielding blown cellulo sic films. Process parameters, such as the draw down ratio and the blow rat io, can be used to control the mechanical film properties in both; the mach ine and transverse directions. In this way, a wide range of properties is c overed, and a completely balanced film can be manufactured. The film thickn ess can be made as small as 5 mu m, and the membrane properties can be vari ed by the conditions of precipitation. The blown cellulosic films exhibit a partially crystalline supermolecular structure and, depending on the coagu lation conditions, a symmetrical or asymmetrical homogeneous morphology and pore structure. Generally, a uniplanar orientation type was found, the cha ins being parallel to the film surface. Around the surface normal, the chai n orientation can be varied from nearly random to strongly uniaxial, in thi s way determining the mechanical properties in the machine acid transverse directions. As compared with the conventional viscose processing route of c ellophane, the blown film's NMMO processing route is less complicated and f riendlier to the environment. Blown films can be made much thinner, and the mechanical properties are superior to viscose films. Possible application fields of blown cellulose films are food casings, particularly small sausag e casings, packaging, and membranes.