Peter Weigel

Structure formation of regenerated cellulose materials from NMMO-solutions

Abstract Cellulose as the most abundant regrowing organic material exhibits outstanding properties and useful applications, but also a tremendous challenge with regard to an economical and environmentally friendly chemical processing. In recent years the N -methylmorpholine- N -oxide (NMMO)-technology turned out to be a simple physical alternative to the yet dominating viscose-technology for producing regenerated cellulosic fibers, films, food casings, membranes, sponges, beads, and others without hazardous byproducts. With consideration of own results, the present paper reviews the state of the art knowledge on structure formation of fibers and films via the NMMO-route comprising the cellulose–NMMO–water phase system, the state of solution, the dry jet-wet shaping, the precipitation, and the drying stages. Dissolving pulp as the starting material can be dissolved easily without pretreatment in NMMO-monohydrate. The fairly (8–12%) concentrated solution of cellulose in NMMO-monohydrate is characterized by a marked elastic behavior similar to a polymer melt which can be quantified by rheological measurements of the storage and loss moduli. As found by light scattering experiments of diluted cellulose–NMMO solutions, there exist aggregates of molecules even in the diluted solution, with the number of molecules corresponding to solid state morphological units (crystallites, microfibrils). As shown by WAXS-RDF analysis of the concentrated solutions at elevated temperature, the typical short-range order of a pure NMMO–water system is only slightly disturbed by the cellulose molecules. Fiber formation occurs in a dry jet-wet spinning process, with several physical factors (e.g. nozzle and air-gap dimensions, draw-down ratio, take-up speed) and dope characteristics (cellulose DP and concentration, temperature, modifiers) influencing the shaping process and the final fibers properties. The precipitation process has been shown to be another stage capable to affect the structure and properties of the fibers as, e.g. by a two-step precipitation leading to a skin–core structure and improved fiber properties (reduced fibrillation). The NMMO method offers for the first time the possibility to produce blow-extruded tube-like films similar to the polyolefine blown film processing. The influencing parameters are discussed and the properties of the new blown cellulosic films are shown to be superior to cellophane. Finally, the structures and properties of the NMMO-type fibers and films have been investigated and differences between the new materials and the traditional viscose based fibers and films were shown and related to the different structure formation routes.

Structure-property relationships in extruded starch, 1 : Supermolecular structure of pea amylose and extruded pea amylose

Separated amyloses with different molecular weight distributions were obtained enzymatically from wrinkled pea starch and processed in a multi-zone twin-screw extruder. The crystalline polymorphs, crystanllinity and crystallite dimensions of amylose (unbranched molecular starch component) and films extruded from it were investigated by wide-angle X-ray scattering. The starting amylose materials exhibit a crystalline V A structure with rather large crystallites (9-25nm) and a degree of crystallinity ranging between 30 and 40%, depending on the history of the amylose sample. The extruded films, on the other hand, recrystallized in the B-type with a slightly higher degree of crystallinity and significantly smaller crystallite dimensions (3-7 nm). In one case, V H -type crystals were observed. The mechanical properties of the extruded materials were determined in tensile tests. The amylose with the highest molar mass produces films with the highest mechanical performance. As compared with cellulose or synthetic polymer films, the mechanical properties of the amylose films appear to be fundamentally limited by the lack of preferred molecular orientation.

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 technique can be applied to a cellulose-amine oxide ...