Progress in cellulose shaping: 20 years industrial case studies at Fraunhofer IAP

Cellulose, the most abundant renewable organic material on earth, exhibits outstanding properties and useful applications, but also presents a tremendous challenge with regard to economical and environmentally friendly chemical processing. The viscose process, more than 100 year old is still the most widely utilized technology to manufacture regenerated cellulose fibers and films. Viscose fibers are produced today worldwide on a 5 million ton scale with various fiber types ranging from high performance tire yarn to textile filaments and staple fibers with excellent properties close to those of cotton. At Fraunhofer IAP, the technical equipment for viscose preparation, wet spinning of fibers, hollow fibers, and tube-like films is available on a min-plant scale. Research focused on raw materials testing, process optimization with regard to economic and ecological aspects, structural analysis of cellulose during processing, and structure-property relations of fibers and films. Similar to the viscose process, cellulosic fibers can be produced via cellulose carbamate as an environmentally friendly route. In a close cooperation of Fraunhofer IAP with industrial partners, a specific process based on cellulose carbamate was developed on a pilot plant scale, giving fiber properties close to those of conventional viscose fibers. In recent decades the N-methylmorpholine-N-oxide (NMMO)-technology turned out to be a nonderivatizing commercial alternative to the still dominant viscose route. From the very beginning, Fraunhofer IAP has been engaged in investigating the structure formation of cellulose fibers precipitated from NMMO-water solution, revealing structural reasons for the fibrillation tendency of these fibers and means to overcome them. Starting from fiber formation via dry-jet wet spinning, for the first time the blown film formation and the meltblown nonwovens technology were developed for cellulosics on a pilot plant scale at Fraunhofer IAP. Based on the elastic behavior of the dope at elevated temperatures, cellulose can be processed like a melt in the air-gap, offering new possibilities of shaping cellulose like meltable mass polymers. Combining cellulose carbamate with NMMO-monohydrate as a solvent, higher polymer concentrations in the dope and outstanding mechanical properties of the resulting fibers were achieved.