Defence of doctoral thesis: Yunus Can Görür – Design of Cellulose-Based Materials via Sustainable and Scalable Processes
Opponent: Professor Tsuguyuki Saito, The University of Tokyo
Supervisor: Professor Lars Wågberg, KTH, co-supervisor Per Larsson, KTH
Plastic pollution is one of the most pressing environmental issues in today’s world. Addressing this problem calls for the development of environmentally friendly alternatives that would reduce the amount of persistent plastic waste. Wood-based cellulose is an excellent candidate as a renewable and biodegradable alternative to oil-based plastics in a variety of applications. However, for their widespread adoption, cellulosic materials need to perform comparably to their oil-based counterparts, while simultaneously attaining similarly high processing efficiencies. A major challenge today is to produce high-performance cellulosic materials at industrially feasible rates using scalable methods.
This thesis demonstrates that with a fundamental understanding of fiber chemistry and behavior, cellulose fibers can be tuned to develop sustainable material streams and advanced functional materials at high process rates. First, a new stimuli-responsive cellulosic fiber material called self-fibrillating fibers (SFFs) was developed, where the mechanisms governing the swelling of the fiber wall were thoroughly investigated. The knowledge and understanding obtained from these fundamental studies were utilized to prepare pH-responsive filters. Secondly, the preparation of SFF papers and nanopapers using conventional papermaking methods and equipment was demonstrated within the context of rapid transparent paper preparation. It was shown that SFFs can be rapidly dewatered to obtain papers, where the constituting fibers can be nanofibrillated in situ, resulting in strong, transparent and gas barrier nanopapers without sacrificing processing speed. Thirdly, the use of SFFs was extended to functional nanocomposites. A new and scalable materials processing platform for the rapid preparation of functional cellulose hybrids was developed. The stimuli-responsive self-assembly of chemically nanofibrillated SFFs was studied and utilized to prepare nanopapers and hybrid materials. Finally, SFFs were used as bio-based binders in the fabrication of graphitic Li-ion battery electrodes with improved processing and electrochemistry. Taking advantage of their facile nanofibrillation and favorable chemistry, SFFs were nanofibrillated during slurry mixing then blade-coated on copper supports to create strong electrodes with excellent performance.
The novel materials and methodologies presented herein combine an aqueous fiber modification strategy with excellent processing properties for the preparation of high-performance cellulosic materials that can compete with oil-based plastics in various applications.