The allomorphism of cellulose is a wellknown fact. Cellulose I and cellulose II are the most important allomorphs, the former term describing "native" cellulose, the latter being cellulose that has either been regenerated from cellulose solutions or obtained by mercerization with concentrated lye. It is commonly accepted that in cellulose the chains are in parallel arrangement, while cellulose II has an antiparallel chain orientation. The transition from parallel cellulose I to antiparallel cellulose II can be easily understood if the "detour" via completely dissolved cellulose is involved: the cellulose chains are separated in solution and will re-aggregate as the thermodynamically most stable allomorph, which is celulose II. However, how the parallel-to-antiparallel transition in solid state (during mercerization) can be imagined is still a mystery and one of the oldest riddles in cellulose science. In our presentation, we will add some pieces to the jigsaw puzzle of the solid-state cellulose I to cellulose II transition (evidently without being able to arrange those pieces into a final, nicely ordered picture), in particular addressing the axiom that always cellulose II is regenrated from cellulose solutions. It will be demonstrated that special regeneration conditions that align the reducing ends to one side through temporary derivative formation allow reprecipitating cellulose I from solution, independent of whether a cellulose I substrate (such as a cellulosic pulp or cotton linters) or a cellulose II substrate (such as viscose fibers) had been dissolved. The latter case represents something like a "reverse mercerization" with regard to the allomorph change. The experiments involve different cellulosic substrates, and the transitions are studied by means of solution and solid-state NMR, light scattering as well as X-ray diffraction experiments.

Regenerating cellulose I from solution?

251st National Meeting (2016)

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