Modification of crystallinity and pore size distribution in coagulated cellulose films
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In this study the effects of altering the coagulation medium during regeneration of cellulose dissolved in the ionic liquid 1-ethyl-3-methylimidazolium acetate, were investigated using solid-state NMR spectroscopy and NMR cryoporometry. In addition, the influence of drying procedure on the structure of regenerated cellulose was studied. Complete conversion of the starting material into regenerated cellulose was seen regardless of the choice of coagulation medium. Coagulation in water predominantly formed cellulose II, whereas coagulation in alcohols mainly generated non-crystalline structures. Subsequent drying of the regenerated cellulose films, induced hornification effects in the form of irreversible aggregation. This was indicated by solid-state NMR as an increase in signal intensity originating from crystalline structures accompanied by a decrease of signal intensity originating from cellulose surfaces. This phenomenon was observed for all used coagulants in this study, but to various degrees with regard to the polarity of the coagulant. From NMR cryoporometry, it was concluded that drying induced hornification generates an increase of nano-sized pores. A bimodal pore size distribution with pore radius maxima of a few nanometers was observed, and this pattern increased as a function of drying. Additionally, cyclic drying and rewetting generated a narrow monomodal pore size pattern. This study implies that the porosity and crystallinity of regenerated cellulose can be manipulated by the choice of drying condition.
KeywordsCrystallinity NMR cryoporometry Porosity Regenerated cellulose Solid-state NMR
Cross polarization magic angle spinning
Nuclear magnetic resonance
Pore size distribution
This work has been carried out within the framework of Avancell—Centre for Fibre Engineering. Financial support from the Swedish Foundation, Södra Skogsägarnas stiftelse för forskning, utveckling och utbildning, and Chalmers Area of Advance Material Science are all gratefully acknowledged. The NMR measurements were carried out at the Swedish NMR Centre, Göteborg, Sweden. Dr. Derek Weightman at Sappi Saiccor in South Africa is kindly acknowledged for supplying samples of the eucalyptus dissolving pulp.
- Kotek R (2006) Regenerated cellulose fibers. In: Lewin M (ed) Handbook of fiber chemistry, 3rd edn. Taylor & Francis, CRC Press, New York, USA, pp 668–764Google Scholar
- Laivins GV, Scallan AM (1993) The mechanism of hornification of wood pulps. In: Baker CF (ed) Products of papermaking, Trans 10th Fund Res Symp, Oxford, pp 1235–1260Google Scholar
- Nocanda X, Larsson PT, Spark A, Bush T, Olsson A, Madikane M, Bissessur A, Iversen T (2007) Cross polarisation/magic angle spinning 13C-NMR spectroscopic studies of cellulose structural changes in hardwood dissolving pulp process. Holzforsch 61:675–679Google Scholar
- Zhang S, Li FX, Yu JY (2010) Structure and properties of novel cellulose fibres produced from NaOH/PEG-treated cotton linters. Iran Polym J 19:949–957Google Scholar
- Ziabicki A (1976) Fundamentals of fibre formation: the science of fibre spinning and drawing. Wiley, Minnesota, USAGoogle Scholar
- Zuckerstätter G, Schild G, Wollboldt P, Roeder T, Weber HK, Sixta H (2009) The elucidation of cellulose supramolecular structure by 13C CP-MAS NMR. Lenzing Ber 87:38–46Google Scholar