Investigation of Moisture Interaction with Cellulose Using Solid-State NMR

1. Investigation of Moisture Interaction with Cellulose Using Solid-State NMR Gary R Gamble USDA-ARS-Cotton Quality Research Station Clemson, SC

2. From: 1H and 13C Solid-state NMR of G. barbadense (Pima) Cotton, J. Molec. Structure, in press. (available online) • R.E. Taylor • A.D. French • G.R. Gamble • D.S. Himmelsbach • R.D. Stepanovic • D.P. Thibodeaux • P.J. Wakelyn • C. Dybrowski

3. Introduction • Moisture content is an important influence on cotton fiber properties, primarily due to its enhancement of fiber strength • The mechanism by which moisture influences strength is poorly understood • A better understanding my lead to improvements in breeding, processing, and yarn quality

4. Purpose • The interaction between moisture and cellulose may be studied by utilizing 1H and 13C nuclear spin dynamics observed by Nuclear Magnetic Resonance (NMR) techniques • The current study addresses the effect of moisture on 1H spin dynamics via spin diffusion experiments which are designed to study heterogeneous systems such as cotton fiber

5. Basic CP/MAS experiment including a proton evolution period

6. 13C CP/MAS spectrum of Pima cotton

7. Basic CP/MAS experiment including a Goldman-Shen pulse sequence

8. 1H wideline spectrum (A) and wideline spectrum using delayed acquisition (B), indicating that delayed acquisition allows selection of mobile 1H component

9. Wideline Spectra acquired with a Goldman-Shen pulse sequence: Mixing times = 0.003, 0.010, 0.5, 1, 10, 25, 50, and 100 ms

10. Fractional recovery of broad 1H component vs. sqrt mixing time: Indicative of 1H spin diffusion

11. (B) 13C CP/MAS Wideline Separation (WISE) spectrum with Goldman-Shen Sequence, including .5 ms mixing time -indicates transfer of polarization from narrow (mobile) 1H component to broad component • 13C CP/MAS Wideline Separation (WISE) spectrum with no Goldman-Shen • 1H evolution period or mixing time • -indicates that only broad 1H component • cross-polarizes with cellulose With a Goldman-Shen sequence including an evolution period but no mixing time, no cross-polarization takes place -indicates that narrow 1H component is not in direct contact with cellulose

12. Under boundary conditions of a lamellar type structure, the diffusion equation described by Fick’s Second Law gives: x = (4Dtm/π)1/2 where x is the average distance travelled, D is the diffusion coefficient, and tm is the mixing time. In the present case, diffusion is observed at mixing up to 100 ms, and using the reported spin diffusion coefficient Of D = 0.15 nm2 /ms (1) x = 4.4 nm (1) Radloff, et al., 1996. Macromolecules 29:1528-1534.

13. A single monolayer of unbound water has a thickness of ~0.31 nm (2). Assuming this to be the case, then 4.4 nm = N(0.31 nm) N = 14 Where N is the number of monolayers in the water domain A typical Pima cotton cell wall thickness is ~ 2.5 μm, or 2500 nm. At 5% moisture, and assuming equal densities of cellulose and water, the total thickness of the combined water layers is 125 nm. This translates to 28 separate layers each of 4.4 nm thickness. The present results are consistent with the Rollins (3) and Haigler (4) models of lamellar layers of cellulose separated by layers of water. (2) French, A.D., et al, 2004. Proc. Beltwide Cotton Conf. pp 2990-2994. (3) Rollins, M.L.,et al, 1965. J. Royal Microscopical Soc. 84:1-11. (4) Haigler, C.H., et al,1991. Plant Physiology 95:88-96.

14. Image from Porter and Rollins, J. Appl. Poly. Sci. 16:217-236, 1972