Characterization of moisture mobility and diffusion in fresh tobacco leaves during drying by the TG–NMR analysis

Abstract

Curing is an essential procedure in tobacco primary processing. The moisture mobility and diffusion characteristics during drying are the key factors that affect the curing condition optimization. In the present study, the thermogravimetric analysis (TG) was integrated to the online nuclear magnetic resonance analysis (NMR) to investigate the drying characteristics of fresh tobacco leaves (FTL) during hot air drying at 50 and 60°C. The results of TG were used to analyze the drying kinetics and obtain the effective diffusion coefficient of moisture of FTL during drying. The moisture diffusion coefficient of FTL was 4.1782E-09 m 2 s-1 at 50°C and 5.7777E-09 m 2 s-1 at 60°C, respectively. The moisture mobility of the samples at different drying stages was monitored by the NMR analyzer. T 2 spectra showed that the initial ratios of semibound water and bound water in FTL were 93.2 and 6.8%, respectively. The drying rate showed a decreasing trend with the reduction in relaxation time of T 22 peak from about 80 ms to about 30 ms, especially for the ones dried at 60°C. The reduced relaxation time of T 22 peak indicated that water activity in FTL was weakened during drying. Moisture distribution obtained by magnetic resonance imaging in FTL at different drying stages can reveal the moisture transfer path.

Investigation of moisture distribution and drying kinetic in noncentrifugal cane sugar during hot‐air drying using LF‐NMR

“…For instance, Mao et al used the FID signal to measure water content and moisture distribution in sludge (Mao et al, 2015). Guo et al (2018) used the same signal to examine the relationship between the T 2 peak area and MC of tobacco. In this study, the relationship between the total peak area A total of the T 2 relaxation curve and MC was examined via linear regression analysis, and the feasibility of using LF-NMR to monitor the MC of NCS was evaluated.…”

Extract of Albizia kalkora leaves

“…The leaf samples were analyzed by a thermogravimetric analyzer. We used nitrogen as the equilibrium gas, and the TGA temperature program was set from 30-850 ℃ at a rate of 15 ℃/min and 30 ℃/min, respectively, and, finally, the temperature was maintained at 850 ℃ for 5 minute [23][24][25] in both procedures. The FT-IR test results showed a similar peak for all three samples at 3500-3250 cm -1 , indicating that there was a -OH bond in the extracts of the leaves of the three species of Albizia kalkora (Roxb.)…”

Mechanism of moisture adsorption in plant fibers surface-modified with glycerol evaluated by LF-NMR relaxation technique

“…Relaxation time demonstrates variations of physical and chemical processes of the inter-facial water from the perspective of molecular structure. Two-dimensional time domain LF-NMR (2D LF-NMR) technique (Guo et al 2019;Wang et al 2020b;Montrazi et al 2018;Zheng et al 2017) combining two sequences between longitudinal (lattice-spin relaxation time, T 1 ) and transverse (the spinspin relaxation time, T 2 ) relaxation time (T 1 -T 2 ) simultaneously has been developed. Among the parameters, T 1 is the time for the protons to relapse to the original energy stage while the additional pulse electromagnetic wave is removed, and T 2 is the time for the actuated protons in the identical frequency but different moving tends to change their directions at the same level (Joardder et al 2019;Wang et al 2020a).…”