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Molecular Level Characterization of the Temperature and Time Dependent Physical Properties of Cellulose Solutions in N, N-dimethylacetamide and Lithium Chloride

Title
Molecular Level Characterization of the Temperature and Time Dependent Physical Properties of Cellulose Solutions in N, N-dimethylacetamide and Lithium Chloride
Author
KHALIQZUBAIR
Advisor(s)
Byoung Chul Kim
Issue Date
2016-08
Publisher
한양대학교
Degree
Doctor
Abstract
In this study, the physical properties of cellulose solutions in N,N-dimethyl acetamide (DMAc) and lithium chloride (LiCl) were investigated regarding temperature, LiCl contents, and concentration and molecular weight of cellulose. Over the concentration range of 0.01 to 2.5 g/dl, the viscosity of the cellulose solutions in DMAc containing 9 wt% LiCl exhibited a lower critical solution temperature (LCST) behavior which proved thermoreversible between 30 and 60oC. Dynamic light scattering (DLS) measurement further supported the LCST behavior. In the concentration range of 0.1 and 2.5 g/dl, both cellulose solutions gave a drastic increase of ηred in the vicinity of critical concentration (C*), 0.9 g/dl. The slope of the curve of ηred versus concentration was higher for the cellulose of higher molecular weight, but it did not change with temperature between 30 and 60oC. In the extremely dilute concentration range, 0.01 to 0.08 g/dl, the reduced viscosity (ηred) of cellulose solutions was increased with decreasing concentration. The anomalous coil expansion with decreasing concentration could be explained by the increasing interaction of Cl- ions with intramolecular hydroxyl groups of the cellulose solutions with decreasing concentration, which was also verified by DLS measurement. The effects of temperature on the physical properties of the cellulose solutions in DMAc containing 9 (solvent-9) or 6 wt% (solvent-6) LiCl were investigated over the temperature range of 30 to 80oC. The cellulose solution, in both solvent systems, exhibited an LCST behavior over the temperature range observed. The content of LiCl affected the thermoreversible LCST behavior of cellulose solutions, which was almost thermoreversible over the temperature range of 30 to 80oC for solvent-9 and 30 to 50oC for solvent-6. The partial thermoreversibility of cellulose chain between 60 and 80oC in solvent-6 could be explained by increased intramolecular interactions between cellulose molecules with increasing temperature. The thermoreversible LCST behavior of cellulose solution for solvent-9 was further supported by DLS measurement which also verified the larger decrease of cellulose chain dimensions in solvent-6 between 60 and 80oC. The long-term aging of cellulose solutions at 80oC seemed to bring about some irreversible gelation through direct coupling between cellulose molecules.
URI
https://repository.hanyang.ac.kr/handle/20.500.11754/126021http://hanyang.dcollection.net/common/orgView/200000429339
Appears in Collections:
GRADUATE SCHOOL[S](대학원) > ORGANIC AND NANO ENGINEERING(유기나노공학과) > Theses (Ph.D.)
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