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Hydration/Dehydration Behavior of Hydroxyethyl Cellulose Ether in Aqueous Solution
Kengo Arai1, Toshiyuki Shikata1,2
1Cellulose Research Unit, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan.
Molecules (Basel, Switzerland)
|October 20, 2020
Summary
Hydroxyethyl cellulose (HeC) exhibits superior water solubility across temperatures due to its high hydration number. This is primarily driven by the behavior of its hydroxyethyl substitution groups, unlike other cellulose ethers.
Area of Science:
- Polymer Science
- Physical Chemistry
- Materials Science
Background:
- Nonionic cellulose ethers like methyl cellulose (MC) and hydroxypropylmethyl cellulose (HpMC) exhibit temperature-dependent solubility, often showing cloud points at elevated temperatures.
- Hydroxyethyl cellulose (HeC) is known for its exceptional water solubility, even at high temperatures where other cellulose ethers precipitate.
- Understanding the molecular basis for HeC's enhanced solubility is crucial for its application in various industries.
Purpose of the Study:
- To investigate the reason behind the high water solubility of Hydroxyethyl cellulose (HeC) over a wide temperature range.
- To examine the temperature dependence of the hydration number (nH) in HeC samples with varying molar substitution (MS).
- To elucidate the role of hydroxyethyl substitution groups in controlling HeC's hydration and solubility behavior.
Main Methods:
- Utilized extremely high frequency dielectric spectrum measuring techniques (up to 50 GHz) to determine hydration numbers.
- Studied HeC samples with molar substitution (MS) ranging from 1.3 to 3.6.
- Measured hydration numbers across a temperature range of 10 to 70 °C.
Main Results:
- All examined HeC samples remained soluble and did not exhibit cloud points between 10-70 °C.
- The hydration number (nH) for HeC (MS=1.3) was 14 at 20 °C, gently decreasing to 10 at 70 °C.
- HeC hydration numbers were significantly higher than the critical value (~5) required for cellulose ether solubility, even at high temperatures.
Conclusions:
- HeC maintains high water solubility across a broad temperature range due to a substantial hydration number.
- The temperature dependence of hydration in HeC is gentle and closely mirrors that of triethylene glycol, a model for its substitution groups.
- The hydroxyethyl substitution groups are the primary determinants of HeC's hydration and dehydration behavior, thus controlling its wide-ranging solubility.
Keywords:
chemically modified cellulose etherdehydrationdielectric spectroscopyhydrationhydroxyethyl cellulosemethyl celluloserelaxation timeMore Related Videos
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