Hydration/Dehydration Behavior of Hydroxyethyl Cellulose Ether in Aqueous Solution.

Kengo Arai,Toshiyuki Shikata

doi:10.3390/molecules25204726

Kengo Arai, Toshiyuki Shikata

Open Access

https://doi.org/10.3390/molecules25204726

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Abstract

Hydroxyethyl cellulose (HeC) maintains high water solubility over a wide temperature range even in a high temperature region where other nonionic chemically modified cellulose ethers, such as methyl cellulose (MC) and hydroxypropylmethyl cellulose (HpMC), demonstrate cloud points. In order to clarify the reason for the high solubility of HeC, the temperature dependence of the hydration number per glucopyranose unit, nH, for the HeC samples was examined by using extremely high frequency dielectric spectrum measuring techniques up to 50 GHz over a temperature range from 10 to 70 °C. HeC samples with a molar substitution number (MS) per glucopyranose unit by hydroxyethyl groups ranging from 1.3 to 3.6 were examined in this study. All HeC samples dissolve into water over the examined temperature range and did not show their cloud points. The value of nH for the HeC sample possessing the MS of 1.3 was 14 at 20 °C and decreased gently with increasing temperature and declined to 10 at 70 °C. The nH values of the HeC samples are substantially larger than the minimum critical nH value of ca. 5 necessary to be dissolved into water for cellulose ethers such as MC and HpMC, even in a high temperature range. Then, the HeC molecules possess water solubility over the wide temperature range. The temperature dependence of nH for the HeC samples and triethyleneglycol, which is a model compound for substitution groups of HeC, is gentle and they are similar to each other. This observation strongly suggests that the hydration/dehydration behavior of the HeC samples was essentially controlled by that of their substitution groups.

Highlights

Cellulose is the most abundant natural organic resource on the globe
We report the temperature dependence of hydration number per glucopyranose unit, nH, for the Hydroxyethyl cellulose (HeC) samples in aqueous solution over a wide temperature range from 10 to 70 ◦ C, determined by using extremely high-frequency dielectric spectroscopic (DS) techniques
All the HeC samples examined in this study keep high water solubility over a wide THe groups

Summary

Introduction

Cellulose is the most abundant natural organic resource on the globe. Cellulose is a high-molecular weight polysaccharide which consists of β-1,4-d-glucopyranose units [1]. Native cellulose is insoluble in most usual solvents including water, due to its highly developed inter- and intra-molecular hydrogen bonding between hydroxy groups [2,3] To improve this insolubility and to make use of cellulose for a wide range of applications, many kinds of chemically modified cellulose derivatives have been synthesized from natural cellulose. A series of chemically modified celluloses, such as water-soluble nonionic methyl, hydroxypropyl, hydroxyethyl and hydroxypropylmethyl cellulose ethers, anionic sodium carboxymethyl cellulose ether, and organic solvent-soluble ethyl and cyanoethyl cellulose ethers, and cellulose nitrate and cellulose acetate, have been developed by several chemical companies [1] These chemically modified cellulose samples have been widely used in various areas because they exhibit useful properties, such as viscosity thickening, surfactant activity, film formation, adhesion, and so on [1,4,5,6,7]

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