Preparation of starch betainate: a novel cationic starch derivative
Introduction
Cationic starches are commercially significant starch derivatives used in large quantities as wet-end additives in the paper industry in order to improve retention, drainage and strength (Rutenberg & Solarek, 1984). In 1997, more than 1.5 million tonnes of starch were used for paper manufacturing in Western Europe alone. About 33% of this amount was cationic starches (Bergh, 1998). Cationic starches can be prepared by reaction of starch with reagents containing amino, imino, ammonium, sulfonium or phosphonium groups, all of which can carry a positive charge (Solarek, 1986). However, the present commercially significant types of cationic starches are tertiary aminoalkyl ethers and quaternary ammonium alkyl ethers.
The objective of this work was to prepare a novel cationic starch ester derivative consisting exclusively of natural products, namely starch and betaine, and to examine its applicability for paper manufacture. Starch betainate was prepared by linking betaine (Scheme 1), (carboxymethyl)trimethylammonium hydroxide inner salt, to starch through an ester bond (Granö, Hase & Yli-Kauhaluoma, 1998). Betaine, like starch, is a natural product which is found in most green plants. It is especially abundant in sugar beets (Beta vulgaris var. altissima Döll). Linking the cationic substituent to the starch backbone through an ester bond should result in a more biodegradable product than the traditional cationic starch ethers.
Section snippets
Materials
Native potato starch was provided by Raision Tehtaat Oy Ab (Raisio, Finland). It was dried for 3 days at 107°C. Anhydrous betaine internal salt was purchased from Merck (Darmstadt, Germany). 1,4-Dioxane was purchased from Riedel-deHaën (Seelze, Germany) and distilled over sodium-benzophenone ketyl. Diethyl ether was purchased from Rathburn (Walkerburn, UK) and distilled over sodium-benzophenone ketyl. Dichloromethane was purchased from Riedel-deHaën (Seelze, Germany) and distilled over calcium
Results and discussion
We were attracted to embark on the preparation of starch betainate by two reasons. Starch betainate consists of two abundant natural products, starch and betaine, and it can thus be considered environmentally more friendly than current cationic starches in commercial use. We also found it interesting to study the characteristics of starch betainate in papermaking processes.
Conclusions
A new cationic starch ester was prepared by reacting starch with betainyl chloride in refluxing 1,4-dioxane in the presence of pyridine as a nucleophilic catalyst. Starch betainate was characterized by IR and 13C NMR spectrometry and its suitability as a wet-end additive in paper manufacturing was studied. Starch betainate was found to increase the strength of paper sheets and to have beneficial influence on retention. We are currently further studying the influence of different degrees of
Acknowledgements
This work was supported by TEKES (Technology Development Centre, Helsinki, Finland). We are grateful to Juha Saari (VTT) for performing the paper tests and to Professor Anneli Hase (VTT) for helpful discussions.
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