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Research article2013Peer reviewed

Molecular structure of citric acid cross-linked starch films

Menzel, Carolin; Olsson, Erik; Plivelic, Tomas S.; Andersson, Roger; Johansson, Caisa; Kuktaite, Ramune; Järnström, Lars; Koch, Kristine


The effect of citric acid (CA) on starch films has been examined. A new method to detect cross-linking of starch by CA in solution-cast films by molecular weight measurements is described. Furthermore, we managed to distinguished between free, mono- and di-esterified CA and quantify di-ester content within starch films by using a modification in the method of complexometric titration with copper(II)-sulfate. Cross-linking of starch by CA occurred at low temperature, 70 ◦ C, which we assumed is so far the lowest temperature reported where cross-linking reaction occurred. This is essential for starch coating applica- tions within paper industry since no high temperatures for curing will be required. However, curing at 150◦C and high CA concentrations, 30pph, increased cross-linking reaction. Furthermore, the physical properties like water solubility, gel content and glass transition temperature, were highly reflected by changes in the molecular structure i.e. cross-linking and hydrolysis, as well as CA content and curing temperature.


Starch-based film, Citric acid, Cross-linking, Molecular weight, Hydrolysis, Amorphous starch, Plasticization

Published in

Carbohydrate Polymers
2013, Volume: 96, number: 1, pages: 270-276