BioFoam
Experimenting with "esterofoam": Citric Acid + Starch
Why Citric Acid + Starch?
Both starch and citric acid are biodegradable and derived from renewable resources.
This makes the cross-linked product environmentally friendly, suitable for applications where sustainability is a concern.
Citric acid is a weak organic acid commonly found in citrus fruits, especially lemons and limes. It is known for its sour taste and is widely used in food and beverage industries as a flavoring and preservative agent.
Citric Acid + Starch
In the context of material science and polymer chemistry, citric acid can act as a cross-linking agent, particularly with biopolymers like starch. The process of cross-linking involves the formation of chemical bonds between polymer chains, enhancing the material's mechanical and thermal properties.
Starch, a natural polysaccharide, consists of long chains of glucose units.Citric acid, with its three carboxyl groups, can react with the hydroxyl (-OH) groups present in the starch molecules.This reaction typically occurs under heat and possibly acidic conditions, facilitating the esterification process.
Image: Thierry Hamaide. Modified Starch-Based Hydrogels Cross-Linked with Citric Acid and their use as Drug Delivery Systems for Levofloxacin. DOI:10.1080/1539445X.2012.710698
Method:
In this research, the methods are quite experimental, as they explore a new approach to creating foam using a combination typically used for films. While the specific procedures differ in each test, the core method is the same: Heating either citric acid alone or mixed with glycerol in an oil bath at 105C, then adding starch and continuing to heat it at the same temperature. After this step, the resulting mixture is baked in an oven at 180C. These experiments are about to explore a new direction in foam production.
This work is done in ChemArts Project, School of Chemical Engineering, Aalto University
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Tests A
November 2023
Key ingredients: Citric Acid and Starch.
Result: Unexpected and surprising. Not a foam. But! Gorgeous material, mirror-like, beautiful. Properties: Dissolves easily in water.
Tests B
November 2023
Key ingredients: Citric Acid, Starch, Glycerol
Results: Way more a foam like. Bubbly and thicker.
Tests C
December 2023
Key ingredients: Same. In tests C preparation is adjusted.
Results: Foamier which is very good. Orange and so Beautiful. Properties: lighter then previous. More porous.
Tests D
December 2023
Key ingredients: Same + sooda
Results: Softer then previous foams. More porous. Easily breakable, light, dissolves in water.
Tests E
December 2023
Key ingredients: Citric Acid, starch, glycerol. In previous tests citric acid part to starch was 3:1. In next test idea is to change ratio to starch: citric acid 3:1 with a goal to make foam softer.
Also was done couple of experiment adding 1) methyl cellulose and 2) microcrystalline cellulose to bind the structure.
Results: It did not become softer. While cooking long was got very beautiful sampes:
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What is next? Now moving to other projects! When will come back to this one - would continue with pH. With literature, cross-linking bettween citric acid and starch is the best at pH 5- 6 - it will be next step when have the time.
ChemArts Project, School of Chemical Engineering, Aalto University
Chem Engineering MSc student Elizaveta Lingonberg