Researchers from the group "Technology and design of multi-component products" at the University of Seville, together with experts from the University of Huelva, have obtained a natural bioplastic from soya protein, which is capable of absorbing up to forty times its own weight.

This new product, which is organic and biodegradable, is environmentally friendly. For that reason, the experts are exploring its use in the area of horticulture, specifically as a raw material from which to make agricultural nutrient dispensers.

Another of the objectives that the researchers set themselves when they started the project was to find a material that could substitute plastics obtained from synthetic polymers, which are currently being used in hygiene and sanitary products like nappies and sanitary towels. They are trying to reduce the use of artificial polymers and use another plastic that is biodegradable and part of the environment.

To achieve the design of the material that is summarised in the article 'Natural superabsorbent plastic materials based on a functionalized soy protein', published in the review Polymer Testing, the researchers have done different experiments in the laboratory by altering the composition of this legume. This project has been carried out in collaboration with the General Service of Functional Characterisation, situated in the Centre for Research, Technology and Innovation at the University of Seville (CITIUS).

Specifically, they have modified its attraction to water and have managed to make it retain a higher percentage of this liquid. "Soya has a great capacity for absorption, which makes it an ideal material. However, we considered whether it could be classed with the super-absorbent bioplastics, which are those that can absorb between ten and a thousand times their weight in water. After introducing different variants, the result obtained has been positive," stated the University of Seville researcher Antonio Guerrero, head of the study.

During the tests, the experts have shown that, according to the variables of the process and the combination of the mix, the absorption properties of soya are altered. "Without interfering with its composition, this legume is capable of absorbing twelve times its own weight, but if we modify its molecular structure to increase its attraction to water, this capacity is multiplied by three so that it reaches 36 times its initial weight, that's to say, an increase of 3600% over its real weight," specified Guerrero.

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To carry out the experiments, they firstly processed the soya to extract the protein. With the aim of separating the liquid part from the solid compounds, the scientists used the technique of freeze-drying. "This method is gentler and less aggressive than atomization, so it has practically no effect on the protein. In this way, we managed to isolate the raw material with which we are going to work," Guerrero says.

After this process of dehydration, the experts have mixed the now-modified isolated compound of the protein with a plasticiser. "We obtained a solid concentrate of proteins and, once this composition was prepared, we introduced it into an injection moulding machine and deposited it in a mould. From there, we obtained the test tube with which we are going to do the tests," explained the researcher.

Organic nutrient distributor

As well as having a higher absorption capacity than other conventional bioplastics, the researcher have made such progress that this compound potentially has the qualities for use in horticulture, specifically as a distribution device for agricultural nutrients.

In fact, the following phase of this project is to study the viability of releasing these compounds in the country using natural dispensers formed from super-absorbent soya. To do this, they will simulate a piece of land in the laboratory and will place the moulds loaded with micronutrients like mineral salts, iron and zinc, to which they will keep adding water.

In this way, they will be able to test if, after the drainage phase and because of the action of these dispensers, the water contains nutrients and, if so, in what quantity. "We want to assure ourselves that what is produced is controlled and suitable for the needs of the soil. Also, as it is a biodegradable plastic made from soya proteins, the actual containers, once empty, will serve as substratum for the soil," Guerrero suggested.

Following this line of study, the researchers will continue experimenting with other products like rape and cotton, from which superabsorbent materials could be obtained with sanitary and agricultural industrial applications.