A group of Mexican researchers has studied the effect of adding the by-products of mango, hibiscus, and coffee in the development of bioplastics made from starch.
Starch is a natural polymer and the material most widely used to manufacture biodegradable plastics due to its renewability, availability, and low cost because it is widely distributed in nature as it is the main energy reserve polysaccharide in plants. However, plastics made from starch exhibit both unsatisfactory properties and limited stability when exposed to moisture, thermal decomposition at low temperatures, and lower resistance to deformation.
To see if they could improve this, researchers evaluated the effect that adding by-products, such as fruit peel and bagasse, would have on a bioplastic's physical properties (color, texture, morphology, water activity, and biodegradability).
"We developed bioplastics out of starch, gelatin, and glycerol to make a spoon-shaped object (for food) adding mango peel, roasted coffee residues, and cooked hibiscus calyces, which are rich in fibers such as cellulose, hemicellulose, and lignin," stated researcher Veronica Flores Casamayor, from Cinvestav Querétaro Unit.
According to the study, which was published in the Biotecnia journal, a good adherence between the reinforcing material (by-products) and the matrix (starch with gelatin) leads to a resistant interface, causing an increase in its mechanical performance. The addition of the by-products doubled the strength of the spoons, avoiding the fracture of the biopolymers.
According to the results published, the addition of natural fibers positively influences the biodegradation rate because they act as channels that facilitate microbial entry into the polymer matrix.
After 48 hours of being discarded in damp earth, there was a visible change in the object's shape, a visual deterioration of the color, and of the mechanical properties of the bioplastics, regardless of the by-product used for their elaboration. After 120 hours, the bioplastics could not be manipulated or identified due to their fragmentation, swelling, and stickiness. Thus, the researchers consider that this product would break down in the environment in less than one week.
The study was carried out by Veronica Flores Casamayor and Geronimo Arambula Villa, from the Cinvestav Querétaro Unit, and Ricardo Salazar Lopez, Yanik I. Maldonado Astudillo, and Javier Jimenez Hernandez, from the Autonomous University of Guerrero (UAGro).