Researchers at the São Paulo State University in Ilha Solteira (UNESP) have developed a biodegradable film made from hydroxypropyl methylcellulose (HPMC) and scraps of bacterial cellulose typically discarded by manufacturers of biofilms.
“One of the limitations of films made of HPMC and other biopolymers is their low mechanical strength compared with traditional films derived from petroleum. They are also highly permeable to water vapour, which limits the available applications. We improved these properties by adding bacterial cellulose,” said Pamela Melo, first author on the study published in the journal Applied Materials & Interfaces.
As described in the paper, the researchers first milled the scraps of bacterial cellulose – obtained from a local company that makes biofilms for dressing wound – into fine powder, and then subjected it to sulphuric acid hydrolysis, producing a bacterial cellulose nanocrystal suspension.
Next, to achieve desired film properties, Melo and colleagues performed a series of tests, eventually arriving at the optimal distribution of the nanocrystals within the HPMC matrix via high-energy dispersion using a Turrax disperser.
Finally, the film-forming dispersion was deposited on a substrate. Once the solvents evaporated – which took between 24 and 48 hours – a transparent food-grade film was achieved. The only reason currently preventing its use in packaging is slightly higher than desired water absorption. On the other hand, the material is stronger and less permeable than films made from HPMC only.
The reason for choosing bacterial over plant cellulose was that it can be produced in the lab year-round and, thanks to being a purer molecule, generates less pollution. In addition, cellulose secreted by bacteria contains nanometric fibres that give it high tensile strength, which is beneficial for producing food packaging.
Melo’s team is currently testing other polymer dispersion techniques to develop a competitive product. “Our main focus is on finding substitutes for materials not considered ecologically correct, such as petroleum products. Such substitutes include biodegradable composites derived from renewable resources,” said co-author Márcia Regina de Moura Aouada from UNESP.