Brazilian researchers develop new polymeric material

Substituting traditional plastic bags for biodegradable polymers is once again fueling discussion about the need to diminish the impact of discarding this type of material in the environment. This switch, however, is hampered by the high costs of a few types of polymers that are degraded in just a few years by the action of natural microorganisms and agents (biodegradable); in contrast, the decomposition of conventional polymers takes centuries.

By Elton Alisson

Agência FAPESP – Substituting traditional plastic bags for biodegradable polymers is once again fueling discussion about the need to diminish the impact of discarding this type of material in the environment. This switch, however, is hampered by the high costs of a few types of polymers that are degraded in just a few years by the action of natural microorganisms and agents (biodegradable); in contrast, the decomposition of conventional polymers takes centuries.

A new category of polymeric materials being developed by researchers at Universidade Federal de São Carlos (UFSCar) could, among other things, help to reduce the cost of the biodegradable polymers currently available on the market, in addition to being the basis of diverse solutions for the areas of medicine and the environment.

The possibilities for development with these new materials, known as nanostructured polymeric systems, were presented in the 1st São Carlos School of Advanced Studies in Materials Science and Engineering (SanCAS-MSE), held from March 25 – 31, 2012.

Held under the auspices of the São Paulo School of Advanced Sciences (ESPCA), a FAPESP-funded program, the event was organized by UFSCar’s Department of Engineering and Material Sciences (DEMa) under the coordination of professors Edgar Zanotto, Elias Hage Junior and Walter Botta Filho.

Through a Thematic Project, funded by FAPESP, the UFSCar researchers began to develop and to characterize diverse nanostructured materials.

Composed of ceramic and polymeric particles spread across a polymeric matrix, with dimensions on a nanometric scale (as small as a billionth of a meter), these new materials offer better mechanical, optical and transport properties than conventional polymers.

“The combination of nanoparticles with the polymer matrix adds better mechanical, optical and transport properties to the final plastic product. In the case of plastic bags, for example, it also allows for a reduction in the quantity of the biodegradable polymer and the financial material costs, improving its mechanical and transport properties, while maintaining the capacity for quicker degradation in comparison to traditional polymers,” says Rosa Elida Suman Bretas, professor at UFSCar and coordinator of the project, in an interview with Agência FAPESP.

These new nanostructured polymeric systems will have several applications in the packaging area, such as transparency, a property that is limited by many commercial polymers.

By mixing commercial polymers on a nanometric scale with other polymers that perform more adequately for use as packaging and creating what is known as a nanoblend, it is possible to improve the properties and maintain the transparent polymeric system.

“The mechanical properties of the two polymers are modified when they are blended. Often, one reinforces or improves the chemical stability of the other,” says Hage, one of the project’s lead researchers.  

Other possible applications for these new materials are in medicine for the development of polymeric nanofibers, which serve to support the growth and differentiation of stem cells.

Formed by polymers with a nanometric diameter, in which nanoparticles of compounds that are biocompatible with the human body are incorporated (such as hydroxyapatite, which represents 70% of the composition of bones), the nanofibers comprise an entanglement that is very similar to the extracellular matrix that sustains human cells. In placing cells in the entanglement of nanofibers, they feel “at home” and anchor to the material, according the observations of DEMa researchers from studies conducted with scientists at the Universidade Federal de Minas Gerais (UFMG) and Strasbourg University in France.

“The plastic has afforded spectacular results in certain areas of medicine because the majority of polymers are biocompatible with the human body,” says Bretas. 

In the environmental area, one of the application possibilities of nanostructured polymer systems is in sensors to measure pH (acidity). Researchers have just developed a fabric for this purpose that incorporates polyaniline (a polymer that changes color according to conductivity) in the form of dispersed nanometrics in another polymer, polyamide 6 (nylon).

“We are developing these products on a laboratory scale, but it will take time for production to occur on an industrial scale, mainly because they are expensive and should result in a much greater energy expenditure than that needed to produce conventional polymers,” says Bretas.

One of the technological challenges that researchers are facing when attempting to blend polymers is making their characteristics compatible. Although they are from the same origin (all are organic), they possess different properties and characteristics.

Another major challenge is dispersing and distributing the particles on a nanometric scale within the polymer matrix, which is generally melted. This is due to the polymer matrix’s viscoelastic strength, which causes the nanoparticles to aggregate, forming agglomerates. Ideally, nanoparticles would remain far apart, reinforcing the properties of the final plastic. “It’s as if one tried to catch hot honey and distribute it among particles that are invisible to the naked eye,” explained Bretas.

To produce these new materials, researchers utilize the same equipment employed to produce conventional plastics, such as extruders. Nevertheless, according to Bretas, in the future, new processes may be needed.

Practical classes

During the 1st São Carlos School of Advanced Studies in Materials Science and Engineering, the UFSCar researchers gave practical classes to Brazilian and foreign graduate students covering topics such as how to develop and characterize polymer nanocompounds by utilizing equipment available at DEMa.

The activities complemented theoretical classes offered by foreign scientists who are specialists in the processing and properties of polymer compounds, such as József Karger-Kocsis, a polymer engineering professor at Budapest University of Technology and Economics in Hungary, Ica Manas-Zloczower, professor at the University of Cleveland in Ohio, and Ramani Narayan, professor at Michigan State University.

Renowned in the area of polymers based on nonpetroleum raw materials such as sugar cane, Narayan showed that although biobased plastic comes from a renewable source, it requires the same amount of time to biodegrade as the polymers used in conventional plastic.