A group of Brazilian researchers have developed strategies to produce polymer-graphene nanocomposites on an industrial scale. The isolation of graphene crystals is one of the most significant recent advances in science and technology, first performed in 2004 and awarded the Nobel Prize for Physics in 2010. However, the creation of graphene nanocomposites with plastics still occurs basically in the laboratory.
“On a small scale, solvents and other techniques are used and work well in experiments, but graphene reagglomerates and loses its properties in the machinery used in the plastics manufacturing industry,” said Guilhermino José Macêdo Fechine, principal investigator for the study and a researcher at Mackenzie Presbyterian University’s Center for Advanced Research in Graphene, Nanomaterials and Nanotechnology (MackGraphe) in São Paulo, Brazil. MackGraphe is supported by FAPESP.
A paper has been published in eXPRESS Polymer Letters, and a presentation was made to the 23rd Brazilian Materials Science and Engineering Conference (CBECiMat), which took place on November 4-8, 2018, at Foz do Iguaçu, Paraná State (Brazil).
The resulting novel techniques considerably improve the dispersion of graphene particles inserted into a plastic polymer material using near-industrial scale machinery. Potential applications for plastic nanocomposites containing graphene range from sports equipment with enhanced abrasive strength to 3D printing filaments and cell culture scaffolds.
“There are a great many possible applications,” Fechine said. “The bottleneck is the manufacturing process, as not everything you can do in the lab is compatible with the plastics manufacturing industry.”
Another paper delivered to the conference described the corrosion behavior of high-strength aluminum alloy structures assembled by friction stir welding (FSW).
“Conventional welding typically involves the use of a specific material that remains in contact with the welded parts and creates a difference in corrosion behavior in the area concerned,” said Hercílio Gomes de Melo, a professor at the University of São Paulo’s Engineering School (POLI-USP) and principal investigator for the study.
“FSW doesn’t involve the addition of another metal. It’s a solid-state joining process. The aluminum is heated to a temperature close to its melting point by friction using a rotating tool with special geometry that heats the workpieces to be welded and causes intense plastic deformation. The softened metal rotates around the tool shaft, cools and solidifies, forging the weld. This creates differences in the microstructure of the joint zone, affecting its susceptibility to corrosion.”
The results obtained so far show that the weld zone may be susceptible to corrosion to a greater or lesser extent depending on the type of aluminum alloy used. In some cases, different alloys can be successfully welded. “The joint zone is normally more fragile, but some alloys make an even stronger weld than the original materials. Every alloy is a universe,” Melo said.
FSW is used in the fabrication of small jet airplanes and by NASA (the US space agency) in rocket fuel tanks. However, many aspects of corrosion still need to be studied and elucidated.
Toxic gas sensor.
Another research field discussed at the conference concerned materials for use as sensors. A paper on the topic was delivered by Valmor Roberto Mastelaro, a professor at the University of São Paulo’s São Carlos Physics Institute (IFSC-USP).
Mastelaro leads one of the few research groups in Brazil that are developing toxic gas sensors and is a member of the Center for Development of Functional Materials (CDMF), one of the Research, Innovation and Dissemination Centers (RIDCs) funded by FAPESP.
“These sensors are made by very few companies in the world,” Mastelaro said. “Demand is high from industries with chemical and physical processes that may produce toxic gases. In addition, there’s growing concern about greenhouse gases and pollutants that constitute a health hazard for city dwellers.” The research was supported by FAPESP.
Nanostructured metal oxides are currently the materials that have the best characteristics for use in portable gas sensors with low energy consumption. Conventional sensors need to be heated to high temperatures to perform reliably, entailing significant energy costs.
“The idea is to develop sensors that don’t require such high temperatures and are also highly selective. There are many gases in the air we breathe, and sensors must be able to detect those of interest very accurately,” Mastelaro said.
CBECiMAT has been held every two years since 1974. This edition was organized by researchers at IPEN’s Center for Materials Science and Technology (CCMAT).
“CBECiMat has expanded so strongly in recent years that it’s had to be divided into five major areas,” said Lalgudi Ramanathan, a researcher affiliated with CCMAT and chair of the executive committee for the conference.
The five areas were coordinated by CCMAT professors Jesualdo Luiz Rossi (metallic materials), Eliana Navarro dos Santos Muccillo (ceramic materials), Gerson Marinucci (composite materials), Leonardo Gondim de Andrade e Silva (polymeric materials), and Nelson Batista de Lima (materials science education).
Other highlights of the event included nanomaterials and biomaterials, which can be used to administer medical drugs more efficiently, for example. “Many researchers at IPEN have worked intensively on the development of drug delivery scaffolds,” Ramanathan said.
The conference lasted three and a half days, with six concurrent sessions on each day, as well as 300 poster presentations all told. It was supported by the National Council for Scientific and Technological Development (CNPq), attached to Brazil’s Science, Technology, Innovation and Communications Ministry; the Education Ministry’s Office for Faculty Development (CAPES); and FAPESP, which supported participation by 157 researchers with PhDs.
“Almost half the attendees were students, who have always been the main focus for the event,” Muccillo said. “Although most were from the South and Southeast regions, there were representatives of all Brazilian states.”