Carbon fibers have been extensively used in the fabrication of light and strong composites such as carbon-fiber-reinforced thermoplastics desirable for numerous applications. However, owing to the emerging environmental concerns, developing an effective technique to allow the recycling of carbon fibers is highly desirable for sustainability. This is quite favored by the life cycles of carbon fibers considering that most of these carbon-fiber-based composite materials are recyclable. Past literature reviews have revealed that the mechanical properties of these composite materials depend on the interfacial properties of the components which are poor for the case of carbon fibers and thermoplastics. As such, polymers and inorganic materials have been lately introduced to modify and enhance the surface adhesion between the carbon fibers and thermoplastic resins. Consequently, the mechanical properties of the carbon fibers should be improved to ensure their effective reusability in fabricating new carbon-fiber-reinforced thermoplastics materials.
In a recent paper published in the Composites Science and Technology journal, researchers: Professor Tetsuya Yamamoto, Sho Yabushita, Toshihira Irisawa and Yasuhiro Tanabe from Nagoya University examined the feasibility of silica colloids in enhancing the mechanical properties of carbon-fiber-reinforced thermoplastics. In particular, the effects of high resistance silica colloids on the carbon fiber surface were evaluated using sol-gel reaction-based surface modification and electrodeposition.
Briefly, the research team started their experimental work by synthesizing heat-resistant silica colloids through a sol-gel reaction. Next, the silica colloids were absorbed onto carbon fibers via electrodeposition. The interfacial and mechanical properties of the resulting carbon-fiber-reinforced thermoplastics were evaluated through fragmentation tests, cross-sectional observations and three-point bending tests. Finally, the tensile properties were accessed to quantify the quality of the reclaimed carbon fibers by heating the carbon-fiber-reinforced thermoplastics.
Reports showed that the surface modification improved the interfacial interactions between the carbon fibers and nylon in the carbon-fiber-reinforced thermoplastics as well as maintained the mechanical properties of the carbon fibers upon removal of the nylon matrix. On the other hand, the fabricated carbon-fiber-reinforced thermoplastics exhibited homogeneous strength. This was attributed to the fact that the silica particles acted as spacers between the carbon fibers making them adhere to each other owing to their hydrophobicity in the nylon resin.
It was worth noting that the mechanical properties of the carbon-fiber-reinforced thermoplastics were maintained above the room temperature. Furthermore, the fiber colloids deposited on the carbon fibers prevented the degradation of the tensile strength of the reclaimed fibers during the heating by limiting the chances of reacting with oxygen.
In summary, the Nagoya University scientists successfully utilized silica colloids to enhance the bending strength, thermal stability, and recyclability of carbon-fiber-reinforced thermoplastics. Based on the results, the study has been selected by Advances in Engineering selection team as a key scientific article and demonstrated a useful technique for the sustainable recycling of carbon fibers. With the increasing demand for carbon fibers, Professor Tetsuya Yamamoto, the first and corresponding author in a statement to AIE noted that the presented results are important step in advancing recyclability of carbon-fiber-reinforced thermoplastics desirable for numerous applications in aviation, automobile, and other industries.
Yamamoto, T., Yabushita, S., Irisawa, T., & Tanabe, Y. (2019). Enhancement of bending strength, thermal stability and recyclability of carbon-fiber-reinforced thermoplastics by using silica colloids. Composites Science and Technology, 181, 107665.