Glass fiber reinforced plastics (GFRP) are gaining a strategic relevance in many sectors because of their excellent properties such as high stiffness and strength combined with an extremely low density.
Even if the environmental benefits offered by the use of GFRP are evident, their waste management remains a big issue. Until now no suitable disposal processes are accessible for end-of-life composites and in the future the waste related to the dismantling of products made of them will get of major importance.
Considering the energy required for production of E-glass fibers (50 GJ/t) and epoxy resins (140 GJ/t) a reuse of the reinforcement is essential to reduce the environmental impact of GFRP waste. Today European legislation demands a waste hierarchy (directive 2008/98/EC) and, thus, landfill shows the lowest priority and has to be replaced at least by recovery (i.e. incineration) and recycling.
The incineration process can only recover the caloric value of the matrix while the inorganic fraction is a zero sum game. In case of typically 70% E-glass fiber and 30% epoxy resin energy recovery would range below 8% of the value already consumed for production. However, during combustion the fiber reinforcement is completely destroyed and, thus, no fiber recovery is possible.
Although thermo-chemical processes for improving recycling the reinforcement phase have been developed the process temperature required to decompose the epoxy resins is too high and drastically reduces tensile strength. According to literature a recovery of fiber strength is possibly by etching processes based on a removal of surface flaws. In this study four different fiber materials have been thermally treated to induce a reduction of the mechanical properties.
Subsequently the fibers were etched in order to determine the possible degree of recovery. It is demonstrated that all materials exhibited a dramatic loss of strength to about the half after the thermal treatment.
The possibility to recover fiber strength of thermally damaged inorganic reinforcement fibers offers great opportunities. However, it is not only necessary to develop an industrial viable process for fiber etching (i.e. recycling) but also to improve the technology of GFRP (i.e. eco-design).
Davide Pico, Andreas Bartl, Vienna University of Technology.
Companies: Mechanical Properties