On the deformation behavior of cellulose aerogel reinforced polymers

Kurzfassung

Cellulose aerogels provide an accessible and highly porous (>85%) structure yielding light -weight yet mechanically strong and stable monolithic materials. The randomly arranged nano fibrous felt of cellulose aerogels serves as a predefined network. Upon replacing the contained air with a suitable matrix resin, we achieve Cellulose-Aerogel Reinforced Polymers (CARPs).While capillary forces must be avoided during the aerogel synthesis, they turn out to be of uttermost importance in a flawless infiltration result. Via capillary force assisted infusion with unsaturated polyester resins for the matrix system results in a fiber-matrix-composite that outstandingly merge materials' characteristics.While the density of such composites slightly exceeds that of the thermoset itself, the 6-22 vol.-% of fiber reinforcement strongly affects the materials properties. Focusing on the mechanical properties of CARPs we observe the Young's and flexural moduli to improve considerably in tensile as well as in 3-point-bending tests, respectively. Moreover, the deformation mechanism itself appears to alter with cellulose aerogel incorporation. While cellulose aerogels from ZnCl2 show cleavage fracture, controlled by tensile stresses, their CARP counterparts yield shear fracture with breaking elongations above 20 %, which is unimaginable for the reference thermoset. In classical mechanical tests, we observe enormous plastic deformation (>350%) with an absent neck-formation during tensile tests. Furthermore, we have found a strong dependence on the strain rate in impulse excitation and dynamic mechanical analysis (IET & DMA). Thus, CARPs show unexpected possibilities in terms of composite moulding. In conclusion, the scale of the nanofibers found in cellulose aerogels (7-12 nm), the strong strain rate dependency, and the enormous plastic deformation allow CARPs to qualify as superplastic materials.