(603c) Thermomechanical Behavior of Poly(vinyl alcohol)/Graphene Nanoplate (GNP) Composite Films for High-Velocity Impact Applications

Poly(vinyl alcohol) (PVA)/graphene nanoplatelet (GNP) composite films have shown promising high-velocity impact resistance.^1,2 The perpendicular and parallel GNP morphologies within the composite films have major benefits for the blast energy dissipation. For example, the perpendicular morphology may confine fracture to the region near the impacting high-velocity object. Similarly, the parallel morphology may prevent the penetration of the object and cause energy absorption through crack propagation (delamination) parallel to the GNP planes and sliding of planes over each other. In this respect, aligned GNPs will absorb the blast energy by a combination of fracture and shearing between the GNPs and the PVA-GNP interface. Moreover, owing to the high thermal conductivity of graphene, heat dissipation in the event of thermal shock are expected to occur efficiently in the PVA/GNP composite film, mitigating the thermal stresses in the substrate. In this work, we used solution casting to fabricate PVA/GNP films with high GNP concentrations (40-60 wt.%) for high-velocity impact applications. Our aim was to treat these PVA/GNP films as ceramic-like sacrificial layers within a multilayer material system to absorb most of the kinetic energy of the impacting object. Specifically, we prepared an aqueous solution of high-molecular-weight PVA (98-99%) and mixed it with an aqueous suspension of xGnP (Grade C, XG Sciences) nanoparticles in deionized water. Previous studies had used graphite (multilayer graphene, MLG) in PVA at about 35 vol.%.² However, we specifically used a GNP grade with a large surface area for better composite film performance. We further sonicated the resulting suspension for 30 min (20 Hz, continuous) and cast into films that were dried overnight at 40°C. Next, we hot-pressed the dried films at 160°C under 10,000 lb pressure for two hours to eliminate film shrinkage. The final thicknesses of the films were about 0.5 mm. To further investigate the layering effect of the PVA/GNP composite film on its thermomechanical performance, we fused two 0.5-mm films into one double-layer film (final thickness of about 1 mm) by hot-pressing the films under the same conditions as those mentioned above. We are currently performing dynamic mechanical analysis (DMA) (both temperature and frequency sweep), thermogravimetric analysis (TGA), split-Hopkinson pressure bar (SHPB) test, nano-indentation, and dart drop test of the specimens. Our aim is to fully characterize the films to determine the glass transition temperatures, temperatures of the onset of degradation, dynamic stress-strain data, etc. Moreover, we are investigating the cross-sectional morphologies of the films using scanning electron microscopy (SEM). This work is ongoing, and we will present our preliminary data.

References:

(1) Xu, Y.; Hong, W.; Bai, H.; Li, C.; Shi, G. Strong and Ductile Poly (Vinyl Alcohol)/Graphene Oxide Composite Films with a Layered Structure. Carbon N. Y. 2009, 47 (15), 3538–3543.

(2) O’Masta, M. R.; Russell, B. P.; Deshpande, V. S. An Exploration of the Ballistic Resistance of Multilayer Graphene Polymer Composites. Extrem. Mech. Lett. 2017, 11, 49–58.