Insight into thermo-mechanical enhancement of polymer nanocomposites coated microsand proppants for hydraulic fracturing

The present work reports the fabrication of ultra-high strength microsand proppants (100 mesh) through a polymer nanocomposite dual coating approach and gives insight into their thermo-mechanical reinforcements. The dual coating can be of 3D-cross-linked poly(styrene-methyl methacrylate)/divinylbenzene) (PS-PMMA/DVB) porous network and thermally cross-linked epoxy with graphene nanosheets. The inner layer of PS-PMMA/DVB was prepared using bulk polymerization of styrene (S) and methyl methacrylate (MMA) at 70 °C with a free radical initiator azobisisobutyronitrile (AIBN). The outer layer was prepared by mixing epoxy resin, a cross-linker, and commercial graphene (CG) followed by thermally curing the mixture. The dual-coated microsand proppants exhibited enhanced mechanical characteristics of elastic modulus (E) as high as 7.78 GPa, hardness (H) of 0.35 GPa, and fracture toughness (K_c) of 3.19 MPa m^1/2 along with largely improved thermal properties. Moreover, the dual-coated microsand proppants exhibit a very high-stress resistance up to 14000 psi, and to the best of our knowledge, this is the highest stress resistance value attained for the modified sand-based proppants so far.