Highly improved mechanical and thermal properties of alkali silicate and graphene nanoplatelet composite adhesives

Abstract Inorganic adhesives have received increased attention due to their high temperature resistance, non-toxicity, and environment friendliness. However, poor adhesion strength of inorganic adhesives hinders their application. Further, graphene improves the mechanical and thermal properties of polymer composites. Herein, graphene nanoplatelets (GNP) with different specific surface areas were added into a mixed silicate (MS) containing different ratios of alkali silicates. The results revealed that lap shear strengths increased from 7.4 MPa with the unmodified MS to 9.42 MPa with the MS/GNP 750_10% composite. In addition, the GNP powder with the highest surface area (MS/GNP 750_10% composite) formed maximum interfaces with the silicate matrix, leading to effective load transfer and reduction in stress concentration sites. Hardness and modulus increased as the GNP surface area increased; unmodified MS had the highest values because GNP changed MS from brittle to ductile. In addition, at room temperature, thermal conductivity increased by 60% in the vertical direction and 173% in the horizontal direction in the MS/GNP 750_10% composite compared to the unmodified MS. Furthermore, at a higher temperature (100 °C), the thermal conductivity of the MS/GNP 750_10% composite increased by 273% in the vertical direction and 412% in the horizontal direction.