Nanoclay protonation and silane functionalization to enhance mechanical and fracture performance of epoxy nanocomposites

Abstract Nanoclay is considered to be one of the best fillers for reinforcement in structural polymer composites because of its low cost, easy availability, and ability to improve mechanical, thermal, corrosion resistance, barrier properties and nonflammability in corresponding nanocomposites. Pristine nanoclay is hydrophilic and therefore needs surface modification to make it compatible for uniform dispersion with polymer matrix. In the present work, montmorillonite nanoclay was protonated for generating more hydroxyl groups to facilitate silane functionalization and is reinforced to prepare epoxy nanocomposites with a varying content of 0.5 to 20 wt%. Studies are also conducted to investigate the effect of silanization of unprotonated nanoclay on epoxy nanocomposites. Interestingly, uniform highly exfoliated reduced‐size nanoclay platelets are obtained for functionalized protonated nanoclay. This behavior is attributed to the increase in the d ‐spacing between the interlayers of the nanoclay during protonation and silanization. Tensile performances are found best with 0.5 wt% of silanized clay with an improvement of ~50%, ~84% and ~177% in strength, modulus and absorbed failure energy compared to neat epoxy. Although flexural and fracture performance are found highest with 2 wt% of silanized protonated clay with an improvement of ~57.5% in flexural strength and a remarkable ~241% and ~964% enhancement in fracture toughness and fracture energy compared to neat epoxy. The toughening mechanism investigation endorses the improvement in interfacial adhesion of the protonated silanized nanoclay that enhances the properties of the interfacial region, which significantly enhances the resistance for in‐panne crack propagation in epoxy nanocomposites. Highlights Synthesized silanized and silanized protonated montmorillonite clay. Protonation facilitated silane moiety attachment onto nanoclay. Maximum improvement of flexural strength by ~57.5% for ESPrC2. K IC and G IC were highest showing ~1.74 MPam 1/2 and ~830.28 J/m 2 for ESPrC2. Enhanced interfacial adhesion due to SPrC with the epoxy matrix.