Enhancing Fracture Toughness and Stress Energy Release Rate of Vinyl Ester Matrix Using Dual Reinforcement of CNT and GNP

Abstract

In this paper, we report a method of increasing fracture toughness (K_IC) and strain energy release rate (G_IC) of vinyl ester matrix by adopting a dual reinforcement strategy. Reinforcements were carbon nanotubes (CNT) and graphene nanoplatelets (GNP). Both categories of nanoparticles were functionalized with COOH. The idea was to enhance crack bridging and interface sliding with CNT inclusions, given their high aspect ratio. In addition, promote crack-tip blunting and cross-linking density with GNP inclusions, due to their platelet structures. Both K_IC and G_IC were measured using ASTM D5045-14. An exhaustive experimental study revealed an optimum loading of both nanoparticles to be 0.25 wt% CNT and 0.5 wt% GNP, based on the highest combination of K_IC and G_IC values. We observed that stress intensity factor, K_IC, of neat vinyl ester increased by 43% from 1.14 to 1.62 MPa*(m^½). Meanwhile, the improvement in G_IC was even greater with an increase of 65%, i.e., from 370 to 610 J/(m²). Differential scanning calorimetry (DSC) studies showed a discernible shift in glass transition temperature (T_g) from 123 to 128°C. The slight temperature increase was similar in thermogravimetric analysis (TGA). We observed the maximum thermal decomposition temperature (T_p) increase from 410 to 414°C, as was evident in the derivative TGA (DTG) curves.