Low content of modified-SCF in waterborne epoxy: mechanical properties and interfacial microstructure

Silanization treatment technology for carbon fiber (CFs) has achieved significant advancements, leading to enhancing the interfacial behavior of polymer matrix. Unfortunately, there has been limited research on the impact of silanized short carbon fiber (SCF) on the mechanical properties of waterborne epoxy (WEP) resin. Herein, to improve the interfacial behavior between SCF and WEP, 3-Glycidoxypropyltrimethoxy Silane (GPMS) was applied to SCF. To extend the successful surface modification, waste CFs was utilized to produce SCFs and subsequently treated with low amount of GPMS (0.1 g). The appearance of new peaks at 1000-1110 cm⁻¹ in the FTIR spectra confirm the formation of Si-O-C bonds on the surface of SCF, creating a chemical bridge between the epoxy matrix and SCF. EDS analysis shows that adding 0.1 g of silane resulted in a 1.7 at% Si on the SCF surface. Higher silane concentrations increased the SCF diameter and its surface smoothness. The effect of functional groups containing Si, on the mechanical properties of SCF reinforced WEP were investigated. The Raman analysis results indicated that the I_D/I_G ratio of SCF increased from 0.86 to 0.95, while the graphitic structure on the surface of SCF diminished after desizing treatment. The Shore D hardness of silanized-SCF/WEP composite increased from 60 to 80 Shore D compared to other specimens. The tensile strength of WEP reinforced with silanized-SCF increased by about 50 % compared to pure-SCF. The results showed that in presence of silanized-SCF, the distinctive feature in WEP structure is displayed after tensile test. Cross-linking formed from the entanglement between GPMS molecules and WEP lead to improving interfacial adhesion, preventing crack growth and preserve the parabola form in WEP structure. In addition, the results showed that with the same load cell in bending test, WEP containing silanized-SCF did not break at all after applying the load. These findings can be applied to the economically development of WEP composite.