Glass fiber treated with a glycine bridged silane coupling agent reinforcing polyamide 6(PA6): effect of hydrogen bonding

Silane coupling agents play an indispensable role in improving interfacial adhesion of composite materials, but their interaction mechanism is often unclear. This article combines experiments and theoretical calculations to reveal the importance of hydrogen bonds between silane coupling agents and the matrix polyamide 6 in improving the mechanical properties of composite materials. Firstly, glycine bridged silane (GBSilane) was synthesized and the structure was confirmed by FT-IR, ¹H NMR and HRMS. Secondly, with glass fiber treated using GBSilane as a filler, the mechanical properties of glass fiber/PA6 composite materials were studied. Compared with untreated glass fiber/PA6 composites, under the optimal treatment concentration of 1.5%, the tensile strength of glass fiber/PA6 composites treated with 3-aminopropyl triethoxysilane (APTES) and GBSilane increased by 41% and 67%, respectively, and the notch impact strength increased by 55% and 96.5%, respectively. Lastly, density functional theory (DFT) calculations revealed that stronger hydrogen bonds have formed between GBSilane and PA6 than APTES, which have induced the stronger PA6–GBSilane binding energy of 58.20 kJ mol⁻¹. By comparison, the binding energy of PA6–APTES is only 30.91 kJ mol⁻¹. These results demonstrated that the as-synthesized GBSilane could improve the mechanical properties of PA6 composites through an enhanced hydrogen bonding mechanism.