Enhancing performances of natural zeolite-compounded thermoplastic polyurethane eco-composites through interfacial engineering

In this work, the surface of natural zeolite (Zeo) was modified via four different silane coupling agents containing epoxy, octyl, amino, and triamine functional groups to enhance surface interactions between thermoplastic polyurethane (TPU) matrix and Zeo phases. The chemical compositions and functionalities of silane coatings on Zeo surfaces were confirmed by EDX and FTIR spectroscopy. Additionally, contact angle measurements were conducted in terms of surface hydrophobicity for pristine and silane-coated Zeo powders. The melt-blending and injection-molding processes were utilized to fabricate TPU/Zeo composite samples. Mechanical tests revealed that Zeo inclusions led to an increase in tensile strength and hardness values of the polymeric matrix while its flexibility stayed constant. The triamine-silane-modified Zeo yielded the best mechanical performance. The addition of modified Zeo shifted the decomposition temperature of TPU to higher values according to the TGA study. Regardless of modification type, Zeo inclusions improved the thermal stability of unfilled TPU. Modified Zeo-containing composites exhibited lower MFI values than neat Zeo-loaded samples. SEM micrographs of composite surfaces visualized that silane-modified Zeo surfaces were covered by polymer phase which confirmed their enhanced interfacial adhesion to TPU matrix. Silane modifiers comprising amine and epoxy groups improved the properties of Zeo-filled TPU composites significantly. Because of the strong interfacial interactions between the epoxy functional group and the isocyanate segment of TPU, epoxy-based silane displayed the greatest performance levels regarding examined behaviors of composites.