Water-mediated chelation dynamics of dicarboxylic acid functionalized TiO2 nanoparticles for β-nucleation enhancement in isotactic polypropylene composites

Abstract

ABSTRACT Isotactic polypropylene (iPP) is the most prominent form of polypropylene, and β-phase is the most resistant to impact compared to the crystalline forms. However, β-phase is the least frequently obtained under conventional operating conditions. TiO2 nanoparticles were functionalized with dicarboxylic acids as nucleating agents to promote β-crystal formation in iPP. The effects of three dicarboxylic acids – glutaric, pimelic, and azelaic – were characterized on TiO2-modified surfaces. Additionally, the interactions between TiO2 and water molecules, crucial for the formation of chelating or bridging linkages, were analyzed using Fourier Transform Infrared spectroscopy. For pimelic and azelaic acids at the polymer processing temperature, the carboxyl group band disappeared, suggesting a transition of the acid-calcium union from a bridging to a chelating linkage due to the presence of water molecules. These molecules help maintain the stability of the chains during processing. X-ray diffraction (XRD) analysis confirmed a higher content of β-crystalline structures in iPP when modified with pimelic and azelaic acids. The research indicates that water molecules, desorbed during manufacturing, facilitate the chelating form, thereby enhancing β-nucleation and improving the surface properties of iPP composites. These β-nucleated PP composites represent a promising material solution for medical device applications, offering a compelling combination of enhanced properties and cost-effectiveness.