Polyurethane/Silane-Functionalized ZrO2 Nanocomposite Powder Coatings: Thermal Degradation Kinetics

Farimah Tikhani,Henri Vahabi,Hossein Hosseini,Amin Esmaeili,Behzad Shirkavand Hadavand,Maryam Jouyandeh,Ahmad Mohaddespour,Krzyszof Formela,Hamed Fakharizadeh Bafghi,Seyed Mohammad Reza Paran,Mohammad Reza Saeb

doi:10.3390/coatings10040413

Abstract

A polyurethane (PU)-based powder coating reinforced with vinyltrimethoxysilane (VTMS)-functionalized ZrO2 nanoparticles (V-ZrO2) for thermal stability was developed. Chemical structure, microstructure and thermal degradation kinetics of the prepared coatings were investigated. The peak of aliphatic C–H vibrating bond in the Fourier transform infrared (FTIR) spectrum of V-ZrO2 was a signature of VTMS attachment. Scanning electron microscopy (SEM) images reveled that, by increase of V-ZrO2 content from 0.1 to 0.3 wt.% and then 0.5 wt.%, some agglomerations of nanoparticles are formed in the PU matrix. Thermogravimetric analysis (TGA) of the PU/V-ZrO2 powder coatings was performed at different heating rates nonisothermally to capture alteration of activation energy (Ea) of degradation of PU/V-ZrO2 powder coatings as a function of partial mass loss by using Friedman, Kissinger–Akahira-Sunose (KAS), Ozawa–Wall–Flynn (FWO) and modified Coats–Redfern isoconversional approaches. It was observed that by addition of 1 wt.% V-ZrO2 to PU resin the early state degradation temperature at 5% weight loss increased about 65 °C, suggesting a physical barrier effect limiting the volatility of free radicals and decomposition products. Incorporation of 5 wt.% ZrO2 led to about 16% and 10% increase in Ea and LnA of blank PU, respectively, which was indicative of higher thermal resistance of nanocomposite powder coatings against thermal degradation. There was also obvious agreement between model outputs and experimental data. The results reveal that nanocomposite coating shows superior thermal properties compared to neat PU powder coatings, and the presence of nano ZrO2 in sufficient amount causes retardation of the thermal decomposition process.

Highlights

IntroductionPU coatings prominent candidates for decorative and protective purposes [3,4,5,6]
Solid, eco-friendly and cost-efficient are a number of characteristics that polyurethane (PU)thermoset powder coatings are known for among all the emerging coatings, and the reason why PU has been considered as the best alternative for construction and building materials to reduce the hazardous volatile organic chemicals quite frequently used in the paint and varnish industry [1,2].The high cross-link density, energy saving features and excellent application performance have madePU coatings prominent candidates for decorative and protective purposes [3,4,5,6]
When it comes to the applications where stability and resistance to harsh conditions, such as thermal or stress shock, UV solar radiation and temperature elevations, are among the criteria, such coatings lose their properties as a consequence of cracking and thermal degradation that seriously shortens their service lifetime [7,8,9]

Summary

Introduction

PU coatings prominent candidates for decorative and protective purposes [3,4,5,6]. When it comes to the applications where stability and resistance to harsh conditions, such as thermal or stress shock, UV solar radiation and temperature elevations, are among the criteria, such coatings lose their properties as a consequence of cracking and thermal degradation that seriously shortens their service lifetime [7,8,9]. Yu et al [14] used CaCO3 nanoparticles as a modifier in epoxy powder coatings and reported the remarkable enhancement in tensile property and corrosion resistance of the polymer. Zirconium oxide (ZrO2 ) nanostructures have proved good chemical resistance and mechanical properties as well as high resistance to thermal shock and low thermal conductivity [15]

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Conclusion