Characterization of Polymer-Coated TiO2 Particles by TGA and DSC

When polymeric binders are used in paints with hydrophilic pigments such as titanium oxide, the pigments must be treated beforehand with polymers that are compatible with the binder. Otherwise, large agglomerates can form due to poor adhesion between the binder and the particles. This can lead to brittle films and fractures in the paint coating. This article shows how TGA and DSC can be used to determine important properties of the coating using titanium dioxide as an example.

Introduction

Paints consist mainly of pigments, a binder and a solvent. In addition, numerous additives are used in order to obtain a multitude of specific properties, for example drying time, flow behavior, UV stability, gloss, etc. The binder binds the pigments as a thin film on the substrate after the solvent has dried. Binders are usually polymers (e.g. acrylates, polyurethanes, polyesters, melamine, etc.).

If polymeric binders are used together with hydrophilic pigments such as titanium dioxide (TiO₂), large agglomerates of pigments can be formed due to poor adhesion between the binder and the particles. This can lead to brittle films and to fractures in the coating of the paint. To prevent this, the particles are coated beforehand with polymers that are compatible with the binder.

This article describes how TGA and DSC can be used to investigate important properties of the coating such as thermal stability, the influence of polymerization time on the thickness of the coating, and the glass transition temperature, using titanium dioxide as an example.

Coating of the Titanium Dioxide Powder

The titanium dioxide used was crystalline TiO₂ powder (rutile). In a first step, the surface of the TiO₂ was hydroxylated and chemically modified with trimethylamine chlorosilane (see Figure 1). The modified TiO₂ particles were then encapsulated by grafting P(EG)MEMA onto their surface using a technique known as living radical polymerization (LRP) starting from oligo(ethylene glycol) methyl ether methacrylate (OEGMEMA) as shown in Figure 2 [1]). The result of this encapsulation process is shown in Figure 3.

Conclusions

Experiments using TiO₂ particles grafted with P(EG)MEMA particles showed how important properties of coatings such as the glass transition temperature, the thickness of the polymer coating, and the thermal stability of the polymer coating can be determined by TGA and DSC.

_{Characterization of Polymer-Coated TiO2 Particles by TGA and DSC | Thermal Analysis Application No. UC 447 | Application published in METTLER TOLEDO Thermal Analysis UserCom 44}