Progress in Organic Coatings 65 (2009) 222–228 Contents lists available at ScienceDirect Progress in Organic Coatings journal homepage: www.elsevier.com/locate/porgcoat Surface modification of TiO 2 nano-particles with silane coupling agent and investigation of its effect on the properties of polyurethane composite coating M. Sabzi, S.M. Mirabedini ∗ , J. Zohuriaan-Mehr, M. Atai Colour, Resin & Surface Coatings Dept., Iran Polymer and Petrochemical Institute, P.O. Box 14965-115, Tehran, Iran article info Article history: Received 2 June 2008 Received in revised form 29 October 2008 Accepted 18 November 2008 Keywords: Surface modification TiO2 nano-particles Dispersion Mechanical properties abstract Surface modification and characterization of TiO 2 nano-particles as an additive in a polyurethane clear coat were investigated. For the improvement of nano-particles dispersion and increasing possible inter- actions between nano-particles and polymeric matrix, the surface of the nano-particles was modified with amino propyl trimethoxy silane (APS). Equivalent amount of APS for monolayer formation on the nano-particles surface was determined by means of elemental analysis (CHN). The grafting of APS on the TiO 2 nano-particles surface was characterized with TGA and FTIR techniques. Mechanical proper- ties of coatings containing various amount of TiO 2 nano-particles were evaluated with DMA technique and tensile strength measurement. UV–vis spectroscopy was employed to evaluate the absorbance and transmittance of the nano-TiO 2 composite coatings in the wavelength range of 230–700 nm. The results showed that surface treatment of TiO 2 nano-particles with APS improves nano-particles dispersion, mechanical properties and UV protection of the urethane clear coating. © 2008 Elsevier B.V. All rights reserved. 1. Introduction In the recent years, the preparation of polymer nanocompos- ite materials has been intensely considered due to their relatively remarkable various properties including mechanical properties, such as scratching and abrasion resistance, optical properties, and wide-spread potential applications [1–2]. Titanium dioxide (TiO 2 ), with high refractive index, 2.7, in the crystal form of rutile, is one of the most important inorganic pigments, because of its potential applications in many differ- ent activities. TiO 2 pigment has attracted interest as an inorganic material for nanocomposites. Currently, the requirement for optical materials with high refractive index and transparency in the fields of optical waveguides [3], clear coatings, antireflection coatings and adhesives for optical components is increasing. For producing suit- able nanocomposites for optical materials [4–5], it is necessary to disperse the nano-particles without aggregation in organic binders. Due to their extremely large surface-area/particle-size ratio, nano-particles tend to strongly agglomerate, hence reducing the resultant mechanical properties of the nanocomposite materials [6]. Many efforts have been taken in order to overcome this prob- lem and to enhance the filler matrix interaction. One approach is breaking down the agglomerated nano-particles applying mechan- ical shear forces such as ultrasonic irradiation [7–8]. However, this ∗ Corresponding author. Tel.: +98 21 4458 0040; fax: +98 21 4458 0023. E-mail address: m.mirabedini@ippi.ac.ir (S.M. Mirabedini). approach is restricted due to the limited interaction between the inorganic materials and the polymeric matrix, compared with the very strong interaction between individual nano-particles. Polymer/TiO 2 composites have been successfully synthesized in different polymer matrixes such as polycarbonate [9], polyamide 6 [10], epoxy [11], unsaturated polyester [12], polyacrylate [13], poly(methyl methacrylate) [14], polyimide [15], polystyrene [16], dental composites [17] and silicone elastomer [8]. The majority of nano-particle coatings are based on the nanoclay particles, silica and layered silicate nano-particles for improv- ing mechanical properties such as flexibility, ductility, hardness, strength and stiffness [18–22], whereas investigations on the TiO 2 nano-particles are relatively rare, while TiO 2 nano-particles have board UV rays absorption that it may cause an increase in UV resis- tance of coatings. To achieve proper dispersion of nano-particle polymer matrix and to yield a better compatibility between the nano-particles and host polymeric materials, the use of different coupling agents such as trialkoxy silanes for surface modification of nano-particles is recommended. The appropriate surface modification on nano- particles, not only leads to better dispersion and compatibility of them in polymer matrix, but also by formation of chemical and physical interactions with polymer matrix, could guarantee a durable chemical junction between two incompatible phases [23–25]. The purpose of this study was to investigate the effect of different wt.% of amino propyl trimethoxy silane (APS) on the surface grafting of TiO 2 nano-particles. Surface modification and characterization of 0300-9440/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.porgcoat.2008.11.006