Synthesis and properties of alkoxysilane-functionalized urethane oil/titania hybrid films
Introduction
Organic/inorganic hybrid materials possess advantages of organic polymers such as lightweight, flexibility, good impact resistance and good process ability as well as advantages of inorganic materials such as good chemical resistance and high thermal stability. As these properties are also expected from the coating materials, organic/inorganic hybrid composites are widely used in coating applications [1], [2], [3], [4].
One of the challenges in producing hybrid materials with high performance is to control phase separation between organic and inorganic domains. To overcome this difficulty, formation of hydrogen bonding or covalent bonding between the organic and inorganic network has been utilized. Concerning this, a number of researchers have used alkoxysilanes to retard phase separations by facilitating crosslink reactions. In this context, Qin et al. prepared transparent poly(methyl acrylate-co-itaconic anhydrate)/TiO2 [P(MA-co-Itn)/TiO2] hybrid materials by using 3-aminopropyltriethoxysilane (APES) as a coupling agent [5]. It was reported that without APES, opaque hybrid material was obtained, and phase separation was observed.
The synthesis of polymer/titania materials through Si–O–Ti bonding was mainly carried out by sol–gel method [6], [7], [8], [9], [10], [11], [12]. In these studies, tetrabutyl titanate (TBOT), titanium tetra-isopropoxide (TTIP), titanium(IV) chloride, titanium(IV) n-butoxide were used as Ti sources, and (3-isocyanatopropyl)triethoxysilane (IPTEOS), (3-methacryloxypropyl)trimethoxysilane, methyltrimethoxysilane (MTMS), (3-trimthoxysilyl)propyl methacrylate (MSMA), 3-(isocyanatopropyl) triethoxysilane, tetraethyl orthosilicate (TEOS), 3-aminopropyl triethysilane were used as Si sources. Chen et al. produced poly(methyl silsesquioxane) (MSQ)-titania films from titanium n-butoxide and MTMS [6]. The results showed that the prepared films were very uniform with an amorphous nanoscale titania segment. In another study, Xiong et al. synthesized homogeneous organic–inorganic hybrid materials with excellent thermal and optical performance by mixing of (3-methacryloxypropyl)trimethoxysilane-capped acrylic resin with titanium n-butoxide [7]. Moreover, Lu et al. prepared hybrid optical films of TiO2-triethoxysilane-capped polythiourethane (TCPTU) with high refractive indices by titanium butoxide as titania precursor and IPTEOS as Si source [8].
In the present study, alkoxysilane funtionalized urethane oil-titania hybrid coatings were prepared. Oil-modified organo-soluble polyurethanes, urethane oils, have been widely used as an organic coating since utilization of renewable sources in various industrial applications has become an important aspect in respect of the environmental and economic concerns. Urethane oils are produced via the reaction of diisocyanates with hydroxyl-containing oil or oil derivatives [13], [14]. Linseed, sunflower, safflower, soybean, tall and dehydrated castor oils (DCO) are among the oils used in the formulation of urethane oils. A number of reports have been appeared in the literature on the modification of oil component to improve the properties of the coatings [15], [16], [17], [18]. Several studies have been carried out on urethane oils in our laboratory as well. In these studies, Ecballium elaterium and Prunus mahaleb L. seed oils were used in the formulation of urethane oils [19]. In another study, the effect of the amount and the type of isocyanate component on the film properties of the final product was investigated [20]. In addition to these studies, the flow behavior of some urethane oils prepared at different reactant ratios was determined as well as the flow properties of some mixture prepared from urethane oil and alkyd resin (AR-UO) [21], [22].
As mentioned above in the present study, alkoxysilane-funtionalized urethane oil-titania hybrid coatings were prepared with TIP (titanium isopropoxide) as the inorganic precursor to react with aminosilane-functionalized urethane oil by sol–gel technique. The structure and thermal properties of the hybrid materials were studied by FTIR, TGA and DSC. Film properties such as flexibility [23], adhesion [24], Sward Rocker hardness [25], water resistance [26], alkali resistance [26] and acid resistance [26] were also determined according to the related standards.
Section snippets
Materials
Refined sunflower oil purchased from the market was used as received. Toluene diisocyanate (TDI, 98%, Aldrich), 3-aminopropyltriethoxysilane (APES, 98%) and titanium(IV) isopropoxide (TIP) were purchased from Sigma–Aldrich and were used without further purification.
Preparation of partial glyceride (PG)
PG was prepared by glycerolysis reaction between triglyceride oil and glycerol. Sunflower oil and glycerol (glycerol:oil (in g) = 1:0.085) were placed into a reaction flask and heated. When the temperature reached 218 °C, Ca(OH)2 (0.1
Results and discussion
The aim of this study is to improve film properties of classical urethane oils. For this purpose, APES and TIP were inserted to the urethane oil structure. As mentioned before, APES was, firstly combined to the urethane oil structure through the reaction between NH2 groups of APES and –NCO groups of TDI. Then, TIP was combined with AFUO in order to investigate effects of titania domain on the properties of the film samples. The representative structures of AFUO and AFUO/titania are shown in
Conclusions
In conclusion, synthesis of AFUO/titania hybrid films was successfully achieved by sol–gel method. AFUO was firstly synthesized by the reaction of APES and PG mixture with TDI. Then, this intermediate was combined with TIP. FTIR and DSC results indicated that the titania phase was incorporated into the urethane oil structure through Si–O–Ti bonding. Both AFUO film samples and AFUO/titania hybrid films showed better film properties than CUO. Improvements in adhesion, alkali resistance and water
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