Investigation of synergistic effect of nano sized Ag/TiO2 particles on antibacterial, physical and mechanical properties of UV-curable clear coatings by experimental design
Introduction
Coatings have been used to protect surfaces from biodegradation and environmental degradation [1]. UV curable coatings are known as environmentally friendly with excellent mechanical properties and chemical resistance [2], [3]. Moreover, they have numerous advantages such as low curing time [4] high cross linked networks [5] and low energy consumption [6].
In this regard, many studies have been conducted on properties of UV curable coatings. Among different resins, UV curable polyurethane offers properties such as: excellent hardness [5], high gloss [7], good chemical and weather resistance [8], good adhesion and film forming performance [9].
Antibacterial coatings are a kind of functional coatings that have wide range of applications in clothing, textiles, floor and medical instruments. Anti-microbial agents such as Ag, TiO2, ZnO, Au, chitosan, SiO2, Mg(OH)2 and carbon nanotubes have been used to prevent microbial infection in coating [1], [10]. Among these materials, nano-sized Ag has received considerable attention because of its greater efficacy and durability [11].
The antimicrobial mechanism of the silver nanoparticles has not yet been fully understood. It is believed that silver nano particles release Ag+ ions which band to sulphur, oxygen or nitrogen in proteins, DNA and RNA molecules and disrupt their functions. For example, Ag+ ions affect the replication of DNA by interacting with the thiol groups in bacteria proteins [12], [13].
Furthermore, the ability of TiO2 to improve the antibacterial performance of coatings has been proven [14]. Titanium dioxide can create electron–hole pairs as a result of UV radiation. The electron–hole pairs in this reaction with the available water and oxygen molecules can generate reactive oxygen species such as hydroxyl and superoxide radicals. The oxidation of all organic compounds in the microorganisms by these reactive oxygen species leads to cell death [15].
Recently, researchers have been used Ag–TiO2 nanocomposite to expand antibacterial function to a broader range of working conditions [16], [17].
Various methods have been presented to synthesis of Ag/TiO2 nano composites [18], [19]. Likewise, anti-bacterial efficiency of Ag/TiO2 in different kinds of fabrics such as polypropylene [20], polyester [21] has been reported. The antibacterial activity of Ag/TiO2 in thin solid films has been also investigated [22], [23], [24], [25].
The synergistic effect of nano silver and nano titanium dioxide on organic coating especially UV curable coating has not yet been studied.
This work intends to study the synergistic effect of nano silver and nano titanium dioxide on antibacterial and subsequently mechanical properties of UV curable polyurethane acrylate coating. For this purpose, the software experimental design was used to optimize the amount of nano particles.
Section snippets
Materials
Trimethylolpropanetriacrylate (TMPTA), 1,6 hexanediol diacrylate (HDDA) and dipentaerythritol pentaacrylate (DIPEPA) as monomers, also Eterphoto PI BP and Etermer 641 as photoinitiator and amine respectively were obtained from Taiwan Eternal Company. Aliphatic urethane triacrylate oligomer (Ebecryl 204) was purchased from Cytec – UV/EB curable resins and additives. Buthyl acetate was purchased from Merck. Dispersant and leveling agent were obtained from BYK and EFKA, respectively.
Nano titanium
Results and discussion
Antibacterial and physical–mechanical properties of twenty designed coatings are investigated and optimized using experimental design in response surface method. In addition to these twenty designed samples, two other samples are added for better comparison as follows.
Sample 0 is a sample without any nano particles and sample 21 is a sample with 170 ppm Ag nano particles.
The results of antibacterial and physical–mechanical tests are shown in Table 4. Also, the effect of nanoparticles (amount and
Conclusion
The synergistic effect of nano TiO2 (10 nm and 30 nm) and nano silver (10 nm) incorporated into the UV curable clear coating was assessed through antibacterial test as well as physical–mechanical tests. According to these results, equal amounts of TiO2 10 nm and 30 nm caused an acceptable dispersion of nano silver in UV curable coating and had synergistic effect with nano silver on antibacterial properties.
With these situations the samples 9, 10, 11 and 19 exhibited 100% antimicrobial properties
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