Preparation of organic–inorganic hybrid silica nanoparticles with contact antibacterial properties and their application in UV-curable coatings
Graphical abstract
The organic–inorganic hybrid nanoparticles imparted suitable mechanical properties and excellent antibacterial activity to UV-curable coating.
Introduction
Ultraviolet (UV) curing is a relatively new type of high-efficiency, energy-saving, and environmentally friendly technology. UV-curable coating has attracted wide attention and application since its discovery owing to its unique properties such as a rapid curing rate, low energy consumption, excellent film performance, and a broad formulation and base material range [1], [2]. In recent years, the function of UV-curable coating has been widely studied, mainly for its self-healing [3], [4], anti-staining [5], and antibacterial[6] properties.
With the increasing requirements of antibacterial in various fields, such as the medical device, food packaging, and household sanitation fields, antibacterial UV-curable coating has attracted considerable attention [7], [8]. A conventional method for imparting coatings with antibacterial properties entails adding antibacterial agents to coating formulations. Depending on the antibacterial mechanism, antibacterial agents are classified as releasing antibacterial agents and contact antibacterial agents (i.e., nonreleasing antibacterial agents). Releasing antibacterial agents, which gradually leach biocides in the surroundings to kill bacteria, mainly include antibiotics [9], [10], [11], silver [12], [13], [14], and titanium [15], [16]. The main drawbacks of this type of antibacterial agent are the loss of antibacterial ingredients and the release of undesirable toxic biocides into the environment [17], [18], [19].
The antibacterial mechanism of nonreleasing antibacterial agents is not based on a release killing principle, but rather a contact killing principle, which can overcome the previously mentioned disadvantages of releasing antibacterial agents. Quaternary ammonium compound (QAC), a kind of contact antibacterial agent, has attracted substantial attention because of its high antibacterial efficiency and perdurable antibacterial property [20]. This was exemplified in a study by Asri et al [21], in which a shape-adaptive coating containing QAC molecules was synthesized to increase the contact area for bacterial adhesion. And the contact-killing, multi-layered coating they prepared is based on novel hyperbranched polymers, comprising blocked isocyanates, on which multiple QAC molecules can be covalently tethered. In a previous study, our group synthesized a QAC with a 16-carbon alkyl chain and a terminal methacrylate as both an antibacterial agent and photocurable monomer, successfully applying it to non-releasing UV-curable antibacterial coatings [22]. However, the mechanical properties of the coatings diminished to varying degrees with the added amount of QAC with a single double bond group. Consequentially, it becomes increasingly crucial that the rapidly formed coating after irradiation exhibits not only excellent antibacterial activity but also suitable mechanical properties.
Organic–inorganic hybrid coating is highly promising for both academic and industrial applications; it offers a new research direction for preparing high-performance coating, owing to the combination of flexible and processable organic polymer, as well as the high rigidity and thermal stability of inorganic particles. [23], [24] Some researchers have investigated in introducing antibacterial groups onto the surface of silica nanoparticles (NPs) to obtain performance-enhanced antibacterial coatings. Procaccini et al. [25] prepared a silver-doped silica-methyl hybrid coating with releasing antibacterial abilities, in which the effect of stabilization of cyclosiloxanes and Si-OH groups provided a controlled silver release rate. Farah et al. [26] reported an efficient preparation process for stable silica particles loaded with cross-linked quaternary ammonium-polyethylenimine chains exhibiting efficient distribution in polymeric coatings and high antibacterial activity.
To obtain an antibacterial coating with high mechanical properties, a facile strategy was developed in this study for preparing silica NPs with photo-cross-linking and antibacterial properties as organic–inorganic hybrid UV-curable antibacterial agents. The series of functional NPs was added to soybean oil-based UV-curable coating formulations. The silica inorganic core with excellent chemical inertness and optical transparency combined with the antibacterial functional groups as a long aliphatic chain imparted suitable mechanical properties to the coating and demonstrated excellent antibacterial activity.
Section snippets
Materials
N,N-dimethyl ethanolamine (DMEA), 1-Bromohexadecane (HB), tetraethyl orthosilicate, γ-aminopropyltriethoxysilane (γ-APS), Dibutyltin dilaurate (DBTDL), and ammonia used in this study were purchased from Shanghai Chemical Reagent Co., Ltd. CN2302 (hyperbranched polyester acrylate, HBP) was purchased from Sartomer. Isophorone diisocyanate (IPDI), pentaerythritol triacrylate (PETA), SM6103 (acrylated epoxidized soybean oil, AESO) were purchased from Jiangsu Sanmu group company. Irgacure 184 (PI)
Results and discussion
Fig. 2 presents the images of NP dispersions in water and ethanol (10 mg/mL). As shown in Fig. 2A, the NPs before modification (i.e., SiO2–NH2 NPs) clearly exhibited high dispersion in ethanol, whereas the SiO2–NH2 NPs deposited in water showed low dispersion. Both the SiO2–DM100–PETA0 NPs and SiO2–DM50–PETA50 NPs (Figs. 2 B and 2C) exhibited high dispersion in water and ethanol. However, as with the SiO2–NH2 NPs, the dispersion of SiO2–DM0–PETA100 NPs in water was low (Fig. 2D). These results
Conclusions
A facile strategy was developed for preparing UV-curable coatings with contact-killing antibacterial ability. Organic–inorganic hybrid SiO2–DM50–PETA50 NPs, as both the antibacterial agent and photocurable monomer, exhibited efficient dispersion and antibacterial activity. The coating showed excellent mechanical properties including gloss (60°), pencil hardness, pendulum hardness, and crosshatch adhesion, and additionally possessed antibacterial properties against both E. coli and S. aureus.
Acknowledgement
We acknowledge financial support from the Innovation Foundation of Jiangsu (BY2015019-06)and the National Science & Technology Pillar Program (2015BAD16B06).
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