Along with society’s progress, high-quality coatings are widely used. Although fluorinated polymers were successfully prepared by semicontinuous emulsion polymerization with surfactants, chlorotrifluoroethylene (CTFE), and acrylate monomers, the optimization collocation of surfactants still has room for improvement. The traditional emulsifiers are physically absorbed onto the surface of latex particles. The latex film generated by latex particles is unstable in water, which limits its application. Herein, a novel series of cationic quaternary ammonium polymerizable surfactant was selected because it can react with CTFE and acrylate monomers and can become a part of the polymers. We also studied the effects of emulsifier type on resultant emulsion properties. In addition, wonderful weatherability, water resistance, and antibacterial and antifouling of the multifunctional fluorinated films were observed, which would open up a bright future for coating industries.
Fluoropolymers have recently attracted considerable attention due to their excellent chemical resistance, low dielectric constant, good hydrophobicity/oleophobic, and weatherability [
Nowadays, various methods have been proposed to prepare polymers, such as suspension polymerization, solution polymerization, controlled radical polymerization, and emulsion polymerization [
In this sense, polymerizable quaternary ammonium surfactants with vinyl groups pave a new avenue for emulsifier innovation owing to advantageously introducing direct free radical polymerization and antibacterial properties [
Motivated by these considerations, in this paper, a series of novel fluoropolymers was successfully prepared by semicontinuous emulsion polymerization of CTFE, vinyl acetate (VAc), n-butyl acrylate (BA), versatic acid 10 esters (Veova10), and acrylic acid, using a special polymerizable quaternary ammonium salt as the emulsifier. Meanwhile, the effects of emulsifier type on conversion, particle size, and storage stability were adequately discussed. The chemical structure and latex particle size distribution were investigated by FTIR and dynamic light scattering (DLS), respectively. Weatherability, water resistance, antibacterial properties, and protein adsorption as well as their relationship with chemical composition were also characterized.
CTFE, vinyl acetate (VAc), n-butyl acrylate (BA), versatic acid 10 (Veova10) esters, hexadecyltrimethylammonium bromide (CTAB), octylphenol polyoxyethylene ether (NP-10), 2,2
The chemical structure of different cationic quaternary ammonium polymerizable surfactants.
Pre-emulsion was fabricated by a similar recipe based on the previous report in our lab [
Recipes for the pre-emulsion process.
Sample | KJH-1 (g) | KJH-2 (g) | KJH-3 (g) | R303 (g) | CTAB (g) | 600#A (g) | NP-10 (g) | SDS (g) | Pre-emulsion stability |
---|---|---|---|---|---|---|---|---|---|
L1 | 9.39 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | Good |
L2 | 0 | 9.39 | 0 | 0 | 0 | 0 | 0 | 0 | Poor |
L3 | 0 | 0 | 9.39 | 0 | 0 | 0 | 0 | 0 | Poor |
L4 | 0 | 0 | 0 | 9.39 | 0 | 0 | 0 | 0 | Good |
L5 | 0 | 0 | 0 | 0 | 9.39 | 0 | 0 | 0 | Poor |
L6 | 9.39 | 0 | 0 | 0 | 0 | 4.06 | 0 | 0 | Good |
L7 | 0 | 9.39 | 0 | 0 | 0 | 4.06 | 0 | 0 | Good |
L8 | 0 | 0 | 9.39 | 0 | 0 | 4.06 | 0 | 0 | Good |
L9 | 0 | 0 | 0 | 9.39 | 0 | 4.06 | 0 | 0 | Good |
L10 | 0 | 0 | 0 | 0 | 9.39 | 4.06 | 0 | 0 | Good |
L11 | 0 | 0 | 0 | 0 | 0 | 6.72 | 5.2 | 1.34 | Good |
The 10% (wt.%) resultant pre-emulsion and 80.00 g of CTFE were introduced into a 1 L autoclave at vacuum state with the assistance of agitation at 500 r/min for 30 min. Afterwards, 5% (wt.%) resultant pre-emulsion, 0.34 g of AIBA, and 176.79 g of deionized water were slowly added to the reactor. Under constant stirring, the system was heated to 75°C and kept for 25 min. The rest of the resultant pre-emulsion were mixed with AIBA (0.99 g) and deionized water (52.74 g) and injected dropwise with modest stirring for 3 h. Subsequently, AIBA (0.34 g) dissolved in the deionized water (18.26 g) was dripped into the autoclave. Finally, the polymerization was continued to maintain for an additional 3 h.
Monomer conversion was measured by the gravimetric method. The samples were dried at 120°C for 2 h, and the residual polymer was weighed. Conversion (%) was calculated as follows:
In fact, the fluorine content (
The amount of coagulum was measured by collecting coagulum after filtering the latex (mesh 300) and calculating as percentage of the total added weight. The viscosity of the emulsion was recorded on a rotating viscometer with 2# rotor (NDJ-1 style, Shanghai Jingke Instrument Company, China). For the freeze/thaw stability test, 50 g of latex (in a 100 mL plastic bottle) was kept at −5°C for 18 h. After another 6 h at room temperature, flocculation of the latex sample was observed. Next, the electrolyte stability was tested with 1 mL of CaCl2 solution (0.25 M) added into a 10 mL test tube containing 5 mL of emulsion, with the delamination, precipitation, and flocculation observed after 24 h. Storage stability of the emulsion was carried out in 250 mL glass bottles with 200 mL of emulsion, at airtight condition and room temperature. The emulsion was examined whether there was diversion water, stratification, and precipitation phenomenon after storage of one month.
The FTIR spectrum was measured using pellets of the emulsion with an EQUINOX 55 spectrometer (Bruker Optics, Karlsruhe, Germany) in the range of 400 to 4000 cm−1. The particle diameter was collected from DLS (Zetasizer 1000/DTS-5101, Malvern Instruments, UK); the polydispersity index (PDI) of the particle diameter was calculated automatically. The QUV accelerated weathering test was performed on the sample by an Accelerated Aging Tester (Q-PANEL, Q-Lab Corporation, Cleveland, OH, USA) under the conditions of 0.6 W/m2 irradiance, 60°C base panel temperature, and wavelength of 343 nm UV.
Water resistance: latex films were obtained by placing the required amount of latex on a glass substrate and air-drying at room temperature for 24 h. Films were removed carefully, and square (2.5 × 2.5 cm) samples were prepared and dried at 40°C under vacuum for 24 h. The preweighed dry films were immersed into water for some days. At various times (approximately one time every 4 days), after careful blotting of the surface liquid with filter paper, the samples were weighed as quickly as possible.
Water absorption of films: the emulsion is put in a petri dish for uniform film and maintained dry for 7 days. Dry film thickness was about 1.0 mm, and it was cut into the size of 2 cm × 2 cm. The initial mass of film is defined as
Antimicrobial characteristic of the latex film was investigated according to a test method (GB/T 21866-2008) from the Technical Standard for Disinfection (2008 edition) published by the State Administration of Quality Supervision, Inspection, and Quarantine. The film was stuck on the aluminum plate twice, brushing second time after the first desiccation, which was followed by drying for 7 days at 23 ± 2°C and 50 ± 5% RH. The test plate was divided into 50 mm × 50 mm in size. As for bovine serum albumin (BSA) and lysozyme solution, they were prepared in 10 mM phosphate-buffered saline (PBS), keeping an initial concentration of 1 mg/mL. Firstly, the film was incubated in BSA solution (10 mL) for 24 h with a shaker bath at 25°C. Secondly, the film was removed from the glass bottle, and the BSA equilibrium concentration was monitored by a UV-vis spectrophotometer (UL2100, GE, USA) at 526 nm. Finally, adsorption capacity (
There is no denying that pre-emulsion stability plays an important role in polymerization progress. A comparative trial was applied by using pure or mixed emulsifier systems. Table
The results of polymerization using various stable pre-emulsions are listed in Table
Influence of the nine stable pre-emulsions on the prepared emulsion properties.
Sample | Conversion (%) | Coagulum (%) | Viscosity (mPa⋅s) | Particle size (nm) | PDI | Freeze/thaw stability | Electrolyte stability | Storage stability | ||
---|---|---|---|---|---|---|---|---|---|---|
L1 | 95.22 | 11.99 | 11.19 | 0.108 | 17.5 | 189.4 | 0.037 | Pass | Pass | No change |
L4 | 93.76 | 11.99 | 10.26 | 0.130 | 20.0 | 195.8 | 0.03 | Pass | Pass | No change |
L6 | 94.16 | 11.99 | 10.67 | 0.135 | 35 | 130.1 | 0.021 | Pass | Pass | No change |
L7 | 94.92 | 11.99 | 10.29 | 0.187 | 150 | 53.6 | 0.147 | Pass | Pass | Demix |
L8 | 86.85 | 11.99 | 9.37 | 8.925 | 173 | 66.4 | 0.17 | Pass | Fail | Demix |
L9 | 96.13 | 11.99 | 11.40 | 0.177 | 27.5 | 142.9 | 0.023 | Pass | Pass | No change |
L10 | 88.25 | 12.34 | 9.88 | 9.238 | 370 | 87.1 | 0.191 | Pass | Pass | No change |
L11 | 99.34 | 12.34 | 12.01 | 0.010 | 15.5 | 179.5 | 0.042 | Pass | Pass | No change |
Additionally, we give a comprehensive discussion on preparative latex stability. Whether polymerizable surfactant or conventional emulsifier, all the preparative emulsion could resist these freeze/thaw cycles under −5°C. This hints that the polymerizable surfactant with long-chain nonionic groups such as ethylene oxide was of great importance for freeze/thaw stability. Apart from L8, others had wonderful stability against low concentration electrolytes, so that no visual coagulation or precipitation was detected. That is because the contents of the ethylene oxide (EO) in polymerizable quaternary ammonium surfactant were higher than those in the traditional quaternary ammonium surfactant (CTAB). In storage stability test, most of the latexes did not demix and remained in the original state. However, for L7 and L8, the latexes’ stability deteriorates markedly after one month. Furthermore, other methods, for instance, increasing the amount of traditional emulsifier might be used to improve storing stability, which will be studied in the following experiments.
The specific chemical structure of fluorinated acrylate copolymers is depicted in Scheme
The chemical structure of fluorinated acrylate copolymers.
FTIR spectrum of L9.
Particle size distribution of different latex particles.
The most common use of polymers is guarding the system against exterior exposure. Therefore, the study of accelerated UV exposure onto the polymeric membranes is indispensable to evaluate their weatherability. The contrast experiment shown in Figure
Accelerated weathering test of coatings with different polymers.
Water absorption is a vital evaluation criterion for waterproofing grade. In allusion to each latex film, individual variation of water absorption is intimately related to the selection of emulsifiers. In light of this, the results of Figure
Water absorption of the films in 15 days.
It is well known that quaternary ammonium salts would render the obtained polymer emulsion antibacterial property. Nevertheless, some small-molecule quaternary ammonium salts are easily migrated and bring about the loss of antibacterial effect [
The antibacterial test of latex films with regard to a set number of bacteria.
Sample | The average recovery of bacteria for blank control sample after 24 h (cfu/piece) | The average recovery of bacteria for coating sample after 24 h (cfu/piece) | Antimicrobial rate (%) |
---|---|---|---|
L6 | 2.1 × 106 | <20 | >99.99 |
L9 | 2.1 × 106 | <20 | >99.99 |
P6 | 2.1 × 106 | <20 | >99.99 |
P9 | 2.1 × 106 | <20 | >99.99 |
Protein fouling is a detrimental element for lengthening the lifespan of latex films. To gain an insight into the actual protein resistance of our films, lysozyme and BSA adsorption experiments were conducted. In this study, the preparation procedure of benchmark reference group (P1) is analogous to L1 except that the monomer CTFE is not employed. Figures
Comparison of the lysozyme adsorption levels of L1, L6, L11, and P1.
Comparison of the BSA adsorption levels of L1, L6, L11, and P1.
In summary, with the aid of cationic quaternary ammonium polymerizable surfactant and CTFE, fluoropolymers were synthesized by semicontinuous emulsion polymerization, using VAc, BA, and Veova10. Unlike exploiting conventional emulsifier or hexafluorobutyl methacrylate, the synthetic fluoropolymers exert preeminent emulsification effect and latex stability which can strengthen resistance capability for electrolytes, freezing/thawing, storage, weather, water, bacteria, and protein. Thanks to this pretty straightforward method, manufacturers would offer more practical coatings for all walks of life.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare no conflicts of interest regarding the publication of this article.
Hongzhu Liu and Lingnan Wang contributed equally to this work.
The authors thank the Fundamental Research Funds for the Central Universities (DUT16LAB11) for the financial support of this research.