Preparation of PANI–CuZnO ternary nanocomposite and investigation of its effects on polyurethane coatings antibacterial, antistatic, and mechanical properties
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In this study, a facile method for the production of Antibacterial and Antistatic polyurethane coatings was investigated using copper modified ZnO nanoparticles–polyaniline nanofibers (PANI–CuZnO) ternary nanocomposite. PANI–CuZnO ternary nanocomposite was synthesized through two steps. First, copper-modified ZnO nanoparticles were produced through the hydrolysis method using acetate precursors, and then they were mixed with polyaniline nanofibers, which were synthesized by seeding method. The obtained nanocomposite was characterized by FTIR, XRD, and FESEM techniques. Results of evaluating the antibacterial action of the polyurethane coatings with the content of ternary nanocomposite showed that the obtained coatings have a proper antibacterial action against Gram-positive and Gram-negative bacteria. In addition, measuring the coatings’ surface electrical resistance revealed that addition of the ternary nanocomposite to the polyurethane coatings’ matrix causes the surface electrical resistance of the coatings significantly decreases and reaches 8 × 107 Ω/sq. Thereby, they could be categorized as an antistatic coating. Moreover, the addition of PANI–CuZnO enhanced adhesion strength and scratch resistance of the final polyurethane coatings.
KeywordsTernary nanocomposite Modified ZnO nanoparticles Polyaniline nanofibers Antibacterial Antistatic
Nowadays, human’s life is always under threat of different infectious agents, and bacterial species have a major role in the emergence of such infections and their consequences. Considering bacteria adhesion to different surfaces as one of the main stages in bacterial species’ growth and proliferation processes, developing antibacterial surfaces have an undeniable effect on preventing damages caused by bacteria growth . Moreover, increase in resistance of bacterial species to the common antibacterial agents leads to a growing demand for novel and effective antibacterial agents for the production of antibacterial coatings [2, 3, 4]. In some industries, especially in the chemical and pharmaceutical industries, utilizing the coatings with antibacterial and antistatic properties would be necessary to safety and efficacy of such plants to be guaranteed . In this regard, nanocomposite material owing to their improved physical and chemical properties could be counted as a proper choice for creating antibacterial and antistatic properties in polymer coatings [5, 6].
Studies showed that ZnO nanoparticles have an effective antibacterial property against different bacteria and have a good compatibility with human cells and have no toxic effect on mammalians’ cells . Moreover, ZnO nanoparticles modification with some transition metals causes an enhancement in efficacy and antibacterial action of these nanoparticles. Among different metals, copper due to its advantages like low cost, accessibility, and proper antibacterial property has gained much attention . Antibacterial mechanism of action of copper could be originated from creating active oxygen species and disrupting bacterial cells’ membrane processes [9, 10]. Modification of ZnO nanoparticles by Cu ions can improve the antibacterial property of resultant nanohybrids . Moreover, the presence of ZnO nanoparticles in polymer coatings matrix could noticeably increase the produced coatings mechanical properties [12, 13].
Polyaniline owing to benefiting from high environmental stability, facile synthesis method, and low production cost is counted as one of the most used conducting polymers. With regard to these unique characteristics, polyaniline could have applications in various fields like sensors, batteries, wastewater treatment, anticorrosion coatings, and antistatic coatings [14, 15, 16, 17, 18, 19, 20]. Furthermore, polyaniline’s different shapes with regard to their improved properties could, even more, increase its applicability. For example, polyaniline production in nanofiber and nanowire forms causes improvement in its electrical conductivity [21, 22]. Addition of inorganic nanoparticles to polyaniline’s matrix leads to increased electrical conductivity and efficacy of polyaniline to be utilized in antistatic coatings production . Addition of ZnO nanoparticles would also have a noticeable effect on increasing polyaniline’s electrical conductivity and its electrical efficiency .
In current research work, mesoporous copper-modified ZnO nanoparticles were produced through the hydrolysis method. Then, polyaniline nanofibers were synthesized through the seeding method and were mixed with modified ZnO nanoparticles to obtain PANI–CuZnO ternary nanocomposite. Afterwards, the produced ternary nanocomposite was utilized in polyurethane resin’s matrix and antibacterial and antistatic properties of the produced coatings were evaluated. Moreover, the effect of ternary nanocomposite on the improvement of final coatings’ adhesion strength and scratch resistance was also investigated.
Materials and reagents
Zinc acetate dihydrate (≥ 99%), copper acetate (≥ 98%), diethylene glycol (DEG ≥ 99%), polyethylene glycol (Mw = 400, pure), ammonium persulfate salt (≥ 99%), aniline (≥ 99%), and hydrochloric acid (37%) were purchased from Merck. Aniline was double distillates prior to use. The Polyester polyol (technical grade) and Polymeric Methylene Diphenyl Diisocyanate (PMDI, technical grade) were provided by Bayer.
Synthesis of Cu-modified ZnO nanoparticles
To produce copper-modified ZnO nanoparticles, zinc acetate dihydrate was hydrolyzed in the presence of copper acetate salt (10 wt% of zinc acetate) in diethylene glycol (DEG) as the reaction medium. For this purpose, 2 mmol of zinc acetate along with copper acetate were added to 25 ml DEG. Then, 0.5 g PEG was added to the reaction medium and the resulting mixture was refluxed up to 170–180 °C for 1 h. After completion of the reaction, the reactor was cooled and participates were centrifuged and washed by deionized water, ethanol, and acetone, respectively. Finally, the products were dried at 80 °C for 2 h.
Synthesis of PANI nanofibers
Polyaniline nanofibers were synthesized by the seeding method. First, 0.0037 g of aniline monomers were dispersed in 50 ml 1 M HCl solution. Then, 0.0045 g of ammonium persulfate (aniline:APS molar ratio is 2:1) was dissolved in 1 M HCl solution and was added to the above mixture. Final mixture’s temperature was kept at 0 °C (using a refrigerator and an ice bath) and left to rest for 48 h. After completion of the polymerization reaction, participates were collected and washed by DI water and ethanol, respectively and dried at 60 °C for 12 h.
Preparation of PANI–CuZnO ternary nanocomposite
To prepare PANI–CuZnO ternary nanocomposite, first, the desired amount of PANI nanofibers (0.5 g) were added to DI water and then an equal amount of modified ZnO nanoparticles were added to this mixture and homogenized by the ultrasonic method for 10 min (PANI:CuZnO ratio = 1:1). Finally, the resultant participates were collected and dried at 60 °C for 6 h.
Production of polyurethane coatings
Polyurethane coatings with antibacterial and antistatic properties were produced by adding appropriate amounts of PANI–CuZnO ternary nanocomposite (equal to 1, 2, 3 and 5 wt%) to the 10 g of polyester polyol and mixing with a mechanical stirrer. Then, 2 g PMDI was added to the obtained mixture and after gently mixing for several minutes, the final mixture was applied to glass plates and after 24 h, polyurethane films were detached from the glass plates for further studies.
FTIR spectra of the modified ZnO nanoparticles and PANI–CuZnO ternary nanocomposite were collected by Perkin-Elmer (USA) in the range of 400–4000 cm−1. X-ray diffraction patterns of the samples were recorded by D8 Advance-Bruker (Germany). Modified ZnO nanoparticles and PANI–CuZnO ternary nanocomposite’s morphological properties were studied by TeScan-Mira III microscope (Czech Republic).
The antibacterial property of the produced coatings was investigated against Escherichia coli as a Gram-negative and Staphylococcus aureus as Gram-positive bacteria. For this purpose, the plate colony counting method was utilized. First, original bacterial suspensions were diluted to 108 CFU/ml using nutrient broth. Then 0.1 ml of diluted bacterial suspensions was transferred to vessels containing 0.9 ml of physiological serum (0.9% NaCl solution). Pure polyurethane and polyurethane with the content of PANI and PANI–CuZnO ternary nanocomposite was applied to the sterile paper blank discs and they were put in contact with the bacteria contained solutions. After 1 h, these solutions were ten times diluted by consecutive addition of 0.1 ml of solution from one vessel to another vessel with the content of physiological serum. Finally, 0.1 ml solution from each vessel was applied on plates with the content of solidified agar. The plates were incubated at 37 °C for 24 h. Finally, the number of formed bacterial colonies was counted.
Evaluation of the coatings’ antistatic property
Measuring coatings’ adhesion strength and scratch resistance
The strength of polyurethane coatings adhesion to the concrete substrates was studied by the pull-off method based on ASTM D4541. In this method, tensile Dollies were glued to the coating, when the adhesive cured, the force required to pull the coating off the surface was measured. To evaluate the scratch resistance of the coatings, based on ISO 1518 standard, a pen hardness tester was utilized. In this method, a pen-like device with a tungsten carbide tip was drawn over the coating’s surface with a defined constant pressure. A pressure needed for creating a scratch on the coatings’ surface was reported as the coatings’ scratch resistance.
Results and discussion
Evaluating the coatings antibacterial property
The antibacterial property of the polyurethane coatings with 5 wt% content of PANI nanofibers and PANI–CuZnO ternary nanocomposite after 60-min exposure to the bacterial strains
Evaluating antistatic property
Evaluation of the coatings’ adhesion strength and scratch resistance
The results of measuring adhesion strength and scratch resistance of the pure polyurethane coating and the coatings with 3 and 5 wt% content of PANI–CuZnO ternary nanocomposite
Nanocomposite content in the coating (%)
Adhesion strength (MPa)
Scratch resistance (N)
The significance of this study was synthesizing PANI–CuZnO ternary nanocomposite and its utilization as a multifunctional additive for creating antistatic and antibacterial properties in polyurethane coatings. This ternary nanocomposite was produced using copper-modified ZnO nanoparticles and PANI nanofibers and through the two facile steps. The obtained nanocomposite was characterized in term of structural, crystallographic, and morphological properties. The antibacterial and antistatic coatings were produced by addition of the ternary nanocomposite to the polyurethane matrix. Evaluation of the coatings’ antibacterial property showed that the produced coatings have a proper ability to inhibit Gram-positive S. aureus and Gram-negative E. coli bacteria growth. In addition, utilizing 2 wt% ternary nanocomposite in the polyurethane coating led to the coating’s surface electrical resistance reached 8 × 107 Ω/sq which caused the obtained coating could be categorized as an antistatic coating. Moreover, increasing the content of ternary nanocomposite resulted in improved adhesion strength and scratch resistance of the polyurethane coatings.
The authors greatly acknowledge the financial support of the University of Tabriz.
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