Facile one-pot synthesis of silver nanoparticles encapsulated in natural polymeric urushiol for marine antifouling

In Situ Reduction of Silver Nanoparticles/Urushiol-Based Polybenzoxazine Composite Coatings with Enhanced Antimicrobial and Antifouling Performances

Marine anti-fouling coatings represent an efficient approach to prevent and control the marine biofouling. However, a significant amount of antifouling agent is added to improve the static antifouling performance of the coatings, which leads to an issue whereby static antifouling performance conflicts with eco-friendly traits. Herein, this work reports an in situ reduction synthesis of silver nanoparticles (AgNPs) within polymers to produce composite coatings, aiming to solve the aforementioned issue. Firstly, urushiol-based benzoxazine monomers were synthesized by the Mannich reaction, using an eco-friendly natural product urushiol and n-octylamine and paraformaldehyde as the reactants. Additionally, AgNPs were obtained through the employment of free radicals formed by phenolic hydroxyl groups in the urushiol-based benzoxazine monomers, achieved by the in situ reduction of silver nitrate in benzoxazine. Then, the urushiol-based benzoxazine/AgNPs composite coatings were prepared by the thermosetting method. AgNPs exhibit broad-spectrum and highly efficient antimicrobial properties, with a low risk to human health and a minimal environmental impact. The composite coating containing a small amount of AgNPs (≤1 wt%) exhibits effective inhibition against various types of bacteria and marine microalgae in static immersion, thereby displaying outstanding antifouling properties. This organic polymer and inorganic nanoparticle composite marine antifouling coating, with its simple preparation method and eco-friendliness, presents an effective solution to the conflict between static antifouling effectiveness and environmental sustainability in marine antifouling coatings.

Biobased Chicken Eggshell Powder for Efficient Delivery of Low-Dose Silver Nanoparticles (AgNPs) to Enhance Their Antimicrobial Activities against Foodborne Pathogens and Biofilms

Despite the current sanitation practices to decontaminate food-contact surfaces, persistent biofilms still pose significant threats to human health by inducing cross-contamination. This study aims to enhance the antimicrobial activity of low-dose silver nanoparticles (AgNPs) against foodborne pathogens and their biofilms through the development of a biobased delivery carrier for metallic nanoparticles. In this study, chicken eggshell powder (EP) was used as a biocompatible delivery carrier, and it possesses a strong ability to encapsulate green-synthesized AgNPs with an encapsulation efficiency of 80.18%. The EP carriers stabilized AgNPs in an organic-rich environment and prevented the aggregation of nanoparticles. The results of antimicrobial test demonstrate that EP significantly enhanced the antimicrobial efficacy of low-dose AgNPs (2 μg/mL), enabling 5-log reductions of planktonic Escherichia coli and Listeria innocua within 25 min and 60 min treatments, respectively, even in the presence of high organic content (chemical oxygen demand, COD = 1000 mg/L). Due to the high affinity of EP to bind biofilms, the encapsulated low-dose AgNPs can inactivate approximately 2-log CFU/cm2 of biofilms within a 2-h treatment. The proposed AgNPs@EP composite with a low silver concentration (2 μg/mL) can effectively inactivate and remove biofilms from food-contact surfaces in which such a low concentration of AgNPs is unlikely to induce negative impacts on human health and environment. Therefore, this antimicrobial AgNPs@EP composite can potentially be used as a biobased sanitizer for food-contact surfaces in a food manufacturing plant.

Synthesis of a Compound Phosphorus-Nitrogen Intumescent Flame Retardant for Applications to Raw Lacquer

Raw lacquer (RL) is a natural polymer compound with highly promising applications; however, its inflammable attribute restricts the industrial applications. In this study, melamine is used to formulate tri (1-melamine-2-propanol) phosphate (FR-1), after which it is synthesized with ammonium phosphate (FR-2) and diatomite to form a compound phosphorus-nitrogen intumescent flame retardant (IFR). Next, IFR is used as the filling agent that then cross-links with RL, and as such RL/IFR membranes are formed after the curing. The limiting oxygen index (LOI) measurement, the vertical combustion test (UL-94), the microshape calorimetric analysis (CCT), and the thermal gravimetric analysis (TGA) are conducted to examine the combustion resistance and thermal stability of the membranes. Fourier transform infrared spectroscopy (FT-IR) and electron scanning microscope (SEM) are performed to separately characterize the structure and compatibility; the mechanical properties of the membranes are also evaluated. The vertical combustion test results confirm that with 30 wt% of IFR, RL/IFR membranes acquire 12.3% higher LOI and a vertically combustion of V-0 level. The TGA indicates that RL/IFR membranes demonstrate a greater adhesion level, a higher rigidity, and better luster than pure RL membranes.

Preparation of Nanoscale Urushiol/PAN Films to Evaluate Their Acid Resistance and Protection of Functional PVP Films

Different amounts of urushiol were added to a fixed amount of polyacrylonitrile (PAN) to make nanoscale urushiol/PAN films by the electrospinning method. Electrospinning solutions were prepared by using dimethylformamide (DMF) as the solvent. Nanoscale urushiol/PAN films and conductive Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)/polyvinyl pyrrolidone (PVP) films were prepared by electrospinning. In order to prepare an electrospun sandwich nanoscale film, urushiol/PAN films were deposited as both the top and bottom layers and PEDOT:PSS/PVP film as the inner layer. When the PAN to urushiol ratio was 7:5, the fiber diameter ranged between 150 nm and 200 nm. The single-layer urushiol/PAN film could not be etched after being immersed into 60%, 80%, and 100% sulfuric acid (H2SO4) for 30 min, which indicated the improved acid resistance of the PAN film. The urushiol/PAN film was used to fabricate the sandwich nanoscale films. When the sandwich film was immersed into 80% and 100% H2SO4 solutions for 30 min, the structure remained intact, and the conductive PVP film retained its original properties. Thus, the working environment tolerability of the functional PVP film was increased.

Synthesis of 4-substituted catechols with side-chains of different CC bond number as urushiol analogues and their anticorrosion performance

4-Substituted catechols with different CC bonds as urushiol analogues were synthesized through the a three-step route including reductive amination reaction of 3,4-dihydroxybenzaldehyde with N-Boc-piperazine, Boc deprotection, and amidation with various fatty acids. Electrochemical polymerization of these analogues on a copper surface afforded robust coatings with desirable adhesive force, hydrophobicity and thermal stability. Cyclic voltammetry and infrared spectroscopic characterizations revealed that the coating formation of urushiol analogues resulted from the electrooxidation-induced radical coupling of phenoxyl radicals with a phenyl ring and the side chain CC bond. The coating of the urushiol analogue bearing only one side chain CC bond exhibited the best performance in copper corrosion inhibition, with an inhibition efficiency of 99.99% and long-term effect (99.9% after 4 weeks of immersion in 3.5 wt% NaCl). The desired performance of these urushiol analogues suggests that they could be of practical applications as an alternative to the resource-limited natural urushiol.

Reductive amination reaction was achieved on a catechol ring, leading to urushiol analogues that could be electropolymerized with desirable urushiol-like performance.

Microfluidic Encapsulation of Hydrophobic Antifouling Biocides in Calcium Alginate Hydrogels for Controllable Release

Microencapsulation of biocides is used in long-life antifouling coating paints for marine applications and building materials. Here, we report the microfluidic production of calcium alginate (Ca-alginate) hydrogel particles to modulate the release of the encapsulated drug Irgarol (N-cyclopropyl-N'-(1,1-dimethylethyl)-6-(methylthio)-1,3,5-triazine-2,4-diamine), which is a hydrophobic and specifically phytotoxic antifoulant that inhibits photosystem II in aquatic plant species. We first encapsulated the drug inside the highly spherical Ca-alginate hydrogels of an average diameter ∼160 μm with a coefficient of variation of less than 4% and an average roundness of more than 0.96. The release speeds of the encapsulated and nonencapsulated drugs in pure water were measured separately by ultraviolet-visible spectroscopy. A stable and controllable release rate of the loaded drug was achieved by hydrophilic encapsulation. In addition, cellulose fibers were incorporated to enhance the mechanical strength of the hydrogels. Finally, the antifouling effect of the encapsulated drug was demonstrated using water grass (Bacopa monnieri).