Waterborne Coatings Research Articles

Superhydrophobic film from silicone-modified nanocellulose and waterborne polyurethane through simple sanding process

How to improve the water and pollution resistance of films has been a major stumbling block in applications of waterborne coatings. To solve this problem, a new strategy was developed to construct waterborne superhydrophobic polyurethane composite films by modifying cellulose nanocrystal (CNC) with polysiloxane and doping the modified CNC into waterborne polyurethane (WPU). The super-hydrophobic functionalization with a water contact angle >150° was achieved by simple sanding. The effects of CNC on the morphology, thermal, mechanical, and hydrophobic properties of the obtained superhydrophobic composite films were investigated. The simple sanding process formed a large number of rough porous structures on the surface of the film, which improved the superhydrophobic properties of the film. And after 30 sanding cycles, the film still had excellent hydrophobicity (water contact angle >150°). This easy and effective method for the preparation of superhydrophobic films has great practical application value in the area of waterborne coatings.

Non-targeted screening for contaminants derived from food contact water-borne coatings and risk assessment based on (Q)SAR matrix

Because of great knowledge gaps between toxicological data and chemical constituents for substances involved, water-borne coating paper and board have emerged as a sort of particular concern for the safety of consumers. Herein, we describe a step-by-step method including extraction, gas chromatography-mass spectrometry (GC-MS) fractionation, tentative identification of related substances and risk assessment of chosen tentatively identified substances based on (Quantitative) Structure-Activity Relationships ((Q)SARs) matrix. Three water-borne coating samples possessing different compositions were investigated. Polyacrylates were first determined as the possible compositions of coating samples based on Fourier transform infrared spectrophotometer (FTIR) and differential scanning calorimetry (DSC) analysis. 7 out of 23 elemental compositions determined by inductively coupled plasma emission spectrometry (ICP-OES) were demonstrated for peaks over a specific migration limit evidencing the likely heavy metal contamination from water-borne coatings. Of 359 tentatively identified substances, 85 and 38 substances were assigned to Hazard Ⅳ and Risk Ⅳ, respectively, disclosing the particular concern for consumer safety, which may originate from decomposition products and impurities from industrial processing. Overall, understanding the identity of contaminant will allow it easier to find the possible source, and to study which part of the water-borne coating paper-producing process that could be amended to mitigate the risk.

A multifunctional and long-term waterborne anti-corrosion coating with excellent ‘hexagonal warrior’ properties

Environmentally friendly waterborne coatings tend to form polar pathways due to more hydrophilic groups, resulting in poor coating corrosion resistance and reduced coating service life. The anisotropic Janus is used as a filler for waterborne epoxy (WEP) coatings to reduce the number of hydrophilic groups and improve interface compatibility by cross-linking the hydrophilic end with the resin; at the same time, the hydrophobic groups are used to improve the water resistance of the coating. In this paper, we synthesized sheet-like silica Janus (JNS) materials by interface-induced self-assembly via sol–gel reaction in oil-in-water emulsions to prepare novel water-based JNS/WEP anticorrosion coatings. The excellent corrosion resistance of JNS/WEP coatings is explained by the fact that the hydrophilic end of JNS reduces internal defects in the coating and enhanced interfacial interaction; the hydrophobic end improves the water resistance of the coating. Similarly, the physical barrier advantage of flake JNS is brought into play to reduce the high availability of water and oxygen, inhibit electrochemical corrosion on the surface of carbon steel and form a passivation film; the active group at the hydrophilic end of JNS can be chelated with Fe3+ for active protection by synergistic. Among them, immersed in 3.5 wt% NaCl solution for 130 days, the impedance modulus of 1.0 % JNS/WEP coating is 2 orders of magnitude higher than that of WEP coating, up to 2.59 × 1010 O cm2. Therefore, it exhibits outstanding anti-corrosion performance under multiple synergistic protection.

Synthesis of phase change microcapsules based dispersants for waterborne coatings and their effects on paint film properties

The hyperdispersant SSS-MPEGA-MA (SMM) is prepared through aqueous polymerization using sodium p-styrenesulfonate (SSS), polyethylene glycol monomethyl ether acrylate (MPEGA) and maleic anhydride (MA) as monomers for dispersing phase change microcapsules (PCM). It is also concluded that the best dispersion effect is achieved when the starting concentration of SMM dispersant in aqueous solution with a solid content of phase change microcapsules of 20% occupies 2% of PCM content. The phase change microcapsules are added to a waterborne varnish with a solid content of 20%, and after adding a certain mass of SMM dispersant dropwise, phase change performance is still found on the film, which is the best with a dispersant concentration of 2%. At the same time, the hyperdispersant SMM can make the phase change microcapsules evenly distributed on the water-based varnish, and the dispersion effect is good without affecting the properties of the paint film itself.

Towards improved performance of waterborne polymer dispersions through creation of dense ionic interparticle network within their films

To overcome the main challenge of low performance of the waterborne polymer coatings due to the particulate nature of the polymer dispersions and the complex film formation process, in this work we implemented the strategy of ionic complexation between oppositely charged waterborne polymer particles. For that aim, doubled charged ionic monomers ithaconic acid (IA) and styrenic 1,4-diazabicyclo[2.2.2]octane (DABCO) were used to densely functionalize (meth)acrylic film forming polymer particles, synthesized by seeded semi-batch emulsion polymerization to produce high solids content anionically and cationically charged polymer dispersions, respectively. The main advantage of the double charges in the selected ionic monomers is that they provide high ionic charge density onto charged particles at lower content of ionic monomers.The blending of these oppositely, densely charged and concentrated dispersions resulted in instantaneous coagulation. To postpone the immediate complexation, water-soluble non-ionic polymeric stabilizing species as steric obstacles around the colloids were employed, which allowed to prepare colloidally stable blends and to prepare ionic complexed films. Certainly, the established ionic complexes between carboxylic acids of IA anionic monomer and quaternary ammonium groups of DABCO units within the films improved substantially the mechanical properties and the water sensitivity of the ionic complexed polymeric films with respect to individual films and the reference blend, in which ionic bonding was prevented by pH control. Moreover, the dense ionic network formed within the film actuated as a strong barrier to the leakage of all the water-soluble species during film immersion in water. Beside simple strategy towards improved performance of waterborne coatings, these results offer further extension of their application potential.

Efficient downstream valorization of lignocellulose after organosolv fractionation: Synergistic enhancement of waterborne coatings by co-assembled lignin@cellulose nanocrystals

The simultaneous downstream valorization of cellulose and lignin is an important aspect of efficiently extracting value from lignocellulose. The present work, we demonstrated the preparation of a novel bio-based filler by the co-assembly of cellulose and lignin obtained from a one-pot ethanosolv lignocellulose fractionation process. The cellulose was valorized by forming cellulose nanocrystals (CNCs) through simple bleaching and ultrasonication processes. The lignin fractions demonstrated greater solubility (19.2 mg/mL) and lower molecular weight (6980 g/mol) than conventional industrial lignins. Various lignin@CNCs specimens were prepared via a facile co-assembly of the lignin and CNCs. These entirely bio-based materials could be used as a multifunctional filler to enhance the properties of a waterborne coating (WBC). Specifically, the mechanical properties, coating performance and ultraviolet resistance of a WBC were all significantly improved, demonstrating a synergistic enhancement effect obtained from the CNCs and lignin. In this manner, both cellulose and lignin components were efficiently transformed to value-added fillers for WBC, demonstrating a highly efficient pathway for lignocellulose utilization and downstream value-added applications.

About Gas Barrier Performance and Recyclability of Waterborne Coatings on Paperboard

For preserving food packed in environmentally friendly and recyclable paperboard packages, it is important to have sufficient gas barrier performance of the paperboard container. Paperboard has poor intrinsic barrier properties and to overcome this deficiency, so a barrier coating is needed that does not hinder the recycling of the paperboard substrate. However, the gas barrier properties and the recyclability of such coatings have been rarely studied. Here, both the gas barrier performance and the removal of an alkali-soluble resin (ASR)-stabilized waterborne barrier coatings from paperboard are investigated. For barriers for gases, such as nitrogen, carbon dioxide, and oxygen, defect-free coatings are needed which is achieved by applying three coating layers. The oxygen transmission rate (OTR) of the three-layered coating on paperboard was 920 cm3/(m2∙day). For water vapor barriers, two coating layers already show a strong improvement, as water follows a different penetration mechanism than the other tested gases. The water vapor transmission rate WVTR of double coated paperboard was 240 g/(m2∙day). Preliminary results show that the coating is removed by immersion of the coated paperboard in an aqueous alkaline solution at room temperature. This causes de-protonation of the carboxylic acids of the ASR and subsequent re-dispersion of the coating in water. Removing double-layer coatings from the paperboard is more challenging, possibly due to the coating/coating interface between the two coating layers and enhanced adhesion between coating and paperboard.

Three sources-in-one bio-MOFs doped silicone acrylic emulsion-based waterborne flame-retarding coatings with formaldehyde adsorption property

Novel three sources-in-one bio-MOFs doped silicone acrylic emulsion-based waterborne coatings are prepared, using the as-prepared γ-cyclodextrin-based bio-metal-organic framework materials (CD-MOF) as the flame-retarding filler, which has a BET surface area of 451 cm2·g−1. The flame retardant and formaldehyde adsorption performance are investigated by various microstructural characterizations. Additionally, pyrolysis and adsorption kinetics are employed to probe the flame-retarding and adsorption mechanisms. The results show that the synergistic flame-retarding effect of ammonium polyphosphate (APP) with CD-MOFs is superior to that of 9,10-dihydro-9-oxa-10-phosphaphenanthr-ene-10-oxide (DOPO) blended CD-MOF, evidenced by the FGI decreasing from 1.91 to 1.47 kW·m−2·s−1, FPI climbing from 0.19 to 0.34 s·m2·kW−1, and FRI rising from 1.61 to 3.56, respectively. Because of the as-formed vitreous superphosphates, the pyrolysis activation energy Eα climbs from 88.8 kJ·mol−1 to 239.4 kJ·mol−1 at 330–450 °C according to the 3D Jander model (n = 2). In addition, the adsorption kinetics show that the monolayer adsorption model dominates the composite coating with a formaldehyde absorption capacity of 63.57 % within the first 24 h. The results propose a novel and ecological strategy to optimize the compatibility of organic-inorganic hybrid fireproof coatings, exploring ecological and cleaner technologies for the development of a low-carbon economy.

Optical Patterning in Photoresponsive Azobenzene-Based Waterborne Coatings

Optical Patterning in Photoresponsive Azobenzene-Based Waterborne Coatings

Influence of Photochromic Microcapsules on Properties of Waterborne Coating on Wood and Metal Substrates

With the development of the economy and science and technology, consumers have put forward higher requirements for the functionality of surface coatings on wood products and metal products, which requires us to endow traditional coatings with new functions. Innovative research of coatings has been a research hotspot in recent years, and the combination of microencapsulation technology with coatings is a research direction attracting much attention. In this paper, a kind of spirooxazine color-changing microcapsules containing photochromic purple dye was selected to explore the effect of different loadings of the photochromic microcapsules on the properties of the coatings. The photochromic microcapsules were added to the waterborne coating with loadings of 5.0%, 10.0%, 15.0%, 20.0% and 25.0%. The coatings were coated on Tilia europaea boards and aluminum alloy plates to explore the optical properties, mechanical properties, cold liquid resistance and aging resistance of the coatings. The results showed that the coating had good photochromic property on wood substrate and metal substrate. When the loading was 15.0% and 10.0%, the comprehensive performance of the coating was good. The color difference of the coating before and after photochromism was 51.0 and 62.0, the glossiness was 7.1% and 15.9%, the hardness was 3H, the adhesion grade was 1, the impact resistance was 4 kg·cm, the roughness was 1.2 μm and 0.9 μm and the liquid resistance grade was 1. The research results show that the photochromic microcapsule can endow the paint with a reversible color change function and improve some mechanical properties of the coating, which indicates that the composite prepared in this study can be used in the surface finishing of wood and metal and has certain research value and application potential.

Durability and Corrosion Properties of Waterborne Coating Systems on Mild Steel Dried under Atmospheric Conditions and by Infrared Radiation.

Increasing attention is given to waterborne coatings for corrosion protection due to the lower ecological impact on the environment. It has been found that by using waterborne coatings, the emission of harmful volatile organic compounds (VOCs) is reduced by more than 50 g/L. However, they require longer drying time, their anti-corrosion performance is not as good as solvent-borne coatings and they still have not been developed for all corrosion environments. Another way to reduce VOCs is by using infrared (IR) drying technology. With catalytic infrared radiation, it is possible to cure all surfaces at notably reduced costs compared to traditional systems and in total respect for the environment, thanks to significant energy savings and minimal CO2 emissions. The aim of this paper was to evaluate corrosion protective properties of waterborne coatings which were dried with traditional and accelerated drying techniques, i.e., under atmospheric conditions and by using IR technology. Two different coating systems were applied, with and without Zn in the primer. To achieve this goal, the test samples were subjected to electrochemical, corrosion, and physical tests. It was shown that infrared technology does not affect the quality of the coating and it drastically reduces the intercoating interval. A coating system with zinc in the primer showed better overall protection properties after being subjected to impedance and salt spray testing, but generally, solvent-borne coatings still have higher durability than waterborne in extreme marine conditions according to recent research. Microstructure and porosity remained intact and the atomic force microscope confirmed that the flash-off was conducted correctly since there were no pinholes and blisters detected on the coating's surface. This study can serve as a foundation for further investigations of IC-dried waterborne coatings because there are not many at the moment.

Benzotriazole corrosion inhibitor loaded nanocontainer based on g-C3N4 and hollow polyaniline spheres towards enhancing anticorrosion performance of waterborne epoxy coatings

Multi-dimensional composite nanocontainers provided an opportunity to prolong the service life of waterborne self-healing coatings through combining intelligent protection with physical barrier. Herein, we constructed a benzotriazole (BTA) corrosion inhibitor loaded nanocontainer with barrier/controlled release/corrosion inhibition properties by assembling graphitic (g)-C3N4 lamella, hollow polyaniline capsule and outer polydopamine wall. Hollow polyaniline and g-C3N4 lamella with adsorption properties provide effective space and sites for loading BTA corrosion inhibitor. Outer polydopamine wall can not only realize the controlled release of corrosion inhibitor, but also ensure the good compatibility between the composite container and the water-based epoxy resin. In addition, polydopamine (PDA) and polyaniline (PANI) as a container frame can also serve as active inhibitors after the release of corrosion inhibitor to enhance the self-healing protection effect of waterborne coatings. In comparative evaluation, the composite coatings containing BTA-loaded nanocontainers (0.5 wt.%) exhibit obviously physical barrier effect after soaking in 3.5 wt.% NaCl solution for 40 days, and maintains good protective performance after immersion for 80 days. Meanwhile, the artificial scratch experiment verified the effective self-repair protection of the composite container to the coating under the condition of damage. To be sure, it will provide an effective improvement idea for the long-term application of waterborne epoxy coating in marine environment.

Design of waterborne coatings using crosslinking agent for enhancing drying

Waterborne Coatings are in demand since they are eco-friendly and non-toxic, however exhibits higher drying time. In this work, the drying rate of waterborne coatings have been tried to improve by incorporating the cross linking agent. PVA-water coatings have been prepared using solution casting technique and crosslinking agent used is glutaraldehyde (GA) to enhance the drying and minimizing the residual solvent. The loading of GA are varied and its effect on various parameters are examined. At higher loading of GA content, residual solvent is minimized and drying time is also slightly decreased.

Development of Waterborne Heavy-Duty Anticorrosive Coatings with Modified Nanoscale Titania

The steel structures of coastal engineering in the moist tropics and subtropics are always under a C5/CX level corrosion environment with high temperature, high humidity, and high salt fog. Anticorrosive waterborne coatings with high weatherability and reliability are urgently to be developed. In this work, one kind of waterborne heavy-duty anticorrosive coatings, with the advantages of excellent corrosion resistance, self-repairing ability, self-cleaning ability, and high film compactness, was successfully achieved through modifying the side chains on the surface morphologies of the spherical nanoscale titania. The micromorphology and structure of the coating were characterized by a scanning electron microscope (SEM), transmission electron microscope (TEM), and atomic force microscope (AFM). The anticorrosion characteristics and forming mechanism of the modified nanoscale titania coating were analyzed. The salt spray tests showed that the neutral salt spray resistance time of the modified nanoscale titania coating was 1440 h. Its durability reached the H level and met the design requirements for 15 years of anticorrosion lifetime. The modified nanoscale titania coatings had been large-scale commercially applied at some typical steel structures under an extreme harsh corrosion environment in one coastal thermal power plant. The results showed that no rusting, peeling, or crack phenomena were observed after 3 years of service under different harsh coastal corrosion conditions.

Preparation of Zn5Mo2O11·5H2O@Sulfonated Graphene by Template Method and Its Anticorrosion Mechanism in Polyurethane Coatings

Currently, waterborne coatings are widely used, but their poor anticorrosion performance compared with solvent-based coatings hinders their further application. In this study, a series of Zn5Mo2O11·5H2O@sulfonated graphene (SZMO@SG) composites are prepared using the template method. SZMO@SG is a type of two-dimensional material with a large diameter and low thickness compared to traditional zinc molybdate. Combining SZMO@SG with waterborne hydroxy acrylic latex and isocyanate, the polyurethane coatings with 3 wt% SZMO@SG achieve the best anticorrosion performance in the 3.5 wt% NaCl immersion test. In electrochemical impedance spectroscopy (EIS), the charge transfer resistance (Rct) of polyurethane coatings with 3 wt% SZMO@SG reaches 283,100 Ω·cm2 after soaking in a 3.5 wt% NaCl solution for 48 h. Its corrosion potential and corrosion current are only −0.453 V and 1.71 × 10−3 mA/cm2, respectively. After metal substrate corrosion, the metal substrate of polyurethane coatings with SZMO@SG contain more Mo, Zn and low-state Fe atoms. It confirms that a passivation film was deposited on the metal substrate and prevents Fe from oxidation. The elemental content and distribution of the coatings after the NaCl solution immersion test indicate that SZMO@SG may have the Na+ adsorption function.

Self-initiated UV-curable polyacrylate using soybean isolate as hydrogen donor

Using the seed emulsion polymerization method, photoinitiator 4-hydroxybenzophenone (HBP) and co-initiator soy protein isolate (SPI) were simultaneously grafted onto a polyacrylate molecular chain, and an innovative UV-curable waterborne polyacrylate resin based on biomass SPI-HBP macromolecular photoinitiator system was prepared, which can be rapidly self-initiated. It was successfully developed into a type of waterborne coatings with excellent mechanical properties for woodware. The results showed that the PA-SPI-HBP composite emulsion showed good UV absorption performance near 284 nm, where the absorbance of the photoinitiator decreased to 73.71 % of the initial value under UV light exposure for 1 min. With an increase in HBP content, the UV curing time of the coating was shortened from 10.68 s to 5.18 s. When the addition of HBP was increased from 0 % to 4 %, the tensile strength of the films increased from 1.85 MPa to 16.39 MPa, the tensile modulus of elasticity increased from 2.88 MPa to 374.81 MPa, and the elongation at break decreased from 559.03 % to 38.46 %. This study provided a new method for the preparation of biomass-derived macromolecular photoinitiators and highly efficient self-initiating UV-curable wood coatings.

Functional properties of coatings based on novel waterborne polyurethane dispersions with green cosolvents

Three green sustainable cosolvents were used to produce polyurethane waterborne coatings. The effect of dihydrolevoglucosenone, gamma valerolactone and propylene carbonate on the performance of different coatings from a range of polyurethane structures with different hard segment content and different chain extender (a diol and a diamine) was studied. Properties of both synthesised polymers and water dispersions, like particle size distribution, stability, and pH, were carefully examined. The key properties of obtained coatings, including Koning hardness, specular gloss, hydrophobicity, abrasion resistance, adhesion or chemical resistance were detailly investigated to validate the use of these alternative green solvents in industrial coatings. The results indicated that the performance of materials based on sustainable cosolvents were equivalent to that of PUD coatings from commonly used cosolvent, N-methyl-2-pyrrolidone (NMP) maintaining a high gloss finished, as the properties of the dispersions keep optimal. Monomodal water dispersions with particle's diameter below 180 nm and stable for at least one month were achieved.

Influence of Metal Oxide Nanoparticles as Antimicrobial Additives Embedded in Waterborne Coating Binders Based on Self-Crosslinking Acrylic Latex

This article deals with the simple preparation of environmentally friendly acrylic latex binders, which are functionalized with nanoparticles of metal oxides, namely MgO, ZnO, La2O3 and combinations of MgO and ZnO, serving as functional components to achieve antimicrobial properties, but also to improve physical–mechanical properties and chemical resilience. The incorporation of uncoated powder nanoparticles was performed during the synthesis, using the two-stage semi-continuous emulsion radical polymerization technique, to obtain latexes containing 0.5%–1.3% nanoparticles relative to the polymer content. Changes in latex performance due to nanoparticles were compared from the point of view of the type and concentration of metal oxide nanoparticles in latex. The results of the tests showed that all types of nanoparticles showed very promising properties, while with increasing concentration of nanoparticles there was an improvement in properties. The nanoparticles in latex provided interfacially crosslinked transparent smooth coating films with high gloss and good physical–mechanical properties. Latexes containing the highest concentration of nanoparticles provided coatings with significant antimicrobial activity against all tested bacterial and fungal strains, but also in-can preservative stability of liquid latex. Furthermore, the coatings were resistant to solvents, and in addition, latexes with MgO nanoparticles showed a significant decrease in the minimum film-forming temperature, and latex with a concentration of about 1.3% MgO did not show any flash corrosion under the coating film cast on a steel substrate. The latexes containing MgO and La2O3 nanoparticles provided coatings that were very resistant to water bleaching.

Preparation of Resin-Coated Waterborne Coating Microcapsules and Its Effect on the Properties of Waterborne Coating for Wood Surfaces

In this paper, the related experiments were carried out on microcapsules, with the aim of making the prepolymer react with the core emulsion by in situ polymerization using urea–formaldehyde resin as the wall material and waterborne acrylic wood coating as the core material. The prepared microcapsules were added to the waterborne acrylic wood coating and brushed on wood boards. Then, the gloss, hardness, adhesion, impact resistance and color difference were compared with paint surfaces without microcapsules. When the ratio of the microcapsule core-to-wall material was different from the increase in microcapsule content, the gloss of the coating decreased continuously; the decreasing range was basically the same, and the gloss values of the three core-wall ratio microcapsules were rather similar. With the increase in microcapsule content, the impact resistance of the coating first increased and then decreased. With the increase in microcapsule content, the color difference of the coating also increased continuously. The color difference of the coating with a microcapsule core-wall ratio of 0.67 changed the least, and the coating performance was good. When the core-wall ratio of the microcapsules was 0.67, and the proportion of microcapsules in the paint was 7.0%, the comprehensive properties of this coating were good. This research is of great significance to the future protection and development of wood.

Improvement of anticorrosion properties of waterborne coatings by designing a new type of modified graphene with high dispersion and low conductivity

Gallic acid modified and reduced graphene coated by polydopamine (DM-GO) is synthesized. The results show that gallic acid can reduce graphene oxide and promote the stable dispersion of graphene in solution, and repair some defects of graphene surface through π-π interactions. Polydopamine can effectively mitigate serious corrosion caused by graphene due to its high electrical conductivity. Because of the barrier effect of well-dispersed graphene and the presence of polydopamine, the addition of DM-GO into waterborne coating leads to the significant improvement of the adhesion and long-term corrosion resistance of coatings.