Water-borne Systems Research Articles

Grafting α-aminoketone to SMA via highly efficient amide bond and their performances as macrophotoinitiators

Water-soluble macrophotoinitiators that can realize a high photoactivity together with low migration in waterborne photopolymerization systems are very necessary. However, the precise, highly efficient preparation of macrophotoinitiators remains a substantial challenge, such as grafting side chains according to stoichiometric ratios. Herein, based on styrene maleic anhydride copolymer (SMA) prepared by photopolymerization, water soluble macrophotoinitiators SMA5k-Ns and SMA13k-Ns series with controllable structure were successfully prepared through the amino bond of α-aminoketone small-molecule photoinitiator with maleic anhydride moieties. All of them exhibited excellent water dispersion properties, and solution photopolymerizations investigation showed they can be used as photoinitiators for radical polymerization with high conversion (up to 95%) in waterborne systems under LED@365–405 nm. Furthermore, the migration stabilities of these photoinitiators in photocured hydrogels were better than those of commercial photoinitiators. High efficiency and low migration make them have great potential applications in food packaging and biological materials.

Comparative Electrochemical Impedance Spectroscopy Quantification of Coating Weathering, Long-Term Immersion, and Salt Spray Test Outcomes

In the present study, we repeatedly used the surface-applied paste electrolyte cell to record the electrochemical impedance spectroscopy (EIS) spectra of four coating systems with different barrier properties exposed to different environments. The absence of a liquid electrolyte allows direct recording of the electrolyte-unaltered coating response to environmental stressors. Exposures included humidity between 23% and 95%, temperatures between 10°C and 50°C, 720 h of ISO 9227 neutral salt spray (NSS), 1 y in mild continental urban climate, and for comparison, 3 y of ISO 16773 3.5% NaCl immersion. The coatings showed significantly different temperature susceptibility of impedance revealing two temperature ranges with activation energies corresponding to ionic conductivity below 20°C and conductivity influenced by polymer chain movements above 30°C. Impedances measured for intact coatings or impedances calculated from the assumed range of dielectric constant and coating thicknesses can be used as references. The EIS outcome of the laboratory tests and the time- and temperature-resolved EIS responses under atmospheric exposure were compared with the reference impedances of the coatings. Mild continental climate exposure at temperatures <35°C and immersion at 23±2°C yielded better barrier performance for the two solvent-based coating systems compared to the two waterborne systems of comparable thickness and number of layers. The NSS test that proceeds at 35°C yielded better performance of both solvent-based coatings over the waterborne coatings, regardless of the thickness. EIS quantification of barrier performance, which excludes the influence of the liquid electrolyte, has provided insight into the temperature effect on the barrier behavior of the coatings under nonaccelerated and accelerated exposures and the final coating rating.

Sustainable associative thickeners based on hydrophobically modified ethoxylated poly(hydroxy-urethane)s end-capped by long alkyl chains

Hydrophobically modified ethoxylated urethanes (HEURs) are associative polymers applied as thickening additives in various waterborne systems, such as emulsions, coatings and printing inks. Their conventional synthesis, based on diisocyanates, poses environmental and health threats during both manufacture and application. Hence, in this paper we present an approach for the next generation of sustainable and CO2-rich polyurethane rheological modifiers – isocyanate-free HEURs (IFHEURs) obtained through poly(hydroxy-urethane) route. The hydrophilic core of the IFHEURs was prepared by step-growth polyaddition between diamine and poly(ethylene glycol) bis(cyclic carbonate) – synthesized using CO2 as a green source of the carbonate bonds. Such obtained prepolymer with terminal carbonate groups was subsequently modified with hydrophobic amines using reactive extrusion method, which enabled efficient homogenisation of the viscous reaction systems and reaching high end-capping functionality after only 2 h. In contrast to previously reported studies, the synthetic procedure was both solvent- and catalyst-free and allowed to incorporate up to 11 wt% of CO2 into the backbone of the final products. The structural analysis of the obtained IFHEURs using NMR and FT-IR spectroscopy and MALDI-ToF mass spectrometry confirmed obtaining the desired telechelic architecture resembling standard HEUR materials. The associative behavior of the IFHEURs in aqueous solutions was addressed in a rheological study, which revealed typical thickening mechanisms exhibited by rheological additives.

Self-stratification studies in waterborne epoxy-silicone systems

Waterborne epoxy‑silicone coating formulations are prepared by combining selected ingredients in optimum quantities to produce ~250–275 μm films (dry film thickness, DFT) applied on polyester, sandblasted steel, smooth steel, acrylic, polypropylene and aluminum substrates. The self-stratification of the applied coatings is then evaluated using Fourier Transform Infrared spectroscopy – Attenuated Total Reflectance (FTIR–ATR) and Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray (EDX) analysis. The difference in the absorption spectra of the top and bottom surfaces of these films as well as a significant difference in topography seen from the SEM images and elemental mapping through an EDX analysis of the cross-section has confirmed the occurrence of stratification on polyester substrate. The observed stratification results are subsequently compared with a theoretical model where the primary mechanism driving the separation is assumed to be the surface free energy difference of the resins and their respective wetting of the substrate. The influence of using two different theories, Wu's Harmonic Mean Method and Owens-Wendt Method for the interfacial surface tensions and the solid surface free energy computations, on the predictions from this model is also tested. The theoretical predictions support the observed results for most cases of the formulated waterborne systems; except for the case of sandblasted steel, the observed results do not match the predictions. The possible reasons for the difference in between the prediction and observation for this specific case has also been elucidated.

Air quality improvement via modal shift: Assessment of rail-water-port integrated system planning in Shenzhen, China

The escalating concerns regarding air pollution problems surrounding port cities have attracted much research attention. The Port of Shenzhen is one of the busiest container ports worldwide, only third to Shanghai and Singapore globally. However, 70% of the freight transportation demand is satisfied via on-road trucks, leading to serious traffic congestion, road accidents and air pollution issues in the city of Shenzhen. This study aims to assess the environmental benefits of modal shift of port-connecting freight transportation by increasing the use of rail and waterborne systems in Shenzhen. To evaluate the environmental benefits of the multimodal transportation strategy in 2025, we employed traffic datasets with a high spatial resolution and a transportation demand model to establish emission inventories and applied them in air quality simulations. Our results indicate that the implementation of multimodal transportation systems could notably reduce the truck volume along major freight corridors, except for roads adjacent to the planned inland ports. The freight traffic activities along the major freight corridors are reduced by nearly 70% over the original freight volume, resulting in a drastic reduction in the emission intensity. Under the most progressive policy-enhanced strategy (PPP) scenario, the total well-to-wheel (WTW) NOX, fine particulate matter (PM2.5) and CO2 emissions could be reduced by 8881 t, 104.8 t and 688 × 103 t, respectively. The NO2 concentration in traffic-intensive areas could be reduced by 5 μg/m3, and the 8-h maximum O3 concentration could be reduced by 0.34 μg/m3 on the average (up to 1.1 μg/m3 in certain areas). Our research indicates that a shift from traditional road transport to cleaner railway and waterway transport could deliver transportation and environmental benefits to port cities.

Molding and Encoding Carbon Nitride-Containing Edible Oil Liquid Objects via Interfacial Toughening in Waterborne Systems.

Charge interaction-driven jamming of nanoparticle monolayers at the oil–water interface can be employed as a method to mold liquids into tailored stable 3D liquid objects. Here, 3D liquid objects are fabricated via a combination of biocompatible aqueous poly(vinyl sulfonic acid, sodium salt) solution and a colloidal dispersion of highly fluorescent organo-modified graphitic carbon nitride (g-C3N4) in edible sunflower oil. The as-formed liquid object shows stability in a broad pH range, as well as flexible pathways for efficient exchange of molecules at the liquid–liquid interphase, which allows for photodegradation of rhodamine B at the interface via visible light irradiation that also enables an encoding concept. The g-C3N4-based liquid objects point toward various applications, for example, all-liquid biphasic photocatalysis, artificial compartmentalized systems, liquid–liquid printing, or bioprinting.

Green nanocomposites from Salvia-based waterborne polyurethane-urea dispersions reinforced with nanocellulose

Waterborne polyurethane-urea (WBPUU) dispersions, products having none or low contents of organic solvents, depending on the used synthesis process, can provide suitable environmentally-friendly strategies to prepare novel materials. Moreover, waterborne systems enable the incorporation of aqueous dispersible nanoentities and soluble additives, which provides a strategy to design versatile functional materials with tailored properties. Having demonstrated in previous work the bacteriostatic properties of a 3 wt% Salvia-based WBPUU against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa, this work is focused in the preparation of Salvia-based WBPUU added with cellulose nanocrystals (CNC) tackling the preparation of functional green nanocomposite films with increased mechanical properties. Through this strategy, nanocomposites loaded with 1, 3 and 5 wt% of CNC were prepared, showing an effective CNC incorporation avoiding agglomerates. CNC addition is able to modulate soft and hard phase’s segregation, inducing enhanced mechanical stiffness, together with improved deformability, while retarding thermomechanical instability to higher temperatures.

Polymerizable Hydrophobically Modified Ethoxylated Urethane Acrylate Polymer: Synthesis and Viscoelastic Behavior in Aqueous Systems

Hydrophobically modified ethoxylated urethanes (HEURs) comprising hydrophilic poly(ethylene glycol) backbone and hydrophobic end groups are widely applied as rheological additives to regulate the viscoelastic behavior of waterborne systems such as coatings and inks. However, the conventional HEURs are usually nonreactive and remain free in final films, which may bring some defects and damages to the final cured films during the service time. An appealing way to improve filming properties may be to design reactive HEURs, which can participate in the post-crosslinking reactions with other components in formula during the film curing. In this work, a polymerizable acrylic-type HEUR (acrylic-HEUR) end-functionalized by the reactive methacrylate group and hydrophobic octadecyl tail is reported. The typical free radical polymerization feature of acrylic-HEUR based on the highly reactive methacrylate group is carefully clarified by dynamic light scattering, in situ nuclear magnetic resonance (1H NMR), and rheological measurements. The excellent thickening performance of acrylic-HEUR in waterborne UV emulsions and its effective copolymerization reactivity with the UV-curable matrix resin are demonstrated by in situ rheological measurements under UV irradiation in detail. Compared to conventional nonreactive HEURs, the copolymerization reactivity of acrylic-HEUR may make it especially suitable for applications in waterborne UV coatings to avoid its migration from final UV-cured films. This work may not only open a new perspective for the fabrication of HEUR polymers with high chemical reactivity but also promise the potential of polymerizable HEURs as superior associative thickeners in industry.

Supramolecularly Reinforced Films from Polyurethane–Urea Dispersions Containing the Tris-Urea Motif

Because of the drive toward more green and sustainable processes for polymer synthesis, there is a growing desire to avoid solvent-borne polymer systems where possible and exchange for waterborne alternatives. Here, it isdemonstrated that the use of carbohydrazide as a chain extender of polyurethane prepolymers dispersed in water leads to the generation of polyurethane–urea dispersions that are supramolecularly reinforced by the tris-urea motif. Despite being incorporated as a small percentage of the total formulation by weight, films cast from polyurethane–urea dispersions that incorporate the tris-urea motif allow for more than an order of magnitude increase in Young’s modulus and an order of magnitude increase in tensile strength without any compromise in the elongation at break. It is also demonstrated that the tris-urea group provides better mechanical strength than a chemically cross-linked structure and also undergoes stress relaxation on a longer time scale. Furthermore, DMTA measurements demonstrate that the increased strength of supramolecular hydrogen bonding interactions increase the mechanical stability at elevated temperatures. The improvement in mechanical properties shown by tris-urea containing polyurethane–urea dispersions should allow for the use of waterborne systems where previously only solvent-borne polymers have been used.

From Architectures to Cutting-Edge Properties, the Blooming World of Hydrophobically Modified Ethoxylated Urethanes (HEURs)

Hydrophobically modified ethoxylated urethanes (HEURs) are associative polymers that, compare to others, are far less sensitive to solution parameters, especially pH and ionic strength. Therefore, they are widely used as rheology modifiers in many different waterborne systems such as inks, coatings, emulsions, etc. In solutions, HEURs form transient networks through molecular associations between their hydrophobic groups. The transient network formation and its characteristics are responsible for the rheological properties and depend on the HEUR chains architecture. Many parameters such as molecular weight, size and nature of hydrophobic groups, polymer concentration, etc must be controlled to tune the several physicochemical properties of HEUR solutions. This article aims to give an overview of the HEUR studies reported in the literature in order to highlight the structure/rheological properties relationship. The article also draws attention to new trends in HEURs with innovative architectures and stimuli-responsive properties.

On which grounds a decision is taken in waterborne transport technology to reduce air pollution?

Recent extreme events in Venice lagoon place emphasis on the air quality impact and its relationship with local air emissions production especially waterborne transport. The general concern for the impact of air pollutants on environment and human health has led to the introduction of more restrictive regulations (both marine and inland water vessels) and new technologies have been developed. Despite this, some specific scenarios require different approaches because of their peculiarity. Venice, as a water town, is a very distinctive case where transport is supplied by waterborne systems. Local and regional pollution causes high pollutants concentrations that can duplicate in correspondence of some lagoon's channels especially for NOx. Causes are not completely studied yet, but several small boats navigate in small channels and micrometeorology could have a great impact. In this context ACTV S. p.A. in collaboration with the Dep. DAIS, Ca’ Foscari University, has developed a project aimed to assess ACTV fleet emission estimate (actual and future scenarios) using a mathematical model, WATERBUS (now upgraded v. 2.1). Novelty is in the introduction of specific elements generally not listed causing a misrepresentation of emissions. From results, current situation shows a low percentage impact on total emissions in Venice (1–5%) at province level, but it increases at municipal one (0–20%). Highest percentages refer to NOx. From forecast emission analysis, a new hybrid solution has been evaluated to reduce emission impact of 1–3%. Higher decrease could be extended by an intelligent management of the electric motor of hybrid propulsion in the different lines.

Surface Modification of Graphene for Use as a Structural Fortifier in Water-Borne Epoxy Coatings

Graphene, the typical two-dimensional sp2 hybridized carbon allotrope, is widely used as a filler for improving the mechanical performance of polymers. However, its superhydrophobic surface makes it a big challenge to obtain stable graphene dispersions, especially in water-borne systems. On the contrary, graphene oxide (GO) shows excellent dispersibility in water, but strong oxidants and acids destroy its structure and degrade its mechanical properties. This largely limits its application in water-borne coatings. In this work, graphene from mechanical exfoliation was surface modified by p-aminophenol derived diazonium salt to achieve a homogenous dispersion. Moreover, the hydroxyl groups in p-aminophenol are able to combine with epoxy resins during the curing process to improve mechanical performance of the final coatings. The result shows that functionalized graphene shows a lower coefficient of friction and better abrasion resistance compared to GO.

Sanitation game changing: paradigm shift from end-of-pipe to off-grid solutions

Abstract The toilet-wastewater-pollution nexus – the provision of safe, hygienic and appropriate sanitation solutions – is an emerging, priority issue world-wide. Developed nations have followed a linear design approach to achieve their sanitation needs, with conventional waterborne systems continuously improved to meet more stringent control and pollution regulations while minimising the load on the natural environment. Developing countries, on the other hand, continue to struggle to implement such systems, due to a myriad of factors associated with financing, affordability and revenue, and thus rely heavily on on-site systems. On-site systems pose a different set of technical challenges related to their management, which is often overlooked in the developing world. Whereas, while technology strides increase in conventional sanitation processes towards zero-effluent, these come at a significant cost and energy requirement. Further, climate variability and water security put added pressure on the resources available for flushing and transporting human waste. A new paradigm for sanitation, proposed in this paper, introduces and is based on technology disrupters that can safely treat human excreta, and matches user preferences without the need for sewers, or reliance on large quantities of water and/or energy supplies. Through innovation and smart-chain supply, universal access can be achieved sustainably, and linked to water security and business opportunities. The opportunity arises for leapfrogging these solutions in growing cities in the developing world, reducing water consumption and eliminating pollutant pathways.

A reactive hydrophobically modified ethoxylated urethane (HEUR) associative polymer bearing benzophenone terminal groups: Synthesis, thickening and photo-initiating reactivity

Hydrophobically modified ethoxylated urethanes (HEURs), as a representative class of associative polymers, are widely used as rheology modifiers in waterborne systems such as coatings, emulsions, inks etc. due to their unique associative network structure and finite relaxation behavior in solution. However, conventional HEURs are non-reactive and generally stay free in final cured films, which may induce some damages to the performance of the coatings. To solve the problem, a new concept of reactive HEUR has been proposed. That is, a reactive HEUR should bear reactive hydrophobic end-groups which can chemically crosslink with matrix resins during the curing process of waterborne coatings. In this work, with the help of the hydrogen abstraction photo-initiating reactivity of benzophenone (BP) group, a reactive HEUR (BPC11HEUR) end-functionalized by a photo-initiator BP moiety has been prepared. In aqueous solution, as demonstrated by steady shear measurement, an exponential increment of solution viscosity along with the increasing of polymer concentration (C) was found when C surpassed its critical percolation concentration (Cp ≈ 23.6 g/L). Besides, ultraviolet (UV) light induced photolysis in aqueous solution manifested a typical photochemical reaction behavior of BPC11HEUR polymer with a final photolysis degree (D) of approximate 78% after 300 s of irradiation. In situ 1H NMR and rheological measurements collectively revealed the efficient photo-initiating reactivity of BPC11HEUR for waterborne UV monomers or resins. Further, rheological measurements demonstrated that the emulsion zero/low shear viscosity can be greatly enhanced by ca. 50 folds for a commercially available waterborne UV polyurethane acrylate emulsion when the addition amount of BPC11HEUR varied from 0 to 1.0 wt%. These results shown that the reactive BPC11HEUR polymer can not only be used to efficiently modify the rheological properties of solutions or emulsions but also can chemically crosslink with waterborne UV acrylic monomers or resins by light irradiation. The work may be of interest for development of reactive HEURs used in waterborne UV coatings, inks, and adhesives, etc.

One pot stimuli-responsive linear waterborne polyurethanes via Diels-Alder reaction

Different strategies were used to obtain waterborne polyurethanes containing Diels-Alder moieties. In the first one (two pot), furan and maleimide end capped waterborne polyurethane dispersions were synthesized with the aim of obtaining a stimuli-responsive material after drying a mixture of both dispersions. However, the maleimide hydrolysis that took place at basic pH prevented the use of this strategy. The only way to introduce maleimide groups in the furan capped dispersions was after water removal, which limits the application. In the second strategy (one pot), a Diels-Alder adduct was introduced in the polyurethane chain. Using this strategy, stable waterborne polyurethane dispersions were successfully synthesized.Both strategies allowed the obtaining of films that according to FTIR, DSC and NMR experiments showed cyclic temperature responsive behaviour, as at high and low temperature the Diels-Alder adduct was opened and regenerated respectively. As a consequence of this reaction, the temperature increase provoked chain scission reducing both the polymer molecular weight and the viscosity.Using the one pot strategy, a Diels-Alder adduct containing polyurethane film was obtained for the first time from waterborne systems. This can be of great interest in order to obtain functional self-healing coatings with reduced volatile organic compounds (VOC).

The Treatment of Aluminium Pigments with Inorganic Polymers for Environment-Friendly Applications

Aluminium pigments are used in industrial and decorative coatings, automotive industry and printing inks. The encapsulation of aluminium pigments is used because the industry wants to avoid the organic solvents, for environmental reasons, by shifting towards water-borne systems. However, aluminium pigments easily react with water and a large amount of hydrogen is released leading to degradation of optical properties. This work presents experimental results concerning the encapsulation of aluminium pigments in silica matrices, by a sol-gel method using TEOS as precursor and ethylendiamine or ammonia as catalysts for the hydrolysis and condensation reactions. The samples of encapsulated pigments were characterized by gas stability tests: a boiling method and a gassing method.

Fungal Growth on Coated Wood Exposed Outdoors: Influence of Coating Pigmentation, Cardinal Direction, and Inclination of Wood Surfaces

Four coating systems were exposed for one year outdoors at 45° south. They consisted of solventborne (alkyd based) and waterborne (acrylic based) systems in both clear and pigmented versions. Fungal growth visually assessed was compared to fungal enumeration, and the influence of exposure time on the main fungal species was studied. Results clearly showed that fungal growth was lower on the pigmented coating systems compared with their pigment-free versions. Although the clear solventborne coating included a higher amount of biocide, it was more susceptible to blue stain than the pigmented version. A new multifaceted exposure rig (MFER) also contributed to the study of fungal growth. It allowed samples to be exposed with nine different exposure directions and angles. Exposure using this MFER has shown that the worst cases (highest area and intensity of blue stain fungi) were for samples with the clear coating system exposed to north 45° and at the top of the MFER (horizontal surfaces). For any cardinal direction, all surfaces inclined at 45° displayed more blue stain fungi than vertical surfaces, due to a higher moisture content of the panels. Depending on the cardinal direction and the orientation, some surfaces were free of visible cracking, but colonized by fungi. It was concluded that the growth of blue stain fungi was not linked with cracking development.

Environmentally friendly polymer latex

Research in the area of coatings focuses primarily on the mechanism for the formation of film on different substrates. Because of environmental hazards related to solvent evaporation and its cost, the ambient cured waterborne systems are emerging as one of the better option for achieving superior properties in high performance applications. The properties like adhesion, gloss, hardness, water resistance, and so on may also get affected by incorporating higher acrylate in the formation of copolymers based on methyl methacrylate (MMA). The swelling behavior of any polymer network depends upon the nature of the polymer, polymer solvent compatibility, and degree of cross-linking. The swelling kinetics of emulsion polymerization of monomers MMA/butyl acrylate was studied to investigate the effect of cross-linkable monomer polypropylene glycol diacrylate (PPGDA). The prepared latex was coated on glass panels and cured at appropriate temperature. According to diffusion-controlled mechanism, the diffusion coefficient for these films varied with degree of cross-linking of the films. From the above discussed swelling behavior of different polymer films, it has been observed that PPGDA content improved the water resistivity of films. This may be due to the cross-linking nature of PPGDA molecule, which increased the cross-link density of the films.

An environmentally benign methodology to elaborating polymer nanocomposites with tunable properties using core-shell nanoparticles and cellulose nanocrystals

An environmentally benign concept based on waterborne systems is developed for preparation of novel nanocomposite materials with tunable properties. The designed nanocomposites are based on combination of core-shell latex nanoparticles, cellulose nanocrystals (CNC) and polyethylene glycol (PEG). First, core-shell latex nanoparticles from copolymer (methyl methacrylate-ethylene glycol dimethacrylate)-core and copolymer (methyl methacrylate-butyl acrylate)-shell (CS15) are prepared by starved emulsion polymerization. Likewise, incorporation of CNC aqueous suspension into the core-shell latex without any further chemical modification of the nanofiller while assuring good compatibility between both entities is achieved. PEG is effectively added to the suspension to assure multiple functions in the final material. After mixing of the ternary systems, the nanocomposites are prepared by three approaches, i.e. solution casting, solution casting followed by compression molding, and freeze drying followed by compression molding. SEM analysis shows that compression molding processes lead to the highest degree of coalescence of CS15 nanoparticles. This effect is however reduced in presence of PEG or PEG/CNC. It is further observed that the presence of PEG helps protecting CNC from thermal degradation. Thermal and thermo-mechanical analyses prove a high plasticizing performance of PEG and its good confinement between the nanoparticles and at interstitial spaces. Furthermore, it is revealed that the level of material reinforcement by CNC depends strongly on the ratio between CNC and PEG due to the establishment of strong interactions via hydrogen bonding between both components, which can affect the formation of CNC percolating network. These findings allow tuning the microstructure and related properties of the nanocomposites.

Reduction–Coagulation Preparation of Hybrid Nanoparticles of Graphene and Halloysite Nanotubes for Use in Anticorrosive Waterborne Polymer Coatings

Graphene has been extensively concerned as an ideal modifier in the exploration on mordern polymer coatings with high performance. However, the poor dispersibility of graphene in water strongly limits the application in waterborne systems. Here, we demonstrate a simple but effective reduction–coagulation method for the preparation of hybrid nanoparticles of halloysite nanotubes (HNTs) and reduced graphene oxide (rGO). The work was started from the simple mixture of the aqueous dispersion of graphene oxide(GO) and HNTs. As the subtle introduction of the reducing agent, GO was reduced into rGO and co-coagulated with HNTs. Tailored by the residual hydrophilic groups inside the nanotube of HNTs, the phase separation was controlled in colloidal scale, and stable aqueous dispersion of HNTs–rGO hybrid nanoparticles was thereafter obtained conveniently. We directly blended the product into the polymer latex for the formation of coating films. The tests reveal that the composite coating system with the addition of...