The coating backbone was assembled from an unsaturated polyester polyol (UNPES), isophorone diisocyanate (IPDI), and 2-hydroxyethyl methacrylate (HEMA), with PEG 400-diacrylate and the photoinitiator TPO enabling UV-induced crosslinking. Three thermally triggered self-healing formulations containing different HEDS concentrations reached gel contents of up to 90 percent. When scratched and held at 90 degrees Celsius, the coatings closed scratches extensively within 30 minutes, an outcome the team assessed qualitatively by optical microscopy.

The reversible sulfur–sulfur exchange reactions underlying this repair are what allow the crosslinked network to rearrange and flow back together at moderate temperature. To add antimicrobial function, the optimized formulation was modified with ZnO nanoparticles surface-functionalized with 3-(methacryloyloxy)propyltrimethoxysilane (MAPTMS) at three loading levels. The reactive vinyl groups on the modified particles covalently participated in the crosslinked network, which enhanced crosslink density, thermal stability, and surface hardness.

Because the particles are chemically incorporated into the network rather than merely blended in, they reinforce the coating structure itself. The nanocomposite coatings showed potent antibacterial activity against both Staphylococcus aureus and Escherichia coli, alongside exceptional abrasion resistance and strong adhesion to steel substrates exceeding 1.2 megapascals. Together with the healing and crosslinking results, these measurements point to a coating designed for applications where durability, self-repair, and microbial resistance are required at the same time.

The authors position the waterborne system as an eco-friendly platform that converges damage-responsive healing, UV-driven crosslinking, and sustained antimicrobial protection, making it a candidate for next-generation multifunctional protective coatings.

Subject of Research: Self-healing antibacterial UV-cured waterborne polyurethane acrylate coatings with disulfide dynamics and ZnO nanostructures

Article Title: Multifunctional UV-cured waterborne polyurethane acrylate coatings with dynamic disulfide healing and antibacterial ZnO nanostructures

Article References: Javadi, H., Sedghi, R., & Omrani, I. (2026). Multifunctional UV-cured waterborne polyurethane acrylate coatings with dynamic disulfide healing and antibacterial ZnO nanostructures. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13986-0

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13986-0

Keywords: waterborne polyurethane acrylate, self-healing coatings, disulfide exchange, UV curing, ZnO nanoparticles, antibacterial activity, MAPTMS silane, crosslink density, scratch repair, protective coatings, Multifunctional, UV-cured

The economic stakes in the region are enormous. According to a 2011 study cited by the authors, the total cost of corrosion in Qatar was estimated at approximately 7.8 billion US dollars, representing roughly 4.6 percent of the country’s nominal GDP, slightly above the 3.4 percent global GDP cost of corrosion estimated in 2016. Saudi Arabia and the United Arab Emirates spent roughly 24.8 and 14.3 billion dollars respectively. These figures underscore why accurately predicting how long a coating will remain effective matters so much: service-life predictions drive maintenance schedules, budgeting, and asset management decisions for buildings, bridges, pipelines, and industrial facilities across the Gulf Cooperation Council region.

The research team, led by Alexander Saul and Qingyang Liu along with Monir Aljaradli and Brahim Aissa, prepared flat carbon steel panels of grade HA250 and applied four distinct commercial coating systems. System A combined a zinc-rich epoxy primer, an epoxy intermediate layer, and an acrylic polysiloxane topcoat. System B paired a zinc-rich epoxy primer with a thick polyurethane topcoat. System C used a dual-epoxy base and intermediate topped with a thin polyurethane, while System D consisted of a polyamine-cured epoxy base coat with an acrylic polyurethane topcoat. Each system was applied according to manufacturer specifications for nominal dry film thickness, surface cleanliness, and curing conditions, with three independent panels prepared per exposure condition.

The laboratory regime followed ISO 12944-9, the cyclic aging standard widely used for coatings destined for C5 or CX corrosivity environments. It consists of 25 cycles totaling 4,200 hours, alternating 72 hours of ultraviolet and condensation exposure with 72 hours of neutral salt spray in a 5 percent sodium chloride brine, followed by 24 hours at low temperature. Meanwhile, the field samples were mounted at a 45-degree angle facing south on a wooden test rack in Doha, approximately nine kilometers from the sea. Although the site’s carbon steel mass loss classified it as C2 corrosivity under ISO 9226, the panels endured summer daytime temperatures frequently exceeding 40 degrees Celsius, nocturnal humidity often above 70 percent, and annual solar irradiance on the order of 2,000 to 2,200 kilowatt-hours per square meter.

The team deployed a battery of assessment techniques, and the contrasts between them proved to be the study’s most striking finding. Visual inspection under ISO 4628 showed almost no visible defects on unscribed samples in either environment, yet this apparent perfection masked serious underlying damage. Corrosion creep measurements around artificial scribes told a very different story: after 4,200 hours of laboratory aging, creep values ranged from about 3.3 to 21.6 millimeters, compared with roughly 0.6 to 15.1 millimeters after two years in the field. Under the ISO 12944-9 qualification criteria, all coatings except System A would have failed, despite looking pristine to the naked eye. The authors note that visual assessment evaluates only the visible symptoms of failure, long after water uptake and swelling have begun beneath the surface.

Perhaps the most counterintuitive result came from pull-off adhesion testing. Conventional wisdom holds that adhesion should decline as coatings weather, yet for three of the four systems, adhesion tensile strength actually increased over time in both laboratory and field samples, a behavior the researchers attribute to post-curing effects beyond the typical 24 to 72 hour window. Only System B showed the expected decline, plummeting from 8.3 megapascals after one year in the field to below 3.4 megapascals after two years, with failure analysis revealing 100 percent adhesive failure at the coating-substrate interface. Scanning electron microscopy of cross-sections confirmed a continuous air gap and cracks along the interfaces in System B, validating interfacial debonding as its dominant degradation mechanism.

Electrochemical impedance spectroscopy, increasingly favored as a non-destructive, time-resolved technique, also delivered a sobering lesson. All samples, regardless of exposure environment, maintained low-frequency impedance above 10 to the ninth power ohm-square centimeters, the threshold conventionally associated with excellent barrier protection, with many values approaching the potentiostat’s own measurement ceiling near 10 to the eleventh power. Yet System B, which retained high impedance, had failed catastrophically in the mechanical tests. The explanation lies in what EIS actually measures: the dielectric properties of an intact film area, which remains blind to interfacial delamination and localized breakdown at scribes. A coating can lose its mechanical integrity entirely while still behaving as a superb electrical barrier over undamaged regions.

The statistical analysis quantified this decoupling with unusual precision. The Pearson correlation coefficient between corrosion creep and pull-off adhesion was a near-zero 0.04, demonstrating that a strong bond does not guarantee resistance to lateral delamination and rust creep from defects. EIS correlated weakly with adhesion at 0.39 and, counterintuitively, showed a moderate positive correlation of 0.55 with corrosion creep, meaning systems with higher bulk film resistance were actually associated with greater scribe-driven degradation. Dry film thickness correlated moderately with bulk properties but negatively with creep, suggesting that interfacial chemistry rather than simple film build governs resistance to underfilm corrosion. Fourier-transform infrared spectroscopy added a chemical dimension, showing that laboratory aging induced more aggressive oxidative changes in polyurethane topcoats than natural weathering did, indicating that accelerated cycling may not faithfully reproduce field degradation mechanisms at all.

The overall performance ranking that emerged, from best to worst, was System A, followed by D, then C, then B. System A, with its zinc-rich primer, epoxy intermediate, and acrylic polysiloxane topcoat, showed the lowest creep at approximately 3.2 to 3.3 millimeters, strong adhesion, and stable high impedance. System C presented a particularly instructive paradox: it retained the highest impedance values and adhesion strength exceeding 20.7 megapascals, yet exhibited the worst corrosion creep, confirming that high scores on individual metrics can coexist with poor protection of the underlying steel. The authors caution that performance differences reflect the complete system, including layer architecture, number of coats, primer chemistry, and application quality, not binder chemistry alone.

For engineers and asset managers, the practical message is clear but nuanced. Accelerated testing under ISO 12944-9 proved genuinely useful as a screening tool, reliably identifying the poorer performers, Systems B and C, and producing more severe scribe degradation than the field for all four systems. However, it was overly conservative for the durable systems, A and D, which performed considerably better in real-world exposure. The authors conclude that laboratory hours cannot be converted directly into years of field service, and that qualification of coatings for high-value or safety-critical infrastructure should combine accelerated testing with representative field exposure. Crucially, no single performance indicator, whether impedance, adhesion strength, or visual rating, should determine acceptance. A multi-parameter assessment that probes bulk barrier performance, interfacial integrity, and defect-driven degradation together offers the only reliable path to service-life prediction in the world’s most aggressive climates, and the two-year Doha dataset now provides a rare, quantified foundation for building that integrated approach.

Subject of Research: Predicting the field durability of protective anti-corrosion coatings by comparing accelerated laboratory weathering with two-year atmospheric exposure in Qatar

Article Title: From lab to field: case study of predicting the capability of accelerated weathering for protective coatings in Qatar

Article References: Saul, A., Aljaradli, M., Aissa, B., & Liu, Q. (2026). From lab to field: case study of predicting the capability of accelerated weathering for protective coatings in Qatar. Results in Engineering, 32, Article 113290. https://doi.org/10.1016/j.rineng.2026.113290

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113290

Keywords: protective coatings, corrosion, accelerated weathering, ISO 12944-9, electrochemical impedance spectroscopy, pull-off adhesion, corrosion creep, Qatar, service life prediction, atmospheric corrosion, coating durability, field exposure testing

The significance of the achievement lies in the chemistry it replaces. Conventional polyurethanes, found in everything from furniture foam to automotive clearcoats, are formed when isocyanates react with polyols. Isocyanates are potent respiratory sensitizers, and their production depends on the equally hazardous and fossil-derived phosgene. NIPU chemistry sidesteps both hazards by coupling cyclic carbonates with amines, a polyaddition reaction that produces polyhydroxyurethanes bearing hydroxyl groups along the backbone. Those pendant hydroxyls form additional hydrogen bonds, which can enhance adhesion and cohesion, but the field has struggled to match the mechanical performance of conventional systems, particularly in crosslinked coatings.

The Turkish team’s strategy began with two complementary bio-based epoxides. The first was epoxidized linseed oil, a triglyceride derived from flax seeds whose long, flexible fatty acid chains are prized for imparting elasticity. The second was Cardolite NC514S, a cardanol-based epoxy derived from cashew nut shell liquid, an agricultural byproduct rich in phenolic lipids. Cardanol brings a rigid aromatic structure and a long C15 alkyl side chain, a combination that can simultaneously stiffen a network and provide hydrophobic character. By converting both epoxides into cyclic carbonates and then blending them in varying ratios, the researchers created a tunable platform in which flexibility and rigidity could be dialled in at will.

The conversion of epoxide to cyclic carbonate is where the carbon dioxide enters the story. The researchers bubbled CO2 through the epoxidized oils in the presence of tetrabutylammonium bromide, a quaternary ammonium salt that catalyzes the insertion of carbon dioxide into the strained epoxide rings. Each epoxide ring thus becomes a five-membered cyclic carbonate, chemically locking atmospheric carbon into the monomer itself. This CO2 fixation step, performed catalytically and without solvents, transforms a greenhouse gas into a structural building block, a strategy that aligns with the broader push toward carbon capture and utilization across the chemical industry.

With the cyclic carbonates in hand, the team carried out a solvent-free polyaddition with Priamine 1071, a renewable diamine derived from dimerized fatty acids. The amine groups ring-open the carbonate rings, forming urethane linkages and generating secondary hydroxyls that hydrogen-bond throughout the growing network. Because both the carbonate monomers and the diamine hardener are bio-based, the resulting thermoset coatings are fully renewable in origin. The crosslinking reaction proceeds without added catalysts or volatile solvents, an important consideration for coatings manufacturers seeking to reduce volatile organic compound emissions and simplify regulatory compliance.

To verify that the networks had formed properly, the researchers measured gel content, the fraction of the material insoluble in a good solvent, which serves as a proxy for crosslink density. The hybrid coatings achieved gel fractions of 83 to 85 percent, remarkably consistent across the range of linseed-to-cardanol ratios tested. This indicated that well-developed three-dimensional networks formed regardless of formulation, giving manufacturers a wide processing window. The consistency suggests that the two carbonated monomers, despite their very different architectures, participate cooperatively in the amine-carbonate reaction rather than one dominating the cure chemistry.

Thermal analysis told an encouraging story about durability. Thermogravimetric experiments showed a single-step degradation profile between 300 and 500 degrees Celsius, with degradation onset and mid-point temperatures spanning 270 to 455 degrees Celsius depending on composition. For coatings that must survive baking ovens, sunlight, and abrasive service, this level of thermal robustness is competitive with petrochemical benchmarks. The char yields were low, between 0.22 and 0.31 percent, which the authors attributed to residual inorganic components from the catalyst rather than to the polymer itself. Differential scanning calorimetry revealed glass transition temperatures rising from minus 17.2 to minus 11.2 degrees Celsius as the cardanol content increased, confirming that the aromatic cardanol segments stiffen the network even in these elastomeric formulations.

Mechanical testing showed the trade-offs the formulation ratio makes possible. As the cardanol-derived carbonate fraction grew, the elastic modulus climbed from 0.26 to 0.39 megapascals and yield strength rose from 0.31 to 0.42 megapascals, while toughness improved from 24.6 to 29.3 joules. Elongation at break decreased moderately, as expected when rigid aromatic units replace flexible fatty acid chains. In practical terms, the linseed-rich formulations behave as soft, extensible films suited to substrates that flex, while cardanol-rich versions deliver harder, stronger, and tougher coatings for demanding protective applications. The ability to engineer this spectrum from just two renewable monomers is precisely what industrial formulators need.

Surface performance, the ultimate test for any coating, proved equally compelling. Water contact angles between 72 and 88 degrees indicated moderately hydrophilic surfaces, while gloss values exceeding 100 gloss units signaled the smooth, mirror-like finishes demanded by architectural and consumer products. Hardness and adhesion both improved with cardanol content, and in accelerated salt-spray corrosion testing the cardanol-rich formulations delivered superior protection of the underlying metal. The long alkyl side chains of cardanol likely contribute to this barrier effect, packing densely at the surface and slowing the ingress of chloride-laden water toward the substrate, a mechanism consistent with cardanol’s established reputation in anticorrosive coating research.

The study, partially funded by the Scientific and Technological Research Council of Türkiye under grant number 222O017, with analytical support from Kordsa Teknik Tekstil, arrives at a moment of intense interest in isocyanate-free polyurethanes. Recent literature has explored NIPUs from carbonated soybean oil, lignin, vanillin, tannins, and terpenes, but few reports combine fully bio-based monomers, solvent-free processing, CO2 utilization, and a complete thermo-mechanical and protective characterization in a single coating platform. By demonstrating that a simple two-monomer blend of carbonated linseed oil and carbonated cardanol can span soft to stiff, elastic to corrosion-resistant, the Marmara University team has provided a practical blueprint for greener coatings. If such systems can be scaled from the laboratory bench to industrial application lines, the humble flax seed and the cashew shell, with a helping of recycled carbon dioxide, may soon be protecting bridges, appliances, and vehicles alike.

Subject of Research: Fully bio-based non-isocyanate polyurethane coatings synthesized from carbonated linseed oil and cardanol

Article Title: Sustainable NIPU coatings based on carbonated linseed oil and cardanol: synthesis and thermo-mechanical performance

Article References: Atılal, E., & Apohan, N. K. (2026). Sustainable NIPU coatings based on carbonated linseed oil and cardanol: synthesis and thermo-mechanical performance. Polymer Bulletin, 83(12), Article 670. https://doi.org/10.1007/s00289-026-06715-9

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06715-9

Keywords: non-isocyanate polyurethane, NIPU, linseed oil, cardanol, cyclic carbonates, CO2 utilization, bio-based polymers, protective coatings, corrosion resistance, thermal stability, green chemistry, solvent-free synthesis