Colored Radiative Cooling and Flame-Retardant Polyurethane-Based Coatings: Selective Absorption/Reflection in Solar Waveband.

The aesthetic demand has become an imperative challenge to advance the practical and commercial application of daytime radiative cooling technology toward mitigating climate change. Meanwhile, the application of radiative cooling materials usually focuses on the building surface, related tightly to fire safety. Herein, the absorption and reflection spectra of organic and inorganic colorants are first compared in solar waveband, finding that iron oxides have higher reflectivity in NIR region. Second, three kinds of iron oxides-based colorants are selected to combine porous structure and silicon-modified ammonium polyphosphate (Si-APP) to engineer colored polyurethane-based (PU) coating, thus enhancing the reflectivity and flame retardancy. Together with reflectivity of more than 90% in near-infrared waveband and infrared emissivity of ≈91%, average temperature drops of ≈5.7, ≈7.9, and ≈3.8 °C are achieved in porous PU/Fe2O3/Si-APP, porous PU/Fe2O3·H2O/Si-APP, and porous PU/Fe3O4·H2O/Si-APP, compared with dense control samples. The catalysis effect of iron oxides in the cross-linking reaction of pyrolysis products and dehydration mechanism of Si-APP enable PU coating to produce an intumescent and protective char residue. Consequently, PU composite coatings demonstrate desirable fire safety. The ingenious choice of colorants effectively minimizes the solar heating effect and trades off the daytime radiative cooling and aesthetic appearance requirement.

Water-Triggered Segment Orientation of Long-Lasting Anti-Biofouling Polyurethane Coatings on Biomedical Catheters via Solvent Exchange Strategy.

The formation of biofilm and thrombus on medical catheters poses a significant life-threatening concern. Hydrophilic anti-biofouling coatings upon catheter surfaces with complex shapes and narrow lumens are demonstrated to have the potential in reducing complications. However, their effectiveness is constrained by poor mechanical stability and weak substrate adhesion. Herein, a novel zwitterionic polyurethane (SUPU) with strong mechanical stability and long-term anti-biofouling is developed by controlling the ratio of sulfobetaine-diol and ureido-pyrimidinone. Once immersed in water, as-synthesized zwitterionic coating (SUPU3 SE) would undergo a water-driven segment reorientation to obtain much higher durability than its direct drying one, even under various extreme treatments, including acidic solution, abrasion, ultrasonication, flushing, and shearing, in PBS at 37 °C for 14 days. Moreover, SUPU3 SE coating could achieve a 97.1% of exceptional reducing protein fouling, complete prevention of cell adhesion, and long-lasting anti-biofilm performance even after 30 days. Finally, the good anti-thrombogenic formations of SUPU3 SE coating with bacterial treatment are validated in blood circulation through an ex vivo rabbit arteriovenous shunt model. This work provides a facile approach to fabricating stable hydrophilic coating through a simple solvent exchange to reduce thrombosis and infection of biomedical catheters.

[Endoscopic treatment of gastroduodenal perforations]. / Endoskopicheskoe lechenie gastroduodenal'nykh perforatsii.

A 93-year-old patient underwent endoscopic treatment of perforated duodenal ulcer after previous laparoscopic suturing complicated by failure of sutured defect. A self-expanding nitinol stent with partial polyurethane coating was used. Positive effect of the treatment was noted. Further study of this method and its clinical introduction in case of favorable results can significantly reduce the incidence of complications and mortality in patients with perforated gastroduodenal ulcers.

Acylase-containing polyurethane coatings with anti-biofilm activity.

Due to the prevalence of biofilm-related infections, which are mediated by bacterial quorum sensing, there is a critical need for materials and coatings that resist biofilm formation. We have developed novel anti-biofilm coatings that disrupt quorum sensing in surface-associated bacteria via the immobilization of acylase in polyurethane films. Specifically, acylase from Aspergillus melleus was covalently immobilized in biomedical grade polyurethane coatings via multipoint covalent immobilization. Coatings containing acylase were enzymatically active and catalyzed the hydrolysis of the quorum sensing (QS) molecules N-butyryl-L-homoserine lactone (C4-LHL), N-hexanoyl-L-homoserine lactone (C6-LHL), and N-(3-oxododecanoyl)-L-homoserine lactone (3-oxo-C12-LHL). In biofilm inhibition assays, immobilization of acylase led to an approximately 60% reduction in biofilm formation by Pseudomonas aeruginosa ATCC 10145 and PAO1. Inhibition of biofilm formation was consistent with a reduction in the secretion of pyocyanin, indicating the disruption of quorum sensing as the mechanism of the coating activity. Scanning electron microscopy further showed that acylase-containing coatings contained far fewer bacterial cells than control coatings that lacked acylase. Moreover, acylase-containing coatings retained 90% activity when stored dry at 37°C for 7 days and were more stable than the free enzyme in physiological conditions, including artificial urine. Ultimately, such coatings hold considerable promise for the clinical management of catheter-related infections as well as the prevention of infections in orthopedic applications (i.e., on hip and knee prostheses) and on contact lenses. Biotechnol. Bioeng. 2016;113: 2535-2543. © 2016 Wiley Periodicals, Inc.

Insight into Degrading Effects of Two Fungi on Polyurethane Coating Failure in a Simulated Atmospheric Environment.

Two different fungi, Talaromyces funiculosus (T. funiculosus) and Phanerochaete chrysosporium (P. chrysosporium), were collected from the Xishuangbanna atmospheric corrosion site and incubated on a polyurethane (PU) coating at 30 °C for two weeks under 95% relative humidity (RH). The biodegrading effects of these fungi on the coating failure were investigated from aspects of metabolism and electrochemistry. The results showed that T. funiculosus contributed more to the degradation of the PU coating failure than P. chrysosporium, and two factors played dominant roles. First, the weight of the T. funiculosus mycelium was nearly 3 times more than that of P. chrysosporium, indicating there was more substrate mycelium of T. funiculosus deep into the coatings to get more nutrition in atmospheric during colonization. Second, T. funiculosus secreted carboxylic acids, such as citric, propanoic, succinic, and tartaric acids, and accelerated the hydrolysis of the ester and urethane bonds in the PU coatings. As a result, the mycelium of T. funiculosus readily penetrated the interface of the coating and substrate resulting in a rapid proliferation. Thus, the |Z|0.01Hz value of the coating decreased to 5.1 × 104 Ω·cm2 after 14 days of colonization by T. funiculosus while the value remained at 7.2 × 107 Ω·cm2 after colonization by P. chrysosporium. These insights suggest that the biodegradation process in simulated atmospheric environments would provide theoretical guidance and directions for the design of antifungal PU coatings.

Investigating Different Local Polyurethane Coatings Degradation Effects and Corrosion Behaivors by Talaromyces funiculosus via Wire Beam Electrodes.

The degradation effect of mold on the coating in a hot and humid environment is one of the important factors that cause layer failure. Combined with the wire beam electrode (WBE) and the traditional surface analysis technique, the local biodegradation of the coatings and the corrosion behaviors of metal substrates can be characterized accurately by a WBE. Herein, a WBE was used to study the degradation impact of Talaromyces funiculosus (T. funiculosus) isolated from a tropical rainforest environment on the corrosion of polyurethane (PU) coating. After immersion for 14 days, the local current density distribution of the WBE surface can reach ~10-3 A/cm2 in the fungal liquid mediums but maintains ~10-7 A/cm2 in sterile liquid mediums. The |Z|0.01Hz value of the high current densities area (#85 electrode) was 1.06 × 109 Ω cm2 in a fungal liquid medium after 14 days of immersion. After being attacked by T. funiculosus, the degradation of the PU was more severe, and there were wrinkles, cracks, blisters, and even micro-holes distributed randomly on the surface of electrodes. This resulted from the self-corrosion caused by the T. funiculosus degradation of the coating; the corrosion caused by the electric coupling effect of the coating was introduced. Energy dispersive spectroscopy (EDS) and Raman spectra results showed that the corrosion products were flakey and globular, which consisted of γ-FeOOH, γ-Fe2O3, and α-FeOOH.

Siloxane-Modified UV-Curable Castor-Oil-Based Waterborne Polyurethane Superhydrophobic Coatings.

In recent years, superhydrophobic coatings with self-cleaning abilities have attracted considerable attention. In this study, we introduced hydroxyl-terminated polydimethylsiloxane (OH-PDMS) into castor-oil-based waterborne polyurethanes and synthesized silicone-modified castor-oil-based UV-curable waterborne polyurethanes (SCWPU). Further, we identified the optimal amount of OH-PDMS to be added and introduced different amounts of micro- and nanoscale heptadecafluorodecyltrimethoxysilane-modified SiO2 particles (FAS-SiO2) to prepare rough-surface SCWPU coatings with dense micro- and nanostructures, thus realizing waterborne superhydrophobic coatings. The results show that when the OH-PDMS content was 11 wt% and the total addition of FAS-SiO2 particles was 50% (with a 1:1:1 ratio of 100 nm, 1 µm, and 10 nm particles), the coatings exhibited a self-cleaning ability and superhydrophobicity with a contact angle of (152.36 ± 2.29)° and a roll-off angle of (4.9 ± 1.0)°. This castor-oil-based waterborne superhydrophobic coating has great potential for waterproofing, anti-fouling, anti-corrosion, and other applications.

Mussel-inspired polyurethane coating for bio-surface functionalization to enhance substrate adhesion and cell biocompatibility.

Considerable implant materials are prone to cause a severe inflammatory reaction due to poor histocompatibility, which leads to various complications and implant failure. Surface coating modification of these implant materials is one of the most important techniques to settle this problem. However, fabricating a coating with both adequate adhesiveness and excellent biocompatibility remains a challenge. Inspired by the adhesion mechanism of mussels, a series of mussel-inspired polyurethanes (PU-LDAs) were synthysized through a step growth polymerization based on hexamethylene diisocyanate as a hard segment, polytetra-methylene-ether-glycol as a soft segment, lysine-dopamine (LDA) and butanediol as chain extenders with different mole ratios.The coatings of PU-LDAs were applied to various substrates, such as stainless steel, glass and PP using a facile one-step coating process. The introduction of 3,4-dihydroxyphenylalanine (DOPA) groups can greatly improve the adhesion ability of the coatings to the substrates demonstrated by a 180° peel test. The peel strength of the PU-LDA100 coating containing high LDA content was 76.3, 48.5 and 67.5 N/m, which was 106.2%, 246.4% and 192.2% higher than that of the PU-LDA00 coating without LDA on the surface of stainless steel, glass and PP, respectively. Meanwhile, this PU coating has a lower immune inflammatory response which provides a universal method for surface modification of implant materials. Moreover, the DOPA groups in PU-LDAs could combine with the amino and thiol groups on cell membrane surface, leading to the improvement of cell adhesion and growth. Therefore, it has great potential application in the field of biomedical implant materials for the clinic.

A Study on the Preparation and Cavitation Erosion Mechanism of Polyether Polyurethane Coating.

Polyurethane elastomers are anticipated to be applied in the field of cavitation erosion (CE) resistance, but their protection and damage mechanisms are not clear, which greatly restricts their further development. In this article, five polyether polyurethanes (PUx) with different crosslinking densities were prepared. Their mechanical properties, thermal properties, water absorption, surface morphology and chemical structure before and after CE tests were compared with ESEM, OM, TG-DSC, FTIR and XPS in detail. The results showed that with an increase in crosslinking density, the tensile strength of PUx increased first and then decreased, elongation at break and water absorption reduced gradually and thermal decomposition temperature and adhesion strength increased steadily. During the CE process, cavitation load aggravated the degree of microphase separation and made brittle hard segments concentrate on the coating surface; meanwhile, cavitation heat accelerated hydrolysis, pyrolysis, oxidation and the fracture of molecular chains. As a result, the mechano-thermal coupling intensified the formation and propagation of fatigue cracks, which should be the fundamental reason for the CE damage of polyurethane elastomer. PU0.4 exhibited the best CE resistance among the five coatings thanks to its good comprehensive properties and may find potential applications on the surface of hydraulic components.

Bio-polyols based waterborne polyurethane coatings reinforced with chitosan-modified ZnO nanoparticles.

The development of environmentally friendly waterborne polyurethane (WPU) coatings from bio-based polyols has received much attention due to increasing environmental concern and the depletion of petroleum resources. In this study, the WPU coatings derived from castor oil and soy polyol were modified by chain extender [bis(2-hydroxyethyl)amino]-methyl-phosphonic acid dimethyl ester. The effect of chitosan-modified ZnO (CS-ZnO) nanoparticles content on the properties of WPU/CS-ZnO coatings and their films were systematically investigated. The results indicated that WPU/CS-ZnO coatings displayed excellent storage stability and the particle sizes firstly decreased and then increased with CS-ZnO loading. CS-ZnO could improve tensile strength and Young's modulus but reduce the optical transparency of WPU/CS-ZnO films. CS-ZnO has a prominent reinforcement effect on the WPU/CS-ZnO matrix. With the addition of 2 wt% CS-ZnO, the tensile strength and Young's modulus of the WPU/CS-ZnO2 film reached 13.4 and 112.1 MPa, 1.68 and 2.6 times over neat WPU film, respectively. TGA results showed that the thermal stability of WPU/CS-ZnO films improved with increased CS-ZnO content. Furthermore, the WPU/CS-ZnO films' wettability decreased with the introduction of CS-ZnO. This work provides a simple and efficient strategy for preparing environmentally friendly bio-based WPU coatings, which are promising for application in the surface coating industry.

Designing Smart Microcapsules with Natural Polyelectrolytes to Improve Self-Healing Performance for Water-Based Polyurethane Coatings.

Active anticorrosive organic coatings adopting microcapsules (MCs) have lately attracted extensive attention as they were proven to be effective to minimize metal corrosions and offer a long-lasting protection performance. Herein, a novel environmental-friendly active corrosion protection system was designed for aluminum alloy 2024 (AA2024) based on water-based polyurethane coatings with the addition of water and alkaline pH-responsive smart MCs, which is fabricated by utilizing 2-mercaptobenzothiazole (2-MBT) as an inhibitor, halloysite clay nanotubes (HNTs) as an inhibitor carrier, and the natural polyelectrolytes ε-poly-l-lysine (ε-PLL) and sodium alginate (SA) as layer-by-layer (LBL) encapsulation polyelectrolytes. Salt spray tests and electrochemical measurements prove that the scratched coatings with embedded MCs possess an excellent self-healing performance by forming an adsorption layer of released 2-MBT on the AA2024 surface, thereby providing over 90% inhibition efficiency within 6 days' immersion. The UV-vis spectrophotometer results further showed that the release of 2-MBT is a three-stage long-term process sensitive to water and alkaline pH value, while the outward release rate is both regulated by the solubility of 2-MBT and the SA layer. The fabricated MCs not only offer a great promise to provide an excellent self-healing performance but also shed light on the future design of advanced MCs on demand based on the LBL technique.

Microstructure and Properties of Poly(ethylene glycol)-Segmented Polyurethane Antifouling Coatings after Immersion in Seawater.

Polyurethane has a microphase separation structure, while polyethylene glycol (PEG) can form a hydrated layer to resist protein adsorption. In this paper, PEG was introduced to polyurethane to improve the antifouling properties of the polyurethane, providing a new method and idea for the preparation of new antifouling polyurethane materials. The mechanical properties, hydrophilicity, swelling degree, microphase separation and antifouling performance of the coatings were evaluated. The response characteristics of the polyurethane coatings in a seawater environment were studied, and the performance changes of coatings in seawater were tested. The results showed that the crystallized PEG soft segments increased, promoting microphase separation. The stress at 100% and the elasticity modulus of the polyurethane material also markedly increased, in addition to increases in the swelling degree in seawater, the water contact angle decreased. A total of 25% of PEG incorporated into a soft segment can markedly improve the antibacterial properties of the coatings, but adding more PEG has little significant effect. After immersion in seawater, the coatings became softer and more elastic. This is because water molecules formed hydrogen bonding with the amino NH, which resulted in a weakening effect being exerted on the carbonyl C=O hydrogen bonding and ether oxygen group crystallization.

Evaluation of Disposable Protective Garments against Isocyanate Permeation and Penetration from Polyurethane Anticorrosion Coatings.

BACKGROUND: Polyurethanes are a class of isocyanate-based organic coatings commonly used to control corrosion on high-value metallic structures. Despite their widespread use, dermal exposure to these isocyanate-containing coatings presents a significant occupational health risk to workers, including the development of allergic and irritant contact dermatitis and systemic sensitization. At present, little is known about the effectiveness of the protective garments commonly used to prevent dermal exposure to polyurethane coatings in construction trades. OBJECTIVES: The primary objective of this study was to measure the permeation and penetration of isocyanates from polyurethane anticorrosion coatings though a selection of protective garments. In addition, a standardized spray procedure using a fixed-position spraying technique was evaluated as an option to minimize variability in coating application. METHODS: Five disposable garment materials were evaluated for resistance to isocyanates during this study: latex gloves (0.076 mm), nitrile gloves (0.078 mm), Tyvek coveralls (0.105 mm), polypropylene/polyethylene (PP/PE) coveralls (0.116 mm), and a cotton t-shirt (0.382 mm). A permeation test cell system was used to evaluate each garment material against two products: a polyurethane zinc-rich primer based on 4,4'-methylene diphenyl diisocyanate and an aliphatic finish coating based on prepolymers of 1,6-hexamethylene diisocyanate. Glass fiber filters pretreated with 1-(9-anthracenylmethyl)piperazine were used to collect penetrating isocyanates during the 120-min test period, which were analyzed by liquid chromatography-tandem mass spectrometry. Polytetrafluoroethylene loading filters were sprayed in series with permeation test cells and analyzed gravimetrically to assess the homogeneity of coating application. RESULTS: The latex gloves demonstrated the highest rate of isocyanate permeation of all evaluated garments during testing with both coatings (primer: 27.38 ng cm-2 min-1; finish coating: 7.39 ng cm-2 min-1). Nitrile gloves were much more resistant than latex gloves (primer: 1.89 ng cm-2 min-1; finish coating: 1.26 ng cm-2 min-1) and were not permeated by the finish coating until after 15 min. The PP/PE coverall provided the most consistent resistance to both coatings (primer: 0.08 ng cm-2 min-1; finish coating: 1.27 ng cm-2 min-1), whereas the Tyvek coverall was readily permeated by the primer (primer: 3.47 ng cm-2 min-1; finish coating: 0.87 ng cm-2 min-1). The cotton t-shirt was rapidly permeated by the primer during the first 5 min of exposure (primer: 146.65 ng cm-2 min-1; finish coating: 4.64 ng cm-2 min-1). In addition, the fixed-position spraying technique used during this study demonstrated a significant reduction in loading variability within each batch of test cells when compared to manual spray application. CONCLUSION: Nitrile gloves demonstrated superior resistance to both isocyanate-containing coatings in comparison to latex gloves. Although both coverall materials were resistant to permeating isocyanate within the established thresholds, the PP/PE coverall provided more consistent resistance to both coatings. Owing to the cotton t-shirt's high rate of penetration with both coatings, it is recommended only as a secondary barrier. Study results showed that the use of fixed-position spray techniques provided consistent and reproducible results within each batch of test cells. Additional test design modifications are necessary to further reduce variability between batches and ensure more consistent coating thickness.

Gemcitabine-incorporated polyurethane films for controlled release of an anticancer drug.

BACKGROUND: Local delivery of anti-cancer drugs through a stent is a very promising and anticipated treatment modality for patients who have obstructions in their gastrointestinal tract with malignant tumors. Anticancer drug release via stents, however, needs to be optimized with respect to drug delivery behavior for the stents to be effective for prolonged containment of tumor proliferation and stent re-obstruction. Local stent-based drug delivery has been tested using an effective anti-cancer drug, gemcitabine, but the release from the stent-coated polyurethane films is often too fast and the drug is depleted from the coated film virtually in a day. METHODS: To moderate the drug release from a polyurethane film, a gemcitabine-incorporated polyurethane film was enveloped with a pure polyurethane film, with no drug loading, and with a silicone film by solution casting after activation of the silicone film surface with plasma treatment. RESULTS: The pure polyurethane barrier film was effective; the interface of the two were indistinguishable on scanning electron microscopy, and the initial burst, i.e., the cumulative release in a day, decreased from 90 to 26%. The silicone film barrier, on the other hand, was defective as voids were seen using a scanning electron microscope, and micro-separation of the two layers was observed after the film was immersed in phosphate-buffered saline for 1 day during the in vitro drug release study. CONCLUSIONS: Enveloping a gemcitabine-releasing polyurethane film with a homo-polymer barrier film was quite effective for moderating the initial burst of gemcitabine, thus, prolonging the release time of the drug. Enveloping the polyurethane film with a silicone film was also possible after plasma treatment of the silicone film surface, but the two films eventually separated in the aqueous environment. More studies are needed to tune the drug release behavior of gemcitabine from the stent covering film before attempting a clinical application of an anti-cancer drug releasing stent.

Mechanical Properties of Multi-Walled Carbon Nanotube/Waterborne Polyurethane Conductive Coatings Prepared by Electrostatic Spraying.

Electrostatic spraying (ES) was used to prepare multi-walled carbon nanotube (MWCNT)/waterborne polyurethane (WPU) abrasion-proof, conductive coatings to improve the electrical conductivity and mechanical properties of WPU coatings. The dispersity of MWCNTs and the electrical conductivity, surface hardness, and wear resistance of the coating prepared by ES (ESC) were investigated. The ESC was further compared with coatings prepared by brushing (BrC). The results provide a theoretical basis for the preparation and application of conductive WPU coatings with excellent wear resistance. The dispersity of MWCNTs and the surface hardness and wear resistance of ESC were obviously better than those of BrC. With an increase in the MWCNT content, the surface hardness of both ESC and BrC went up. As the MWCNT content increased, the wear resistance of ESC first increased and then decreased, while the wear resistance of BrC decreased. It was evident that ESC with 0.3 wt% MWCNT was fully capable of conducting electricity, but BrC with 0.3 wt% MWCNT failed to conduct electricity. The best wear resistance was achieved for ESC with 0.3 wt% MWCNT. Its wear rate (1.18 × 10-10 cm3/mm N) and friction coefficient (0.28) were the lowest, which were 50.21% and 20.00% lower, respectively, than those of pure WPU ESC.

TEMPO-oxidized cellulose nanofibers (TOCNs) as a green reinforcement for waterborne polyurethane coating (WPU) on wood.

In this work, TEMPO-oxidized cellulose nanofibers (TOCNs) were investigated as a green additive to the waterborne polyurethane (WPU) based coating, for improving its mechanical properties. The structure, morphology, mechanical properties and performances of the WPU/TOCNs coating were determined. Results showed that TOCNs had good compatibility to the WPU coating, and significantly enhanced the mechanical properties of the coating. The Halpin-Tsai and Ouali models were used to fit for the Young's modulus of the resulting coating, and good agreements were found between the Ouali model and experimental results when the TOCNs content exceeded the critical percolation threshold (0.7vol% or 1.0wt%). It was also found that the pencil hardness of the coating was improved with the addition of TOCNs. However, AFM and pull-off test revealed the negative effects of the TOCNs addition on the surface roughness and adhesion strength of the coating to the wood surface.