Polyurethane-based Coatings Research Articles

Scalable, Controlled Bimodal Pore-Structured Polymer Coating for Efficient Passive Daytime Radiative Cooling.

Outdoor thermal irritation poses a serious threat to public health, with the frequent occurrence of increasingly intense heat waves. With the global goal of carbon peaking and carbon neutrality, there is an urgent need for a strategy that is efficient and can provide localized outdoor cooling without an intensive energy input. This paper demonstrated a rapidly formable polyurethane-based coating with controlled bimodal spherical micropores. Nano-Al2O3 particles (300 nm) embedded in the polymer were used for targeted enhancement of reflectance at 0.38-0.5 wavelengths. The enhanced film reflected 93% solar irradiance and selectively transmitted 95% thermal radiation (8-13 μm), enabling rapid cooling and the creation of a comfortable thermal microclimate to avoid overheating of 6-11 °C during daytime conditions. The ultrawide material compatibility and excellent adaptive mechanical strength of polyurethane-based coatings are expected to benefit the sustainable development of society in a wide range of fields, from health to economics.

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.

TiO2-Mesoporous Ceria Carrier Modified with Sodium Benzoate: An Innovative Polyurethane Matrix for Enhanced Corrosion Protection of steel

An advanced corrosion protection system, distinguished by multilevel corrosion inhibition, was developed by integrating modified hybrid carriers strategically reinforced within a polyurethane (PU) matrix. For this purpose, mesoporous ceria (mCeO2) was synthesized via a hydrothermal hydrolysis process and incorporated with titanium butoxide to synthesize a hybrid core-shell titania mesoporous ceria (TiO2/mCeO2) carrier system. The TiO2/mCeO2 carrier system was modified with sodium benzoate (SB used as a corrosion inhibitor) to develop a modified TiO2/mCeO2-SB system. The synthesized modified particles were then reinforced into the polyurethane-based matrix to study the corrosion inhibition performance. Benefitting the corrosion-inhibiting properties of modified polyurethane-based coatings, the reinforcement of these modified TiO2/mCeO2 particles resulted in a notably improved anti-corrosion performance in the coating after immersion in 3.5 wt. % NaCl solution for four weeks, the impedance was estimated to be 96.65 GΩ.cm2, which is nearly four orders of magnitude than that of blank PU coatings. This is attributed to the synergistic anti-corrosion performance of TiO2 and SB. The protective layer formed due to the interaction of titania and hydroxyl ions resulted in the formation of Ti(OH)4 and SB absorbed on the steel surface, making iron unavailable for further electrochemical reaction. This work reports on the strategy to build a corrosion inhibition coating system, which introduces a new perspective for extending the lifespan of metals.

Effect of bridged DOPO/polyurethane nanocomposites on solar absorber coatings with reduced flammability

In households, considerable costs are related to energy losses, which are a consequence of maintaining comfortable living temperatures. Improved isolation and utilization of energy harvesting devices is the key to reducing energy losses and the related costs. Polymeric solar absorbers are cost-effective solar energy harvesters that can significantly reduce the energy cost for individual households. One of the concerns related to polymers is their flammability. To mitigate the flammability risk, the present work explores the development of solar absorber paints with flame-retardant properties. Bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivatives (NED and PHED) in concertation ranges of 10–15 wt% were used in a polyurethane-based matrix to demonstrate the effect of additives on the fire retardancy of the material. Additionally, the rheological and thermal properties of the composite materials were evaluated and described. Furthermore, aluminium and PPS (polyethylene sulphide) substrates were coated with solar absorber paint based on a 15% FR (fire retardant) additive formulation, for which the thermal stability at 150 °C for 655 h was evaluated. It was discovered that PHED is more compatible with the polyurethane matrix than NED, and as expected, a greater amount of FR additives resulted in improved flame retardancy. The long-term stability of absorber paint coatings on Al and PPS was also successfully confirmed by confirming stable solar absorptance and thermal emittance. In future prospects, we believe that the flame retardancy of polyurethane-based coatings could be further improved, and the utilization of covalently bonded FRs should also be considered.

A Wind Tunnel Experimental Study of Icing on NACA0012 Aircraft Airfoil with Silicon Compounds Modified Polyurethane Coatings.

Ice formation on the aerodynamic surfaces of an aircraft is regarded as a major problem in the aerospace industry. Ice accumulation may damage parts, sensors and controllers and alter the aerodynamics of the airplane, leading to a range of undesired consequences, including flight delays, emergency landings, damaged parts and increased energy consumption. There are various approaches to reducing ice accretion, one of them being the application of icephobic coatings. In this work, commercially available polyurethane-based coatings were modified and deposited on NACA 0012 aircraft airfoils. A hybrid modification of polyurethane (PUR) topcoats was adopted by the addition of nanosilica and three-functional spherosilicates (a variety of silsesqioxane compound), which owe their unique properties to the presence of three different groups. The ice accretion on the manufactured nanocomposites was determined in an icing wind tunnel. The tests were performed under three different icing conditions: glaze ice, rime ice and mixed ice. Furthermore, the surface topography and wetting behavior (static contact angle and contact angle hysteresis) were investigated. It was found that the anti-icing properties of polyurethane nanocomposite coatings strongly depend on the icing conditions under which they are tested. Moreover, the addition of nanosilica and spherosilicates enabled the reduction of accreted ice by 65% in comparison to the neat topcoat.

Adhesion of functional layers based on epoxy and polyurethane resins for aluminum substrate

The paper concerns pull-off strength test results of epoxy- and polyurethane-based coatings with three different powder fillers (carbonyl iron, ferrites, and graphite flakes). Polymer coatings were applied on an aluminum substrate that was degreased and/or pre-treated by means of abrasive blasting using electrocorundum. The roughness profile and the basic roughness parameters were determined, and the results showed a decisive effect of substrate preparation on the coating's adhesion. The highest values of pull-off strength were obtained from epoxy (3.88 MPa) and polyurethane (3.12 MPa) coatings containing MG192 graphite flakes. During the pull-off tests a cohesive detachment mechanism was observed only between the mentioned coatings and the substrate.

Polyurethane-Based Coatings with Promising Antibacterial Properties

In coatings technology, the possibility of introducing specific characteristics at the surface level allows for the manufacture of medical devices with efficient and prolonged antibacterial properties. This efficiency is often achieved by the use of a small amount of antibacterial molecules, which can fulfil their duty while limiting eventual releasing problems. The object of this work was the preparation and characterization of silver, titanium dioxide and chitosan polyurethane-based coatings. Coatings with the three antibacterials were prepared using different deposition techniques, using a brush or a bar coater automatic film applicator, and compared to solvent casted films prepared with the same components. For silver containing materials, an innovative strategy contemplating the use and preparation of silver nanoparticles in a single step-method was employed. This preparation was obtained starting from a silver precursor and using a single compound as the reducing agent and stabilizer. Ultraviolet-visible spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, contact angle measurements and adhesion test experiments were used to characterize the prepared coatings. Promising antibacterial properties, measured via direct and indirect methods, were registered for all the silver-based materials.

Mathematical modelling of sound transmission loss performances of different coloured surfaces coated with polyurethane-based paint

ABSTRACT The aim of this study is to investigate the effect of morphologies and the structure of polyurethane-based coatings created by different colour pigments, on sound transmission loss properties. To achieve this goal, coatings were created in different concentrations of 5%, 7% and 9% with red, green, orange and yellow pigments. The coatings were applied on glass surfaces and the sound transmission loss was measured by an experimental arrangement containing a microphone and a decibel meter. The effect of surface tension energy, surface roughness, reflection percentages and concentration of pigments were found to be negligible on the sound transmission loss, whereas the LAB colour codes have a determining effect. In the scope of this study, a new method and mathematical model were created to help measure the sound transmission loss on a surface, in which sound signal was carried with a laser beam via a system created in the laboratory.

Studies on Greener Anticorrosive Coating to Steel Rebars with Waterborne Polyurethane Binders

Corrosion of steel in concrete is a natural phenomenon causing severe distress to structures situated in areas with high humidity, sea coasts, high salinity, etc. This menace can destroy even the strongest buildings, bridges, ports, dams, plants, runways, etc. Various surface coatings are in practice for protecting the steel reinforcing bars from corrosion. However, the available coatings are solvent based and hence toxic and pollute the atmosphere. This paper deals with the formulation of suitable greener protective anticorrosive coating to steel rebars in order to enhance the corrosion resistance and protect the rebars. Fifteen polyurethane-based coatings with suitable functional pigments, fillers, corrosion inhibitor and hiding agent (titanium dioxide) were developed and their properties on resistance to corrosion were studied and the results are presented.

Enhancing the adhesion strength of polyurethane coatings by dispersing layered silicates via sonication and high-shear mixing method

Low adhesion strength of polyurethane coating to a steel substrate is often attributed to poor steel preparation. However, the ratio of diisocyanate/polyol and dispersion of fillers within a polyurethane coating matrix influence the adhesion strength, optical and corrosion resistance properties. Poor dispersion of nano-fillers in a polymer coating matrix can lead to low adhesion strength, because close packing of nanoparticles often hides the hydroxyl groups required to form polar–polar bonds with the steel surface. This study combines sonication and high-shear mixing methods with shorter mixing times to prepare polyurethane nanocomposite coatings with various clay concentrations while keeping the ratio of diisocyanate/polyol constant. Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and X-ray diffraction, thermogravimetric analysis and pull-off are used to characterize polyurethane nanocomposite coatings. FTIR results confirm that sonication and high-shear mixing successfully prepare polyurethane-based coatings. TEM shows uniformly dispersed clay particles in polyurethane matrices. The adhesion strength improved on addition of 1–5 wt% C30B organoclay, with the highest improvement (34.4%) at 3 wt% loading. The corrosion resistance of polyurethane coatings was improved by the incorporation of organoclays into their matrices. Onset degradation temperature is also delayed by 4.1–8.5% as the clay concentration increased from 1 to 5 wt%.

Highly wear-resistant UV-curing antibacterial coatings via nanoparticle self-migration to the top surface

It is highly desirable that surface coatings such as kitchen furniture coatings, hospital wall, furniture coatings and many other coatings used in public areas possess antibacterial properties. Although many antibacterial coatings have already been developed and are now commercially available for some time, effective antibacterial properties often require the addition of antibacterial agents in large amount which deteriorate the mechanical properties of the coatings and hence limit their wide-spread uses. Herein we show the fabrication of a robust and wear-resistant polyurethane-based coatings via addition of fluoro-containing quaternary ammonium compounds (QACF) modified silica nanoparticles. The nanoparticles are obtained from a classical Stöber process with a thin layer of thiol groups on the particle surface and the QACF is then further linked to particle surface through double bond and thiol group reaction. QACF and its modified silica nanoparticles both show high levels of antibacterial properties toward Gram positive and Gram negative bacteria. Addition of the nanoparticles in as less as 10 wt% in the formulation recipe would be enough to produce an antibacterial coating with excellent anti-wear resistance due to the self-migration of the modified silica nanoparticles to the surface layer of the coating. We have used XPS and confocal microscopy to show the particle migration to the top of the coatings enables us to clarify the mechanism. Compared to coatings with added pure antibacterial reagents, our coating shows enhanced anti-wear property at relatively low particle additions.

Improved adhesion of polyurethane-based coatings to tin surface

Polyurethane (PU)—based conformal coatings which protect electronic components and boards from harsh environmental exposures were further developed to mitigate the tin (Sn) whisker growth in lead (Pb)—free electronics. As a means of achieving this goal, the adhesion mechanics of PU-based conformal coating on tin surfaces was investigated. We attempted to improve the interfacial adhesion between PU-based conformal coatings and tin (Sn) as it slows down the formation of tin whisker growth. A multi-layer sandwiched specimen made between two Si beams was employed to create an interface between PU coating and Sn for four-point bending testing (4PBT). The result shows that PU has strong adhesion to Sn while polyurethane acrylate (PUA) has much weaker adhesion to Sn. The PUA adhesion, however, increased by introducing a silane agent ((3-Aminopropyl)triethoxysilane) on the tin surface, which is covalently bonded to PUA. The adhesion improvement of a modified tin surface was also confirmed by a simple cross-cut tape peeling test. Post fracture analysis suggested that blocking the reaction between bare Sn surface and the acrylate component contribute to improved adhesion.

The biodegradation of polyester and polyester polyurethane coatings using Papiliotrema laurentii

The rate and severity of polyurethane (PU) coating degradation is due to a combination of both abiotic and biotic factors. The contribution of biotic factors to the degradation process has not been fully realized, in part, because it is assumed that microorganisms cannot survive exclusively on polyurethane-based coatings. We isolated a strain of Papiliotrema laurentii that, as a biofilm, is capable of degrading a polyester-based polyurethane coating. The biodegradation potential of this strain was screened initially with Impranil®-DLN and then against biodegradable polyesters (polyethylene succinate and polyethylene adipate) and a thermoset polyester polyether polyurethane, Irogran®, with no additional carbon sources over 8 days at a relative humidity of >95%. We confirmed that P. laurentii preferentially hydrolyzed both polyesters coatings and the polyester segment of Irogran® coatings using optical and infrared microscopy techniques. The chemical and metabolic differences observed during the degradation of PES coatings compared to PEA and Irogran® coatings indicate that growth was not required for these coatings to be degraded. This strain of P. laurentii can both hydrolyze and metabolize polyester-based coatings under high humidity over 8 days. These microscopic and analytical data revealed how biodegradation was potentially linked to survival using this fungus isolated from the environment.

Impedance sensor for the early failure diagnosis of organic coatings

A miniature impedance sensor used for field diagnosis of the early failure of coatings has been developed based on microelectronics and electrochemical impedance spectroscopy (EIS). The aging process of polyurethane-based coatings in salt spray test chamber was studied using the impedance sensor. Several critical indexes related to EIS such as phase angle (θ10Hz, θ15kHz), breakpoint frequency (fb), specific capacitance (C10Hz, C15kHz), and impedance modulus (Z0.1Hz) were proposed to evaluate the severity of coating degradation. The results indicated that the impedance sensor could accurately monitor the degradation process of coatings, and once Z0.1Hz 100 Hz, or θ10Hz < 20°, the coating may be regarded as completely degraded and fails to protect the metal substrate.

Carbon black instead of multiwall carbon nanotubes for achieving comparable high electrical conductivities in polyurethane-based coatings

In this work, we present a simple, reproducible and efficient method for the preparation of uniform and compact highly conductive coatings obtained from surfactant-free water-based mixtures of micro-beads made of cross-linked polyurethane (PU) with either carbon black (CB) or multiwall carbon nanotubes (MWNTs). Low percolation thresholds, 2.9wt.% with CB and 0.8wt.% with MWNTs, and high saturated conductivities, 200S/cm for PU/CB and 500S/cm for PU/MWNT, were achieved. This finding shows that, firstly, highly conductive carbon-based nanocomposite coatings can be made in water without surfactants using N-methylpyrrolidinone (NMP) as dispersing aid, and, secondly, carbon black can be used in place of multiwall carbon nanotubes for making cheaper coatings without sacrificing the electrical performance.

Development of Novel Corrosion Techniques for a Green Environment

The synergistic effect of air pollution, brown clouds and greenhouse gasses is deleterious to human health and industrial products. The use of toxic inhibitors, chemicals in water treatment plants, and anti-fouling agents in desalination plants has contributed to the greenhouse effect. Conventional anti-corrosion techniques such as paints, coatings, inhibitor treatments, and cathodic protection paid no regard to greenhouse effect. Work on eco-friendly anti-corrosion techniques is scanty and largely proprietary. The use of nano-TiO2particles introduced in alkyds and polyurethane-based coatings showed a higher corrosion resistance compared to conventional TiO2coatings with significant photocatalytic activity to kill bacteria. The use of UV radiations for photo-inhibition of stainless steel in chloride solution can replace toxic inhibitors. Corrosion inhibition has also been achieved by using natural materials such as polymers instead of toxic chemical inhibitors, without adverse environmental impact. TiO2films exposed to UV radiation have shown the capability to protect the steel without sacrificing the film. Self-healing materials with encapsulated nanoparticles in paints and coatings have shown to heal the defects caused by corrosion. These innovative techniques provide a direction to the corrosion scientists, engineers, and environmentalists who are concerned about the increasing contamination of the planet and maintaining a green environment.

Effects of ZnO nanoparticles on the mechanical and antibacterial properties of polyurethane coatings

Polyurethane-based coatings reinforced by ZnO nanoparticles (about 27 nm) were prepared via solution blending. The ZnO/PU films and coats were fabricated by a simple method of solution casting and evaporation. The mechanical properties of the films were investigated by a universal material test, and the abrasion resistance of the prepared coats was evaluated by a pencil-abrasion-resistance tester. It was found that significant improvement of the PU films in Young’s modulus and tensile strength was achieved by incorporating ZnO nanoparticles up to 2.0 wt%, and that the abrasion resistance of the PU coats was greatly enhanced due to the addition of ZnO nanoparticles. Moreover, the antibacterial property test was carried out via the agar dilution method and the result indicated that PU films doped with ZnO nanoparticles showed excellent antibacterial activity, especially for Escherichia coli.

Surface rearrangement of tailored polyurethane-based coatings

Polyurethane coatings with different network composition were prepared from an oligomeri diol, a diisocyanate, and a low molecular weight triol. The glass transition temperature of the network was tuned by the ratio of diol and triol and the composition (aromatic or aliphatic) of the diisocyanate. All coatings were studied for their bulk properties as well as their surface properties. It was found that by the addition of a fluorinated additive the surface free energy of the coating was lowered by approximately 15 mN·m−1, leaving the bulk properties intact. It was also shown that these polyurethane coatings are able to adapt their surface free energy in a reversible manner when exposed to water. The magnitude and rate of surface rearrangement is strongly dependent on the network density of the coating.

Performance of polyurethane-coated concrete in sewer environment

Polyurethane-based coatings are used to protect concrete facilities against corrosive environments. The performances of two commercially available polyurethane coatings were evaluated under sulfuric acid environment (representing sewer condition) for over 5 years. Both dry (representing new construction) and wet (representing rehabilitation) concretes were used in this study. A combination of the full-scale hydrostatic test, bonding test, and chemical resistance tests were performed to evaluate the coatings to protect concrete structures below ground water. The full-scale hydrostatic test was used to evaluate the application and performance of coatings under hydrostatic pressure to simulate underground concrete structures below ground water. Visual inspections and in situ bonding tests were performed on coated concrete under a hydrostatic pressure of 105 kPa. Test results showed that bonding strength of one coating was affected by the moisture condition and hydrostatic water pressure in the full-scale test. Coated cement concrete specimens with pinholes were used to study the chemical resistance of the coated concrete in sulfuric acid to represent the worst sewer condition. Change in weight of coated concrete specimens was measured at regular intervals. Types of failures in coated concrete under acidic environment have been identified. Test results showed that the performance of the two coatings were noticeably different and one coating with pinholes extended the service life of concrete by 14 times while the other coating extended the service life of concrete by 57 times. There was no direct correlation between bonding strength and chemical resistance of the polyurethane-coated concrete. Although both coatings were polyurethane-based, their performances were different under the testing conditions adopted in the study.