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Journal of Coatings Technology and Research

Current research reports and chronological list of recent articles..




The international scientific Journal of Coatings Technology and Research - JCTR - is a forum for the exchange of original research, experience, knowledge and ideas among those with a professional interest in the science, technology and manufacture of functional, protective and decorative coatings including, but not limited to, paints, inks and related coatings and their raw materials.

The publisher is Springer. The copyright and publishing rights of specialized products listed below are in this publishing house. This is also responsible for the content shown.

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Additional research articles see Current Chemistry Research Articles.



Journal of Coatings Technology and Research - Abstracts



Practical adhesion measurements of protective coatings on bronze by three-point bending test

Abstract

When attempting to sufficiently protect outdoor bronze monuments from corrosion, searches for an effective solution are usually based on coating applications which have a high anticorrosive efficiency. In order to correctly assess the level of protection provided by such coatings, adherence (practical adhesion) measurements need to be performed for the proper evaluation of the deterioration of coating systems with aging. Although a coupled study of adherence with aging would be of great interest, very few such studies are available. In this work, a methodological approach is proposed for the evaluation of coatings applied to metallic cultural heritage monuments of, based on the use of a three-point bending test. Adherence characterization of different protective coatings has been performed both on bare and on traditionally black-patinated bronze coupons (Cu–Sn alloy with 5.9 wt% Sn), which were used as basic model substrates. The investigated coatings were Incralac®, silane, sol–gel oxysilane, and a silane-modified polymethacrylate (an adhesion promoter for fluoropolymer). The results of measurements which were obtained before and after accelerated aging in concentrated acid rain made it possible to more easily differentiate between the various adherence levels of different coating systems. Coupled with adherence measurements, the results of systematic optical and SEM observation of the different failure morphologies are also presented. In the case of the coated bare alloy, adhesive failures were mainly observed. The silane (PropS-SH) coating showed the best adherence. In the case of the patinated bronze test specimens, only cohesive failures occurred. Adherence is directly related to the cohesion of the black patina rather than that of the applied coating. It was observed that aging reduces the level of the adherence.


Datum: 25.06.2019


Wet clay adhesion to antistick coatings: effects of binder type and surface roughness

Abstract

The handling of sticky raw material can cause problems during operation of process equipment in the cement production industry. These handling problems are generally observed when raw material (e.g., wet clay) sticks to machine walls and causes blockage of outlets. This leads to frequent production shutdowns and expensive cleaning operations. In this work, the effects of surface material and process parameters on the friction forces between wet clay and surface were investigated. Various surface materials and clay impact speeds were investigated. The results demonstrate that not only the equipment surface material but also the surface roughness influences the observed frictional behavior. The ranking of the materials in terms of effective static friction coefficients fell in two groups with equal performance within the group: (1) Two Teflon-based coatings (Accofal 2G54 and Accolan LB), polished AISI 304 stainless steel, Matrox lining, and a polyurethane-based coating (best performing surfaces), (2) Mild steel, a silicone-based coating, and AISI 304 stainless steel (worst performing surfaces). However, the friction coefficients of the two groups only varied by a factor of two, suggesting that adhesion of wet clay to surfaces is difficult to avoid by the use of coatings.


Datum: 25.06.2019


Preparation and characterization of electrically conductive multiwalled carbon nanotube/polyoxazoline nanocomposite films using spray coating

Abstract

Multiwalled carbon nanotube/poly(2-ethyl-2-oxazoline) (MWCNT/PEtOx) nanocomposites with different MWCNT content were successfully prepared by amidation reaction between amine-terminated PEtOx (PEtOx–NH2) and carboxylic acid-functionalized MWCNTs (MWCNT–COOH). First, the living cationic ring-opening polymerization of 2-ethyl-2-oxazoline was initiated by methyl p-toluenesulfonate and terminated with ammonia to obtain PEtOx–NH2. Then, amidation reaction between amino groups of PEtOx–NH2 and carboxylic acid groups of MWCNT–COOH was carried out to obtain MWCNT/PEtOx nanocomposites. Finally, nanocomposite films were deposited by spray coating on glass substrates. The structural, thermal, morphological, and electrical properties of the nanocomposites and their films were investigated in detail by gel permeation chromatography, nuclear magnetic resonance, Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, field emission scanning electron microscopy, and two-point probe digital multimeter. All nanocomposites showed higher thermal stability than neat polymer, whereas the spray-coated nanocomposite films exhibited well-dispersed morphology and enhanced electrical conductivity with increase in MWCNT content.


Datum: 24.06.2019


A process model for slot coating of narrow stripes

Abstract

Selective deposition of patterned films, without masks or subtractive postprocessing steps, can potentially be achieved by extending the capabilities of traditional slot coating. Realization of a fully additive-only approach of this nature will elevate the viability of slot coating for numerous emerging technologies such as flexible optoelectronic devices, sensors, and wearables. In this study, we develop a process model for slot coating of variable-width narrow stripes, as a fundamental and representative pattern feature for patterned slot coating. Our process model addresses the sensitivity of stripe output to fluid deposition rate, substrate speed, and coating gap for a given coating material. To explain the observed process behavior, we distinguish between separate configurations of contact line pinning of the liquid bridge at the coating tool surface and show experimentally how these configurations relate to regimes in the process model that must be characterized separately. We also demonstrate how the geometry of the liquid bridge and range of intermediate contact angles along its contact line correspond to observed hysteresis of the coated stripe width.


Datum: 24.06.2019


Effect of operating parameters on the structural growth of ZnAl layered double hydroxide on AA6082 and corresponding corrosion resistance properties

Abstract

In this study, a series of ZnAl layered double hydroxide (ZnAl-LDH) thin films were synthesized on an AA6082 alloy by a single-step hydrothermal process at different synthesis parameters, including reaction temperature, reaction time, pH, and the relation between the LDH structural variations, and the corresponding corrosion resistance properties are briefly reported. The as-prepared synthetic coatings were characterized by scanning electron microscopy and X-ray diffraction. The corresponding corrosion properties were evaluated through potentiodynamic polarization curves and through electrochemical impedance spectra. The findings demonstrated that synthesis parameter variations impart an influential effect on the geometry of LDH, film thickness, and structural morphologies which have a significant  impact on LDH corrosion resistance properties. The ZnAl-LDH corrosion resistance was found to increase with respect to extended high temperature and aging time, while the synthetic pH conditions also promoted LDH growth and film thickness, relative to lower-pH reaction conditions. The optimization results are attributed to high ZnAl-LDH corrosion resistance and act as a strong barrier film and ion-exchange surface area. The ZnAl-LDH films at 80°C-18r-6.5pH have shown much lower corrosion current density compared to bare AA6082, and a decrease of up to five orders of magnitude is observed.


Datum: 21.06.2019


Effects of surface modification of cellulose nanocrystals (CNCs) on curing behavior, optical, and thermal properties of soybean oil bio-nanocomposite

Abstract

In this study, UV cured bio-nanocomposite coating systems were developed. An acrylated epoxidized soybean oil (AESO) and cellulose nanocrystals (CNCs) were used to make these coating systems. The CNC surface was modified by two different methods so as to achieve good compatibility between the CNC and AESO. Thermal stability, glass transition temperature, optical clarity (transparency), and curing behavior of the coating systems were assessed. The addition of CNC altered the thermal stability of the bio-nanocomposites slightly. Addition of CNC increased glass transition temperature of AESO. This increase was a function of the CNC surface modification method and CNC loading level. The transparency of the bio-nanocomposites was reduced by the addition of CNC. The curing behavior of these coating systems was not significantly different from that of a pure cured AESO matrix. A study of the morphology of the nanocomposite films by AFM demonstrated that the modified CNC had good compatibility with the AESO matrix.


Datum: 21.06.2019


Synthesis of rubber seed oil waterborne alkyd resin from glucitol

Abstract

Solubility properties of alkyd resins from phthalic and maleic anhydrides, glucitol and rubber seed oil (RSO) as raw materials were examined. Four types of glucitol-based medium oil length alkyd resins (ALKYD A–D, two for each acid anhydride) samples were formulated with phthalic anhydride, maleic anhydride, glucitol aqueous solution, and RSO. The physical, chemical, and film characteristics of the glucitol-modified alkyd resins were examined, and the result was compared with the standard alkyd resins and soybean-based alkyd resin. It was observed that all samples were soluble in xylene and butoxyethanol but not water. All of the samples have varying solubilities in water/xylene ratio (%) and complete solubility in water/butoxyethanol (%) ratio of 40:60, 50:50, and 60:40, respectively. ALKYD A is soluble in all solvents except water where it was sparingly soluble at room temperature. The spectral analysis revealed the polyesterification reaction and hydrogen-bonding integrity of the alkyd resins and the polybasic acid. The physical and chemical properties and the performance indices of the glucitol-based alkyd resin results show that they possess acceptable drying properties, chemical resistance, and mechanical properties. Performance of ALKYD A and C gave nearly the same result as the standard alkyd resins and soybean-based alkyd resin. It has potential as a choice waterborne binder for alkyd resin paint and can help in reducing VOC.


Datum: 21.06.2019


Effects of surface pretreatment and deposition conditions on the gas permeation properties and flexibility of Al 2 O 3 films on polymer substrates by atomic layer deposition

Abstract

The effects of surface pretreatment and deposition conditions on the gas permeation properties—including permeability of He, O2, and H2O; the size; and the density of permeation-enhancing defects—and mechanical flexibility of Al2O3 films on polymer substrates by atomic layer deposition (ALD) were investigated to develop flexible gas barrier films for organic and flexible electronics. Pretreating polyimide (PI) and poly(ethylene terephthalate) (PET) substrates with an aqueous KOH solution greatly lowered the gas permeability of the ALD Al2O3 films as a result of improved affinity between the substrate surface and the ALD precursors. Varying the ALD conditions—including lengthening the precursor exposure, elevating the deposition temperature, and changing the precursor sequence—enhanced physisorption of ALD precursors on the polymer substrate, which improved nucleation of the ALD films to reduce defects in the films and lower their gas permeability. Activation energy for permeation determined from the temperature dependence of the permeability of the ALD films indicated that the ALD films deposited under the optimized condition contained smaller and few permeation-enhancing defects. The optimized ALD films possessed a low water vapor transmission rate of ~ 10−6 g/m2 day that met the stringent requirement of organic and flexible electronics, while also exhibiting excellent mechanical flexibility by withstanding repeated bending with small increases in gas permeability. Our results provide valuable insights into the development of flexible barrier thin films for the encapsulation of organic and flexible electronics.


Datum: 21.06.2019


Effect of aluminum hydroxide on the fireproofing properties of ammonium polyphosphate–pentaerythritol-based intumescent coating

Abstract

A fireproof composition based on ammonium polyphosphate and pentaerythritol with a number of functional additives was developed and studied. The additives are able to form a protective char during fire exposure below the thermal decomposition temperature of the polymer composites. The decrease in the char formation temperature of the fire-protective coating provides a molar excess of ammonium polyphosphate with respect to the mole fractions of pentaerythritol and aluminum hydroxide. Introducing the latter in the composition of the flame-retardant coating also contributes to the decrease in the char formation temperature. The fire-protection coating can be used to protect various combustible materials, e.g., wood, laminates, plastics, etc.


Datum: 13.06.2019


Environmentally friendly Zn–Al layered double hydroxide (LDH)-based sol–gel corrosion protection coatings on AA 2024-T3

Abstract

Zn–Al layered double hydroxide (LDH) intercalated with various corrosion inhibitors namely vanadate (E1), 2-mercapto benzothiazole (E3), molybdate (E7), phytic acid (E8) and 8-hydroxyquinoline (E9) was dispersed in a hybrid sol–gel silica matrix sol. Bilayer coatings with configurations E3|E1, E7|E1, E8|E1 and E9|E1 were generated on aluminum alloy AA 2024-T3 substrates using the inhibitor intercalated LDH modified sols by dip coating technique followed by UV curing and thermal curing at 80°C for 1 h in air. Corrosion resistance of coatings deposited from matrix sol with and without inhibitor intercalated LDH was studied by electrochemical impedance spectroscopy, potentiodynamic polarization after exposure to 3.5% NaCl and salt spray tests, results of which were compared with those of uncoated and chromated substrates. A non-chromated primer was applied on the sol–gel coated substrates. Adhesion of the coatings to the substrate and to the primer was evaluated by peel-off tape test and found to be rank 5. The sol–gel coated substrates did not exhibit corrosion during salt spray tests. Electrochemical tests showed that all the sol–gel coated substrates exhibited superior corrosion resistance when compared to bare and chromated substrates. More specifically, coatings generated using the corrosion inhibitors phytic acid and 8-hydroxy quinoline intercalated Zn–Al LDH were seen to render maximum corrosion protection, exhibiting two orders of magnitude lower corrosion currents than bare substrates and one order lower corrosion current than chromated substrate, after 120-h exposure to 3.5% NaCl solution.


Datum: 13.06.2019


Primary breakup of a non-Newtonian liquid using a high-speed rotary bell atomizer for spray-painting processes

Abstract

The present contribution deals with numerical and experimental studies of the primary liquid breakup process using a high-speed rotary bell atomizer. The first part of the investigations focuses on the film formation on the distributor disk and the inner surface of the rotary bell. Numerical simulations using the volume-of-fluid approach were carried out. A non-Newtonian liquid that has shear-thinning behavior is used to investigate the effect of the viscosity on the initial wetting, the film formation process, and the film thickness distribution on the bell. A nonhomogeneous film structure is found on the inner surface of the rotary bell. This is also observed in experimental investigations using a high-speed camera. The second part focuses on the disintegration process of the paint liquid in the near bell region. As inlet conditions for the breakup simulations, the properties of the liquid film at the bell edge, i.e., film thickness, velocities, and apparent viscosity, resulting from the film formation simulations were applied. Two different liquid disintegrations in the near-field were found, which were also observed in experimental investigations using a high-speed camera. Furthermore, user-defined functions were compiled in ANSYS Fluent to uniquely identify and characterize droplets formed through the breakup process. In this way, droplet properties such as diameter, velocity, and position can be determined.


Datum: 13.06.2019


Preparation and evaluation of degradable polyurethane with low surface energy for marine antifouling coating

Abstract

Two polyurethanes were prepared through the reaction of 1,6-diisocyanatohexane (HDI) with two kinds of alcoholates. The first alcoholate was synthesized from alcoholized lactide (PLA) and dodecafluoroheptyl methacrylate (DFHMA) with the solid super acid (SO42−/ZrO) acting as the catalyst, and the other alcoholate was a mixture of PLA and DFHMA. The composition and structure of these two polyurethanes were investigated by infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The mass loss, attachment of bacteria and algae, and the water contact angle were used to evaluate the degradable and antifouling performance of the two polyurethane coatings. The results showed that the maximum contact angle of PLIPFI reached 129°, its mass loss was higher than 10% in 65 days, and after 65 days, the mass loss appeared to be stable, and the antiadhesion performance of the polyurethanes coatings was also enhanced. All of these results indicated that the PU modified with a graft segment may be promising for obtaining antifouling materials that not only can resist the adhesion of microorganisms but also show self-renewal.

Graphical Abstract


Datum: 13.06.2019


Comparative release rates from controlled release polymer coatings—comparisons between models and experiment

Abstract

Controlled release devices and coatings are used heavily in widely varying applications. Here, we focus on applications to antifouling coatings by adding an active agent to polymeric coatings. Quantitative models were developed for four distinctively different methods of dispersing the active agent in the coating. The predicted release rates from these models were contrasted to reveal the inherent differences in the time-dependent release rate profiles achievable from these types of coatings. The majority of these four coatings (monolithic, dispersed particle and reservoir membrane) release the active agent with greatly varying rates over their effective lifetimes, while a microcapsule-based coating has the potential to produce relatively constant rates of release. While the models are potentially of great value, they require a number of parameters, particularly the diffusion coefficient of the active agent through the polymer, to be quantified. We demonstrate how such parameters can be quantified through release rate measurements from simple experimental coatings.


Datum: 13.06.2019


The influence of hydrophobic protection on building exterior claddings

Abstract

This study presents the results of an experimental campaign with the aim of investigating the hydrophobic protection of three substrates (stone, render, and external thermal insulation composite system—ETICS) with the application of three hydrophobic products: silicon and titanium dioxides-based nanostructured dispersion (HNST); a silane/oligomeric siloxane (HSila/Silox); and a siloxane (HSilox). To determine the effectiveness of the hydrophobic treatments, specimens of the untreated and treated wall coatings were characterized with different laboratory tests. The results showed that all products introduced significant improvements in the hydric properties of the substrates, leading to lower capillary water absorption (98%), water permeability with Karsten pipes (99%), drying index (39%), and higher water repellency assessed through the contact angle (283%). The application of hydrophobic materials also had a negative effect, leading to up to a 227% increase in resistance to water vapor diffusion. Among the assessed wall coatings, the rendering mortar appears to have the best initial performance after the application of all the types of hydrophobic materials tested. In general, the hydrophobic product HSilox was proved to be the most suitable for rendering mortars, while HNST was more appropriate for stone substrates.


Datum: 13.06.2019


Effect of particle shape on the wear and friction behavior of particle-reinforced epoxy coatings

Abstract

Epoxy coatings are increasingly becoming popular choices as barriers against acids and alkali for protection of concrete and metal products. In applications, metal containers are often coated with epoxy-based coatings to prevent rusting and corrosion. In this study, an experimental examination was carried out to investigate the effect of particle shape and size on the friction and wear behavior of epoxy coatings. Friction and wear experiments were conducted using a pin-on-disk tribometer. Epoxy resin was filled with four different shapes of glass particles (spherical, flake, rod, and irregular shape) and varying particle sizes. Fillers were settled down and filler surface area fraction through thickness was characterized using microcomputed tomography (micro-CT). The wear mechanisms such as matrix wear, matrix cracking, particle fracture, particle debonding, and pullout and debris formation were studied using scanning electron microscopy. According to observations, it was found that particle shape has an effect on the wear characteristic. Particle fracture and particle pullout mainly dominated the wear in the samples of flake- and rod-shaped fillers, perpendicular matrix cracks occurred in the samples of spherical fillers, large debonding at the particle–matrix interface without particle pullout occurred in the samples of large irregular-shaped fillers (75–150 µm), and matrix cracks dominated the wear as the size of irregular-shaped fillers decreased to 50–75 µm. Further, it was found that friction coefficient depends on the shape of the particle. The samples with spherical- and irregular-shaped fillers had higher friction coefficient as compared to the samples with flake and rod fillers.


Datum: 13.06.2019


Phosphorus-containing reactive agent for UV-curable flame-retardant wood coating

Abstract

An attempt to develop a phosphorus-based flame-retardant UV-curable agent (UV-RA) for coating application led to the synthesis of a reactive compound which can be used as crosslinker along with UV-curable epoxy acrylate oligomer to form a coating. UV-RA was characterized via FTIR, NMR, hydroxyl, and iodine values. Study based on the effects of varying amount of UV-RA incorporated in the formulation was investigated by checking thermal, mechanical, and flame-retardant properties. An enhancement in all the properties was observed with an increase in concentration of UV-RA and each coating containing UV-RA successfully portrayed flame-retardant properties. The highest loss on ignition (LOI) value obtained was 27 while the initial and final degradation temperatures increased along with the char yield. The mechanical properties did not vary much except for the low values for 20UV-RA.


Datum: 12.06.2019


Concentration profiles in phase-separating photocuring coatings

Abstract

We directly measured the local composition profiles in phase-separating photocurable thin films using confocal Raman spectroscopy. To avoid light scattering at phase interfaces, we developed a novel technique to replace the solvent with a monomer to match the reflective indices in the cured films. The results indicated that the concentration distribution of the polymer was uniform in solvent-free monomer/initiator binary solutions, while it was spatially nonuniform when the solvent-based films were thermodynamically unstable and promoted reaction-induced phase separation upon UV irradiation on the top surface. In the latter case, the film exhibited a dual-layer structure, in which the polymer concentration was almost uniform near the top surface, while concentration gradients developed near the bottom surface. The thickness of the top layer with a uniform concentration profile increased with the increase in the UV light intensity. These results implied that the propagation of the reaction front and the resulting light-driven transport of the solvent toward the bottom coating layer played key roles in the formation of nonuniform concentration profiles in photocuring solution coatings.


Datum: 10.06.2019


Strong and sustainable chemical bonding of TiO 2 on nylon surface using 3-mercaptopropyltrimethoxysilane (3-MPTMS): analysis of antimicrobial and decomposition characteristics of contaminants

Abstract

In this study, the antimicrobial and photodegradation properties of nylon fabric were improved by chemical treatment using 3-mercaptopropyltrimethoxysilane (3-MPTMS), which binds to photocatalyst TiO2, on a nylon fabric surface. The nylon fibers were impregnated with a solution containing isopropanol, titanium dioxide (TiO2), and 3-MPTMS at optimum ratios, and then stirred for 90 min. To remove the nonreactive impurities, the sample was washed twice with isopropanol and distilled water, and then dried. The TiO2 concentration, agitation temperature, and time were varied to determine suitable coating conditions for attachment to the nylon surface; the resulting properties were confirmed by scanning electron microscopy/energy dispersive spectroscopy. To evaluate the antimicrobial and photodegradation properties of TiO2, antimicrobial tests were conducted using the microbial reduction method and contact angle tests. The fiber contamination rate was measured by computer color matching after the sample was contaminated with methylene blue. Moreover, the antimicrobial activity of Staphylococcus aureus and Escherichia coli strains on the treated nylon was investigated.


Datum: 07.06.2019


Effect of practical parameters on the structure and corrosion behavior of vanadium/zirconium conversion coating on AA 2024 aluminum alloy

Abstract

In this research corrosion behavior of the hexafluorozirconic acid-based conversion coating (ZrCC) applied on the surface of AA2024 aluminum alloy, in the absence and presence of sodium metavanadate (ZrVCC), has been investigated. At the first step, practical parameters of ZrCC conversion coating were optimized using data of polarization resistance (Rp) and corrosion current density (icorr) obtained from electrochemical impedance spectroscopy and polarization techniques, respectively. In the next step the effect of sodium metavanadate presence by assessment on the effect of parameters including concentration of sodium metavanadate, immersion time, and solution pH on surface and electrochemical properties was investigated. The optimized practical conditions for ZrCC were immersion time of 60 s in 0.01 M of H2ZrF6 solution at room temperature and solution pH = 2. For the ZrVCC sample, the best results appeared for the immersion time of 60 s in the bath containing 1 g/lit sodium metavanadate at room temperature and pH = 2. Corrosion current density value of the ZrVCC sample was 0.07 µA/cm2 which seems to be 10 times smaller than its amount for the uncoated sample. Film formation of conversion coatings was investigated by field emission scanning electron microscope (FE-SEM) and atomic force microscope (AFM). FE-SEM and EDS test results revealed that zirconium compounds mostly precipitated on the surface of intermetallic particles.


Datum: 03.06.2019


Multilayer OLEDs with four slot die-coated layers

Abstract

For the first time, multilayer OLEDs with four solution-processed layers are fabricated step-by-step using slot die coating. A suitable choice of coating parameters and fluid formulation enables the application of different material classes as large-area homogeneous layers with thicknesses in the nanometer range. The AFM measurements of the slot die-coated layers consisting of small molecules showed Ra values of 0.21–0.28 nm, less than previously reported in the literature. Based on a two-layer reference OLED consisting of a HIL and EML, the stack architecture is first extended by a crosslinked HTL. These three-layer OLEDs with a crosslinked HTL achieve 70% higher efficiency, compared to that of the reference devices, thus assuming successfully separated layers. In a further step, an additional ETL is applied via the orthogonal solvent approach to obtain four solution-processed layers. The averaged power efficiency of the four-layer OLEDs is increased by a factor of 2.2 compared to the reference OLEDs up to a value of 3.5 lm/W. Based on these results, it can be assumed that both approaches, the use of orthogonal solvents as well as the application of crosslinkable materials, have been successfully combined to fabricate multilayer OLEDs with four separated slot die-coated layers.


Datum: 03.06.2019


 


Category: Current Chemistry Research

Last update: 28.03.2018.






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