Pull-off Test Research Articles

Anticorrosion and adhesion performance of a monolayer and double layer silane-epoxy coating systems applied on carbon steel

Carbon steel is one of the widely used metallic material, although its limited corrosion resistance. To improve its anti-corrosion performance, organic coatings such as epoxy have been an excellent option due to their barrier mechanism. Nevertheless, the elevated brittleness and porosity observed in this type of coating, coupled with the weak bonding interface between epoxy and carbon steel, significantly hampered their protective capabilities. The organofunctional silanes are candidates to be used as pre-treatment between epoxy coating and carbon steel interface because of their good corrosion resistance but as a limitation they can present small pores and microcracks.Therefore, the anticorrosive and mechanical properties of silane films can be adapted and further improved by strengthening the coatings through some modifications, such as the incorporation of green corrosion inhibitors into the film, reducing the access of aggressive species to the metal. In this context, the objective of this research is to evaluate the adhesion and anticorrosive properties of an epoxy-based organic coating pre-treated with a silane film obtained by tetraethoxysilane (TEOS) with γ-glycidoxypropyltrimethoxysilane (GPTMS) modified with the garlic peel powder as a corrosion inhibitor (Allium sativum L.). The investigation of the surface features as morphology and the corrosion resistance of the silane-epoxy coatings were studied by scanning electron microscope (SEM) and electrochemical characterization techniques, such as, electrochemical impedance spectroscopy (EIS), linear and potentiodynamic polarization. Also, the coating adherence was evaluated by pull-off tests. The results of the EIS showed that all samples coated with silane+ epoxy coating have better anticorrosion performance than the sample coated with just epoxy painting. Besides, SEM images showed that the silane film improved the cohesion between substrate and coating system, with the clear appearance of delamination in the system silane free. In general, the results of these different techniques indicate that the film modified with the natural inhibitor has improved anticorrosive properties compared to the film without silane or natural green inhibitors.

Surface engineering of aerospace aluminium alloys: Understanding alloying effects on chemical pre-treatment and sol-gel coating adhesion

The sol–gel process is a chemical surface preparation method based on hydrolysis and polycondensation reactions for enhanced adhesion for metallic substrates in adhesive bonding and coating applications. This paper describes an investigation into the effect of the microstructural complexity of two commonly used aerospace aluminium alloys (AAs) 2024-T3 and 7075-T6, on the response to different surface pre-treatments before deposition of the sol-gel coating and subsequent adhesive bonding.Different surface pre-treatments, including two abrasive treatments and three chemical surface pre-treatments were used, and their effect on surface chemistry, wettability and roughness was assessed. Surfaces were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, profilometry and static contact angles. A hybrid silane sol-gel film was deposited on the differently pre-treated aluminium alloys, an epoxy adhesive was applied and the adhesion properties were evaluated using pull-off testing. The role of the altered physicochemical properties of the pre-treated surfaces was related to the adhesion strength of the sol–gel reinforced epoxy/aluminium interfaces.The microstructural complexity of the aerospace alloys caused non-uniform responses to the pre-treatments, proving the importance of compatibility between material and treatment conditions. Statistical analysis revealed that, despite that overall higher adhesion values were obtained on rougher surfaces, only a strong correlation exists between the surface hydroxyl fraction and adhesion strength. The relation of roughness and water contact angle to interfacial adhesion was found to be non-significant.The findings of this study underscore the critical role of surface pre-treatments and their impact on adhesion strength in aerospace aluminium alloys, providing valuable insights for the effective utilization of sol-gel coatings in adhesive bonding and coating processes.

Metallization of polypropylene substrates through surface functionalization and physical vapor deposition of chromium coatings

Physical vapor deposition (PVD) of chromium coatings represents an interesting alternative to electroplating to obtain metallized plastic parts for a variety of manufacturing sectors. This process is however hampered by the limited adhesion of the metallic layer on the underlying polymeric substrates. Within this context, PVD metallization of polypropylene substrates has so far been particularly challenging given the low surface energy and poor wettability of this commodity plastics. To address this issue, a comprehensive approach is proposed here to enable the production of PVD-metallized PP substrates with excellent and stable interlayer adhesion. The adhesive properties of the PP substrate are modified by a selective UV-induced photografting process in which vinyl-, glycidyl- or 2-hydroxyethyl methacrylate species are covalently attached to the PP surface, as confirmed by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy and surface wettability measurements. Based on the chemistry of the photografted functionality, different resin systems are selected and investigated for use as primers to enable subsequent chromium deposition, including acrylic, epoxy and polyurethane systems. The effect of the photografting process on the adhesion between PP and the primers is systematically assessed by means of pull-off tests, highlighting a significant improvement of the adhesion force after surface functionalization with appropriate grafting agents. Finally, functionalized PP substrates are chromated through PVD, obtaining homogeneous and crack-free chromium surfaces upon judicious selection of suitable primer-grafting agent combinations. This also led to outstanding interlayer adhesion and micromechanical performance. This work provides the first demonstration of chromium-metallization of PP substrates via PVD for metallized plastic components with excellent surface characteristics, and paves the path for the design of mechanically durable and aesthetically-compliant PVD-metallized PP components.

3D printed auxetic metal stiffener for lightweight metal–composite T-joints with high strength and toughness

A novel auxetic structure-based stiffener for stainless steel–carbon reinforced polymer (CFRP) T-joints with outstanding strength and toughness improvement is proposed. The stiffener was composed of a bulk web and re-entrant structure flange that was 3D printed using a selective laser melting 3D printer. The stiffener was bonded to a CFRP skin, and a pull-off test was performed to evaluate the pull-off strength, stiffness, and toughness of the joint. The results demonstrated that the proposed structure has specific strength and toughness that were 3.4 and 77 times greater than those of the baseline joint, respectively. The improvement in strength was due to the delayed damage initiation caused by the mismatch between the bending stiffness of the bulk web and the stiffener under the first re-entrant structure. However, the damage initiation in the baseline joint was located at the stiffener edge. Moreover, the negative Poisson's ratio of the re-entrant structure arrested the delamination growth after damage initiation, which enhances the toughness of the joint. By optimizing the structure of the stiffener, a joint with 2.66 and 38.2 times larger specific strengths and toughness compared to the baseline joint with the same specific stiffness was achieved.

One pot synthesis of amino silane grafted cerium phosphate (AS@CePO4) as an effective anticorrosion nanopigment for epoxy coating

This work proposed a facile method to synthesize an effective anticorrosion nanopigment based on amino silane grafted cerium phosphate for epoxy coated steel system. CePO4 nanoparticles were synthesized from Ce(NO3)3 and Na3PO4 precursors, then surface-grafted with a coupling agent N-2-(aminoethyl)-3-aminopropyl trimethoxysilane (denoted as AS) via a one-pot reaction to obtain the AS@CePO4 nanopigment. The effectiveness of this nanopigment on corrosion protection, dry/wet adhesion strength, and cathodic disbondment resistance was thoroughly evaluated on an epoxy-coated steel system. The composition and morphology of pigments as well as epoxy containing pigments were characterized by Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) methods. The adhesion strength, cathodic disbondment resistance and corrosion protection performance characteristics of the coatings were evaluated by pull-off test, cathodic disbondment test, electrochemical and salt spray tests, respectively. The synergic effect from stronger bonding of AS coupling agent and excellent inhibitory ability of CePO4 led to strengthened adhesion strength, better corrosion protection performance, and higher cathodic disbondment resistance of epoxy coated steel system.

Research on deicing performance and environmental impact of anti-freezing asphalt mixtures

Snow and ice on pavement surface can cause a significant safety concern for drivers. This research investigates the deicing performance of the asphalt mixtures containing a self-prepared salt-storage additive (SSA), as well as their environmental impacts. A pull-off test was developed to evaluate the adhesion between the ice layer and asphalt mixture surface. The self-prepared SSA was incorporated into the asphalt mixtures by replacing mineral filler at percentages of 0 %, 20 %, 50 %, and 100 % by volume. The influence of self-prepared SSA on the pavement performance of asphalt mixtures was firstly investigated in this study, including the high-temperature stability, low-temperature performance, and water stability. The deicing performance of the asphalt mixtures containing self-prepared SSA and commercial product was determined by using the freezing point tests, ice-melting tests, and self-designed pull-off tests. To evaluate the environmental impacts of those anti-freezing asphalt mixtures, corrosion tests and seed germination tests were also employed in this study. Testing results showed that the addition of self-prepared SSA compromised the pavement performance of asphalt mixtures, but all measured properties met the specified requirements. The self-prepared SSA can effectively reduce the freezing point of the asphalt mixtures and shorten the ice melting time by 30 %, which has a similar or even better deicing effect as compared to the commercial salt-storage additive. Notably, the pull-off tests showed that the self-prepared SSA can significantly reduce the adhesion force between ice layer and asphalt mixture surface. The environmental impacts of asphalt mixtures containing self-prepared SSA were found to be within a reasonable range.

A new strategy to improve the anticorrosion performance of waterborne polyurethane coating on AA7075

In this study, Ce3+ functionalised halloysite nanotubes (HNTs) were prepared, and their impact on the anticorrosion properties of waterborne polyurethane (WPU) coating on 7075 aluminium alloy (AA7075) was investigated. HNTs were grafted by 3-aminopropyltriethoxysilane (APTES) to enhance Ce3+ loading, which was confirmed by X-ray diffraction (XRD) and Fourier-transform infrared (FT-IR) spectrum. The release behaviour of Ce3+ from HNTs was tested by inductively coupled plasma optical emission spectrometry (ICP-OES), and the inhibition effect of Ce3+-loaded HNTs for AA7075 was tested by polarization plots. The anticorrosion property of WPU doped with Ce3+-loaded HNTs was investigated by electrochemical impedance spectroscopy (EIS) and pull-off adhesion test. The results showed that APTES modification improved the Ce3+ loading amount on HNTs, and Ce3+ acts as an effective cathodic inhibitor for AA7075. After soaking for 40 days, the |Z|0.01Hz of Ce-HNTs/WPU was two orders of magnitude higher than that of pure WPU, while wet put-off adhesion was higher than pure WPU.

Trisodium phosphate-loaded magnesium‑aluminum layered double hydroxides/oxidized-multiwalled carbon nanotubes self-assembled 2D-nanohybrid for designing a multifunctional smart epoxy nanocomposite

In this study, a hybrid nanomaterial based on layered double hydroxides (LDH) and multi-walled carbon nanotubes (MWCN) was fabricated using a co-precipitation method. Trisodium phosphate (TP) was loaded into the designed nanocarrier to enhance the corrosion resistance of mild steel in 3.5 wt% NaCl media. Fourier transform infrared (FT-IR) spectroscopy, Raman, and X-ray diffraction (XRD) analyses were carried out to investigate the magnesium‑aluminum layered double hydroxides/oxidized-multiwalled carbon nanotubes (Mg-AL-LDH/O-MWCN) structure and morphology before and after loading of trisodium phosphate. Furthermore, the nanocarrier inhibition capability was evaluated through electrochemical impedance spectroscopy (EIS), polarization, and field emission-scanning electron microscopy (FE-SEM) techniques. Electrochemical impedance spectroscopy (EIS) was also employed to estimate the anticorrosion properties of the epoxy coating loaded with TP-LDH/O-MWCN. The EIS evaluation of the intact coating revealed the impedance at the lowest frequency (|Z|0.01 Hz) of about 109 Ω.cm2 after 42 days of immersion for the trisodium phosphate-layered double hydroxides/oxidized-multi-walled carbon nanotubes@epoxy (TP-LDH/O-MWCN@EP) sample and the lowest value of breakpoint frequency was obtained for this sample (fb = 0.063 Hz). These findings prove the trisodium phosphate-layered double hydroxides/oxidized-multi-walled carbon nanotubes (TP-LDH/O-MWCN) particles' effectiveness in the epoxy coating water/ion barrier function enhancement. EIS results indicated the enhancement of the charge transfer resistance (Rct) of the scratched coatings, from 65.97 kΩ.cm2 for the pure epoxy (EP) sample to 94.87 kΩ.cm2 for the trisodium phosphate-layered double hydroxides/oxidized-multi-walled carbon nanotubes@epoxy (TP-LDH/O-MWCN@EP) sample, revealing the self-repairing behavior of the designed coating. In addition, the adhesion properties of the samples coated with LDH/O-MWCN@EP and TP-LDH/O-MWCN@EP were studied by pull-off and cathodic disbonding tests, leading to a 33% reduction in adhesion loss and a 52.23% reduction in the diameter of cathodic delamination. The tensile test conducted on the samples indicated an increase in the ultimate tensile strength (σUTS), elongation break (Ɛb), and toughness values by 188%, 223%, and 800%, respectively, in comparison with the pure epoxy (EP) sample.

Superior interface adhesion and protective mechanism of room-temperature-curable polymer composite coating on engineering substrates with lower roughness

In view of the technology bottleneck of the adhesion failure of traditional functional protective coatings on the smoother surface of precise parts served in the marine atmosphere, a room-temperature-curable fluoropolymer/polyurethane (denoted as RFP) polymer composite coating of 20–30 μm is prepared on the metal substrates. Static pull-off and dynamic friction test methods are used to evaluate the interface adhesion of the coating. The coating shows superior adhesive strength of 18–24 MPa on a variety of metal substrates with a wide range of surface roughness (Ra = 0.1–1.6 μm). The friction coefficient of the coating surface is about 0.05–0.08, and the wear life is up to 9–12 km/μm. Furthermore, the adhesion strength of the coating remains 12–14 MPa after 1600 h of salt spray while the wear life of the coating keeps 3–9 km/μm after 720 h of salt spray. The influences of surface roughness (Ra), surface free energy (γOxide), surface potential (φOxide) of the metal substrates and the bonding force at substrate-coating interface on the adhesive energy (Eadh.) are discussed, and the mechanism of "physical-chemical-surface" synergetic enhanced interface adhesion is proposed. The RFP coating is used as the intermediate layer for traditional PU and EP coatings to improve their adhesion on smooth aluminum substrate from 1.39 MPa to 17.5 MPa (increased by 1260 %). Thus, the polymer coating has the potential to provide technical support for the development of long-term anticorrosive coating technology for precision components of marine high-tech equipment.

PVC gel-based electro-adhesion on extremely rough surfaces

Electrostatic adhesion, also known as electro-adhesion, has been employed in many robotic devices for dynamic adhesion and shows fast switching between adhesive/non-adhesive states on demand. However, a well-known challenge for electro-adhesion is to achieve strong adhesion on rough surfaces with a reasonably low operating voltage. Herein, we report a simple strategy to fabricate electro-adhesion pads based on polyvinyl chloride (PVC) gel, which can achieve strong adhesion (ten times stronger than silicone rubber-based electro-adhesion pads) on rough conductive surfaces with a relatively low operating voltage (<1 kV). When a PVC gel is subjected to a DC voltage, its local creep deformation can increase the contact area between the gel and the rough surface, which enhances the adhesion strength. We experimentally measure the electro-adhesion strength of PVC gel pads in both lap shear and pull-off adhesion tests. Compared to silicone rubber-based electro-adhesion pads, PVC gel pads show much higher adhesion strength in both loading conditions with a lower operating voltage. Finally, we showcase a proof-of-concept demonstration of the electrically controllable adhesion between a PVC gel pad and rough conductive surfaces.

A multiscale experimental study of CFRP-UHPFRC interfacial bond behaviour: Failure mechanisms and a fibre volume dependent bond-slip law

Carbon fiber reinforced polymer (CFRP) materials are being increasingly used with ultra high performance fiber reinforced concrete (UHPFRC) to construct composite structural members making use of their unique properties. As the interfacial bond behaviour between CFRP and UHPFRC plays a key role in the design of such members, it was investigated in detail by multiscale experiments of single shear pull-off tests of 26 CFRP-UHPFRC bonded joints with different bond lengths and widths of CFRP laminates and 0.5–4% volume fraction (Vsf) of straight high-strength steel fibers (length = 13 mm, diameter = 0.2 mm). 12 CFRP-normal strength concrete (NSC) bonded joints were also tested for comparison. The surface strain evolution and the interfacial debonding process were captured and analysed by the digital image correlation (DIC). The complex microscale failure mechanisms, such as the mortar cracking, the CFRP-UHPFRC interfacial debonding, and the steel fibers’ slipping and pulling out of the mortar, were visualised and analysed by the 3D micro X-ray Computed Tomography (μXCT) scanning. It was found that the debonded layer of mortar under the laminates was much thinner than that in the CFRP-NSC bonded joints, due to the lack of coarse aggregates in UHPFRC. The peak pulling forces for the specimens with Vsf = 0.5%, 1%, 2%, and 4% were 9%, 21%, 28%, and 29% higher than those without steel fibers, respectively. An empirical bond strength model and an interfacial bond-slip model were proposed based on the test results, accounting for Vsf, the material properties, and the laminate to UHPFRC width ratio. Finally, the proposed bond-slip model was applied in finite element modelling to simulate the flexural behaviour of an FRP-UHPFRC composite deck in the literature, with the interfacial debonding failure and the ultimate loads successfully predicted.

Investigation of interfacial degradation mechanism and debonding behavior for degraded rubber asphalt-aggregate molecular system using a molecular dynamics method

This study aims to investigate the debonding damage behaviors in rubber asphalt-aggregate interfaces under different rubber degradation degrees from a molecular-scale perspective. The pull-off test was simulated using molecular dynamics (MD) to determine the damage patterns at the asphalt-aggregate interface. The digital image processing (DIP) technique was employed to quantify the percentages of cohesive debonding, and the radial distribution function (RDF) and mean square displacement (MSD) was performed to explain the adhesion and cohesion damage mechanisms. In addition, the pull-out test results were compared with the simulated values to verify the reliability of the asphalt-aggregate molecular model. The findings of this study reveal that the presence of rubber powder molecules enhances the cohesion among asphalt molecules and mitigates damage to the cohesion at the asphalt-aggregate molecular interface. As rubber degradation progresses, the damage mode undergoes a gradual transition from adhesive damage to cohesive damage at the asphalt-aggregate interface. At lower temperatures, there is an increase in the internal aggregation of asphalt molecules, and the debonding rate of asphalt molecules at the mineral-aggregate interface rises from 7.67% to 35.67% following complete rubber degradation. Conversely, at higher temperatures, the asphalt-aggregate molecular system is primarily governed by the bonding of “double bond” and “single bond” groups, with cohesive damage dominating the asphalt matrix. The pull-out test results showed similar trends with the simulated values, indicating that the asphalt-aggregate molecular model in this study was relatively reasonable. The present study provides some guidance on the damage behavior of degraded rubberized asphalt-aggregate interface.

Thermal insulation capability and adhesion strength of unpyrolyzed thick thermal barrier coatings

Thermal insulation capability and adhesion strength of thick thermal barrier coatings (TBC) produced by unpyrolyzed powder (UPTTBC) were compared with those of the conventional TBC, thick TBC (TTBC), and dense vertically cracked (DVC) TTBC. Thermal insulation capability was evaluated using temperature drop. The adhesion strengths of the coatings were also measured by pull-off test method according to ASTM C633. The results indicated that the adhesion strength of UPTTBC and DVC TTBC was 35% and 25% higher than that of the TTBC, respectively. This could imply that the non-melted areas with sub-micron dimensions in UPTTBC structure, act as a trap and prevent the cracks propagation. In addition, the results of thermal insulation tests showed that DVC TTBC coatings had the lowest thermal insulation capability with temperature drop rate of 0.28 °C/µm and UPTTBC coatings had the highest insulation capability with temperature drop rate of 0.40 °C/µm. Due to the presence of sub-micron zones in the microstructure of UPTTBCs, the coatings exhibited superior thermal insulation capability. In contrary, the DVC TTBC showed the lowest thermal insulation capability because of its dense structure.

Laboratory evaluation of the effect of cement concrete overlays on the existing asphalt concrete pavement with different degrees of bonding

ABSTRACT The utilisation of cement concrete overlays has been on the rise owing to the growing demand for the repair and enhancement of existing pavements, emphasising cost-effectiveness and prolonged overlay lifespan. The primary objective of this study is to ascertain the performance and scrutinise the impact of various types of separating layers on the mechanical parameters of cement concrete overlays. Upon the acquisition of requisite materials and the preliminary testing pertaining to the design of mixtures utilised in both asphalt concrete and cement concrete, three-layer samples were employed in pull-off tests and bending beam tests. These samples incorporated separating layers of different material types, namely AC60/70 neat bitumen (neat bitumen with Pen 60/70), AC85/100 neat bitumen (neat bitumen with Pen 85/100), bitumen emulsion (tack coat), polymer-modified bitumen, bituminous thin layer mixture, and a control sample without a separating layer. Subsequently, through a comparative analysis of the tensile strength and flexural strength results derived from the three-layer samples, the separating material demonstrating the highest and lowest potential for bonding was identified and compared through diverse diagrams. Furthermore, to ensure the reliability of the obtained results, a comparative analysis was conducted against the Darter and Barenberg criterion, along with average stress (mean fatigue).

Full-scale experimental investigation on the performance of seamless asphalt plug joint through mixture design and structural enhancements

The seamless asphalt plug expansion joint integrates a traditional asphalt plug joint (APJ) with an overlying continuous asphalt concrete layer, preventing block failure of the asphalt plug joint and enhancing driving comfort. However, typical damages such as fatigue cracking, rutting, and permanent deformation often occur in the upper asphalt layer. This is attributed to the inadequate stiffness of the lower joint plug mastic, particularly under high temperatures and heavy loads. To extend the service life of asphalt plug expansion joints under such conditions and enhance their durability, efforts were made to bolster the performance of the lower asphalt plug joint mixture and improve anti-rutting performance. This study involved: (1) Qualifying APJ mixture requirements under high temperature and heavy load by focusing on two critical material properties: good rutting resistance and permanent deformation resistance. High temperature rheological properties of these binders were examined through temperature scanning tests and multi-stress creep recovery tests (MSCR). (2) Exploring the impact of binder-aggregate ratios and specimen molding methods (standard compaction, paving vibration and pre-mixing) on the bonding strength and rutting resistance of the APJ mixture. This analysis was conducted using pull-off tests and dynamic stability tests. (3) Development of a novel APJ featuring dowel bars to enhance vertical deflection resistance and joint horizontal movement. Comprehensive laboratory tests showcased the modified joint structure's resilience after numerous test cycles, demonstrating exceptional resistance to bending and vertical deformation. The significant findings from this research provide valuable insights for optimal material selection, appropriate joint design, and installation guidelines for seamless asphalt plug expansion joints.

A Molecular Dynamics Analysis of the Thickness and Adhesion Characteristics of the Quasi-Liquid Layer at the Asphalt-Ice Interface.

The quasi-liquid layer (QLL), a microstructure located between ice and an adhering substrate, is critical in generating capillary pressure, which in turn influences ice adhesion behavior. This study employed molecular dynamics (MD) methods to obtain QLL thickness and utilized these measurements to estimate the adhesive strength between ice and asphalt. The research involved constructing an ice-QLL-asphalt MD model, encompassing four asphalt types and five temperature ranges from 250 K to 270 K. The QLL thickness was determined for various asphalts and temperatures using the tetrahedral order parameter gradient. Additionally, capillary pressure was calculated based on the QLL thickness and other geometric parameters obtained from the MD analysis. These findings were then compared with ice adhesion strength data acquired from pull-off tests. The results indicate that QLL thickness varies with different asphalt types and increases with temperature. At a constant temperature, the QLL thickness decreases in the order of the basal plane, primary prism plane, and secondary prism plane. Furthermore, the adhesion strength of the QLL diminishes as the temperature rises, attributed to the disruption of hydrogen bonds at lower temperatures. The greater the polarity of the asphalt's interface molecules, the stronger the adhesion strength and binding free energy. The MD simulations of the asphalt-ice interface offer insights into the atomic-scale adhesive properties of this interface, contributing to the enhancement in QLL property prediction and calibration at larger scales.

The Formation of Phytic Acid–Silane Films on Cold-Rolled Steel and Corrosion Resistance

In this work, phytic acid (PA) and 3-mercaptopropyltrimethoxysilane (MPTS) underwent a condensation process to produce a phytic acid–silane (abbreviated PAS) passivation solution. Additionally, it was applied to the surface of cold-rolled steel to create a composite phytic acid–silane film. The functional groups of the passivation solution were analyzed by Fourier transform infrared spectroscopy (FT-IR). The composite film was evaluated using an electrochemical workstation, scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS) and pull-off test. These techniques allowed for the characterization of the film’s micromorphology, oxidation, chemical composition and adhesion strength. The results show that the PAS composite film provides higher protection efficiency compared to cold-rolled steel substrates, low phosphorus passivation films, single phytate passivation films and commercial phosphate films. This composite film also has a higher adhesion strength, which is beneficial for subsequent coating, and a possible corrosion resistance mechanism was proposed as well. The PAS layer successfully prevents the penetration of corrosive media into the cold-rolled steel surface utilizing P–O–Fe bonds, thus improving the corrosion barrier effect of the substrate.

Epoxidized technical Kraft lignin as a particulate resin component for high-performance anticorrosive coatings

Deterioration of steel infrastructures is often caused by corrosive substances. In harsh conditions, the protection against corrosion is provided by high-performance coatings. The major challenge in this field is to find replacements for the fossil-based resins constituting anticorrosive coatings, due to increasing needs to synthesize new environmentally friendly materials. In this study, softwood Kraft lignin was epoxidized with the aim of obtaining a renewable resin for anticorrosive coatings. The reaction resulted in the formation of heterogeneous, solid, coarse agglomerates. Therefore, the synthetized lignin particles were mechanically ground and sieved to break up the agglomerates and obtain a fine powder. To reduce the use of fossil fuel-based epoxy novolac resins in commercial anticorrosive coatings, a series of formulations were prepared and cured on steel panels varying the content of epoxidized lignin resin. Epoxidized lignin-based coatings used in conjunction with conventional epoxy novolac resin demonstrated improved performance in terms of corrosion protection and adhesion properties, as measured by salt spray exposure and pull-off adhesion test, respectively. In addition, the importance of size fractionation for the homogeneity of the final coating formulations was highlighted. The findings from this study suggest a promising route to develop high-performing lignin-based anticorrosive coatings.

Amino-Modified Graphene Oxide from Kish Graphite for Enhancing Corrosion Resistance of Waterborne Epoxy Coatings.

Waterborne epoxy (WEP) coatings with enhanced corrosion resistance were prepared using graphene oxide (GO) that was obtained from kish graphite, and amino-functionalized graphene oxide (AGO) was modified by 2-aminomalonamide. The structural characteristics of the GO and AGO were analyzed using X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). And the anti-corrosive performance of waterborne epoxy-cased composite coatings with different addition amounts of AGO was investigated using electrochemical measurements, pull-off adhesion tests, and salt spray tests. The results indicate that AGO15/WEP with 0.15 wt.% of AGO has the best anti-corrosive performance, and the lowest frequency impedance modulus increased from 1.03 × 108 to 1.63 × 1010 ohm·cm-2 compared to that of WEP. Furthermore, AGO15/WEP also demonstrates the minimal corrosion products or bubbles in the salt spray test for 200 h, affirming its exceptional long-term corrosion protection capability.

Performance of Phenolic-Epoxy Coatings after Exposure to High Temperatures

Phenolic-epoxy coatings, which are designed to protect substrates from thermal damage, are widely applied in many fields. There remains an inadequate understanding of how such coatings change during their service life after exposure to various temperature conditions. To further elucidate this issue, this case study investigated the effects of high temperatures on carbon steel panels coated with phenolic epoxy and exposed to different heating conditions. A general trend of decreasing barrier performance was observed after exposure to 150 °C for 3 d, as evidenced by the appearance of cracks on the panel surfaces. In contrast, the coating performance improved after exposure to isothermal conditions (120 °C) or thermal cycling from room temperature to 120 °C, as indicated by the increased low-frequency impedance modulus values of the coating. This unexpected improvement was further examined by characterising the coatings using transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), pull-off adhesion tests, and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The maximum pull-off adhesion force (24.9 ± 3.6 MPa) was measured after thermal cycling for 40 d.