Journal of Coatings Technology and Research最新文献

Ultraviolet curable composite coatings are an eco-friendly option with the absence of volatile organic compound emissions. Achieving a better interface between epoxy acrylate (EA) and mica is essential for the enhanced mechanical and barrier properties of composite coatings. This paper presents a strategy for modifying mica through in situ grafting with various silane coupling agents (KH550, KH560, and KH570) and preparing composite coatings of EA/mica using a blending method. The results indicate that the silane-modified mica exhibited enhanced compatibility with EA coatings. The mechanical properties, thermal stability, and corrosion resistance of epoxy acrylate/silane-modified mica coatings were improved compared to epoxy acrylate/unmodified mica composite coatings. KH570 was found to be the most effective modifier for enhancing these properties of the coatings. Relative to EA/unmodified mica composite coating, the impact resistance of EA/KH570-modified mica composite coatings doubled, with increases in T₅ and T₁₀ by 49.7°C and 9.7°C, respectively. During the 9 day monitoring period using electrochemical impedance spectroscopy, the total impedance modulus |Z|_f=0.01 Hz of EA/KH570-modified mica composite coatings was discovered to be 6–9 times higher than that of unmodified mica coatings, with the R_t value higher by two orders of magnitude.

The inherent combustibility of waterborne polyurethane (WPU) with a limiting oxygen index (LOI) of only 18.0% has impeded its versatile applications in the automotive industry, furniture coatings, leather, and other domains. Therefore, enhancing the fire safety of WPU is imperative. This work reports the synthesis of novel reactive flame retardants and their subsequent chemical grafting onto WPU to ameliorate its flammability weakness. Using the novel flame-retardant intermediate 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and para-hydroxybenzaldehyde as precursors, phosphorus-based flame retardants (DOPOs) were prepared. Hollow glass microspheres (HGB) were modified with a silane coupling agent (KH550) and incorporated into the WPU prepolymerization. Finally, chemical grafting occurred between the hydroxyl groups of DOPOs and the modified HGB to produce dual-component flame retardants involved in the prepolymerization. The addition of 2 wt% synergistic flame retardants to WPU increased its LOI to 26% and eliminated dripping during combustion.

With urbanization and the reduction in forest land, there has been an increase in the temperature around urban areas resulting in the urban heat effect (heat island). As a measure of the urban heat effect, the use of organic polymer thermochromic material (OPTCM) as a building material seems to be a feasible solution. OPTCM is used as a reflective coating that reflects the sunlight, reducing the electricity load on cooling system. The OPTCM easily gets degraded under sunlight and thereby limits its usage in building coating applications. To reduce the photodegradation of OPTCM, it is generally encapsulated with an inorganic metal oxide such as titanium dioxide, zinc oxide, etc. Different methods are discussed and illustrated further to achieve the necessary microencapsulation. It is necessary to study the properties of different inorganic metal oxides as the encapsulating material. The effects of these encapsulating materials on the properties of OPTCM are further discussed in this review paper.

Graphical abstract

A glucose-modified double crosslinked waterborne polyurethane (WPCU) was synthesized by glucose (GLC) and trimethylolpropane (TMP) as crosslinking agents, polycarbonate diol (PCDL) as the functional soft segment material, and isophorone diisocyanate (IPDI) as the hard segment. The effects of GLC and TMP on the structure and material characteristics of WPCU were examined and evaluated using Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and other tests. The experimental results demonstrate the favorable comprehensive performance of the modified WPCU. The double-crosslinked polyurethanes exhibited excellent mechanical strength (30.9 MPa for WPCU-0.9 film), a higher water contact angle (82.9° for WPCU-0.3 film), and superior thermal stability compared to single-crosslinked polyurethanes modified solely with GLC. In addition, a new type of double crosslinked waterborne wood paint was formulated by adding various additives. It was subjected to painting experiments on wood panels. The newly developed wood coatings using double crosslinked WPCU emulsions exhibit good chemical resistance (to alcohols, acids, and bases), dry heat resistance, and adhesion (adhesion class I). Paint films achieve a hardness of 2H when the GLC content exceeds or equals 1.2%, exhibiting excellent adhesion resistance, which could contribute to the development of high-stiffness waterborne polyurethanes in the future.

With the continuous growth of the inkjet printing market, it has become particulary important to endow dye thermal transfer paper with fast-drying performance and fine transfer effect. In order to achieve this goal, the nanohybrid materials of HNTs/MSN (halloysite nanotubes/mesoporous silica) were prepared by Stöber method and in situ growth method, and then, the thermal sublimation transfer papers coated with CMC/MSN, CMC/HNTs, and CMC/HNTs/MSN were prepared, respectively. Characterizations of MSN, HNTs, and HNTs/MSN were conducted using TEM, FTIR, XRD, XPS, and BET techniques, followed by testing the properties of the coated papers. The results showed that the HNTs/MSN nanohybrid materials were formed by deposited MSN on HNTs with the Stöber method and in situ growth method. Among the three types of papers, CMC/HNTs/MSN paper exhibited the best comprehensive performance with fast-drying performance and fine transfer effect. Therefore, CMC/HNTs/MSN can be used as a novel type of thermal transfer paper coating with fast ink drying speed and fine transfer effect.

To determine the feasibility of crosslinker-free epoxy systems as an applied coating solution, this study investigated the cure-by-design behaviors and functional performance of anionically catalyzed crosslinker-free epoxy functional coatings. A fusion boned epoxy (FBE) powder platform was utilized, and formulation index (FI)-oriented optimizations were performed, with the FI extended to infinity (or ∞), which corresponds exclusively to 100% epoxy self-crosslinking from an applied chemistry standpoint. Depending on the catalyst type and loading, the cure kinetics and rheology of these homogeneous crosslinker-free systems varied significantly from those of heterogeneous crosslinker-containing coatings. In addition to thermal curing responses (including viscoelastic gelation and vitrification), the structural properties, particularly glass transition temperature (T_g), flexibility, cohesive toughness, impermeability, and adhesion, are closely correlated to the T_g-capability or -potential of their formulations, as well as the chemical structures, molecular weights (MWs), epoxy equivalent weights (EEWs), and functionality (f) of the underlying epoxy resins or monomers. Other interesting findings, such as the concurrence and sequences of epoxy-crosslinker copolymerization and epoxy-epoxy homo-polymerization by differential scanning calorimetry (DSC) exothermic profile analysis, are reported and explained.

Microphase separation within the polyurethane (PU) matrix is caused by thermodynamic incompatibility between the soft and hard segments and the movement of them. Although degree of phase separation (DPS) is a sensitive and important parameter and reflects the formation of the internal hydrophobic network structure, research on the relationship between DPS and the corrosion resistance performance of PU coatings is very limited. This study prepared a series of PU coatings with different soft and hard segment ratios, quantitatively calculated DPS, and analyzed the residual situation of the -NCO groups of each coating using infrared spectroscopy (FTIR). The crosslinking density (XLD) of the coatings was obtained using the swelling equilibrium method. The corrosion resistance performance of the coatings was periodically tested through salt water immersion experiments, Tafel tests, and electrochemical impedance spectroscopy (EIS). It was found that coatings with a high hard segment content have higher DPS and XLD. The samples with the highest hard segment content (sample PU3-5-10 and PU3-5-11) possessed the highest DPS values (24.28 and 41.95%) and showed the lowest corrosion current density (9.3 × 10⁻¹¹ and 3.25 × 10⁻¹¹ A/cm²) and the highest impedance values (6.22 × 10⁸ and 1.24 × 10⁹ Ω cm²) before salt water immersion; however, PU3-5-11 showed a much more rapid decline in impedance after 40 days of immersion. FTIR analysis indicated that the presence of easily hydrolyzable residual -NCO groups should be the main reason for the worsening. It was also found that the DPS of the coatings is highly correlated with their XLD, and the relationship between DPS and various corrosion resistance indicators is basically consistent with that of XLD.

Encapsulating smart nano-containers loaded with corrosion inhibitors into coating is a promising approach to functionalize micro-arc oxidation (MAO) coating. The encapsulation strategy of smart containers has a great influence on the microstructure, corrosion resistance and self-healing performance of the smart MAO coating. In order to provide a comprehensive understanding, two kinds of MAO coating encapsulated smart containers (HNT-8HQ), MAO-HNT-8HQ (1S) coating (one-step preparation in an MAO electrolyte containing smart nano-containers) and MAO + HNT-8HQ (2S) coating (pre-prepared MAO coating through an embedding nano-container processing) were prepared on AZ31 magnesium alloy. The incorporated HNT-8HQ in electrolyte can effectively reduce coating porosity and increase coating thickness. Both smart MAO coatings show considerable improvements in the corrosion resistance and a certain self-healing capacity. The post-embedding treated coating (MAO + HNT-8HQ (2S)) has better long-term durability and self-healing performance than one-step preparation coating (MAO-HNT-8HQ (1S)). The low-frequency impedance modulus (|Z|_ƒ=0.01 Hz) of MAO + HNT-8HQ (2S) coating is 1.33 times that of MAO-HNT-8HQ (1S) coating after immersion in 3.5 wt% NaCl solution for 168 h. The MAO + HNT-8HQ (2S) coating has higher impedance values than MAO-HNT-8HQ (1S) coating during the entire self-healing process. The low-frequency impedance modulus of scratched MAO + HNT-8HQ (2S) coating is 3.33 times that of scratch MAO-HNT-8HQ (1S) coating after a 72 h self-healing process.