Search

This research presents the effect of the chemical structure of new crosslinking agent on the properties of powder coatings. A method of synthesis of blocked polyisocyanates and the formation of powder coatings with low curing temperature are presented. In the synthesis of blocked polyisocyanates (bPIC) TDI, glycerine, xylitol, polyethylene glycol, polysiloxane KF-6000 and butanone oxime were used. By using FT-IR, the chemical structure of the obtained blocked polyisocyanates was confirmed. The thermal behavior and the deblocking process were investigated by means of TGA, DSC and DMA. Performance tests were performed on the obtained coatings to assess their hardness, adhesion to steel, roughness, gloss, scratch resistance, and water contact angle. An accelerated weathering test was also conducted to examine the coatings' resistance to weather conditions (UV radiation, water). • The method of new blocked polyisocyanates synthesis for powder coatings was developed. • The influence of curing agent structure on thermal behavior and curing process was described. • The deblocking process of PICs was investigated. [ABSTRACT FROM AUTHOR]

In this work, epoxy/clay (Closite 30B) nanocomposite samples were prepared by using solution and melt dispersion methods The quality of clay dispersion in epoxy matrix was evaluated by using XRD and TEM techniques. The prepared nanocomposite samples were used in epoxy powder coating formulations (named as nano powder coatings). DSC analysis was used to study the curing behavior of samples. The physical, mechanical and thermal properties of prepared samples were evaluated by using tensile, DMTA, microhardness, TGA and LOI tests. Finally, the corrosion resistance of prepared epoxy nano powder coatings was determined using the salt spray test. The results illustrated that closite 30B nanoparticles could be dispersed properly in epoxy resin by using both solution and melt dispersion methods It was found that Closite 30B could accelerate the epoxy curing reaction. The results showed that the mechanical properties of nano powder coatings improved when various concentrations of clay nanoparticle (in the range of 1–5 phr) were used in formulation. It was observed that sample with 3 phr clay nanoparticles presented the best thermal and fire resistance properties. The salt spray measurements confirmed the superiority of corrosion resistance of epoxy nano powder coatings in comparison to that for neat epoxy powder coating formulation. [ABSTRACT FROM AUTHOR]

In this study, the thermal behavior of new blocked polyisocyanate crosslinkers for polyurethane powder coatings was investigated. Blocked polyisocyanates were synthesized on the basis of biuretization process using isophorone diisocyanate (IPDI) and formic acid as biuretizing agent. ε-caprolactam was employed as blocking agent. Blocked polyisocyanates were additionally modified with α,ω-bis(hydroxyethyleneoxypropylene)-poly(dimethylsiloxane). The thermal behavior was investigated by means of coupled thermal analysis, differential scanning calorimetry and Fourier transform infrared spectroscopy (TG/DSC/FTIR). The TG analyses reveal that thermal decomposition of the blocked diisocyanate and blocked polyisocyanate comprising biuret moieties occurs in two main steps in the range of 120–275 °C and 310–375 °C, respectively. However, two additional stages in the range of 275–310 °C and 375–500 °C, for blocked polyisocyanate modified with polysiloxane, were observed. [ABSTRACT FROM AUTHOR]

The levelling performance of polyester powder coating is not as well as liquid coating due to its matrix polyester resin. 1,6-hexanediol (HDO), neopentyl glycol (NPG), terephthalic acid (PTA), isophthalic acid (IPA) were used to synthesize semi-crystalline polyester resin (HDO, PTA and IPA) and amorphous polyester resin (NPG, PTA and IPA). The semi-crystalline polyester resin was introduced to powder coating for further use. The structure of semi-crystalline polyester resin was characterized by 1H-nuclear magnetic resonance (1H NMR) and X-ray powder diffraction (XRD). The viscosity of the polyester resins were investigated by cone-and-plate viscometer (CPV). The reactivity of the coatings was characterized by differential scanning calorimetry (DSC). The levelling performance was studied by flow, cone-and-plate viscometer (CPV), atomic force microscope (AFM) and scanning electron microscope (SEM). The results showed that the semi-crystalline polyester powder coating had higher reactivity and better levelling performance than that of amorphous polyester powder coating. [ABSTRACT FROM AUTHOR]

The effect of the addition of the zinc molybdenum phosphate pigment, on the corrosion resistance properties of powder coating on steel, has been investigated by means of different electrochemical methods: electrochemical impedance spectroscopy (EIS) and the accelerated cyclic electrochemical technique (ACET). Anticorrosive properties obtained from both techniques showed similar results. Powder coatings incorporating this pigment have shown better performance which is attributed to both barrier properties enhancement and inhibition action of the pigment. This behavior can be correlated to the results obtained in the pigment extract study (polarization test and EIS). Finally, salt fog spray test was performed to confirm the electrochemical tests results. [ABSTRACT FROM AUTHOR]

In this study, polyurethane powder clear coating systems consisting of polyester resin, blocked polyisocyanate and hydrotalcites (HT) intercalated with carbonate, aminododecanate, and ethylenediaminetetraacetate were examined. The blocked polyisocyanate crosslinkers for powder coatings were synthesized using trimethyhexamethylene diisocyanate (TMDI), formic acid, ε-caprolactam, dibutyltin dilaurate and triethylamine as catalysts. The powder coatings were investigated by atomic force microscopy (AFM) and X-ray diffraction analysis (XRD). The surface structure was correlated with the chemical structure of the coatings and macroscopic surface behavior: contact angle, surface free energy, gloss, elasticity, cupping, impact and scratch resistance, hardness as well as adhesion to steel surface. [ABSTRACT FROM AUTHOR]

Great progress has been devoted recently in the applications of conducting polymers and their composites in corrosion protection of metals by coatings. The ultimate goal of this study is to formulate anti-corrosive hybrid epoxy/polyester and polyester powder coating composites based on phosphate pigments containing poly-o-aminophenol for corrosion protection of steel. The formulations were prepared in two steps. The first step involved In situ emulsion polymerization of o-aminophenol in presence of some phosphate pigments (mainly zinc phosphate, Ca phosphate and Ca–Zn phosphates) via chemical oxidation process using ammonium peroxydisulphate. The second step involved the formulation of the various ingredients of the powder coating composites using hybrid epoxy/polyester and polyester as binders with various doses of phosphate pigments and other inorganic pigments and fillers. The prepared powder coating composites were applied on a cold rolled steel panels and were investigated for physico-mechanical properties and evaluated for their corrosion protection properties via salt spray chamber for 1000 h. The obtained results showed high performance anti-corrosive powder coatings formulations for steel protection. [ABSTRACT FROM AUTHOR]

Polyurethane powder coating systems consisting of polyester resin, blocked polyisocyanate and two types of “nanopowders” containing core–shell nanoparticles where the core was silicone resin of very low glass transition temperature and the shell was poly(methyl methacrylate) were examined. The blocked polyisocyanate was synthesized using biuretpolyisocyanate obtained from ureapolyisocyanate as starting material capable for blocking and ɛ-caprolactam as blocking agent. The surface properties of cured powder coatings were investigated using scanning electron microscopy (SEM) combined with energy dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The surface structure was correlated with the chemical structure of the coatings and macroscopic surface behavior: contact angle, surface free energy, gloss, abrasion resistance, hardness and adhesion to the steel surface. [ABSTRACT FROM AUTHOR]

The effect of the addition of the anticorrosive zinc molybdenum phosphate (ZMP) with superficial modification (an organic titanate), on the corrosion resistance properties of powder coating on galvanised steel has been investigated by means of different electrochemical techniques: electrochemical impedance spectroscopy (EIS) and an accelerated cyclic electrochemical technique (ACET). Powder coating based on carboxylated polyester resin and N,N,N,N-Tetrakis-(2-hydroxyethyl)-hexanediamine (95:5) were prepared with different contents of the anticorrosive pigment ZMP (0, 1, 2.5, 10 and 15% in weight ratio to total formulation). The optimum quantity of anticorrosive phosphate pigment ZMP (maximum anticorrosive performance) was in the range 10–15%, depending on the technique applied, and can be ascribed to both barrier properties enhancement and inhibition action of the pigment. Finally, salt fog spray test was performed to confirm the electrochemical tests results. [ABSTRACT FROM AUTHOR]

In this study, blocked polyisocyanate crosslinkers (PIC) for powder coatings were synthesized using isophorone diisocyanates (IPDI), formic acid, poly(dimethylsiloxane), ɛ-caprolactam, dibutyltin dilaurate as well as triethylamine as catalysts. The chemical structures of these compounds were confirmed by means of IR and NMR spectroscopy and the molecular weight distributions were investigated using gel permeation chromatography (GPC). Polyurethane powder coating systems consisting of polyester resin and synthesized polyisocyanate were examined. The surface structure of powder coatings was investigated with confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM) equipped with energy dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS). The surface structure was correlated with the chemical structure of the coatings and macroscopic surface behavior: contact angle, surface free energy, gloss, abrasion and scratch resistance, hardness as well as adhesion to steel surface. [ABSTRACT FROM AUTHOR]

Highlights: [•] Silicone-acrylic core–shell dispersions were obtained by emulsion polymerization. [•] Core–shell structure of silicone-acrylic dispersion particles was confirmed by TEM. [•] Drying the dispersions led to nanopowders (agglomerated core–shell particles) – SEM. [•] Dispersion particle size, T g and swell ability depended on silicone core composition. [•] That phenomenon was explained by differences in degree of silicone resin crosslinking. [ABSTRACT FROM AUTHOR]

Highlights: [•] Prepared and characterized bio-based dimethyl-2,5-furandicarboxylate-based polyester resins. [•] Solvent-borne and powder coatings were prepared from the (co)polyester resins. [•] No influence of the coating preparation method on the mechanical properties of the coatings. [•] Coatings based on branched copolyester resins were hard and showed good solvent resistance. [Copyright &y& Elsevier]

Highlights: [•] Various particles are added into the polyester powder coatings via slurry method. [•] Mechanical and adhesion properties of nanocomposite powder coatings are studied. [•] Characterization results show successful silica nanoparticles dispersion. [•] Mechanical properties of powder coatings are enhanced by nanoparticles addition. [•] The extent of enhancing properties depends on the wt.% and size of particles. [ABSTRACT FROM AUTHOR]

Abstract: The role of the interface on the deformation response in scratch tests of epoxy-polyester films deposited by electrostatic spraying is investigated. A comparative study of the scratch deformation behaviour of films deposited on micro- and macro-corrugated rigid substrates and on ‘soft’ silicon sub-layers is made. Scratch deformation parameters were evaluated by contact gauge inductive profilometry, whilst morphological examinations of the residual scratch patterns were performed by electron microscopy. 3-Response models based on a 2-D and 3-D reconstruction of the scratch pattern during the application and after the release of the load were used to perform the deformation response analysis and calculate the key geometrical features of the residual scratch patterns. In particular, the influence on the residual scratch patterns of the applied loads, sliding speeds, contact geometries, and the test modes were looked into. [Copyright &y& Elsevier]

Abstract: In nanotechnology and nanoscience the development of hybrid (organic–inorganic) nanocompounds has attracted particular attention due to the significant improvement in the properties and the wide diversity of applications compared to conventional composites. In this study, formulations of commercial powder coatings were investigated with 2 and 4% (w/w) of montmorillonite (MMT) in the polyester resin matrix. The coatings were applied by electrostatic spraying on AISI 1008 carbon steel panels. The samples were characterized by TGA, DSC, XRD and TEM. The corrosion performance was evaluated using the salt spray test. Transmission electron microscopy revealed the presence of MMT in the coatings in the exfoliated form. The formulations with MMT presented better performance in terms of the corrosion protection properties. [Copyright &y& Elsevier]

Abstract: Metal-flake powder coatings are a special class of metallic paint finishes composed of two superimposed layers: a pigmented decorative base coat and an overlaying transparent protective top coat. In the present investigation, a novel curing procedure for such bilayer coatings is proposed. Flash IR pre-curing of the base coat promotes the formation of a surface diffusion barrier and limits movement of the decorative pigments and metal flakes around their initial positions. Oven baking after deposition of the top coat then completes curing of the bilayer coating. The influence of the IR intensity and irradiation time on the final properties of bilayer coatings was investigated. The visual appearance, surface morphology and scratch resistance were evaluated. Experimental findings revealed that the hybrid IR/oven baking curing procedure is a viable method for obtaining bilayer powder coatings with outstanding properties in a shorter processing time and with considerable energy savings. [Copyright &y& Elsevier]

Abstract: A key area driving developments in the powder coatings industry today is that of improved energy efficiency through reduction of cure temperature. The ability to cure at lower temperatures offers the dual benefit of both reduced energy use on application and broadening the appeal of powder coatings to include temperature sensitive substrates, such as MDF and plastics. One of the main challenges for low temperature curing powders is to have the ability to sufficiently flow and level at the reduced cure temperature in order to obtain a smooth final appearance while keeping good mechanical properties and powder stability. In order to facilitate and support development of such powder coatings, we have recently developed a unique method that allows determination of the sag and levelling behaviour of powder coatings in a quantitative manner. The use of this technique gives valuable insight into the influence of both experimental conditions as well as material properties on the flow and levelling behaviour of powder paints. Furthermore, we have developed a Flow–cure model allowing the quantitative prediction of the sag and levelling behaviour of powder coatings from their rheological and curing properties. Excellent agreement between prediction and experiments was found. [Copyright &y& Elsevier]

Abstract: Hybrid IR/convective oven baking of high quality industrial powder coatings is one of the most attractive method to achieve significant economic and process time savings. This method is based on two curing steps: at first, a pigmented decorative basecoat is electrostatically sprayed and, then, pre-cured with IR-radiation, secondly, a transparent protective topcoat is sprayed on the basecoat and the resulting bilayer coating is oven baked. The optimization of the IR pre-curing conditions and the correlation between the effect of polymerization degree of the basecoat and the wear resistance of the whole coating system are investigated. In particular, an experimental study in which the degree of chemical conversion of the pigmented basecoat, the overall coating morphology and its thermal, mechanical and tribological properties are analyzed in the light of IR-radiation time and power, has been carried out. Experimental results show that the intermediate range of curing time and IR power investigated leads to properly cured basecoats and subsequently to better morphological, mechanical and tribological behavior of the whole coating system. These results were also validated by comparison with the coatings cross-linked by the traditional two-step oven baking process. [Copyright &y& Elsevier]

Abstract: The present investigation analyzes the deformation behaviour under static and dynamic loading conditions of electrostatically sprayed epoxy-polyester powder coatings by local and uniaxial tests, trying to account for the separate contribution of the raw polymeric material alone and of the adhesion to the underlying metal substrate. First, thermo-rheological properties of the basic material (i.e., the thermosetting powder paints) were characterized by differential scanning calorimetry (DSC) and rheometry. Secondly, free-standing films were manufactured by electrostatic spraying of the thermosetting powders onto stainless steel substrates pre-coated with an intermediate layer of silicon-based heat curable release coating. The resulting free standing-films were macroscopically characterized by combined dynamic-mechanical analyses (DMA) and tensile tests. Finally, local mechanical characterization of the coating performance was carried out by micro-scale depth sensing scratch and indentation on coatings ‘free-standing’ and ‘rigidly adhering’ onto metal substrate. The experimental findings show the different mechanical behaviour of the polymeric coatings, whose thermal, rheological, dynamical properties were fully characterized, when deposited on untreated or pre-treated substrates as well as on intermediate layers of release coating, thus contributing to better understand how much of the coating properties are ascribable to the material chosen or to the interfacial adhesion between coating and substrate. [Copyright &y& Elsevier]

Abstract: The economy of high quality metal flakes powder coatings process is remarkably influenced by the curing procedure involving two cost and time consuming steps in convective oven. Significant savings can be achieved accelerating the baking process by IR pre-curing the outermost layers of the basecoat and following this with a conventional oven-baking of the whole coating system. In the present investigation, the IR pre-curing process of the basecoat was analyzed by studying the influence of the IR radiation intensity and exposure time on the adhesion strength and scratch resistance of the coating varying the contact load of the scratching indenter. [Copyright &y& Elsevier]

Abstract: Co- and terpolyesters based on 1,4:3,6-dianhydro-d-glucitol (isosorbide), 1,4:3,6-dianhydro-l-iditol (isoidide) and succinic acid were evaluated for their applicability in solvent-cast and powder coatings. These biobased polyesters have functionalities and T g values in the appropriate range for such applications and were cross-linked using conventional curing agents. Introduction of poly-functional monomers such as glycerol and citric acid led to coatings with enhanced performance with respect to mechanical and chemical resistance, compared to formulations based on linear polymers. The curing behavior of these systems was investigated with DSC and rheological experiments. Formulations containing citric acid-modified polyester resins showed rapid curing, probably facilitated by anhydride formation at the chain ends. Hydroxy- as well as carboxylic acid-functional 1,4:3,6-dianhydrohexitol-based polyesters proved to be suitable materials for coating applications with respect to solvent resistance, impact resistance and hardness, with performance comparable to commercially available systems. Accelerated weathering experiments showed that functional groups such as hydroxyl groups, carboxylic acids, anhydrides and peroxides are formed during UV-exposure. The weathered coatings have reduced impact stability. On the other hand, the appearance of the coatings does not change significantly. Isosorbide-based coating systems appear to have similar weathering resistance as conventional terephthalic acid-based poly(ester urethane) coatings. [Copyright &y& Elsevier]

Abstract: Electrostatic spray deposition (ESD) of aesthetic and protective low curable transparent powder coatings onto carbon fibre-reinforced epoxy composites (i.e., carbon laminates) is the matter of the present investigation. An original environment friendly pretreatment of the substrate, based on fluidized bed peening of glass beads followed by a moderate temperature oven baking, has been proposed. Then, the influence of ESD operational parameters on coating performance has been looked into. Design of experiments (DOE) was used to schedule the experimental trials. Coating thickness and its uniformity over the coated substrates upon curing was systematically evaluated. Further, visual appearance of the coatings was analyzed by both optical and stereoscopic microscopy. Finally, analysis of variance (ANOVA) was performed to model the available experimental data. Detailed examinations of the experimental results allowed to define the best settings of ESD process as well as the maximum deposition time before the occurrence of severe electrical breakdown in the powder layer and/or the increase in the incidence of massive back-ionization phenomena. Accordingly, 3D process maps of the coating thickness versus the operational parameters, applied voltage, feeding and auxiliary pressure, were developed, thus supporting the practitioners in their choices and in the identification of processing windows wide enough for practical purposes. [Copyright &y& Elsevier]

Abstract: The knowledge of the properties of the coatings in terms of scratch and wear resistance is of paramount importance in order to prevent the formation of severe damages. Nonetheless, dealing with the evaluation scratch or wear resistance of an organic coating can be troublesome. They can be strongly dependent on the status of the organic material as well as on the contact condition, applied load and strain rate. Besides, reliable responses cannot be achieved if an appropriate experimental design and a combined usage of proper equipments is not scheduled. In this respect, the present analysis deals with the application of variable speed and load scratch tests to characterize the scratch response and wear resistance of bilayer metal flakes powder coatings. Experimental findings allowed the achievement of consistent trends of the deformation response vs. curing temperature, scratch load and speed as well as their empirical modelling. This way, the overall scratch resistance of the bilayer coatings could be usefully predicted on a broad range of operational conditions, thus providing helpful indications to paint manufacturers and coaters on how to best deal with the application of metal flake powders. [Copyright &y& Elsevier]

Abstract: Polyester based powder coatings containing different types of aluminium metallic flake pigments have been investigated with respect to their chemical stability in acid environments. The metallic flakes are made chemically stable by covering them in silica. The degree of silica coverage and the silica morphology are far more important for the chemical stability of the pigments than the silica thickness. The acid resistance of the final powder coating is found to depend on the pigment embedment depth, on the chemical composition and morphology of the powder coating, and on the silica coating of the pigment. The latter being the single most important factor in our study. New chemical resistance tests have been developed. One for the testing of the metallic pigments alone before embedding the pigment in a coating, and another for the cured coating containing these pigments. Additionally TEM cross-sections have been used for investigating the quality of the silica coating on pigments, and optical absorption for comparison of pigment embedment depth. This approach to powder coating development emphasizing the measurement of the quality of each component separately has proven to be robust, reliable, and time and cost effective. By testing of separate components the need for time-consuming quality cheques of cured coatings is reduced while maintaining the ability to predict final paint properties. Further, the uncertainty related to testing many process parameters simultaneously is considerably reduced. [Copyright &y& Elsevier]

Abstract: The carboxyl group-containing acrylic resin for powder coatings can be obtained by succinic anhydride reacting with hydroxyl group-containing acrylic resin, which was prepared by radical copolymerization of methyl methacrylate (MMA), n-butyl methacrylate (BMA) and β-hydroxypropyl methacrylate (HPMA) using 2,2′-azobisisobutyronitrile (AIBN) as initiator in toluene solution. The influence of synthesis method, weight ratio of monomers, and the amount of succinic anhydride on carboxyl group-containing acrylic resin was investigated. The 1H NMR results reveal that carboxyl group was successfully attached to acrylic resins. The optimum monomer weight ratio is MMA:BMA:HPMA=65:20:15. The acid value of resin increases with the increasing of the amount of succinic anhydride, while the T g of resin decreases. [Copyright &y& Elsevier]

Abstract: This paper deals with the analysis of a multi-layer polymeric film made from a hybrid organic–inorganic bond-layer, a decorative epoxy-based basecoat and, finally, a protective polyurethane-based topcoat. The establishment of visual appearance and mechanical strength of the multi-layer polymeric films has been investigated by varying both baking time and temperature on a very wide range. Furthermore, two different two-step baking procedures (i.e., with and without full post-curing of the topcoat) were also proposed and comparatively evaluated. Improved trends of average roughness and mechanical strength of the multi-layer films were found at any time progressively higher baking time and/or temperature was set. Accordingly, the overall adhesion between multi-layer films and underlying metal surfaces was found to increase, as well. Nonetheless, experimental results show that even though satisfactory surface roughness and mechanical properties of the multi-layer films can be established over wide enough ranges of baking time and temperature with both baking procedures, an acceptable visual appearance is only achievable if the topcoat is superimposed at least on an almost fully cured basecoat. [Copyright &y& Elsevier]

Abstract: This study deals with the interrelation between the thermo-rheological behaviour of an epoxy-based powder coating system and its mechanical strength and wear endurance. Matte-finish protective polymeric films deposited by electrostatic fluidized bed (EFB) and conventional hot dipping fluidized bed (CHDFB) on metal substrates were examined. First, the analysis of thermo-rheological behaviour of the epoxy-based powder coating system was detailed. Secondly, the adhesion strength and wear endurance of polymeric films was related to the thermo-rheological behaviour of the starting material formulation. Finally, based on the experimental data, generalized scratch and wear map, in which the overall mechanical performance of the matte-finish polymeric films at different curing levels is reported, was usefully provided. The experimental findings lead to further advances in the understanding of the mechanisms involved in the establishment of the overall mechanical performances of fluidized bed (FB) deposited polymeric films. They also provide important indications for the settings of curing parameters or preheating temperatures in FB coating processes as well as for the development of new powder coating formulations. [Copyright &y& Elsevier]

Abstract: This study focuses on the correlation between the thermo-rheological properties of a thermosetting powder coating system with its surface structure build-up. Epoxy powder coating systems, which displayed surface matting and surface wrinkling, were examined. Firstly, the evolution of the complex viscosity was correlated with the cure kinetic. Secondly, the structure build-up on the surface of the coatings was investigated with a combined SEM-CLA profilometry analysis at different stages of curing process for both EFB and CHDFB coating processes. Different finishes were found to characterize the films applied by using EFB and CHDFB coating processes as a result of the different way the film is heated by. Finally, a strict relationship of film morphology to the degree of conversion and to the evolution of the complex viscosity was found out for both EFB and CHDFB coating processes. The surface structure is built up after gelation point and continues to evolve after gelation with a full development of the film fine structure. Differences were observed in the surface structure build-up when different curing temperature was used, thereby indicating an influence of minimum viscosity on achievable finishing. These experimental results lead to further advances in a better understanding of the formation of surface topography and morphology of polymeric films. They also provide important indications for the settings of curing parameters in both EFB and CHDFB coating processes as well as for the development of new powder coating formulations. [Copyright &y& Elsevier]

Abstract: A novel method for manufacturing powder coating through one step minisuspension polymerization is described. The conventional production of powder coating includes six steps—synthesizing resins, mixing the raw material, extrusion, cooling, pre-crushing and pulverization. Comparatively, the present method can simplify the complicated processes, reduce equipment and save energy. Before polymerization, the TiO2 particles were treated with a reactive silane coupling agent 3-methacryloxypropyltrimethoxysilane (MPTMS) to obtain enough compatibility with the monomers. The powder coating was directly synthesized through employing one step minisuspension polymerization in the presence of titanium dioxide white particles. The powder coating was characterized using Fourier transform infrared spectra (FT-IR) and thermogravimetric analysis (TGA). The results show that TiO2 particles and polymer are successfully linked up via MPTMS in the powder particles. The morphology of powder coatings produced via different methods was observed by scanning electron microscope (SEM). The powder coatings obtained from minisuspension polymerization consist of regular spherical morphology particles with narrow particle size distribution. The powder flowability and surface film smoothness were enhanced compared to the pulverization powder coating. [Copyright &y& Elsevier]

Abstract: Lowering the curing temperature for powder coatings is desirable with regard to the coating of temperature sensitive substrates. However, commercial available weather-resistant stable powder coatings need curing temperatures >180°C. The reactivity of various catalysts on the reaction between an uretdione cross-linker and OH groups were carried out on the basis of low molecular model systems. The results were transferred to polymeric systems consisting of the reactive components of a powder coating composition. The investigations were carried out using non-isothermal and isothermal DSC measurements as well as rheological measurements of the complex melt viscosity. However, the curing reaction occurred in a two-step reaction mechanism whereas the first reaction step could by quantitatively separated applying non-isothermal DSC measurements. [Copyright &y& Elsevier]

Abstract: In spite of obvious advantages of radiation curable powder coatings some of their physical and mechanical properties such as impact resistance, flexibility, hardness and tensile strength are poorer than thermally curable powder coatings. It is believed that UV-curable powder coatings containing interpenetrating polymer networks (IPNs) inherently have the ability to develop these properties. In the present study, two different UV curing systems (i.e. free radical and cationic types) were used in order to obtain the prospective IPNs. Interesting properties are to be found by these coatings founded in the different possible morphologies caused by phase separations. These modified radiation curable powder coatings showed significant improvements in the mechanical and physical properties of such powder coatings. [Copyright &y& Elsevier]

Abstract: The performance of powder coatings on hot-dip galvanized steel has been studied by testing in 5 years field exposure in marine and industrial atmospheres, as well as in accelerated tests. The aim was to assess the quality of such coating systems in corrosive environments and to establish criteria for how to obtain good quality. The test data demonstrates that polyester powder coatings are a good alternative to wet paint as top coat on hot-dip galvanized steel. The phosphate layer is identified as the most crucial step to ensure high quality. Recommendations for how to obtain good quality are provided. [Copyright &y& Elsevier]

Abstract: Thermosetting resins based on semi-crystalline poly(dimethyl trimethylene carbonate) (PDTC) were synthesised and characterised. Polymers with linear and branched architectures were synthesised through cationic ring opening polymerisation (CROP) of dimethyl trimethylene carbonate (DTC) using a series of polyols as initiators and fumaric acid as catalyst. The best powders were stable during storage at 45°C for one week and could subsequently form films at temperatures between 100 and 115°C. Functionalisation of the resins with methacrylic anhydride enabled curing by UV-initiated radical polymerisation. Rheology measurements showed that the architecture had a significant effect on the melt viscosity, which shows that the rheological properties can be tuned for use as low temperature curing powder coatings. [Copyright &y& Elsevier]

The curing behavior of a liquid crystalline oligoester (LCO), based on 4,4′-diacetoxybiphenyl and dodecanedioic acid, as a model resin for powder coatings, in presence of triglycidyl isocyanurate (TGIC), as a curing agent, was studied by isothermal differential scanning calorimetry (DSC). The analysis of isothermal data was performed using the model-free isoconversional method. Activation energy as a function of extent of conversion, α, has been calculated by the Friedman technique. It showed an ascending trend from about 133.7 kJ/mol, at α=0.1 to 177.2 kJ/mol, at α=0.4, then it reached approximately a constant value of about 150±5% kJ/mol in the range of 50–90%.The results indicated that the kinetic process does not follow a single-step curing reaction model. To verify the isothermal analysis result, we carried out further, non-isothermal differential scanning calorimetry and depolarizing transmittance measurements on the stoichiometric mixture of LCO/TGIC, at different heating rates. The results of these experiments exhibited that the kinetic process of the investigated system is strongly influenced by curing condition which alters the liquid crystalline state of the sample. [Copyright &y& Elsevier]

Blocking agent free polyurethane powder coating formulations are emission free and thus comply with the highest ecological requirements. In addition the resulting coatings exhibit an excellent performance in non-yellowing light-stable applications for exterior use. Essential component of the formulations is isophorone diisocyanate (IPDI)-uretdione, an internal blocked derivative of IPDI. For the first time it is now possible to identify each of the 10 isomers by 13C-NMR-spectroscopy. This opportunity leads to fundamental conclusions concerning the selectivity of IPDI in the uretdione generating step and the reactivity of the different uretdione isomers in the crosslinking reaction. Quantumchemical calculations confirm the experimental results. [Copyright &y& Elsevier]

The mechanism of action of benzoin as a degassing agent in powder coatings has been analyzed. The gas bubble shrinkage was monitored using a light microscope equipped with a hot stage. In the absence of benzoin, the air bubbles start to shrink very slowly as a result of a diffusion-controlled process. Because of the continuing cross-linking reaction and increase in the viscosity, the bubble shrinkage halts at elevated temperatures. Quite remarkably, we observed that in the presence of benzoin the process of bubble shrinkage is accelerated to such an extent that most air bubbles disappear before any significant increase in the viscosity occurs. This suggests that benzoin functions by accelerating the rate of bubble shrinkage. To analyze the mechanism of action of benzoin in detail, we studied the coating formulations using various techniques. X-ray diffraction in combination with deuterium NMR using labeled benzoin indicated that benzoin dissolves on a molecular level in polyester resin and becomes mobile above the glass transition temperature of the matrix. Mass spectroscopy experiments revealed that benzoin, in its oxidized form (benzil), starts to evaporate above 100 °C. At 200 °C more than 90% of the initial concentration of benzoin has evaporated from the coating. As was to be expected, the conversion of benzoin to benzil halted when the experiments were carried out in nitrogen. We postulated that the action of benzoin as a degassing agent is somehow related to its ability to oxidize in situ. This claim is substantiated by the results of bubble dissolution experiments using different gases such as oxygen and nitrogen. It is shown that in the presence of benzoin oxygen bubbles shrink much faster than air bubbles. On the other hand, the shrinkage of nitrogen bubbles is not affected by benzoin. Based on the above results, a two-step mechanism is proposed for the action of benzoin as a degassing agent. This mechanism has been successfully used as a guideline to identify alternative degassing agents with higher efficiency and fewer side-effects, such as less severe yellowing. [Copyright &y& Elsevier]

The effect of addition of conductive pigments like carbon blacks on the corrosion behavior of zinc-rich powder paints coated steel in artificial sea water was investigated. Open circuit potential measurements were used to characterize the cathodic protection ability and duration. Micro-Raman spectroscopy analysis was performed in order to identify the corrosion products and to follow the penetration of the solution inside the coatings.Two different effects were pointed out: an increase of the porosity induced by carbon addition and a galvanic action between zinc and carbon pigments. The performance of the powder coatings, strongly improved if the carbon amount is sufficient, was compared to the one reported for solvent-based zinc-rich paints. [Copyright &y& Elsevier]

Poly(2-vinylpyridine)-b-poly(ϵ-caprolactone) copolymers have been used as dispersants for TiO2 pigments in a polyester/TGIC powder coating. In coatings without TGIC, the block copolymer dispersants prevented the flocculation of the TiO2 pigments at typical curing temperatures, by the formation of a steric barrier around the pigment particles. Consequently, non-crosslinked powder coatings with high gloss and excellent flow were obtained. In the presence of TGIC, the dispersants were found to catalyse the crosslinking reaction, leading to powder coatings with lower gloss and poor levelling. By replacing the basic poly(2-vinylpyridine) anchor block of the dispersants with an acidic or neutral anchor group, this undesired effect may be avoided. Alternatively, the poly(2-vinylpyridine)-b-poly(ϵ-caprolactone) dispersants are expected to be of special benefit in powder coatings with alternative crosslinking mechanisms, such as UV curable powder coatings. [Copyright &y& Elsevier]

Using a rheometer coupled with an UV-light generator, the viscoelastic behaviour during the fast cure of star-branched polyester is investigated. The 32 arm star polymers consist of a hyperbranched polyester core, Boltorn™ and linear grafts of poly(ϵ-caprolactone) (degree of polymerisation: 20–52) with methacrylate end groups. The resins are crystalline and the melting points range from 34 to 50 °C; films can be formed and cured below 80 °C. The crossover of G′ and G″ was used as the gel point. The time to reach the gel point, a few seconds, increases linearly with molecular weight. [Copyright &y& Elsevier]

The method of the synthesis of blocked polyisocyanates (bPIC) used as a crosslinking agent for hydrophobic and low temperature curing powder coatings was developed. In the synthesis of polyisocyanates (PIC) isophorone diisocyanate, glycerine, xylitol, polyethylene glycol and polysiloxane KF-6000 as well as two different blocking agents, i.e. acetone oxime and butanone oxime were used. The chemical structure of the obtained blocked polyisocyanates was confirmed by IR and NMR spectroscopy and the molecular mass distribution was investigated using gel permeation chromatography (GPC). The thermal behavior and the deblocking process were investigated by means of TG, DSC and DMA. The obtained coatings were evaluated by performing the following tests: roughness, gloss, scratch resistance, hardness, adhesion to the steel and water contact angle. As part of this research, the hydrophobic and high scratch resistance coatings cured at 150 °C were developed. • The method of new blocked polyisocyanates synthesis for powder coatings was developed. • The influence of curing agent structure on coating curing process was described. • The deblocking process of PICs and thermal behavior of cured coatings were investigated. • The coatings cured at 150 °C characterized by high hydrophobicity and scratch resistance [ABSTRACT FROM AUTHOR]

Powder coating systems are becoming more and more popular due to their unique properties. Nowadays, the ecological aspect is important and powder systems meet the following requirements. Powder systems do not contain VOC, they are more productive than liquid systems. Modifications of old powder systems and development of new ones stem from the need to replace liquid systems and extend the application of powder systems. UV-curable powder coatings present some new possibilities for the curing of heat sensitive substrates and offers more advantages compared to thermally cured powder coatings. UV-curing can be performed at lower temperatures than possible by thermally activated systems. This paper reviews the most recent advances in the field of ultraviolet cured powder coatings. The selected chemical structures of the resins (unsaturated polyester, urethane acrylates, acrylate and methacrylate resins, epoxy oligomers, polyamides and hyperbranched polymers) photoinitiators and additives used in formulation of UV-curable powder coatings were presented. The physical properties and rheological behavior of the resin depending on their chemical structure, molecular weight, amorphous and crystalline structure as well as their influence on properties of crosslinked coatings were described. The curing conditions used in UV curing technology and its advantages such as fast curing and high efficiency, low capital investment, solvent elimination, low cost and energy consumption were also presented. • Recent advances in the field of UV cured powder coatings were reviewed. • Photoinitiators and reaction mechanisms during the UV curing process were described. • Curing process and polymers resin used for UV curing powder coatings were described. • The influence of curing condition on properties of crosslinked coatings was presented. [ABSTRACT FROM AUTHOR]

• Fully biobased functional polycarbonates were prepared by copolymerization of limonene oxide with CO 2. • The formation of TENs with high T g obtained by UV thiol-ene reactions was studied in-depth via real-time ATR-FTIR spectroscopy.. • DMTA analysis indicated a wide range of thermomechanical properties for the high T g films. • The biobased coatings using the polycarbonates as binders obtained by UV-powder coating revealed outstanding properties. The evaluation of poly(limonene carbonate)s (PLCs), derived from orange oils and carbon dioxide, as UV-curable (powder) coating binders is described. PLCs with moderate molecular weight were prepared by copolymerization of limonene oxide with CO 2 and a subsequent molecular weight reduction step by transcarbonation with 1,10-decanediol (1,10-DCD). These PLCs were cured with a trifunctional thiol monomer in the presence of a photoinitiator via thiol-ene chemistry to form poly(thioether-co-carbonate) networks. The UV curing of the resins following solvent casting was studied at 130 °C using ATR-FTIR, revealing a fast curing and a quick thiol-ene network (TEN) formation, realized by the addition reactions of thiol groups of the curing agent onto pendant isopropenyl groups of PLC. An ene addition enhanced by thiol-ene crosslinking was also observed, known as a 'cage effect', which was discovered for the first time in a UV-curable thiol-ene system. The efficient TEN formation was also evidenced by the high sol fractions in those UV-cured samples and their dynamic mechanical thermal analysis (DMTA). The DMTA results of these TENs showed high T g s (up to 125.9 °C) and a wide range of thermomechanical properties, including rubbery moduli from 4.4–27.5 MPa. The UV-cured powder coating employing PLCs as binders showed outstanding properties such as high transparency, good acetone resistance, high pencil hardness (H-2 H) and high König hardness (174−199 s), suggesting their potential as very promising biobased alternatives to conventional powder coating resins. [ABSTRACT FROM AUTHOR]

• Novel eco-friendly BaSO 4 /poly(toluidines and phenylenediamines) corrosion inhibitor composites were prepared by in-situ chemical oxidative polymerization of toluidines and phenylenediamines monomers in the presence of BaSO 4 filler. • The barium sulphate/ conducting polymer composite was characterized by FTIR, XRD, TGA, DSC, EDX, SEM and physico-mechanical properties. • The corrosion inhibitor composite was added by a fixed dose (2%) of the total powder coating epoxy composite. • The steel panels coated with powder coating formulations in absence and presence of the corrosion inhibitor composite were impregnated 1500 h in salt spray cabinet. • The coated steel panels containing the corrosion inhibitor composite showed high performance protection against corrosion, blistering and pitting as evidenced from the visual observations, electrochemical impedance spectroscopy and poteniodynamic polarization. This study presents new smart eco-friendly and environmentally acceptable conducting polymer composites. These composites represent high efficient anti-corrosive coatings based on (toluidines and phenylenediamines) /BaSO 4 polymer composites for steel protection. These polymer composites were prepared by in-situ chemical oxidative polymerization of (ortho, meta or para) toluidines and phenylenediamines monomers each alone in the presence of BaSO 4 extender pigment. The polymerization process was carried out using ammonium peroxydisulphate as an initiator at 0-5 °C. The prepared composites were characterized using spectrophotometric measurements (FTIR, XRD, EDX, SEM), in addition to thermal analysis (DSC & TGA). Small doses of these composites (not exceed 2%) were incorporated into powder coating formulations. The coating formulations including the (toluidines or phenylenediamines / BaSO 4) polymer composites were evaluated as corrosion inhibitors. The coated steel panels were examined in a salt spray cabinet for 1500 h with a continuous follow up every 200-300 h. The coating formulations containing conducting polymer/BaSO 4 composites achieved impressive and high performance effect in protecting steel panels from corrosion compared with the blank sample. Moreover, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization results also confirmed the high performance corrosion protection properties of polyester/epoxy/conducting polymers/BaSO 4 hybrid composites. [ABSTRACT FROM AUTHOR]

• Two methods of the modification of PU powder clear coatings by means of MWCNTs was proposed. • The good dispersion of MWCNTs in powder coatings was confirmed by TEM microscopy. • An improvement in the electrical conductivity and corrosion resistance of modified coatings was observed. In this work, two dispersing methods of multiwalled carbon nanotubes (MWCNTs) in polyurethane powder clear coatings based on a polyester resin and a blocked polyisocyanate were developed. TEM micrographs confirmed that additional sonication of MWCNTs in the polyester resin (before extrusion of the coatings) causes significantly better dispersion of the nanofiller in a polyurethane matrix in relation to a simple prepared without the sonification stage. Several properties of cured coatings were investigated such as roughness, gloss, adhesion to steel surface, cupping, hardness, scratch resistance, water contact angle, surface resistivity and corrosion resistance. The obtained results indicated that the water contact angle, electrical conductivity and the corrosion resistance of the PU coating were increased by the MWCNTs addition. [ABSTRACT FROM AUTHOR]