Method for the evaluation of the degree of pigment dispersion in powder coatings

The quantitative method for the evaluation of the degree of pigment dispersion in powder coatings is described here. The quantitative information is obtained using selective oxygen plasma etching, scanning electron micrography and image analysis. This procedure was used in order to analyse the influences of the input power of the extrusion equipment on the pigment dispersion in powder coatings. The correlation between the particle size distribution graphs and the energy input during the extrusion process is discussed and compared to the colorimetric analysis.     

Functional coatings for anti-biofouling applications by surface segregation of block copolymer additives

Temperature responsive or bactericidal coatings with poly(n-butyl methacrylate) (PBMA) as bulk material and surface segregated poly(n-butyl acrylate)-block-poly-(N-isopropylacrylamide) (PBA-b-PNIPAAm) or poly(n-butyl acrylate)-block-quaternized poly(2-(dimethylamino)ethyl methacrylate) (PBA-b-PDMAEMAq) as additive were prepared via sequential solvent evaporation of polymer solutions in a solvent mixture. The degree of enrichment at the air surface of the coating and the functionality were examined for different molecular weight additives with different block ratios obtained via Atom Transfer Radical Polymerization (ATRP). The design of the block copolymers with an anchor block (PBA) which is compatible with the bulk polymer (PBMA) and water-compatible functional blocks (PNIPAAm and PDMAEMAq) along with the selection of suited solvent mixtures based on pre-estimation of the selective solubility and sequential evaporation via the Hansen solubility parameters and vapor pressures, respectively, were found to work very well. A small fraction of water in the solvent mixture had been crucial to obtain surface segregation of the functional block, e.g., a PNIPAAm surface with temperature-switchable wettability. Reversible temperature dependent wettability and long term stability of the functionalization, based on contact angle data, were obtained for an optimized PBA-b-PNIPAAm additive. Surface charge density, estimated from dye binding and zeta potential measurements, and killing efficiency against Staphylococcus aureus were investigated for PBA-b-PDMAEMAq as additive. Both block copolymer additives were found to dominate the surface properties and the functionality of the PBMA coating.     

Improving pigment dispersing in powder coatings with block copolymer dispersants

The effect of three block copolymer dispersants with a poly(2-vinylpyridine) anchor block and a poly(ɛ-caprolactone) buoy block on the dispersing of TiO₂ pigments in a polyester powder coating has been studied with digital image analysis on scanning electron micrographs. The mixing in a lab-scale extruder resulted in a virtually complete break-up of the pigment agglomerates. The average TiO₂ particle size was only slightly reduced after further treatment of the TiO₂ pigments with any dispersant. However, a significant change in the colloidal stability of the dispersions was observed. Without dispersants, the pigments reagglomerated when heated to 200°C and 235°C. This reagglomeration was completely suppressed by the use of dispersants, as a result of a steric layer around the TiO₂ particles. Based on a presentation given at the 26th International Waterborne, High-Solids, and Powder Coatings Symposium, on February 10–12, 1999, in New Orleans, LA. Laboratory of Polymer Chemistry and Coatings Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.     

Mechanism of action of benzoin as a degassing agent in powder coatings

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.     

Enabling nanotechnology with self assembled block copolymer patterns

Block copolymers (BCPs) have received great attention for the past 40 years but only within the past decade have they been seriously considered for nanotechnological applications. Their applicability to nanotechnology stems from the scale of the microdomains and the convenient tunability of size, shape, and periodicity afforded by changing their molecular parameters. The use of the tensorial physical properties of BCPs in such areas as transport, mechanical, electrical, and optical properties will provide substantial benefits in the future. In this review article, we first focus on the current efforts to utilize BCPs in nanotechnologies including nanostructured membranes, BCP templates for nanoparticle synthesis, photonic crystals, and high-density information storage media. In order to realize these applications, control over microdomain spatial and orientational order is paramount. This article reviews various methods to control BCP microdomain structures in the bulk state as well as in thin films. A variety of biases such as mechanical flow fields, electric fields, temperature gradients, and surface interactions can manipulate the microstructures of BCPs. A particular emphasis is made on two approaches, epitaxy and graphoepitaxy, and their combinations. Manipulation of BCP microdomain structures employing multiple external fields promises realization of many potential nanotechnological applications.     

Time and cost effective methods for testing chemical resistance of aluminium metallic pigmented powder coatings

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.     

Self-assembly of block copolymer complexes in organic solvents

Micelles have been prepared by mixing poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) copolymers and poly(acrylic acid) (PAA) homopolymers in organic solvents. Complexation via hydrogen bonding occurs between the P4VP and PAA blocks. Further aggregation of the accordingly formed complexes results in micelles stabilized by a corona of PS blocks. The influence of the relative lengths of the different blocks and of the quality of the solvent towards the complexes on the micellar characteristic features is studied. Soluble, non-aggregating, complexes have been observed in DMF, provided that the complexes are sufficiently small. In all other cases, the complexes were insoluble and aggregated in micelles. The size of those micelles depends strongly on the length of the P4VP blocks but only weakly on the PAA length.     

Structure and phase transition in thin films of block copolymer micelles complexed with inorganic precursors

Block copolymer micelle can be used as nano-reactor where separated domains serve as a compartment for the production of nanomaterials, ultimately creating nanocomposite materials. In this work, thin nanocomposite films generated from polystyrene-b-poly(acrylic acid) (PS-b-PAA) micellar solution in which small amount of inorganic precursor was added were investigated. The films were prepared by spin coating onto silicon substrate, and then solvent-annealed. As-spun films exhibit typical micellar structure with spherical shape along which inorganic nanoparticles are dispersed. Such morphology remains unchanged after solvent annealing for micellar films with small amount of inorganic precursor. However, further increase in the amount of inorganic precursors brings about the morphological changes, producing different organization of inorganic nanoparticles in composite films. This behavior was found to strongly depend on the types of precursors and solvents used for annealing. These results illustrate a simple yet useful route to generate the polymeric nanocomposites with diverse structure and composition.     

Carboxybetaine,sulfobetaine, and cationic block copolymer coatings: A comparison of the surface properties and antibiofouling behavior

Two different zwitterionic block copolymers (BCs) and a cationic BC were synthesized from the same BC precursor, which consisted of a polystyrene (PS) block and a poly[N‐(3‐dimethylamino‐1‐propyl)acrylamide] block. The zwitterionic BCs contained the dimethylammonioacetate (carboxybetaine) and dimethylammoniopropyl sulfonate (sulfobetaine) groups. Thin films cast from these polymers were investigated for surface wettability, surface charge, and protein adsorption. Surface‐energy parameters calculated with advancing contact angle (θ_a) and receding contact angle (θ_r) of different probe liquids showed that it was θ_r and not θ_a that was representative of the polar/ionic groups in the near‐surface regions of the coatings. Electrophoretic mobility was used to characterize the influence of pH on the net surface charge. In aqueous dispersions, the carboxybetaine polymer showed an ampholyte behavior with an isoelectric point of 6, whereas the sulfobetaine polymer was found to be anionic at all pH values between 2 and 10. Protein adsorption on the carboxybetaine BC was relatively independent of the net charges on the protein or the polymer, but the negatively charged sulfobetaine polymer showed a higher adsorption of positively charged protein molecules. Regardless of the net protein charge, both zwitterionic coatings adsorbed less protein compared to the PS and poly(2,3,4,5,6‐pentafluorostyrene) controls. The sulfobetaine and cationic BCs adsorbed higher amounts of oppositely charged protein molecules than like‐charged protein molecules. However, the adsorption of oppositely charged protein was much higher on the cationic surface than on the sulfobetaine surface. The zwitterionic BCs, particularly the carboxybetaine polymer, from this article are expected to function as stable, low‐fouling surface modifiers in different biological environments. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Polyester-based powder coatings with montmorillonite nanoparticles applied on carbon steel

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.     

Reduced graphene oxide suspension with a comb copolymer and its effects on the corrosion resistance of hydroxyl polyacrylate coatings

A comb copolymer (CC) is designed and prepared in present article, by grafting epoxy resin (E-20) on poly(styrene-co-acrylate). The CC is used as a special dispersant, which leads to a stabilizable reduced graphene oxide (rGO) suspension in organic coatings. The dispersing mechanism is deduced as π-π attraction between CC and rGO, which is supported by the analysis data of Fourier transform infrared (FTIR) spectra, Raman spectroscopy, scanning electron microscope, transmission electron microscope, and X-ray photoelectron spectroscopy. The corrosion resistance of CG suspension is determined by electrochemical impedance spectroscopy, the results implies that the anti-corrosion behavior performed obviously, and protective efficiency is up to 99.53% in Tafel analysis. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48898.     

Molybdate‐doped copolymer coatings for corrosion prevention of stainless steel

The polypyrrole and polyaniline copolymer coating (PPy‐PAni) and PPy‐PAni doped with sodium molybdate copolymer coating ( ) were synthesized on stainless steel by cyclic voltammetry. The effect of molybdate on the passivation of stainless steel was investigated by linear sweep voltammetry in 0.2 mol L^?1 of oxalic acid. The corrosion prevention performances of these copolymer coatings for stainless steel were investigated by linear sweep voltammetry, electrochemical impedance spectroscopy in 1 mol L^?1 of sulfuric acid, and potentiodynamic polarization in 0.1 mol L^?1 of hydrochloric acid. Copolymer coating doped with molybdate could accelerate the formation of the passive oxide film and have better corrosion prevention efficiencies than PPy‐PAni coating on stainless steel. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40602.     

Flash IR pre-curing of the decorative layer in metal-flake powder coatings

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.     

Microstructure and performance of block copolymer modified epoxy coatings

The effects of two diblock copolymers, poly(ethylene-alt-propylene)-b-poly(ethylene oxide) (PEP–PEO) and poly(1,2-butadiene)-b-poly(2-vinyl pyridine) (PB–P2VP) on the mechanical properties of epoxy coatings were studied. Both modifiers self-assembled into spherical micelles of 10–20 nm diameter in cured bulk epoxy. This morphology was preserved in 15 μm thick coatings; however, micelle segregation to the coating/substrate interface was also observed. The critical strain energy release rate, G_1c, of bulk thermosets was enhanced by up to fivefold with the addition of block copolymers. Likewise, the abrasive wear resistance of thin coatings increased with modifier inclusion. The results showed that at 5 wt.% of loading, block copolymers were able to impart a 40% increase in abrasive wear resistance to modified coatings over neat ones. Block copolymer modifiers did not sacrifice the modulus and glass transition temperature of bulk thermosets and coatings, or the hardness and transparency of coatings.     

Small-angle neutron scattering measurement of block copolymer interphase structure

The notion of an interfacial layer at the domain boundary in block copolymers is reviewed and the possibility of its measurement by small-angle X-ray and small angle neutron scattering discussed. Values of the interfacial layer thickness and its volume fraction have been obtained for a range of styrene-isoprene copolymers. Interfacial layer thickness is not strongly dependent on molecular weight whilst the volume fraction shows a dependence more in line with the theory of Helfand.     

Effects of IR pre-curing conditions on wear resistance of metal flake powder coatings

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.     

Chain extension and block copolymer synthesis using silane radical atom abstraction coupled with nitroxide mediated polymerization

Silane radicals were used to abstract bromine termini from monobrominated polystyrene (PStBr) in the presence of excess monomer and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), generating polymer radicals that underwent chain extension. Typically, 70-85% of the PStBr precursors were activated by silane radical atom abstraction (SRAA) and were elongated by nitroxide mediated polymerization (NMP), shifting to higher number-average molecular weight (M_n) values as observed by gel permeation chromatography (GPC). Chain extension did not occur until the temperature was elevated to 130 °C, with no increase in M_n values observed when the reaction was held at 80 °C, which is the temperature of the SRAA phase. The NMP phase of the reaction showed a linear correlation between M_n values and monomer consumption, along with first order kinetics with respect to styrene. SRAA/NMP was then applied to the synthesis of polystyrene-b-poly(n-butyl acrylate) and polystyrene-b-poly(p-methylstyrene), with analysis by GPC indicating the formation of block copolymers with a similar amount of unreacted PStBr remaining. Quantitative activation and elongation of the polymer precursors were prevented due to the ability of both the t-butoxy radicals and tris(trimethylsilyl)silane radicals to add across monomeric double bonds, competing with atom abstraction. Reactions were thus performed in which the monomer was added only after the transition to the higher temperature, which resulted in improved activation of the PStBr.     

Scratch resistance of ‘fast-cured’ metal flake powder coatings

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.     

A novel approach to the preparation of powder coating—Manufacture of polyacrylate powder coatings via one step minisuspension polymerization

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.