Inorganic precursor peroxides for antifouling coatings

Modern antifouling coatings are generally based on cuprous oxide (Cu₂O) and organic biocides as active ingredients. Cu₂O is prone to bioaccumulation, and should therefore be replaced by more environmentally benign compounds when technically possible. However, cuprous oxide does not only provide antifouling properties, it is also a vital ingredient for the antifouling coating to obtain its polishing and leaching mechanism. In this paper, peroxides of strontium, calcium, magnesium, and zinc are tested as pigments in antifouling coatings. The peroxides react with seawater to create hydrogen peroxide and highly seawater-soluble ions of the metal. The goals have been to establish the antifouling potency of an antifouling coating that releases hydrogen peroxide as biocide, and to investigate the potential use of peroxides as water-soluble polishing and leaching pigments. The investigations have shown that it is possible to identify particulates that, when applied as pigments in antifouling coatings, will provide polishing and leaching rates comparable to those of Cu₂O-based coatings. Furthermore, the combination of polishing and hydrogen peroxide leaching by a coating based on zinc peroxide in a suitable binder matrix provides antifouling properties exceeding those of a similar coating based entirely on zinc oxide.     

Replacement of traditional seawater-soluble pigments by starch and hydrolytic enzymes in polishing antifouling coatings

The use of starch and hydrolytic enzymes as replacement for traditional polishing pigments (e.g., Cu₂O and ZnO) in antifouling coatings has been investigated. The enzymes facilitate a slow conversion of water-insoluble starch into water-soluble glucose, and dissolution of glucose causes the development of a leached (porous) layer in the wetted, outermost part of the coating. Subsequent water–binder interaction at the pore walls gives rise to polishing, in a manner similar to that of conventional antifouling coatings. Different starch types have been evaluated and classified as potential coating ingredients, and the impact of the addition of starch on the functional properties of the coating is described. Starches from rice, corn, and tapioca have been tested, and due to a smaller amount of water-soluble content and lesser tendency to agglomerate, corn starch is preferred. Leaching occurs in all the starch-enzyme coatings tested; however, polishing is only detected for two out of four binder systems investigated. Suitable polishing rates of 7–10 μm/month, based on the enzymatic starch-degradation, have been measured. Controls containing only starch (no enzyme) did not polish.     

Dissolution rate measurements of sea water soluble pigments for antifouling paints: ZnO

The dissolution of soluble pigments from both tin-based and tin-free chemically active antifouling (AF) paints is a key process influencing their polishing and biocide leaching rates. In this context, a low time- and resources-consuming method capable of screening the pigment behaviour in the search for the most promising materials or mixtures is of great interest. A preliminary attempt to develop such a method is presented in this paper based on the widely used ZnO pigments.

While highly pure, nano-polished, monocrystalline ZnO substrates yielded very low dissolution rates in the order of 17.3 ± 3.7 μg Zn²⁺ cm⁻² day⁻¹, pellets prepared by compacting and sintering technical grade ZnO pigments dissolved about three times faster according to inductively-coupled plasma mass spectrometry (ICP-MS) measurements. The rougher and more porous surface exposed, together with the larger number of defects in the lattice structure, are hypothesised to be responsible for the faster sea water attack of the pellets compared to the ZnO crystals. In any case, the ZnO dissolution rates reported in this paper are markedly lower than those associated with the sea water dissolution of cuprous oxide (Cu₂O) particles which are also used in AF paints. Experimental performance testing of model antifouling paints formulated with ZnO and/or Cu₂O demonstrates that the binder/pigment interaction should not be disregarded if the leaching of sea water soluble pigments from paint systems is to be determined.     

Use of poly(2-vinylpyridine)-b-poly(?-caprolactone) copolymers as pigment stabilizers in powder coatings

Four poly(2-vinylpyridine)-b-poly(ɛ-caprolactone) copolymers, differing in buoy block length and anchor/buoy block length ratio, have been used as TiO₂ pigment dispersants in a polyester powder coating resin. When the TiO₂ surface was fully covered with the block copolymers, the colloidal stability of the TiO₂ dispersions at typical curing temperatures was significantly improved because of the formation of a steric layer around the pigment particles. As a result, powder coatings with excellent flow, high gloss, and low haze values were obtained. Because of the high affinity of the dispersants for the TiO₂ surface, pretreatment of the pigments with the block copolymers was not necessary. At full pigment surface coverage, the chain length of the stabilizing polymer had little effect on the performance of the dispersants used. Dept. of Polymer Chemistry and Coatings Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.     

Study on electrochemical behavior of Nano‐ZnO modified alkyd‐based waterborne coatings

A nano‐composite coating was formed using nano‐ZnO as pigment in different concentrations, to a specially developed alkyd‐based waterborne coating. The nano‐ZnO modified composite coatings were applied on mild steel substrate by dipping. The dispersion of nano‐ZnO particles in coating system was investigated by scanning electron microscopic and atomic force microscopic techniques. The effect of the addition of these nano‐pigments on the electrochemical behavior of the coating was investigated in 3.5% NaCl solution, using electrochemical impedance spectroscopy. Coating modified with higher concentration of nano‐ZnO particles showed comparatively better performance as was evident from the pore resistance (R_po) and coating capacitance (C_c) values after 30 days of exposure. In general, the study showed an improvement in the corrosion resistance of the nano‐particle modified coatings as compared with the neat coating, confirming the positive effect of nano‐particle addition in coatings. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Plasma-sprayed TiO2 coatings: Hydrophobicity enhanced by ZnO additions

Titanium dioxide (TiO₂) powder mixed individually with 10 and 30 weight percentage (wt%) ZnO was thermally sprayed onto a grade B API 5 L carbon steel substrate by atmospheric plasma spraying. The effect of the addition of ZnO (10 wt% and 30 wt%) on the microstructures and wettability properties of the TiO₂/ZnO coatings was investigated. The characterization of the coatings was carried out using scanning electron microscopy, X-ray diffraction (XRD), laser confocal microscope, and sessile droplet system. The XRD analysis of the coating revealed that the anatase phase of TiO₂ in the powder state transformed into rutile phases for the produced TiO₂/ZnO coatings. Surface microstructure analysis revealed that the coatings had typical micro-roughened surfaces of plasma spraying products. The coating with 30 wt% ZnO produced a coating with remarkable pores and microcracks compared with the TiO₂ coating and coating with 10 wt% ZnO. Additionally, the increase in the wt% of ZnO increased the surface roughness value of the produced coatings and substantially changed the wettability properties of the TiO₂ coating from hydrophilic to hydrophobic.     

Characterization of absorptivities to solar radiation for colored pigments in coatings

Colored pigments absorptivities to solar radiation have been characterized quantitatively by measuring the absorption coefficients of the colored pigments mixed in white titanium dioxide standard coating. The standard coating contains white TiO₂ with 17% pigment volume concentration (PVC). Dry white coating with more than 134 μm thickness is opaque and used as a dispersion medium for colored pigments. The reflectances of the coatings of white TiO₂ and three kinds of colored pigments (perylene black, toluidine red, and benzidine yellow) to solar radiation are measured by means of a UV-3100 recording spectrophotometer operating in the 250∼2500 nm spectral range. It is found that the plots of lg 1/R (R, reflectance of coating to solar radiation) againstV _coloredV_{Ti0 2} (volume ratio of the colored pigment to TiO₂ in coating) are straight lines of increasing slopes in the range ofV _coloredV_{Ti0 2} less than five percent. From the slopes of the straight lines, the absorption coefficients of colored pigments can be measured quantitatively. Beijing, 100029, China. Email: guohy@public.fhnet.cn.net.     

Effects of size, shape and floatage of Cu particles on the low infrared emissivity coatings

Low infrared emissivity coating was prepared by the copper (Cu) particles and ethylene–propylene–diene monomer (EPDM) binder. The effect of size, shape and floatage of Cu particles on infrared emissivity of the coatings was systematically investigated. The results indicated that the optimized Cu particles with the minimum coating emissivity are several micron-sized, flaky and high-leafing, exhibiting 0.78, 0.72 and 0.10 emissivity value, respectively. The formation of low infrared emissivity coatings depends strongly on the floatage of Cu particles, not the size or shape, and the results obtained by leafing aluminum (Al) and bismuth oxide (Bi₂O₃) pigment are in good agreement with this standpoint. A theoretical model was proposed to account for the mechanism, which indicated that the low porosity of the coatings with leafing pigments plays an important role in the formation of low emissivity coatings.     

The depth profiling of TiO2 pigmented coil coatings using step scan phase modulation photoacoustic FTIR

The depth distribution of a TiO₂ pigment within the polyurethane (PU) coil coatings is investigated using step scan phase modulation photoacoustic (SS-PM-PA) FTIR. Coil coatings with different pigment contents were prepared and the modulation frequency (MF) of the SS-PM-PA FTIR varied to record the depth distribution of the pigment within the coating. The TiO₂ pigment was shown to contribute significantly to the SS-PM-PA FTIR signal. A TiO₂ aggregated region within the topcoat is found close to the topcoat-primer interface and further away from the topcoat surface. A deeper TiO₂ aggregated region can be identified when pigment content is relatively low. The SS-PM-PA FTIR signal shows a considerable contribution from the primer originated signal, provided the TiO₂ pigment content is sufficiently high and the modulation frequency applied is relatively low. SEM cross-section imaging results show a strong correlation of the TiO₂ depth distribution with SS-PM-PA FTIR results, which confirms the applicability of the SS-PM-PA FTIR technique to the depth profiling study of TiO₂ pigmented coil coatings.     

Synthesis and Characterization of Anti-fungus,Anti-corrosion and Self-cleaning Hybrid Nanocomposite Coatings Based on Sol–Gel Process

Anti-corrosion, anti-fungus, and self-cleaning properties of coatings containing ZnO–TiO₂, SiO₂–TiO₂ and SiO₂/TiO₂/ZnO nanoparticles synthesized based on sol–gel precursors using tetra methoxysilane, 3-glycidoxypropyl trimethoxysilane, tetra (n-butyl orthotitanate) and zinc acetate dihydrate were investigated by FESEM, EDAX and TEM analyses. Results indicated uniform dispersion of inorganic nanoparticles in the range of 20–40 nm in size. Anti-corrosion property of the hybrid coating was characterized by EIS measurements and parametrically analyzed in an equivalent circuit when the coating was exposed to salt solution. Results showed that, ZnO and TiO₂ nanoparticles enhance anti-corrosion property of the hybrid coatings. Anti-fungus and anti-bacterial properties of the coatings were determined by diameter of inhibition zone and inhabitation of bacterial growth, respectively. The coating containing ZnO and TiO₂ nanoparticles showed anti-fungus and anti-bacterial properties which were related to their photocatalytic properties. Degradation of methylene blue in aqueous solution was determined by UV–Visible tests which indicated self-cleaning property of the coatings containing ZnO and TiO₂ nanoparticles.     

Low surface energy self-polishing polymer grafted MWNTs for antibacterial coating and controlled-release property of Cu2O

Marine biofouling had been a headache when engaging in marine activities. The most effective and convenient method for dealing with this problem was to apply antifouling coatings. But now a single anti-fouling system was hard to satisfy the requirement of anti-fouling simultaneously. Therefore, it was particularly important to develop novel multi-system anti-fouling technology. In the work, a novel polymer coatings with polydimethylsiloxane (PDMS) segments in the main chain and hydrolysable side chain was designed and synthesized which showed low surface energy and self-polishing performance, and then we creatively covalently immobilized the polyurethane on the surface of multi-carbon nanotubes (MWNTs) to form multisystem antifouling coating. The results showed that the polymer coating would produce hydrolysable regions in the hydrophobic PDMS segment to endure the polymer coating hydrophobic and hydrolysis properties when contacted with water. In addition, the self-polishing rate and the surface energy could be regulated by varying its copolymerization, and the addition of MWNTs could kill the microorganisms and endowed the polymer coating itself enhanced antibacterial effect. Furthermore, considering the high specific surface area and physicochemical characteristics of MWNTs, it could be combined with antifoulant Cu₂O through a polar or non-polar combination as a carrier to control the release rate of Cu₂O in coatings.     

Preparation of electrochromic Ni1−xO and TiO2 coatings from pigment dispersions and their application in electrochromic foil based devices

Thin (100–400 nm) electrochromic TiO₂ and Ni_1−xO coatings providing transmissive light modulation were made from an anatase pigment dispersion obtained by co-grinding nanocrystalline titanium particles (6–10 nm in size) with trisilanol heptaisobutylsilsesquioxane as dispersant, while Ni_1−xO based pigment dispersions were made by milling pre-prepared Ni_1−xO pigment with nickel oxyhydroxide (NiO_xH_y) dispersant. Dispersions were obtained by milling the pigments with zirconia beads of various sizes (0.1, 0.2 and 0.4 mm) and the particle size was determined with the dynamic light scattering technique (DLS). Pigment dispersions were deposited by spin-coating on glass and plastic (PET) film and thermally treated at 150 °C to obtain thin TiO₂ and Ni_1−xO pigment coatings. SEM and AFM were used for determination of the surface morphology, revealing their homogenous structure and low surface roughness (up to 20 nm). The optical transmittance and haze of the coatings deposited on glass and PET film were determined from the UV–vis spectra. Their electrochromic effect was analyzed by electrochemical charging/discharging the coatings in a LiClO₄/PC electrolyte. The results demonstrated a convenient, simple and robust technique for making “electrochromic paint” coatings. Pre-prepared TiO₂ and pigments were used for construction of foil-based electrochromic devices with transmissive modulation of light.     

Engineering an ultrathin amorphous TiO2 layer for boosting the weatherability of TiO2 pigment with high lightening power

TiO₂ pigments are typically coated with inert layers to suppress the photocatalytic activity and improve the weatherability. However, the traditional inert layers have a lower refractive index compared to TiO₂, and therefore reduce the lightening power of TiO₂. In the present work, a uniform, amorphous, 2.9-nm-thick TiO₂ protective layer was deposited onto the surface of anatase TiO₂ pigments according to pulsed chemical vapor deposition at room temperature, with TiCl₄ as titanium precursor. Amorphous TiO₂ coating layers exhibited poor photocatalytic activity, leading to a boosted weatherability. Similarly, this coating method is also effective for TiO₂ coating with amorphous SiO₂ and SnO₂ layers. However, the lightening power of amorphous TiO₂ layer is higher than those of amorphous SiO₂ and SnO₂ layers. According to the measurements of photoluminescence lifetime, surface photocurrent density, charge-transfer resistance, and electron spin resonance spectroscopy, it is revealed that the amorphous layer can prevent the migration of photogenerated electrons and holes onto the surface, decreasing the densities of surface electron and hole, and thereby suppress the photocatalytic activity.     

The effect of TiO2, pigmentation on the hydrolysis of amino resin crosslinked epoxy can coatings

Pigmented (TiO₂), amino resin crosslinked coatings, designed for applications in can coatings’ internal lacquers, were formulated, characterized, applied, and cured. Three grades of a pigmentary form of TiO₂ were characterized in terms of their particle size, their particle morphology, their zeta potential, and their moisture retention behavior. Epoxy coatings that were crosslinked using one of several, different amino crosslinkers were prepared. The effect of the presence of the TiO₂ pigments on the hydrolysis of the cured coatings was monitored via the controlled retorting of the coatings. The different grades of TiO₂ pigment were selected, to establish whether or not they could be used interchangeably with respect to hydrolysis and to melamine release. Also, the effects of the aging of the fluid coatings on the amount of melamine released from the coatings (after curing and retorting) were monitored. Storage under laboratory conditions for 2, 20, and 40 weeks was used for this purpose. The TiO₂ pigment contributed significantly to the hydrolysis behavior of the epoxy coatings in that their presence substantially reduced the amount of melamine released and the extent of crosslinker hydrolysis. Typical results show that excluding the TiO₂ pigment particles from the formulation results in there being 50% more hydrolysis of the crosslinker to melamine. With respect to the melamine release and crosslinker hydrolysis, the different grades of the pigment gave similar results.     

TiO2/ZnO double-layer broadband antireflective and down-shifting coatings for solar applications

Making full use of sunlight in solar cells requires reducing the reflection of light and minimizing spectral mismatch. Here, a TiO₂/ZnO double-layer coating with both wider band antireflection and down-shifting performance was prepared. TiO₂ sols and ZnO nanoparticles were synthesized via the sol-gel method and then successively coated on the surface of the Si substrate by dip-coating. Computational simulations were used to obtain the optimal refractive index and thickness of the coatings. In the experiments, the thicknesses of the TiO₂ and ZnO coatings were adjusted by changing the lifting speed, and the refractive index of the TiO₂ and ZnO coatings were adjusted by adding the porosity inducing agent and varying the concentration of the solution. The TiO₂/ZnO coating reduces the reflectivity of the silicon substrate by 24.97% in the 400–1100 nm band, and the ZnO nanoparticles can convert light at approximately 345 nm–527 nm, reducing the spectral mismatch of the solar cell. The photocurrent of solar cells coated with TiO₂/ZnO coatings was markedly improved, with an increase of 29% in the average photocurrent at 300–800 nm. Herein, TiO₂/ZnO coatings have the potential to benefit the development of multifunctional coatings that are important for improving the efficiency of solar cells.     

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.     

Urushiol titanium polymer-based composites coatings for anti-corrosion and antifouling in marine spray splash zones

Seawater is highly corrosive, and the alternating dry and wet environment can cause severe corrosion in metal equipment. Moreover, marine equipment is also seriously affected by marine biofouling. These harsh conditions pose a serious threat to the integrity of marine equipment as well as their associated maritime activities and necessitate the development of effective coatings to minimize damage to the equipment. Urushiol titanium polymer/acrylic resin (UTP/AR) composite materials were developed. Then, marine anti-corrosion and antifouling coatings were prepared from the UTP/AR composite materials using rosin-modified Cu₂O as an antifoulant. The composite coating with a UTP:AR mass ratio of 1:1 (UTP/AR3) showed the best chemical resistance and light aging resistance. UTP/AR3 also exhibited a good corrosion current density (2.009 × 10⁻⁷ A cm⁻²) and corrosion potential (−0.5007 V), further indicating that the UTP/AR composite coatings have excellent anti-corrosive properties. Marine field tests showed that the UTP/AR/Cu₂O composite coatings with rosin-modified Cu₂O contents less than 20% showed stable, long-term antifouling performance after immersion in seawater for 360 day. Briefly, the UTP/AR/Cu₂O composite coatings have broad application prospects in the marine industry for materials in the spray splash zone.     

Reflective properties of hollow microspheres in cool roof coatings

Hollow ultra-low-density thermoplastic microspheres can be used as filler in elastic waterproof coatings to improve a number of important properties of the coatings. The hollow microspheres help reflect solar radiation and reduce the temperature in cool roof coatings. This can improve the indoor climate of buildings without air conditioning, or save energy by reducing the need for air conditioning. The mechanism for the reflection is described in this paper and is compared with the mechanism for reflection by pigment particles like titanium dioxide (TiO₂). Results from solar reflection measurements show that the coating system filled with hollow microspheres reflects solar radiation of all incoming wavelengths, which is different from how TiO₂ reflects light. The number of reflecting units is still important for the total solar reflection and suggests that the average size of the microspheres should be as small as possible. Like most other fillers, hollow low-density thermoplastic microspheres can be used in combination with pigments.     

Characterization and property of bifunctional Zn-incorporated TiO2 micro-arc oxidation coatings: The influence of different Zn sources

In the present work, Zn-incorporated TiO₂ coatings are prepared through a one-step micro-arc oxidation (MAO) method on a grade 4 pure titanium with the addition of either Na₂Zn-EDTA solution or ZnO nanoparticles (NPs) as Zn sources. The microstructural features of both Zn-incorporated TiO₂ coatings were systematically examined. It is revealed that different Zn sources result in significant difference of phase component, chemical state, composition and morphology between the resultant Zn-incorporated MAO coatings. Zn species could be present as ZnO and Zn(OH)₂ in the coating when Na₂Zn-EDTA was used as Zn source whereas the presence of ZnO nano-clusters is obvious on the coating surface with ZnO NPs as Zn source. The addition of ZnO NPs during the MAO process also leads to a lower Zn content of the resultant coating, which is more defective with increased thickness in comparison to that of Na₂Zn-EDTA. Further, antibacterial property and osteogenic activity of both Zn-incorporated coatings were examined. Both Zn-incorporated coatings exhibit favourable bacterial inhibition ability and bone formability, suggesting the successful synthesis of bifunctional coatings through the facile one-step micro-arc oxidation method.     

Study of the anticorrosive efficiency of zincite and periclase-based core–shell pigments in organic coatings

The objective of this work was to identify the anticorrosive efficiency of synthesized, MeO/core pigments and of MeO pigments (MeO = ZnO, MgO) with varied morphology of particles. The synthesized MeO-type pigments displayed varied particle morphologies and the MeO/core core–shell pigments exhibited surface of particles made of zincite and periclase. These core–shell pigments have the properties of both the ZnO layer and of the core (wollastonite or graphite). Epoxy-ester based coatings containing the synthesized pigments were also formulated. To test the anticorrosion properties of the coatings, accelerated corrosion tests were carried out in the environment of condensed water, of NaCl mist, and of condensing water and SO₂. The synthesized core–shell pigments have good anticorrosion efficiency in an epoxy-ester coating.