Aqueous Coatings Research Articles

Influence of pigment packing behavior on the adhesive requirements of aqueous paper coatings

The amount of adhesive included in an aqueous paper coating formulation is critical to the performance and appearance of the final product. While the time-honored “weight ratios” are typically used to formulate pigmented coatings for paper, pigment volume concentration (or alternatively, % void volume) has been found to be much more useful in determining the interactions of pigments with the adhesive on the properties of such aqueous coatings. In this study, slurries of commercial kaolin clay and ground calcium carbonate pigments used in papermaking applications were blended and then centrifuged to determine the maximum packing efficiency of the pigments. Isolated films of coatings made from selected pigment blends and increasing levels of latex adhesive were tested for void volume percentage and tensile modulus. Based on these results, a regression equation between pigment interstitial space and the mechanical strength of different coating films was established.

Micro- and Nanofibrillated Cellulose as a Rheology Modifier Additive in CMC-Containing Pigment-Coating Formulations

Suspension rheology of aqueous coatings influences the coating application performance at high speeds and during high rates of change of the shear rate, as well as the quality of the coated end product determined by the relationship between dewatering, immobilization, and coating coverage. In the case of paper coatings, the end-use printing can be significantly affected by the coating uniformity, pore structure, and surface chemistry. Nanocellulose-containing materials, such as microfibrillated (MFC) and nanofibrillated (NFC) cellulose, are potential additives that could at least partly substitute other natural and synthetic cobinders, including viscoelasticity-inducing starch, carboxymethyl cellulose (CMC), and polyacrylic thickeners, in paper-coating color formulations. Work is reported here in which a systematic comparison of dewatering and rheological characteristics of coating colors, based on three different pigments and mixtures thereof, is illustrated using CMC as the cobinder and incorporated wit...

Stimuli-Responsive Nanolatexes: Porating Films

A new class of very stable and stimuli-responsive nanolatexes based on copolymers of reactive and stimuli responsive ionic liquid surfactants is synthesized by microemulsion polymerization to yield dispersions of 22-30 nm diameter particles. Aqueous coatings of these nanolatexes dry to form robust films that exhibit stimuli-responsiveness to certain ion exchangeable anions. The nature of the reactive ionic liquid surfactant monomers induces an ion exchange capacity in the resulting copolymers and films. Transparent films of such nanolatexes can be transformed into opaque and porous films and membranes as a stimulus-response to anion exchange. These nanolatexes are ionic nanogels that are insensitive to Debye-Hückel screening by an indifferent salt and exhibit very soft interparticle interactions, qualifying them as ideal candidates as waterborne dispersing aids; in addition, these nanogels appear to be experimental examples of osmotic nanospheres emanating from the theoretical development of osmotic brushes.

Assessment of Genotoxicity and Histopathological Changes Induced by Polyethylene Glycol (PEG6000) in Male Mice

Polyethylene Glycols (PEG) the synthetic polymers are intended for use as plasticizers in aqueous film coatings used in the preparation and formulation of food supplement products, in coating of pharmaceutical products, as carrier for sweeteners, in various types of approved medical products, such as laxatives and ophthalmic products. Authorization of polyethylene glycols for use in pharmaceutical products and food supplements focuses the attention to verify the safety of this compound. So the aim of this study is to estimate the genotoxicity and histopathological effects of polyethylene glycol in male mice. The study was conducted by comet assay and micronucleus test in bone marrow cells, diphenylamine assay of DNA fragmentation in liver tissue and histological, histochemical examination in liver and kidney cells. Results showed that PEG6000 exhibited DNA damage, represented in dose-dependent increase in %DNA in comet tail, tail moment and olive tail moment, micronuclei number, DNA fragmentation and decrease in DNA content of liver and kidney cells. Histopathological examination showed dose dependent degenerative changes in both of liver and kidney cells. The histopathological changes were represented in vacuolar degeneration, few inflammatory cellular infiltration and necrosis and pyknotic nuclei in liver cells and sever tubular degeneration and vacuolar degeneration in their tubular epithelial cells and cloudy degeneration, marked interstitial cellular infiltration in kidney cells. Histochemical study showed that PEG600 caused significant decrease in DNA content in liver and kidney cells. We concluded that the repeated exposure to high dose of PEG6000 shows genotoxic activity and histopathological changes in male mice cells. So that special attention must be paid to legalization of indiscriminate use of this compound to reduce the risk affecting human health.

Development of low VOC additives to extend the wet edge and open time of aqueous coatings

One of the challenges of formulating waterborne coatings is achieving an acceptable balance of properties both during the film application and drying process as well as in the final film. This difficulty is compounded by regulations relating to the reduction of volatile organic compounds (VOCs) in architectural coatings. There is a competition between the requirements for adequate workability time of the coating with appropriate film formation and recoat behavior. The period in which irregularities in a freshly applied coating can be repaired without resulting in brush marks is referred to as the open time, while the period in which a coating can be applied over an existing paint film without leaving lap marks is deemed the wet edge time. Aqueous coatings generally employ dispersed high molecular weight polymers as binders. These binders often provide short open times when the coating is dried since the dispersed polymer particles tend to be immobilized quickly in the edge region of an applied coating. As a result, the viscosity of the coating increases rapidly, which leads to a limited window of workability. Small molecule alkylene glycols such as ethylene and propylene glycol are routinely incorporated in aqueous coatings as humectants, but are limited in utility since they are considered to be VOCs. This paper describes the process by which new, low VOC additives were developed to improve open time and wet edge in aqueous coatings. Mechanisms for the enhanced performance will be outlined through use of rheological techniques. Paint performance properties will be exemplified in a typical architectural formulation.

Evaluation of recent advances in continuous film coating processes

Background: Continuous film coating processes are recognized for their high production rates but have had slow acceptance for pharmaceutical production because of perceived high product losses during start-up and shut-down. In this article, the recent improvements in continuous coater designs were evaluated with respect to coating uniformity and reduction in product losses. Two separate studies represent trials conducted in newly redesigned continuous coating pans from two different coating pan manufacturers. Method: Multivitamin tablets were coated with Opadry® II, high performance film coating system, in both batch and continuous modes in the continuous coater. Tablet samples collected throughout all phases of the process were tested for color development and uniformity. Soft gelatin capsules were coated with a delayed release coating formulation, Nutrateric®, nutritional enteric coating system. Samples of the soft gelatin capsules were taken throughout the process and tested for resistance to simulated gastric fluid as a measure of coating uniformity and delayed release functionality performance. Conclusions: The results from both the immediate release and delayed release case studies support the assertion that continuous coating processes are capable of applying aqueous film coatings with significant improvements in coating uniformity and reduction in product loss.

Formation of highly hygroscopic soot aerosols upon internal mixing with sulfuric acid vapor

The hygroscopic properties of submicron soot particles during internal mixing with gaseous sulfuric acid have been investigated using a combined tandem differential mobility analyzer (TDMA) and differential mobility analyzer–aerosol particle mass analyzer (DMA‐APM) technique. Fresh particles exhibit no change in mobility size and mass at subsaturated conditions, whereas particles exposed to gaseous sulfuric acid (109–1010 molecule cm−3, 12 s contact time) experience significant mobility size and mass changes with increasing relative humidity (RH). The DMA‐APM measurements reveal that particles of all sizes exposed to H2SO4 vapor gain mass with increasing RH because of absorption of water by sulfuric acid coating. However, on the basis of mobility size measurements using TDMA, upon humidification H2SO4‐coated soot agglomerates display distinct hygroscopic growth patterns depending on their initial size and the mass fraction of condensed sulfuric acid. While small particles experience an increase in their mobility sizes, larger particles exhibit a marked shrinkage due to compaction. We suggest that determination of the hygroscopic properties of soot particles using a TDMA alone can be inconclusive. Restructuring of the soot agglomerates and filling of the voids that accompany the condensation of water‐soluble materials and subsequent water absorption lead to little or no observable changes in particle mobility size at subsaturated RH even for particles that contain aqueous coatings. Extrapolation of our experimental results to the urban atmosphere indicates that initially hydrophobic soot particles acquire sufficient sulfate coating to become efficient CCN (cloud condensation nuclei) within a time period ranging from a few hours to a few days, dependent on the ambient H2SO4 level. The results imply that internal mixing with sulfuric acid through H2SO4 vapor condensation likely represents a common aging process for a variety of atmospheric aerosols. The variations in the size and hygroscopicity of soot particles during atmospheric processing influence their optical properties, cloud‐forming potential, and human health effects.

Adhesion of food-borne bacteria to stainless steel is reduced by food conditioning films

Preconditioning of stainless steel with aqueous cod muscle extract significantly impedes subsequent bacterial adhesion most likely due to repelling effects of fish tropomyosin. The purpose of this study was to determine if other food conditioning films decrease or enhance bacterial adhesion to stainless steel. Attachment of Pseudomonas fluorescens AH2 to stainless steel coated with water-soluble coatings of animal origin was significantly reduced as compared with noncoated stainless steel or stainless steel coated with laboratory substrate or extracts of plant origin. Coating with animal extracts also decreases adhesion of other food-relevant bacteria. The manipulation of adhesion was not attributable to growth inhibitory effects. Chemical analysis revealed that the stainless steels were covered by homogenous layers of adsorbed proteins. The presence of tropomyocin was indicated by appearance of proteins with similar molecular weight based in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, in several extracts that reduced adhesion but also extracts not containing this protein reduced bacterial adhesion, indicating that several molecular species may be involved in the phenomenon. It is a common perception that food materials facilitate bacterial adhesion to surfaces; however, this study demonstrates that aqueous coatings of food origin may actually reduce bacterial adhesion. Compounds from food extracts may potentially be used as nontoxic coatings to reduce bacterial attachment to inert surfaces.

Newly UV-curable polyurethane coatings prepared by multifunctional thiol- and ene-terminated polyurethane aqueous dispersions mixtures: Preparation and characterization

A series of newly developed UV-curable polyurethane coatings were prepared by blending multifunctional thiol- and ene-terminated polyurethane aqueous dispersions. The composition, structure, solution stability and mechanical properties of the title coatings were characterized in detail by FT-IR, photo-DSC and DMA measurements. It was found that the resulting polyurethane coatings showed good solution stability and high photopolymerization activity even after a long time (i.e. 1 month). The incorporation of a waterborne polyurethane chain into the both multifunctional thiols and ene monomers promoted their solution stability and avoided any reaction between thiols and ene groups as a result of their high reacting activity in non-aqueous systems. UV-cured films prepared by this method were found to exhibit excellent physical properties with improvements over what can be attained directly with current UV-curable urethane–acrylate based systems. This method allows for the preparation of high performance UV-curable polyurethane aqueous coatings based on thiol-ene chemistry systems.

Synthesis and characterization of hybrid fluoro‐emulsion based on silica/copolymer composite particles

AbstractBACKGROUND: To create a hydrophobic surface, a commonly used two‐step process is the formation of a rough surface and its subsequent modification with materials of low surface energy. Here, a new method for making a hydrophobic surface is proposed using emulsion copolymerization with a low‐surface‐energy fluoropolymer in the presence of a high percentage of silica particles creating a well‐spread roughness.RESULTS: Irregular core–shell structural composite particles such as of snowman shape and sandwich shape were obtained and characterized. The hydrophobicity and chemical structure of the hybrid film were investigated. It was found that strong inter‐ and intramolecular chemical bonding in the composite film may improve the properties of the hybrid film. Enrichment of fluorine on the film surface and well‐distributed roughness due to the silica particles covered by the fluoropolymer contribute to the increased hydrophobicity of the film. The water contact angle on the film increased from 106 ± 2° to 135 ± 2°.CONCLUSION: The stable core–shell hybrid latex synthesized in this work will be of use in preparing high‐performance hydrophobic aqueous coatings. Copyright © 2008 Society of Chemical Industry

Modified low molecular weight acrylics in coating application: synthesis and property evaluation

Low molecular weight resins containing relatively high levels of acrylic acid were converted to oxidatively curable materials by reacting the carboxylic acid groups with oxazoline functional alkenes. The oxazolines were obtained by reacting fatty acid with 2-amino-2-methyl-1-propanol. The oxazolines were then reacted with the acrylic resins at elevated temperature. Relatively high yields of the desired reaction products were obtained in relatively short reaction times. The resulting resins were formulated into aqueous coatings and films were made over metal substrates. The films were cured oxidatively and evaluated for property development. The films had good general solvent resistance but poor resistance to dilute sodium hydroxide.

A Comparative Study of Aqueous and Organic-Based Films and Coatings of PEGylated Rosin Derivative

Rosin was partially esterified with polyethylene glycol 400 and reacted with maleic-anhydride to form an ester-adduct derivative. Derivative and native rosin were characterized for physicochemical properties. Aqueous coating system of derivative was developed by ammonia neutralization method. Organic-based films were produced using acetone. Aqueous and organic-based films were comparatively evaluated. Derivative exhibited an excellent coat-forming ability on spherical-units. Aqueous-based film exhibited very high water vapor transmission rate, wettability, water uptake, and leaching at pH 6.8. A 20% w/w aqueous-based coat could sustain diclofenac sodium release for 8 h, whereas, 20% w/w organic-based coat released 20.11% of drug in 8 h. In conclusion, aqueous coating system of synthesized rosin derivative can be developed; however, aqueous-coats are less efficient to retard the drug release rate. Instead, the organic-based coatings can efficiently be used for sustained drug delivery.

Nanomorphology control in aqueous coatings

Using catalytic chain transfer polymerisation (CCTP) in emulsion polymerisation results in efficient molecular weight reduction. An additional benefit of polymers prepared with CCTP is that they have a chain terminal unsaturated group that can be used in a subsequent graft copolymerisation to yield comb-shaped polymer chains. By careful optimisation of the polymer parameters, film properties can be optimised to yield coatings with very interesting combinations of properties.

Determination of the Interfacial Characteristics of a Series of Bolaamphiphilic Poly(fluorooxetane) Surfactants through Molecular Dynamics Simulation

Constant surface tension (NgammaT) and constant volume (NVT) molecular dynamics simulations have been conducted on a series of bolaamphiphilic alpha,varpi-(diammonium disulfato)poly(fluorooxetane)s and on a typical "long-chain" anionic fluorosurfactant used to improve the flow-and-leveling characteristics of aqueous coatings, to compare their behavior at a water/air interface. Recent research has shown that the poly(fluorooxetane) surfactants considered in this paper could serve as an effective substitute for traditional fluorosurfactants used in flow-and-leveling applications.(1) From molecular dynamics simulation, we have determined the saturated interfacial area per surfactant, interfacial area per surfactant as a function of surface tension, density profiles, the degree of hydration for various atoms in each surfactant, the degree of counterion binding, and order parameters. Our results for saturated interfacial area per surfactant molecule are greater than what has been obtained by other researchers through parametric fitting of interfacial area from experimental surface tension data using the Davies isotherm. Possible explanations for this difference are discussed. The low interfacial areas occupied by each poly(fluorooxetane) at the water/air interface are the result of their ability to adopt a "looped" conformation, in which the carbon and oxygen backbone of each surfactant and the attached perfluoroalkyl chains are forced into the air phase. A geometrically defined penetration parameter was calculated from the density profiles, which reveals that each poly(fluorooxetane) surfactant is more effective at separating the air and water phases than the "long-chain" anionic fluorosurfactant. The degree of hydration measured for different atoms in poly(fluorooxetane) during simulation confirms that a "looped" conformation is adopted in which the surfactant backbone and the perfluoroalkyl chains are lifted away from the water surface. Calculation of order parameters revealed a much lower degree of ordering for the perfluoroalkyl side chains in each bolaamphiphile than in the "long chain" anionic fluorosurfactant. When viewed in the context of the penetration parameter analysis, the density profiles and hydration data suggest why each poly(fluorooxetane) is capable of significantly reducing surface tension when other fluorosurfactants with similarly short perfluoroalkyl moieties provide inadequate surface tension reduction for practical flow-and-leveling applications.

Development of novel aqueous coatings which meet the requirements of ecology-conscious society: novel cross-linking system based on the carbonyl–hydrazide reaction and its applications

This paper reviews the results of our research on the reaction between a carbonyl group and a hydrazide group, especially the cross-linking, physical characteristics of the cross-linking system, and the reverse (decomposition) reaction. Discoveries in this investigation may lead to development of various novel products which would answer the requirements of today's coatings industry. The reaction, which proceeds rapidly in aqueous media at ambient temperature, can be used in one-component cross-linkable latex paints offering many advantages, such as good water and stain resistance, without detracting the workability. Applications of this reaction to aqueous two-component emulsion paint were also examined and the possibility for practical use was envisaged. Exploitation of the physical properties of dihydrazide compounds has resulted in the development of a novel curing system, namely, a “penetrative cross-linking process”. This process, where the paint films are cured by the penetration of a cross-linker, exploits three features of dihydrazide compounds to enable both easy penetration of the cross-linker and quick removal of excess cross-linker: low molecular weight, good water-solubility, and poor compatibility with paint resins. With this cross-linking reaction the reverse reaction can take place under specific conditions. This finding leads to the development of decomposable cross-linked coatings which are desirable for the recycling of coated substrates.

Interfacial Rheological Properties of a Series of Bolaamphiphilic Poly(fluorooxetane)s

Interfacial rheological studies were performed on a series ofbolaamphiphilic α,ω-(diammonium disulfato)-poly(fluorooxetane)s of several perfluoroalkyl chain lengths. Similar measurements were performed on a small-molecule, anionic fluorosurfactant with a -C 8 F 1 7 perfluoroalkyl group that is known to be an effective flow and leveling aid in aqueous coatings. Dilational viscoelasticities were measured for the fluorosurfactants as a function of concentration and oscillation rate. Elasticities were found to increase with increasing perfluoroalkyl chain length. All elasticities exhibited a strain rate dependence indicative of the influence of diffusional relaxation on elasticity values. Phase angles were found to be in the range for diffusional relaxation and decreased with increasing concentration and strain rate. Using interfacial rheological data, characteristic fluid dynamics numbers were calculated for the fluorosurfactants. Among these was the Marangoni number. Calculated Marangoni numbers for the poly(fluorooxetane)s were of the same order of magnitude as that for the small-molecule, long perfluoroalkyl chain surfactant. The poly(fluorooxetane)s all have equilibrium surface tensions greater than that of the small-molecule, long perfluoroalkyl chain surfactant, yet show similar abilities to aid in flow and leveling in aqueous coatings at comparable concentrations. Rheological measurements demonstrate that equilibrium surface tension alone is not enough to explain the fluid dynamics processes occurring during flow and leveling.

Surface Tension and Adsorption Properties of a Series of Bolaamphiphilic Poly(fluorooxetane)s

Studies of surface tension, adsorption parameters, and dynamic surface tension were performed on a series of bolaamphiphilic α,ω-(diammonium disulfato)poly(fluorooxetane)s of several perfluoroalkyl chain lengths. Similar measurements were performed on a small-molecule, anionic fluorosurfactant with a −C8F17 perfluoroalkyl group that is known to be an effective flow and leveling aid in aqueous coatings. Molecular area demands for the poly(fluorooxetane)s were found to be relatively small for a polymeric species and may indicate a change in conformation between bulk solution and interface. Other adsorption parameters were found to be similar to those of the small-molecule fluorosurfactant. Diffusion coefficients were found to be slightly smaller for the poly(fluorooxetane)s compared to the small-molecule fluorosurfactant.

Clay–polymer nanocomposite coatings for imaging application

Aqueous coatings of intercalated smectite clay particles in a polymeric matrix have been evaluated for application in inkjet media. The state of clay intercalation, as measured by X-ray diffraction (XRD) technique, plays a significant role in determining the crystallinity of the polymer and the transparency and gloss of the coatings. Results of practical tests on the nanocomposite coatings operating as inkjet-receiving layers are discussed.

Comparative Studies with Kollicoat MAE 30 D and Kollicoat MAE 30 DP in Aqueous Spray Dispersions and Enteric Coatings on Highly Swellable Caffeine Cores

A film formulation containing Kollicoat MAE 30 D, Kollidon 30, Sicovit Rot 30, titanium dioxide, talc, and a plasticizer for the aqueous manufacture of enteric coatings was studied for the coagulations occurring with certain plasticizers and for differences in resistance on highly swellable caffeine cores. Also included in these investigations were the latices Kollicoat MAE 30 DP and Eudragit L 30 D-55. The coagulations occurring with all three film latices can be attributed to the presence of Kollidon 30 together with certain excipients. Preparations with Kollidon 30, but without color pigments, showed no tendency to coagulate. The advantage of propylene glycol (PG) compared to other plasticizers such as triethyl citrate (TEC) is that no coagulations occurred, even in the presence of Kollidon 30 and color pigments. Among the Kollidon 30–free film formulations examined, a plasticizer content of 10–15% PG or TEC gave the best results. Optimal pigment distribution in the coat originally produced by Kollidon 30 can optionally be achieved by prolonged stirring of the pigment suspension. The resistance can be further improved by inclusion of a subcoating with Kollidon VA 64. Kollicoat MAE 30 D and MAE 30 DP and Eudragit L 30 D-55 showed identical behavior in this study.

Effects of morphology and surface treatment of inorganic pigments on waterborne coating properties

Inorganic pigments in aqueous coatings are investigated using atomic force microscopy and microprobe analysers. The first method characterises the topography at a very high resolution. The findings obtained using the second method reveal the distribution of the pigment in the paint film. Taking selected titanium dioxide and iron oxide pigments, the effects of particle morphology as well as inorganic and organic surface treatment on the dispersibility and flocculation stability are shown. These two phenomena are factors in gloss, hazing, hiding power, tinting strength and viscosity – key quality parameters in waterborne coatings.