Effect of organosilicon additives on surface segregation of components of epoxyurethane adhesive compositions and their adhesive behavior

The effect of organosilicon additives of various molecular weights—phenyltributyleneglucoxysilan (PBS) and phenyltrioligooxypropyleneglycoxysilan (KMS1052)—on the surface segregation of components of epoxyurethane adhesive compositions and their adhesive behavior is studied It is shown that the surface concentration of components differs considerably from that of the volume as a result of their selective redistribution under the influence of a solid surface. The dependence of the surface segregation of components of epoxyurethane compositions and their adhesive behavior on the concentration of the mentioned additives exhibits an extreme behavior (the effect of small additives).     

Acid-resistant lignosiloxane coatings

Acid-resistant lignosiloxane coatings based on hydrolysis lignin and KO-915 organosilicon lacquer were developed. The acid resistance of these coatings in 25% H₂SO₄ at 100°C and their physicomechanical properties were studied.     

Transparent ultraviolet-barrier coatings

A number of phenyl polyesters have been synthesized to furnish molecules whose backbones rearrange under ultraviolet irradiation to an o-hydroxybenzophenone structure. This photochemical Fries rearrangement produces ultraviolet opacity in the irradiated film while maintaining visual transparency. Thin coatings of these polyesters completely protect substrates ordinarily sensitive to ultraviolet light. Spectroscopic analysis of various rearranged films and coatings clearly shows that the o-hydroxybenzophenone polymer formed is concentrated at the irradiated surface of the original polyester coating as a “skin”. Such a skin, formed in situ during the irradiation, functions to protect both the original polyester coating as well as the coated substrate from degradation by ultraviolet irradiation. Furthermore, a significant “healing” mechanism appears inherent in these coatings, for as the exposed skin ultimately degrades under extended ultraviolet irradiation, more of the underlying polyester layer apparently rearranges to compensate for the loss. Thus the clear coating functions both as a protective skin and a rearrangeable reservoir. Modified structures of the polyesters have been prepared which possess, in addition to their protective film properties, a useful solubility spectrum and a good solution shelf life.     

Nanogradient optical coatings

Basic optical coatings with refractive-index gradient along the light propagation direction, structures of gradient coatings, and technology of their manufacturing are considered. Issues relating to longitudinal-nanogradient coatings are discussed.     

Waxes for powder coatings

Since the first beginnings at the end of the 50^th, the powder coating technology has become a perfected alternative in product and procedure respect to liquid paints. Powder coatings are primarily a mixture of synthetic resins, pigments and additives offering economical and ecological advantages compared to other coating systems. The raw materials are mixed, extruded and ground to coating powders. Waxes play an important part as additives in powder coatings. Production, storage and processing as well as the properties of the applied powder coating can be influenced positively by different waxes. Various waxes and their advantages are demonstrated by practical advantages.     

Composite coatings on titanium

Composite coatings on the surface of metallic titanium containing calcium carbonate, calcium phosphate, chondroitin sulfate and/or gelatin were obtained in a new way. By the methods of XRD, IR spectroscopy, elemental analysis, and electron microscopy the presence in the samples of calcite and hydroxyapatite crystals as the main phase was demonstrated. Inorganic coatings were found to show better adhesion and resistance compared with the coatings containing the corresponding biopolymers.     

Stress in polyimide coatings

The effect of film thickness on in-plane molecular orientation and stress in polyimide films prepared from pyromellitic dianhydride with 4,4′-oxydianline was investigated using a prism coupling technique to measure the refractive index. Film thickness was controlled by varying both solution concentration and spinning conditions. Birefringence, the difference between the in-plane and out-of-plane refractive indices, was used to characterize the in-plane molecular orientation. The observed birefringence is a combination of the birefringence resulting from molecular orientation and the birefringence induced by the residual stress present in the films. The birefringence decreases with increasing film thickness over the range of thicknesses studied (3–20 μm) indicating that the molecular orientation decreases with increasing film thickness. The in-plane coefficient of linear thermal expansion (CTE), controlled by the level of orientation in the film, increases from 18 to 32 × 10^?6/°C over the same thickness range. The birefringence of free-standing films was lower than that of adhered films due to the release of residual stress in the film once the film is removed from the substrate. The residual film stress arises primarily from the mismatch in CTEs between the polyimide film and the substrate to which the film is adhered. Thus, since the film anisotropy decreases with increasing thickness, the film stress increases with increasing thickness. Residual stress calculated by integrating the product of the film modulus and the CTE mismatch assuming temperature-dependent properties is comparable to experimentally measured film stress. Ignoring the temperature dependence of the film properties leads to an overestimation of stress. Moisture uptake was used to study the stress dependence of the optical properties. Moisture uptake increases both the in-plane and out-of-plane refractive indices by equal amounts in free-standing films due to an isotropic increase in the polarizability. In adhered films, an increase in moisture uptake leads to a decrease in the birefringence due to a swelling-induced decrease in the residual film stress. © 1994 John Wiley & Sons, Inc.     

Tribo charging powder coatings

At present tribo-guns have captured a fairly large market share of the electrostatic spraying equipment used in the powder coating industry for powder paint applications. However, powder paint system based on carboxyl functional polyesters and some special powder paint formulations cannot be sufficiently charged with tribo guns to obtain a good deposition efficiency of the powder on the object. Attempts have been made to solve this problem through addition of special additives to the powder coatings premix or to the ready-to-use powder. Additives of this type have been proven not to be ideal because they can have a catalytic activity and thus effect the powder coatings properties. We developed oligomeric additives that enhance the tribo charging of carboxylic polyester resins based powder coatings, without influencing to the kinetics of the curing process and other properties of the coating.     

Electrodeposited lead dioxide coatings

Lead dioxide coatings on inert substrates such as titanium and carbon now offer new opportunities for a material known for 150 years. It is now recognised that electrodeposition allows the preparation of stable coatings with different phase structures and a wide range of surface morphologies. In addition, substantial modification to the physical properties and catalytic activities of the coatings are possible through doping and the fabrication of nanostructured deposits or composites. In addition to applications as a cheap anode material in electrochemical technology, lead dioxide coatings provide unique possibilities for probing the dependence of catalytic activity on layer composition and structure (critical review, 256 references).     

Ice releasing block-copolymer coatings

Summary The ice releasing characteristics of a series of polydimethylsiloxane-polycarbonate block-copolymers films have been investigated. The abhesion is not only a function of the hydrophobic nature of the surface of the films but is also dpendent of the polysiloxane content, its block chain length and the glass temperature of the polymer, i. e. it is dependent on the rheological properties of the films telative to ice. Addition of some silicone oil to the films only improves the abhesion of the optimum block-copolymers which have a suitable polydimethylsiloxane composition. The oil acts as plasticizer and lubricant. Attenuated infrared reflectance measurements show that the polydimethylsiloxane blocks lie preferentially in the polymer/air interface, i. e. the methyl groups are located uppermost.

---

Zusammenfassung Die eislösenden Eigenschaften einer Serie von Polydimethylsiloxanen-Polycarbonaten Block-Copolymer Filmen wurde studiert. Die Abhäsion ist nicht nur eine Funktion der hydrophobischen Eigenschaften der Filme sondern ist auch abhängig von dem Polysiloxan-Anteil, ihrer Block-Länge und Glas-Temperatur, das heißt sie hängt auch von den rheologischen Eigenschaften der Filme relativ zum Eise ab. Zugabe von etwas Silicon-Öl zu den Filmen verbessert nur die Abbäsion der optimalen Block-Copolymeren, die einen günstigen Polydimethylsiloxane-Gehalt haben. Das Öl wirkt als Plasticizer und Schmiermittel. Messungen der Infrarot-Reflektionen zeigen, daß das Polydimethylsiloxan hauptsächlich in der Polymer/Luft-Grenzfläche liegt und im besonderen, daß die Methyl-Gruppen zuoberst liegen.

---

---

With 12 figures and 2 tables     

Positron implantation in polymer coatings

The implantation of positrons from a²²Na source has been studied in two polymer coatings. Transmitted intensities, effective mass absorption coefficients and implantation profiles have been determined.     

Nanostructured ultraviolet resistant polymer coatings

Nanoparticle-embedded acrylic coatings that can absorb copious amounts of UV radiation yet scatter little were developed to protect base fabrics from sun-induced degradation. Zinc oxide and titanium dioxide nanoparticles with diameters ranging from 15 to 70 nm were used. Nanoparticles (5 wt%) were dispersed in acrylic emulsions. Nanoparticle-embedded acrylic films of 10 μm and 20 μm thick were prepared and bonded to Kevlar fabric. Mechanical tests as well as infrared, visible and UV spectroscopy were used to characterize nanoparticle-embedded acrylic emulsions and coated Kevlar fabric.The changes in mechanical and chemical properties of Kevlar fabric after a day and week of intense UV exposure were assessed using tear and strip tensile testing, UV, visible and infrared spectroscopy, and wide and small angle X-ray analysis. Tear and tensile data, with support from UV results, showed that 20 μm nanoparticle-embedded coatings largely prevented degradation of Kevlar fabric, allowing only 5% of the degradation that occurred in the unprotected fabric after a week of UV exposure.     

Soot-based coatings for solar cookers

Journal of Thermal Analysis and Calorimetry - Different kinds of soot were evaluated as selective coverings for use in solar cookers. The coatings were analyzed by measuring their thermal...     

Bioinspired synthesis of superhydrophobic coatings

A superhydrophobic material prepared by precipitating calcium phosphate on TiO2 films under in vitro conditions is described. Crystalline calcium phosphate is very porous with octacalcium phosphate as the main phase. The films are made hydrophobic by the surface grafting of a perfluorophosphate surfactant (Zonyl FSE). The as-prepared coatings were strongly hydrophobic, with advancing contact angles exceeding 165 degrees and receding angles exceeding 150 degrees . The formation of the calcium phosphate layer is self-organizing, and the coating is easily functionalized. The material was characterized with dynamic contact angle measurements, SEM, XRD, and XPS. The strong water repellency is explained by the open porous morphology of the calcium phosphate coating together with the successful attachment of the hydrophobic function.     

Application of sealed mercury-impermeable coatings

The technology of application of sealed mercury-impermeable coating by adhesive bonding of vinyl blend is described. Results of comparative mechanical testing of adhesives of several types that can be used for bonding vinyl blend to concrete are reported on and it is concluded that the application of 88-N adhesive is optimal under production conditions.     

UV-cured coatings for functional protection

Photopolymerizing formulations of urethane-acrylate and epoxy-acrylate oligomers with active diluents of varied functionality and molecular mass were studied. It was found that the functionality of the monomers strongly affects the mechanism by which protective properties of a coating are formed. The limits of the range of optimal concentrations of the active monomers were found. It was confirmed that the maximum protective properties of the coatings are observed when unifunctional and bifunctional active diluents are used in the mixture formulation in a stoichiometric or nearly so ratio. The possibility of creating formulations with nanosize particles of functional additives determining the purpose of a formulation (anticorrosive, decorative) was revealed and substantiated.     

Corrosion processes below organic coatings

The protective mechanisms of paint systems of a 1-pack polyurethane- and an epoxy/2-pack polyurethane-coating system with zinc dust priming coats were investigated on blast-cleaned and on hand-cleaned steel substrates. The coated panels were exposed to the salt spray test and to a cyclic alternating test (VDA 621-415). The protective effect was assessed in determining adhesion, undermining at scratches, water uptake and the corrosion potential. On blast cleaned steel substrates the adhesion of the investigated coating systems was not influenced by water uptake of the coatings. Scratches are especially cathodically protected. On hand-cleaned steel surfaces the rust layer between steel substrate and coating can participate in the corrosion process with rust reduction as cathodic partial reaction. The change of rust morphology is the reason for the loss of adhesion of coating. At scratches rust reduction takes also place at the edge of the defect which is independent from pigments of the base coating.