Paint Degradation Research Articles

Degradation of an alkyd polymer coating characterized by AC impedance

Alternating current (AC) impedance was used to evaluate the degradation of a high solids alkyd primer paint coating in a 3% NaCl solution, a 100% relative humidity (RH) environment after immersion in a 3% NaCl solution, and a 95% RH environment after immersion in a 3% NaCl solution. The results indicate AC impedance measures the amount of water absorbed into the coating through resistance results. A significant increase in capacitance may indicate a build up of corrosion products which causes blistering or debonding at the coating/metal interface, which may also be determined by diffusion tail analysis.

The role of canvas attachments in the strain distribution and degradation of easel paintings

Cusping, tearing along tacking margins and failure around tacking points are common features of easel paintings. They are related to the methods used to attach the canvas to the wooden support. These features are part of the mechanical degradation process and therefore important in understanding the overall deterioration of a painting. The attachments have a significant effect on the strain distribution within the painting. Understanding these effects will help to identify vulnerable areas and aid the choice of attachment method when re-stretching a painting which has undergone treatment. The historical evolution of attachments and present- day methods used as part of structural conservation treatments are discussed briefly. The strain distribution resulting from attachments on butt-jointed stretchers has been investigated experimentally using a combination of electronic speckle pattern interferometry (ESPI) and biaxial tensile testing. The results showing the strain distribution are presented and the contribution to strain concentrations introduced by the type of attachment (tacks and staples), orientation and spacing are compared.

Infrared spectroscopic evaluation of the photodegradation of paint Part II: The effect of UV intensity & wavelength on the degradation of acrylic films pigmented with titanium dioxide

This paper reports the application of a previously described i.r. spectrometric method, which measures the evolution of carbon dioxide, and hence the rate of photo-oxidation, caused by UV irradiation of paint films, to a study of the dependence of paint degradation on UV wavelength. Measurements have been made on both unpigmented and TiO2-pigmented acrylic films. Preliminary measurements demonstrate that, for both pigmented and unpigmented acrylic films, the rate of carbon dioxide generation is proportional to I 0.5, the square root of the UV intensity. As the rate of carbon dioxide generation is a measure of paint film degradation, this implies that the rate of film degradation is proportional to the square root of UV intensity. This is the first time that this square root dependence, previously predicted from photo-oxidation studies of model compounds, has been directly measured on a practical paint film. Photo-oxidation of unpigmented, anatase-pigmented and rutile-pigmented acrylic films has been measured by using optical filters to isolated selected portions of the output of a Xenon lamp. Results have been analyzed semi-quantitatively taking into account the measured transmission characteristics of the filters, the lamp output and the I 0.5 relationship. The disproportionate deleterious effects of short wavelength, <300 nm, radiation on unpigmented films have been confirmed and the stability of anatase pigmented films to 405 nm radiation has been demonstrated directly. The FTIR assay of carbon dioxide produced by paint film degradation could be applied to other polymer films and combined with measurements of carbonyl band development.

Microbial degradation of paintings

“… l’alliance possible et desiderable de la Science et de l’Art… ,” Louis Pasteur, when he was nominated to the first chair in physical chemistry at the Ecole des Beaux Arts in Paris. In 1940 four young men discovered the Lascaux Cave in the Dordogne region of France. The cave

Compactness and Degradation of Cataphoretic Coating on Phosphatized Steel

Electrochemical Impedance Spectroscopy (EIS) was applied to study the degradation of cataphoretic paint on phosphatized steel obtained with and without the use of control resistance during the cataphoretic painting. The samples obtained with this technique were more compact and thinner and these samples, as well as others obtained without the use of this technique, were immersed in 2% NaH 2 PO 4 solutions at 25°C. The EIS results indicate that the more compact coating is subjected to a higher water uptake and a higher swelling. Also the porous resistance of this coating, despite initially showing a sharp decrease, remains higher than the resistance of the less compact and thicker samples. The comparative EIS study of the two kinds of samples indicates that the compactness of the cataphoretic coating, obtained using the control resistance technique, is more effective than the thickness to obtain higher shielding,properties.

Examination of the Photochemical Curing and Degradation of Oil Paints by Laser Raman Spectroscopy

In the present study, the curing and the degradation of oil paints by irradiation with ultraviolet light was investigated by laser Raman spectroscopy. At present, the curing reaction of oil paints is interpreted by several reaction schemes, although none of them is considered to be based on definite experimental evidence. The most typical examples are as follows: one is the radical termination reaction of the crosslinking type; the other, the polymerization reaction of the Diels—Alder reaction (diene reaction) type. In the present investigation, oil paint film (ZnO White and TiO2 White) was irradiated with a Xe lamp, and the time dependence of the Raman spectra of the films was examined. It is shown that the curing reaction cannot be explained by either of the above-mentioned reaction schemes. A new reaction mechanism for the curing and the degradation of paint films is proposed. It is concluded that the microscopic approach to the elucidation of the degradation mechanism of oil paint films based on Raman spectroscopy is very useful for the improvement of oil painting techniques.

Mycological and ultrastructural studies to evaluate biodeterioration of mural paintings. Detection of fungi and mites in Frescos of the monastery of St Damian in Assisi

Abstract The role of fungi in the biodeterioration of frescos has been investigated by microbiological and ultrastructural techniques. With this aim, the mycoflora present on samples taken from deteriorated indoor wall paintings (frescos) in the Monastery of St Damian in Assisi was isolated and identified. The results showed that the fungal colonization of the two paintings ‘Crocifisso con Francesco giovane’ and the ‘Mensa di S. Chiara’, located inside St Clare's Refectory, was mainly due to Cladosporium, Aspergillus, Alternaria, Penicillium and Fusarium genera. Although considered not uncommon in frescos, their direct involvement in enzymatic degradation of paints was not confirmed. Interestingly, the presence of mites in proximity to actively growing fungal mycelium, as revealed by scanning electron microscopy, although considered an example of parasitic nutritional relation, could also suggest a metabolic interaction resulting in the synthesis of biodeteriogenic substances.

Corrosion and Weathering of Paints for Atmospheric Corrosion Control

Abstract Three laboratory-based accelerated corrosion tests were investigated to develop improved procedures for assessing corrosion protection properties of organic paint films. The methods investigated were: standard salt-spray (ASTM Standard B-117), a wet/dry cycle corrosion test using a low-concentration ammonium sulfate/sodium chloride [(NH4)2SO4/ NaCl] electrolyte, and a corrosion/weathering test combining wet/dry corrosion cycles with ultraviolet (UV) condensation cycles. Results were reported for an epoxy-polyamide/ Polyurethane paint system on phosphated steel and for an alkyd/alkyd system on cold-rolled steel. Corrosion and paint degradation were assessed visually and by scanning electron microscopy and x-ray photoelectron spectroscopy. Salt-spray testing resulted in corrosion, blistering, and paint degradation that appeared unrealistic compared to results after 12-month exterior exposures to natural industrial atmospheres. Wet/dry cycle corrosion testing produced paint delamination from scribe ...

Use of DC Electrochemical Methods for Evaluation of Paint Films on Steel, Aluminum, and Zinc

Abstract Degradation of paints that were applied on steel, aluminium, and zinc and exposed to air-saturated seawater has been studied by using direct current (DC) electrochemical methods and by visual examination of long-term exposed specimens. The DC measurements were performed on surfaces with a continuous paint film, and the long-term specimens were polarized by a defect in the paint film. The DC measurements on coated aluminium, steel, and zinc have been found to give information about the mechanism of corrosion. The results illustrate the importance of the properties of the metal substrate and of the paint film. Coated steel galvanically coupled to bare steel was found to have a high potential and, hence, to act as a cathode vs bare steel. For coated aluminium, however, initiation of corrosion at the metal/coating interface was found to give a much lower potential. The behavior of coated zinc was found to be similar to that of coated steel. The potential was high compared to bare zinc, which means th...

The application of impedance methods to study the effects of water uptake and chloride ion concentration on the degradation of paint films—II. Free films and attached/free film comparisons

Impedance and gravimetric methods have been applied to study the uptake of water over a range of solution chloride ion concentration in free films (i.e. paint films not attached to a substrate). The paint films were 25 μm experimental silicone modified polyester. Comparisons have been made between the impedance and gravimetric methods to highlight advantages/disadvantages of each technique, and between the attached and free film results. Water uptake on the free films, calculated from gravimetric tests, increases with immersion time and with decreasing solution chloride ion concentration, in agreement with similar tests on attached films. The calculation of water uptake by the 1 kHz capacitance method was unreliable due to other processes occurring, such as paint film degradation and changing modes of distribution of water uptake at longer times. Sample failure time calculated by the single frequency (1 kHz) impedance test is a better measure of performance life than that calculated from wide frequency range tests. Both the free and attached film results show failure time decreasing with increasing solution chloride ion concentration. This suggests that the paint film degradation is caused predominantly by the solution and not by secondary effects such as build-up of alkalinity in the accumulated water layer at the metal/film interface on the attached films caused by cathodic reduction of oxygen. The marked drop in paint film resistance or the large rise in the 1 kHz capacitance with time is thought to be a measure of the extent of degradation of the paint film, caused by hydrolysis of the silicone modified polyester paint film. Water uptake, calculated by either the 1 kHz capacitance or gravimetric method, is greater but sample failure time is longer for the attached films than for the free films. Initially, water appears to enter the paint film rapidly, but slows down after a few hours when paint degradation becomes increasingly significant, and dependent on the solution chloride ion concentration.

Evaluation technology of corrosion behavior for automotive steel sheet.

An appropriate evaluation technology of corrosion is essential for the development of precoated steels for automotive use. There are various test methods: field surveys, monitor car tests, proving ground tests, vehicle exposure tests, under- and on-vehicle tests, the Volvo test and laboratory tests. They are briefly explained.A cyclic corrosion test (CCT) which simulates and accelerates the field situations is usually carried out in the laboratory. For the design of a CCT, micro-climate in vehicles, corrosion mechanism and environmental tactors must be clear. The environmental factors taken into account for CCT are salt, temperature, humidity, wet/dry ratio and cyclic frequency. In addition, water immersion, ultraviolet rays and air pollutants are of importance in their own ways.A perforation test is conducted with hem flange models or lapped panels in the CCT. Cosmetic evaluation consists of paint adhesion, wet adhesion in water and paint degradation by ultraviolet ray.When a corrosion test is carried out in the CCT, it is recommended to test cold rolled steel and certain zinc coated steel, the behaviors of which in the field are well-known, together with other specimens. The lifespan of these specimens could be estimated in comparison with such steels.

Exposure to Paint Degradation Products when Welding, Flame Cutting, or Straightening Painted Steel

Welding or flame cutting of coated steel gives rise to organic contaminants in addition to inorganic fumes and gases. The exposure of metal workers to paint degradation products was studied by measuring the concentrations of characteristic pollutants in the breathing zone during welding, flame cutting, and straightening painted steel in Finnish shipyards. The sampling was done using an XAD-2 adsorption tube with a preconnected glass fiber filter and a chemosorbent tube for aldehydes. In each measurement 20 to 50 different organic pollutants could generally be identified. Air concentrations were usually below the threshold limit values for the individual compounds. The highest concentrations were measured in ship repairing and shipbreaking works. Noticeable concentrations were also measured at outfitting work on new ships during straightening and flame cutting processes. Many of the pollutants identified are known irritants, e.g., acrolein, formaldehyde, alkylbenzenes, phenols, and some are potential sensitizers, e.g., methacrylates, phthalic anhydride. Complaints about irritation do occur, indicating the need for preventive measures, although the measured concentrations are clearly below the threshold limit values for the individual compounds detected.

STUDIES ON THE PHOTOCHEMICAL STABILITY OF SYNTHETIC RESIN-BASED RETOUCHING PAINTS: THE EFFECTS OF WHITE PIGMENTS AND EXTENDERS

AbstractThe durability of a paint vehicle can be strongly influenced by the pigments which it contains. This report describes an initial investigation of the photochemical degradation of paints formulated with a commercial poly(n-butyl methacrylate) and a variety of white pigments and extenders. Upon exposure to near-ultraviolet light this resin predominantly cross-links, eventually becoming almost completely insoluble. White pigments such as rutile TiO2 and Green Seal zinc oxide do not alter this tendency but they do slow the cross-linking rate, probably by their ability to absorb UV light. By contrast, a non-absorbing light scatterer like barium sulfate increases the rate of cross-linking, perhaps by increasing the path length of light as it becomes diffused within the paint film. Finally, pigments such as anatase TiO2 and Kadox 515 zinc oxide not only decrease the overall degradation by screening UV light but also increase the relative importance of chain-breaking chemistries through their photocatalyt...

An Electrochemical Monitor for the Detection of Coating Degradation in Atmosphere

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An interpretation of electrical impedance diagrams for painted galvanized steel

The physical significance of various arcs which appear on impedance diagrams for painted galvanized steel exposed to an aggressive medium is discussed. These diagrams undergo various changes during exposure, i.e. when the paint coating is still intact the response is almost purely capacitive, but as the coating degrades the impedance value decreases and the plots exhibit two arcs. Measurements with detached films confirm the relationship between the single arc appearing in the impedance diagrams during early stages of paint degradation and the intrinsic paint properties. However, it is more difficult to find an interpretation for the two-arc diagrams. The hypothesis that the low-frequency arc arises from effects associated with the double-layer capacitance and charge-transfer control at the pore base leads to unacceptable conclusions. Various arguments seem to support the view that the low-frequency arc is determined by a finite diffusion impedance.

Determination of the Presence of Bisphenol-A and the Absence of Diglycidyl Ether of Bisphenol-A in the Thermal Degradation Products of Epoxy Powder Paint

Thermal degradation of an epoxy powder paint was studied by thermogravimetry. The temperature tolerance range appeared rather narrow, as the degradation began below 250° C. The formation of bisphenol-A and its diglycidyl ether in the degradation was investigated. The generation of bisphenol-A was found to be temperature-dependent. The maximum formation of bisphenol-A was about 0.02% of the sample weight. The diglycidyl ether was not observed. An isocratic HPLC method for the determination of bisphenol-A was developed. The limit of detection at 279 nm was 0.002 mg/ m3 for a 200-L sample. Filter collection was used for aerosols formed in the degradation. The collection and desorption efficiencies were good.

Determination of the Presence of Bisphenol-A and the Absence of Diglycidyl Ether of Bisphenol-A in the Thermal Degradation Products of Epoxy Powder Paint

Thermal degradation of an epoxy powder paint was studied by thermogravimetry. The temperature tolerance range appeared rather narrow, as the degradation began below 250° C. The formation of bisphenol-A and its diglycidyl ether in the degradation was investigated. The generation of bisphenol-A was found to be temperature-dependent. The maximum formation of bisphenol-A was about 0.02% of the sample weight. The diglycidyl ether was not observed. An isocratic HPLC method for the determination of bisphenol-A was developed. The limit of detection at 279 nm was 0.002 mg/ m3 for a 200-L sample. Filter collection was used for aerosols formed in the degradation. The collection and desorption efficiencies were good.

Thermal Degradation of Painted Wood. an Experimental Study

A comparative study of thermal degradation of painted and unpainted parti cle board specimens has been carried out. Experiments based mainly on the measurements of piloted ignition delay, mass loss rate and temperature profile have been performed using a radiative heat flux equal to 2.4 W/cm2. Thermo gravimetric analysis has complemented these measurements. It has been shown that thermal degradation of paints produces a solid residue which strongly affects exchange phenomena at the wood surface and consequently the thermal behavior of wood.

Co-metabolism of paint byAureobasidium pullulans BH-1-ATCC 34621

Although the ability ofAureobasidium pullulans BH-I-ATCC 34621 to cause paint deterioration during its growth on wood has been reported, the mechanism by which paint degradation occurred was unclear. Evidence now indicates that co-metabolism of acrylic, resins in the paint is the cause of paint deterioration byA. pullulans.

Photochemical degradation of alkyd paints

Alkyd paints make up two thirds of the paints made in Australia and in fact three quarters of the paint used by the Armed Services is alkyd based. It can be seen, therefore, that increasing the service life of alkyd paints would effect considerable savings both to our defence effort and to the community at large. Photodegradation is a major cause in the reduction of a paints service life. It may cause chalking, checking, cracking, blistering and embrittlement and these in turn may lead to loss of adhesion. This could allow water, oxygen, air pollutants and grit to attack the underlying substrate causing corrosion and possibly loss of expensive equipment.