Anticorrosive properties of an epoxy-Meldrum acid cured system catalyzed by erbium III trifluromethanesulfonate

New low curing temperature powder epoxy coatings cured with Meldrum's acid and catalyzed by the use of erbium III trifluoromethanesulfonate have been formulated. Their curing kinetics and anticorrosive properties have been studied and compared with a system commonly used in industry (o-tolylbiguanide/epoxy resin) and with an epoxy powder coating homopolymerized by erbium III trifluoromethanesulfonate. Three different tests of anticorrosive properties (EIS, AC/DC/AC and salt fog spray) have been used together with an adherence test, in order to establish the best system. Results show that systems crosslinked with Meldrum's acid and catalyzed with erbium triflate present very fast curing kinetics and very good anticorrosive properties. The technique AC/DC/AC has shown its ability to evaluate properly and much faster than other techniques the anticorrosive properties of powder coatings.     

A comparative study between the results of different electrochemical techniques (EIS and AC/DC/AC): Application to the optimisation of the cataphoretic and curing parameters of a primer for the automotive industry

Companies producing organic coatings for the automotive industry often need to test newly formulated products, which may have used different production or application parameters, to determine their actual behaviour before large-scale production and use of the coating. Proper choice of the test for this characterisation and the method of evaluation are critical. The results must be obtained in relatively short times so it is impracticable for manufacturers to wait for the completion of outdoor exposure tests. To reduce lead times in the development process, the use of an accelerated aging test (such as salt spray resistance) to predict durability of the coating is essential. Yet, the time needed to perform such tests is usually at least 500 h. This article proposes the use of electrochemical impedance spectroscopy (EIS) and an electrochemical test, AC/DC/AC, which consists in a combination of impedance results and cathodic polarisations, in order to optimise in a very short time the cataphoretic process parameters (mean applied voltage) and the curing temperature needed for a primer in order to obtain the maximum anticorrosion performance. Results show very good degree of concordance between the two electrochemical tests although the AC/DC/AC method is much faster. The accelerated electrochemical test lasted 24 h to differentiate anticorrosive coatings performance, while same conclusions were obtained after more than 100 days by electrolyte immersion and evaluated by EIS.     

Investigation of corrosion protection properties of an epoxy nanocomposite loaded with polysiloxane surface modified nanosilica particles on the steel substrate

In this study, it has been aimed to investigate the corrosion protection properties of an epoxy/polyamide coating loaded with different concentrations (ranged from 3 to 6% (w/w)) of the polysiloxane surface modified silica nanoparticles (nano-SiO₂). The nanocomposites were applied on the steel substrates. Field emission scanning electron microscope (FE-SEM) and UV–vis techniques were utilized in order to investigate the nanoparticles dispersion in the coating matrix. The effects of addition of nanoparticles on the corrosion resistance of the coating were studied by an electrochemical impedance spectroscopy (EIS) and salt spray test. The coating surface degradation was studied by optical microscope and Fourier transform infrared radiation (FT-IR) spectroscopy. Results obtained from UV–vis and FE-SEM analyses revealed proper and uniform distribution of surface modified nanoparticles in the epoxy coating matrix. It was shown that the coating corrosion protection properties were significantly enhanced in the presence of 5 wt% silica nanoparticles. Less degradation occurred on the surface of the coatings loaded with 5 wt% nanoparticles.     

Effect of nano-sized calcium carbonate on cure kinetics and properties of polyester/epoxy blend powder coatings

Today's strict environmental laws pose significant challenges for coating's formulators to look for eco-friendly products. Powder coatings, particularly polyester/epoxy blends have demonstrated their ability as alternatives to traditional solvent-borne coatings. Recently, the use of nanoparticles such as nano-CaCO₃ (nCaCO₃) has been suggested as a beneficial strategy towards powder coating application with improved properties. Here, we study the effect of nCaCO₃ on morphology, cure behavior, adhesion and hardness of polyester/epoxy systems. The nanoparticles shape, size and dispersion state were investigated through X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) methods. Furthermore, isothermal cure characterization of the neat and filled systems was performed using a torque rheometer. The most important finding based on the rheological studies was the catalytic effect of nCaCO₃ on cure reaction of polyester/epoxy, leading to the shorter curing time. Moreover, the kinetic analyses of rheograms revealed a marked decrease in the activation energy of the cure process upon raising nCaCO₃ content. Interestingly, pull-off adhesion and hardness tests showed that the hardness and adhesion strength were dramatically increased by the addition of nCaCO₃ into the polyester/epoxy system compared to pure blend resin. Therefore, considering the strong competition in powder coating market, the use of nCaCO₃ as a commercial and inexpensive nanofiller is necessary not only to reduce the dwell time which has benefits in terms of the energy consumption and economics, but also to improve the performance of final polyester/epoxy coating.     

A mechanistic study of the effect of pigment loading on the appearance of powder coatings: The effect of surface topography on the optical properties of powder coatings: Modelling and experimental results

Gloss is a critical property for many powder coating applications and is related to the amount of light reflected by the coating layer on a substrate. Gloss of powder coatings can, depending on the composition, vary from excellent to matt. It is well known in the powder coatings industry that increasing loadings of pigment, especially TiO₂, causes a detrimental loss of gloss. In order to understand the cause of this phenomenon two questions have to be addressed: firstly, what is the relation between the optical properties and the surface topography of the powder coating and, secondly, how do the powder coating composition and curing conditions affect the surface topography? In order to answer the first question, the typical features of the surface of a cured powder coating have been studied in detail. Using a white light interferometer, it has been shown that the surface topography consists of both short wave and long wave patterns. Each of these patterns could be described by using two statistical parameters only, the root mean square height of the roughness and its correlation length. The effect of both the short and long wave roughness on the gloss has been simulated with a single wave pattern model, based on an approximation of the Kirchoff scattering theory [9]. These simulations illustrated that neither the short nor the long wave roughness on itself determines the optical properties. In order to quantify the combined effect of the long and short wave surface features a two-scale modelling approach was followed. The predictions of this model were in good agreement with experimental gloss data of coatings containing different amounts and types of pigments.     

Influence of thermo-analytical and rheological properties of an epoxy powder coating resin on the quality of coatings on medium density fibreboards (MDF) using in-mould technology

Powder coating of engineered wood panels such as medium density fibreboards (MDF) is gaining industrial interest due to ecological and economic advantages of powder coating technology. For transferring powder coating technology to temperature-sensitive substrates like MDF, a thorough understanding of the melting, flowing and curing behaviour of the used low-bake resins is required. In the present study, thermo-analysis in combination with iso-conversional kinetic data analysis as well as rheometry is applied to characterise the properties of an epoxy-based powder coating. Neat resin and cured powder coating films are examined in order to define an ideal production window within which the resin is preferably applied and processed to yield satisfactory surface performance on the one hand and without exposing the carrier MDF too high a temperature load on the other hand to prevent the panel from deteriorating in mechanical strength. In order to produce powder coated films of high surface gloss – a feature that has not yet successfully been realized on MDF with powder coatings – a new curing technology, in-mould surface finishing, has been applied.     

A study of the promoting effect of noble metal addition on niobia and niobia alumina catalysts

The catalytic activity of Nb₂O₅ and Nb₂O₅/Al₂O₃-supported metal catalysts was evaluated in the n-heptane conversion, CO hydrogenation and butadiene hydrogenation. After high temperature of reduction (HTR), the metal adsorption capacity decreases on all the samples, due to the reduction of Nb₂O₅ with subsequent blocking of metal atoms and bimetallic effect.

It was also observed that the activity decay caused by metal-support interaction was remarkably inhibited on the bimetallics with respect to the monometallics by comparing reaction rates after HTR. Thus, the addition of Rh to Co, Cu to Pd and Sn to Pt on niobia catalysts significantly altered the product distribution in Fischer–Tropsch synthesis (FTS) and in the hydrogenation and dehydrogenation of hydrocarbons, respectively. In addition, an unusual bifunctional effect was obtained in Pt/Nb₂O₅/Al₂O₃ catalyst.