Preparation of surface energy controlled automotive clearcoats loaded with functional silicon additives: Studying the resistance against tree gum attack

The aim of this study is enhancing an automotive clearcoat easy-to-clean property against simulated tree gum (Arabic gum) using hydroxyl-functional silicone polyacrylate additives having different hydroxyl contents. The clearcoat surface, mechanical and chemical properties were studied using a contact angle measuring device, dynamic mechanical thermal analysis (DMTA) and Fourier Transform Infrared spectroscopy (FT-IR) respectively. It was found that additive with lower hydroxyl content gave rise to better easy-to-clean properties of the clearcoat against Arabic gum. This additive also resulted in lower contact angles and higher cross-linking density, tensile stress and work of break of the clearcoat.     

Effect of polysiloxane additives on the scratch resistance of an acrylic melamine automotive clearcoat

Many attempts have been carried out to increase the scratch resistance of clearcoats using various appropriate additives. These additives may increase surface hardness or surface slippage, and/or enhance the bulk mechanical strength of the clearcoat. In the present study, the influence of various added loads of three differently structured polysiloxane additives on the scratch resistances of an acrylic melamine clearcoat was investigated. A series of analytical instruments, such as a laboratory carwash simulator, a scanning electron microscope, an optical microscope and an attenuated total reflectance Fourier transform infrared spectroscope, and others were used to compare the effects of the various added contents of polysiloxane additives on changes in the viscoelastic properties and scratch morphologies of the resultant clearcoats. The results illustrated that all polysiloxane additives improve the scratch resistance of such clearcoats, yet the optimum load varied for each individual additive. There is also a good indication that polyether-modified polysiloxanes improve scratch resistance by increasing surface hardness, while the fluorocarbon-modified polysiloxane tends to change the viscoelastic properties of the clearcoats. It was also found that scratch resistance varied linearly with Micro-Vickers’ hardness for brittle clearcoats.     

Evaluation of the weathering performance of basecoat/clearcoat automotive paint systems by electrochemical properties measurements

The aim of the present study was to investigate the possibility of evaluating the weathering performance of a basecoat/clearcoat automotive paint system through the determination of its electrochemical properties. To this end, the electrochemical properties of a basecoat/clearcoat automotive paint in a 3.5% solution of NaCl in deionized water were measured at different weathering exposure times. A constant phase element (CPE) was used for describing the electrochemical behavior of the coatings under test. The values of the CPE parameters, i.e. Y₀ (the CPE constant) and n (the CPE power) were subsequently correlated to the extent of photo-oxidation (as measured by appearance, surface roughness, FTIR, surface tension and adhesion measurements) of clearcoat at the surface, in the bulk and at the interface between the basecoat and the clearcoat. The result showed that the electrochemical parameters Y₀ and n provide ready means for comparing the weathering performances of basecoat/clearcoat automotive paint systems. Increases in the value of Y₀ together with decreases in the value of n with increasing weathering exposure times suggest increased possibilities for the onset of cracking in the clearcoat itself in addition to its propagation towards the basecoat. Additionally, sudden variations in the values of Y₀ and n are indicative of increases for the clearcoat to peel off.     

Studying the role of polysiloxane additives and nano-SiO2 on the mechanical properties of a typical acrylic/melamine clearcoat

Effects of conventional polysiloxane additives and nano-SiO₂ on the mechanical properties of an automotive acrylic/melamine clearcoat (CC) are studied. Clearcoats formulations were prepared by addition of different concentrations of polysioloxane additives (with different modifications) and hydrophobic nano-SiO₂ particles. Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) and atomic force microscope (AFM) were utilized to evaluate the effects of nano-SiO₂ and polysiloxane additives on the surface properties of the CCs. The mechanical properties of the surface and the bulk of the CCs were studied by nano-indentation and tensile tests, respectively. Results showed that polysiloxane additives can mostly affect the mechanical properties of the surface of the CC. Additives with shorter side chains and therefore higher surface activity caused higher changes on the surface properties the CC. Unlike conventional polysiloxane additives, the nano-SiO₂ particles mainly influenced the mechanical properties of the bulk of the CC.     

Role of surface active additives on reduction of surface free energy and enhancing the mechanical Attributes of easy-to-clean automotive clearcoats: Investigating resistance against simulated tree gum

The objective of this work is enhancing the clearcoat resistance against simulated tree gum (Arabic gum) using surface active additives including hydroxyl-functional polydimethyl siloxane (PDMS) and hydroxyl-functional silicone polyacrylate which are able to reduce gum adhesion to the clearcoat surface by reducing its surface free energy and work of adhesion. Using a contact angle measuring device, the surface free energy, contact angle and work of adhesion were obtained. The mechanical and structural properties of the clearcoats were studied by tensile test, dynamic mechanical thermal analysis (DMTA) and Fourier transform Infrared spectroscopy (FT-IR). Results showed that both additives enhanced the clearcoat easy-to-clean properties and reduced work of adhesion and surface free energy. The decrease in surface free energy and work of adhesion was more pronounced in presence of hydroxyl-functional polydimethyl siloxane. It was found that polydimethyl siloxane could produce contact angles much greater than silicone polyacrylate. Both additives increased clearcoat cross-linking density and toughness by participating in curing reaction. Results showed that the increase in cross-linking density and toughness was more effective when polydimethyl siloxane based additive was used. Results also revealed that additives could significantly improved the clearcoat resistance against Arabic gum by reducing gum adhesion to the surface. Both number of cracks and etched areas were reduced in presence of the additives especially in presence of polydimethyl siloxane. Both the chemical structure and functionality of the additives were found influential parameters which could alter the clearcoat surface cleanability and biological resistance against simulated tree gum.     

Studying the role of polysiloxane additives and nano-SiO2 on the mechanical properties of a typical acrylic/melamine clearcoat

Effects of conventional polysiloxane additives and nano-SiO₂ on the mechanical properties of an automotive acrylic/melamine clearcoat (CC) are studied. Clearcoats formulations were prepared by addition of different concentrations of polysioloxane additives (with different modifications) and hydrophobic nano-SiO₂ particles. Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) and atomic force microscope (AFM) were utilized to evaluate the effects of nano-SiO₂ and polysiloxane additives on the surface properties of the CCs. The mechanical properties of the surface and the bulk of the CCs were studied by nano-indentation and tensile tests, respectively. Results showed that polysiloxane additives can mostly affect the mechanical properties of the surface of the CC. Additives with shorter side chains and therefore higher surface activity caused higher changes on the surface properties the CC. Unlike conventional polysiloxane additives, the nano-SiO₂ particles mainly influenced the mechanical properties of the bulk of the CC.     

Attributing the resistance against simulated tree gum of an acrylic/melamine film loaded with an active silicone additive to its surface free energy

The present work reports preparation of acrylic/melamine based clearcoats with different loadings of a functionalized polysiloxane additive. The resulting films were applied over a black basecoat automotive coating system. Dynamic mechanical thermal analysis (DMTA), contact angle measurement, optical microscopy and gonio-spectrophotometery were utilized to investigate the mechanical (viscoelastic/viscoplastic), surface and optical properties of the coating system before and after exposure to Arabic gum (simulated tree gum). The resistance of film surface against gum attack showed high dependence on gum adhesion to the films. It was revealed that depreciation of surface free energy of additive loaded films could greatly improve their behavior against gum, apparently due to their enhanced non-stick characteristic. Tg and loss peak height also increased, indicating that additive did not negatively influence coating curing state. However, at loading contents exceeding 4 wt% both Tg and loss peak height decreased, revealing that a phase separation had occurred. The improved resistance of films against Arabic gum was corresponded to the low clearcoat shrinkage and crack formation. Weaker interactions between gum and clearcoat surface was seen in presence of additive. The shape and size of defects (of gum exposed films) were also significantly changed.     

Surface tension studies of additives in acrylic resin-based powder coatings using the Wilhelmy balance technique

A modified Wilhelmy balance technique using thin fibers as solid probes has been applied to study the effect of silicone additives in acrylic resin-based powder coatings on the surface tension of non-reactive binder systems. By measuring the temperature dependence of the surface tension in the temperature range between 140 and 180°C, it could be shown that the silicone additives investigated had a very different surface activity in the molten acrylic resin. Due to the high accuracy of the measuring technique and the good reproducibility of the experiments the influence of different additive concentrations on the surface tension was detectable even at very low concentrations (below 1 wt.%).

Compared to the pure powder coating binder which has a surface tension of about 30 mN/m the values decreased between 2–15 mN/m depending on the type of the silicone additive. In addition, the temperature coefficient −(dγ/dT) of the surface tension of the binder melt was changed. In the case of two additives, the surface tension of the powder coating and its temperature coefficient were lowered considerably. This effect of additives is desirable to reach good wetting and leveling of the powder coating.     

Thermomechanical and chemorheology properties of a thermosetting acrylic/melamine clearcoat modified with a hyperbranched polymer

The work presented here aims at studying the thermomechanical and chemorheological properties of an automotive clearcoat containing an acrylic/melamine resin modified with a hyperbranched poly ester‐amide (HBP) additive. Rheological experiments were conducted at ambient (25°C) and curing temperature (140°C). Dynamic mechanical thermal analysis and hardness measurements were performed to reveal the influence of HBP content on the behavior of the cured samples. It was found that the viscosity of the resin containing HBP samples considerably decreased. Although curing degree and mechanical properties were improved at low HBP loadings, a reverse effect was seen at higher contents. Dynamic rheological results during curing showed that although low amount of HBP resulted in an early gel point (GP), higher HBP loading postponed the GP. This loading‐dependent behavior was explained by the influence of HBP on viscosity and reactivity of the system on which the curing performance was influenced oppositely. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Influence of coalescence and interfacial tension on the morphology of PP/HDPE compatibilized blends

In this paper, the compatibilization of polypropylene (PP)/high-density polyethylene (HDPE) blend was studied through morphological and interfacial tension analysis. Three types of compatibilizers were tested: ethylene-propylene-diene copolymer (EPDM), ethylene-vinylacetate copolymer (EVA) and styrene-ethylene/butylene-styrene triblock copolymer (SEBS). The morphology of the blends was studied by scanning electron microscopy. The interfacial tension between the components of the blends was evaluated using small amplitude oscillatory shear analysis. Emulsion curves relating the average radius of the dispersed phase and the interfacial tension to the compatibilizer concentration added to the blend were obtained. It was shown that EPDM was more efficient as an emulsifier for PP/HDPE blend than EVA or SEBS. The relative role of interfacial tension reduction and coalescence reduction to particle size reduction was also addressed. It was observed that the role of coalescence reduction is small, mainly for PP/HDPE (90/10) blends compatibilized by EPDM, EVA or SEBS. The results indicated that the role of coalescence reduction to particle size reduction is lower for blends for which interfacial tension between its components is low at compatibilizer saturation.     

Effects of liquid viscosity and surface tension on atomization in two-phase, gas/liquid fluid coker nozzles

This is an experimental study of the effects of liquid viscosity (μ_L) and surface tension (γ) on the size of droplets produced by an atomizer fed with a two-phase gas/liquid (TPGL) mixture. The nozzle is a one-quarter scale model of an industrial fluid coker nozzle used for bitumen upgrading. The primary objective of this study was to compare the Sauter mean diameter of the TPGL sprays for different μ_L and γ. Compressed air was used as the gas phase; the liquid phases were water, canola oil and a glycerine-water solution. The μ_L was varied from 1 mPa s to 67 mPa s, and γ was varied from 25 mN/m to 61 mN/m. The liquid flow rates were varied from 0.095 L/s to 0.105 L/s, and the gas-to-liquid ratio , by mass, was fixed at 2%, similar to the ratio used in commercial fluid coker nozzles. Fluid mixing pressures in the test were between 400 kPa and 700 kPa. The D₃₂ within the spray was measured using a Dantec 2D-Fibre mode Phase-Doppler-Particle-Anemometer (PDPA). With measurements performed at axial distances of 100 and 202 mm from the nozzle orifice and within a spray radius of 40 mm. The results showed that the 67-fold increase in μ_L results in 46 μm increase in D₃₂ which roughly extrapolates to a power law relationship exponent of 0.11 (based on two points). In contrast, the 2.4-fold increase in γ indicates roughly 42 μm increase in D₃₂, giving an exponent of −0.24. For both parameters the exponent is small, indicating weak dependence. The γ effects appear stronger, but the modest increase is barely exceeds the margin of error.     

Surface tension prediction and thermodynamic analysis of the surface for binary solutions

The surface tensions of 100 aqueous and 200 non-aqueous binary solutions are correlated by Shereshefsky model and excellent results are obtained. The average percent deviations are about ∼1.8% for aqueous and ∼0.56% for non-aqueous binary solutions. The free energy change in the surface region is calculated and is used to obtain the excess number of molecular layers in the surface region. Furthermore, the model is used to derive an equation for the standard Gibbs energy of adsorption. Where experimental data is available for the standard Gibbs energy of adsorption, the agreement between the calculated and the experimental data is found to be very good.     

Modeling bubble column reactor with the volume of fluid approach: Comparison of surface tension models

This work aims at comparing surface tension models in VOF (Volume of Fluid) modeling and investigating the effects of gas distributor and gas velocity. Hydrodynamics of a continuous chain of bubbles inside a bubble column reactor was simulated. The grid independence study was first conducted and a grid size of 1.0 mm was adopted in order to minimize the computing time without compromising the accuracy of the results. The predictions were validated by comparing the experimental studies reported in the literature. It was found that all surface tension models can describe the bubble rise and bubble plume in a column with slight deviations.     

Effect of additives on the adsorption of sodium bis(2-ethyl hexyl sulfosuccinate) at the air-water interface studied by equilibrium and dynamic surface tension measurements

Using equilibrium and dynamic surface tension measurements, we have studied the effect of the addition of poly(sodium 4-styrenesulfonate) (PSS), sodium chloride, and 1,4,7,10,13,16-hexaoxyacyclooctadecane (18-crown-6) on the surface properties of sodium bis(2-ethyl hexyl sulfosuccinate) (AOT). The addition of PSS or NaCl weakly increases the maximum packing of AOT, whereas the presence of 18-crown-6 slightly decreases the maximum surface coverage. The surfactant adsorption kinetics on the interface is a diffusion-controlled process. The two asymptotic solutions at long times and at short times to the classic Ward Tordai equation were used to fit dynamic results. At long times there is evidence of the existence of an electrostatic barrier at high surfactant concentration when using pure AOT and AOT mixed with PSS. In binary mixtures of AOT with sodium chloride or 18-crown-6, the electrostatic barrier is not observed over the surfactant concentration range studied.     

Interfacial tension from the height and diameter of sessile drops and captive bubbles with an arbitrary contact angle

A method has been developed to calculate the interfacial tension of sessile drops and captive bubbles of arbitrary contact angle by measuring the drop diameter and vertical distance to the apex at arbitrary horizontal planes within the drop. The procedure works in theory for any contact angle with an accuracy on the order of 0.1%. However, practical limitations reduce the range of angles to roughly 50°–180° but do not restrict the range of interfacial tensions (at least 0.01 mJ/m² to 72.0 mJ/m²). The optimal strategy is to use the method at several points on a single drop and to calculate the mean and standard deviation of the resulting interfacial tensions.     

Interfacially compatibilized LDPE/POE blends reinforced with nanoclay: investigation of morphology,rheology and dynamic mechanical properties

Morphological, melt rheological and dynamic mechanical properties of low-density polyethylene (LDPE)/ethylene–octene copolymer (POE)/organo-montmorillonite (OMMT) nanocomposites, prepared via melt compounding were studied. The XRD traces indicated different levels of intercalated structures for the nanocomposites. Addition of a compatibilizer (PE-g-MA) improved the intercalation process. TEM results revealed existence of clay layers in both phases but they were mainly localized in the elastomeric POE phase. Addition of 5 wt% OMMT to the LDPE/POE blend led to reduction in the size of the elastomer particles confirmed by AFM. The complex viscosity and storage modulus showed little effect of the presence of the clay when no compatibilizer was added. As the extent of exfoliation increased with addition of compatibilizer, the linear viscoelastic behavior of the composites gradually changed specially at low-frequency regions. The interfacially compatibilized nanocomposites with 5 wt% OMMT had the highest melt viscosity and modulus among all the studied nanocomposites and blends. Also, this particular composition showed the best improvement in dynamic storage modulus. The results indicated that clay dispersion and interfacial adhesion, and consequently different properties of LDPE/POE/clay nanocomposites, are greatly affected by addition of compatibilizer.     

Influence of temperature,molecular weight,and molecular weight dispersity on the surface tension of polystyrene,polypropylene, and polyethylene. II. Theoretical

Experimental data for the surface tension of polystyrenes of different molecular weights (3400–200,000) and different molecular weight dispersities (1–3) and of different polyolefins are compared with the predictions of the Patterson–Rastogi and Dee–Sauer cell theories, which infer the surface tension from pressure–volume–temperature (PVT) data. PVT data for these polymers were obtained from the literature and experimentally and are fitted to the Flory–Orwoll–Vrij equation of state. Both theories predict that the surface tension will decrease linearly with increasing temperature and increase with molecular weight, thereby corroborating the experimental data. However, both theories underestimate the entropy change in the surface formation per unit area at a constant volume for low molecular weight and polydisperse systems and underestimate the effect of molecular weight dispersity on surface tension. Both theories feature two parameters, m and b, that quantify the enthalpic and entropic contributions to surface tension. The theoretical predictions are fitted to the experimental data for monodisperse polystyrene (with a molecular weight above the molecular weight of entanglement), polypropylene, and linear low‐density polyethylene to quantify the enthalpic contribution to surface tension. b is then evaluated as a function of molecular weight and molecular weight dispersity and is found to decrease with increasing molecular weight and to increase with increasing molecular weight dispersity, showing that end‐group excess at the surface has some effect on surface tension. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2201–2212, 2002     

On the thermodynamic functions of gas-solid adsorption and liquid-solid immersion,and their relation to adhesion,contact angle and surface tension

The thermodynamic functions of gas-solid adsorption and liquid-solid immersion are summarized on a literature basis. For adsorption, the isosteric and calorimetric methods are compared; for immersion, the Gibbs free energy of adhesion as a function of relative pressure is introduced.The thermodynamic functions reported are enthalpy, Gibbs free energy and entropy of adsorption, immersion and adhesion. All the formulae given contain only those values that result from adsorption, immersion, contact angle or surface tension of the liquids measurements.Interrelations between the thermodynamic functions of adsorption, immersion and adhesion are also given. They permit cross checks and substitution of measurements, e.g., of immersion for adsorption measurement.Typical values are reported and plots of some thermodynamic functions versus coverage are discussed with respect to height and decrease of the powder-adsorptive interaction with layer thickness.     

Hydrophilic modification of polypropylene microporous membranes by grafting TiO2 nanoparticles with acrylic acid groups on the surface

Hydrophilic microporous membranes were prepared based on polypropylene (PP) cast films blended with a commercial acrylic acid grafted polypropylene (PP-g-AA) via melt extrusion followed by grafting titanium dioxide (TiO₂) nanoparticles on its surface, annealing and stretching. ATR-FTIR, XPS and EDS analyses showed that the hydrophilic segments of an amphiphilic modifier (PP-g-AA) acted as surface functional groups on the film surface. The results indicated that the presence of the modifier was very important for grafting TiO₂ nanoparticles on the film surface. Compared to PP and PP/PP-g-AA blend films, the water contact angle decreased by a factor of 2.5 after grafting TiO₂ on the surface of the films, meanwhile the water vapor permeability of the microporous membranes prepared from those films increased by a factor of 1.5. All these results indicated that the hydrophilicity of the modified PP membranes was improved.     

Selectivity of high surface area Ce0.68Zr0.32O2 for the new generation of TWC under environments with different redox character

A number of experiments were carried out with fresh and aged high surface area Ce_0.68Zr_0.32O₂ mixed oxide samples with complex feed-streams in order to determine their performance as three way catalyst (TWC). The results confirmed the oxygen storage capacity (OSC) of these samples, which favour NO conversion in cycled versus stationary stoichiometric operation. Several experiments carried out with different feed-streams have shown that a pre-reducing treatment can significantly improve both NO reduction at low-temperature and selectivity to N₂, which can be very useful to reduce the emission of nitrogen oxides immediately after starting the automobile. Although a significant reduction of the specific surface area of the mixed oxide takes place during ageing at 1173 K, it has been shown that the performance of the sample remains similar or even better than when fresh, due to an increased OSC. Thus, the reduction of CO and hydrocarbon emissions during start could be achieved by situating the catalytic converter nearer the exhaust to the engine, where the catalyst will be heated faster.