An evaluation of an automotive clear coat performance exposed to bird droppings under different testing approaches

Department of Polymer Engineering of Amirkabir University of Technology, P.O. Box 15875-4413, Tehran, Iran
Progress in Organic Coatings (Impact Factor: 2.36). 10/2009; 66(2):149-160. DOI: 10.1016/j.porgcoat.2009.06.010


In this study, the effects of two types of biological materials, i.e. natural bird droppings and pancreatin, on properties of an automotive acrylic melamine clear coat were studied. In addition, two different testing approaches including pre-aging and post-aging were utilized to investigate the biological resistance. To this end, effects of these biological materials on clear coat surface properties and appearance were investigated by different techniques including digital camera, SEM, AFM, optical microscopy and a gloss meter. In addition the mechanical properties of clear coats were evaluated by micro Vickers measurement and DMTA analysis. For further investigation FTIR analysis was utilized to have a more understanding of the failure mechanism.Results showed that the biological materials have an extremely vital effect on the appearance of the coatings. Decreasing of tg and hardness of the films made by pancreatin and bird droppings were observed and were attributed to the chemical alterations as proved by FTIR analysis. It was also found that the biological degradation occurred on the samples experienced the post-aged testing method was more severe than the samples exposed to pre-aged testing. On the other hands, although bird droppings and pancreatin revealed a same failure mechanism, the effect of the former was more severe. In addition, it has been shown that the enzymatic structure of biological materials is responsible for the catalyzing the hydrolytic degradation of clear coat at neutral pH. Therefore, the biological degradation mechanism may be regarded as an enzymatically induced hydrolytic cleavage.

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    • "This can be mainly explained by the lost NH 2 -terminated degradation products which have been released from the coating during aging process. This fact has been previously illustrated else- where[15,24]. In CL2, the NH peak changes with the same trend as NH-CO peak which again proves the validity of post-curing during initial hours of aging process and release of degradation products after 300 h. "
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    ABSTRACT: In this study the effect of bird droppings and tree gums on two different polyurethane refinish coatings has been investigated. To this end, Arabic gum and pancreatin were used as simulated tree gum and bird dropping, respectively. These substances were applied on coatings exposed to UV radiation and moisture for different exposure times. Various techniques were used to study the appearance of the degraded coatings. Structural analysis of samples was done by FTIR spectroscopy. Surface free energy and thermo mechanical characteristics of refinish coatings were studied by contact angle measurement and DMTA respectively. All experiments were carried out before and after degradation process. In general, it was revealed that while pancreatin degraded the coatings chemically, Arabic gum affected it mechanically and chemically, leading to wrinkle-like deformations on the coating surface. It was also concluded that the cross-linking density and surface free energy have vital roles in the degradation of automotive refinish coatings. It was demonstrated that low cross-linking density and Tg of polyurethane system created a dynamic system which can be post-cured during experiment, leading to enhanced biological resistance. According to this finding, it was also revealed that coating history before bio attack is an important factor in the biological performance of polyurethane systems.
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    ABSTRACT: Biological resistance of coatings can be regarded as one of the main properties in automotive industries. This study aims to investigate the effects of biological materials on the mechanical performance of an automotive clear coat. To this end, two acrylic melamine clear coats containing different melamine cross-linker contents were used. In addition, biological resistance of these clear coats were studied at two different ageing processes including pre-ageing and post-ageing which involve various hot-cold, humid shockings and UV radiation of sunlight. By the aid of optical microscopy, micro Vickers and DMTA analyses, different optical and mechanical properties such as micro hardness, T g, cross-linking density and storage modulus were studied. Results revealed an inverse impact of both biological materials to decrease the clear coats mechanical attributes. In addition, a complicated effect of ageing conditions was observed for both clear coats exposed to these materials. It was shown that the coating having a higher mechanical properties and T g even resulted in a lower biological resistance.
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    ABSTRACT: This work aims to study the effect of various natural and artificial biological compounds on an automotive acrylic/melamine clearcoat applied over silver and black basecoats containing pigments. The visual performance of the coating system was evaluated at different aging conditions. To this end, analytical techniques including optical microscopy, scanning electron microscopy, gonio-spectrophotometery, gloss measurement, ATR-FTIR spectroscopy, and DMTA analysis were utilized to investigate the optical and mechanical response of the system upon exposure to the biological materials. Results indicated different effects produced by gums and bird droppings on both silver and black systems at all aging processes. In addition, a more severe effect of biological attacks was observed on the clearcoat samples applied on the black basecoat which had experienced postaging conditions. However, it was found that pancreatin and bird droppings influence the coating systems more severely compared to the natural and synthetic Arabic gums. KeywordsDegradation-Electron microscopy-FTIR
    No preview · Article · Nov 2010 · Journal of Coatings Technology and Research
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