http://www.revmaterialeplastice.ro MATERIALE PLASTICE ♦54♦No.2 ♦2017 331 The Resistance to the Action of Molds of Some Painting Materials Aged by Thermal Cycling and Exposed to an Electrical Field of 50 Hz ALINA CARAMITU 1 , NICOLETA BUTOI 1 , TRAIAN RUS 2 , ANA MARIA LUCHIAN 1 *, SORINA MITREA 1 1 National Institute for Research and Development in Electrical Engineering INCDIE ICPE-CA , 313, Splaiul Unirii, Bucharest, Romania, 2 University Politehnica of Bucharest, Faculty of Applied Chemistry and Materials Science, 313 Splaiul Independentei, Bucharest, Romania In order to evaluate the durability of paint layers exposed to simultaneous action of climatic and electrical stresses, the influence of 50 Hz electrical field and of aging by thermal cycling on the resistance to the action of molds of some painting materials was evaluated by specific microbiological determinations. Comparative measurements were carried out on initial paint samples and samples aged by applying of 1000 successive thermal cycles (between –38 o C and 85 o C, with the duration of a cycle of 90 min), exposed to Czapek-Dox culture media (with and without sucrose), inoculated with a salt solution containing approximately 10 6 mold spores (of 10 different species), and incubated at 30± 2 o C and RH 90± 5%. It was found that for the samples exposed to a controlled field of 5V/cm and 50Hz the resistance to the action of molds is almost two times less than in the absence of the disruptive electric field. Also, it was noticed that the field of 5V/cm and 50Hz stimulates the growth of Aspergillus niger, but completely inhibit those of Trichoderma viride and Aspergillus flavus. Key words: painting materials, epoxy resins, polyurethane resins, thermal aging, molds, biodeterioration The durability and the safety in exploitation of various metallic structures protected against corrosion by painting is a complex problem with special practical and economic implications. The complexity of this issue is given both by the diversity of metallic structures and paints and by the great diversity of the stress factors acting on them. During operation, the painted metallic structures can be exposed simultaneously to mechanical stress (vibration, wind, etc.), climatic influences (humidity, diurnal temperature variations, frost deposits, etc.), pollutants and atmospheric aggressive substances (SO 2 , NO x , CO 2 , aerosols- marine climate, powders, etc.), UV and IR radiations, microbiological factors, etc. Under the concentrated action of the stress factors, often with synergistic complex effects, the paint layers deteriorate and initiate complex metal corrosion processes. As a result of metallic support corrosion, the mechanical strength of the structure decreases, which can conduct to the compromise of the structure under extreme solicitations, with the corresponding economic, ecological and social complications. Thus, in the case of supporting pillars of the power lines especially those in alpine areas (exposed to intense UV radiation), but also those on the seashore (exposed to marine climate) after excessive aging of the paint layers and metal corrosion there is a risk of both tearing down the pillars and leakage of the corrosion products on the insulators for supporting the conductors; in both cases an interruption of electricity supply occurs [1, 2]. Basically, the polymeric material presents a good resistance to the action of microorganisms due to high molecular weight and volume [3-5]. Biodeterioration and biodegradation of polymers occur only after the result of aging processes. Under the action of atmospheric stress factors [6, 7], UV radiation [8, 9] and / or mechanical stress [10], the polymer chain is fractionated molecularly and the molecular mass and volume decrease [11, 12]. Under the action of the enzymatic activity of microorganisms [13], the carbon metabolization from the resin becomes possible. Thus, by laboratory experimental studies [3-5, 14] and by landfield investigations [2] the biodeterioration of the polymers exposed to atmospheric and to soil stressors was reported [15-19]. As a result of the excessive industrialization and of the continuous increase in production and consumption of electrical energy, the electromagnetic pollution of the environment with disturbing signals coming both from transport and distribution lines, as well as from different consumers that generate deforming regime [20] and/or of electromagnetic waves is becoming more pronounced [21]. The anthropogenic electromagnetic fields accelerate the natural processes of corrosion [22-24] and produce changes in metabolism, the growth and the reproduction of microorganisms [25-29]. On the other hand, various studies report the increase of the corrosion rate of the general purpose metals in the presence of microorganisms [30-34], an increase that is more pronounced (synergistic effect) when the culture medium (electrolyte) is disturbed by the alternating electric field (50Hz - linear regime and/ or deforming) [24]. It is established that the usual coated materials exhibit a limited resistance to the action of microorganisms, which has imposed the development of paints with antibacterial activity and low biodegradability, required for special applications (such as furniture and medical equipment) [35-37]. Taking into account these considerations, the aim of this paper consists in the experimental evaluation of the resistance to the action of molds of some usual painting materials aged by thermal cycling. Experiments part In order to assess the resistance to the action of mold of different origin paints, film samples were prepared from the investigated materials (table 1). * email: anamaria.luchian@icpe-ca.ro