Mihai Marin

This research investigates novel polymeric composite materials for automotive interior trim applications. The composites utilize recycled polypropylene (PPr) matrix and carboxymethylcellulose (CMC) as filler (PPr/CMC: 100/0, 95/5, and 90/10 wt.%). The materials were processed by extrusion and injection molding. Considering their intended application, the composites were evaluated for resistance to key climatic factors, i.e., temperature, humidity, and UV radiation. In addition, structural analyses and FTIR analyses were performed to assess potential heterogeneity and thermal stability. Following FTIR tests, the incorporation of carboxymethyl cellulose in polypropylene is confirmed by the detection of characteristic CMC bands for -OH, C=O, and C-O-C groups. The results indicate slight structural heterogeneity in the 5% and 10% CMC composites. However, no thermal distortions were observed in either the composites or the PPr matrix itself. The behavior of PPr/CMC composites under the action of the mentioned climatic factors has been assessed from the variation of dielectric characteristics with frequency. The strong polarization of CMC leads to a sharp increase in composites electrical conductivity after submersion in water for 480 h, suggesting weakening of the composite structure. After exposure to UV radiation, a sharp increase in conductivity is observed even after the first cycle (72 h) of UV radiation. Following the experimental results obtained in our study, it is recommended to use the PPr +10% CMC composite for obtaining different interior ornaments (carpets, supports, etc.). At the same time, the use of these materials also has the advantage of lightening the mass of the vehicle due to their lower density than polymers.

Metal oxide varistor (MOV) discs (Ø28 mm × 12 mm) made of 97.5 mol.% zinc oxide (ZnO), and 0.5 mol.% each of vanadium pentoxide (V2O5), tin (IV) oxide (SnO2), antimony(III) oxide (Sb2O3), cobalt(II, III) oxide (Co3O4), and chromium(III) oxide (Cr2O3) additives were produced using powder metallurgy. The obtained MOVs were polycrystalline with high density. This study focused on analyzing the microstructure and mechanical and electrical properties of the MOVs. The developed MOVs had a fine-grained microstructure with an average ZnO grain size of about 10 μm. The Ag-coated MOV discs tested in a range of 100 – 1300 V ac exhibited a leakage current of 0.033 – 1.420 mA and a minimum varistor voltage of 2.37 ± 0.15 kV. After conducting functional tests on Ag-coated MOVs installed in polymer-housed surge arresters, it was found that they are suitable for use in medium voltage arresters with a nominal voltage (Un) of 25 kV, a continuous operating voltage (Uc) of 12 kV and a leakage current (IL) of 1 mA.

This paper presents the obtaining and characterization of recycled polypropylene/strontium ferrite (PP/SrFe₁₂O₁₉) polymer composite materials with applications in the electromagnetic shielding of vehicle interiors (mainly automotive electronics—carcasses) from the electromagnetic radiation emitted mainly by exterior sources—electrical lines and supply sources—in terms of the development of the new electrical vehicles. With this aim, suitable polymer composite materials were developed using SrFe₁₂O₁₉ filler in two forms (powder and concentrate). The recycled PP polymer and composite materials with a PP/SrFe₁₂O₁₉ weight ratio of 75/25 and 70/30 were obtained in two stages, i.e., pellets by extrusion and samples for testing through a melt injection process. The characterization of the obtained materials took into account the requirements imposed by the desired applications. It consisted of determining the mechanical and dielectric properties, and microstructure analyses, along with the determination of the resistance to the action of a temperature of 70 °C, which is higher than the temperatures created during the summer inside vehicles. The performance of these materials as electromagnetic shields was assessed through functional tests consisting of the determination of magnetic permeability and the estimation of the electromagnetic shielding efficiency (SE). The obtained results confirmed the improvement of the mechanical, dielectric, and magnetic properties of the PP/SrFe₁₂O₁₉ composites compared to the selected PP polymers. It is also found that all the composite materials exhibited reflective shielding properties (SE_R from −71.5 dB to −56.7 dB), with very little absorption shielding. The most performant material was the composite made of PP/SrFe₁₂O₁₉ powder with a weight ratio of 70/30. The promising results recommend this composite material for potential use in automotive shielding applications against electromagnetic pollution.

Due to electrical energy reduction need, in the recent years, alternative light sources like Compact Fluorescent Lamps (CFL) and Light Emitting Diode lamps (LED) are replacing the classical incandescent light bulbs. Although they consume less power, these lamps have the disadvantages of being a significant source of harmonics. This means that the lightning network should be redesigned taking into account the magnitude of the current harmonic components and of the null current. To this aim, an accurate model easy to build and a fast analysis are very useful. This paper presents three models for different types of energy saving light bulbs, two existing ones and a new implementation, a procedure for model parameters identification and a comparison of the models. Some errors criteria are considered, both qualitative and quantitative. The periodic steady state response is computed using a frequency domain analysis.