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The effect of graphene oxide (GO) functionalized with 3‐amino‐propyl‐triethoxy‐silane(APTS), organo‐vermiculite(OVMT), and magnesium hydroxide (MH) combinations on mechanical, thermal, and flame retardant (FR) properties of polypropylene (PP) was studied. GO was obtained via a slight modification of the Hummers method and then chemically surface functionalized with APTS. VMT clay was modified with maleic anhydride (MA) via a chemical reaction with acetic acid to increase its inter‐laminar spacing. The results of Fourier‐transform infrared analysis, X‐ray diffraction, and transmission electron microscopy demonstrated that APTS had been successfully attached to the GO and that VMT was modified with MA. Subsequently, each functionalized filler was incorporated in combination with MH to the flame‐retardant‐polypropylene system. The performance of PP composites with each filler as well as with their combinations, including a reduced “30 wt% of MH” were compared with the reference PP composite with 55 wt% of MH as the only FR additive. PP grafted with MA (PP‐gMA) and PP grafted with amine‐alcohol(PP‐gDMAE) were used as compatibilizer agents between each filler and the polymer matrix. The results obtained confirmed a better mechanical and FR performance when using PP‐gDMAE. Composites with 30 wt% MH combined with very low contents of GO (0.5 and 1.0 wt%) showed improved FR properties, similar to the reference sample, with an evident reduction in peak of the heat release rate (pHRR) and total heat release and increased limiting oxygen index (LOI) values. The combination of MH and GO showed the best FR and mechanical properties: LOI of 22.5% and pHRR of 540 kW/m2 which were very similar to the reference sample. In addition, PP‐gDMAE improved the OVMT exfoliation with a slight increase in the intergallery spacing but OVMT and modified GO combinations did not significantly improve the FR and mechanical properties compared with the effect of MH and modified GO combinations. The combination of MH and modified GO makes it possible to reduce the total MH filler content from 55 to 30 wt% to accomplish the FR requirements and with enhanced mechanical properties. This filler combination promoted the formation of a continuous, intact residual char layer on the PP surface, which acts as an insulating barrier to protect the base material. These filler combinations offer an option to meet the FR properties using halogen‐free FR with better mechanical properties.

We report on measurements of a magnetorheological model fluid created by dispersing nonmagnetic microparticles of polystyrene in a commercial ferrofluid. The linear viscoelastic properties as a function of magnetic field strength, particle size, and particle size distribution are studied by oscillatory measurements. We compare the results with a magnetostatic theory proposed by De Gans et al. [Phys. Rev. E 60, 4518 (1999)] for the case of gap spanning chains of particles. We observe these chain structures via a long distance microscope. For monodisperse particles we find good agreement of the measured storage modulus with theory, even for an extended range, where the linear magnetization law is no longer strictly valid. Moreover we compare for the first time results for mono- and polydisperse particles. For the latter, we observe an enhanced storage modulus in the linear regime of the magnetization.

The effect of organopalygorskite (OPGS), molybdenum sulfide (MoS2), and magnesium hydroxide (MH) combinations on fire retardant and flammability characteristics of low‐density polyethylene/ethylene vinyl acetate (LDPE/EVA) blends was investigated using the limited oxygen index (LOI), horizontal burning test (UL‐94), and cone calorimeter measurements. The combination of OPGS with exfoliated MoS2 nanosheets is employed to reduce the conventional hydroxide content and enhance the PE/EVA blend flame‐retardant properties with a notable improvement in mechanical and processing characteristics. The flame‐retardant properties of the composites were compared with a reference PE/EVA sample with 55 wt% of MH, which is commonly used for wire coating. The effect of each additive and the use of a maleated polyethylene (PEgMA) as a compatibilizing agent on PE/EVA flame‐retardant properties were analyzed. The results of the LOI and UL‐94 tests confirmed that the addition of OPGS combined with MoS2 substantially increases the LOI value (26%) and reduces the burning rate (66%) and the pHRR (83%) compared with neat polymer blend and passes V‐0 rating during UL‐94 vertical test, which were very similar to the values obtained for the reference sample with higher MH content. In addition, the results indicate that the addition of these additives simultaneously increases the tensile modulus with mechanical properties even higher than the reference sample. Most important, the results indicated that these additive combination allows to reduce the total MH filler content to achieve the flame‐retardant requirements and with enhanced mechanical properties and with higher melt flow rates and lower viscosities facilitating the processing of the polymer composites at lower pressure in the processing extruder. Therefore, this additives combination provides a favorable way to obtain efficient flame‐retardant materials with halogen‐free, low smoke, and easy processing characteristics. J. VINYL ADDIT. TECHNOL., 26:434–442, 2020. © 2020 Society of Plastics Engineers

Transformers are very expensive apparatuses and are vital to make the whole power system run normally. The failures in such apparatuses could leave them out of service, causing severe economic losses. The life of a transformer can be effectively determined by the life of the insulating paper. In the present work, we show an alternative diagnostic technique to determine the ageing condition of transformer paper by the use of FTIR spectroscopy and an empirical model. This method has the advantage of using a microsample that could be extracted from the transformer on-site. The proposed technique offers an approximation quantitative evaluation of the degree of polymerization of dielectric papers and could be used for transformer diagnosis and remaining life estimation.