Thermal Stability Evaluation of Polystyrene-Mg/Zn/Al LDH Nanocomposites

Abstract

A series of samples of Mg/Zn/Al LDHs (layered double hydroxides) materials was prepared by the co-precipitation and urea hydrolysis methods. They were modified with organic surfactants (acrylate and oleate anions) and characterized by X-ray diffraction, which corroborated the intercalation of anionic species into the interlayer space. The hydrophobized materials were incorporated at low contents (10 and 15 wt.%) to polystyrene, which was synthesized by emulsion polymerization techniques. The polymeric composites were analyzed by thermogravimetry to determine the decomposition temperature. The results demonstrated that the materials with Zn presented the greatest increment in the degradation temperature (7 °C < T < 54 °C). Moreover, the Friedman, Flynn–Wall–Ozawa, and Coats–Redfern models were compared to obtain the kinetic parameters of degradation process. The obtained order of decomposition of the Coats–Redfern model showed that the decomposition process occurs in at least two stages. Finally, the addition of environmentally friendly modified Layered Double Hydroxides (LDH) nanomaterials to the polystyrene (PS) matrix allowed for obtaining polymeric composites with higher thermal stability, retarding the decomposition process of PS.

Use of Ethylamine, Diethylamine and Triethylamine in the Synthesis of Zn,Al Layered Double Hydroxides

“…Figure 1 shows the PXRD diagrams of these samples without hydrothermal treatment. The positions and relative intensities of the recorded diffraction peaks revealed a layered structure of the solids, characteristic of an ordered 3R 1 polytype of solids with the LDH structure (JCPDS: 22-0700) [29][30][31]. In all cases, the most intense diffraction peak, attributed to the diffraction plane (003) of the crystal structure, was recorded at a position 10.0 • (2θ), with a spacing of 8.93 Å.…”

“…The application of a conventional hydrothermal treatment (HT) resulted in a greater increase in the crystallinity of the solids synthesized in the presence of DEA and TEA However, the same effect is not observed for the samples synthesized in the presence of EA, where the application of HT treatment resulted in the collapse of the layered structure, as can be observed in Figure 3. Thus, the PXRD recorded for samples synthetized using EA showed the formation of a zinc oxide (ZnO) like zincite phase (JCPDS: 00-036-1451 [29]). This ZnO phase is identified mainly by the reflections recorded in the range of 28°-38° (2θ).…”