Articles
Thermal Science and Engineering Progress (24519049)55
Metal–organic frameworks (MOFs) are known for their excellent physical and thermal properties. In the current paper, the use of thermally stable MOFs in the preparation of epoxy composites were studied and their tolerance to high temperatures was investigated in terms of degradation kinetics and operating temperature. UiO-66 and UiO-66-NH2 were used to prepare a series of novel composites from epoxy resin and Novolac (EU and EUN samples, respectively). The effect of the amine groups presented in the UiO-66-NH2 structure on the thermal stability was studied using decomposition activation energy (Ea). The Flynn–Wall–Ozawa (FWO), Kissinger-Akahira-Sunose (KAS) and Ozawa models were used to study the Ea, where it was increased from 166.7 kJ·mol−1 in neat epoxy samples to 238.58 kJ·mol−1 in EUN samples by using only 0.5 Phr of the UiO-66-NH2. Moreover, the operating temperature of the prepared composites was calculated and compared for four sets of heating rates. Up to 10 % mass loss, the mean operating temperature for using the neat epoxy, EU, and EUN composites for 20,000 h, was found to be 184.17 ℃, 246.26 ℃, and 247.73 ℃, respectively. This approach can pave the way for using MOFs as fillers in preparing innovative thermoset composites. © 2024 Elsevier Ltd
Polymer Engineering and Science (15482634)64(3)pp. 1258-1273
Today, the use of biodegradable polymers has become widespread in a wide range of industries. This research scrutinized the physical, mechanical, and rheological properties of poly (lactic acid)/poly (ethylene oxide)/carbon nanotube (PLA/PEO/CNTs) blend nanocomposites, as a good candidate for usage in the packaging industry. PEO and CNTs were added at various concentrations to improve the flexibility, toughness, gas permeability, thermal stability, and mechanical properties of PLA via solution blending. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Field Emission Scanning Electron Microscope (FESEM), water contact angle (WCA), rheometric mechanical spectrometer (RMS) test, gas permeability, and tensile characterization were performed to characterize the properties of the prepared blends and nanocomposites. The experimental results revealed that the addition of 25 wt% PEO to the PLA matrix made a partially miscible blend with a droplet-matrix morphology. PEO at this concentration increased the elongation at break (from 2.2% to 18%) while reducing the modulus (from 25 to 6 MPa). Also, the experimental results indicated that the miscibility of PLA and PEO was enhanced by the addition of 1 wt% CNTs to the prepared blend, associated with diminished entropy of mixing in the LCST phase diagram. Theoretical calculations predicted that the CNTs would be localized in the PLA phase which increased the total crystallinity of the sample by 28%, considerably reducing the amount of gas permeation into the nanocomposite. In addition, the introduction of the CNTs to the blend increased the elongation at break and tensile strength by 13% compared to pure PLA and lowered the rate of thermal degradation effectively. Also, the final results showed that the COOH-CNTs located in the PEO phase caused a decline in the crystallinity and an increase in the gas permeability of the prepared nanocomposite. Highlights: Improvement of physical properties of PLA by blending with PEO and CNTs. A deep investigation on rheological behavior of the prepared nanocomposite. Increasing the crystallinity degree of PLA/PEO blend by adding CNTs. Improvement of the miscibility between PLA and PEO in the presence of CNTs. Controlling the CNTs localization by surface modification. © 2024 Society of Plastics Engineers.