Showing papers on "Differential scanning calorimetry published in 2018"

Improving the Impact Strength and Heat Resistance of 3D Printed Models: Structure, Property, and Processing Correlationships during Fused Deposition Modeling (FDM) of Poly(Lactic Acid).

Abstract: A fused deposition modeling method was used in this research to investigate the possibility of improving the mechanical properties of poly(lactic acid) by changing the thermal conditions of the printing process. Sample models were prepared while varying a wide range of printing parameters, including bed temperature, melt temperature, and raster angle. Certain samples were also thermally treated by annealing. The prepared materials were subjected to a detailed thermomechanical analysis (differential scanning calorimetry, dynamic mechanical analysis, heat deflection temperature (HDT)), which allowed the formulation of several conclusions. For all prepared samples, the key changes in mechanical properties are related to the content of the poly(lactic acid) crystalline phase, which led to superior properties in annealed samples. The results also indicate the highly beneficial effect of increased bed temperature, where the best results were obtained for the samples printed at 105 °C. Compared to the reference ...

3D Printing of PLA/clay Nanocomposites: Influence of Printing Temperature on Printed Samples Properties.

Abstract: In this study, the possibility of using a layered silicate-reinforced polylactic acid (PLA) in additive manufacturing applications was investigated. In particular, the aim of this work was to study the influence of printing temperature in the 3D printing process of PLA/clay nanocomposites. For this reason, two PLA grades (4032D and 2003D, D-isomer content 1.5 and 4, respectively) were melt-compounded by a twin screw extruder with a layered silicate (Cloisite 30B) at 4 wt %. Then, PLA and PLA/clay feedstock filaments (diameter 1.75 mm) were produced using a single screw extruder. Dog-bone and prismatic specimens were 3D printed using the FDM technique at three different temperatures, which were progressively increased from melting temperature (185⁻200⁻215 °C for PLA 4032D and 165⁻180⁻195 °C for PLA 2003D). PLA and PLA/clay specimens were characterized using thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and tensile tests. Moreover, the morphology of the 3D printed specimens was investigated using optical microscopy and contact angle measurements. The different polymer matrix and the resulting nanocomposite morphology strongly influenced 3D printed specimen properties. DMA on PLA/clay filaments reported an increase in storage modulus both at ambient temperature and above the glass transition temperature in comparison to neat PLA filaments. Furthermore, the presence of nanoclay increased thermal stability, as demonstrated by TGA, and acted as a nucleating agent, as observed from the DSC measurements. Finally, for 3D printed samples, when increasing printing temperature, a different behavior was observed for the two PLA grades and their nanocomposites. In particular, 3D printed nanocomposite samples exhibited higher elastic modulus than neat PLA specimens, but for PLA 4032D+C30B, elastic modulus increased at increasing printing temperature while for PLA 2003D+C30B slightly decreased. Such different behavior can be explained considering the different polymer macromolecular structure and the different nanocomposite morphology (exfoliated in PLA 4032D matrix and intercalated in PLA 2003D matrix).

Synthesis and Characterization of Conductive Polypyrrole: The Influence of the Oxidants and Monomer on the Electrical, Thermal, and Morphological Properties

Abstract: Conductive polymer, polypyrrole (PPy), was synthesized by chemical oxidative polymerization technique for a period of four hours at room temperature using pyrrole monomer (mPPy) in aqueous solution. Different oxidants such as ferric chloride (FeCl3) and ammonium persulphate (N2H8S2O8) and surfactant sodium dodecyl sulphate (C12H25NaO4S) were used. The produced PPy samples were characterized by using different techniques such as the electrical resistivity by four probe technique, thermogravimetry analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The performance of the oxidants has been investigated and compared. It was found that both oxidants, FeCl3 and N2H8S2O8, have decreased electrical resistivity as a function of temperature, which means increased conductivity. However, FeCl3 has achieved better performance than N2H8S2O8, where it has achieved a lower resistivity of about 60 ohms at room temperature, which indicates higher conductivity of PPy samples with FeCl3 as an oxidant. Similarly, further investigation of FeCl3 oxidant has been conducted by varying its concentration, and its influence on the final properties was reported. It has been observed that the morphology of PPy samples has a significant influence on the conductivity. It was found that 0.1 M and 0.05 M concentrations of FeCl3 oxidant and monomer, respectively, have achieved better thermal stability, which is FeCl3/mPPy ratio of 2 as an optimum value. FTIR and XRD results confirmed the structural formation of polypyrrole from pyrrole monomer during the synthesizing process.

Modified Phase Change Microcapsules with Calcium Carbonate and Graphene Oxide Shells for Enhanced Energy Storage and Leakage Prevention

Abstract: Environmentally friendly microencapsulated phase change materials (MEPCMs) with calcium carbonate (CaCO3) shells were modified with graphene oxide (GO), and the effects of GO content and methodology on MEPCMs were examined. The core–shell structure of MEPCMs and crystal structure of CaCO3 shells were confirmed by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffractometer (XRD). The thermal properties and stability of MEPCMs were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), suggesting that the addition of GO contributed to improving the heat storage capacity and thermal stability of MEPCMs. When the GO content was 1.0 wt %, the encapsulation ratio of MEPCMs was as high as 73.19%, and the leakage rate was reduced by 89.6% compared to the MEPCMs without GO. Furthermore, the thermal conductivity and mechanical properties of GO modified MEPCMs were improved significantly. The considerable latent heat storage, the...

Chemically Enhanced Wet‐Spinning Process to Accelerate Thermal Stabilization of Polyacrylonitrile Fibers

Abstract: In this study, a fast and inexpensive approach is introduced to assist stabilization of polyacrylonitrile (PAN) fibers by adding ammonium iron(II) sulfate in coagulation bath. Effects of chemical treatment on stabilization process and structural evolution of fibers are studied using calorimetric, infrared, and X-ray techniques. A stepwise infrared study confirms the assisted cyclization reaction, and an X-ray analysis reveals a significant improvement in crystallinity and orientation of polymer chains which lead to an increase in tensile strength and modulus of PAN fibers. Differential scanning calorimetry results show 13 °C reductions in peak temperature of the stabilization reaction which means a sign of chemical activation at lower temperature by adding sulfate ions. Quantification of IR spectra shows a 7% increase in extent of reaction of chemically treated fibers and higher degree of conjugation compared with untreated and post-treated fibers. Finally, mechanical properties of chemically treated fibers are improved due to an increase in size and orientation of polymer chains after chemical treatment in the coagulation bath. Compared to control and post-treated PAN fibers, thermochemical properties of presented fibers are improved due to chemically assisted stabilization, and as a consequence, energy consumption of the stabilization step will be reduced by a simple and facile treatment.

C8N26H4: An Environmentally Friendly Primary Explosive with High Heat of Formation

Abstract: The synthesis and characterization of the metal-free polyazido compounds 3,6-bis-(2-(4,6-diazido-1,3,5-triazin-2-yl)-hydrazinyl)-1,2,4,5-tetrazine (2) and 3,6-bis-(2-(4,6-diazido-1,3,5-triazin-2-yl)-diazenyl)-1,2,4,5-tetrazine (4) are presented. Two compounds were characterized by NMR spectra, IR spectroscopy, mass spectrometry, and differential scanning calorimetry (DSC). Additionally, the structure of 2 was confirmed by single-crystal X-ray diffraction. Compounds 2 and 4 exhibit measured densities (1.755 g cm-3 and 1.763 g cm-3 ), good thermal stabilities (194 °C and 189 °C), high heat of formation (2114 kJ mol-1 and 2820 kJ mol-1 ), and excellent detonation performance (D, 8365 m s-1 and 8602 m s-1 ; P, 26.8 GPa and 29.4 GPa). Furthermore, compounds 2 and 4 have been tested for their priming ability to detonate RDX. The results indicate that the title compound 2 is a potential environmentally friendly alternative candidate to lead-based primary explosives.

Making Benzoxazines Greener: Design, Synthesis, and Polymerization of a Biobased Benzoxazine Fulfilling Two Principles of Green Chemistry

Abstract: Sesamol and furfurylamine are used to synthesize a novel benzoxazine monomer as part of the quest to develop greener benzoxazine monomers simultaneously fulfilling two Principles of Green Chemistry, the use of renewable feedstocks and safer solvents and auxiliaries. Respecting principle 5, the so-called preferred solvents (ethanol and ethyl acetate) are used in both the syntheses and purification processes. The chemical structure of the synthesized monomer is verified by proton and carbon nuclear magnetic resonance spectroscopy (1H and 13C NMR), 2D 1H–13C heteronuclear single quantum correlation (HSQC) spectroscopy, and Fourier transform infrared spectroscopy (FT-IR). The polymerization behavior of the monomer and the thermal stability of fully polymerized polybenzoxazine are studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). A thermally stable polymer has been obtained as shown by the 5% and 10% weight reduction temperature (Td5 and Td10) values of 374 and 419 °C, re...

Synthesis and thermophysical properties of RETa3O9 (RE = Ce, Nd, Sm, Eu, Gd, Dy, Er) as promising thermal barrier coatings

Abstract: Thermal barrier coatings (TBCs) are one of the most important materials in gas turbine to protect the high temperature components. RETa3O9 compounds have a defect-perovskite structure, indicating that they have low thermal conductivity, which is the critical property of TBCs. Herein, dense RETa3O9 bulk ceramics were fabricated via solid-state reaction. The crystal structure was characterized by X-ray diffraction (XRD) and Raman Spectroscope. Scanning electron microscope (SEM) was used to observe the microstructure. The thermal physics properties of RETa3O9 were studied systematically, including specific heat, thermal diffusivity, thermal conductivity, thermal expansion coefficients and high-temperature phase stability. The thermal conductivities of RETa3O9 are very low (1.33-2.37 W/m.K, 373-1073 K), which are much lower than YSZ and La2Zr2O7; and the thermal expansion coefficients range from 4.0×10-6 K−1 to 10.2×10-6 K−1 (1273 K), which is close to La2Zr2O7 and YSZ. According to the differential scanning calorimetry (DSC) curve there is not phase transition at the test temperature. Due to the high melting point and excellent high-temperature phase stability with these oxides, RETa3O9 ceramics were promising candidate materials for TBCs. This article is protected by copyright. All rights reserved.