The formation of conjugated structure and its transformation to pseudo-graphite structure during thermal treatment of polyacrylonitrile

2016 ◽  
Vol 29 (9) ◽  
pp. 1097-1109 ◽  
Author(s):  
Shuai Lei ◽  
Shuai Wu ◽  
Aijun Gao ◽  
Weiyu Cao ◽  
Changqing Li ◽  
...  
Keyword(s):  
Nitrogen Atmosphere ◽  
Structural Defects ◽  
Scanning Calorimetry ◽  
Thermogravimetric Analyzer ◽  
Graphitization Degree ◽  
Temperature Ramp ◽  
Graphite Structure ◽  
Chemical Groups ◽  
Graphite Sheets

Three types of polyacrylonitrile (PAN) were considered in order to investigate the effect of molecular composition and configuration on the formation of conjugated structures during stabilization and the conversion of that to pseudo-graphite sheets after carbonization. The stabilization process was performed in an inert or oxidative atmosphere with a temperature ramp from 180°Cto 280°C. The thermal behavior was studied by differential scanning calorimetry, and the change of chemical groups and conjugated structures was detected by in situ measurement of infrared (Fourier transform infrared) and ultraviolet–visible spectroscopy, respectively. The carbonization process of the stabilized samples was performed using a thermogravimetric analyzer under nitrogen atmosphere in the temperature range of 150°C–1200°C, and Raman spectra were applied to study the pseudo-graphite sheets of the residuals. It is suggested that the introduction of comonomer or the improvement of the isotactic regularity of the polymer chain are helpful to promote the stabilization reactions and accelerate the formation of conjugated structures rather than the extent of conjugation during stabilization in nitrogen. Moreover, they are also beneficial to obtain higher degree of graphitization and larger size of the pseudo-graphite sheets with less structural defects after carbonization. While stabilization is performed in air, atactic PAN copolymer has the highest extent of stabilization among these three PAN samples, but they are extremely close. PAN samples with comonomer or higher isotacticity still show a little advantage in the formation speed of the conjugated structures. After carbonization, PAN with higher isotacticity has the highest carbon yield and graphitization degree and the largest size of pseudo-graphite sheets with least structural defects. In addition, the presence of oxygen during stabilization is contributory to increase the extent of stabilization and generate some bigger conjugated structures, which leads to obtain higher graphitization degree and larger size of pseudo-graphite sheets, but it also brings more structural defects.

scholarly journals Structure and Properties of Polylactic Acid Biocomposite Films Reinforced with Cellulose Nanofibrils

Molecules ◽  
2020 ◽  
Vol 25 (14) ◽  
pp. 3306
Author(s):  
Qianqian Wang ◽  
Chencheng Ji ◽  
Jianzhong Sun ◽  
Qianqian Zhu ◽  
Jun Liu
Keyword(s):  
Polylactic Acid ◽  
Cellulose Nanofibrils ◽  
Nitrogen Atmosphere ◽  
Scanning Calorimetry ◽  
Enzymatic Pretreatment ◽  
Thermogravimetric Analyzer ◽  
Degradation Temperature ◽  
Biocomposite Films ◽  
Renewable Feedstock ◽  
Vis Spectroscopy

Polylactic acid (PLA) is one of the most promising biodegradable and recyclable thermoplastic biopolymer derived from renewable feedstock. Nanocellulose reinforced PLA biocomposites have received increasing attention in academic and industrial communities. In the present study, cellulose nanofibrils (CNFs) was liberated by combined enzymatic pretreatment and high-pressure homogenization, and then subsequently incorporated into the PLA matrix to synthesize PLA/CNF biocomposite films via solution casting and melt compression. The prepared PLA/CNF biocomposite films were characterized in terms of transparency (UV-Vis spectroscopy), chemical structure (attenuated total reflectance-Fourier transform infrared, ATR-FTIR; X-ray powder diffraction, XRD), thermal (thermogravimetric analyzer, TGA; differential scanning calorimetry, DSC), and tensile properties. With 1.0–5.0 wt % additions of CNF to the PLA matrix, noticeable improvements in thermal and physical properties were observed for the resulting PLA/CNF biocomposites. The 2.5 wt % addition of CNF increased the tensile strength by 8.8%. The Tonset (initial degradation temperature) and Tmax (maximum degradation temperature) after adding 5.0 wt % CNF was increased by 20 °C, and 10 °C, respectively in the nitrogen atmosphere. These improvements were attributed to the good dispersibility and improved interfacial interaction of CNF in the PLA matrix.

Preparation and Properties of PLLA-co-bis A/VMT Nanocomposites

2010 ◽  
Vol 150-151 ◽  
pp. 1466-1469
Author(s):  
Ya Li Bai ◽  
Hong Xu ◽  
Zhi Ping Mao
Keyword(s):  
Thermal Stability ◽  
Differential Scanning Calorimetry ◽  
Crystallization Behavior ◽  
Crystallization Rate ◽  
Scanning Calorimetry ◽  
Polarized Optical Microscopy ◽  
Thermogravimetric Analyzer ◽  
Melt Polycondensation ◽  
The Fourier Transform

Poly(L-lactic acid)-co-bisphenol-A epoxy resin/vermiculite nanocomposites（PLLA-co-bis A /VMT）were prepared by in-situ melt polycondensation of L-LA in the presence of amino-modified vermiculite. The fourier transform infrared (FTIR) spectra were used to investigate molecular interactions between the modified vermiculite and PLLA. The detailed thermal property and crystallization behavior of samples were studied by using polarized optical microscopy (POM), differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA). The result indicated that the thermal stability, overall crystallization rate and spherulitic texture of PLLA-co-bis A were strongly influenced in the presence of vermiculite particles.

scholarly journals Preparation and modification of inverse opal zirconia pigment

2020 ◽  
Vol 52 (3) ◽  
pp. 299-306
Author(s):  
Feng Lina ◽  
Wang Lili ◽  
Li Xiaopeng ◽  
Zhou Yemin ◽  
Wang Xiufeng ◽  
...  
Keyword(s):  
Colloidal Crystal ◽  
Nitrogen Atmosphere ◽  
Raw Material ◽  
Structural Defects ◽  
Inverse Opal ◽  
Angle Dependence ◽  
Color Saturation ◽  
Before And After ◽  
Ordered Porous

Inverse opal zirconia pigment prepared by traditional process has the disadvantages of low color saturation and variegated color which restrict its further application. In this work, the inverse opal zirconia pigment was prepared by colloidal crystal template fabricated using polystyrene microspheres with particle size of 340 ? 10 nm as raw material and further modified by sintering at 600 ?C for 2 h with heating rate of 2 ?C/min in an atmosphere tube of 0.8 L min-1 nitrogen flow. The morphology, phase crystallinity and color performance of the inverse opal zirconia pigment before and after modification were characterized in detail and the modified mechanism was investigated. The results showed that morphology of the inverse opal zirconia pigment before modification was basically a highly ordered porous structure, the phase was relatively pure, and the overall appearance was variegated color. Some parts of the samples exhibited low color saturation and different areas showed various colors, indicating that the samples had certain angle dependence. After modification, the samples showed bigger-area single blue-green color, suggesting that the color saturation was significantly improved and the angle dependence was reduced evidently. The mechanism for modification was that the zirconia precursor and polystyrene templates were carbonized when sintered in nitrogen atmosphere. The generated in-situ carbon remained in the samples and absorbed the tray background light, which significantly suppressed the multiple scattering of structural defects.

scholarly journals Strain-Induced Graphitization Mechanism of Coal-Based Graphite from Lutang, Hunan Province, China

Minerals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 617 ◽  
Author(s):  
Wang ◽  
Cao ◽  
Peng ◽  
Ding ◽  
Li
Keyword(s):  
Structural Evolution ◽  
Local Stress ◽  
Basic Structure ◽  
Hunan Province ◽  
Structural Defects ◽  
X Ray Diffraction ◽  
Graphitization Degree ◽  
Transmission Electron ◽  
Graphite Structure ◽  
Coal Macerals

Anthracite and coal-based graphite (CBG) samples were collected at varying distances from a granite intrusion. Optical microscopy, X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM) were used to characterize the structural evolution of CBG at different scales. The results indicated differences in the graphitization rates of coal macerals and crystallization degree of different graphite-like particles. Differentiated graphitization of coal was caused by deformation, which led to the discontinuous distribution of CBG. This indicates that samples located at the same distance from the intrusion were graphitized to different degrees or that CBG with a similar graphitization degree occurred at varying distances from the intrusion. A possible mechanism for graphitization is strain-induced graphitization, where the local stress concentration leads to preferred orientations of the basic structure units (BSUs), as well as the motion and rearrangement of structural defects, resulting in the formation of a locally ordered structure. The graphitization degree is enhanced as the local graphite structure spreads.

Thermal Behaviour of Candesartan Active substance and in pharmaceutical compounds

2017 ◽  
Vol 68 (8) ◽  
pp. 1895-1902
Author(s):  
Ioana Cristina Tita ◽  
Eleonora Marian ◽  
Bogdan Tita ◽  
Claudia Crina Toma ◽  
Laura Vicas
Keyword(s):  
Thermal Behaviour ◽  
Active Substance ◽  
Pharmaceutical Research ◽  
Pharmaceutical Product ◽  
Nitrogen Atmosphere ◽  
Pure Substance ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Ft Ir

Thermal analysis is one of the most frequently used instrumental techniques in the pharmaceutical research, for the thermal characterization of different materials from solids to semi-solids, which are of pharmaceutical relevance. In this paper, simultaneous thermogravimetry/derivative thermogravimetry (TG/DTG) and differential scanning calorimetry (DSC) were used for characterization of the thermal behaviour of candesartan cilexetil � active substance (C-AS) under dynamic nitrogen atmosphere and nonisothermal conditions, in comparison with pharmaceutical product containing the corresponding active substance. It was observed that the commercial samples showed a different thermal profile than the standard sample, caused by the presence of excipients in the pharmaceutical product and to possible interaction of these with the active substance. The Fourier transformed infrared spectroscopy (FT-IR) and X-ray powder diffraction (XRPD) were used as complementary techniques adequately implement and assist in interpretation of the thermal results. The main conclusion of this comparative study was that the TG/DTG and DSC curves, together with the FT-IR spectra, respectively X-ray difractograms constitute believe data for the discrimination between the pure substance and pharmaceutical forms.

Injectable in-situ Forming Depot Of Doxycycline Hyclate/α-Cyclodextrin Complex using PLGA for Periodontitis Treatment: Preparation, Charac-terization, and In-Vitro Evaluation

2020 ◽  
Vol 17 ◽  
Author(s):  
Elham Khodaverdi ◽  
Farhad Eisvand ◽  
Mohammad Sina Nezami ◽  
Seyedeh Nesa Rezaeian Shiadeh ◽  
Hossein Kamali ◽  
...  
Keyword(s):  
Complex Form ◽  
Docking Studies ◽  
Morphological Properties ◽  
Burst Release ◽  
Cyclodextrin Complex ◽  
Doxycycline Hyclate ◽  
Scanning Calorimetry ◽  
In Situ Forming

Background:: Doxycycline (DOX) is used in treating a bacterial infection, especially for periodontitis treatment. Objective: To reduce irritation of DOX for subgingival administration and increase the chemical stability and against enzy-matic, the complex of α-cyclodextrin with DOX was prepared and loaded into injectable in situ forming implant based on PLGA. Methods:: FTIR, molecular docking studies, X-ray diffraction, and differential scanning calorimetry was performed to char-acterize the DOX/α-cyclodextrin complex. Finally, the in-vitro drug release and modeling, morphological properties, and cellular cytotoxic effects were also evaluated. Results:: The stability of DOX was improved with complex than pure DOX. The main advantage of the complex is the al-most complete release (96.31 ± 2.56 %) of the drug within 14 days of the implant, whereas in the formulation containing the pure DOX and the physical mixture the DOX with α-cyclodextrin release is reached to 70.18 ± 3.61 % and 77.03 ± 3.56 %, respectively. This trend is due to elevate of DOX stability in the DOX/ α-cyclodextrin complex form within PLGA implant that confirmed by the results of stability. Conclusion:: Our results were indicative that the formulation containing DOX/α-cyclodextrin complex was biocompatible and sustained-release with minimum initial burst release.

scholarly journals Phase Transition and Coefficients of Thermal Expansion in Al2−xInxW3O12 (0.2 ≤ x ≤ 1)

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4021
Author(s):  
Andrés Esteban Cerón Cerón Cortés ◽  
Anja Dosen ◽  
Victoria L. Blair ◽  
Michel B. Johnson ◽  
Mary Anne White ◽  
...  
Keyword(s):  
Phase Transition ◽  
Thermal Expansion ◽  
Thermal Shock ◽  
Monoclinic Phase ◽  
Ceramic Materials ◽  
Precipitation Method ◽  
Scanning Calorimetry ◽  
Orthorhombic Crystal ◽  
Co Precipitation

Materials from theA2M3O12 family are known for their extensive chemical versatility while preserving the polyhedral-corner-shared orthorhombic crystal system, as well as for their consequent unusual thermal expansion, varying from negative and near-zero to slightly positive. The rarest are near-zero thermal expansion materials, which are of paramount importance in thermal shock resistance applications. Ceramic materials with chemistry Al2−xInxW3O12 (x = 0.2–1.0) were synthesized using a modified reverse-strike co-precipitation method and prepared into solid specimens using traditional ceramic sintering. The resulting materials were characterized by X-ray powder diffraction (ambient and in situ high temperatures), differential scanning calorimetry and dilatometry to delineate thermal expansion, phase transitions and crystal structures. It was found that the x = 0.2 composition had the lowest thermal expansion, 1.88 × 10−6 K−1, which was still higher than the end member Al2W3O12 for the chemical series. Furthermore, the AlInW3O12 was monoclinic phase at room temperature and transformed to the orthorhombic form at ca. 200 °C, in contrast with previous reports. Interestingly, the x = 0.2, x = 0.4 and x = 0.7 materials did not exhibit the expected orthorhombic-to-monoclinic phase transition as observed for the other compositions, and hence did not follow the expected Vegard-like relationship associated with the electronegativity rule. Overall, compositions within the Al2−xInxW3O12 family should not be considered candidates for high thermal shock applications that would require near-zero thermal expansion properties.

scholarly journals Torrefaction Thermogravimetric Analysis and Kinetics of Sorghum Distilled Residue for Sustainable Fuel Production

2021 ◽  
Vol 13 (8) ◽  
pp. 4246
Author(s):  
Shih-Wei Yen ◽  
Wei-Hsin Chen ◽  
Jo-Shu Chang ◽  
Chun-Fong Eng ◽  
Salman Raza Naqvi ◽  
...  
Keyword(s):  
Kinetic Model ◽  
Pso Algorithm ◽  
Nitrogen Atmosphere ◽  
Computational Method ◽  
Weight Changes ◽  
Design And Optimization ◽  
Thermogravimetric Analyzer ◽  
Model Free ◽  
Different Temperatures ◽  
Kinetics Of

This study investigated the kinetics of isothermal torrefaction of sorghum distilled residue (SDR), the main byproduct of the sorghum liquor-making process. The samples chosen were torrefied isothermally at five different temperatures under a nitrogen atmosphere in a thermogravimetric analyzer. Afterward, two different kinetic methods, the traditional model-free approach, and a two-step parallel reaction (TPR) kinetic model, were used to obtain the torrefaction kinetics of SDR. With the acquired 92–97% fit quality, which is the degree of similarity between calculated and real torrefaction curves, the traditional method approached using the Arrhenius equation showed a poor ability on kinetics prediction, whereas the TPR kinetic model optimized by the particle swarm optimization (PSO) algorithm showed that all the fit qualities are as high as 99%. The results suggest that PSO can simulate the actual torrefaction kinetics more accurately than the traditional kinetics approach. Moreover, the PSO method can be further employed for simulating the weight changes of reaction intermediates throughout the process. This computational method could be used as a powerful tool for industrial design and optimization in the biochar manufacturing process.

Crystallization of Amorphous Silicon-Aluminum thin Films: IN-SITU Observation and Thermal Analysis.

1991 ◽  
Vol 237 ◽  
Author(s):  
Toyohiko J. Konno ◽  
Robert Sinclair
Keyword(s):  
Activation Energy ◽  
Amorphous Alloys ◽  
Amorphous Matrix ◽  
In Situ Observation ◽  
Scanning Calorimetry ◽  
Transmission Electron ◽  
High Resolution Tem ◽  
Higher Temperature ◽  
Sputter Deposited

ABSTRACTThe crystallization of sputter-deposited Si/Al amorphous alloys was examined by transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). In-situ high-resolution TEM reveals the existence of an Al layer between the amorphous matrix and the growing crystalline phase. The activation energy for the growth is about 1.2eV, roughly corresponding to the activation energy of Si diffusion in Al. These two observations support the view that a crystallization mechanism, in which an Al buffer layer provides the shortest reaction path, is responsible for the reaction. The product microstructure exhibits secondary crystallization at a higher temperature.

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