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Chemical degradation of diglycidyl ether of bisphenol A (DGEBA) epoxy resin cured with an aliphatic amine in supercritical 1-propanol was investigated under different reaction temperature and time. The combination of GC-MS and LC-MS proved that the epoxy resin was decomposed to five main products including phenol, 4-isopropylphenol, 4-isopropenylphenol, bisphenol A, and 4,4′-(cyclopropane-1,1-diyl)diphenol. The 13C-NMR results verified the chemical structures of the degradation products. The change of the products’ yield with time was evaluated by an effective means of HPLC. In addition, the GPC analysis confirmed the formation of soluble low molecular weight clusters during the degradation reaction. A possible free-radical reaction mechanism was proposed for chemical depolymerization of the epoxy resin in supercritical 1-propanol. After the homolytic cleavage of the aromatic ether linkages, the resulting bisphenol A biradical either produced 4,4′-(cyclopropane-1,1-diyl)diphenol after intramolecular rearrangement or generated bisphenol A after capturing hydrogen from 1-propanol.

Redox-active organic electrode materials are highly desirable in realizing next-generation all-in-one bendable electronic systems. Herein, a novel flexible supercapacitors (SCs) electrode is fabricated from poly(anthraquinonyl sulfide) (PAQS) and single-walled carbon nanotubes (SWCNTs) suspension by a simple vacuum filtration and named as PAQS-SWCNTs. The PAQS-SWCNTs electrode offered an initial capacitance of 223 F-g−1 and outstanding capacitance retention up to 78.4% after 3 × 104 charge-discharge cycles at 0.5 A-g−1 current density. In a high potential range (0-3 V) and aprotic electrolyte, the PAQS-SWCNTs electrodes in coin cell exhibited an outstanding energy density of 69 Wh-kg−1 at a power density of 90.6 W-kg−1, whereas in the fabricated flexible SCs it retained 63.2 Wh-kg−1. The PAQS-SWCNTs electrodes also showed extraordinary performance at a higher current density (20 A-g−1) and maintained a specific capacitance of 55 and 47 F-g−1 for coin and flexible SCs, respectively. Moreover, the flexible SC is further verified to be able to illuminate up multiple LEDs. These futuristic findings showed that the SCs assembled with flexible PAQS-SWCNTs electrodes have potential application in energy-storage devices and make them highly appealing for future redox supercapacitors.

The results of X-ray diffraction on polyacrylonitrile-based carbon fibers graphitized at temperatures from 1800 to 2500 °C are reported. The carbon crystallites consist of graphene-layer stacks. A Hirsch analysis showed that the average graphene stack height increased with temperature up to ~2000 °C, reaching a relatively stable stack height thereafter. The average lateral layer size increased from 0.88 nm for the as-received fibers to 3.37 nm at 2500 °C. With increasing temperature the formation of microfibrillar structures was observed, accompanied by the flattening of carbon layers. The changes in electrical and thermal properties were in good agreement with the aspect ratio of carbon layers.

Thermal properties of acrylonitrile (AN)-acrylamide (AM) copolymers for carbon fibers were studied by DSC and in situ FTIR techniques in nitrogen (N2) and air flows. The cyclization mechanism and stabilization behavior of polyacrylonitrile (PAN) were discussed. In N2 flow, it was found that AM had the ability to initiate and accelerate cyclization process, which was confirmed by the fact that the initiation of nitriles shifted to a lower temperature. Compared to AN homopolymer, the initiation temperature of cyclization was ahead 32 K by introducing 3.59 mol% AM into the copolymer. The exothermic reaction was relaxed due to the presence of two separated exothermic peaks. Accompanied by DSC, in situ FTIR and calculation of activation energy, the two peaks were proved to be caused by ionic cyclization and free radical cyclization, respectively, and the corresponding cyclization mechanism was proposed. With increasing in AM content, the ionic cyclization tends to be dominant and the total heat liberated first increases and then decreases. For AN homopolymer, the activation energy of cyclization is 179 kJ/mol. For AN-AM copolymer (containing 3.59 mol% AM), the activation energy of ionic cyclization is 96 kJ/mol and that of free radical cyclization is 338 kJ/mol. In air flow, similar cyclization routes occur and the difference is the contribution of oxidation. The oxygen in environment has no remarkable effect on cyclization of AN homopolymer but retards the cyclization of AN-AM copolymers. For AN-AM copolymer with 3.59 mol% AM, the cyclization temperature is postponed 10°C in air.

The fracture morphologies of various high-strength type polyacryonitrile (PAN)-based carbon fibers were examined by emission scanning electronic microscopy (SEM) observation, and analyzed based on the Griffith-Irwin’s criterion. The results showed the fracture morphologies of PAN-based high strength carbon fibers were largely controlled by the rate of crack propagation. The fracture mechanisms for the high-strength type carbon fibers were proposed. The role of magnitude of surface defects on determining the fractography was discussed according to the mechanism.

Thermal degradation and stabilization of two kinds of polyacrylonitrile (PAN) fibers have been investigated by a combination of FT-IR, differential scanning calorimetry (DSC), modulated DSC, thermogravimetry (TG), thermal shrinkage behavior, in situ mass spectrometry (MS), and tensile property examinations. The two types of precursor fibers exhibit distinct properties after oxidative stabilization, but they can both make carbon fibers with equivalent mechanical properties. Compared with PAN/itaconic acid precursor fibers, the fibers containing acrylamide comonomers show a doublet appearance, broader exothermic peak, lower threshold degradation temperature, and more amount of heat evolved in DSC thermogram, which is favorable to obtain uniform microstructures in oxidative stabilization process. The two types of samples produce different ring structures in the thermal degradation and stabilization process, as evidenced by results from tensile test, TG–MS and thermal shrinkage behavior analyses. In addition, the molecular rearrangement or melting of ordered structures accompanying with nitrile polymerization was also detected from modulated DSC.

The coating modification of polyacrylonitrile (PAN) fibers with boric acid to enhance the controllability of thermally oxidative stabilization process. The stabilization process, cross-section morphologies of oxidized and carbonized products were investigated by means of optical microscopy, SEM, XPS and in-situ thermal shrinkage indicator. The results indicated that the coating with boric acid on fiber surface was effective to avoid skin-core heterogeneity on the cross section and, in the stabilization process, that boric acid as a crosslinking agent to tie together the adjacent oxidative molecular chains was confirmed. It was suggested that the crosslinked structures should play an essential role in controlling the formation of uniform oxidized structures, which is favorable for tensile properties of carbon fibers.

The Qinghai-Tibet Plateau is the word＇s highest and largest plateau. Due to increasing demands for environment exploration and tourism, a large transitional area is required for altitude adaptation. Hehuang valley, which locates in the transition zone between the Loess Plateau and the Qinghai-Tibet Plateau, has convenient transportation and relatively low elevation. Our question is whether the geographic conditions here are appropriate for adapted stay before going into the Qinghai-Tibet Plateau. Therefore, in this study, we examined the potential use of ecological niche modeling （ENM） for mapping current and potential distribution patterns of human settlements. We chose the Maximum Entropy Method （Maxent）, an ENM which integrates climate, remote sensing and geographical data, to model distributions and assess land suitability for transition areas. After preprocessing and selection, the correlation between variables and spatial auto- correlation input data were removed and 106 occurrence points and 9 environmental layers were determined as the model inputs. The threshold- independent model performance was reasonable according to lO times model running, with the area under the curve （AUC） values being 0.917± 0.01, and 0.923±0.002 for test data. Cohen＇s kappa coefficient of model performance was 0.848. Results showed that 82.22% of the study extent was not suitable for human settlement. Of the remaining areas, highly suitable areas aceounted for 1.19%, moderately for 5.3% and marginally for 11.28%. These suitable areas totaled 418.79 km2, and 86.25% of the sample data was identified in the different gradient of suitable area.The decisive environmental factors were slope and two climate variables： mean diurnal temperature range and temperature seasonality. Our model showed a good performance in mapping and assessing human settlements. This study provides the first predicted potential habitat distribution map for human settlement in Ledu County, which could also help in land use management.

Within a framework of NEG model, this paper intends to show that urbanization rate is determined as a synthetic result of rational behavior of each socio-economic agent. In particular, a model is constructed with bearing in mind to explain the urbanization process in China such that the role of government in managing land use is explicitly incorporated and policy effects can be evaluated. Some results of theoretical analysis and numerical simulation analysis are contrasted with the ones of Fujita-Krugman (Reg Sci Urban Econ 25: 505–528, 1995) incorporating land into a NEG model as well.

An attempt was made to correlate the polymerization temperature and rheological and thermal properties of acrylonitrile (AN)-acrylamide (AM) copolymers. The copolymers were synthesized at different polymerization temperature. The copolymer structure was characterized by gel permeation chromatography (GPC) and Infrared spectrum (IR). The rheological and thermal properties were investigated by a viscometer and differential scanning calorimeter-thermogrametric (DSC-TG) analysis, respectively. When the polymerization temperature increased from $41^{\\circ}C\\;to\\;65^{\\circ}C$, the molecular weight $(\\bar{M}_w)$ of copolymers decreased from 1,090,000 to 250,000, while its conversion increased from $18\\%\\;to\\;63\\%$, and the polymer composition changed slightly. To meet the requirements of carbon fibers, the rheological and thermal properties of products were also investigated. It was found that the relationship between viscosity and $\\bar{M}_w$ was nonlinear and the viscosity index (n) decreased from 3.13 to 2.69, when the solution temperature increased from $30^{\\circ}C\\;to\\;65^{\\circ}C$. This suggests the dependence of viscosity upon $\\bar{M}_w$ is higher at lower solution temperature. According to the result of activation energy, the sensivity of viscosity to solution temperature is higher for AN-AM copolymers synthesized at higher polymerization temperature. The result of thermal analysis shows that the copolymers obtained at higher polymerization temperature are easier to cyclization evidenced from lower initiation temperature. The weight loss behavior changed irregularly with polymerization temperature due to irregular change of liberation heat.