Ling Chen,Xinfu Cao,Jianbing Gao,Yingbo Wang,Yang Zhang,Jie Liu,Weidong He
In this study, a novel three-dimensional (3D) porous cross-link network structure of nitrated bacterial cellulose (NBC) nano-gel, as an energetic gel matrix for fabrication of nanocomposite energetic materials, (nEMs) was synthesized by sol-gel synthetic and the freeze-drying technology. The analysis results revealed that the unique network structure with abundant of nano-porous, which made the thermal behaviour of the NBC gel different from that of raw NBC. The thermal decomposition kinetic and mechanism of the NBC gel indicated that the exothermic peak temperature of the gel matrix decreased at low concentration, and the activation energy ( E a ) of the gel 0.5 (150000 J ⋅ mol −1 ) was much lower than that of raw NBC (223510 J ⋅ mol −1 ). However, the decomposition kinetic parameters of this study were not enough to illustrate the thermal properties, and which needs more effort to study them and complete. Furthermore, the initial reaction of gel decomposition was the splitting of urethane bond, and then the scission of −O−NO 2 bonds happened, and the macromolecular chains’ breakage site of gel first occurred at −C−O−C− in the ring. After then, the chains of NBC break at −C−O−C− between the rings; notably, the heat-release of gel was several times than that of raw NBC, which was liberated during the process of thermal decomposition. This promising research may provide potential application in preparing binder-based nEMs and the basic theory of thermo-analysis used in propellants and explosives.
Yong Liu,Jiaming Guo,Zongwei Guo,Lei Shang,Yuhui Ao
The thermal oxidation stabilization process of polyacrylonitrile (PAN) is a violent exothermic reaction process, which is not conducive to the improvement of carbon fiber quality. The highly exothermic reaction was often alleviated by adding unsaturated vinyl carboxylic acid monomers. In this investigation, poly(acrylonitrile-co-2-carboxyethyl acrylate) P(AN-co-CEA) copolymers with varying contents of CEA monomers were synthesized. The effects of CEA on the thermal behavior and structural evolution of copolymers were systematically investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and thermal gravimetric analyzer (TGA). The results indicated that the introduction of CEA facilitated the cyclization reaction at lower temperatures through the ionic mechanism of the carboxyl group, broadened the exothermic peak, and reduced the heat release rate (Δ H /Δ T ). The activation energies (E a ) decreased from 157.7 KJ/mol for PAN homopolymer to 122.3 KJ/mol for P(AN-co-CEA) copolymer. Moreover, the CEA monomer promoted both the cyclization and dehydrogenation reactions, forming more stable cyclic structures and inhibiting the thermal decomposition of random chain segments. Consequently, higher carbon yield and a greater extent of stabilization (Es) were achieved. Additionally, the combined action of CEA and O 2 jointly enhanced the thermal oxidation stability process, resulting in the formation of oxygen-containing structures and promoting the transition to a graphite-like carbon network. Among the copolymers studied, the composition containing 2 wt% CEA exhibited the most favorable balance in the development of a well-stabilized structure. It was found that the CEA comonomer has the ability to promote the thermal oxidation stabilization process, alleviate the highly exothermic reactions, and reduce the heat release rate. Hence, these findings suggest that P(AN-co-CEA) copolymers have the potential to become carbon fiber precursor materials.
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