Pyrolysis Kinetics and Flammability Evaluation of Rigid Polyurethane with Different Isocyanate Content

Polyurethane (PU) is a typical product of the reaction between isocyanate and polyol, whose ratio would greatly influence material properties. In this paper, to investigate the influence of isocyanate on PU thermal stability and flammability, three kinds of rigid polyurethanes (RPUs) with different isocyanate ratio (1.05, 1.1, and 2.0) were manufactured in a laboratory and employed to have a series of TG (thermogravimetry), DSC (differential scanning calorimetry), and cone calorimetry tests. Kissinger’s method was used to calculate the activation energy and judge their stabilities. However, for such a complex degradation which consists of five reactions, it does not make sense by Kissinger method to obtain only two peak active energies. Considering complexity of PU degradation in air, genetic algorithm (GA) was employed to calculate kinetic triplets of five sub-reactions. The effects of isocyanate contents on each sub-reaction stability were obtained and then analyzed. By cone calorimeter testing, we found that great differences in heat release rate data. However, DSC analysis showed a complete opposite changed trend. Such difference is caused by DSC and calorimeter’s sample morphology, the former using grinded polyurethane powders but the latter polyurethane foam block.

Synthesis, crystal structure, and properties of energetic copper(II) compound based on 3,5-dinitrobenzoic acid and imidazole

Energetic copper(II) compound was synthesized based on 3,5-dinitrobenzoic acid (HDNBA) and imidazole (IMI), and characterized by elemental analysis and FTIR characterization. Single-crystal X-ray diffraction analysis revealed that [Cu(IMI)2(DNBA)2] (1) belongs to monoclinic, pertains to P21/c space group, β= 96.195(2) and Dc= 1.742 g cm–3. Cu(II) ion was coordinated to a plane tetragon, by two oxygen atoms and two nitrogen atoms from different DNBA ions and IMI ligands, which of them present typical monodentate coordination mode. Differential scanning calorimetry (DSC) was applied to assess the thermal decomposition behavior of 1. The non-isothermal kinetics parameters were calculated by the Kissinger’s method, Ozawa’s method and Starink’s method, respectively. Impact sensitivity and friction Sensitivity were also determined by standard method. In the end, the catalytic effects on the decomposition of ammonium perchlorate (AP), HMX and RDX of 1 were studied by DSC. All results supported the potential applications of the energetic complex 1 as additive of solid rocket propellant.

Thermogravimetric analyses (TGA) of lignins isolated from the residue of corn stover bioethanol (CSB) production

In the course of corn stover bioethanol (CSB) production, a lignin-rich residue is left behind, which is a potential feedstock for biofuel and other high-value products. In the present paper, this residual lignin was separated by precipitation from the alkali-solution and by extraction with organic solvents (benzyl alcohol, dioxane, and ethanol), respectively. Thermogravimetric analyses (TGA) at a heating rate of 30 K min-1 showed that the degradation of all lignins took place in a temperature range between 400 K and 1073 K, with maxima at around 600 K. The char yield of alkali-lignin is higher than that of the CSB residue and the lignins isolated by organic solvents. Derivative TG (DTG) curves reflect well the comprehensive thermal degradation processes. The kinetic parameters according to the Kissinger’s method indicate that the CSB residue and all lignins follow approx. the first-order reaction law, except for benzyl alcohol lignin with n=1.4. As for the effects of separation methods, the DTG curves of benzyl alcohol lignin exhibited a less regular form and its wide temperature profile may have contributed to its apparently higher reaction order.

Thermal Performance and Dehydration Kinetics of KAl(SO4)2•12H2O as Phase Change Material

The dehydration kinetics of phase change material KAl(SO4)2•12H2O was studied under non-isothermal conditions and the Kissinger’s method was applied to analyze the TG and DSC data in order to calculation of activation energies and pre-exponential factors for different heating rates. It was concluded that dehydration of KAl(SO4)2•12H2O occurred in three steps. The activation energies and pre-exponential factors were calculated as 95.9 kJ/mol and 1.95×1010min-1 for step I, 128.8kJ/mol and 3.67×1012 min-1 for step II, 159.6kJ/mol and1.92×1013min-1 for step III, respectively. In addition, various materials have been tested to prevent the KAl(SO4)2•12H2O supercooling.

NANOSTRUCTURED AND SURFACE POLYMERIZED IRON PARTICLES FOR MAGNETORHEOLOGICAL FLUIDS

A novel magnetorheological fluid, in which the surface of iron particles is coated with poly (butyl acrylate) by surface initiated atom transfer radical polymerization (ATRP), is investigated. The polymer coating procedure includes two steps, which are immobilization of initiator: 2-4(-chlorosulfonylphenyl)-ethytrichlorosilane (CTCS) on the iron particles surface and graft polymerization of butyl acrylate from the surface. The surface coating is characterized by FTIR and SEM. This magnetorheological fluid has controllable off-state viscosity and high shear yield stress. Coating polymer on the iron particles surface by ATRP can significantly reduce iron particles settling and improve stability of the MR fluid. Polymerization kinetics of bulk butyl acrylate are investigated using differential scanning calorimetry (DSC). Glass transition temperature is obtained using the step-scan DSC method. The molecular weight and conversion can be controlled by the molar ratio of monomer to initiator, reaction temperature and time. The reaction is first order determined by the plot of In ( M / M 0) against polymerization time. The overall activation energy is found to be 126kJ/mol by Kissinger's Method.

Effect of Er3+ Doping on Crystallization of PbF2-SiO2 Based Bulk Xerogels

Transparent glass ceramics with composition of xErF3-10PbF2-90SiO2 (mol%, x=0, 1, 2, 3, 4) were prepared by sol-gel method. The thermal behavior of the xerogels was investigated by DSC. Through non-isothermal experiments, the apparent activation energy for the crystallization of β-PbF2 phase was evaluated by the Kissinger’s method and Chen’s method. XRD and TEM were carried out to study the growth of β-PbF2 nanocrystals and the effect of Er3+ doping on it.