TG In Air Research Articles

Dual‐Control Mechanism of Water and Temperature in Automatically Programmable Shape Memory Polymers

AbstractAuto‐programmable shape memory polymers (AP‐SMPs) can deform automatically without external manipulation, exhibiting either a free‐standing temporary shape or a permanent shape. The unique shape memory behaviors derive mainly from control by two factors, water and temperature. However, the control mechanism is unknown. This study analyzes and demonstrates the dual‐control mechanism of water and temperature in the three shape‐changing processes of AP‐SMPs. First, the AP‐SMP is immersed in warm water (50 °C). Asymmetric swelling of bilayer films provides the driving force for the shape auto‐programming of the AP‐SMP. The solvent effect of water reduces the glass transition temperature (Tg) of the AP‐SMP, which becomes lower than the medium temperature in warm water. AP‐SMP can be programmed automatically. Then, the AP‐SMP is removed from water and placed in air at room temperature. The Tg value of the matrix film increases notably in air and exceeds the medium temperature. The temporary shape of the AP‐SMP can thus be fixed. Finally, the AP‐SMP can quickly return to its permanent shape when the medium temperature exceeds the matrix film Tg in air. The dual control shape memory mechanism provides insights into the design and development of AP‐SMPs.

Synthesis and evaluation of trimethylolpropane triacrylate crosslinked superabsorbent polymers for conserving water and fertilizers

AbstractA series of superabsorbent polymers (SAP) were synthesized by free radical thermal copolymerization of acrylic acid and N‐isopropyl acrylamide monomers using trimethylolpropane triacrylate as crosslinker. They were characterized by FT‐IR and thermal stability (TGA/DTG), and evaluated for their water and fertilizer uptake and release characteristics under different crosslinker levels, temperature, pressure, and pH. The observed maximum absorption of water by the SAP was 1130 g/g of polymer. The release was modeled which showed a non‐Fickian mechanism. The water uptake of SAP was correlated with the average molecular weight between the crosslinks and crosslink density. Analysis of the weight loss data from TG in air revealed a zero order kinetics for the initial degradation step with an activation energy (AE) of 70.8 kJ/mol. The AEs for water uptake and release for thermal degradation were also determined through Arrhenius plots. The results inferred that the synthesized SAP can be exploited for commercial agricultural applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

금속질산염을 이용한 Fe-Ni 나노분말의 제조 및 특성

The calcination and hydrogen-reduction behavior of Feand Ni-nitrate have been investigated. Fe 2 O 3 /NiO composite powders were prepared by chemical solution mixing of Feand Ni-nitrate and calcination at 350C for 2 h. The calcined powders were hydrogen-reduced at 350C for 30 min. The calcination and hydrogenreduction behavior of Feand Ni-nitrate were analyzed by TG in air and hydrogen atmosphere, respectively. TG and XRD analysis for hydrogen-reduced powders revealed that the Fe 2 O 3 /NiO phase transformed to FeNi 3 phase at the temperature of 350C. The activation energy for the hydrogen reduction, evaluated by Kissinger method, was measured as 83.0 kJ/mol.

Thermal decomposition behaviour of lanthanum(III) tris-tartrato lanthanate(III) decahydrate

Lanthanum(III) tris-tartrato lanthanate(III) decahydrate, La[La(C4H4O6)3]·10H2O has been synthesized and characterized by elemental analysis, IR, electronic spectral and X-ray powder diffraction studies. Thermal studies (TG, DTG and DTA) in air showed a complex decomposition pattern with the generation of an anhydrous species at ~170°C. The end product was found to be mainly a mixture of La2O3 and carbides at ~970°C through the formation of several intermediates at different temperature. The residual product in DSC study in nitrogen at 670°C is assumed to be a similar mixture generated at 500°C in TG in air. Kinetic parameters, such as, E*, ΔH, ΔS, etc. obtained from DSC are discussed. IR and X-ray powder diffraction studies identified some of the decomposition products. The tentative mechanism for the thermal decomposition in air of the compound is proposed.

Determination of the Thermal Degradation Kinetic Parameters of Carbon Fibre Reinforced Epoxy Using TG

In this work, a kinetic study on the thermal degradation of carbon fibre reinforced epoxy is presented. The degradation is investigated by means of dynamic thermogravimetric analysis (TG) in air and inert atmosphere at heating rates from 0.5 to 20°C min−1 . Curves obtained by TG in air are quite different from those obtained in nitrogen. A three-step loss is observed during dynamic TG in air while mass loss proceeded as a two step process in nitrogen at fast heating rate. To elucidate this difference, a kinetic analysis is carried on. A kinetic model described by the Kissinger method or by the Ozawa method gives the kinetic parameters of the composite decomposition. Apparent activation energy calculated by Kissinger method in oxidative atmosphere for each step is between 40–50 kJ mol−1 upper than E a calculated in inert atmosphere.

Cure behavior of an epoxy-phenolic magnetic recording ink

The curing behavior of an epoxy-phenolic coating containing a thermoplastic additive and iron oxide is described. Cure response was measured on a DuPont 981 Dynamic Mechanical Analyzer (DMA) and a Perkin-Elmer TGS-2 Thermogravimetric Analyzer (TGA). Samples coated onto a glass fiber ribbon were cured isothermally in the DMA, allowed to cool, and then scanned to measure the glass transition and related phenomena. During cure the thermoplastic additive was observed to phase separate, as evidenced by a secondary damping peak near its glass transition temperature. Above 200° oxidative reactions made a major contribution to the crosslink density. Isothermal TG in air and nitrogen showed evidence for oxygen uptake and an oxidative weight loss at temperatures >200°. Iron oxide, oxygen content of the purge gas, and flow rate of the purge gas were observed to affect cure behavior.

Thermal decomposition characteristics in air and their relationship with electrochemical activity of different polymorphic forms of MnO2

Thermal decomposition characteristics of various synthetic MnO2 samples were studied with the help of DTA and TG in air. Each crystalline modification group produced its own characteristic thermogram which could be distinguished from the thermogram of other modifications. However, there were a few instances of overlapping, because some samples were not truly homogeneous and contained one or more polymorphic forms as impurities. The results indicate that relationships exist between electrochemical activity and DTA peak temperature for the loss of initial molecular water on the one hand, and DTA peak temperature for the decomposition of MnO2 to Mn2O3, on the other hand. The amount of combined water determined by the difference in weight loss at 400 and 200°C was found to be related to the electrochemical activity or depolarizing capacity of the samples.

Thermal characterisation of the non-stoichiometry and catalytic activity of Ba xLn 1− xCoO 3 (Ln = La, Nd, Sm and Dy) compounds

The compounds Ba x Ln 1− x CoO 3 (Ln = La, Nd, Sm and Dy) were prepared by ceramic technique. They were characterised for oxygen non-stoichiometry using isothermal DTA under varying oxygen partial pressure and TG in air. Isothermal DTA was also employed to study the catalytic activity of the compounds towards CO oxidation. For a given compound, the oxygen deficiency increases with increasing temperature and decreasing oxygen partial pressure. For a given Ba x Ln 1− x CoO 3 series, in general barium-rich compounds were more oxygen deficient. Isothermal DTA study of CO oxidation over Ba x La 1− x CoO 3 compounds at 600 K suggested that the carbon monoxide takes up lattice-labile oxygen from the sample and is oxidised to CO 2, the percent CO conversion being higher for barium-rich samples.

New organic polymers, 4. Synthesis and characterization of polymers containing 3,3′‐dioxo‐5,5′‐biindol‐2,2′‐diyl units

AbstractPolymers containing 3,3′‐dioxo‐5,5′‐biindol‐2,2′‐diyl units were synthesized by high temperature polycondensation of 4,4′‐diaminobiphenyl‐3,3′‐dicarboxylic acid (1) with ethylene dichloride and dibromide, 4‐chloromethylbenzyl chloride and bromide, 4‐chloromethyl‐2,5‐dimethylbenzyl chloride and bis(4‐chloromethylphenyl) ether under different experimental conditions. These resulting polymers 5a–d were characterized by viscometric and IR Spectral studies and by TG in air. Kinetic parameters of their thermal degradation were evaluated.

DTA study of RuO 2 formation from the thermal decomposition of ruthenium(III) hydrate

Ruthenium(III) hydrate has been precipitated in aqueous solution from the soluble hydrated RuCl 3. The thermal behavior of ruthenium(III) hydrate has been investigated by DTA and TG in air and in nitrogen. The compound undergoes a disproportionation reaction between 100 and 150°C yielding Ru(metal)+RuO 2· xH 2O. In nitrogen, the metal crystallizes beyond 450°C whereas it is fully oxidized in air in the temperature range 150–300°C. RuO 2 crystallizes on a sharp exothermic peak, the temperature of which depends on the residual water content. An estimate of the enthalpy of crystallization is given, and the oxidation mechanism is discussed.

Thermal degradation of polymers. XVII. Thermal analysis of polyquinazolones and related systems

The thermal characterization of a series of polyquinazolones, poly(quinazolone diones), and polybenzoxazinones by thermal analytical techniques (TG, DSC) is described. Comparative thermal stability measurements by dynamic and isothermal TG in air and N2 are critically discussed. Kinetic studies by isothermal TG in air and nitrogen leading to activation energies are described. The inherent difficulties in comparative thermal stability studies on complex polymer systems are discussed in terms of their structural and compositional variables and their effect on the assessment parameters used.

Thermal resistance of crosslinked and substituted poly(phenylene sulfide)s

AbstractCrosslinked and substituted poly(phenylene sulfide)s, prepared by reacting p‐chlorosubstituted benzenes with sulfur, were investigated by TG in air. Using the difference method and an assumed first‐order calculation, the reaction order, activation energy and frequency factor were determined. The pyrolyses were carried out under nitrogen and in the presence of 5% oxygen. The IR spectra and the sulfur contents of the polymers and pyrolysis products were determined. The highest activation energies were found for unsubstituted polymers. Linear poly(phenylene sulfide) has the best thermal stability, but also the other polymers show rather good stabilities up to 400–500°C. The IR spectra and sulfur‐contents of the pyrolysis products suggest stable, condensed, and sulfur containing aromatic intermediates formed during the degradations. The obtained polymers can be manufactured over large temperature ranges by common techniques.