Differential scanning calorimetry studies on coal. 1. Pyrolysis in an inert atmosphere

Results of thermal changes involved during the pyrolysis of twelve US coals of various ranks in a helium atmosphere at 5.6 MPa (gauge) and temperatures up to 580 °C are reported. Thermal effects during pyrolysis of coals ranging in rank from anthracite to HVC bituminous are endothermic in nature over the temperature range investigated. Exothermic heats are observed only in the case of sub-bituminous and lignitic coals. The net thermal effects, that is the resultant of endothermic and exothermic heats, go from endothermic to exothermic with increase in carbon content, a transition occurring around 66% carbon and another in the reverse direction at about 75% carbon. A maximum in exothermicity occurs around 71% carbon and in endothermicity at about 81% carbon. Results have been compared with published DTA data on coals. The fallacy in the interpretation of published DTA thermograms of coals, where weight changes accompany thermal effects, is discussed.     

Preparation of Cu/CNT Composite Particles and Catalytic Performance on Thermal Decomposition of Ammonium Perchlorate

Composite particles of carbon nanotubes (CNTs) and Cu were prepared by a chemical reduction method. Characterization of Cu/CNT composite particles was performed by TEM, SEM, FT‐IR, XRD, XPS, AAS, DTA and EDS. The results show that the surface of CNTs is covered by Cu particles, and that the diameter of Cu/CNT composite particles gets larger than that of CNTs. Furthermore, in the presence of Cu/CNT composite particles, the peak temperature of the high‐temperature decomposition of ammonium perchlorate (AP) decreased by 126.3 °C, and the peak of the low‐temperature decomposition disappeared. Compared with a sample of simply mixed Cu and CNTs, the peak temperature of the high‐temperature decomposition of AP‐Cu/CNTs composite particles decreased by 11.4 °C. Compared with Cu, the peak temperature of the high‐temperature decomposition of AP‐Cu/CNT composite particles decreased by 20.9 °C. This work shows that the catalytic performance of Cu on the thermal decomposition of AP can be improved by compounding with CNTs.     

Thermal stabilization of poly(3‐hydroxybutyrate) by poly(glycidyl methacrylate)

Poly(3‐hydroxybutyrate) (PHB)/poly(glycidyl methacrylate) (PGMA) blends with the PGMA content up to 30 wt % were prepared by a solution‐precipitation procedure. The thermal decomposition of PHB/PGMA blends was studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and differential thermal analysis (DTA). The thermograms of PHB/PGMA blends contained a two‐step degradation process, while that of pure PHB sample exhibited only one‐step degradation process. This degradation behavior of PHB/PGMA blends, which have a higher thermal stability as measured by maximum decomposition temperature or residual weight after isothermal degradation for 1 h, is probably due to crosslinking reactions of the epoxide groups in the PGMA component with the carboxyl chain ends of PHB fragments during the degradation process, and the occurrence of such reactions can be assigned to the exothermic peaks in their DTA thermograms. An isothermal study of these blends at 200–250°C for 1 h indicated that the residual weight was directly correlated with the amount of epoxide groups in the PHB/PGMA blends. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2945–2952, 2002; DOI 10.1002/app.10318     

Thermal behaviour of acrylamide and acrylonitrile grafted nylon 6

The thermal behaviour of nylon 6, 20 denier, monofilament (semi-dull) and the graft copolymers of nylon 6 with acrylamide and acrylonitrile was studied using dynamic thermogravimetry in air at a heating rate of 6°C/min. up to a temperature of 550°C. The thermal stabilities of the samples grafted with acrylamide and acrylonitrile to various percentages of grafting were computed from their primary thermograms by calculating the values of initial decomposition temperature (IDT), integral procedure decomposition temperature (IPDT) and activation energy (E). The results show that the thermal stability of the samples grafted with acrylonitrile increases with increase in graft-on percentage and the thermal stability of the samples grafted with acrylamide decreases with increase in graft-on percentage. The reduction is, however, not very significant.     

Studies on biaxial stretching of polypropylene film. X. High-temperature x-ray and optical study of type III orientation

Change of orientation and crystalline state of uniaxially stretched polypropylene film during subsequent restretching with the film width unrestrained was studied by means of x-ray, optical, and calorimetric methods. Uniaxially stretched film immediately after 5 min of preheating at 130°C barely suffers premelting. When the preheating temperature rises above 150°C, the premelting proceeds gradually and the x-ray pattern becomes a halo around 160°C, which, however, returns nearly to the original crystalline pattern after cooling to room temperature. The fraction premelted in the preheating amounts to about ½–? under the condition yielding type III orientation at room temperature, as previously reported. The 130°C restretching brings type II orientation already at that temperature, similar to what has been observed at room temperature. When the restretching is performed above 155°C, the crystalline pattern remaining after the preheating converts to a halo during the restretching, which, however, converts again to the crystalline pattern of type III orientation when it is rapidly cooled. This suggests that the restretching at higher temperatures breaks up lamellae into smaller-sized crystallites. Upon cooling, the smaller-sized crystallites reorganize lamellae, the deformed lattice recovers its ordinary state, and the pulled-out chains crystallize into intermolecular crystallites, aligning in the direction of restretching. Concurrently, disorientation proceeds fairly rapidly at such high temperatures, hence, type III orientation cannot be observed even at room temperature unless the film is quickly cooled after restretching. It is concluded that type III orientation results from restretching when thermal motion of the chains within the crystalline phase becomes so violent that the unfolding occurs easily as compared with lamellar rotation.     

Experimental Study of the Effect of Metal Nanopowders on the Decomposition of HMX,AP and AN

The effect of metal nanopowders (Al, Fe, W, Ni, Cu, and Cu‐Ni alloys) on the decomposition of energetic materials (HMX, AP, and AN) with DTA–TGA method was studied and it was found that the catalytic action appears in the case of Cu‐Ni nanopowders with the three studied energetic materials. The temperature of decomposition of energetic materials with the addition of metal nanopowders could be lowered by 82 °C for AN, 161 °C for AP, and 96 °C for HMX. The reaction mechanism of metal nanopowders enhancing the decomposition of energetic materials is discussed.     

A study of the thermal behavior of graft copolymers of wool and methyl methacrylate

Thermal behavior of the natural and chemically modified wool fibers (treated with sodium hydroxide and formic acid and reduced with sodium bisulfite and thioglycollic acid) and of the graft copolymers of natural and modified wool with methyl nethacrylate (MMA) monomer was studied using dynamic thermogravimetry in air at a heating rate of 6°C/min to 600°C. The thermograms showed three distinct regions of weight loss for all the cases. A comparison of the temperatures of various percentage decompositions reveals that the thermal stability increased slightly with chemical modification of wool as compared to natural wool. Caustic soda and sodium bisulfite probably forms more stable lanthionine linkages, whereas formic acid improves the thermal stability perphas by modifying the noncrystalline region of the fiber. In the case of natural wool after graft copolymerization with MMA, thermal stability improves up to 325°C probably owing to the formation of new crosslinks, but after 325°C the thermal stability decreases owing to early decomposition of the polymer as compared to wool fiber. Similar effects are observed in all the chemically modified fibers except in wool reduced with sodium bisulfite, where thermal stability is found to increase after grafting even at higher temperature. The thermal stability was also computed from the primary thermograms by calculating the integral procedural decomposition temperature; the results show that thermal stability increases slightly with chemical modification of wool as compared to natural wool. In the case of natural wool with graft copolymerization with MMA, the overall thermal stability decreases, because the decrease of thermal stability after 325°C seems to be more prominent than the increase in thermal stability before 325°C. The same effects are observed in all the chemically modified fibers, except for fibers reduced with sodium bisulfite, where the overall thermal stability increases slightly with increase in graft-on.     

Miscibility of poly(vinyl alcohol)/polyacrylamide blends before and after gamma irradiation

Films of polymer blends having various contents of poly(vinyl alcohol) (PVA) and polyacrylamide (PAM) were prepared by the solution casting technique using water as a common solvent. The thermal, mechanical and morphological properties of these blends before and after exposure to various doses of gamma radiation, up to 100 kGy, have been investigated. The visual observation and reflectance measurements show that PVA/PAM blends are miscible over a wide range of composition. Moreover, the differential scanning calorimetry (DSC) thermograms show only a single glass transition temperature (T_g), but not those of PVA or PAM homopolymers, giving further support to the complete compatibility of such blends. The T_g of PVA/PAM blends decreases with increasing content of PAM but increases after exposure to gamma irradiation, indicating the occurrence of crosslinking. These findings were demonstrated by the scanning electron micrographs of the fracture surfaces and the tensile mechanical properties. The TGA thermograms and percentage mass loss at different decomposition temperatures show that unirradiated PVA homopolymer possesses higher thermal stability than PAM homopolymer and their blends within the heating temperature range investigated, up to 250 °C. An opposite trend is observed within the temperature range 300–500 °C. In general, the thermal stability of homopolymers or their blends improves slighly after exposure to an irradiation dose of 100 kGy. These findings are clearly confirmed by the calculated activation energies of the thermal decomposition reaction of the homopolymers and the blends. © 2003 Society of Chemical Industry     

Thermal decomposition behaviors of PVP coated on platinum nanoparticles

TG‐DTA, TEM, and IR were used to investigate the thermal decomposition behavior of poly(N‐vinyl‐2‐pyrrolidone) (PVP). The TG‐DTA results show that the thermal decomposition behavior of PVP on platinum (Pt) is quite different from that of pure PVP. For pure PVP, 95.25% is decomposed when the temperature is increased up to 500°C; while under the same experimental condition, PVP coated on the Pt nanoparticles is only 66.7% decomposed. This is further supported by IR measurement. TEM results exhibited that the partially decomposed PVP still plays a role in stabilizing Pt nanoparticles: after heating treatment at 500°C for half an hour, the platinum nanoparticles did not aggregate heavily. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 23–26, 2006     

Phase transformations of some poly(vinyl alcohol)–NiCl2 composites

Samples of poly(vinyl alcohol)–NiCl₂ composites containing up to 30 wt% NiCl₂ were prepared by casting in order to study phase transformation–structural change relationships of these samples before and after heat treatment. Differential thermal analysis (DTA) thermograms were recorded at 10, 15, 20 and 30 °C min^?1. For untreated samples four endotherms were assigned as: rotation of hydroxyl groups in the glassy state, glass transition, structural transition in the rubber‐like state, and melting transition. Ultrasonic attenuation measurements were carried out to confirm these transitions in the glassy and rubber‐like states. In the glassy state, the effect of NiCl₂ addition is explained in terms of chain stiffness due to the creation of local crosslinked regions in amorphous parts of the polymer. Average values of activation energies for glass transition were calculated using both methods of Kissinger and Ozawa. However, addition of NiCl₂ had an opposite effect on the heating rate independent crystallization melting temperature (T_m), relative to that on T_g. The DTA thermograms of heat‐treated samples indicated that square planar NiCl₂ molecules were embedded in the polymer matrix with no local crosslinking role due to the formation of conjugated polyenes along the polymer chains by thermal treatment. Copyright © 2003 Society of Chemical Industry     

Processing and characteristics of transparent Gd3TaO7 polycrystalline ceramics

Transparent polycrystalline Gd₃TaO₇ ceramics were successfully developed. A sol‐gel process was used to synthesize Gd₃TaO₇ powder with a uniform composition and an estimated average particle size of 100 nm. Simultaneous thermal gravimetric analysis and differential thermal analysis (TGA/DTA) was used to identify the decomposition sequence as a function of temperature for the as‐synthesized sol‐gel powders. Crystallization was confirmed by X‐ray diffraction (XRD) and a single phase was achieved by calcining at 1000°C. The calcined powders were hot‐pressed at 1400°C to achieve >96% theoretical density with closed pore structure followed by a hot isostatic pressing at 1400°C at 207 MPa to achieve a fully dense structure. Microstructural characterization shows a uniform grain size distribution with an average grain size of about 7 μm. In‐line transmission measurements revealed high transparency in the red and infrared. Thermal conductivity was measured to be >1.6 W/mK at room temperature, decreasing to ~1.3 W/mK by 500°C. Dielectric properties remain stable with relative permittivity values just above 200 and loss tangents <0.005 up to 350°C.     

Effects of preheating treatment on thermal property and adhesion performance of soy protein isolates

The objective of this research was to study the effects of preheating treatment and thermal-setting temperature on the thermal properties and adhesion performance of esterified and cross-linked soy protein isolates. Preheating treatment was achieved by heating a soy protein isolate suspension (5% solid) for 20 min at 60, 80, 110 or 130°C. Thermal-setting temperatures of 130, 160, 190 and 220°C were achieved by adjusting the temperature of the hot press. Differential scanning calorimetry and sodium dodecyl sulfate-polyacrylamide gel electrophoresis were used to determine changes in the protein structure before and after preheating treatment. Preheating treatment had a significant effect on protein structure and adhesion performance. Adhesion strength of control and esterified soy protein isolates reached maximum at 80°C preheating temperature. Severe preheating (over 110°C) caused complete denaturation of proteins and loss of their native structure and was, therefore, detrimental to adhesion performance. Thermal-setting temperature also had a significant effect on protein structure and wet strength of the soy protein isolates. Wet adhesion strength of unmodified, esterified, and cross-linked soy protein isolates increased by 170%, 128% and 80%, respectively, as the thermal-setting temperature increased from 130 to 220°C.     

DTA and TGA studies of flame-resistant fabrics

Preliminary thermal studies were made of cotton fabrics which had been made flame resistant by chemical modification or by blending with a flame-resistant modified acrylic fiber. DTA and TGA thermograms were made in both nitrogen and oxygen atmospheres. Differences were found in the thermograms of the untreated controls, depending upon amount of purification. Fabrics treated with the flame-retardant formulations had lower decomposition temperatures and higher percent residue. Decomposition in oxygen was more complete and proceeded at a lower temperature. Infrared spectra of selected samples, which had been partially or completely charred, were examined. These data are related to theories about the degradation of flame-resistant cotton fabrics.     

Dielectric behavior and properties of a cyanate ester containing dicyclopentadiene. I

2,6‐Dimethyl phenol dicyclopentadiene dicyanate ester (DCPDCY) was synthesized through the reaction of 2,6‐dimethyl phenol dicyclopentadiene novolac and cyanogen bromide. The proposed structure was confirmed by Fourier transform infrared, mass spectrometry, NMR spectrometry, and elemental analysis. DCPDCY was then cured by itself or cured with bisphenol A dicyanate ester (BADCY) to form triazine structures. The thermal properties of the cured DCPDCY resins were studied with differential scanning calorimetry, dynamic mechanical analysis (DMA), dielectric analysis, and thermogravimetric analysis; these data were compared with those of BADCY. The cured DCPDCY resins exhibited a lower dielectric constant (2.58 at 1 MHz), a lower dissipation factor (20.2 mU at 1 MHz), less thermal stability (the 5% degradation temperature and char yield were 430°C and 32.1%, respectively), a lower glass‐transition temperature (266°C by thermomechanical analysis and 271°C by DMA), a lower coefficient of thermal expansion (22.5 ppm before the glass‐transition temperature and 124.9 ppm after the glass‐transition temperature), and less moisture absorption (0.88% at 48 h) than BADCY, but they showed higher moduli (6.28 GPa at 150°C and 5.35 GPa at 150°C) than the bisphenol A system. The properties of the cured cocyanate esters (DCPDCY and BADCY) lay between those of cured BADCY and DCPDCY, except for the moduli. The moduli of some cocyanate esters were even higher than those of cured BADCY and DCPDCY. A positive deviation from the Fox equation was observed for cocyanate esters. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2079–2089, 2005     

The Application of Thermal Analysis Methods to the Decomposition of Sodium Bicarbonate

Thermal analysis of sodium bicarbonate by DTA and DSC showed that the decomposition temperature of this salt is about 100±1°C. A decomposition temperature of 270°C given in the Handbooks seems to be an error. Adsorbed water is the cause of the small endotherm between 70 and 75°C.     

Thermal Decomposition of Diammonium Tetrachloroplatinate to form Platinum Nanoparticles and its Application as Electrodes

Pt nanoparticles were obtained via the thermal decomposition of (NH₄)₂[PtCl₄] (diammonium tetrachloroplatinate) by heating from room temperature to 760 °C. The thermal decomposition process was analyzed using thermogravimetric analysis (TGA) and differential thermal analysis (DTA), X-ray thermodiffraction and infrared spectroscopy. The size and structure of the platinum particles were analyzed using transmission electron microscopy (TEM). The electrochemical activity of Pt particles was assessed by cyclic voltammetry in 0.5 M H₂SO₄. The TGA and DTA results suggested that the thermal decomposition of the precursor proceeded in two stages: loss of NH₄Cl at ~300 °C, followed by loss of NH₄Cl and Cl₂ at ~372 °C. Metallic Pt particles were then produced at temperatures of 372 °C and above. At 760 °C, the mean ± SD size of the Pt particles was (4.1 ± 1.6) nm, as determined from TEM measurements. In cyclic voltammetry (CV) measurements, an electrode comprised of glassy carbon and Pt particles in 0.5 M H₂SO₄ exhibited behavior similar to that observed using a polycrystalline Pt electrode.     

Synthesis and characterization of poly(vinyl 2,4,6‐trinitrophenylacetal) as a new energetic binder

Poly(vinyl alcohol) was modified by an aldehyde acetal reaction with 2,4,6‐trinitrophenylacetaldehyde to give a new energetic polymer poly(vinyl 2,4,6‐trinitrophenylacetal) (PVTNP). The structure of PVTNP was characterized by elemental analysis, ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, and nuclear magnetic resonance spectra. The glass‐transition temperature of PVTNP was evaluated by differential scanning calorimetry (DSC), and the thermal stability of PVTNP was tested by differential thermal analysis (DTA) and thermogravimetric analysis (TGA). DSC traces showed that the PVTNP polymer had one single glass‐transition temperature at 105.3°C. DTA and TGA curves showed that the thermooxidative degradation of PVTNP in air was a three‐step reaction, and the percentage of degraded PVTNP reached nearly 100% at 650°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Optimization of the thermomechanical behavior of a poly(chromium(III) trisphosphinate)

A two-component reactive system consisting of a poly(chromium(III) bisphosphinate) and dioctylphosphinic acid reacts to form a poly(chromium(III) trisphosphinate). Extensive thermomechanical hysteresis is displayed throughout the temperature range ?180°C to >300°C by specimens containing filaments of glass. Thermal pretreatment to about 400°C (the limit of thermal stability) eliminated these instabilities. These results correlate with the reported brittle and tough character of films of the poly(chromium (III) bisphosphinate) and poly(chromium (III) trisphosphinate), respectively. Regardless of thermal history (between 200°C and 400°C), the polymer system displayed three major transition regions: the glass transition centered at about 0°C, another centered at about 230°C, and a third at about ?200°C.     

Effects of moisture and temperature ageing on reliability of interfacial adhesion with black copper oxide substrate

The reliability of adhesion performance of bare Cu, as-deposited and surface-hardened black oxide coatings on Cu substrates was studied. The interfacial adhesion with a polyimide adhesive tape and an epoxy moulding compound was measured using the button shear and tape peel tests after hygrothermal ageing in an autoclave, high temperature ageing and thermal cycles. Moisture adsorption and desorption studies at different aging times suggested that the black oxide coating was effective in reducing the moisture adsorption. The bond strengths for all substrates remained almost unchanged after thermal ageing at 150°C for 8 h. Thermal cycling between ?50°C and 150°C for 500 cycles reduced by about 20% the button shear strength of the as-deposited black oxide substrate, but it did change much the bonding performance of the bare Cu substrate. Hygrothermal ageing at 121°C/100% RH in an autoclave was most detrimental to adhesion performance because of the combined effect of elevated temperature and high humidity. The reduction in button shear strength after the initial ageing for 48 h was 50–67%, depending on the type of coating. In all accelerated ageing tests, the residual interfacial bond strengths were consistently much higher for the black-oxide-coated substrates than the bare Cu surface, confirming a higher reliability of black oxide coating. Fracture surfaces analysis of tape-peeled bare copper substrates after 500 cycles of thermal loading revealed a transition in failure mechanism from interfacial to cohesive failure. In contrast, the failure mechanism remained unchanged for black-oxide-coated substrates. The observations made from the button shear and tape peel tests were generally different because of the different fracture modes involved.     

Thermal behavior of polymethacrylonitrile

The intramolecular cyclization by heating and the thermal degradation of polymethacrylonitrile samples prepared with various initiators, AIBN (A), BPO (B), BuLi (C), Et₂Mg (D), and methacrylonitrile–methacrylic acid copolymer (E), were investigated by DTA, TGA, and infrared spectroscopy. The rate of formation of ? C?N? linkages determined by IR was in the order of E > C > D > B > A. An endothermic peak of DTA thermogram due to thermal degradation was observed at approximately 345°C for the ionically initiated samples, whereas two endothermic peaks were observed at approximately 315°C and 365°C for the radically initiated ones. In the TGA thermograms, although the ionically initiated samples decomposed continuously in a single stage, the radically initiated ones showed weight loss in two steps, with an inflection point at about 330°C. The first stage of thermal degradation of radically initiated samples was concluded to be initiated at the terminal double bonds formed as a result of termination by disproportionation, and the second one at higher temperatures is initiated at random in the polymer. The ionically initiated samples without terminal double bond decompose exclusively by random scission.