Crystallization properties and thermal stability of polypropylene composites filled with wollastonite

The influence of wollastonite (CaSiO₃) content on the crystallization properties and thermal stability of polypropylene (PP) composites was investigated. The results showed that the crystallization temperature, crystallization end temperature and crystallization temperature interval, as well as the degree of crystallinity of the composites, were higher than those of the unfilled PP resin, while the crystallization onset temperature was little changed from that of the unfilled PP resin. The increase of degree of crystallinity for the composites could be attributed to the heterogeneous nucleation of the CaSiO₃ in the PP matrix. The thermal stability increased with increasing filler weight fraction (ϕ_f); the thermal decomposition rate decreased nonlinearly with increasingϕ_f. Finally, the dispersion of the filler particles in the matrix was observed, and the mechanisms of thermal stability and crystallizing behavior were discussed.     

Thermal stability and flame retardancy of PET/magnesium salt composites

Nano-Mg(OH)₂ (nanometre magnesium hydroxide, nano-MH) was successfully introduced into the esterification and polycondensation system by in situ polymerization to obtain PET/magnesium salt composites (PETMS). The thermal properties and flame retardancy of PETMS were investigated by differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), UL-94 vertical burning and limited oxygen index (LOI) test. The DSC and TGA results show that magnesium salts in the PET matrix have little effect on the thermal properties of PET, but a significant effect on the thermal stabilities of the composites. The results of LOI and UL-94 test show PETMS have higher LOI values (≥25%) and V-0 rating without melt dripping in the UL-94 test, indicating that PETMS have good flame retardancy and anti-dripping property. Moreover, the residues of magnesium salts and composites after TGA test were also studied by Fourier transform infrared spectroscopy (FTIR) to better understand the mechanism of flame retardancy, which reveals that magnesium salts accelerate the degradation of PET and catalyze the formation of char. The SEM results show the morphological structures of the char effectively protect the composites’ internal structures and inhibit the heat, smoke transmission and reduce the fuel gases when the fire contacts them.     

Thermal stability and flammability of silicone polymer composites

Silicone polymer composites filled with mica, glass frit, ferric oxide and/or a combination of these were developed as part of a ceramifiable polymer range for electrical power cables and other high temperature applications. This paper reports on the thermal stability of polymer composites as determined by thermogravimetric techniques, thermal conductivity and heat release rate as measured by cone calorimetry. The effects of fillers on thermal stability and flammability of silicone polymer are investigated. Of the fillers studied, mica and ferric oxide were found to have a stabilising effect on the thermal stability of silicone polymer. Additionally, mica and ferric oxide were found to lower heat release rates during combustion, but only mica was found to increase time to ignition.     

Thermal stability of polyurethanes

Summary The combined application of thermogravimetry reactiongas chromatography and gel-permeation chromatography permits to follow the heat degradation of polyurethane polymers in inert gas, air and water-saturated environment. The examinations give information on the rate of thermal degradation, the individual volatile degradation components, the critical points of the polymer chains and on the change of their molecular-weight distribution. Gas chromatographic examinations also permit the identification of the chain-extending components of different types of polyurethanes.     

TG-FTIR study of the thermal degradation of polyoxymethylene (POM)/thermoplastic polyurethane (TPU) blends

A series of blends of polyoxymethylene (POM)/thermoplastic polyesterurethane (TPU) has been obtained by mechanical processing using a double screw extruder. The thermal stability and the thermal degradation profiles of POM/TPU blends were investigated by thermogravimetric analysis (TG) coupled on-line with Fourier transform infrared spectroscopy (FTIR). It was found that incorporation of TPU into POM matrix resulted in increase of thermal stability of blends in comparison with pristine materials. The thermal degradation of TPU in inert gas atmosphere proceeds in two steps while the thermal degradation of POM is basically a one step process with a substage in a higher temperature range. The most abundant volatile products of the thermal degradation were identified; the possibly routes of their formation have been presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal stability and degradation products analysis of benzocyclobutene-terminated imide polymers

Benzocyclobutene-terminated imides were prepared and fully characterized with ¹H NMR, MS, and FT-IR. The thermal degradation of polymers was investigated by using thermogravimetric analyzer (TGA) and high-resolution pyrolysis-gas chromatography–mass spectrometry (HR-Py-GC–MS). TGA showed that thermal degradation of the polymer was a single-stage process in N₂, whereas a three-stage degradation in air atmosphere. The major involved products were found to be CO₂, naphthalene and naphthalene derivatives. Degradation mechanism of the polymer was suggested and the relationship between structures of the polymer and degradation products was also discussed.     

Thermal stability and dehydration of anapaite

The thermal behavior of anapaite, Ca₂Fe²⁺(PO₄)₂·4H₂O, has been studied by TG/DTG and DSC techniques, complemented by Fourier-transform IR spectroscopy. The anapaite sample, originating from Bellaver de Cerdena (Spain) was identified as such using X-ray diffraction and qualitative energy-dispersive analysis of X-rays. ⁵⁷Fe Mössbauer spectroscopy at various temperatures could not detect any Fe³⁺. It was found from thermal analyses and IR spectroscopy that two types of hydrogen–bonded water molecules exist in the structure. This feature is related to the distance between the hydrogen atom of a water molecule and the oxygen atom of a phosphate group, the distance between both oxygen atoms and the angle O(H₂O)–HO(PO₄). The dehydration process proceeds in two partially overlapping steps. The removal of the last two, strongly bonded water molecules is accompanied by the decomposition of the crystal structure. From TG curves, the activation energy was calculated for different intervals of dehydration reaction. For this purpose, five slow heating rates between 0.4 and 2°C/min were applied. The activation energy for the entire process was also obtained from DSC (223 kJ/mol) and found to be in reasonable agreement with the average of the various values from the TGA (233 kJ/mol). The heat of reaction for the complete dehydration was found to be 177 kJ/mol.     

Thermal stability of ion-exchange Nafion N117CS membranes

The effect of exchanged ions on the thermal stability of Nafion N117CS membranes was investigated by X-ray photoelectron spectra (XPS), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and ion exchange capacity determinations. The ion exchange of alkaline metal ions was effective in improving the thermal stability of the Nafion N117CS membrane. Findings reveal that when Nafion was exchanged for cations with a larger ionic radius, the membrane attained superior thermal stability. On the other hand, we confirmed that the Na-exchange Nafion N117CS membrane possessed a distinctive degree of thermal stability among the alkaline ion-exchange Nafions, although the order of ionic radii is K > Na > Li. Thermal stability improved the most when the Nafion membrane was exchanged for alkaline ions, followed by divalent ions, then trivalent ions. As for the Nafion membrane when it was exchanged for divalent ions or trivalent ions, Nafion following the ion exchange had a thermal stability proportional to an increase in the ionic radius of the cation. This stability may be explained by the reduction of water content and a greater interaction between the sulfonate groups and the cations with larger ionic radii. Since the Al cations acted as a Lewis acid center, the decomposition of the ether bonds of the perfluoroalkylether pendant-chains of the Nafion membrane was observed for the Nafion N117CS membrane that had been exchanged for Al ions. The activation of molecular mobility in Nafion was observed between the decomposition stages of the loss of water and the loss of sulfonic groups. The temperature of activation of cation-exchange Nafion became much higher than that of Nafion in an acid form.     

Phase and thermal stability of nanocrystalline hydroxyapatite prepared via microwave heating

A simple method to prepare nanocrystalline hydroxyapatite (nHAP) is performed using a precipitation method assisted with microwave heating method. This method can be reported notably with high reproducibility and productivity. The received ceramic powder possesses characteristic of needle-shaped nanocrystals with dimension about 50 nm in diameter and 200 nm in length. The particle size distribution has been confirmed being in the range of 28-159 nm. Thermal analyses revealed that nHAP has at least three thermal events influenced by elevated temperatures. Phase stability and microstructure evolution of the nHAP calcined at temperatures range between 700 and 1200 °C are discussed in terms of the formation of secondary phases, the decomposition of HAP releasing carbonate and water. Various experimental techniques have been employed in this work, including powder X-ray diffraction, IR spectroscopy, DSC and TGA thermal analyses, dynamic light scattering and scanning electron microscopy.     

Thermal stability and degradation behavior of novel wholly aromatic azopolyamide-hydrazides

Thermal stability and degradation behavior of a series of novel wholly aromatic polyamide-hydrazides containing azo groups in their main chains have been investigated in nitrogen and in air atmospheres using differential scanning calorimetry (DSC), thermogravimetry (TG), infrared spectroscopy (IR) and elemental analysis. The influences of controlled structural variations and molecular weight on the thermal stability and degradation behavior of this series of polymers have also been studied. The structural differences were achieved by varying the content of para- and meta-substituted phenylene rings incorporated within this series. Azopolyamide-hydrazides having different molecular weights of all para-substituted phenylene type units were also examined. The polymers were prepared by a low temperature solution polycondensation reaction of p-aminosalicylic acid hydrazide [PASH] and an equimolar amount of 4,4′-azodibenzoyl chloride [4,4′ADBC] or 3,3′-azodibenzoyl chloride [3,3′ADBC] or mixtures of various molar ratios of 4,4′ADBC and 3,3′ADBC in anhydrous N,N-dimethyl acetamide [DMAc] containing lithium chloride as a solvent at −10 °C. All the polymers have the same structural formula except the mode of linking phenylene units in the polymer chain. The results clearly reveal that these polymers are characterized by high thermal stability. Their weight loss occurred in three distinctive steps. The first was small and assigned to the evaporation of absorbed moisture. The second was appreciable and was attributed to the cyclodehydration reaction of the hydrazide groups into 1,3,4-oxadiazole rings by losing water, combined with elimination of azo groups by losing molecular nitrogen. This is not a true degradation but rather a thermo-chemical transformation reaction of the azopolyamide-hydrazides into the corresponding polyamide-1,3,4-oxadiazoles. The third was relatively severe and sharp, particularly in air, and corresponded to the decomposition of the resulting polyamide-1,3,4-oxadizoles. In both degradation atmospheres, the improved resistance to high temperatures was always associated with increased content of para-phenylene moieties of the investigated polymer. The better thermal stability of the wholly para-oriented type of polymer relative to the other polymers is attributed to its greater chain symmetry which is responsible for its greater close packing, rod-like structure and consequently stronger intermolecular bonds which would be more difficult to break and therefore more resistance to high temperatures. Further, with exception of 160-200 °C temperature range, where the lower molecular weight samples showed considerable weight losses which were most probably due to hydrogen bonded DMAc, all the wholly para-oriented phenylene type of polymer samples behaved similarly regardless of their respective molecular weight. This seems to indicate that the structural building units responsible for high thermal stability of the polymers are their characteristic groups, such as aromatic moieties, amide and hydrazide linkages in case of azopolyamide-hydrazides, and 1,3,4-oxadiazole rings, aromatic nuclei and amide linking bonds in case of polyamide-1,3,4-oxadiazoles, rather than the longer chain segments.     

Thermal stability of aromatic polyesters prepared from diphenolic acid and its esters

The thermal performance of aromatic polyesters (poly(DPA-IPC), poly(MDP-IPC) and poly(EDP-IPC)) prepared from isophthaloyl chloride (IPC) with diphenolic acid (DPA) and its esters were studied with DSC and TG, and the decomposition mechanism of poly(DPA-IPC) were investigated using FTIR and integrated TG/FTIR analyses. As compared with ordinary aromatic polyesters, poly(DPA-IPC) has lower glass transition temperature (159 °C) and much lower thermal stability. It starts to decompose at about 210 °C and is characterized by two-stage thermal decomposition behavior, with active energies of decomposition of 206 kJ/mol and 389 kJ/mol, respectively. The analyses of the decomposition process and products indicate that the pendent carboxyl groups in poly(DPA-IPC) are responsible for its low thermal stability. Accordingly, a decomposition mechanism for the first stage is proposed. With this knowledge in mind, we capped the carboxyl groups in DPA with methyl and ethyl groups to prepare poly(MDP-IPC) and poly(EDP-IPC) from methyl diphenolate and ethyl dipenolate. As expected, these two polymers exhibit obviously improved thermal stability, with onset decomposition temperature of about 300 °C.     

Thermal stability of magnesium-rich primers based on glycidyl carbamate resins

Coatings of outstanding thermal stability were obtained by the combination of two novel technologies, that of a magnesium-rich primer and a silane-modified glycidyl carbamate binder. While conducting a study to evaluate the new binder system with respect to properties of the magnesium-rich primer, during thermogravimetric analysis of samples, previously unobserved and unexpected properties were noted. The samples transformed into an intact solid residue, with the amount of the residual char ranging between 40 and 90% weight depending on the pigment volume concentration (PVC) of the magnesium particles in the composition. It appears that the hitherto unobserved property is essentially a function of the metallic pigment particles in the coating. The discovery of the exceptional thermal stability potentially increases the range of application for these primers and these can be further developed for use as a thermal barrier coating.     

Thermal stability and permeability of microencapsulated n-octadecane and cyclohexane

Microencapsulated phase change materials (MicroPCMs) used as thermal insulating coating and fabrics are usually required to have a prominent thermal stability and a lower permeability. MicroPCMs with a prominent thermal stability and a lower permeability were fabricated by feeding an appropriate content of cyclohexane into n-octadecane followed by heat-treatment at a suitable condition. Microcapsules containing 18-19% reserved expandable space are synthesized at 30-40 wt.% cyclohexane in the oil phase, which have a highest thermal resistant temperature −270 °C, and a lower permeability, less than 1.2%. The weight loss of microcapsules is mainly attributed to the leakage of n-octadecane from some broken capsules, so improving their uniformity can efficiently enhance their thermal stability and lower the permeability.     

Thermal and hydrolytic stability of sulfonated polyimide membranes with varying chemical structure

Many important properties required for fuel cell applications including hydrolytic stability, depend on various factors like flexibility of the polymer backbone, ring structure and phase separation. This paper is primarily focused on studying the effect of the chemical backbone structure on the hydrolytic stability and other properties. To study the difference in the hydrolytic stability with change in the chemical backbone structure of sulfonated polyimides we synthesized phthalic sulfonated polyimides and naphthalenic sulfonated polyimides. Two series of phthalic sulfonated polyimides were prepared using 4,4′-oxydiphthalic anhydride (ODPA) and 4,4′-methylene dianiline (MDA), and 4,4′-(hexafluoroisopropylidine) diphthalic anhydride (6FDA) and oxydianiline (ODA). 4,4′-Diaminobiphenyl-2,2′-disulfonic acid (BDSA) was used to introduce sulfonic acid group into both series. Naphthalenic polyimides were synthesized from 1,4,5,8-naphthalenetetra-carboxylic dianhydride, BDSA, MDA and ODA. Also to observe other properties according to variation of sulfonic acid content, the degree of functionalisation was effectively controlled by altering the mole ratio between the sulfonated and non-sulfonated diamine monomers in phthalic sulfonated polyimides. The hydrolytic stability of the polyimides was followed by FT-IR spectroscopy at regular intervals. Polyimides prepared using naphthalenic dianhydride, NTDA, exhibited higher hydrolytic stability than the phthalic dianhydrides. The proton conductivity, ion exchange capacity (IEC) and water uptake measurements revealed the dependence on the molecular weight of the repeating unit. The proton conductivity of the sulfonated polyimides was found to vary with chemical backbone structure.     

Thermal stability of poly(N-vinyl-2-pyrrolidone-co-methacrylic acid) copolymers in inert atmosphere

The thermal stability of poly(N-vinyl-2-pyrrolidone-co-methacrylic acid) copolymers was studied by thermogravimetry and infrared spectroscopy in inert atmosphere. The thermogravimetric curves suggested that the effective degradation of both systems occurred in the temperature range 350–500 °C with more than 60% mass loss. At this temperature, the activation energy was in the range 160–200 kJ mol⁻¹ (average values), suggesting that the degradation occurred by a random scission of the chain. The FTIR results indicated that the main volatile products of degradation are CO₂, CO and hydrocarbons (unsaturated structures) with low molecular weight. Pure PVP also showed the formation of NH₃ which was apparently suppressed in the copolymer by the formation of large amounts of CO₂ and CO. The results suggested that the thermal stability of the copolymers was essentially associated with the N-vinyl-2-pyrrolidone monomer, losing stability when the percentage of methacrylic acid in the copolymer system was increased.     

Thermal stability of microencapsulated epoxy resins with poly(urea-formaldehyde)

A series of microcapsules filled with epoxy resins with poly(urea-formaldehyde) (PUF) shell were synthesized by in situ polymerization, and they were heat-treated for 2 h at 100 °C, 120 °C, 140 °C, 160 °C, 180 °C and 200 °C. The effects of surface morphology, wall shell thickness and diameter on the thermal stability of microcapsules were investigated. The chemical structure and surface morphology of microcapsules were investigated using Fourier-transform infrared spectroscope (FTIR) and scanning electron microscope (SEM), respectively. The thermal properties of microcapsules were investigated by thermogravimetric analysis (TGA and DTA) and by differential scanning calorimetry (DSC). The thermal damage mechanisms of microcapsules at lower temperature (<251 °C) are the diffusion of the core material out of the wall shell or the breakage of the wall shell owing to the mismatch of the thermal expansion of core and shell materials of microcapsules. The thermal damage mechanisms of microcapsules at higher temperature (>251 °C) are the decomposition of shell material and core materials. Increasing the wall shell thickness and surface compactness can enhance significantly the weight loss temperatures (T_d) of microcapsules. The microcapsules with mean wall shell thickness of 30 ± 5 μm and smoother surface exhibit higher thermal stability and can maintain quite intact up to approximately 180 °C.     

Thermal stability of Ba1-xCaxF2 solid solutions

Ba_1-xCa_xF₂ samples with fluorite-type structure were prepared by high-energy ball milling. DSC measurements revealed exothermic decomposition at temperatures of about 450 °C. Decomposition was also observed by high temperature X-ray experiments. As a product, two phases with compositions close to pure BaF₂ and CaF₂ were obtained. The decomposition temperature observed by X-ray measurements is lower than in the DSC experiments. This might indicate that X-ray irradiation could foster the decomposition.     

Thermal stability and bond dissociation energy of fluorinated polymers: A critical evaluation

Intrinsic bond dissociation energies (BDEs) of selected fluorinated polymers are critically evaluated. Two distinctive approaches were followed. In the first one, according to Wu and Rodgers [E.-C. Wu, A.S. Rodgers, J. Am. Chem. Soc. 98 (1976) 6112-6115], starting from the gas-phase enthalpy of polymerization we obtained the polymer backbone BDE through appropriate thermodynamic cycles. Revised experimental results indicate that the CC BDEs of all the polymers taken into account fall within a limited energy interval, comparable to the average experimental uncertainty. Central to the second methodology adopted, is a model compound approach. Thanks to the large number of reliable thermodynamic data available in the scientific literature and to simple end-capping rules, C₂ molecules were chosen as suitable models for infinite linear polymers and alternating copolymers between ethylene and fluorinated olefins. For partially fluorinated polymers, like polyvinylidene fluoride (PVDF), alternating ethylene-tertrafluoroethylene (ETFE) and alternating ethylene-chlorotrifluoroethylene (ECTFE), the weight loss due to HF and HCl evolution during heating experiments was successfully related to the threshold energy E_o(HX) for 1,2-elimination from chemically activated hydrofluoro and hydrofluorochlorocarbons according to the modified Rice-Rampsberger-Kassel (RRKM) unimolecular theory.     

乌龙茶多糖OTPS 2-1的光谱特性、形貌特征及热特性研究

采用纤维素和葡聚糖凝胶柱层析法分离纯化,获得乌龙茶多糖主要组分OTPS2-1.经GC,HPLC,UV,IR和GPC-LLS证实OTPS2-1是富含糖醛酸和少量蛋白质的三元糖复合物,相对重均分子量为8.877×10⁴,糖基由半乳糖、葡萄糖、阿拉伯糖、岩藻糖和鼠李糖组成,其摩尔比为7.58:2.14:7.05:1.76:1.02.利用AFM,QELS及LSCM观察OTPS2-1在溶液中的形貌特征,结果表明,OTSP2-1在溶液中呈直径0.2～0.5μm、高度0.3～0.6μm的短棒形不均一聚集体,并具有强烈的荧光,溶液的pH值显著影响其聚集行为.pH值、离子强度和络合物等环境因素的改变,均导致多糖立体构象和非对称性的变化.OTPS2-1在SEM低倍镜下呈折叠卷曲形貌,在高倍镜下呈现平整的图像.综合热分析结果表明,在加热过程中,多糖有3次大的质量损失过程,出现3次吸热峰和放热峰.提示茶叶经过半发酵处理后,多糖组成、分子质量分布以及分子间相互作用可引起微观形貌、链构象和聚集行为的变化,有利于提高生物活性.     

Thermal stability of anti-rheumatic pharmaceutical drugs parecoxib sodium and valdecoxib

Thermal analysis of antirheumatic drugs, parecoxib sodium (PCX) and valdecoxib (VCX) was achieved. Thermogravimetry (TG), derivative thermogravimetry (DTG), and differential thermal analysis (DTA) were used through the work. The results led to thermal stability data, and also to the determination of kinetic parameters such as activation energy and frequency factor. The differential scanning calorimetry (DSC) was suitable for the purity determination of the compounds. The simplicity, speed, and low operational costs of thermal analysis justify its application in the quality control of pharmaceutical drugs.