Search Results
Abstract
The paper presents the results of testing thermal properties and combustibility of butadiene-acrylonitrile rubber vulcanizates with different contents of bounded acrylonitrile: Perbunan NT 1845 and Perbunan NT 3945 from Bayer. The rubbers were cross-linked by means of dicumyl peroxide. Four types of carbon black with different specific surfaces were used as fillers. The test results were obtained with the use the derivatograph, DSC-204 of Netzsch, measurements of flammability by the method of oxygen index and in air. The results of measurements have shown that the thermal stability and flammability of the vulcanizates under investigation are affected by the activity of solid phase and the degree of surface development as well as the flexibility of polymeric chain and the degree of its unsaturation. A clear relationship has been found between the thermal properties and flammability of the cross-linked butadiene-acrylonitrile rubbers.
Abstract
Thermal properties of recycled triphenylphosphite (TPP) chain extended poly(ethylene terephthalate) (PET) was investigated. As the TPP concentration increases, both reaction residues and molecular mass increase affecting significantly the thermal properties and crystallization behavior of the material. The presence of TPP residues did not affect the crystalline melt temperature (T m), but modified the glass transition temperature (T g), the crystallization temperature on heating (T hc) and the crystallization temperature on cooling (T cc). In the samples submitted to extraction with acetone, the properties were influenced by molecular mass changes, probably due to the presence of some insoluble reaction residue. The thermal stability of the sample purified by extraction after chain extension was comparable to that of the non-extended sample when heating was carried out under nitrogen atmosphere.
Abstract
The paper presents the thermal properties of fibres made of a modified polyimideamide. The effects of as-spun draw ratio and deformation during the fibre drawing stage on the structure, thermal properties, moisture absorption and tenacity of the obtained fibres have been determined. Based on the findings obtained by the DTA and DSC methods, it has been found that the modification of the polymer under investigation causes its glass transition temperature to decrease through the increase of molecular mobility. At the same time, the heat-resistant fibres with the amorphous oriented structure are characterized by a tenacity of 16 cN/tex, good absorption properties and increased porosity. The thermal stability indices of the examined fibres have been determined on the basis of thermogravimetric curves obtained both under air and inert gas.
Abstract
Chemical compositions, crystalline structures and thermal properties of bombax cotton and natural colored cottons including laurel green, bottle green and brown cotton were investigated by chemical analysis, SEM, IR spectra and X-ray diffraction. The results showed that the crystallinity and crystallite sizes of laurel green cotton were lower than those of bottle green cotton because of the excess content of suberin in the former. The crystallinity of brown cotton was similar to that of white cotton, and bombax cotton had the lowest crystallinity but its crystallite orientation was the highest. Thermal property of bottle green cotton was the most stable, whose decomposition temperature was higher of 30°C than that of common white cotton because of its higher lignin content, and bombax cotton had the lowest thermal degradation temperature. But bottle green cotton reached the highest decomposition speed and made decomposition finish within a very short time, and bombax cotton was just the reverse.
Abstract
The crystal structure, thermal properties and growth rates of spherulites of the Tussah silk fibroin, produced upon drying of the silk taken directly from the lumen which is essentially a poly(L-alanine)polypeptide, are investigated. Depending on casting conditions, spherulites with either αhelical chain conformation or β parallel sheet structure are produced. The growth rates display a strong positive temperature coefficient, with an apparent transition, which however cannot be related with the formation of two different crystal structures at this stage.
The thermal properties of cyanatocopper complexes with pyridine, bipyridine and phenanthroline are described in this paper. It was found that the thermal stabilities of the complexes were found to increase in the order py≪bipy<phen ligands. The significantly higher thermal stability of the complexes with bipyridine and phenanthroline is caused by the presence of dimeric structural units in the crystal structure and intermolecular interactions of the cyanate and heterocyclic ligands.
Abstract
The paper presents results of thermal properties measurements of cis-1,4-polybutadienes with different contents of cis-1,4 mers before and after their conventional cross-linking with the use of dicumyl peroxide and non-conventional cross-linking by means of iodoform. The measurements were carried out under the atmosphere of neutral gas using a micro-calorimeter, DSC and thermogravimetry, TG. The thermal curves have been interpreted from the point of view of phase transitions and chemical reactions of investigated elastomers.
Abstract
This work presents a relationship between the thermal properties in different polyethylene samples analyzed by differential scanning calorimetry (DSC). The morphology and structural changes were studied by transmission electron microscopy (TEM). A preparative method involving surface etching was used to obtain surface replicas. The main morphological features of the samples, characterized by lamellar structure, obtained in this work by TEM give values of mean lamellar thickness from 900 to 500 Ĺ in the highest branch content and molecular mass. Enthalpies of melting allowed to calculate crystallinity; given values in the range from 47 to 68%.
Abstract
We have applied photoacoustic (PA) technique to study the thermal properties of porous silicon (PS) films formed on p-type Si substrates by electrochemical anodic etching. Four PS samples with close thicknesses but greatly different porosities (from 20 to 60%) were examined. From the dependences of the PA signals on the modulation frequency of excitation light measured under a transmission detection configuration (TDC), effective thermal diffusivities for the two-layered PS/Si samples were determined and found to decrease greatly from 0.095 to 0.020 cm2 s-1 as the porosity increased from 20 to 60%.
Abstract
Thermal properties of precursor polyacrylonitrile fibres containing nanoparticles of additives such as SiO2, hydroxyapatite and montmorillonite have been examined. The thermal curves of the fibres under investigation obtained by the derivatographic method in air and DSC in a neutral gas atmosphere were interpreted from the point of view of physical and chemical changes in the fibre-forming polymer. Based on the thermogravimetric curves, the coefficients of thermal stability of the fibres were found. It has been found that the thermal stability of PAN fibres is affected by the type of nanoadditives and the value of the as-spun draw out ratio used during fibre spinning.
