Search Results

You are looking at 61 - 70 of 703 items for :

  • "thermal degradation" x
  • Refine by Access: All Content x
Clear All

Abstract  

Polymethacrylonitrile (PMAN) was prepared by bulk, solution and precipitation polymerization. The thermal stability of the polymer, which is affected by the structure of the chain end groups, was studied by non-isothermal thermogravimetry (TG). On the basis of the differential TG curves of samples prepared by polymerization in the presence of chlorinated solvents, it may be concluded that, in addition to end-chain and random main chain scission initiated depolymerization, hydrogen chloride evolution also occurs during the thermal degradation of PMAN.

Restricted access

Abstract  

The thermal degradation of diammoniumhexachloroplatinate (NH4)2PtCl6 is used in technical scale for the production of the pure platinum metal [1] and for this reason of great interest. Our investigations have been focused on the influence of the different atmospheres (oxidizing, inert or reducing) used in the technical processes towards the degradation mechanism and the evolved volatile degradation products. The second main aspect of our investigations was the evolution of volatile platinum species. Regarding the different frequencies of platinum allergies related to the different technical processes, the evolution of volatile platinum species is of great importance, due to the supposed allergic potential of this substances [2–4].

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors:
Thangamani Rajkumar
,
Chinnaswamy Vijayakumar
,
Palanichamy Sivasamy
,
Bojja Sreedhar
, and
Charles Wilkie

Abstract  

Imparting thermal stability to polymethyl methacrylate (PMMA) without affecting its optical clarity is attempted by incorporating HET acid based oligoesters. Pure PMMA and PMMA containing five and 20 wt% of four different oligoesters are separately prepared using bulk polymerization. The thermal properties of the materials studied using DSC, TG, TG–FTIR and Pyr–GC–MS are presented. The main volatile degradation products identified are CO, HCl, CO2, H2O, hexachlorocyclopentadiene, hexachloroendomethylene tetrahydrophthalic acid/anhydride and methyl methacrylate. A detailed mechanism for the influence of the degradation products of HET acid based oligoesters on the thermal degradation of PMMA is also presented.

Restricted access

Abstract  

In the present work Lyocell fibers were subjected to graft copolymerization of poly-N-isopropylacrylamide (pNIPAAm) thermosensitive polymer. The thermal degradation and stability of lyocell/pNIPAAm copolymers gels were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). pNIPAAm/lyocell copolymers are thermally stable and more resistant to temperature than lyocell fibres. Thermal characterization was analyzed as a function of percentage by mass of the pNIPAAm grafted. It has been shown that for pNIPAAm/lyocell copolymers, degradation occurs at higher temperature when increasing the degree of grafting.

Restricted access

The non-oxidative thermal degradation kinetics of poly(di-n-alkyl itaconates), ranging from the methyl to then-octyl derivatives, were studied by non-isothermal and isothermal TG. The thermal degradation activation energy and characteristic mass loss temperatures were found to decrease with increasing substituent size. The shapes of the DTG curves were dependent on the size of the alkyl substituent. The different DTG maxima were ascribed to various modes of initiation of depolymerisation. The thermal stability of poly(di-n-hexyl itaconate) was found to be independent of the initial molar mass of the sample in the range ofM w from 104 to 107 g/mol.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors:
Marta C. D. Silva
,
J. R. Botelho
,
Marta M. Conceiçăo
,
B. F. Lira
,
Monyque A. Coutinho
,
A. F. Dias
,
A. G. Souza
, and
P. F. A. Filho
Restricted access

Abstract  

Copolymers of dimethyl itaconate (DMI) and 4-vinylpyridine (4VP) were synthetized in toluene at 60C with0.26 mol% of AIBN as initiator. Their compositions were determined by differential refractometry and by differential scanning calorimetry. The 4VP contents of the copolymer samples ranged between 7 and 75 mol%. The reactivity ratios calculated via the Fineman-Ross method were r 1=0.24 (DMI) and r 2=0.57 (4VP). The thermal degradations of these copolymers were studied. The results of thermogravimetric measurements indicated that the copolymers degrade at lower temperatures than those of their parent homopolymers. A possible explanation of this anomalous behaviour is the formation of thermally unstable structures during the copolymerisation.

Restricted access

The thermal degradation of chlorine-containing polymers used in a rubber technology has been investigated in a nitrogen atmosphere. The characteristics of degradation have been compared on the basis of thermogravimetry, carbon residues and chlorine elimination. The observed structure-dependent differences in degradation of the investigated polymers are discussed.

Restricted access

Abstract  

Lighter and heavier lanthanide(III) ions react with dihydrazinium salts of ethylenediaminetetraacetic acid (H4edta) in aqueous solution to yield hydrazinium lanthanide ethylenediaminetetraacetate hydrate, N2H5[Ln(edta)(H2O)3]·(H2O)5 where Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb and Dy. The numbers of water molecules present inside the coordination sphere have been confirmed by X-ray single crystal studies. The presence of five water molecules as lattice water is clearly shown by the mass loss from the TG analyses. Dehydration of a known amount (1 g) of each sample were carried out at constant temperature (100–110°C) for about 5 min further confirms the number of non-coordinated water molecules. The complexes after the removal of lattice water undergo multi-step decomposition to give respective metal oxide as the final product. The DTA shows endotherms for dehydration and exotherms for the decomposition of the anhydrous complexes. The formation of the metal oxides was confirmed by X-ray powder diffraction studies.

Restricted access

Pyrolysis in combination with gas chromatography and thermogravimetry were used to study the thermal degradation of some cross-linked copolymers of vinyl acetate with divinylbenzene and ethylstyrene. The temperature was varied in the range 200° and 800°. The thermal decomposition products of the analyzed copolymers vary greatly, both with the temperature and with the composition of the samples. The experimental data obtained led to the assumption of a complex degradation mechanism, evidenced by the overlapping processes and the unexpected contents of certain evolved compounds as a function of composition.

Restricted access