共查询到20条相似文献,搜索用时 31 毫秒
1.
Mariano Pracella Cristiano Pancrazi Md. Minhaz-Ul Haque Aldo D’Alessio 《Journal of Thermal Analysis and Calorimetry》2011,103(1):95-101
Composites of polystyrene (PS) with cellulose microfibres and oat particles, obtained by melt mixing, were examined. The compatibilization
of the composites was carried out by addition of maleic anhydride-functionalized copolymers (SEBS-g-MA, PS-co-MA) and poly(ethylene glycol) to improve the fibre–matrix interfacial interactions. The plain components and their composites
were characterised by FT-IR, DSC, TGA, SEM microscopy and mechanical tests. The properties of the various systems were analysed
as a function of both fibre and compatibilizer amount. The compatibilized PS composites showed enhanced fibre dispersion and
interfacial adhesion as a consequence of chemical interactions between the anhydride groups on the polymer chains and the
hydroxyl groups on the fibres, as demonstrated by FT-IR spectroscopy. DSC analysis pointed out a neat increase of T
g of composites on addition of SEBS-g-MA, as compared to PS-co-MA. The thermal stability of composites was also influenced
by the type and amount of fibres, as well as by the structure and concentration of compatibilizer. The effect of the reactive
copolymers on the composites properties was accounted for on the basis of the polymer–polymer miscibility and chemical interactions
at the matrix/filler interface. 相似文献
2.
Le Xin Song Chuan Feng Teng Peng Xu Hai Ming Wang Zi Qiang Zhang Qing Qing Liu 《Journal of inclusion phenomena and macrocyclic chemistry》2008,60(3-4):223-233
The present work revealed there was a conceptual difference in the thermal decomposition behaviors between the complexed β-cyclodextrin
(CD) in an inclusion system and the β-CD complex of guest. The thermal decomposition behaviors of the solid inclusion complexes
of β-CD with ethylenediamine (Eda), diethylenetriamine (Dta) and triethylamine (Tea) were investigated using nonisothermal
thermogravimetry (TG) analysis based on weight loss as a function of temperature. In view of TG profiles, a consecutive mechanism
describing the formation and thermal decomposition of the three solid supermolecules of β-CD was presented. Heating rate has
very different effects on the thermal decomposition behaviors of these complexes. The faster the heating rate is, the higher
the melting-decomposition point of the complexed β-CD in an inclusion system is, and on the whole the bigger the rate constant
(k) of the thermal decomposition reaction of the complexed β-CD is. The thermal decomposition process of the complexed β-CD
for each inclusion system is determined to be simple first-order reaction using Ozawa method. The apparent activation energies
(E
a) and frequency factors (A) of the thermal decomposition reactions of the complexed β-CD molecules have been also calculated. It is found that when
the decomposition reaction of the complexed β-CD encountered a large value of E
a, such as that in Dta–β-CD system, an apparent compensation effect of A on E
a can provide enough energy to conquer the reaction barrier in prompting the k value of thermal decomposition reaction of the complexed β-CD according to Arrhenius equation. 相似文献
3.
S. F. Santos M. C. de Andrade J. A. Sampaio A. B. da Luz T. Ogasawara 《Journal of Thermal Analysis and Calorimetry》2007,87(3):743-746
TiO2–CeO2 oxides
for application as ceramic pigments were synthesized by the Pechini method.
In the present work the polymeric network of the pigment precursor was studied
using thermal analysis. Results obtained using TG and DTA showed the occurrence
of three main mass loss stages and profiles associated to the decomposition
of the organic matter and crystallization. The kinetics of the degradation
was evaluated by means of TG applying different heating rates. The activation
energies (E
a) and
reaction order (n) for each stage were
determined using Horowitz–Metzger, Coats–Redfern, Kissinger and
Broido methods. Values of E
a
varying between 257–267 kJ mol–1 and n=0–1 were found. According to the kinetic
analysis the decomposition reactions were diffusion controlled. 相似文献
4.
Thermal Decomposition of Some Chemical Compounds Used As Food Preservatives and Kinetic Parameters of This Process 总被引:1,自引:0,他引:1
Thermal decomposition processes of selected chemicals used as food preservatives such as sodium formate, sodium propionate,
sodium nitrates(V and III) and sodium sulphate(IV) were examined by the derivatographic method. Based on the curves obtained,
the number of decomposition stages and characteristic temperatures of these compounds have been found. Mass decrements calculated
from TG curves ranged from 28.9% for sodium formate to 77.8% for sodium nitrate(V), while sodium sulphate showed a mass increment
of 5.6%. Kinetic parameters such as activation energy (E
a ), frequency factor (A ) and reaction order (n ) were calculated from TG, DTG and T curves. Sodium formate shows the highest values of E
a and A which amount to 171.7 kJ mol–1 and 5.8⋅1014 s–1 , respectively, while the lowest ones, E
a =28.2 kJ mol–1 and A =3.65⋅102 s–1 belong to sodium nitrate(V).
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
Hee-Soo Kim Byoung-Ho Lee Sena Lee Hyun-Joong Kim John R. Dorgan 《Journal of Thermal Analysis and Calorimetry》2011,104(1):331-338
This study examined the interfacial adhesion, mechanical, and thermal properties of compatibilizing agent-treated and non-treated
biocomposites as a function of the type of compatibilizing agent. The tensile strength, interfacial adhesion, and heat deflection
temperature (HDT) of maleic anhydride-grafted poly(butylene succinate) (PBS-MA) and maleic anhydride-grafted poly(lactic acid)
(PLA-MA)-treated biocomposites are greater than those of untreated maleic anhydride-grafted poly(styrene-b-ethylene-co-butylene-b-styrene)
triblock copolymer (SEBS-MA) and maleic anhydride-grafted polypropylene (MAPP)-treated biocomposites. The storage modulus
(E′) values and the tan δmax temperatures (T
g) of PBS-MA and PLA-MA-treated biocomposites were slightly higher than that of the untreated biocomposites. 相似文献
6.
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.
The thermo-oxidative degradation illustrated by Ozawa method shows a stable apparent activation energy (E
a ≈130 kJ mol−1 ) even though the thermal degradation in nitrogen flow presents a maximum E
a for 15% mass loss (E
a ≈60 kJ mol−1 ).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
G. Vázquez J. González-Álvarez G. Antorrena 《Journal of Thermal Analysis and Calorimetry》2006,84(3):651-654
The
curing of a phenol–formaldehyde–tannin (PFT) adhesive in the presence
of pine or eucalyptus wood has been studied using differential scanning calorimetry.
The influence of the adhesive/wood ratio on the activation energy (Ea), the temperature of the
maximum of the exothermic peak (Tp)
and the enthalpy of the curing process (ΔH)
was analysed. Ea, Tp and ΔH
of the curing reaction decreased when wood was added in the curing system.
The adhesive/wood interaction did not depend significantly on wood species. 相似文献
8.
We report on the accelerated ageing of cellulose based insulating paper by means of pulsed UV laser irradiation (λ = 248 nm)
under various experimental conditions including paper composition, background gas (He, N2 and air) and moisture content of the paper. The temperature reached by the paper samples during their laser irradiation was
monitored by means of real-time IR imaging. It is shown that the equilibrium temperature (T
eq) reached by the paper increases from ~30 to ~270 °C when the laser energy density was raised from 15 to 550 mJ cm−2. The laser irradiated samples were systematically characterized by means of scanning electron microscopy (SEM) observations
and degree of polymerization (DPv) measurements. Interestingly, it is found that, for a given moisture content, the degradation level of the cellulose is mainly
triggered by the T
eq value reached during the laser irradiation. Moreover, their moisture content was found to influence significantly the number
of laser produced bond scissions (it doubles when the moisture content is increased from 0.5 to 6%); the paper degradation
is apparently not affected by the presence of oxygen as the background gas. These results suggest that the laser induced cellulose
degradation occurs through a direct photolysis (i.e. direct breakage of C–C, C–O and C–H bonds), leading to radicals formation,
which, in turn, are believed to induce the acid hydrolysis degradation mechanism, the latter being moisture dependent. The
activation energy (E
a) of each gaseous species collected after the laser degradation was estimated. Their E
a values were found to be in good agreement with the one associated to the laser depolymerisation of cellulose (i.e. ~56 kJ mol−1), suggesting thereby a direct correlation between the cellulose degradation and the formation of the detected gaseous species.
Finally, the pulsed laser irradiation can be seen as an attractive tool to identify primarily generated molecules, on a very
short time scale, that can be used as relevant chemical markers for the monitoring of the ageing of transformers materials
with cellulose. 相似文献
9.
L. Lugo M. J. P. Comuñas E. R. López J. Fernández 《Journal of Thermal Analysis and Calorimetry》2007,87(1):179-187
New densities are reported over the whole composition range for 1-iodoperfluorohexane+n-octane system at temperatures from 288.15 to 308.15
K at atmospheric pressure. These data have been used to compute the excess
molar volumes, V
m
E.
Large positive V
m
E
values have been obtained over the entire range of composition, which increases
when the temperature rises. The experimental data were used to calculate the
isobaric thermal expansivity, and the quantities (∂V
m
E/∂T)p and (∂H
m
E/∂p)T. Furthermore,
the results have been used to investigate the volumetric prediction ability
of the equations of state Soave–Redlich–Kwong, Peng–Robinson,
Patel–Teja and Soave–Redlich–Kwong with volume translation. 相似文献
10.
Hernani S. Barud Clóvis A. Ribeiro Jorge M. V. Capela Marisa S. Crespi Sidney. J. L. Ribeiro Younes Messadeq 《Journal of Thermal Analysis and Calorimetry》2011,105(2):421-426
Cellulose can be obtained from innumerable sources such as cotton, trees, sugar cane bagasse, wood, bacteria, and others.
The bacterial cellulose (BC) produced by the Gram-negative acetic-acid bacterium Acetobacter xylinum has several unique properties. This BC is produced as highly hydrated membranes free of lignin and hemicelluloses and has
a higher molecular weight and higher crystallinity. Here, the thermal behavior of BC, was compared with those of microcrystalline
(MMC) and vegetal cellulose (VC). The kinetic parameters for the thermal decomposition step of the celluloses were determined
by the Capela-Ribeiro non-linear isoconversional method. From data for the TG curves in nitrogen atmosphere and at heating
rates of 5, 10, and 20 °C/min, the E
α
and B
α
terms could be determined and consequently the pre-exponential factor A
α as well as the kinetic model g(α). The pyrolysis of celluloses followed kinetic model
g(a) = [ - ln(1 - a)]1 \mathord