The thermal behaviour of ultra-high molecular weight polyethylene (UHMWPE) of different molecular weights was examined by
thermal analysis methods. The melting temperatureTm and the heat of melting δH were measured by the DSC method. The thermooxidative degradation process was investigated by using
a MOM Q-1500 D derivatograph at various heating rates in air atmosphere. The initial decomposition temperatureTi was determined from the TG curves, and other characteristic temperatures of decomposition were calculated. It was found thatTm and δH are higher for UHMWPE than those for HDPE, i.e. 146‡C and 195 J g−1 for UHMWPE as compared with 133‡C and 166 J g−1 for HDPE. The thermal behaviour of the investigated UHMWPE samples is not significantly influenced by molecular weight.
Authors:Loredana Feher, B. Jurconi, Gabriela Vlase, T. Vlase, and N. Doca
The thermooxidative degradation of three models of oily soils was studied under non-isothermal conditions, at heating rates
of 5, 10, 15 and 20�C min−1. Di-octyl-sebacate, as model for synthetic oil, was adsorbed on silica, alumina and silico-alumina, considered models for
the inorganic micelle of a soil. For a kinetic analysis, the TG data were processed by three methods: Flynn-Wall-Ozawa, Friedman
and NPK (Nomen-Sempere). The results indicate the NPK as the less speculative method that allows a separation of the elementary
steps and at the same time a separation of the temperature, respective conversion dependent part of the reaction rate.
Many of the isomers of polybutadiene and polyisoprene elastomers can be characterized by thermal analysis.Tg is sensitive to side chain units (1,2 or 3,4 structure) for both polymers. Crystallinity measurements can characterizecis andtrans isomers. DMA and DEA master curves provide an idea of the heterogeneity of the chain units from the width of the loss factor
curves in theTg region. Thermal and thermooxidative degradation, as followed by DSC and DTG, can differentiate specific natural and synthetic
isomers of polyisoprenes in raw and vulcanized states.
Authors:Gheorghe Ilia, Madalina Drehe, Titus Vlase, Gabriela Vlase, Lavinia Macarie, and Nicolae Doca
Metal or metal oxide nanoparticles possess unique features compared to equivalent larger-scale materials. In this paper we
present the synthesis of grafted titania with phosphonic acids, their characterization and an extended non-isothermal kinetic
study. The obtained results show that there in no significant difference between acids and esters in grafting reaction. The
phosphorus content wary between 0.9 and 1.80% and is comparable with literature data. IR and AFM studies confirmed the formation
of grafted titania. Extended non-isothermal kinetic study using different methods confirmed the complexity of thermooxidative
degradation processes in non-isothermal conditions.
Authors:D. Válková, J. Kislinger, M. Pekař, and J. Kučerík
Humic acids represent a complicated mixture of miscellaneous molecules formed as a product of mostly microbial degradation
of dead plant tissues and animal bodies. In this work, lignite humic acids were enriched by model compounds and the model-free
method suggested by Šimon was used to evaluate their stability over the whole range of conversions during the first thermooxidative
degradation step. The kinetic parameters obtained were used to predict the stability at 20 and 180�C, respectively, which
served for the recognition of processes induced by heat and those naturally occurring at lower temperatures. Comparison of
the conversion times brought a partial insight into the kinetics and consequently into the role of individual compounds in
the thermooxidative degradation/stability of the secondary structure of humic acids. It has been demonstrated that aromatic
compounds added to humic acids, except pyridine, increased stability of humic acids and intermediate chars. The same conclusion
can be drawn for acetic and palmitic acids. Addition of glucose or ethanol decreased the overall humic stability; however,
the char of the former showed the highest stability after 40% of degradation.
Authors:J. Kučerík, D. Kamenářová, D. Válková, M. Pekař, and J. Kislinger
DTA/TG technique has been used to study the influence of various model compounds
(aromatics, organic acids, alkanes, ketone, heterocyclic and sterole) on the
thermo-oxidative behavior of lignite humic acids. As a measure of stability
the shift of the onset temperature of the exothermic degradation peak has
been used. Further, the ratio of mass loss recorded in the high and low temperature
ranges (thermogravimetric index) was used to evaluate the role of added compounds
on the recombination reactions occurring during the thermooxidative degradation
of humic acids. It has been demonstrated that most of added compounds play
a role during those processes at relatively low concentrations (1% mass/mass)
and affect the humic acid stability as well as the value of thermogravimetric
index (i.e. the degree of the apparent aromaticity). It has been clearly shown,
that the latter parameter reflects more the ‘qualitative’ than
the ‘quantitative’ relationship between biodegradable humified
parts in the extracted pool of organic matter.
Authors:G. Vlase, T. Vlase, N. Doca, M. Perţa, G. Ilia, and N. Plesu
Samples of an organic–inorganic hybrid were prepared by solvolysis and polycondensation in formic acid of tetraethoxysilane
and diethylbenzyl phosphonate, simultaneous with the oxidative polymerization of aniline. The thermal behavior of the samples
in dynamic air atmosphere and non-isothermal conditions was determined by a coupled thermogravimetric/evolved gas analysis.
Two significant thermal events were established: the elimination from the polymeric matrix of low mass molecules, respectively
the thermooxidative degradation of the organic part of the matrix. The kinetic analysis was performed with the Flynn-Wall-Ozawa,
Friedman and modified Non-Parametric-Kinetic methods. Only the last one allowed an objective analysis of the first process
as a process of two simultaneous thermally induced phenomena with the kinetic functions of the type αm(1 − α)n.
Methods for kinetic description of induction periods,
based on the single-step kinetics approximation and various expressions of
the temperature functions, are presented. The formulas for evaluation of both
isothermal and non-isothermal lengths of induction periods are derived. Use
of the formulas is demonstrated on the thermooxidative degradation of polyolefines.
The kinetic parameters obtained from isothermal and non-isothermal experiments
are compared and possible reasons of inconsistencies are analyzed. Applications
of the determination of induction periods for thermooxidation of various systems
are reviewed. The theory outlined in this paper can be applied not only for
thermooxidation in condensed phase, but also for other processes exhibiting
the induction period, such as the curing of rubber compounds, recrystallization
of nickel sulfide and crystallization of silicate and metal glasses.
Authors:Adriana Fuliaş, Titus Vlase, Gabriela Vlase, and Nicolae Doca
The thermoanalytical curves (TA), i.e. TG, DTG and DTA for pure cephalexin and its mixtures with talc, magnesium stearate,
starch and microcrystalline cellulose, respectively, were drawn up in air and nitrogen at a heating rate of 10 °C min−1. The thermal degradation was discussed on the basis of EGA data obtained for a heating rate of 20 °C min−1. Until 250 °C, the TA curves are similar for all mixtures, up this some peculiarities depending on the additive appears.
These certify that between the pure cephalosporin and the excipients do not exists any interaction until 250 °C. A kinetic
analysis was performed using the TG/DTG data in air for the first step of cephalexin decomposition at four heating rates:
5, 7, 10 and 12 °C min−1. The data processing strategy was based on a differential method (Friedman), an integral method (Flynn–Wall–Ozawa) and a
nonparametric kinetic method (NPK). This last one allowed an intrinsic separation of the temperature, respective conversion
dependence on the reaction rate and less speculative discussions on the kinetic model. All there methods had furnished very
near values of the activation energy, this being an argument for a single thermooxidative degradation at the beginning (192–200 °C).