The overall activation energy of the thermal degradation of polyisobutylene has been measured using factor-jump thermogravimetry to be 206±1 kJ/mole over the range 365 to 405° in N2 at 800 mm Hg pressure and flowing at 4 mm/s over the sample. This is consistent with some values reported for thermal degradation in vacuum and in solution. In 5 mm Hg of N2, an apparent activation energy of 218±2 kJ/mole was found, and in vacuum the apparent activation energy is 238±13 kJ/mole. Troublesome bubbling made the vacuum values difficult to measure. Substitution of reasonable values for the activation energies of initiation,Ei, termination,Et, and the activation energy,Ea, for vacuum degradation in the equationEa=Ei/2Ed-Et/2 yields an activation energy Ed=84 kJ/mole for the unzipping reaction. This equation presupposes a degradation mechanism of random initiation, unzipping, and bimolecular termination. Substitution of reasonable values for the heat of polymerization, ΔH, in the definition ΔH=Ep−ed suggests that the activation energy of the polymerization reaction at 375° is approximately 30 kJ/mole.
The thermal degradation of three monosubstituted hexacarbonyl complexes, M(CO)5(dppm) (whereM=Cr, Mo and W;dppm=Bis-(diphenylphosphino)-methane) has been studied using TG and DSC technics and their results reported. All the complexes facilely lose a carbonyl ligand (CO) below 200 °C. The kinetic analysis on the molybdenum complex suggested a first order dissociation pathway for this decarbonylation process. Dephosphination occurred at high temperature, followed by further decarbonylations. The enthalpy changes associated with the first decarbonylation are reported. The measured kinetic parameters are in good agreement with the literature values on similar systems obtained from solution studies.
Thermogravimetric analysis and pyrolysis in combination with gas chromatography were used to study the thermal behaviour of some cross-linked polymers of ethylene glycol dimethacrylate. The investigated polymers show a complex thermal degradation mechanism. The complexity of the reaction increases together with increase of the ethylene glycol chain in the macromolecule and with increase of the pyrolysis temperature. At low temperature, the thermal decomposition products of the analyzed polymers are mainly the constituent monomers. At high temperatures, besides the monomer, other decomposition products are formed as a result of thermal cracking reactions, i.e. secondary reactions of decomposition and recombination.
The thermal degradation of three monosubstituted hexacarbonyl complexes, M(CO)5py (where M=Cr, Mo, and W; py=pyridine) has been studied by thermogravimetry (TG) and differential scanning calorimetry (DSC) and their results reported. It was found that for each of the three complexes studied, the starting material M(CO)6 was formed which immediately sublimed unchanged with or without concomitant loss of carbonyl (CO) ligands to give the first large weight loss step. This was closely followed by the volatilisation of the pyridine ligands and at higher temperatures the loss of further CO ligands. The enthalpy changes associated with the above-mentioned steps are reported. The conversion of M(CO)5py to M(CO)6 and other products was confirmed by the analysis of residue after pyrolysis in a tube furnace under conditions similar to those observed in TG experiments.
The process of thermal degradation of lignins of hard wood (birch, aspen, oak), obtained under the wood treatment with 66% sulphuric acid in the form of acid-in-soluble and soluble fractions, has been investigated by thermal methods. Activation energy values of lignin pyrolysis have been determined at the stage of increasing rate of weight loss. It has been established that the difference in their thermal properties is conditioned by the structural changes in the process of isolation from wood. It has been suggested that acid-soluble lignins have a higher density than acid-insoluble ones. Sulphuric acid lignins of birch, in particular acid-soluble lignin, are assumed to possess a more homogeneous structure than sulphuric acid lignins of other species
Lyocell, modal and
viscose fibers were subjected to mercerization or to solar degradation. The
ulterior thermal degradation was analyzed by means of differential scanning
calorimetry (DSC). Thermal analysis shows wide exothermic processes that began
between 250 and 300C corresponding to the main thermal degradation and
are associated to a depolymerization and decomposition of the regenerated
cellulose. Thermal degradation was analyzed as a function of concentration
and time. Lyocell fiber is the most stable under thermal degradation conditions.
Furthermore, mercerized samples are initially more degraded and present a
lower thermal stability.
Studies of thermal and fire-resistant properties of the polyethylene/organically modified montmorillonite (PE/MMT) nanocomposites
prepared by means of melt intercalation are discussed. The sets of the data acquired with the aid of non-isothermal TG experiments
have been treated by the model kinetic analysis. The extra acceleration of thermal-oxidative degradation of the nanocomposite
which has been observed at the first stage of the overall process has been analyzed and is explained by the catalytic effect
of the clay nanoparticles. The results of cone calorimetric tests lead to the conclusion that char formation plays a key role
in the mechanism of flame retardation for nanocomposites.
Rice husk is a by-product of rice milling process and are a major waste product of the agricultural industry. They have now
become a great source as a raw biomass material for manufacturing value-added silicon composite products, including silicon
carbide, silicon nitride, silicon tetrachloride, pure silicon, zeolite, fillers of rubber and plastic composites, adsorbent
and support of catalysts. The bulk and true densities of raw rice husk with different moisture and sizes were determined.
The rice husk was subjected to pyrolysis in fluidized-bed reactor in air or nitrogen atmosphere.
The products obtained were characterized by thermogravimetric and X-ray powder analysis, IR-spectroscopy, scanning electron
microscopy and nitrogen adsorption at 77 K. The specific surface area of the products is comparable with this of γ-Al2O3. The kinetics of H2SeO3 adsorption out of aqueous solutions at 298 K was studied. The adsorption capacity of white rice husks ash was found to be
higher than that of black rice husk ash and the adsorption kinetics obeyed the second order kinetic equation.
Thermal degradation of poly(2,2′,-propane-bis-4-phenyl carbonate) or bisphenol A polycarbonate (PC) alone and in presence of metal oxide as additives have been discussed. Thermal degradation of PC in presence of metal oxide additives may be surface induced catalytic thermo-oxidative degradation. Some metal oxides retard thermo-oxidative degradation of PC.