Jozef Rychlý

Chemiluminescence from paper I. Kinetic analysis of thermal oxidation of cellulose

Abstract Kinetic analysis of chemiluminescence intensity—time and chemiluminescence intensity—temperature runs for oxidation of cellulose at elevated temperatures is presented showing a good coincidence of the first-order rate constants from non-isothermal chemiluminescence experiments with those obtained from polymerisation degree determinations and from the literature. Rate constants from isothermal runs are lower than those from non-isothermal runs, however, when repeating non-isothermal runs several times in so-called temperature cycling experiments, the non-isothermal rate constants approach isothermal ones. A method enabling the differentiation of faster and slower processes in oxidation of cellulose based on non-isothermal chemiluminescence runs is demonstrated.

Chemiluminescence during thermal and thermo-oxidative degradation of cellulose

The chemiluminescent phenomena during thermal and thermo-oxidative degradation of cellulosic material and model substances were found to originate in at least three relatively independent processes. The low-temperature chemiluminescent phenomenon typical of samples previously irradiated with an incandescent light source and dependent on both temperature and composition of the surrounding atmosphere during irradiation is attributed to the decay of charge-transfer complexes between oxygen and hydroxyl and/or ether groups in cellulose. A peak in chemiluminescence during dynamic experiments at 135°C typical of pre-oxidised samples can be associated with decomposition of peroxide groups present in the sample. An intense chemiluminescence at temperatures approaching 200°C was found to correlate with polymer chain scissions, resulting in the decrease in the degree of polymerisation determined by viscometry. The results show that the chemiluminescence approach may shed new light on the radical degradation mechanisms of cellulose and related polyhydroxylated polymers.

Use of thermal methods in the characterization of the high-temperature decomposition and ignition of polyolefins and EVA copolymers filled with Mg(OH)2, Al(OH)3 and CaCO3

Abstract Non-isothermal thermogravimetry was used for the estimation of ‘volatilization’ of both water from an inorganic additive (Al(OH) 3 and Mg(OH) 2 ) and flammable volatiles from the polymer (polyethylene, EVA copolymer and polypropylene) for composite systems with high contents of the inorganic component. Each step of the TG trace was examined separately using nonlinear regression analysis, and a model of the decomposition involving termination of active centers has been used for determination of activation energies and pre-exponential factors of decomposition of a particular component. It has been found that the activation energy for the decomposition of polyethylene and polypropylene in the presence of Mg(OH) 2 in air is considerably higher than that for pure polymer. This is obviously due to an efficient blanketing effect of the polymer surface by released water. On the other hand, Al(OH) 3 reduces the activation energy of polymer decomposition to values in the region of 40–60 kJ/mol. DTA indicates that CaCO 3 , which does not release carbon dioxide during the decomposition of polyethylene, increases the relative proportion of exothermic reaction which occurs on or near the surface of the sample. This may promote the flammability of the polymer in opposition to its reduction due to dilution of the polymer. Non-isothermal TG data were used to explain the differences in times to ignition and ignition temperatures determined independently under conditions of natural convection.

Decomposition of peroxides of oxidised polypropylene studied by the chemiluminescence method

Abstract It was found that the initial increase in light emission from pre-oxidised polypropylene, measured in a nitrogen atmosphere, is due to decomposition of hydroperoxides in the system. Decomposition is a bimolecular reaction with the probable participation of chemisorbed oxygen. A new initiation reaction step is proposed which contributes to the deterioration of the polymer properties in the induction period of oxidation.

New approach to understanding chemiluminescence from the decomposition of peroxidic structures in polypropylene

It is suggested that the chemiluminescence from the thermal oxidation of polypropylene arises predominantly from the decomposition of associated hydroperoxides. Measurements of the chemiluminescence response to heating/cooling cycles applied to polypropylene oxidation in the induction period and in an advanced stage of the process is a novel approach to the extrapolation of the oxidation course to the lower temperature region.

Chemiluminescence in thermo-oxidation of polypropylene

Abstract Chemiluminescence in thermo-oxidation of polypropylene was interpreted, noting its course with time at different temperatures and the corresponding spectra. The light emission was attributed to decomposition of α-ketone-hydroperoxides and to chain oxidation of polymer proceeding via secondary peroxy radicals.

Chemiluminescence from oxidation of polyamide 6,6. I. The oxidation of pure polyamide

The chemiluminescence (CL) accompanying the oxidation of both polyamide 6,6 and a model diamide with no reactive endgroups is reported. CL emission for neat diamide starts after melting of crystallites, and the shapes of the intensity-time curve show a sigmoidal behaviour, typical of the chain oxidation of organic compounds. Adipic acid shortens induction period of chemiluminescence increase. A bimolecular hydroperoxide decomposition model can successfully describe the kinetic runs of CL. Polyamide 6,6 CL runs are apparently composed of 3 different kinetic stages: a decay from an initial CL value, due to the termination of peroxyl radicals being trapped in the polymer after processing and storage (stage I), a sudden increase of emission, related to depletion of terminal amino groups (stage II), and a major maximum of emission, decaying again to a lower level of chemiluminescence, indicating chain oxidation of –CONH–CH2– structural units (stage III). Terminal carboxyl groups show the general tendency to shift the induction time of the third stage to a shorter time. # 2003 Elsevier Ltd. All rights reserved.

The effect of inorganic additives on the decomposition of poly (beta-hydroxybutyrate) into volatile products

Abstract Inorganic oxides such as CaO, MgO, PbO, PbO 2 , Al 2 O 3 , ZnO and calcium hydride destabilize PHB to an extent dependent on the basicity of the additive which leads to much easier formation of volatile products compared with PHB itself. Of the additives examined, attention has been focused on the reaction of MgO, which leads to significant formation of a considerably more stable product whose maximum rate of decomposition into volatiles is at 670 K (PHB itself decomposes with a maximum rate at 572 K). An interpretation based on the interaction of MgO with PHB end groups has been proposed.

Degradation of pullulans of narrow molecular weight distribution—the role of aldehydes in the oxidation of polysaccharides

Degradation of pullulan samples of narrow molecular weight distribution was studied in O2 and N2 atmosphere at 180 °C and in air at 80 °C, 65% RH. At higher temperatures, size exclusion chromatographic analyses provided evidence for non-random degradation and formation of cross-links, a phenomenon depending on the concentration of carbonyl groups. Initial degradation rates in oxidative and inert environments were comparable, while at longer reaction times extensive cross-linking was typical of degradation in oxygen. At 80 °C, in a moderately alkaline environment, the degradation remains random, as demonstrated by the mono-modal distributions of molecular weights. Furthermore, there was no evidence of cross-linking. Correlations between the concentration of aldehyde end-groups in the pullulan samples, rates of degradation and the content of peroxides after a pre-oxidation treatment, as determined by the use of chemiluminometry, were demonstrated. This leads to the conclusion that aldehyde groups, via the peroxide intermediates, have the decisive influence on the rates of oxidative degradation of polysaccharides.

The effect of physical parameters of isotactic polypropylene on its oxidisability measured by chemiluminescence method. Contribution to the spreading phenomenon

Abstract The physical parameters of the polypropylene powdered samples like average molar mass, the degree of isotacticity and the resulting crystallinity and melting temperature have quite an important effect on the oxidisability of polypropylene expressed in induction time of oxidation or in maximum chemiluminescence intensity. It was shown that it is the increase of both the average molar mass and the degree of isotacticity which predominantly lead to the longer induction times of oxidation while the opposite is true for maximum chemiluminescence intensity for molar mass 40,000–180,000 and temperature interval 80–130°C. The combined model of the homogeneous increase of concentration of hydroperoxides in the oxidation micro-zones and the spreading of the oxidation from these micro-zones has been proposed which fits well the experimental runs of chemiluminescence intensity–time.