Jozef Rychly

Morphological and Thermal Properties of Cellulose−Montmorillonite Nanocomposites

Cellulose-layered montmorillonite (MMT) nanocomposites were prepared by precipitation from N-methylmorpholine- N-oxide (NMMO)/water solutions. Two hybrid samples were obtained to investigate the influence of the reaction time on the extent of clay dispersion within the matrix. It was observed that longer contact times are needed to yield nanocomposites with a partially exfoliated morphology. The thermal and thermal oxidative properties of the hybrids, which might be of interest for fire-resistant final products, were investigated by thermogravimetry and chemiluminescence (CL). The nanocomposites exhibited increased degradation temperatures compared to plain cellulose, and the partially exfoliated sample showed the maximum stability. This result was explained in terms of hindered transfer of heat, oxygen, and degraded volatiles due to the homogeneously dispersed clay filler. Kinetic analysis of the decomposition process showed that the degradation of regenerated cellulose and cellulose-based hybrids occurred through a multistep mechanism. Moreover, the presence of nanoclay led to drastic changes in the dependence of the activation energy on the degree of degradation. CL analysis showed that longer permanence in NMMO/water solutions brought about the formation of carbonyl compounds on the polymer backbone. Moreover, MMT increased the rate of dehydration and oxidation of cellulose functional moieties. As a consequence, cellulose was found to be less stable at temperatures lower than 100 degrees C. Conversely, at higher temperatures, the hindering of oxygen transfer prevailed, determining an increase in thermo-oxidative stability.

On a transition at 80 °C in polypropylene oxidation kinetics

Abstract The thermal oxidation of isotactic polypropylene homopolymer (PP) in air has been studied between 50 and 150 °C by means of infra-red spectrophotometry and gravimetry. The induction period, ti and oxidation rate in the steady state, rs, were determined from isothermal tests. The Arrhenius plot of rs is linear over the whole temperature range, whereas for ti it displays a slope change at about 80 °C. This transition has been discussed within the framework of ‘closed-loop’ kinetic schemes in which initiation is only due to POOH decomposition. The hypotheses involving a molecular mobility change that influences propagation and termination rate constants can be rejected. Only the initiation step is involved. The transition can be explained by the coexistence of many modes of POOH decomposition. Several hypotheses are compared.

Initial degradation processes of cellulose at elevated temperatures revisited - chemiluminescence evidence

The initial processes governing degradation of cellulose at elevated temperatures are re-examined. The influences of moisture, alkali-earth metal carbonates, and atmosphere at 180 degreesC, were studied. The various effects were studied both conventionally, by determining the changes in the degree of polymerisation by viscometry, and by chemiluminescence measurements. The moisture initially contained in the sample was shown to have no effect on degradation in dry nitrogen although the chemiluminescence of moist samples is initially considerably higher. It was associated with production of singlet oxygen. On the other hand, presence of moisture in oxygen atmosphere enhances oxidation. Some initial degradation occurs during rapid heating and was attributed to mechanical degradation, though no chemiluminescent phenomenon could be associated with it. The degradation rates during the more advanced phases were shown to be related to the presence of earth-alkali metal cations. It is suggested that complex formation between a metal cation and glycosidic oxygen might play an important role in the degradation mechanism

Kinetics of mass changes in oxidation of polypropylene

Abstract Isothermal ageing of isotactic polypropylene films was studied in air, in the temperature range 50–150°C, by using gravimetry. The curves display a nonmonotonic shape owing to the occurrence of mass gain by oxidation and mass loss by evaporation of small molecular fragments. We have tried to construct a kinetic model of these mass changes using a ‘closed-loop’ model in which initiation is only due to bimolecular decomposition of hydroperoxides and volatile formation results directly from the initiation or/and termination reactions. This model gives better results than the corresponding one with unimolecular POOH decomposition but it needs a temperature variation of the initial POOH concentration, which seems physically unrealistic. Certain slightly more complex schemes could be the solution in mathematical terms, but they carry some ambiguity and are presumably more difficult to check.

Chemiluminescence and thermogravimetric study of thermal oxidation of polypropylene

Abstract Thermooxidation of unstabilized polypropylene powders was investigated by chemiluminescence and thermogravimetry methods in the temperature interval 100–190 °C and a model of formal termination of reaction sites has been used for the description of the kinetics of chemiluminescence.

Chemiluminescence and inhibited oxidation of polypropylene

Abstract The efficiency of mixtures of the commercial antioxidants, Hostanox OSP 1, Irganox 1010 and distearylthiodipropionate was examined by chemiluminescence and oxygen uptake methods. Lower induction periods of oxidation, observed by the chemiluminescence method at 190°C, were found with samples which contain more of the less volatile additives. In accordance with earlier findings this is due to the surface nature of chemiluminescence which yields results close to those of the kinetic region.

Antioxidative efficiency of substituted N-phenyl N-pyrazolyl-3, N-phenyl N-benzimidazolyl-2 and N-benzthiazolyl-2 N-benzimidazolyl-2 amines in the thermooxidation of polypropylene

Abstract The antioxidative efficiency of three different series of nitrogen containing compounds derived from N -phenyl N -(1,5-diphenylpyrazolyl-3), N -phenyl N -benzimidazolyl-2 and N -benzthiazolyl-2 N -benzimidazolyl-2 amines in the thermal oxidation of polypropylene were compared on the bases of the results of chemiluminescence, dynamic thermogravimetry and differential scanning calorimetry. The effect of substituents on phenyl rings and on the 1-nitrogen of benzimidazol was examined with respect to the antioxidative behaviour of the compounds. Bad dispersion of the additive and its volatility seems to have a large effect, in some cases, on the results of antioxidation tests.

Inhibited Oxidation of Cumene and Polymerization of Styrene Investigated by Solution Microcalorimetry

The application of solution microcalorimetry was demonstrated on two model examples – inhibited oxidation of cumene and radical polymerization of styrene.From the experimental dependences of the rate of heat release on time, the rate constants k7 of the interaction of an inhibitor with radicals of substrate (RO2. or R.) in oxidation or in polymerization were determined for the set of inhibitors of N-aryl N-(2-quinone) amine series. It was shown that these compounds are weak inhibitors of oxidation of cumene and rather efficient inhibitor of polymerization of styrene.

Synthesis and Application of Hexaallylamino-cyclo-triphosphazene as Flame Retardant in Latex Coatings

ABSTRACT The paper deals with a novel flame retardant and its application in waterborne coatings. The flame retardant was synthesized from hexachloro-cyclo-triphosphazene by nucleophilic substitution with allylamine. Functionalized emulsion copolymers bearing in the structure hexaallylamino-cyclo-triphosphazene were prepared by the semicontinuous emulsion polymerization. The latexes were used as the main component of transparent coating systems cured by melamine formaldehyde resin. The incorporation hexaallylamino-cyclo-triphosphazene did not affect transparency, flexibility, and toughness of resulting coatings and increased their flame stability in terms of the amount of smoke release and maximum average rate of heat emission indicating a slower flame spread during the material combustion. GRAPHICAL ABSTRACT

Preparation and Characterization of Cured Epoxy Resin with Hexachloro-Cyclo-Triphosphazene

ABSTRACT Epoxy resins can exhibit some excellent properties. The basic principle of curing epoxy resins with a curing agent containing multiple amino groups is the crosslinking reaction between active hydrogen atoms from the curing agent and the oxirane groups in the epoxy resin structure. This study deals with the synthesis of derivative of hexachloro-cyclo-triphosphazene (HCCTP) using curing of epoxy resins. The study of our interest is nucleophilic substitution of HCCTP using N-[3-(trimethoxysilyl)propyl]ethylene diamine. The prepared derivative offers two potential advantages over conventional curing systems, namely improving properties during burning. GRAPHICAL ABSTRACT