Katarína Csomorová

Carboxylic acid assisted oxidation of polypropylene studied by chemiluminescence

Abstract The acceleration effect of stearic acid on oxidation of polypropylene (PP) has been examined by chemiluminescence (CL). The presence of acid in PP shortens the induction period of CL increase. The effect becomes more pronounced with increasing temperature. The CL curves of oxidation were analyzed in terms of heterogeneous kinetics considering stearic acid–hydroperoxide interaction as an elementary initiating reaction of PP oxidation. A nonlinear Arrhenius plot of experimental induction period of oxidation of PP has been observed in the presence of stearic acid. It was accounted for as an inherent feature of heterogeneous oxidation kinetics.

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.

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.

A tertiary amine in two competitive processes: reduction of graphene oxide vs. catalysis of atom transfer radical polymerization

Electrically conductive graphene oxide–polystyrene hybrids (GO–PS) were prepared by reduction of graphene oxide (GO) in one step during covalent modification of graphene oxide surface using surface-initiated atom transfer radical polymerization (SI-ATRP) of styrene. The reduction of the GO surface was proven by Raman spectroscopy, electrical conductivity measurements, thermogravimetric analysis and X-ray photoelectron spectroscopy. Electrical conductivity of the synthesized GO–PS particles increased in eight orders of magnitude, depending on the polymerization period. Detailed studies were performed to determine that the tertiary amine, such as N,N,N′,N′,N′′-pentamethyldiethylenetriamine (PMDETA), used in SI-ATRP as a ligand complexing copper catalyst, was responsible for the GO surface reduction. It was shown that due to participation of PMDETA in reduction of graphene oxide, the ATRP in the presence of GO can proceed only above a certain PMDETA–GO ratio.

Thermal degradation of multilayer methacrylate-acrylate particle-bead polymer powders and melts

Abstract The effect of the composition and form of polymer sample on a nonisothermal weight loss study of submicrometric multilayer polymer particles has been examined. Polymer beads consist of a poly(methyl methacrylate) (PMMA) core, poly(butyl acrylate) copolymer (BAC-co) network shell and a further layer of poly (methyl methacrylate) copolymer with butyl acrylate (MMA-co). Dynamic thermogravimetric curves show two stages for multilayer polymer powders and for particle polymer mixtures prepared by mixing emulsions before the freeze-thaw isolation of polymer. The first degradation step, due to PMMA depolymerization starts at a temperature 45 °C lower compared with degradation of the PMMA particle polymer powder alone. The polymer samples which were processed by melt stirring, press molded or even isolated from emulsions as transparent films before thermogravimetry analysis are more stable than polymer powders from emulsion. The weight loss of bulk samples proceeds smoothly in one stage like a one type polymer; nevertheless the PMMA is more sensitive to thermal degradation than the BAC-co network. The stabilization of PMMA in a blend with BAC-co in a bulk polymer sample is possibly due to the BAC-co compressed network which prevents PMMA depolymerization.

Thermal degradation and thermooxidation of O-acetyl-(4-O-methyl-D-glucurono)-D-xylan and related derivatives

Four polysaccharide samples related to (4-O-methyl-D-glucurono)-D-xylan were analyzed by thermogravimetry (TG) and differential scanning calorimetry (DSC) in nitrogen and oxygen environments. The calculated difference in the measured TG-residues run in different environments and obtained at temperatures close to 300°C by a dynamic experiment indicate the action of oxygen on the formation of gaseous products. The rats constants and activation energies of the degradation process in both environments indicate the increase in stability due to the protection of hydroxyls by acetylation. In an inert environment xylans have one broad multicomponent exotherm, as determined by dynamic DSC measurement. In an oxygen environment two or three independent exotherms are observed. The pretreatment of xylan with trifluoroacetic acid (solvent used for acetylation) and acetylation lowers the exothermic effect of both the thermolysis and thermooxidation. The recycling of the acetylated xylan to Na + -salt form leads to a greater exothermic effect of the degradation in both environments.

Flame-retarding properties of ion-exchanging groups introduced into beech sawdust

Ion exchangers prepared from beech sawdust by introduction of weak and strong basic ion-exchanging groups were analysed with thermogravimetry, differential scanning calorimetry and limited oxygen index methods to evaluate their thermal stability and flame-retarding properties. By cross-linking with epichlorohydrin in the presence of NH 4 OH, ion exchangers in free form or in H 3 BO 3 or H 3 PO 4 form were obtained with increased thermal stability in comparison to the starting material. By cross-linking and quaternization of sawdust in one step with 1,3-bis(3-chloro2-hydroxypropyl)imidazolium hydrogen sulfate, a material with better thermal stability and flame-retarding properties was obtained than by the previous procedure. This resulted in greater residues at higher temperatures as measured by dynamic thermogravimetry. The values of rate constants and activation energies of gasification calculated from isothermal thermogravimetric measurements decreased with improved thermal resistance similar to heat effects observed with differential scanning calorimetry. Limited oxygen index values up to 35.6% were obtained.

Comparison of isothermal and non-isothermal chemiluminescence and differential scanning calorimetry experiments with benzoyl peroxide

Difference in the kinetics of chemiluminescence (CL) and differential scanning calorimetry records for decomposition of originally solid benzoyl peroxide continuing as a melt reaction was outlined. While the main portion of heat measured by DSC is released in the spontaneous decomposition of benzoyl peroxide starting as a homolytic scission of peroxidic bonds, the CL light emission in oxygen comes presumably from the subsequent disproportionation reaction of polyphenyl peroxyl radicals and monitors the induced decomposition of peroxide. Thermogravimetry revealed that oxygen remains partially bound to the products of benzoyl peroxide decomposition.

Crosslinked low density polyethylene filled with silica—I. the effect of filler on crosslinking

Abstract Mixtures of low density polyethylene with various types of silica were investigated. The polymer matrix was crosslinked by initiation with peroxides. Four grades of silica were characterized by different methods. The presence of SiO 2 was found to lead to the formation of bound polymer, its proportion depending on the surface area of the filler. On the other hand, the parameters of the polymer-filler interaction determined from equilibrium swelling data for crosslinked mixtures do not correspond to the filler surface area. The crosslinking process in polyethylene, when initiated by peroxide, is affected by the presence of the filler. Both physical (adsorption of the peroxide) and chemical (chemical nature of the filler) effects are important from this point of view.

Thermo-oxidative stability of polypropylene in the presence of substituted 3-anilino-1,5-diphenyl pyrazoles

Abstract The antioxidant efficiencies of a series of 3-anilino-1,5-diphenyl pyrazoles on the thermo-oxidation of isotactic polypropylene have been studied using thermogravimetry, differential scanning calorimetry and chemiluminescence. The efficiencies depend upon the nature of the substituents, their position on the phenyl rings and their distance from the group which is the primary reaction centre. Other factors are the planarity of the molecule, the degree of conjugation and the additional antioxidant efficiency of transformation products.