Lyda Rychlá

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.

Non-isothermal thermogravimetry of polymer

A Model of polymer decomposition is proposed which formally involves the termination of active centres. It yields reasonable activation energies for the decompositions of polypropylene, polyethylene, polystyrene and polymethyl methacrylate investigated by non-isothermal thermogravimetry. In the value of a formal reaction orders the model reflects the reaction conditions, such as initial sample weight, atmosphere, ventilation conditions, sample holder nature and shape, etc.ZusammenfassungEin Modell für Zersetzungsreaktionen von Polymeren wurde entworfen, das auf dem Abbau von aktiven Zentren basiert. Es liefert richtige Aktivierungsenergien für die Zersetzung von Polypropylen, Polyäthylen, Polystyren und Polymethylmethakrylat (bestimmt durch nichtisotherme Thermogravimetrie) und macht es ausserdem möglich, die „äusseren“ Reaktionsbedingungen, wie Einwaage, Atmosphäre, Ventillationsbedingungen, Art und Form des Probenhalters usw. zu berücksichtigen.РезюмеПредложена модель ра зложения полимера, которая формально вк лючает обрыв активных центров. Так ая модель дает возмож ность получать приемлемые энергии активации реакций разложения п олиэтилена, полипроп илена, полистирола и полиме тилметакрилата, изученных неизотерм ической термогравим етрией. Предложенная модель допускает включение таких «внешних» усло вий реакций, как начал ьный вес образца, атмосферы, ус ловий продувки, характера и формы дер жателя образца и т. п.

Kinetic aspects of chemiluminescence response to periodic changes of temperature during thermal treatment of cellulose

Measurements of chemiluminescence under conditions of periodic temperature changes (temperature cycling) may well be related to the changes of the polymerization degree for cellulose degraded under comparable conditions in isothermal mode. The subsequent deceleration of the degradation process, as seen from the analysis of a series of temperature cycles, has been demonstrated. A second order non-isothermal model of cellulose degradation distinguishing a faster and a slower degrading component in cellulose has been used to fit the experimental data.

Modelling of heat release rate-time curves from cone calorimeter for burning of polymers with intumescence additives

Heat release rate-time curves for intumescent additives used in the mass of polymer during its burning in a cone calorimeter were simulated using the kinetic model of ignition, burning and extinction of polymer flames. The model works with ordinary differential equations and with an average value of heat transfer coefficient to the polymer surface. The mutual correspondance between the production of volatiles from polymer and formation of protecting intumescent carbonaceous foam was demonstrated on curves of surface temperature, mass loss and heat release rate versus time.

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.

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.

Polyolefins: From Thermal and Oxidative Degradation to Ignition and Burning

It has been shown that thermal oxidation and ignition of polyolefins have many mechanistic aspects in common. The essential difference between these two phenomena consists in the mechanism of oxygen with alkyl radicals that is addition reaction in thermal oxidation and disproportionation in ignition.