The kinetics of the thermal decomposition of polypropylene fibres has been investigated on the basis of determining the TGA and DTGA curves at various heating‐up speeds in the temperature range from 100 to 600°C. The activation energy E as a kinetic parameter of the decomposition has been defined by means of the Flynn‐Wall and Freeman‐Carroll methods, respectively. It has been established that the activation energy necessarily grows with growth of the conversion level.

SYNOPSISThe step addition polymerization between toluene diisocyanate and poly ( oxypropylene ) diol and trio1 was carried out in bulk in a closed batch reactor under vacuum and at isothermal conditions. The reactions have been examined under the influence of the catalysts Nphenyl-P-naphthylamine, triethylene-tetraamine, and ferriacetylacetonate. The disappearance of the reactants and the appearance of one of the products were observed during the reaction. The kinetic analysis was brought about on the basis of the supposed reaction scheme and proposed kinetic model. The complex reaction was considered as serial-parallel. The experimental data fit well with the computed theoretical curves. The catalysts utilized were evaluated with respect to their selective catalysis of the primary diisocyanate-polyol reaction relative to the possible secondary reaction. The computed rate constants enabled the prediction of the composition of the reaction mixture. 0 1993 John Wiley & Sons, Inc. INTRODUCTIONThe handling properties of polyurethane elastomers depend on the composition of the reaction mixture at the particular time of the reaction between isocyanates and alcohols. This composition is influenced by the reaction mechanism and kinetics, which are further influenced by the choice, purity, and the concentration of the main reaction components, by the presence and proper choice of the amount of catalyst and solvent, by the mode of the process-conducting, and by the reaction temperature. The mechanism and kinetics of these reactions have been investigated in the past as well as today.'"' Baker et al.1-4 were the first to show that isocyanate reactions with active hydrogen compounds are base catalyzed. They proposed the mechanism of these reactions and reported that these reactions are autocatalyzed by the urethane produced. Mechanistic features of autocatalytic effects were later the subject of considerable contr~versy.~,~ Many authors have studied thoroughly both the catalyzed * To whom correspondence should be addressed. and non-catalyzed reactions of aromatic, aliphatic, and furan-based isocyanates with alcohols in different solvent^.^-'^ The most frequently employed catalysts were amine catalysts and organotin compoUnds.8-10,1Z-14,18 T h e authors '-477-14 ha ve usually investigated both the mechanism and chemical kinetics of the reactions at the same time. They have supposed a variety of intermediates during the reaction, but only using modern methods can the authors 12,14-16 detect various intermediates as well as the final reaction products.The kinetic data have been analyzed mostly according to the classical second order reaction rate equation.~-4,7.11~17.'8 T h e second order rate constant was found to be dependent upon the ratio of alcohol and isocyanate and the reaction order upon the Hbonding of the s01vent.~ The deviation from second order kinetics was often and was first explained as due either to the catalytic effect of the urethane group or due to solvent.3~'0~z2~23 A great difference in reactivity between t...

ABSTRACT:The influence of exposure to artificial light (ultraviolet and visible spectrum) on the thermal degradation process of polypropylene fiber has been investigated. The activation energy E as a kinetic parameter of the fiber thermal decomposition has been defined by means of the Flynn-Wall and Freeman-Carroll methods. The fiber melting temperature range was also defined. The investigations have been made on the basis the of thermal gravimetric analysis and differential thermal gravimetric analysis curves determined at various heating speeds, in the temperature range from 100°-600°C. It was found that thermal stability of polypropylene fiber is reduced by light treatment (i.e., fiber softens and melts at a lower temperature). Activation energy values determined for thermal decomposition of the fiber samples exposed to the influence of light are considerably higher than the values determined on unexposed samples. The decomposition process of aged fiber is more complex and occurs in a larger temperature range. Both the methods used show almost similar results.