Impacto do co-monômero hidroxivalerato na cinética de degradação térmica dos poli(3-hidroxialcanoatos)

Abstract

: a djsouza@uenf.br , b eligio@uenf.br , c sanchez@uenf.br. RESUMOO objetivo deste trabalho foi avaliar o impacto que o conteúdo do co-monômero 3-hidroxivalerato exerce na cinética de degradação térmica de copolímeros P3(HB-x%HV). Filmes dos copolímeros, com diferentes conteúdos de co-monômero 3-hidroxivalerato, foram obtidos pela evaporação controlada de solvente, a partir de suas soluções em clorofórmio (1%m/m). Para o estudo termogramétrico (TGA), foram utilizados 10±0,3 mg de cada amostra, panelas de platina e atmosfera de He (100mL/min). O estudo cinético foi realizado em condições isotérmicas e não isotérmicas. Para as duas condições de análise, foi observado que os copoliésteres estudados apresentaram uma etapa de degradação definida em um curto intervalo de tempo. A análise da cinética do processo de degradação térmica, realizado segundo os métodos isoconversionais de Friedman e Ozawa-Wall-Flynn, indica que a energia de ativação envolvida no processo de degradação térmica é dependente da fração de conversão de massa. Tal dependência pode estar relacionada à ocorrência de clivagem de ligações covalentes com diferentes energias de ligação. Outro fator que pode contribuir para este comportamento é a diferença estrutural provocada pelos co-monômeros 3HB e 3HV. Os resultados obtidos indicam a necessidade de um controle na distribuição das unidades de 3HV, com vista a uma maior estabilidade térmica dos copolímeros. O aumento da estabilidade e, assim, da processabilidade destes copolímeros a partir do fundido, amplia as possibilidades de utilização destes poliésteres ambientalmente corretos. Palavras-chaves:Poli(3-hidroxialcanoatos), degradação térmica, cinética de degradação térmica. Impact of co-monomer hydroxyvalerate on thermal degradation kinetics of P3(HB-x% HV) copolymers ABSTRACTThe aim of this work was to evaluate the impact that the content of the co-3-hydroxyvalerate monomer has on thermal degradation kinetics of P3(HB-x%HV) copolymers. Films of the copolymers with different contents of 3-hydroxyvalerate were obtained by controlled evaporation of solvent from chloroform solution (1% m/m). Thermogravimetry study was carried out in helium atmosphere, platinum pans and sample mass about 10 ± 0.3 mg. The thermal degradation kinetic study was made on isothermal conditions and non-isothermal conditions. For the two conditions of analysis, it was observed that the copolyester studied presented a defined stage of degradation in a short time interval. The analysis of thermal degradation kinetics carried out by the isoconversional methods of Friedman and Ozawa-Flynn-Wall showed that the activation energy for the process of thermal degradation is dependent on the fraction of mass conversion. Such dependence may be related to the occurrence of cleavage of covalent bonds with different bonding energies. Other characteristic could be the structural differences caused by co-monomers 3HB and 3HV. The results obtained indicate the need to control the distribution of 3HV units to improve the thermal stability of the p...

Thermal Stability and Kinetic of Decomposition of Mono- and Dicationic Imidazolium-Based Ionic Liquids

“…The collision factor (A) can be estimated from the linear coefficient values. 23 As previously reported, 14 in ILs based on the imidazolium ring, the biggest component of thermal degradation is neutralization of the imidazolium ring. This reaction occurs through a second order nucleophilic substitution (S N 2), promoting loss of the IL alkyl chain.…”

“…The weight loss variation observed in the TGA analysis is the mass fraction of conversion (α) and given by equation 1. 23 (1) where m 0 is the initial mass, m f is the final mass, and m t is the mass in the time t. The kinetic results of Ea and ln A were obtained using the Ozawa-Wall-Flynn (O-W-F) and Friedman methods by applying equations 2 and 3 to the experimental data, respectively. 23 (2) 3In equations 2 and 3, β is the heating rate, A is the collision factor and represents the total number of collisions between molecules, Ea is the activation energy necessary to break one mole of bonds between the atoms of the molecules, T is the absolute temperature, and R is the constant of ideal gases.…”

“…The Friedman method allowed these kinetic parameter to be determined by linear fitting of the curves ln (βdα/dt) as a function of 1/T (equation 3). 23 The angular coefficient of the linear fragments in each α of both methods provides the energy activation value (Ea) of the decomposition process in each α. The collision factor (A) can be estimated from the linear coefficient values.…”

Phosphonium ionic liquids as new compatibilizing agents of biopolymer blends composed of poly(butylene-adipate-co-terephtalate)/poly(lactic acid) (PBAT/PLA)

“…15 In fact, Teamsinsungvon et al 54 have also shown the appearance of a new peak aer compatibilization of the polymer PBAT/PLA blend with CaCO 3 . 55 Kinetic parameters or Arrhenius parameters, frequency factor (A) and activation energy (E a ), can be obtained from nonisothermal kinetic data by applying the rate law. 26 Many polymer materials exhibit a thermal degradation process which involves consecutive and parallel reactions.…”

“…55 Thermogravimetric measurements done using different heating rates, i.e. The parameters of thermal decomposition kinetics of PBAT/ PLA blends without and with ILs were estimated using the F-W-O method.…”