Kinetics of thermal degradation of flame retardant copolyesters containing phosphorus linked pendent groups

doi:10.1016/S0141-3910(02)00394-4

Polymer Degradation and Stability

Volume 80, Issue 1, 2003, Pages 135-140

https://doi.org/10.1016/S0141-3910(02)00394-4 Get rights and content

Abstract

The thermal decomposition behaviour of phosphorus-containing copolyesters were studied using a conventional dynamic thermogravimetric analysis (TG) in a flowing air atmosphere at several heating rates between 10 and 40 °C/min. The activation energy was determined by using Kissinger method, Flynn–Wall–Ozawa method and Friedman method. The results for copolyesters with the phosphorus linkage as pendent groups, which were synthesized from the condensation of terephthalic acid (TPA), ethylene glycol(EG) and 9,10-dihydro-10 [2,3-di (hydroxy carbonyl) propyl] 10-phosphaphenanthrene-10-oxide (DDP), were compared with those of poly (ethylene terephthalate) (PET) and copolyesters with phosphorus linkage in the main chain, which were synthesized from TPA, EG and 2-carboxyethyl(phenylphosphinic) acid (CEPP). It is shown that the presence of the bulky pendent phosphorus side group in the copolyester tends to decrease the activation energy for decomposition in air.

Introduction

As we know, the demand for poly(ethylene terephthalate) (PET) is bigger and bigger. PET fibres have had the largest yield of all the synthetic fibres. In order to reduce the potential risk in fire incidents, research into flame retardant polyesters has gained much attention. Phosphorus-containing copolyesters are increasingly gaining popularity, as they have excellent flame retardancy and generally give off nontoxic combustion products. Matsunaga [1] prepared a copolyester from the condensation reaction of terephthalic acid (TPA), ethylene glycol (EG) and phosphonic acid (PPA), named as PET-co-PPA. Asrar and Mo [2] studied the synthesis of PET-co-CEPP from TPA, EG and 2-carboxyethyl(phenylphosphinic) acid (CEPP). Wang et al. have synthesized a series of novel phosphorus-containing flame retardants and copolyesters [3], [4], [5], [6], [7].

The mechanism by which flame retardant systems reduce the flammability of PET has been the subject of several investigations. A flame retardant may either act in the condensed phase by altering the rate and/or the pathway of the pyrolytic decomposition of the polymer or, in the gas phase, by scavenging carrier species, which are required during the oxidation of volatile pyrolysis products in the flame. So, it is very important to investigate the degradation of polyesters, in order to study the effects of phosphorus concentration on the pyrolysis and the flammability.

In a continuing effort to develop non-halogen flame retardants for practical applications, our laboratory has successfully prepared a series of phosphorus-containing flame retardants and copolyesters [8], [9], [10]. In the previous study [10], the thermal degradation behaviour of copolyesters with phosphorus linkage in the main chain (PET-co-CEPP) were reported. In this article, we report the degradation behaviour of copolyester with phosphorus linkage on the side chain, a novel phosphorus-containing copolyester, PET-co-DDP[11], which was obtained from the condensation of TPA, EG and 9,10-dihydro-10 [2,3-di (hydroxy carbonyl) propyl ] 10-phosphaphenanthrene-10-oxide (DDP), and try to find if there are some differences in the degradation behaviour of copolyesters containing phosphorus either in the main chain or on the side chain. The structures of PET-co-CEPP (Scheme 1) and PET-co-DDP (Scheme 2) are shown.

Section snippets

Kinetic methods

Kinetic information can be extracted from dynamic experiments by means of various methods. All kinetic studies assume that the isothermal rate of conversion, dα/dt, is a linear function of a temperature-dependent rate constant, k, and a temperature-independent function of the conversion, α, that is: $d α d t =kf α$ where ƒ(α) depends on the particular decomposition mechanism.

According to Arrhenius, $k=A e^{−ERT}$ where A, the pre-exponential factor, is assumed to be independent of temperature, E is the

Materials

Phosphorus-containing copolyesters, PET-1, PET-2 and PET-3 investigated were synthesized in our laboratory. PET-1 and PET-2, which have the P-group on the side chain, were prepared from TPA, EG and DDP according to the procedure reported by Chang et al. [11], and PET-3 from TPA, EG and CEPP, which has the P-group in the main chain, by the reported procedure [10]. The intrinsic viscosities (I.V.) of the copolyesters were determined with an Ubbelohde viscometer at 30 °C in

Results and discussion

Fig. 1, Fig. 2 show the TG and DTG curves of PET and the two kinds of phosphorus-containing copolyesters in air. Table 2 reveals the special decomposition temperatures of various polyester samples. PET-co-DDP (PET-1 and PET-2) have lower initial decomposition temperature (T_di) and temperature at the maximum decomposition rate (T_max) than PET and PET-3(PET-co-CEPP), and their decomposition temperatures become lower as their phosphorus content increases.

The thermogravimetric curves of PET-1 and

Conclusion

In conclusion, both Ozawa and Friedman methods show their applicability to the kinetic description of thermal degradation of copolyesters containing phosphorus both in the main chain (PET-3) and on the side chain (PET-1 and PET-2). They reveal that PET-2 has lower activation energy than that of PET-1, which means the activation energy will decrease with the increase of the phosphorus content of copolyesters. Neglecting the pre-stage in the Kissinger method, we can find the order of activation

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (Contract No: 50173016), the Doctorial Discipline Program and the Key Teacher Training Program of the Ministry of Education of China.

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Kinetics of thermal degradation of flame retardant copolyesters containing phosphorus linked pendent groups

Abstract

Introduction

Section snippets

Kinetic methods

Materials

Results and discussion

Conclusion

Acknowledgements

Polymer

Eur Polym J.

Polymer

Polymer

Polym Degrad Stab