Study of the thermal degradation of high performance fibres—application to polybenzazole and p-aramid fibres

doi:10.1016/S0141-3910(01)00159-8

Polymer Degradation and Stability

Volume 74, Issue 2, 2001, Pages 283-290

https://doi.org/10.1016/S0141-3910(01)00159-8 Get rights and content

Abstract

This work investigates the thermal degradation of high performance fibres. Poly-p-phenylenediamine-terephthalamide fibres (PPTA) and poly(p-phenylene-2,6-benzobisoxazole) (PBO) fibres are examined when degrading in a furnace. Both gas and condensed phase are analysed. When degrading PPTA and PBO, CO, CO₂ and H₂O are detected by FTIR as major compounds composing the gas phase. As minor products, aromatic species, hydrocyanic acid (HCN) and ethylenic species are found (600 °C). Because of the higher thermal stability of PBO, their evolved amounts are always lower than those of PPTA and they are given off at much longer times. Moreover, no aromatic compound and a very low quantity of ethylenic species are detected in the gas phase suggesting they were involved in charring reactions. At 800 °C only nitric oxides are detected as minor products in the gas phase. A mechanism of formation of NO_x from HCN is proposed. The investigation of the condensed phase by solid state NMR shows that PPTA and PBO are transformed into char when degrading. The char is composed of partially oxidised polyaromatic compounds, which can trap free radicals. It is suggested that the char structure of PBO may resist oxidation better than PPTA.

Introduction

The demands of the market for high-performance fibres is “faster, stronger, lighter, safer”. Fortunately, high performance- and high temperature-resistant fibres have been developed to aid in allowing products to meet these challenges. Zylon® developed by Toyobo Co Ltd (Japan) is one new high performance and high temperature resistant fibre. It is poly(p-phenylene-2,6-benzobisoxazole) (PBO) and it is one of the polybenzazoles containing an aromatic hetero-cyclic ring. It is a rigid rod isotropic crystal polymer [1], [2]. PBO fibre is registered under the trademark Zylon® and its commercial production started in 1996.

In previous works [[3], [4], [5]], we showed the exceptional flame and heat resistance of PBO fibre in particular, in comparison with p-aramid fibres. We studied the reaction to fire of PBO fibres as knitted structures in comparison with poly(p-phenylenediamine-terephthalamide) fibres (PPTA) using the cone calorimeter as fire model [6], [7]. Rate of heat release (RHR) curves of knitted PPTA and PBO fibres (Fig. 1) at two external heat fluxes (50 and 75 kW/m²) showed that PBO fibres present a very good fire behaviour in comparison with PPTA. RHR peaks of PBO at 50 and 75 kW/m² are, respectively, only 60 and 150 kW/m² in comparison with 400 and 430 kW/m² for PPTA.

PBO has superior heat resistance compared to PPTA [3]. Thermogravimetric (TG) curves (Fig. 2) showed that whatever the atmosphere was, the heat resistance of PBO fibres was always higher. Under air, PPTA fibres started to degrade at about 450 °C and formed a 3 wt.% residue at 1200 °C whereas PBO fibres degraded at about 600 °C and formed a 3 wt.% residue at 1200 °C. Under nitrogen, the degradation of fibres started at higher temperature (about 550 °C for PPTA and about 700 °C for PBO). Larger amounts of residues were observed at 1200 °C (38 wt.% for PPTA and 65 wt.% for PBO). It shows therefore the strong influence of oxygen on the thermal degradation of the fibres.

In this paper, we investigate the thermal degradation of PBO fibres in comparison with PPTA fibres in the gas phase using FTIR analyses and in the condensed phase by solid state NMR of carbon.

Section snippets

Materials

PBO fibres were supplied by the company Toyobo (Japan) and is registered under the trademark Zylon®. PPTA fibres are classical Kevlar®29.

The yarns used in this study have the following characteristics:

PBO:	Nm 2/34 spun yarn (60 TEX)
PPTA:	Nm 2/28 spun yarn (72 TEX)

PBO and PPTA fibres have been knitted on an automatic rectilinear machine gauge 7. The texture used is a weaved rib. The two samples have the surface weight equalling to 1.08 kg/m² (four yarns knitted together in the case of PPTA and

Gas phase analysis

Using the cone calorimeter connected to the FTIR spectrometer, we investigated the gas phase during the fire degradation (external heat flux was 75 kW/m²) of PPTA and PBO [4]. In these conditions, only CO, CO₂ and H₂O were detected. The amount of the gases was always lower in the case of the combustion of PBO. As the cone combustion is highly overventilated, it was not a surprise that only major products of combustion were detected. In this study, it is expected that degrading fibres in a

Conclusion

The thermal degradation of two high performance fibres, PPTA and PBO, was investigated both in gas phase and condensed phase. When degrading PPTA and PBO at 600 and 800 °C, CO, CO₂ and H₂O are the major compound composing the gas phase. As minor products at 600 °C, aromatic species, HCN and ethylenic species are detected. Because of the higher thermal stability of PBO, their evolved amounts are always lower than those of PPTA and give off at much longer times. Moreover, no aromatic compound and

Acknowledgements

The authors are indebted to Mr. Dubusse and Mr. Noyon from CREPIM for their skillful experimental assistance in cone calorimeter and FTIR experiments. NMR experiments were conducted in the common research centre of the University of Lille and Mr. Bertrand Revel is acknowledged for helpful discussion and experimental assistance.

References (16)

P. Glarborg et al.
Comb. Flame
(1986)
W.L. Earl et al.
J. Magn. Reson.
(1982)
S. Supaluknari et al.
Org. Geochim.
(1990)
G.E. Maciel et al.
Fuel
(1979)
T. Kitagawa et al.
J. Polym. Sci. Part B: Polym. Phys.
(1998)
S. Kumar
Indian J. Fibre Text. Res.
(1991)
S. Bourbigot et al.
Polym. Int.
(2001)
Bourbigot S, Flambard X, Duquesne S, Poutch F. In: Wilkie CA, Nelson G, editors. ACS Symp. Series No. 797, “Fire and...

There are more references available in the full text version of this article.

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Study of the thermal degradation of high performance fibres—application to polybenzazole and p-aramid fibres

Abstract

Introduction

Section snippets

Materials

Gas phase analysis

Conclusion

Acknowledgements

Comb. Flame

J. Magn. Reson.

Org. Geochim.

Fuel

J. Polym. Sci. Part B: Polym. Phys.

Indian J. Fibre Text. Res.

Polym. Int.