thermal decomposition of nitrophenol-formaldehyde...

Indian Journal or QemistryVoL 21A, April 1982, pp. 353-356

Thermal Decomposition of Nitrophenol-Formaldehyde-AmmoniumPerchlorate/Potassium Perchlorate Systems

H. L. GIRDHAR*, A. J. ARORA & G. N. MALIKDepartment of Chemistry, University of Kashmir, Srinagar J 90 006

Received 23 July 1981; revised and accepted 16 November 1981

lbermal decomposition of nitrophenol-rormatdehyde polymers and their composite mixtures l..'OntainingNH,CJO, or KCIO, has been studied by thermogravimetry and differential thermal analysis. The presence of nitro-&Ubstituentin the basic polymeric structure has been found to enhance the solid phase decomposition. These studies alsoreveal the existence of condensed-phase exothermic reactions prior to the ignition in composite mixtures containingNH,CIO, or KCtO •.

MUCH work has been done on the thermaldecomposition of both the oxidisers and thepolymeric binders but there is some doubtregarding the applicability of such data to the multi-component mixtures encountered in propellants.Waesche et aU studied the decomposition of poly-butadiene-acrylic acid/ammonium perchlorate systemsand showed that condensed-phase reactions wererapid and intense enough to supply a significantportion of energy required to maintain combustion.Rastogi et 01.2,3 studied the thermal degradation ofpolystyrene/ammonium perchlorate systems. Theyhave shown that the endothermic process (in therange SlS-525aK) involves the' degradation of thepolymer, and the products of degradation enter intosome sort of exothermic condensed-phase reaction.The work of Pai Verneker and Kishore- has revealedthat the rate control\ing process in the thermal de-composition of polystyrene/ammonium perchloratecomposite system is the decomposition of oxidiser.Using TLC technique, these workers" were also ableto separate the decomposition products whichsupported the occurrence of condensed-phase reac-tions.

The main objective of the present investigation isto see how the thermal decomposition of some con-densation polymers as well as of their compositemixtures with inorganic solid oxidisers such asammonium perchlorate, potassium perchlorate, etc.is influenced by the presence of nitro substituent inthe phenyl ring of the polymeric structure. The mainreason for selecting the nitro group is that it is quiteenergetic and the oxygen is expected to acceleratethe decomposition process.

Materials and Methods

The polymers, phenol-formaldehyde (PF), o-nitro-phenol-formaldehyde (o-NPF), m-nitrophenol-formal-

dehyde (m-NPF) and p-nitrophenol-formaldehydo(p-NPF) were prepared by refiuxing the respectivephenol-formaldehyde mixtures (molar ratio 1 : 2.3)in the presence of a base as catalyst. The compositemixtures based on these polymers were preparedusing NH4CI04 (AP) or KCI04 (KP) of particle size67-75p.. The weight percentage of polymer/oxidiserwas 25/75. The complete details of preparation andcuring of the polymers and the composite systemsbased on them are described elsewhere". The curedsamples were powdered by grinding in a glass mortarand the fraction with particle size 151-295 p. wasused for thermal decomposition studies. The pow-dered materials were always kept in vacuo.

The thermogravimetric studies were made innitrogen atmosphere using a manual therrnogravi-metric balance and a heating rate of soC/ min. Ineach case zs 400 mg of the sample was taken in aplatinum crucible. A Pt-Pt/Rh(l3 %) thermocoupleplaced just below the sample holder was used tomeasure the temperatures.

Differential thermal analyses were carried out atthe Chemistry Division, Bhabha Atomic ResearchCentre, Bombay using an indigenously made appara-tus. About 50 mg of the sample was taken in a plati-num cup and DTA was carried out in a static atmos-phere of air at a heating rate of SaC/min. Aluminawas used as the reference and temperatures weremeasured using Platinel II thermocouple. Somemeasurements were made in nitrogen atmospherealso but the results did not differ much except thatthe positions of the peaks shifted towards lower tem-peratures by about 10°C.

Results and DiscussionTG curves in the form of fraction decomposed,

I.t vs temperature for the three polymers and theircomposite mixtures are given in Figs 1-3.

353

INDIAN J. CHEM., VOL. 21A, APRIL 1982

It is seen from Fig. 1 that PF continues todecompose in a normal way even upto 550"Cwhereas in the cases of o-NPF, m-NPF andp-NPF, drastic decomposition occurs at tempera-tures 140°, 120" and 180"C respectively. Further,p-NPF explodes at about 240°C. Similarly, itis also evident from the plots in Figs 2 and 3that both AP and KP type composite systemsbased on nitro substituted polymers have higherrates of weight loss than those based on PF. Further,it is interesting to note from these plots (Figs 1~3)

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· INDIAN J. CHEM., VOL. 21A, APRIL 1982

References1. WA~CHE, R. H. W., WENOORAD, J. & FEINANER, L. R.,

ICRPGIAIAA Second solid propulsion conference, June6-8, 1967.

2. RASTOGI, R. P., KIsHORE, K. & SINGH, G., AIAA J.• 12(1974),9.

3. RAsTOGI, R. P., KISHORE, K. & SINGH, G., Thermochim.Acta, 12 (1~7S), 89.

356:

4. PAl VERNEKOR, V •. R •. .5l.KISHORE, K, Thermachim, Acta,17 (1976), 73.

S. KISHORE, K., PAT V£RNEICER, V. R., CHATUlWEDI, B. K.& GAYATHRI, V., AIAAJ .• 15 (1977), 114.

6. GIRDHAR, H. L., ARORA, A. J. & MALIK, G. N., Com-bustion &: Flame. 39 (1980), 283.

7. Macromolecular reviews, Vol. 3, edited by A. Peterlin,M. Goodman. S. Okamura, B. H. Zimm & H. F. Mark(Interscience, New York), 1968, 94.