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INVESTIGATION OF EPOXY INTUMESCENT COMPOSITES MODIFIED BY METALCONTAINING TUBULES
S.G. SHUKLIN*, V.l. KODOLOV*, A.P. KUZNETSOV*, S.G. BYSTROV**, L.G. MAKAROVA**, O.V. DEMICHEVA***, T.A. RUDAKOVA***
* Basic Research-High Educational Center of Chemical Physics and Mesoscopy. Udmurt Scientific Center, Urai Division, RAS **Physico-Technical Institute, Ural Division, RAS ** ""Institute of Synthetic Polymer Materials, RAS
ABSTRACT. The paper is dedicated to the research of intumescent composites based on epoxy resin cross-linked by polyethylene polyamine and containing ammonium polyphosphate and such modifying additives as calcium borate, manganese dioxide, nickel and chromium containing tubulenes as gas-formers and carbonization stimulators.
The changes in composition and physico-chemical properties of modified compositions under thermal and fire actions have been investigated by X-ray photoelectron spectroscopy, atomic force microscopy and local force spectroscopy.
It is found out that ammonium polyphosphate mainly stimulates carbonization processes on the inner surface of a bubble being formed during foam coke formation. It is shown that the introduction of metal containing tubulenes leads to the formation of fire retardant and low flammable compositions with high coke and carbon structures content, and the use of calcium borate in the compositions sufficiently increases the strength of foam coke being fonned.
INTRODUCTION
Intumescent fireproof coatings are of great interest for civil construction industry, machine-building, transport as the main characteristics of the materials used do not practically get worse. Compositions for intumescent coatings containing polyammonium-phosphate as foam coke formation stimulator were suggested in [1]. Mathematical model for foam coke formation was developed on the basis of this coating [2, 3]. However, despite of good coating adhesion to polymer materials [4], the foam cokes formed could not bear mechanical loads. It is also of interest to foresee the structure of foam cokes being formed in order to organize regulated foams with certain strength and porosity. Therefore, it is advisable to use modifying additives, which can be active structure-formers.
The purpose of this paper - to provide the results of compositions formation and to investigate their structures and properties during stepped temperature growth.
INVESTIGATION OBJECTS AND METHODS
Epoxy resin ED-20 modified by ammonium polyphosphate (APP), calcium borate, phenan-threne dehydropolycondensation product containing chromium (tubulene T-Cr) and nickel (T-Ni) is used as epoxy intumescent compositions. Epoxy resin is cross-linked by polyethylene polyamine.
The preparation of intumescent composition consists in the preparation of the components mixture in the ratios shown in Table 1. Components mixing is carried out at normal conditions as follows: powder components are successively introduced into the vessel containing the measured quantity of epoxy resin without a hardener and thoroughly mixed after each component is added. After that the hardener is introduced into the vessel and stirred during two minutes. The prepared system, the vitality of which is 1.5-2.0 hours, is protected from moisture action and stored not more than 30 minutes before application.
The flash temperature is measured by high-temperature pyrolysis. The device allows register synchronously the continuous sample mass changes during pyrolysis and combustion, as well as the temperatures in the surface layer of the polymer under pyrolysis action and in the flame of the burning sample, including the time of inflammation delay of various polymer materials depending on external conditions. Thermal investigations are carried out in the open flame mode, the temperature increases up to 800°C during first 10 seconds. The time of heat resistance testing is two minutes. The changes in surface chemical composition and intumescent systems volume are investigated by X-ray photoelectron spectroscopy at ES-2401 spectrometer (MgKa radiation) and magnetic photoelectron spectrometer (AlKa radiation). The samples are subjected to pyrolysis in accordance with the following method: a sample is-placed into molybdenum cell and then put into a tube quartz furnace. The pyrolysis tempera-
Table 1.
Components Composition, mas.pat.
1 16 2 3 36 4 46 5 56 6 7 8
3/1-20 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10,0
PAF 2.0 3.0 2.0 2.0 3.0 2.0 3.0 2.0 3.0 3.0 3.0 3.0
Tubules(Ni) 0.8
Tubules (Cr) 0.4 0.4 0.4 0.4 0.8
Calcium borate 0.4 0.4 0.4 0.4 0.4 0.4
Mn02 0.4 0.4 0.4 0.8 0.8
PEPA 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5
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XMMMHECKAfl <t>H3HKA M ME30CK0flMR Tom 3, № 1
ture is provided by an electronic control block with a feedback. The accuracy of temperature support is 2%. The pyrolysis is carried out step by step in nitrogen atmosphere cleaned from oxygen additives. The pyrolysis temperature is chosen according to DTG and TG data. The investigation of heat-physical properties of materials is carried out with the help of a standard calorimeter IT-S-400. The samples for the investigation are obtained by pouring the composition into the cylinders of the corresponding sizes.
RESULTS AND DISCUSSION
The modification of the compositions based on epoxy resin hardened by polyethylene polv-amine and containing fine ammonium polyphosphate is carried out by the introduction of manganese dioxide and calcium borate into the compositions to form mineral net struciures in surface layers, and also by the use of carbon-metal containing tubulenes favoring the formation of foam cokes of a certain structure. As foam cokes formation process can be considered like successive stages during the compositions heating, it can be assumed, that due to the difference in thermal spreading micro cracks are formed near the particles of ammonium polyphosphate. Ammonium and water vapor enter these cracks and simultaneously polyphospho-ric acid is formed at the walls. The latter can act as a dehydrating agent and carbonization stimulator. So, it is possible to expect the formation of a carbon (close to graphite-like) layer on the inner surface of a bubble being formed. In fact, according to XPE spectra Cls. a graphite-like layer is formed on a bubble inner surface at a certain stage of a temperature heating (ECB=283,5 - 284 eV) (Table 2). As surface and boundary layers of a hardened resin, its thermolysis products and residues of materials pyrolysis are investigated by XPES method, it is necessary mention the results of initial resin investigation.
For initial resin the differences in bond energy of elements in boundary and surface layers are not observed, carbon is shown in the spectra by the lines with bond energies Cls 285,0; 286,0; 288 eV, which correspond to epoxy resin fragments CH2(CH); C-OR; -O-C-O. Two lines 400,0 - 400,2 (nitrogen in polyethylene polyamine) and 402,1 (nitrogen in ammonium polyphosphate - APP) are observed in nitrogen spectrum. In accordance with the scheme of chemical shifts, nitrogen bond energy Nls in APP should not have such great value. Apparently, the formation of RNH3+groups takes place in APP. The adjunct of this nitrogen line to APP is proved by the fact that it is found in volume layers of epoxy resin together with phosphorus with bond energy P2p 134,5 - 134,6 eV (P-O-P'^NHsR) which is characteristic of phosphorus with a maximum oxidation degree. On the crack surface of the initial sample a high content of oxygen due to the presence of APP is observed in comparison with the sample surface (Table 2).
When the sample is heated up to pyrolysis temperature (533 K), the egress of phosphorus containing substances is observed on the sample surface (ammonium salts of poly-phosphoric acid are formed). It is necessary to mention that the temperature of APP decompo
Table 2. XPES results on Cls, Ols, Nls and Pip lines during the investigation of ep-oxy composition containing ammonium polyphosphate
Sample type Temperature °C Cls Ols Nls P2p
Eb, eV C, at % Eb, eV C, at % Eb, eV C, at % Ec, eV C,at%
T=20°C surface 285 46,48 533,6 12,6 398,9 1,18 134,1 0,7
286,5 28,22 400,5 1,67
288 8,3 402,4 0,6
403,9 0,25
T=20°C crack surface 285 41,9 533,6 16,3 399,8 1,98 133,3 1,6
286,5 27,16 401,8 1,35
288 8,54 403,8 1,17
T=l50°C surface 285 48,1 533,2 19,6 400,7 2,42 134,4 2,0
286,5 21,46 401,9 1,98
288 4,44
T=150°C crack surface 285 38,12 533,4 22,0 400 3,19 134,3 3,0
286,5 24,94 401,8 2,5
288 6,24
T=260°C surface 285 31,42 532,8 10,37 400,7 3,23 134,6 9,2
286 15,15 533.7 16,27 402,1 5,06
288 9,54
T-260°C crack surface 285 38,02 533,7 13,5 401,3 2,2 134,7 2,5
286.5 24,55 402,1 5,06
288 12,68
290 3,96
T=300°C surface 285 47,04 531,9 15,7 400,5 3,07 134,4 5,0
286,5 22,05 402,4 2,72
288 4,41
T=300°C crack surface 283,7 7,24 531,3 9,27 401,7 4,03 134,5 8,1
285 27,74 533,3 15,13 403,4 3,17
286,5 22,92
289.4 2.41 i
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XMMHHECKAfl CDH3HKA M ME3OCX0nMR Tom 3, Ns 1
sition beginning is 463K. As nitrogen line with bond energy Nls 402.1 eV is the same in the spectra up to 573K, decomposition reaction has a more complex character. It is possible that total APP deamination and, consequently, its total decomposition are difficult in a polymer due to the high density of polymer and its destruction products even at very high temperatures. The data obtained are confirmed during the determination of temperature dependence of heat capacity of materials investigated.
The egress of phosphorus containing products is followed by the increase of phosphorus concentration on the surface and by the redistribution of nitrogen lines intensity in X-ray photoelectron spectrum (the increase of the most high-energy line). When the temperature increases in boundary layers, the decrease of relative quantity of C-OR groups in material volume and carboxyl groups is observed (Table 2).
Intensive formation of liquid pyrolysis products starts at 573K (pyrolysis beginning temperature), this is proved by a sharp increase of Cls line intensity accredited to CH groups. Carbon products accumulate on samples surface masking all other fragments of pyrolysis products, therefore, it is possible to assume that the process of coke formation starts at 573K. Not more than 7,24% of carbon from total content are found on the crack surface of the samples. Apparently, the interaction of APP with a polymer continues at the temperature mentioned as nitrogen line intensity with Eb=402,l eV decreases with phosphorus bond energy decrease.
In comparison with the results obtained, the introduction of nickel containing tubule-nes into the composition in APP and Ni-T 10:1 ratio leads to the increase of carbon-carbon and carbon-metal groups in approximately three times (Fig. 2). The increase of carbon products content in foam coke leads to the sufficient change of character of heat capacity dependence on temperature (Fig. 1). First, the heat capacity of compositions modified by structure-formers is 3-7 times higher than the heat capacity of composition containing only ammonium polyphosphate, this can be explained by different structure-formation degree of the compositions. Secondly, the heat capacity of composition containing APP increases sharply, in 10-11 times, at 373-403K and 430-480K; this is. apparently, due to the evolution of water and ammonium vapor into the bubbles being formed and pressure increase in the bubbles. In contrast to the picture presented, the heat capacity in modified compositions changes without any considerable peaks owing to a smoother gas-formation process; and if calcium borate is introduced into the composition, heat capacity deviations are not practically observed due to the formation of calcium-phosphorus-borate net. More sufficient heat capacity changes (in 2-3 times) can be seen when manganese dioxide is introduced with calcium borate. In our opinion this can be explained by competing thermal destruction processes of samples containing manganese dioxide with the formation of easily volatile inflammable products. Intumescent degree of this composition is 16 p, and flash temperature - 463K.
Heat-physical characteristics data and XPE spectra investigation agree with the results obtained during the examination of flash temperatures, cokes intumescence and strength degrees. Below you can see CPK/CP" values of the compositions at 323 - 573K, their intumes-
cence degrees and flash temperatures:
Compositions numbers
1 2 3 4 5 6 7 8
Cp7Cpn 1,90 1,60 2,30 1,03 (11,5)*
B,p 4 16 6 12 9 10(6)** 7(3)**
fini» K 643 463 583 603 523 593 513
In accordance with the given data it is seen that in the compositions into which manganese dioxide is introduced, the flash temperature decreases in most cases. This can mean the formation of sufficient concentrations of combustible gases at small temperatures. The cokes obtained lose their shape with the increase of intumescence degree when removed from flame (samples 7 and 8). The introduction of chromium and nickel containing tubulenes decreases the intumescence degree but leads to the increase of flash temperature. The increase of ignition time and the decrease of self-combustion time of samples including metal containing tubulenes and/or calcium borate should also be noted.
0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400 425
0
T, °c
Fig. 1. Heat capacity dependence on temperature
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xwmmheckafl oh3hka m me30ck0rimr tom 3, n8 1
281 282 283 284 285 286 287 288 289 290 291 292 293 29
Ecb, dB
Fig.2. XPES results on lCs line during investigation of epoxy composition containing ammonium polyphosphate and T-Ni
The investigation of the topography of inner and outer layers of foamcokes formed is carried out with the help of atomic force microscopy on the example of two foam cokes obtained on the basis of compositions 2 and 4b (composition 4b differs from composition 4 by the increased calcium borate content (in 1.7 times)). The differences in topography of the samples being investigated and in the topography of outer and inner layers of the same foam coke are registered. It is found out that r.m.s. roughness R<, of sample 2 outer surface is 9,769 nm (Fig. 3), and the analogous parameter for inner layers is 0,015 nm (Fig. 4). For sample 4b for the outer surface is 0,026 nm (Fig. 5), and for inner layers - 0,01 lnm (Fig. 6). The de struction of the outer surface and inner layers of foam coke samples being studied is different: the outer surface of sample 2 does not destruct at maximum loads and the inner layer is damaged at load Fu=2,7 mcN, at the same time weak destruction traces are observed on the inner-surface of sample 4 and there is no any destruction of outer surface at minimal load. The pres-
S.G. SHUKLIN, V.I. KODOLOV, A.P. KUZNETSOV, S.G. BYSTROV, L.G. MAKAROVA,
O.V. DEMICHEVA, T.A. RUDAKOVA
ence of polar surface of the foam coke obtained from composition 4 and the above results prove the presence of a net structure of calcium phosphorus-borate in surface layers.
Thus, on the basis of the results given, it is possible to declare that calcium borate and metal containing tubulenes are effective as structure-formers during foam coke formation. It is also possible to assume that the introduction of metal containing tubulenes influences the changes of stimulator and gas-former structures, together with the influence of a hardening polymer on the structure promoting the formation of foam cokes of a certain surface structure and composition.
XMMMHECKAfl a>M3MKA M ME30CK0I"1HR Tom 3, № 1
t
references
1. S.G. Shuklin, V.I. Kodolov, K.I. Larionov, S.A. Tyurin. Physico-chemical processes in modified two-layer fire-heat-proof filled epoxypolymers under fire sources effect - Physics of combustion and explosion. №2, 1995, p. 73-80 (in Russian).
2. A.M. Lipanov, E.N. Bajenova, V.I. Kodolov, I.N. Efimov. Modeling foam coke formation. Fire science and technology.- Proceedings of the second Asia-Oceania symposium, Khabarovsk, 1995, p. 397-409.
3. A.M. Lipanov, E.N. Bajenova, V.I. Kodolov, I.N. Efimov. Mathematical modeling of processes and calculation of some substances parameters during foam cokes formation. -Modern problems of internal ballistics of solid propellant propulsions, 1996, p. 292-302.(in Russian)
4. V.I. Kodolov, K.I. Larionov, K.I. Larionov, S.G. Shuklin et al. Method of surface preparation of items made of organic- and fiber-glass plastics before applying fire-proof coat-ings.Russian Patent №5007963/05 dated 25.10.91.
