(Received September 3. 1990)
EFFECTS OF NITROGEN AND PHOSPRORUS ONPYROLYTIC GAS FORMATION FROM CELLULOSIC FIBERS
Shigeko Nakanishi, Fumiko Ohkouchi, Fumi Masuko, and lkuko Nishimoto'.Department of Clothing. Faculty of Home Economics. Japan Women's University.
2-8-1. Mejirodai, Bunkyo-ku. Tokyo. 112 Japan
ABSTRACT: Flame retardant effects of nitrogen and / or phosphorous treatments of cotton fabrics werein-vestigated through the analysis of pyrolytic gas formation. While the pyrolytic behavior of N- and/or Ptreated samples with low limiting oxygen index (LOI) was similar to that of the untreated material. the behavior of samples with high LOI was remarkably altered. In particular, the sample treated with 20% diammonium hydrogen phosphate showed a large decrease in the generation of a poisonous gas (acrolein) andflammable gases. and showed an increase in the formation of unsaturated cyclic compounds. which contributed to the self-extinguishing behavior. These results were attributed to the synergistic effect of nitrogenand phosphorus compounds added to the cellulosic materials.
1. INTRODUCTlON
For preventing the generation of hazardous gases
in fire incidents. it is important to investigate the behavior of pyrolytic gas formation from flammable polymers. Thermal degradation of ceIIulosic fibers wasinvestigated by lnagaki et al. [1-4] and other groups[5-9]. However. the effect of the individual flame retardant and the synergistic effect on pyrolytic gas
formation have not been fully elucidated. Nakanishi[10] studied the effects of flame retandant finishingsfor ceIIulosic fibers in terms of the generation of CO.
CO2 and smoke. However. the information is still limited on the effects of flame retandant elements.
In this study. we attempted a quantitative analysis
of pyrolytic gases from flame retardant-finished cellulosic fibers. with special emphasis on the effects of N
and /or P as flame retardant elements.
2. EXPERIMENTAL
2.1 Materials
2.1.1 Substrate
Cotton 100% fabric was purified by Soxhlet extraction with chloroform-methanol (1 : 1 Vol/Vol) for 24 h.

2.1.2 Reagents
Compounds used for treatments are shown in Table
1. Ammonium hydroxide (Nn4OH) and urea wereusedas nitrogen soures. phosphoric acid (H3PO4) alld disodium hydrogen phosphate (Na2HPO4) as phosphorus
sources. and diammonium hydrogen phosphate[(NH4)2 HPO4] as a compound containing both nitrogen and phosphorus in the same molecule. X-source
and P-source compounds were combined for studying
the effect of the combination of N and P for comparison with (NH4)2HPO4.

packed in a glass column. 3 mm in diameter. GC
analysis was carried out under the following conditions: The temperature was raised from 50℃ (cooled
down with dry ice) to 200℃ at a rate of 5℃/min
under a nitrogen flow of 40-60mL/min. The injection inlet was kept at 200℃
2.2.3 Pyrolysis Gas Chromatography - Mass
Spectrometry (PGC - MS)(1) Apparatus
The pyrolyzer mentioned above was connected to agas chromatograph-mass spectrometer. Type JMS-DX
300 (Nihon Denshi) for the identification of gaseouscompounds. The data were analyzed with JMA 3000
(Nihon Denshi):(2) Conditions for analysis(i) Pyrolysis: Pyrolysis was carried out under theConditions described in 2.2.2, (2). (i).
(ii) PGC-MS analysis: Porapak Q. same as that used in
PGC analysis was packed in a glass column. EIectron
2.2 Methods
ionization (El) and chemical ionization (CI) methods
2.2.I Treatment
were adopted for analysis at an ionization voltage of
70eV. PGC-MS analysis was carried out from 50℃
Five percent and 20% solutions of the above mento 240℃ at a programmed rate of 4 ℃/min. The reptioned reagents were prepared. in which the purified
etition was made by a 6-second cycle in a scan
Cotton fabric was immersed for 5min. The sample
range of 15 – 300 m/z. The temperatures of the separawas mangled and dried indoors after a 2 dip-2 nip
tor and the ionization chamber were set at 260oC
process. The pick up was adjusted to about 90%.
and 200 ℃. respectively. The ion acceleration voltage
was 3.5kV and the flow rate of He was adjusted to2.2.2 Pyrolysis G&s Chromatography (PGC)
40mL/min. Repetition ion current chromatograms
were used for the identification of gases. The struc(1) Apparatus
ture of each pyrolytic gaseous product was identified
A high-frequency induction-heating-furnace pyrolfrom pseudo-molecular ions and mass fragments. The
yzer. Type JHP-2 (Nihon Bunseki Kogyo) was conidentification was also confirmed with authentic comnected with a gas chromatograph (GC) Type 063
pounds.
(Hitachi Seisakusho) with a FID detector to pyrolyze Pyrolysis and chromatographic analysis were reand analyze pyrolytic gases simultaneously (see Fig. peated 5 - 10 times for each sample and the results
I). The data were treated with Chromatopack C-RIB wereaveraged. The amount of each pyrolytic compound(Shimadzu Seisakusho).
was shown as an amount per 1 g of the substrate (cot(2) Conditions for' analyses(i) Pyrolysis: Three kinds of Pyrofoiles (foils made of ton) in each treated sample after determining its addferromagnetic derivatives. Nihon Kagaku Kogyo) for on.
445. 590 and 764 ℃
were selected for
2.2.4 Evaluation of Fume Retardancy
representative
As a measure of flame retardancy. we adopted thepyrolysis. A 200-300μg portion of a sample. prelimiting oxygen index (LOI) which is defined as thecisely weighed, was wrapped with a foil and pyroly- value of minimum volume % of oxygen in 02-N2 mixzed by high frequency heating. The furnace tempera- ture requited for the combustion of materials under,
ture was 160oC and the pipe temperature was 210
the regulated testing conditions. LOI values were de℃.
(ii)GC analysis: Porapak Q of 80-100 mesh wastermined based on JIS K 720l-l976 by using aburning tester ON-1 (Suga Shikenki).
3. RBSULTS AND DISCUSSION
The thermal treatment was carried out in N2 flowby the instaneous Pyrolysis which reaches the fixed
temperature within 0.2 s. This is to avow or minimize
the influence oxidation and secondary decompositions.

3.1 Temperature Dependence of Pyrolytic Gas
Formation
The purpose of this experiment was to determine
the optimal heating conditions with reliability for thepresent study. An attempt was made to observe
pyrolytic gas formation ill three temperature ranges.
i.e.. 400- 500℃. around 600℃ and 700- 800℃.
The result of GC analysis clearly showed a temperature dependence of pyrolytic gas formation as illustrated in Fig. 2. The amounts of hydrocarbons withlow boiling point increased with a rise in temperatureand showed a remarkable increase in a temperature
range higher than 700℃. This tendency is similar tothat shown by Hofmann and Raschorof (5). On thecontrary. the amounts of acetoI, dimethylfuran. furfural, 5-methyl-2-furfural. and peaks n i. (not identified) No. 8 and No. 19 decreased with a rise intemperature. No. 19 gas was characterized by fragment ions of m/z = 29. 57 and 69. and by molecularweight of 114 which is the highest among those of thepyrolytic gaseous compounds detected in this study.
The same pyrolytic product Was observed from ceIIuLose by Wedly (6) as a not-identified product.
The comparison of furan (without -CH3 group).
methylfuran (with one -CH3 group) and dimethylfuran(with tow. -CH3 groups) showed that the amounts offuran and methylfuran increased while that ofdimethylfuran decreased as the temperature rose.
Such a tendency means that the scission of -CH3
group from dimethylfuran occurred to form methylfuran and / or furan. The decrease in the amount offurfural suggests another route to furan by removalof -CHO group from furfural.
The amounts of compounds with boiling point from
60℃ to aroud 115 ℃. i.e., acetone, hydroxyacetaldehyde arid acetic acid. showed maxima at
around 600 ℃ and decreased at 700℃ or higher.
The amount of benzene increased markedly, as muchas 50times. above 700℃. This suggests that theformation of benzene is attributed to the double-bondformation between C atoms through dehydration ofcellulose in thermal decomposition.
Above findings show that the thermal decomposition was insufficient in a range of 400 - 500℃ and
too much proceeded in a range of 700-800℃.
Therefore. the pyrolysis temperature of about 600℃

is the most appropriate for the purpose of this study.
3.2 Effect or N and P on Pyrolytic Gas Formation
3.2.1 Effeces on LOI
The LOI value was chosen as an indicator of flame
retardancy to examine the relationship between- flame
retardancy and the pyrolytic gas formation. A high
LOI valtle means that the material requires higher
concentration of oxygen to keep burning, and the LOIof 27-28 is regarded as the critical level for thematerial to be flammable.
Table 1 shows that samples treated with compounds containing N or P alone except those treatedwith H3PO4 had LOI values lower than the criticallevel. 27- 28%. High LOI values of H3PO4-containing
samples can be attributed not only to P element but
also to high moisture content owing to hygroscopicityof H3PO4. High flame-retarding effect was also
observed for the sample treated with 20% (NH4)2
HPO4. Probably because of the synergism of N and P.
However, those treated with a mixture of urea andNa2HPO4 showed little flame-retarding effect though
they contain both N and P. This fact suggests that thecontribution of N and P together to flame retardancy
requires a proper mutual position of the elements toshow the synergism for flame retardation. It was also
found that the insufficient add-on of flame retardants
failed to give flame retardancy.
Taking the above results into consideration. attention was paid to the relationship between LOI values
and pyrolytic gas formation. PG chromatograms of
untreated and treated samples obtained by PGC-MS
analysis showed approximately 46 peaks of pyrolytic
gaseous compounds. of these. we paid attention to 19
compounds definitely identified and two unidentified
compounds. No. 8 and No. 18. which showed markedly different behavior in the formation between flame
retardant samples and samples with low LoI values.
Fig. 3 shows relative amounts of these pyrolytic
gaseous compounds from various samples. The
amount from the untreated sample is indicated by abroken line for each product. In this figure. the following different behavior is-observed between the untreated sample and the samples containing N and/or
P. and also between samples with high LoI values
and those with low LoI values.

3.2.2 Reduction of Flammable Gas Formation
The amounts of propylene, acetaldehyde, butadiene,
acrolein, acetone, hydroxyacetaldehyde, acetol, benzene, dimethylfuran, ethane and n.i. No. 8 from flame
retardant samples were considererably less thanthose from flammable samples with low LOI values(see Table 1), e.g., acetaldehyde and benzene decreased to 1/8-1/13: acetol to 1/30-1/40: and,acetone, hydroxyacetaldehyde, dimethylfuran and n.i.
No. 8 entirely disappeared.
3.2.3 Inhibition of Acrolein Generation
Samples without flame retardancy such as thosetreated with urea or NH4OH, containing N alone,
showed little change in the generation of acrolein.
Those treated with Na2 HP04 alone or urea + Na2
HPO4 showed only a small decrease. On the other
hand, flame retardant samples treated with (NH4)2
HPO4, H3PO4, urea + H3PO4 and NH4OH + H3P04
etc. showed much larger reduction. Byrne et al. [7]suggested that the presence of P and / or N might inhibit the formation of acrolein.
3.2.4 Increase in the Amount of Unsaturated
Compounds
Methyl vinyl ketone, furan and its derivatives, i.e.,
methylfuran, furfural and 5-methyl- 2-furfural containing carbon-carbon double bonds produced fromthe treated samples showed an increase in amount ascompared with those from the untreated sample. A
larger increase was observed for the samples containing N and P with higher LOI values. These products
are likely to be related to char formation, because thefindings well correspond to the observation of IR
absorption spectra of residual condensed phaseobtained by the thermal treatment･of cellulose-ammonium phosphate [C8].
Since peaks of methylfuran and diacetyl could not
be resolved from each other. combined values are indicated in Fig. 3. However, the amounts of methylfuran can be calculated from the relative molar ratios ofmethylfuran and diacetyl based oh the intensity ratios
in the fragmentation patterns obtained by PGC-MS
analysis. The molar ratio of methylfuran is around
l0% for the untreated sample, 24% for samples containing P alone, 38% for those containing N alone andup to 66% for those containing both N and P. The result, by Hofm.ann and Raschorof [5] also showed asimilar tendency, i.e., finished samples generated
methylfuran twice as much as an unfinished sample.
3.2.5 Acetonitrile Generation
Acetonitrile is an extremely useful substance for
Flame retardation as a radical scavenger in the vapor
phase. Acetonitrile was. detected neither from untreated sample nor from those treated with compounds
containing N or P alone, but was generated from samples containing both N and P. It is notable that samples with high LOI values treated with 20% (NH4)2
HPO4, NH4OH + H3PO4 and urea +H3PO4 gave thelargest amounts, while samples with low LOI values
because of the low level of add-on yielded much lessamounts of acetonitrile even though they contain both
N and P. This fact confirms a close relationship between the formation of acetonitrile and the flame retardancy.
According to Garn and Denson [9], acetonitrile isformed from acetic acid, a pyrolytic product from cellulose, and ammonia generated from flame retardants,e.g., ammonium salts, with the aid of catalytic actionof P. Acetonitrile is converted into nitrogen oxides
which play a role to give the self-extinguishability. byacting as an inhibitor for radical side chain reactions.
In contrast to our results. Hofmann and Raschorof [5]reported the production of very toxic and explosive
acrylonitrile from fabric finished with PyrovatexR(N-methyloldialkyl-phosphonopropionamide, produced
by Albright & Wilson Co.). This difference is probably due to the difference between ammonium salts
and the organic phosphonocarbamate containing -CH2
CH2CONHCH2OH. Acrylonltrlle was also detected In

Fig. 4. Mutua] change in amounts of acetic acid andhydroxyacetaldehyde pyrogramatically, observed in untreated and treated cotton samples, (A), Uutreated: (B),treated with Na2HPO4 and (D), treated with (NH4)HPO4

our investigation for a sample treated with Pyrovatex.
The quantitative change in the amount of acetic
acid is important in connection with the formation ofacetonitrile. Acetic acid was detected as a shoulder ofthe peak of hydroxyacetaldehyde for the untreatedsample and samples treated with compounds containing N or P alone. On the other hand, hydroxyacetaldehyde disappeared and only acetic acid became
detectable for samples treated with (NH4)2HPO4 (Fig.
4).
According to Byrne et al., [7], hydroxyacetaldehyde is formed from 1,2-ethenediol, an intermediatepyrolytic product generated by the spliting of a glucose unit through the following process:The pyrolysis of the untreated sample or samples
containing N or P alone will proceed mainly throughthis route.
On the other hand, it has been considered that acetic acid is formed from ketone, a dehydration productof hydroxyacetaldehyde, by the addition of water
generated during the pyrolysis of cellulose. Whensamples treated with (NH4)2HPO4, containing N and P
together, are pyrolyzed, this process seems to proceed
mainly to form acetic acid.
The compound n.i. No. 18 is also. worth. paying
attention since it was detected in a very large amount
only from samples containing (NH4)2HPO4 and / or,
H3P04. This product showed fragment ions of m/z =39, 53 and 68, typical for furan The molecularweight detemined by CI-MS was 96 which is the sameas that of furfural.
3.2.6 Comparisop of Total Amounts of Pyrolytic
Gases
Fig. 5 shows the total amounts of pyrolytic gases
from the samples. The untreated sample gave thelargest amount and those treated with NH4OH (B) andNa2HPO4 (D) containing N or P alone showed slightly
lower level of gas formation. Such findings are consistent with their low LOI values, while samples containing urea (A, E, F, G) showed less amounts than B or D
though they contain N alone and LOI values are low
just as samples B and D. Ali samples with high LOI
values gave much less amounts of pyrolytic gases.

Fig. 5. Total amount of pyrolytic gases. (U), Untreated.
Treated samples with: (A), 20% urea; (B), 20% NH4OH:(C), 20% H3PO4; (D). 20% Na2HPO4: (E), 20% urea+ Na2
HPO4; (F), 5% urea + H3PO4; (G), 20% urea + H3PO4:(H), 20% NH4OH + H3PO4; (1), 5% (NH4)2HPO4 and (J),20% (NH4)2HPO4 ･ Numbers in parentheses indicate
LOI values,
Sample J treated with 20% (NH4)2HPO4 Showed theleast amount exhibiting a synergistic effect of N and
P present in the same molecule.
It is concluded from the above results that theflame retarding effects, particularly the synergistic
effects of N and P, are well reflected in the pyrolytic
behavior, and showed a good agreement with the inhibition of flammable gas formation.