performance of intumescent fire retardant for wood

704

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2008, Vol. 81, No. 4, pp. 704 �707. � Pleiades Publishing, Ltd., 2008.Original Russian Text � N.K. Luneva, L.I. Petrovskaya, 2008, published in Zhurnal Prikladnoi Khimii, 2008, Vol. 81, No. 4, pp. 667� 671.

MACROMOLECULAR CHEMISTRY�� AND POLYMERIC MATERIALS

Performance of Intumescent Fire Retardant for Wood

N. K. Luneva and L. I. Petrovskaya

Institute of General and Inorganic Chemistry,National Academy of Sciences of Belarus, Minsk, Belarus

Received December 6, 2007

Abstract�Performance characteristics of new fire-retardant formulations are studied, including their waterresistance and the effect of additives.

DOI: 10.1134/S1070427208040265

Wood has always been high among man’s pre-ferred building materials for many reasons. It is highlyworkable and has minimal environmental pollution.However, the use of wood can be restricted by safetyrequirements and regulations concerned with its ig-nitability and fire spreading characteristics. The mostsignificant loss by fire falls at untreated wood con-structions and buildings. Of course, one can raisethe fire resistance only to a certain limited extent, andno building is completely fireproof. Until now, theproblem of wood protection against fire remains verytopical. At present, intumescent fire retardants (FRs)are mostly used for treatment of timbers. However,the mechanisms of chemical transformations in in-tumescent FRs under heating still remains to be un-derstood. The reasons are their complex composi-tion and the fact that the main reactions occur at hightemperatures.

The goals of this study were to develop new greenintumescent fire retardants for wood and to examinethe effect of their composition and kind of binder(of various viscosities) on the protective action andwater resistance. The formulations studied consistedof polyposphorous compounds, a water-organic dis-persion, and fire inhibitors (organic amides and poly-ols providing expansion of the intumescent fire-re-tardant coating). Finally, thermal degradation ofFR-treated wood was studied at 20�700�C.

Therefore, we report here the properties of phos-phorus�nitrogen-containing fire retardants: effect oftheir composition on the protective action, water re-sistance of the formulations, and thermal decompos-ition and stability of phosphorus- and nitrogen-con-taining compounds in FR-treated wood samples.

EXPERIMENTAL

Among diverse organic amides and polyols, we se-lected those whose thermal decomposition occurswithin the same temperature range as the thermal de-gradation of wood. We used as a binder water�or-ganic dispersions of various kinds. The componentswere intimately ground and then mixed with a bind-er for 30 min to obtain a homogeneous paste. Assamples served 30 � 60 � 150 mm wood blocks.The FR consumption was 270�300 g m�2. The fireand water-resistance tests were performed accordingto GOST (State Standard) 16 363�98 [1] and GOST16 712�71 [2], respectively.

A DTA analysis of FR-treated wood samples(200 mg) was carried out on a Paulik�Paulik�Erdeyderivatograph at a heating rate of 20 deg min�1. Foranalysis, we used sawdust (3�5 mm) treated withphosphorus�nitrogen-containing formulations (wetweight increment of the fire retardant was 170% rela-tive to dry sawdust) and then dried to constant weightat 45�C. The initial and heat-treated samples wereanalyzed for phosphorus and nitrogen. Phosphorus wasdetermined photocolorimetrically [3], and nitrogen, bythe method described in [4]. X-ray diffraction patternswere obtained using a DRON-3 instrument with CuK

�

radiation (Ni filter) over the 2� range 2��60�.

Currently, phosphorus�nitrogen-containing intu-mescent fire retardants are most widely used for wood.We have developed high-performance green phosp-horus�nitrogen-containing intumescent fire retardantsconsisting of Craymul 2322 vinyl acetate aqueous-or-ganic dispersion [CRAY VALLEY (Italia)], ammo-nium phosphate, a polyol, an organic amide, and or-ganometallic compounds [5]. It was demonstrated that

RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 81 No. 4 2008

PERFORMANCE OF INTUMESCENT FIRE RETARDANT FOR WOOD 705

Table 1. Composition of phosphorus�nitrogen-containing fire retardants and their efficiency for wood (pH 5 of the FRformulation)��

FR � Additives � Weight loss in � Rank of fire retardancycomposition* � to PMA, wt % � fire test, wt % � [GOST (State Standard) 16 363�98]

��PMA (1 + 2 + 3 + 4) � � � 22.9 � SecondPMA + 5 � 10.0 � 14.0 � �

PMA + 6 � 10.0 � 7.2 � FirstPMA + (5 + 6) � 10.0 � 5 + 10.0 � 6 � 5.0 � �

PMA + (5 + 6) � 7.0 � 5 + 10.0 � 6 � 4.5 � �

PMA + (5 + 6) � 5.0 � 5 + 7.0 � 6 � 6.4 � �

��* (1) Craymul 2322, (2) ammonium phosphate, (3) aluminum hydroxide, (4) water, (5) organic amide, and (6) polyol.

Table 2. Phosphorus content in FR-treated samples after water-resistance test��

Dispersion�

Dispersion� �

Viscosity,� Phosphorus content of samples, wt %

� � Polymer** � �� no.* � grade � � mPa s � after test � initial

��1 � HW 1 � VAc � 12 000�20 000 � 7.2 � 9.52 � H474 N � VAc � 9000�14 000 � 4.4 � 9.43 � H400 E8 � VAc � 16 000�20 000 � 4.4 � 7.54 � A-10 � St/A � 200�1000 � 5.2 � 9.55 � A-160 � St/A � 100�800 � 4.8 � 9.86 � H 50 � VAc � 4000�7000 � 5.0 � 8.77 � K 24 � VAc/A � 1500�3500 � 4.7 � 9.58 � K 65 � VAc/A � 1400�4000 � 5.0 � 9.09 � K 200 � VAc/Veo � 3000�7000 � 4.8 � 8.8

10 � A�30 � A � 100�300 � 5.1 � 9.111 � Craymul 2322 (Italia) � VAc � 4800 � 4.1 � 9.112 � Polyvinyl alcohol � PVA � � � 4.7 � 9.213 � B/St 65 � B/St � � � 3.8 � 8.7

��* Sample nos. 1�10: FINNDISP dispersions.

** (A) Acrylate, (B) butadiene, (VAc) vinyl acetate, (Veo) vinyl versatate, and (St) styrene.

the fire retardancy is a function of the FR composi-tion. Fire tests showed that the formulations devel-oped are classed with the First Group in their fire-re-tardant efficiency, and FR-treated wood, with poorlyflammable materials (Table 1) [6].

Fire tests showed (Table 1) that the phosphorus�nitrogen-containing formulation consisting of ammo-nium phosphate, vinyl acetate dispersion, and alumi-num hydroxide (PMA formulation) is characterized bya weight loss of 22.9 wt %. Samples treated withthis formulation meet the requirements for poorlyflammable materials. Introduction of an organicamide (10 wt %) reduces the weight loss from 22.9 to17.2%, whereas introduction of the same concentra-tion of a polyol, from 22.9 to 7.2%. When both ad-ditives were introduced (10 wt % each), the weightloss decreased to the minimal value of 5.0%. The de-

crease in the polyol content from 10 to 7 wt % andin the amide content from 10 to 5 wt % had onlya slight effect on the fire retardancy (weight lossranged from 6.4 to 4.5%).

It is known that introduction of polyvalent or-ganometallic compounds into some fire retardantsimproves the fire retardancy [7, 8]. Our previousresults show that introduction of the inorganic ad-ditives into the phosphorus�nitrogen-containing for-mulations in amount of 2�4 wt % has practically noeffect of the weight loss [6]. We also studied the ef-fects of the nature of aqueous dispersions on the wa-ter resistance of FR-treated wood. With this purpose,we replaced Craymul 2322 vinyl acetate dispersionin the formulation providing the best fire retardancywith other aqueous-organic dispersions. Results ofwater-resistance tests are summarized in Table 2.


706 LUNEVA, PETROVSKAYA

Fig. 1. TG and DTA curves. (�m) Weight loss, (�m/�T ) weight loss rate, and (T ) temperature. Samples: wood treatedwith (a) initial fire retardant formulation and (b) that containing natural oxide additive.

Our results show that the smallest phosphorus lossis observed for HW-1 aqueous-organic dispersion(FINNDISP). With this dispersion, the phosphorus lossis lower by a factor of 1.9 as compared to Craymul2322 (the phosphorus content increases from 18.2 to

34.4 wt %). Note that all the dispersions tested al-lowed keeping the phosphorus content after soakingin water or water treatment in amounts considerablyexceeding (by a factor of 1.9 to 3.6) the critical value(�2%) required for providing the fire retardancy.

Table 3. Chemical analysis of pyrolysis products of wood treated with phosphorus�nitrogen-containing FR formulations��

T, �C�

Weight� Content, wt % � Conservation of element,* wt %

� �� loss �m, % � nitrogen � phosphorus � nitrogen � phosphorus

��Fire retardant (HW-1) dispersion

20 � 0 � 8.0 � 4.5 � 100 � 100200 � 4.8 � 8.4 � 4.7 � 82.5 � 96.4300 � 22.5 � 8.5 � 5.6 � 55.0 � 88.9400 � 48.0 � 8.5 � 7.7 � 42.5 � 88.9500 � 56.6 � 7.8 � 9.2 � 16.3 � 80.0

Fire retardant + 1**

20 � 0 � 7.9 � 4.0 � 100 � 100200 � 6.1 � 8.3 � 5.0 � 97.5 � 100300 � 27.9 � 7.8 � 6.7 � 70.0 � 100400 � 47.4 � 7.8 � 8.9 � 51.3 � 100500 � 54.7 � 7.6 � 10.5 � 42.5 � 100


20 � 0 � 7.9 � 4.0 � 100 � 100200 � 4.2 � 8.1 � 4.3 � 98.7 � 100300 � 25.2 � 6.9 � 5.3 � 65.8 � 100400 � 46.9 � 7.3 � 7.6 � 49.4 � 100500 � 52.7 � 6.9 � 8.7 � 41.8 � 100


20 � 0 � 6.9 � 4.0 � 100 � 100200 � 5.0 � 6.8 � 4.2 � 94.2 � 100300 � 27.2 � 6.5 � 5.5 � 68.1 � 100400 � 48.5 � 6.9 � 7.8 � 52.2 � 100500 � 58.6 � 7.6 � 9.7 � 46.4 � 100

��* Conservation of element is defined as the ratio between the current element content at a fixed temperature (recalculated to

the current weight) and its initial content (before heating).** Additives 1, 2, and 3 differ in the natural oxide content varied within the following ranges (%): SiO2 75�33, Al2O3 0.5�18,

MgO 1�31, and Fe2O3 1�17.


PERFORMANCE OF INTUMESCENT FIRE RETARDANT FOR WOOD 707

Fig. 2. X-ray diffraction patterns of pyrolysis productsof wood treated with the formulation containing naturaloxide additive. (I ) Intensity and (2�) Bragg angle. Pyrolysistemperature (�C): (1) 20, (2) 200, (3) 300, (4) 400, and(5) 500.

Pyrolysis products (20�700�C) of wood treatedwith the fire retardant formulation containing HW-1suspension and some special inorganic additives(5 wt %) were examined by DTA, XRD, and chem-ical analyses. Figure 1 shows DTA curves for the ini-tial fire retardant and that containing some natural ox-ides. Pyrolysis proceeds essentially within the temper-ature range 200�350�C, and the maximal decomposi-tion rate is observed at 275�285�C, 0.93 to 1.02 �m,depending on the formulation. A chemical analysisof the pyrolysis products of the FR-treated woodrevealed that, on heating from 20 to 500�C, the phos-phorus content in the carbonaceous residue increases,and its loss, as recalculated to the reduced mass,decreases for the formulations containing inorganicadditives (Table 3). No weight loss was observedafter pyrolysis (500�C) of wood treated with FR for-mulations containing additives, whereas without ad-ditives, the weight loss was 11.1%. It should bepointed out that the stability of the FR-treaded woodwith respect to nitrogen loss is considerably lower,41.8 to 46.4, depending on the FR formulation. In-troduction of additives into the fire retardant formu-lation proved to have no significant effect on the TGcurves (ash content is 38�41% at 700�C). An X-raydiffraction analysis revealed that, as FR-treated woodis heated, the diffraction peaks of the componentsconstituting the FR formulation disappear, and at500�C, only the peaks of inorganic additives are

observed (Fig. 2). The residue after pyrolysis (500�C)of wood treated with the formulation containing noadditives has no crystalline phases.

CONCLUSIONS

(1) Phosphorus�nitrogen-containing fire retardantdeveloped for wood, containing ammonium phos-phate, a polyol, an organic amide, organometalliccompounds, and HW-1 dispersion, provides high fireretardancy and high water resistance of FR-treatedwood.

(2) Introduction of natural oxide materials intothe protective layer using HW-1 aqueous�organicdispersion has no significant effect on the thermaldegradation of fire-retardant treated wood. Thermaldegradation (weight loss) is observed essentially with-in the temperature range 250�350�C. The ash contentis 38�41% at 700�C.

REFERENCES

1. GOST (State Standard) 16 363�98, Protective Agentsfor Wood: Fire Resistance Test.

2. GOST (State Standard) 16 712�71, Leaching Test ofFire-Retardant Treated Wood.

3. Prodan, E.A. and Shashkova, I.L., Izv. Akad. NaukBSSR, Ser. Khim. Nauk, 1978, no. 4, pp. 79�81.

4. Losev, I.P. and Fedotova, O.Ya., Praktikum po khimiivysokomolekulyarnykh soedinenii (Practical Course ofMacromolecular Chemistry), Moscow: Khimiya, 1962.

5. Luneva, N.K. and Petrovskaya, L.I., Abstracts of Pa-pers, VI Mezhdunarodnaya nauchno-tekhnicheskayakonferentsiya �Energo- i materialosberegayushchieekologicheski chistye tekhnologii� (6th Int. Scientificand Technical Conf. �Energy- and Materials-SavingGreen Technologies�), Grodno (Belarus), November1�2, 2005, p. 175.

6. Luneva, N.K., Petrovskaya, L.I., Vorob’ev, V.K., andDmitrichenko, A.S., Abstracts of Papers, III Mezhdu-narodnaya nauchno-prakticheskaya konferentsiya�Chrezvychainye situatsii: preduprezhdenie i likvida-tsiya� (III Int. Scientific and Practical Conf. �Emer-gency Situations: Prevention and Elimination�), Minsk(Belarus), 2005, vol. 1, pp. 282�283.

7. Korol’chenko, A.Ya. and Petrova, E.I., Zh. Ross.Khim. O�va. im D.I. Mendeleeva, 2003, vol. 47, no. 4,pp. 49�54.

8. Seredina, M.A., Tyuganova, M.A., and Gol’braikh, L.S.,Khim. Volokna, 2001, no. 6, pp. 21�24.

performance of intumescent fire retardant for wood

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