Liquid flame retardant composition

Abstract

A liquid flame retardant composition is in the form of an admixture which includes a phosphate-based flame retardant, ammonium hydroxide and zinc borate. The invention extends to a method of providing a phosphate-based liquid flame retardant composition, to the use of a phosphate-based flame retardant, ammonium hydroxide and a zinc borate in the manufacture of a liquid flame retardant composition, to a cellulosic material treated with the liquid flame retardant composition and to a method of inhibiting strength loss in a cellulosic material when the cellulosic material is exposed to heat.

Claims

1. A method of inhibiting strength loss in a cellulosic material which is in the form of a textile or cloth and that forms part of a composite material, when the cellulosic material is exposed to heat, the method comprising treating the cellulosic material, prior to incorporation of the cellulosic material in the composition material, with an aqueous liquid flame retardant composition, wherein the aqueous liquid flame retardant composition comprises a non-durable or semi-durable phosphate-based flame retardant, ammonium hydroxide and a zinc borate, to provide the cellulosic material with non-durable flame retardancy, wherein the treated cellulosic material after exposure to a heat profile of 100 C. for 90 minutes and then 160 C. for 120 minutes shows a tensile strength, determined in accordance with ISO 13934-1:1999 TextilesTensile properties of fabricsPart 1: Determination of maximum force and elongation at maximum force using the strip method, at least 1.2 times higher than the tensile strength of cellulosic material treated with just the phosphate-based flame retardant, after exposure to the same heat profile.

2. The method of claim 1, wherein the cellulosic material is flax.

3. The method of claim 1, wherein the cellulosic material is cotton.

4. The method of claim 1, wherein the cellulosic material comprises hemp, kenaf, or bamboo fibres.

5. The method of claim 1, wherein the treated cellulosic material is incorporated into a pre-preg.

6. The method of claim 1, wherein the aqueous liquid flame retardant composition is a non-halogenated flame retardant composition, wherein the non-halogenated flame retardant composition comprises a non-halogenated flame retardant as the only flame retardant or as the major flame retardant, and wherein the major flame retardant is the flame retardant present in an admixture in the highest concentration.

7. The method of claim 6, wherein the non-halogenated major flame retardant is the phosphate-based flame retardant or wherein the non-halogenated major flame retardant is present in an admixture with the phosphate-based flame retardant.

8. The method of claim 1, wherein the phosphate-based flame retardant is or comprises a phosphorous-nitrogen compound.

9. The method of claim 1, wherein the phosphate-based flame retardant comprises or is diammonium phosphate, a mixture of diammonium phosphate and urea, an organic phosphorous-nitrogen phosphate compound, a mixture of organic and inorganic phosphorous and nitrogen compounds of which at least one is a phosphate, or a nitrogen-containing phosphoric acid salt, or any mixtures of two or more of the foregoing.

10. The method of claim 1, wherein the aqueous liquid flame retardant composition comprises between 5% and 50% by mass of the phosphate-based flame retardant on a solids basis.

11. The method of claim 1, wherein the aqueous liquid flame retardant composition comprises between 5% and 30% by mass of the ammonium hydroxide.

12. The method of claim 1, wherein the aqueous liquid flame retardant composition comprises between 1% and 25% by mass of the zinc borate.

13. The method of claim 1, wherein the aqueous liquid flame retardant composition comprises between 5% and 40% by mass of the phosphate-based flame retardant on a solids basis.

14. The method of claim 1, wherein the aqueous liquid flame retardant composition comprises between 10% and 30% by mass of the phosphate-based flame retardant on a solids basis.

15. The method of claim 1, wherein the aqueous liquid flame retardant composition comprises between 5% and 25% by mass of the ammonium hydroxide.

16. The method of claim 1, wherein the aqueous liquid flame retardant composition comprises between 8 and 20% by mass of the ammonium hydroxide.

17. The method of claim 1, wherein the aqueous liquid flame retardant composition comprises between 2% and 15% by mass of the zinc borate.

18. The method of claim 1, wherein the aqueous liquid flame retardant composition comprises between 3% and 7% by mass of the zinc borate.

19. A method of inhibiting strength loss in a cellulosic material, selected from the group consisting of flax, cotton, hemp fibres, kenaf fibres and bamboo fibres, which is in the form of a textile or cloth and that forms part of a composite material, when the cellulosic material is exposed to heat, the method comprising treating the cellulosic material, prior to incorporation of the cellulosic material in the composite material, with an aqueous liquid flame retardant composition, wherein the aqueous liquid flame retardant composition comprises a non-durable or semi-durable phosphate-based flame retardant, ammonium hydroxide and a zinc borate, to provide the cellulosic material with non-durable flame retardancy, wherein the non-durable or semi-durable phosphate-based flame retardant comprises or is diammonium phosphate, a mixture of diammonium phosphate and urea, an organic phosphorous-nitrogen phosphate compound, a mixture of organic and inorganic phosphorous and nitrogen compounds of which at least one is a phosphate, or a nitrogen-containing phosphoric acid salt, or any mixtures of two or more of the foregoing, wherein the aqueous liquid flame retardant composition comprises between 5% and 50% by mass of the phosphate-based flame retardant, on a solids basis, wherein the aqueous liquid flame retardant composition comprises between 5% and 30% by mass of the ammonium hydroxide, wherein the aqueous liquid flame retardant composition comprises between 1% and 25% by mass of the zinc borate, and wherein the treated cellulosic material after exposure to a heat profile of 100 C. for 90 minutes and then 160 C. for 120 minutes shows a tensile strength, determined in accordance with ISO 13934-1:1999 TextilesTensile properties of fabricsPart 1: Determination of maximum force and elongation at maximum force using the strip method, at least 1.2 times higher than the tensile strength of cellulosic material treated with just the phosphate-based flame retardant, after exposure to the same heat profile.

Description

EXAMPLE 1

(1) A flame retardant composition in accordance with the invention was prepared. To 183 ml water there was added 140 ml Flammentin TL833. 77 ml ammonium hydroxide (25%) was then added drop-wise with stirring. 17.56 g zinc borate (ZB-223, i.e. 2ZnO.Math.2B.sub.2O.sub.3.Math.3H.sub.2O) was added gradually with stirring. The product was maintained at 35-40 C.

EXAMPLE 2

(2) A flame retardant composition in accordance with the invention was prepared. To 142 ml of water there was added 55.44 g of diammonium phosphate and 101.76 g urea. The solution was heated to 25-30 C. 58 ml ammonium hydroxide (25%) was then added drop-wise with stirring. The solution was heated to 35-40 C. 13.17 g zinc borate (ZB-223) was added gradually with stirring. The product was maintained at 35-40 C.

EXAMPLE 3

(3) A flame retardant composition in accordance with the invention was prepared. To 71 ml of water there was added 27.72 g diammonium phosphate. 29 ml of ammonium hydroxide was then added drop-wise with stirring. The solution was heated to 35-40 C. 6.58 g zinc borate (ZB-223) was added gradually with stirring. The product was maintained at 35-40 C.

EXAMPLE 4

(4) A flame retardant composition in accordance with the invention was prepared. To 114 ml water there was added 116 ml Flammentin MSG. 70 ml of ammonium hydroxide (25%) was then added with stirring. 17.56 g zinc borate (ZB-223) was added gradually with stirring. The product was maintained at 35-40 C.

EXAMPLE 5

(5) A flame retardant composition in accordance with the invention was prepared. To 229 ml of water there was added 175 ml Flammentin KRE. 96 ml of ammonium hydroxide (25%) was then added drop-wise with stirring. The solution was heated to 35-40 C. 21.95 g zinc borate (ZB-223) was added gradually with stirring. The product was maintained at 35-40 C.

EXAMPLE 6

(6) A comparative flame retardant composition not in accordance with the invention was prepared. To 78 ml of water there was added 42 ml of Flammentin MSG. The solution was heated to 35-40 C. 5.27 g zinc borate (ZB-223) was added gradually with stirring. The product was maintained at 35-40 C.

EXAMPLE 7

(7) A comparative flame retardant composition not in accordance with the invention was prepared. To 162.5 ml of water there was added 82.5 ml of Flammentin KRE. The solution was heated to 35-40 C. 10.98 g zinc borate (ZB-223) was added gradually with stirring. The product was maintained at 35-40 C.

EXAMPLE 8TOTAL HEAT RELEASE

(8) The efficacy of the flame retardant composition of the invention was examined using a cone calorimeter in accordance with ISO 5660-1:2002 Reaction-To-Fire TestsHeat release, smoke production and mass loss rate, (Heat flux 35 kW/m.sup.2, horizontal orientation of the cellulosic material (woven flax fabric), spark ignition, two layers of fabric, data reduced to 290 seconds). The flame retardant composition of the invention was compared to a flame retardant or flame retardant composition used in the composition of the invention but excluding ammonium hydroxide and zinc borate, i.e. on its own. Woven flax fabrics were treated with Flammentin TL833 at two levels: intermediate (18-20% on weight of fabric (owf)) and high (23-26% owf). Woven flax fabrics were also treated with the flame retardant composition of the invention prepared in similar fashion to the flame retardant composition of Example 1, using the same concentrations of Flammentin TL833 but with two levels of zinc borate: low (1.6-1.8% owf) and high (4.6-5.1% owf). The total heat release values after 2 minutes and 5 minutes are set out in Table 1.

(9) TABLE-US-00001 TABLE 1 Total heat Flame release retardant Zinc Total heat (5 min) (Flammentin borate release (2 min) (kW .Math. min Sample TL833) level level (kW .Math. min/m.sup.2) /m.sup.2) Flammentin intermediate none 24.2 56.1 TL833 as is Invention flame intermediate low 22.0 45.3 retardant composition Invention intermediate high 15.3 43.8 Flammentin high none 24.9 53.9 TL833 as is Invention flame high low 18.1 47.6 retardant composition Invention flame high high 12.0 17.7 retardant composition

(10) Compared to the Flammentin TL833 as is, the invention flame retardant composition resulted in lower levels of total heat release at 2 and 5 minutes. Compared to the low level, a high level of zinc borate in the invention resulted in a decrease in the total heat release for both concentrations of Flammentin TL833.

EXAMPLE 9PEAK HEAT RELEASE AND SMOKE FACTOR

(11) The peak heat release and smoke factor for each sample were also determined and are shown in Table 2.

(12) TABLE-US-00002 TABLE 2 Peak heat Smoke Flammentin Zinc borate release rate Factor Sample TL833 level level (kW/m.sup.2) (kW/m.sup.2) Flammentin intermediate none 18.8 442 TL833 as is Invention flame intermediate low 18.1 438 retardant composition Invention flame intermediate high 14.9 301 retardant composition Flammentin high none 21.8 521 TL833 as is Invention flame high low 17.8 429 retardant composition Invention flame high high 9.2 195 retardant composition

(13) Compared to the Flammentin TL833 on its own, the invention flame retardant composition resulted in lower peak heat release rates. The peak heat release rate is a measure of how large a fire will grow. Compared to the Flammentin TL833 on its own, the invention flame retardant composition resulted in lower smoke factors.

(14) The smoke factor is a product of the peak heat release rate and total smoke release and compensates for incomplete combustion of flame retardant treated samples. Compared to the low level, a high level of zinc borate in the flame retardant composition of the invention resulted in a lower peak heat release rate and smoke factor for both concentrations of Flammentin TL833 flame retardant.

EXAMPLE 10

(15) Flax samples were treated with the invention flame retardant composition prepared in accordance with Example 5 or with Flammentin KRE on its own or with Flammentin KRE admixed with zinc borate only. Treated samples were exposed to a heat profile in an oven and tensile strength was determined according to ISO 13934-1:1999 TextilesTensile properties of fabricsPart 1: Determination of maximum force and elongation at maximum force using the strip method. The gauge length was 200 mm and the rate of extension was 100 mm/min. The results are shown in Table 3.

(16) TABLE-US-00003 TABLE 3 Tensile Tensile strength - strength - Tensile after after strength - 1.sup.st and 2.sup.nd treatment after 1.sup.st stage stages (N), Sample (N) (N) % loss in brackets Flammentin KRE as 1144 998 162 (86) is Flammentin KRE with 1042 1044 609 (42) no ammonium hydroxide but admixed with zinc borate Invention flame 1138 1113 815 (28) retardant composition Heat profile: 1.sup.st stage: 90 minutes at 100 C., second stage: 120 minutes at 160 C., flax woven fabric.

(17) The fabric treated with the invention flame retardant composition of Example 5 had a percentage loss of tensile strength of 28% after being exposed to the full heat profile compared to 86% for fabric treated with the Flammentin KRE on its own and 42% for fabric treated with the Flammentin KRE admixed with zinc borate.

EXAMPLE 11

(18) Flax samples were treated with the invention flame retardant composition prepared in accordance with Example 4 or with Flammentin MSG on its own or with Flammentin MSG admixed with either ammonium hydroxide or zinc borate, but not both. Treated samples were exposed to a heat profile in an oven and tensile strength was determined according to ISO 13934-1:1999 TextilesTensile properties of fabricsPart 1: Determination of maximum force and elongation at maximum force using the strip method. The gauge length was 200 mm and the rate of extension was 100 mm/min. The results are shown in Table 4.

(19) TABLE-US-00004 TABLE 4 Tensile Tensile strength - strength - Tensile after 1.sup.st and 2.sup.nd after strength - stages treatment after 1.sup.st stage (N), % loss in Sample (N) (N) brackets Flammentin MSG as 1080 1122 591 (45) is Flammentin MSG 1024 520 (49) admixed with ammonium hydroxide Flammentin MSG 1201 795 (34) with no ammonium hydroxide but admixed with zinc borate Invention flame 1177 1238 888 (25) retardant composition Heat profile: 1.sup.st stage: 90 minutes at 100 C., second stage: 120 minutes at 160 C., flax woven fabric.

(20) The fabric treated with the invention flame retardant composition had a percentage loss of tensile strength of 25% after being exposed to the full heat profile compared to 45% for fabric treated with the Flammentin MSG on its own, 49% for fabric treated with the Flammentin MSG admixed with ammonium hydroxide and 34% for fabric treated with the Flammentin MSG admixed with zinc borate.

EXAMPLE 12

(21) Flax samples were treated with the invention flame retardant composition prepared in accordance with Example 1 or with Flammentin TL833 on its own. Treated samples were exposed to a heat profile in an oven and tensile strength was determined according to ISO 13934-1:1999 TextilesTensile properties of fabricsPart 1: Determination of maximum force and elongation at maximum force using the strip method. The gauge length was 200 mm and the rate of extension was 100 mm/min. The results are shown in Table 5.

(22) TABLE-US-00005 TABLE 5 Tensile Tensile Tensile strength - after strength - after strength - 1.sup.st and 2.sup.nd stages treatment after 1.sup.st stage (N), % loss Sample (N) (N) in brackets Flammentin TL833 1318 1395 148 (89) as is Invention flame 1340 1337 361 (71) retardant composition Heat profile: 1.sup.st stage: 90 minutes at 100 C., second stage: 120 minutes at 160 C., flax woven fabric.

(23) The fabric treated with the invention flame retardant composition of Example 1 had a percentage loss of tensile strength of 71% after being exposed to the full heat profile compared to 89% for fabric treated with the Flammentin TL833 on its own.

EXAMPLE 13

(24) Flax samples were treated with the invention flame retardant composition prepared in accordance with Example 2 or with a mixture of diammonium phosphate and urea in the proportions described in Example 2. Treated samples were exposed to a heat profile in an oven and tensile strength was determined according to ISO 13934-1:1999 TextilesTensile properties of fabricsPart 1: Determination of maximum force and elongation at maximum force using the strip method. The gauge length was 200 mm and the rate of extension was 100 mm/min. The results are shown in Table 6.

(25) TABLE-US-00006 TABLE 6 Tensile strength - Tensile Tensile after 1.sup.st and 2.sup.nd strength - strength - stages after treatment after 1.sup.st stage (N), % loss in Sample (N) (N) brackets Mixture of diammonium 1408 1391 362 (74) phosphate and urea Invention flame 1459 1262 449 (69) retardant composition Heat profile: 1.sup.st stage: 90 minutes at 100 C., second stage: 120 minutes at 160 C., flax woven fabric.

(26) The fabric treated with the invention flame retardant composition of Example 2 had a percentage loss of tensile strength of 69% after being exposed to the full heat profile compared to 74% for fabric treated with a mixture of diammonium phosphate and urea only.

EXAMPLE 14

(27) Flax samples were treated with the invention flame retardant composition prepared in accordance with Example 4 or with Flammentin MSG on its own. Treated samples were exposed to a heat profile in an oven and tensile strength was determined according to ISO 13934-1:1999 TextilesTensile properties of fabricsPart 1: Determination of maximum force and elongation at maximum force using the strip method. The gauge length was 200 mm and the rate of extension was 100 mm/min. The results are shown in Table 7.

(28) TABLE-US-00007 TABLE 7 Tensile Tensile strength - strength - Tensile after 1.sup.st and 2.sup.nd after strength - stages treatment after 1.sup.st stage (N), % loss in Sample (N) (N) brackets Flammentin MSG as is 1080 1122 861 (20) Invention flame retardant 1177 1238 1003 (15) composition Heat profile: 1.sup.st stage: 90 minutes at 100 C., second stage: 120 minutes at 145 C., flax woven fabric.

(29) The fabric treated with the invention flame retardant composition of Example 4 had a percentage loss of tensile strength of 15% after being exposed to the full heat profile compared to 20% for fabric treated with the Flammentin MSG on its own.

EXAMPLE 15

(30) Flax samples were treated with the invention flame retardant composition prepared in accordance with Example 1 or with Flammentin TL833 on its own. Treated samples were exposed to a heat profile in an oven and tensile strength was determined according to ISO 13934-1:1999 TextilesTensile properties of fabricsPart 1: Determination of maximum force and elongation at maximum force using the strip method. The gauge length was 200 mm and the rate of extension was 100 mm/min. The results are shown in Table 8.

(31) TABLE-US-00008 TABLE 8 Tensile strength - Tensile Tensile after 1.sup.st and 2.sup.nd strength - strength - stages after treatment after 1.sup.st stage (N), % loss in Sample (N) (N) brackets Flammentin TL833 as 1318 1396 431 (67) is Invention flame 1340 1337 995 (26) retardant composition Heat profile: 1.sup.st stage: 90 minutes at 100 C., second stage: 120 minutes at 145 C., flax woven fabric.

(32) The fabric treated with the invention flame retardant composition of Example 1 had a percentage loss of tensile strength of 26% after being exposed to the full heat profile compared to 67% for fabric treated with the Flammentin TL833 on its own.

EXAMPLE 16

(33) Flax samples were treated with the invention flame retardant composition prepared in accordance with Example 4 or with Flammentin MSG on its own. Treated samples were exposed to a heat profile in an oven and tensile strength was determined according to ISO 13934-1:1999 TextilesTensile properties of fabricsPart 1: Determination of maximum force and elongation at maximum force using the strip method. The gauge length was 200 mm and the rate of extension was 100 mm/min. The results are shown in Table 9.

(34) TABLE-US-00009 TABLE 9 Tensile strength - Tensile Tensile after 1.sup.st and 2.sup.nd strength - strength - stages after treatment after 1.sup.st stage (N), % loss in Sample (N) (N) brackets Flammentin MSG as 1080 1122 865 (20) is Invention flame 1177 1238 1009 (14) retardant composition Heat profile: 1.sup.st stage: 90 minutes at 100 C., second stage: 180 minutes at 145 C., flax woven fabric.

(35) The fabric treated with the invention flame retardant composition of Example 4 had a percentage loss of tensile strength of 14% after being exposed to the full heat profile compared to 20% for fabric treated with the Flammentin MSG on its own.

EXAMPLE 17

(36) Flax samples were treated with the invention flame retardant composition prepared in accordance with Example 1 or with Flammentin TL833 on its own. Treated samples were exposed to a heat profile in an oven and tensile strength was determined according to ISO 13934-1:1999 TextilesTensile properties of fabricsPart 1: Determination of maximum force and elongation at maximum force using the strip method. The gauge length was 200 mm and the rate of extension was 100 mm/min. The results are shown in Table 10.

(37) TABLE-US-00010 TABLE 10 Tensile strength - Tensile strength - after Tensile strength - after treatment 1.sup.st stage after 1.sup.st and 2.sup.nd stages Sample (N) (N) (N), % loss in brackets Flammentin 1318 1396 296 (76) TL833 as is Invention flame 1340 1337 738 (45) retardant composition Heat profile: 1.sup.st stage: 90 minutes at 100 C., second stage: 180 minutes at 145 C., flax woven fabric.

(38) The fabric treated with the invention flame retardant composition of Example 1 had a percentage loss of tensile strength of 45% after being exposed to the full heat profile compared to 76% for fabric treated with the Flammentin TL833 on its own.

EXAMPLE 18

(39) Flax samples were treated with the invention flame retardant composition prepared in accordance with Example 1, or as modified as shown in Table 11 or with Flammentin TL833 on its own. Treated samples were exposed to a heat profile (different from the heat profile used in Example 17) in an oven and tensile strength was determined according to ISO 13934-1:1999 TextilesTensile properties of fabricsPart 1: Determination of maximum force and elongation at maximum force using the strip method. The gauge length was 200 mm and the rate of extension was 100 mm/min. The results are shown in Table 11.

(40) TABLE-US-00011 TABLE 11 Tensile strength - Tensile Tensile after 1.sup.st and 2.sup.nd strength - strength - stages after treatment after 1.sup.st stage (N), % loss in Sample (N) (N) brackets Flammentin TL833 as 1318 1396 148 (89) is Invention flame retardant 1340 1337 361 (73) composition according to Example 1 Invention flame retardant 1187 1287 366 (69) composition according to Example 1, but with lower Flammentin TL833 concentration (~16%) Invention flame retardant 1412 1421 403 (71) composition according to Example 1, but with zinc borate ZB-467 (4ZnO6B.sub.2O.sub.37H.sub.2O) substituted for ZB-223 Heat profile: 1.sup.st stage: 90 minutes at 100 C., second stage: 120 minutes at 160 C., flax woven fabric.

(41) The fabric treated with the invention flame retardant composition of Example 1 had a percentage loss of tensile strength of 73% after being exposed to the full heat profile compared to 89% for fabric treated with the Flammentin TL833 on its own. A lower concentration of Flammentin TL833 (16%) in the flame retardant composition of the invention resulted in a strength loss of 69%, and substituting ZB-467 for ZB-223 in the flame retardant composition of the invention resulted in a strength loss of 71%. The strength losses were lower than for the Flammentin TL833 on its own (89%).

EXAMPLE 19

(42) Flax samples were treated with the invention flame retardant composition prepared in accordance with Example 1, or as modified as shown in Table 12 (see below) or with Flammentin TL833 on its own. Treated samples were exposed to a heat profile in an oven and tensile strength was determined according to ISO 13934-1:1999 TextilesTensile properties of fabricsPart 1: Determination of maximum force and elongation at maximum force using the strip method. The gauge length was 200 mm and the rate of extension was 100 mm/min. The results are shown in Table 12.

(43) TABLE-US-00012 TABLE 12 Tensile strength - Tensile Tensile after 1.sup.st and 2.sup.nd strength - strength - stages after treatment after 1.sup.st stage (N), % loss in Sample (N) (N) brackets Flammentin TL833 as 1318 1396 431 (67) is Invention flame retardant 1340 1337 995 (26) composition according to Example 1 Invention flame retardant 1187 1287 638 (46) composition according to Example 1, but with lower Flammentin TL833 concentration (~16%) Invention flame retardant 1412 1421 652 (54) composition according to Example 1, but with zinc borate ZB-467 (4ZnO6B.sub.2O.sub.37H.sub.2O) substituted for ZB-223 Heat profile: 1st stage: 90 minutes at 100 C., second stage: 120 minutes at 145 C., flax woven fabric.

(44) The fabric treated with the invention flame retardant composition of Example 1 had a percentage loss of tensile strength of 26% after being exposed to the full heat profile compared to 67% for fabric treated with the Flammentin TL833 on its own. A lower concentration of Flammentin TL833 (16%) in the flame retardant composition of the invention resulted in a strength loss of 46%, and substituting ZB-467 for ZB-223 in the flame retardant composition of the invention resulted in a strength loss of 54%. The strength losses were lower than for the Flammentin TL833 on its own (67%).

EXAMPLE 20

(45) Cotton woven fabric samples were treated with the invention flame retardant composition prepared in accordance with Example 1, or as modified as shown in Table 13 (see below) or with Flammentin TL833 on its own. Treated samples were exposed to a heat profile in an oven and tensile strength was determined according to ISO 13934-1:1999 TextilesTensile properties of fabricsPart 1: Determination of maximum force and elongation at maximum force using the strip method. The gauge length was 200 mm and the rate of extension was 100 mm/min. The results are shown in Table 13.

(46) TABLE-US-00013 TABLE 13 Tensile Tensile Tensile strength - strength - strength - after 1.sup.st and 2.sup.nd after treatment after 1.sup.st stage stages (N), % Sample (N) (N) loss in brackets Flammentin TL833 as 910 617 31 (97) is Invention flame 930 911 290 (69) retardant composition according to Example 1 Invention flame 870 870 237 (73) retardant composition according to Example 1, but with lower Flammentin TL833 concentration (~12%) Heat profile: 1.sup.st stage: 90 minutes at 100 C., second stage: 120 minutes at 160 C., cotton woven fabric.

(47) The cotton fabric treated with the invention flame retardant composition of Example 1 had a percentage loss of tensile strength of 69% after being exposed to the full heat profile compared to 97% for fabric treated with the Flammentin TL833 on its own. A lower concentration of Flammentin TL833 (12%) in the flame retardant composition of the invention resulted in a strength loss of 73%. The strength loss was lower than for the Flammentin TL833 on its own (97%).

(48) Cellulosic materials, such as flax and cotton, treated by known conventional methods using the flame retardant composition of the invention surprisingly show a lower loss of strength when exposed to short-term heating compared to cellulosic material treated with a phosphate-based flame retardant on its own, or mixtures of the phosphate-based flame retardant with only ammonium hydroxide or with only zinc borate. When the phosphate-based flame retardant is admixed with zinc borate only, because of its low water solubility, the zinc borate settles out as soon as stirring of the solution ceases.

(49) An advantage of this invention, as illustrated, is that there is lower strength loss of flame-retardant treated cellulosic materials when exposed to short-term heating as would be experienced, for example, in the production of natural fibre-based composite materials. In short, the invention, as illustrated, helps to reduce strength loss of cellulosic materials when exposed to heat. The cellulosic materials treated with the flame retardant composition of the invention showed a tensile strength of between about 1.2 times and about 8 times higher compared to cellulosic materials treated with a phosphate-based flame retardant such as Flammentin KRE on its own.