Flame retardant composition comprising graphene nanoplatelets

Abstract

A flame retardant composition comprising graphene nanoplatelets and a condensation product of a sulfonated aromatic compound with formaldehyde, wherein the w/w ratio between the graphene and the condensation product is in the range of 1:15 to 4:1. The composition may be in the form of a water dispersion applied to the surface of the article to be treated. The composition has optimal flame retardant properties even when applied in relatively modest quantities.

Claims

1. A flame retardant composition comprising graphene nanoplatelets and a condensation product of a sulfonated aromatic compound with formaldehyde, wherein the weight ratio between the graphene nanoplatelets and the condensation product is from 1:15 to 4:1; wherein a starting mixture of three components that form the condensation product is represented by the following formula: ##STR00003## wherein Ar is a sulfonated aromatic compound selected from the group consisting of: ##STR00004## and X is the cation of a metal that forms a salt with the sulfonated group; R is an alkyl group with from 1 to 12 carbon atoms, linear or branched; p, q and r are the moles of formaldehyde, urea and sulfonated aromatic compound, respectively, with a ratio p/r from 0.2 to 4; and a ratio q/r from 0.5 to 5, in which q can be equal to 0; wherein when q=0 the product is obtained by condensation of a sulfonated aromatic compound and formaldehyde only.

2. The flame retardant composition according to claim 1, characterized in that said condensation product of a sulfonated aromatic compound with formaldehyde has the following formula (II)
(ArCH.sub.2-).sub.n-Ar(II) wherein: n is from 1 to 100.

3. The flame retardant composition according to claim 1, characterized in that said condensation product is a polymer with a molecular weight Mw of up to 15,000.

4. The flame retardant composition according to claim 1, characterized by being in the form of water dispersion wherein the concentration of graphene nanoplatelets is from 1% to 40% by weight of the water dispersion, and the concentration of the condensation product is from 1 to 40% by weight of the water dispersion.

5. The flame retardant composition according to claim 1, comprising nanoplatelets of graphene in water, characterized in that: the C/O ratio in said particles of graphene nanoplatelets is 10:1; at least 90% of said nanoplatelets of graphene have a lateral size (x, y) from 200 to 20000 nm, and a thickness (z) from 0.34 to 30 nm, the lateral size being always greater than the thickness (x, y >z).

6. The flame retardant composition according to claim 5, characterized in that the concentration of said nanoplatelets of graphene is from 5% to 35% by weight of the composition.

7. The flame retardant composition according to claim 3, characterized in that said nanoplatelets of graphene have a lateral size (x, y) from 500 to 10000 nm.

8. The flame retardant composition according to claim 5, characterized in that said nanoplatelets of graphene have a thickness (z) from 0.34 to 20 nm.

9. The flame retardant composition according to claim 5, characterized in that said C/O ratio in said nanoplatelets of graphene is 100:1.

10. The flame retardant composition according to claim 2, characterized in that said condensation product has the formula ArCH.sub.2Ar wherein Ar is the compound of formula (Ia).

11. A polymeric article comprising a flame retardant composition comprising graphene nanoplatelets and a condensation product of a sulfonated aromatic compound with formaldehyde, wherein the weight ratio between the graphene nanoplatelets and the condensation product is from 1:15 to 4:1; wherein a starting mixture of three components that form the condensation product is represented by the following formula: ##STR00005## wherein Ar is a sulfonated aromatic compound selected from the group consisting of: ##STR00006## and X is the cation of a metal that forms a salt with the sulfonated group; R is an alkyl group with from 1 to 12 carbon atoms, linear or branched; p, q and r are the moles of formaldehyde, urea and sulfonated aromatic compound, respectively, with a ratio p/r from 0.2 to 4; and a ratio q/r from 0.5 to 5, in which q can be equal to 0; wherein when g=0 the product is obtained by condensation of a sulfonated aromatic compound and formaldehyde only.

12. The article according to claim 11, wherein said composition forms a coating layer.

13. The flame retardant composition according to claim 1, wherein the weight ratio between the graphene nanoplatelets and the condensation product is from 1:10 to 2:1.

14. The flame retardant composition according to claim 1, wherein the weight ratio between the graphene nanoplatelets and the condensation product is from 1:5 to 1:1.

15. The flame retardant composition of claim 8, wherein said nanoplatelets of graphene have a thickness (z) from 0.34 to 15 nm.

16. The flame retardant of claim 1, wherein X is the cation of an alkali metal.

17. The flame retardant of claim 16, wherein the alkali metal is sodium.

18. The flame retardant of claim 1, wherein the ratio p/r is from 0.5 to 2.

19. The flame retardant of claim 1, wherein the ratio q/r is from 1 to 3.

20. The flame retardant of claim 3, wherein the molecular weight Mw is up to 10,000.

21. The flame retardant of claim 6, wherein the concentration of said nanoplatelets of graphene is from 10% to 20% by weight of the composition.

22. The flame retardant of claim 7, wherein said nanoplatelets of graphene have a lateral size (x, y) from is from 1000 to 5000 nm.

Description

EXAMPLE 1

(1) Preparation of the Dispersion of Graphene Nanoplatelets and Condensation Product (Ratio 1:5) Starting from Graphite.

(2) 50 g of commercial intercalated graphite (hereinafter IG=intercalated graphite) grade ES 250 F5, marketed by Graphit Kropfmhl AG, having a lateral size of approximately 300 m, were expanded by inclusion in an induction plasma having the following characteristics:

(3) type of plasma/auxiliary/carrier gas supply: argon

(4) feed rate (IG): 5 g/min

(5) plasma gas flow: 15 I/min

(6) auxiliary gas flow: 1.5 I/min

(7) carrier gas flow: 1 I/min

(8) RF: 40 MHz

(9) Power: 1400 W

(10) The expansion temperature was 1300 C. and the transit time approximately 0.2 seconds. The resulting expanded graphite (EG) had an apparent density of 2.5 g/l and a C/O ratio of approximately 150:1. The expanded graphite was then dispersed in 1000 mL of deionised water containing the condensation product of sulfonated naphthalene and formaldehyde according to the formula (Ia), marketed under the brand name Setamol WS by BASF AG, as a dispersing agent in quantities of 500% w/w of the expanded graphite, in order to obtain a suspension. The dispersing agent comprised an apolar aromatic group (naphthalene) with a high affinity for graphite, and a (sulfonated) polar group that promotes graphite-water affinity.

(11) For the ultrasound treatment, which induces the exfoliation and dimensional reduction of the expanded graphite, an energy level of 400 W (UIP400S, Hielscher) was applied for a period of 15 hours.

(12) The final dispersion had a graphene nanoplatelets concentration of 5% in w/w and the graphene to dispersant ratio was 1:5. This dispersion was diluted 1:1000 in deionised water and poured drop by drop onto a silicon oxide substrate placed on a plate heated to 100 C. When the substrate was analyzed under the scanning electron microscope (SEM), the graphene nanoplatelets revealed a lateral size in the range of 500-3000 nm, and a thickness in the range of 0.34-15 nm.

EXAMPLE 2

(13) Preparation of the Dispersion of Graphene Nanoplatelets and Condensation Product with Formaldehyde (Ratio 1:2) Starting from Graphite.

(14) The procedure in Example 1 was repeated to obtain the expanded graphite, and then the following variants were introduced.

(15) 100 g of expanded graphite were dispersed in 1000 mL of deionised water containing the condensation product of sulfonated naphthalene and formaldehyde according to the formula (Ia), marketed under the brand name Setamol WS by BASF AG, as a dispersing agent in the amount of 200% w/w of the expanded graphite in order to obtain a suspension. The dispersing agent contained an apolar aromatic group (naphthalene) with a high affinity for graphite, and a (sulfonated) polar group that promotes graphite/water affinity.

(16) For the ultrasound treatment to induce the exfoliation and dimensional reduction of the expanded graphite, an energy level of 400 W (UIP400S, Hielscher) was applied for a period of 30 hours.

(17) The final dispersion had a graphene nanoplatelets concentration of 10% w/w.

(18) The final dispersion was diluted 1:1000 in deionised water and poured drop by drop onto a silicon oxide substrate placed on a plate heated to 100 C. The substrate was analyzed under the scanning electron microscope (SEM) and showed that the graphene platelets had a lateral size in the range of 200-2000 nm, and a thickness in the range of 0.34-10 nm.

EXAMPLE 3

(19) Preparation of the Dispersion of Graphene Nanoplatelets and Condensation Product with Formaldehyde (Ratio 1:1) Starting from Graphite.

(20) The procedure of Example 1 was repeated to obtain the expanded graphite, after which the following variations were introduced.

(21) 200 g of expanded graphite were dispersed in 1000 mL of deionised water containing the condensation product of sulfonated naphthalene and formaldehyde according to the formula (Ia), marketed under the brand name Setamol WS by BASF AG, as a dispersing agent in proportions of 100% w/w of the expanded graphite, to obtain a suspension. The dispersing agent included an apolar aromatic group (naphthalene) with a high affinity for graphite and a (sulfonated) polar group that promotes the affinity between graphite and water.

(22) For the ultrasound treatment to induce the exfoliation and dimensional reduction of the expanded graphite, an energy level of 400 W (UIP400S, Hielscher) was applied for a period of 60 hours.

(23) The final dispersion had a graphene nanoplatelets concentration of 20% w/w and the ratio of graphene nanoplatelets to dispersant was 1:1.

(24) The final dispersion was diluted 1:1000 in deionised water and poured drop by drop onto a silicon oxide substrate placed on a plate heated to 100 C. The substrate was analyzed with the scanning electron microscope (SEM) and it was found that the graphene platelets had a lateral size in the range of 200-1000 nm, and a thickness in the range of 0.34-6 nm.

EXAMPLE 4

(25) Preparation of the Dispersion of Graphene Nanoplatelets and Condensation Product with Formaldehyde (Ratio 1:1)

(26) Pure anhydrous graphene nanoplatelets were obtained with the following characteristics. The lateral sizes of the graphene particles averaged less than 15 m, and the thickness less than 8 nm, with a surface area in the range of 200 and 400 m.sup.2/g. The C/O ratio was higher than 100:1. 100 g of graphene nanoplatelets powder were dispersed in 1000 mL of deionised water containing the condensation product of sulfonated naphthalene and formaldehyde according to the formula (Ia), marketed under the brand name Setamol WS by BASF AG, as a dispersing agent in the amount of 100% w/w of the expanded graphite to obtain a suspension. The dispersing agent consisted of an apolar aromatic group (naphthalene), with a high affinity for graphite, and a (sulfonated) polar group that promotes the affinity between graphite and water. The ingredients were mixed for several minutes with a stirrer or by means of an ultrasound treatment to obtain a homogeneous dispersion. The final dispersion had a graphene concentration of 10% w/w and a graphene to dispersant ratio of 1:1.

EXAMPLE 5

(27) Preparation of a Dispersion of Graphene Nanoplatelets and Condensation Product with Formaldehyde and Urea (Ratio 1:1)

(28) Pure anhydrous graphene nanoplatelets were obtained with the following characteristics. The lateral sizes of the graphene nanoplatelets averaged less than 15 m, and the thickness less than 8 nm, with a surface area in the range of 200 and 400 m.sup.2/g. The C/O ratio was higher than 100:1. 100 g of graphene nanoplatelets powder were dispersed in 1000 mL of deionised water containing the condensation product of hydroxyl benzene sulfonic acid of formula Ig, urea and formaldehyde, marketed by the Chemwill Asia Co. Ltd. This condensation product was used as a dispersing agent in the amount of 100% w/w of the expanded graphite to obtain a suspension. The ingredients were mixed for several minutes with a stirrer to obtain a homogeneous dispersion. The final dispersion had a graphene nanoplatelets concentration of 10% w/w and a graphene nanoplatelets to dispersing agent ratio of 1:1.

EXAMPLE 6

(29) Preparation of a Dispersion of Graphene Nanoplatelets and Condensation Product with Formaldehyde (Ratio 1:1)

(30) Pure anhydrous graphene nanoplatelets were obtained with the following characteristics. The lateral sizes of the graphene particles averaged less than 15 m, and the thickness less than 8 nm, with a surface area in the range of 200 and 400 m.sup.2/g. The C/O ratio was higher than 100:1. 100 g of graphene nanoplatelets powder were dispersed in 1000 mL of deionised water containing the condensation product of naphthalene sulfonic acid (formula Ia) and methyl naphthalene sulfonic acid (formula Ie, with R=methyl) with formaldehyde marketed under the brand name Supragil MNS 88 by RHODIA. This condensation product was used as as a dispersing agent in the amount of 100% w/w of the expanded graphite to obtain a suspension. The ingredients were mixed for several minutes by means of an ultrasound treatment to obtain a homogeneous dispersion. The final dispersion had a graphene nanoplatelets concentration of 10% w/w and a graphene to dispersing agent ratio of 1:1.

EXAMPLE 7

(31) Horizontal Flammability Tests with the Flame Retardant Composition of Example 1

(32) Specimens of rigid polyethylene terephthalate foam (PET, BASF) were prepared in accordance with the standards. Each specimen was subsequently treated with a dispersion of graphene nanoplatelets and dispersing agent prepared as in Example 1, and consequently with a graphene nanoplatelets to dispersing agent ratio of 1:5. The composition was painted over the whole surface of the specimen to obtain a homogeneous coating. The coating was then dried by means of a warm airflow. After drying, the weight of the coating could be calculated from the difference between the weight of the virgin specimen and the weight of the treated specimen, which amounted to 11%. The specimens were submitted to horizontal flammability tests in accordance with ASTM D635. The results are given in Table 1, by comparison with the results obtained for an untreated reference specimen. The table shows the type of coating in terms of the ratio of graphene nanoplatelets to dispersing agent (Specimen), the percentage weight of the coating vis--vis the original untreated specimen (Weight of coating), the time taken by the flame to reach the first reference point at 25 mm (T.sub.1), the time taken by the flame to reach the second reference point at 100 mm (T.sub.2), any flame dropping from the specimen during the test (Drop), any ignition of the cotton under the specimen caused by the drops, if any (Ignition), the initial weight of the specimen consisting of the polymer plus the coating (P.sub.initial), and the final weight of the specimen after the flame test (P.sub.Final).

(33) Table 1 shows that the untreated specimen burns completely, while the specimen coated with the graphene nanoplatelets and dispersing agent does not burn at all, and consequently produces no drops of flame, and thus passes the horizontal test.

EXAMPLE 8

(34) Horizontal Flammability Tests with the Flame Retardant Composition of Example 3

(35) Specimens of rigid polyethylene terephthalate foam (PET, BASF) were prepared and treated as described in Example 7, with the following variations.

(36) The dispersion used to coat the specimens was as described in Example 3, and therefore with a graphene nanoplatelets to dispersant ratio of 1:1, and it was calculated that it amounted to 4% w/w of the initial untreated specimens. The results are shown in Table 1, together with the results obtained with the untreated specimens (As is) and those of Example 7. Here again, there was no ignition of the specimen, which did not burn at all, it developed no flaming drops, and it passes the horizontal flame test. It should be noted that using a formulation with a graphene nanoplatelets to dispersant ratio of 1:1 enables a considerable reduction in the weight of the coating, while retaining the same flame retardant properties of the composition.

EXAMPLE 9

(37) Horizontal Flammability Tests with the Flame Retardant Composition of Example 5

(38) Specimens of rigid polyethylene terephthalate foam (PET, BASF) were prepared and treated as described in Example 7, with the following variations.

(39) The dispersion used to coat the specimens was as described in Example 5, and therefore with a graphene nanoplatelets to dispersant ratio of 1:1, and it was calculated that it amounted to 3.4% w/w of the initial untreated specimens. The results are shown in Table 1, together with the results obtained with the untreated specimens and those of Example 7. Here again, there was no ignition of the specimen, which did not burn at all, it developed no flaming drops, and it passed the horizontal flame test. It should be noted that the use of a formulation with a graphene nanoplatelets to dispersing agent ratio of 1:1 allows to achieve a considerable reduction in the weight of the coating, while retaining the same flame retardant properties of the composition.

EXAMPLE 10 CAS: 68425-94-5 (1:1)

(40) Horizontal Flammability Tests with the Flame Retardant Composition of Example 6

(41) Specimens of rigid polyethylene terephthalate foam (PET, BASF) were prepared and treated as described in Example 7, with the following variations.

(42) The dispersion used to coat the specimens was as described in Example 6, and therefore with a graphene nanoplatelets to dispersing agent ratio of 1:1, and it was calculated that it amounted to 10.1% w/w of the initial untreated specimens. The results are shown in Table 1, together with the results obtained with the untreated specimens and those of Example 7. Here again, there was no ignition of the specimen, which did not burn at all, it developed no flaming drops, and it passed the horizontal flame test. It should be noted that the use of a formulation with a graphene nanoplatelets to dispersing agent ratio of 1:1 allows to achieve a considerable reduction in the weight of the coating, while retaining the same flame retardant properties of the composition.

(43) TABLE-US-00001 TABLE 1 HORIZONTAL TEST Flame retardant Weight Speci- composi- of T.sub.1 T.sub.2 Igni- P.sub.Initial P.sub.Final men tion coating (s) (s) Drop tion (g) (g) Un- none 0 35 110 Yes Yes 14.36 0 treated Example Example 1 .sup.11% 0 0 No No 17.50 17.40 7 (1:5) Example Example 3 4% 0 0 No No 15.54 15.45 8 (1:1) Example Example 5 3.4% 0 0 No No 15.43 15.43 9 (1:1) Example Example 6 10.1% 0 0 No No 16.97 16.97 10 (1:1)

EXAMPLE 11

(44) Vertical Flammability Tests with the flame retardant composition of Example 1

(45) Specimens of rigid polyethylene terephthalate foam (PET, BASF) were prepared and treated as described in Example 5, with the following variations.

(46) The dispersion used for the coating was as described in Example 1, and therefore with a graphene nanoplatelets to dispersing agent ratio of 1:5, and it was calculated at 11% w/w of the initial untreated specimen. The results are given in Table 2. In this case, there was ignition of the specimen, which burned completely, generating flaming drops that fell onto the cotton underneath. The ratio (1:5) and the weight of the coating 11% were not sufficient to pass the vertical test.

EXAMPLE 12

(47) Vertical Flammability Tests with the Flame Retardant Composition of Example 2

(48) Specimens of rigid polyethylene terephthalate foam (PET, BASF) were prepared and treated as described in Example 7, with the following variations.

(49) The dispersion used for the coating was as described in Example 2, and therefore with a graphene to dispersing agent ratio of 1:2, and it was calculated at 26% w/w of the initial untreated specimen. The results are given in Table 2. In this case, there was ignition of the specimen, but the flame front advanced more slowly. There were also no flaming drops during the test and the weight loss due to the test was only 1.5%.

EXAMPLE 13

(50) Vertical Flammability Tests with the Flame Retardant Composition of Example 3

(51) Specimens of rigid polyethylene terephthalate foam (PET, BASF) were prepared and treated as described in Example 7, with the following variations.

(52) The dispersion used for the coating was as described in Example 3, and therefore the graphene to dispersing agent ratio was 1:1, and was calculated at 14% w/w of the initial untreated specimens. The results are given in Table 2. In this case, there was no ignition of the specimen. Nor were there any flaming drops developing during the test, so the specimen complies with the classification V0.

(53) TABLE-US-00002 TABLE 2 VERTICAL TEST Flame retardant Weight Speci- composi- of T.sub.1 T.sub.2 Igni- P.sub.Initial P.sub.Final men tion coating (s) (s) Drop tion (g) (g) Example Example 1 11% 1 Si Si 17.40 0 11 (1:5) Example Example 2 26% 2 22 No No 19.12 18.85 12 (1:2) Example Example 3 14% 0 0 No No 17.05 17.0 13 (1:1)
Comments

(54) Horizontal flammability tests were carried out with the flame retardant compositions of Example 1, 3, 5 and 6 used in different amounts to form a flame retardant coating on a plastic specimen. The test was passed in each case.

(55) Vertical flammability tests were carried out with the flame retardant compositions of Example 1, 2 and 3, used in different amounts to form a flame retardant coating on a plastic specimen. The test was passed in the case of the flame retardant compositions of Examples 2 and 3. Example 11, which used the flame retardant composition of Example 1, passed the horizontal test but did not pass the vertical test. It is nevertheless a useful flame retardant composition since certain applications require that only the horizontal test is passed.