CA1337435C - Foaming agent - Google Patents

Abstract

A foaming agent comprising a blend of alkyl sulfates and alkyl ether sulfates having an improved foaming performance. The blend has the general formula:
Rx- (OCH2CH2)y-OSO3M wherein at least 90% of x is between 8 and 10. The Rx forms an alkyl chain that is either linear and/or branched and the average y is between 0.4 and 1.3. M is a cation producing a water soluble surfactant. A method of using these foaming agents in the making of gypsum products and in the resulting gypsum products is also disclosed. The foaming agents may also be used for other purposes, for instance, as fire fighting foams.

Description

- 2 - , The invention relates to an improved foaming agent having a greater capacity for producing foam. This invention is particularly directed to such foaming agents to be used in the making of gypsum products and to the products so made, to other end uses, for instance, fire fighting foams.
PRIOR ART
Samuel Cukier, in C.P. 1,085,880 dated 16 September 1980 and in U.S. 4,156,615, discloses an alkyl ether sulfate having an improved performance for the manufacture of gypsum, wherein said alkyl ether sulfate is:
CH3(cH2)xcH2-(ocH2cH2)y OS03M
in which:
CH3(CH2)xCH2 is the alkyl group (OCH2CH2)y is the ether group M is the cation (NH4 or Na) wherein x is between 6 and 8, and has an average value of 6.5-7.5 and y is between 1.5 and 2.5 (which herein is also referred to as Type A).
It should be noted that: in Cukier's patent the performance is measured on the basis of the stiffening time of the gypsum slurries (Example 1), heat savings (Example 2) and reduced product consumption to achieve similar thermal set times (Example 3).
U.S. 4,678,515 as invented by Green et al discloses surfactants with improved foaming properties by means of mixing about 11 to 33% of alkyl ether sulfates in which x =
10 to 12 and y = 1 to 3.0, with surfactants of Type A as described above to obtain an average x between 6 to 12.
In Green et al's patent performance is measured on the *

basis of the amount of foam and foam stability produced by the surfactants when added to the supernatant liquid of a saturated gypsum solution, as seen in column 2, line 34 of the patent, from which gypsum, which is mainly composed of calcium sulfate, has been removed. By operating in this manner, the foaming tests are conducted in the presence of a constant or "static" amount of Ca ions, which is determined by the solubility product of calcium sulfate.
Alkyl ether sulfate surfactants are sensitive to Ca ions: they react to form the calcium salt of the ether sulfate which may be water insoluble.
In a Ca ion "static" system, as that used by Green et al to conduct the foaming tests, when a free Ca ion reacts with the ether sulfate to form an insoluble surfactant, the reacted Ca ion cannot be replaced by another Ca ion, as governed by the solubilty product because the source of Ca ions, i.e, gypsum, has been removed from the system.
In the actual manufacturing of gypsum board, the ether sulfate is exposed to a continuous flow of Ca ions, in the sense that for every free Ca ion removed from solution due to reaction with ether sulfate, another Ca ion is supplied by the gypsum material (to maintain constant the solubilty product) which, in turn, may form another insoluble Ca surfactant, and so on.
As a result of this, the foaming profile of an ether sulfate surfactant may be different in a "static " foaming test and in the actual manufacturing of gypsum board, specially if the "static" foaming test is carried-out under conditions in which the surfactant is tested using great amounts of surfactant relative to the amount of free and/or replaceable Ca ions than the foaming agent may encounter during the actual manufacturing of gypsum board.
It should be borne in mind that in the Green et al patent there is not indication o-f the performance of the foaming agents on the actual manufacturing of gypsum material made from gypsum slurries in terms of foam entrained in finished gypsum, as in the real manufacturing, i.e. when the foaming agent is exposed to a continuous flow of free Ca ions. In fact, Green et al best results are obtained when the foamers are evaluated in "static" foaming tests with large amounts of surfactants, i.e. undér excess of foaming agent relative to the "static" amount of Ca ions.
'1'~; lN V~. LlON
Broadly stated, the invention is directed to a foaming agent comprising a blend of alkyl sulfates and alkyl ether sulfates having an improved foaming performance, wherein said blend has the general formula:
Rx ~ (OCH2CH2 ) y~OS03M~ wherein at least 90% of x is between 8 and lO, said Rx forming an alkyl chain selected from at least one member of the group consisting of linear and branched chains, the average y is between 0.4 and 1.3, and wherein M is a cation producing a water soluble surfactant.
The invention i6 also directed to an improvement in a method of making gypsum board using a blend of alkyl sulfates and alkyl ether sulfates having the general formula:
Rx ( CH2 CH2 ) y OS03M as described above, the improvement comprising mixing with gypsum a catalytic amount of said sulfates, wherein at least 90% of x is between 8 and 10, said Rx forming an alkyl ch~in selected from at least one member of the group consisting of linear and branched chains, the average y is between 0.4 and 1.3 and wherein M is a cation producing a water soluble surfactant.
The invention is also directed to a new gypsum product containing the residual foaming agent as defined above. The improved foaming performance can be evidenced, for instance, from Table III and IV on pages 12 and 13.

~K~KK~V WAY OF CAKK~lNG OUT THE lNv~NllON
A preferred way of carrying out the invention consists in reacting in a molar ratio in the order of 0.4-1.3:1 and most preferably 0.8:1 ethylene oxide with linear and/or branched fatty alcohols having at least 90~, preferably 98%

and more, of 8-lO carbon atoms, in the presence of a catalyst to incorporate the ethylene oxide groups. Typical examples of such catalysts include NaOH and KOH. Once the ethylene oxide groups are incorporated, the ethoxylated fatty alcohols are then sulfated with a sulfating agent and then neutralization is accomplished to obtain directly the new foaming agent.
Typical examples of a cation producing a water soluble surfactant includes sodium, potassium, calcium, magnesium and the like, and preferably ammonium.

The foaming agent i6 preferably diluted with a carrier wherein the foaming agent i6 the ma;or constituent, i.e. at least 50%. Typical carriers are preferably alcohols having low molecular weight such as methanol, ethanol, propanol.
` This foaming agent is particular useful in the making 3~ of gypsum board and used in catalytic amounts. Preferably that catalytic amount is 0.03+0.01% per 100 parts of stucco as determined by the (CTFA) method 8-1 of the Cosmetic Toiletry & Fragrance Association of Washington, D.C. This foaming agent is generally used for such a purpose in a diluted form such as those described hereinbelow.
The novel product contains a greater % foam in gypsum product with respect to the amount on weight basis of foaming agent.
OT~R MEANS OF CAKK~lNG OUT THE lN V~N'l'lON

There are other indirect ways of carrying out the invention such as by blending fatty alcohols with ethoxylated fatty alcohols to obtain the average y of between 0.4-1.3 and preferably 0.7-0.9, followed by sulfation of the blend with a sulfating agent and then neutralizing the mixture, or by reacting fatty alcohols with a sulfating agent neutralizing it and blending this reaction product with an alkyl ether sulfate to obtain the average y of between 0.4-1.3 and preferably 0.7-0.9.
The following examples will serve to illustrate particular embodiments of the invention.

The foaming agent of Example 1 was prepared by blending 25% of the ethoxylate of Sample A with 75% of a linear fatty alcohol wherein at least 90% of x is between 8 and 10 and having 0 as y value (which we will call Sample E) and then sulfating the blend.
The foaming agent of Example 2 was prepared by blending 50% of Sample E and 50% of the ethoxylate of Sample A and then sulfating the blend.

The foaming agent of Example 3 was prepared by the direct method.
The foaming agent of Example 4 was prepared as in Example 3 but replacing approximately 50% of linear octanol by an equivalent amount of branched ethyl hexanol.
The foaming agent of Example 5 was prepared by blending 25% of Sample E and 75% of the ethoxylate of Sample A and then sulfating the blend.
The foaming agent of Example 6 was prepared by blending 50% of the ethoxylate of Example 3 and 50% of the ethoxylate of Sample A and then sulfating the blend.
THE GYPSUM BLOCR METHOD
Using a method simulating the manufacture of gypsum wallboard, gypsum blocks were made as follows:
1. The foaming agent is diluted in water to obtain a solution having a concentration of 0.50% for a 100% active basis alkyl ether sulfate wherein at least 90% of x is between 8 andl0 and the average y is as shown in Table 1.
2. The following blend is then prepared: 10g of above solution; 145g of water; 200g of stucco; and about 2g of additives normally used in the manufacturing of wallboard, such as binders, accelerators, etc.
3. The above blend is allowed to stand for 30 sec. and then mixed for 15 sec. in a Hamilton Beach Mixer.

4. The resulting slurry is poured into plastic moulds.
The blocks are then dried at 43C for 48 hrs.

5. The performance of the foamers i~ measured in terms of % foam entrained in the blocks. This value is obtained via a simple mathematical calculation which considers the weigh of the blocks before and after drying and the density of stucco. The % foam of the gypsum blocks is shown in Table _ - 8 -1, Examples 1-6.
The same was carried out according to the prior art:
Sample A using Cukier's patent.
Samples C and D using amongs the best species of Table 52 of Green et al patents i.e. Material Tested I and IV of Table 2 Column 2 of the patent.
Results are shown in Table 2, as Samples A, C and D.

y average % volume foam Ether in gypsum ExamPle Group Blocks 1 0.4 25.6 2 0.8 26.4 3 0.8 26.4 4 0.8 26.0 1.3 26.1 6 1.3 25.8 1 33743~

x value y average % foam in Sample (Alkyl qroup) (Ether group) gypsum blocks A) Cukier's about 50% by 2.2 24.4 patent weight of x=6 and 50% of x=8 B) about 50% by 3.0 23.0 weight of x=6 and 50% of x=8 C) As per Table 2, Example I of Green et al's patent a mixture of surfactant of Sample A and 12.5% of surfactant having about 67% of x=lO
with an average y value of 1.2 22.S
D) As per Table 2, Example IV of Green et al's a mixture of 75% of Sample B
and 25% of surfactant having about 67% of x=lO and 33% of x = 12 with an average y value of of 3.0 19.9 The performance of the foaming agents as can be clearly seen, are directly assessed by the actual making of gypsum products, i.e. blocks, and measuring in the gypsum blocks, the "% volume of foam" which relates to the amount of air entrained in the blocks. This is contrary to the prior art that use arbitrary and indirect methods. According to this test in the making of the gypsum blocks containing the foaming agent left as residuum, the higher the % volume of foam the lighter the block and, therefore, the better the performance of the foamer.

-As can be seen, Example 1 of Green et al produces a gypsum block having 22.5% volume foam (our sample C).
Example IV produces a gypsum block having 19.9% volume foam (our sample D). Cukier's product yields a gypsum block having 24.4% volume foam, as compared to applicant's product of 25.8 to 26.4%. This means substantial improvement of applicant's product and particularly improvement of 10-25%
over the products made according to the Green et al's teaching. No foaming agent is taught in the prior art which shows the % volume foam in gypsum blocks that is equal to those shown in Examples 1-6. It is clear that foaming agents comprising a blend of alkyl ether sulfates as described in Examples 1 to 5 have substantial improved foaming performance.
Such a result cannot be obtained when following Green et al's patent (19.9-22.5%) an even when following Cukier's patent.
Applicant has also determined the distribution ratio of the oxyethylene oligomers of the foaming agents by High Performance Liquid Chromotography (HPLC).
RX (OCH2CH2)y~OH

y=o ~(CH2CH2)y~H
y=n n = 0, 1, 2, 3, 4, 5, ..... 12 The denominator represents the total oligomeric content.

Results are shown in Table III in % weight and Table IV in % mole, where a Sample E when y=0 and a new Sample ~ when y=3 were introduced to clearly demonstrate applicant's invention.

As seen herein below, the distribution ratio of the oligomers is an important characteristic of the foaming agents since the distribution affects both the sensitivity to Ca ions and the intrinsic foaming performance of the foaming agents.

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It is clear from Table III that best performance in %
foam gypsum blocks is when the % weight ratio is between 85 and 25 for the oligomer y=o and 96 to 80 for y = the sum of oligomers from 0 to 5.
It is also clear from Table IV that the % mole must be for y = the sum of oligomers from 0-3 of between 70 to 92.
It is also clear that applicant's invention yields a foaming agent having improved foaming performance. The % foam in the gypsum block as made herein, having at least 25.6% foam as compared against 19.9 - 22.5 for Green et al and 24.4 for Cukier's patent according to the above test.
In summary two criteria are of the outmost importance to produce a foaming agent having improved foaming performance in the making of gypsum panels: the carbon length of the alkyl group Rx and the degree of ethoxylation.
The alkyl group is determined by x, and ideally x should be between 8 and 10. However since the foaming agents are usually made from industrial grade fatty alcohols of mixed carbon lengths, it is from a practical purpose acceptable to have at least 90%, but preferably 98% and more, of said x between 8 and 10. Other carbon lengths for which x is not between 8 andlO, particularly those greater thanlO are detrimental and inhibit the foaming properties, since in the presence of gypsum products, when y is low the sulfates having x greater than 10form a water insoluble product with gypsum that precipitates out of the water, and as it precipitates out, additional amounts of the water soluble foaming agent react with additional amounts of the 30 A gypsum products to cause further precipitations, and thereby to that extent reducing the effectiveness of the blend as a foaming agent. This problem increases as the length of x increases, (over x=10). This problem is effectively evaluated only when the foaming agent for gypsum products is evaluated in situ with the gypsum products (the CaSO4 reacting). Any simulation with a clear solution of CaSO4 does not give the concentration and equilibrium in production lines.
The average y must be between 0,4 and 1.3 as illustrated in Table III and IV.
Alkyl ether sulfates are sensitive to Ca ions, they may react to form the calcium salt of the ether sulfate which depending upon the length of the alkyl group (x) and the degree of ethoxylation (y) may be water insoluble, and thereby may produce low foamers.
If we go back to prior art, Green at al patent is based on their claim that enhanced foaming performance is obtained when ether sulfates having an alkyl group in which x is lO
to 12 are added to ether sulfates in which x=6 to 8.
According to Green, "this is quite surprising since compounds in which x-lO to 12 are poor foam generators compared to their homologs in which x=6 to 8" (column 2, lines 19-22). This foam enhancement is based on foaming tests conducted with saturated gypsum solutions from which gypsum has been removed before the foaming test is done:
our application ~hows that the ether sulfates covered by Green are inferior to our foamers when their performance is measured not in foaming tests but in the making of gypsum ~ blocks using recipes typical of gypsum board manufacturing, as in the real life. This is clearly stated on Table 2.

Nost important is that our patent application is pointing away from Green et al regarding the composition of the alkyl group. In Green et al patented foamers, the content of the alkyl group in which x=6 to 8 must be 89%
maximum and 67% minimum, and the rest must be x=10 to 12.
(column 6, lines 53 to 60). We teach the opposite, i.e., the content of the alkyl group in which x=8 tolO must be 90%
minimum.
This is a key and a very clear difference: for Green, when a minimum of 11% of a foamer having x=10 to 12 is added to a foamer having x=6 to 8, the result is a product with enhanced foaming performance. For us, the result is the opposite, i.e. inferior performance. As a result, what for Green is a must (ie, addition of at least 11% of ether sulfates in which x=10 to 12) for applicant is something to be totally avoided (ie, 10% is the most - not the least -which is tolerable for x other than 8 to 10).
The degree of ethoxylation or y value of the ether group is also very important because the sensitivity of the foaming agents to the Ca ions and its intrinsic foaming profile is also affected by the value of y: As the y value increases, the sensitivity of the foaming agents to the Ca ions decreases, but its intrinsic foaming characteristic that is of the essence, also decreases. Therefore, finding the right balance between low Ca ion 6ensitivity and high foaming characteristics, i.e., the y value is key in a foaming agents intended for wallboard manufacturing. Cukier patent excludes foamers in which the y value is less than 1.5. We are teaching a y value between 0.4 and 1.3, i.e.
completely different to Cukier's range.

_ - 17 - , The reason for this difference is clearly shown in our Tables III and IV. Sample A is the core of Cukier's patent (y value of 2.2). Sample E is outside Cukier's patent (and Green) since y=0. Our examples 1, 2, and 4 were prepared by blending appropriate proportions of samples A and E. In other words, the blending of Cukier's product with an inferior foamer resulted in a synergistic effect, since the blends were superior to the individual products. This is clearly illustrated in Tables III and IV.
Having described the invention, modifications will be evident to those skilled in the art without departing from the spirit of the invention, as defined in the appended claims.

Claims (15)

1. A foaming agent comprising a blend of alkyl sulfates and alkyl ether sulfates having an improved foaming performance, wherein said blend has the general formula:

RX-(OCH2CH2)y-OSO3M
wherein at least 90% of x is between 8 and 10, said Rx forming an alkyl chain selected from at least one member of the group consisting of linear and branched chains, the average y is between 0.4 and 1.3, and wherein M is a cation producing a water soluble surfactant.

2. The foaming agent as defined in claim 1 wherein at least 98% of said x is between 8 and 10.

3. The foaming agent as defined in claim 1 wherein, on a weight percent distribution of the oxyethylene oligomers, the oligomeric species in which y=o is between from 85 to 25% and the sum of oligomeric species from y=o to 5 is between 96 to 80% of the total oligomeric content.

4. The foaming agent as defined in claim 1 wherein said average y is 0.7 to 0.9.

5. The foaming agent as defined in claim 1 wherein M is selected from the group consisting of ammonium, sodium, potassium, calcium and magnesium.

6. The foaming agent as defined in claim 3 being an ammonium alkyl ether sulfate.

7. The foaming agent as defined in claim 1 wherein on a mole percent distribution of the oxyethylene oligomers, the sum of oligomers from y=o to 3 is between from 92 to 70% of the total oligomeric content.

8. The foaming agent as defined in claim 1 wherein said R is a linear chain.

9. The foaming agent as defined in claim 1 wherein the %
foam in gypsum blocks, using the gypsum block method, is at least 25.6%.

10. The foaming agent as defined in claim 1 being diluted with a carrier, said foaming agent being the major constituent.

11. The foaming agent as defined in claim 1 wherein said carrier is a member selected from the group consisting of low molecular weight alcohols.

12. In a method of making our improved gypsum board using an alkyl ether sulfate having the formulation:
Rx-(OCH2CH2)y-OSO3M
the improvement comprising mixing with gypsum a catalytic amount of the product of claim 1.

13. The method as defined in claim 9 wherein said catalytic amount is 0.03% + 0.01 per 100 parts of stucco on finished product, as determined by CTFA method 8-1 of the Cosmetic Toiletry and Fragrance Association of Washington D-C.

14. The method as defined in claim 12 wherein said catalytic amount is added in the form of foaming agent diluted in a carrier, said foaming agent being the major constituent.

15. An improved gypsum product containing the foaming agent as defined in claim 1, left as a residuum.