General properties of amphoteric surfactants

Fang Yunxia Yongmei (School of Chemical Engineering, Wuxi University of Light Industry, Wuxi, Jiangsu, 214036)

Abstract: An introduction to amphoteric surfactants General properties of active agents such as rheology, hydrotropy, calcium soap dispersion and hard water resistance. The relationship between the rheology of amphoteric surfactants and surfactant concentration was discussed, and methods for adjusting the rheology of mixed systems were given. Starting from the mixed micelle theory, the author puts forward new insights into the fact that amphoteric surfactants are better calcium soap dispersants than other types of surfactants. At the same time, the ecological properties of amphoteric surfactants, such as biodegradability, fish toxicity, etc., are also introduced in detail.

Keywords: amphoteric surfactant; rheology; calcium soap dispersion; ecological properties

CLC number: TQ423.3 Document identification code: A Article number: 1001- 1803(2000)06-0047-04

1 Rheology

The viscosity of surfactant solution increases as the concentration of surfactant increases, but sometimes when the concentration further increases The solution viscosity will instead decrease. The relationship between surfactant concentration and surfactant cluster shape has been described in the second lecture. The surfactant solution has spherical micelles at low concentrations, and its rheology is basically similar to Newtonian fluid, so the viscosity is very low. Low. As the surfactant concentration increases, the viscosity increases sharply when the spherical micelles transition to modified spherical shapes, especially rod-shaped micelles. It is expected that this is caused by the overlapping of non-spherical micelles, which reduces the free fluidity of the system. At this time, the solution will exhibit the rheological characteristics of non-Newtonian fluids, or be thixotropic or anti-rheological. As the concentration of the system further increases, the micelles will deform into hexagonal rod-shaped micelles, which are generally called entering the mesophase (M phase). At this time, since the micelles are arranged neatly, it is difficult for the micelles to slip between each other, so the viscosity of the system further increases and the rheology resistance is very strong. When the solution concentration is very high, it will enter the lamellar phase (G phase) and transition to lamellar micelles. Since the slip surface of each layer of micelles in the lamellar micelles moves relatively freely, the viscosity is lower than that of the M phase. Of course, the rheological properties of solutions at various concentrations and micelle shapes vary with surfactant types.

Because the amphoteric surfactants themselves have positive and negative charge centers, the interaction between them makes the critical micelle concentration lower than that of the corresponding anionic or cationic surfactants, and reaches a certain concentration (usually 30 %) will easily form a viscous liquid with poor rheology. By adding a third component to change its micelle structure, it is possible to improve the rheology of amphoteric surfactants, making it possible to obtain a higher concentration of amphoteric surfactant solutions. For example, a certain amphoteric concentrate with good rheology contains 5% to 40% water, 36% to 70% amphoteric surfactant, and 5% to 45% water-soluble non-surface active organic solvent, which can be used in personal care products. Due to the addition of non-surface-active organic solvent, the amphoteric surfactant enters the G phase or L1 phase, resulting in better pumpability and free flow.

40.2% cocamidopropyl betaine mixed with 60/40 propylene glycol/water can make the system in G phase. Adding sulfobetaine amphoteric surfactant, amphoteric glycinate, trimethylglycine, etc. to the betaine amphoteric surfactant with a concentration of ≥40% can also improve the rheology and obtain a liquid with good fluidity and storage properties. stability. ChevalierY. studied the relationship between the molecular structure, micelle structure and rheology of amphoteric surfactants. It is reported that the lamellar phase of a new type of dual long-chain amphoteric surfactant in aqueous solution can instantly form a vesicle dispersion through simple dilution.

2 Hydrotrope

Hydrotrope is a type of substance that can prevent the formation of liquid crystal phase and inhibit the formation of micelle phase. Hydrotropes are often used to maintain the fluid state of surfactant solutions at low temperatures, increase the cloud point of polyoxyethylene nonionic surfactants, and also reduce the critical solution temperature of ionic surfactants, that is, the KP temperature. The hydrotropic property of sodium cocoiminodipropionate is due to the presence of two ionic groups in the molecule, which increases the hydrophilicity of the molecule. Surfactant-type hydrotropes destroy the liquid crystal phase by forming mixed micelles with the main surfactant. Their strong hydrophilic heads increase the hydrophilic repulsion between surfactant mixed molecules and convert the liquid crystal into spherical micelles.

Amphoteric surfactants are hydrotropes for soaps, so they can improve water solubility. Due to the synergistic effect of soaps and amphoteric surfactants on KP temperature, the KP temperature of the mixed system can reach a low value that cannot be reached when the two components exist alone. The mixed system of hexadecanoic acid soap and cetylhydroxysulfopropylbetaine (CHSB) shown in Figure 1 has a positive synergistic effect on KP temperature. The lowest KP temperature of the system is 30°C, which is higher than that of sodium hexadecanoic acid soap. Both the KP temperature (58°C) and the KP temperature of CHSB (89°C) are much lower. Even when the mole fraction of CHSB is 10%, the KP temperature of the mixed system can be reduced to about 50°C.

[1]

Figure 1 Synergistic effect of KP

3 Calcium soap dispersion

Anionic and amphoteric surfactants Some varieties can prevent soap from forming soap scum suspension in hard water. Substances with this function are called calcium soap dispersants. The calcium soap dispersion value of some amphoteric surfactants is the lowest value currently achievable. The calcium soap dispersion value is less than 2% and even difficult to measure. Alkyl betaine has a certain dispersion of calcium soap in hard water, but the calcium soap dispersion of sulfobetaine is better than that of sulfobetaine. The calcium soap dispersion value of amidopropyl sulfobetaine is as low as 2%. Parris[2～5] reported many calcium soap dispersion values ??of sulfobetaine, amidosulfobetaine and sulfobetaine, and pointed out the calcium soap dispersion properties of sulfobetaine and amidosulfobetaine. Better than sulfobetaine. Bisamidobetaine has a strong ability to reduce surface tension and has good calcium soap dispersion. Fang Yun synthesized hydroxysulfobetaine with a polyoxyethylene group on the amide nitrogen in the molecule

:

[6]

As can be seen from Table 2 Phosphobetaine has stronger calcium soap dispersing power than sulfobetaine.

The two major disadvantages of soaps are low low-temperature solubility and poor resistance to hard water. As mentioned above, ionic or amphoteric surfactants serve as hydrotropes, which can lower their KP temperature and increase their low-temperature water solubility. sex. In addition, some varieties of anionic and amphoteric surfactants can prevent soaps from forming soap scum suspensions in hard water.

The earliest proposed calcium soap dispersion mechanism is that the calcium soap dispersant only has a simple dispersion effect on calcium soap. However, it is difficult to explain using this mechanism why the calcium soap dispersant obtained when the calcium soap dispersant is added at different times is different. Experimental facts show that the dispersion effect is different. The calcium soap dispersion mechanism proposed later is that the calcium soap dispersant is inserted into the soap micelles to form mixed micelles. Typical soap micelles are formed in soft water. Once calcium and magnesium ions are added to them, the soap micelles will reverse, resulting in calcium soap precipitation or suspension

When p=1 Or 2, the calcium soap dispersion power is 2%, and the calcium soap dispersion power of the counterpart without polyoxyethylene is 3%.

Zhu Shuixing[7] reported a hydroxysulfobetaine compound with a polyoxyethylene chain introduced into the hydrophobic group. However, if there is a calcium soap dispersant and mixed micelles are formed with soaps, the carboxyl groups of the soap are separated from each other by the calcium soap dispersant, which is not enough to form insoluble calcium and magnesium soaps and cause the micelles to reverse.

Considering the mixed micelle mechanism of calcium soap dispersion and the synergistic effect or compounding effect that may be produced by mixed micelles, it can explain why amphoteric surfactants are more effective than anionic or nonionic surfactants. A better calcium soap dispersant than type surfactant. From the third lecture (see "Daily Chemical Industry" 2000 No. 5"), the intermolecular interaction of the mixed system listed in Table 2

The calcium soap dispersion force is 3%. The calcium soap dispersion power of analogues with a hydrophobic chain carbon number of 18 but no -O-bond is 5%. The calcium soap dispersing power of sulfonium betaine reported by Qin Shanmu [8] is shown in Table 1. He Yuanjun[9] reported

the calcium soap dispersing power of phosphobetaine, see Table 2

. It can be seen from the numerical value of parameter B that the B of the anionic-anionic surfactant mixed system is <-1, the B of the anionic-nonionic surfactant mixed system is -1~-5, and the B of the anionic-amphophilic surfactant mixed system is B=-5～-15. Intermolecular interactions in the formation of mixed micelles

Issue 6, December 2000

Fang Yun et al.: Amphoteric surfactants (4) General properties of amphoteric surfactants< /p>

In terms of surfactants, it is obvious that the anionic-ampoteric surfactant mixed system is the strongest.

The reason is that the cationic groups in amphoteric surfactants can have strong interactions with anionic groups in anionic surfactants similar to anionic-cationic surfactants, and at the same time, the anionic groups carried in amphoteric surfactants can also Maintain the water solubility of the composite system after interaction. In the third lecture, it was also proved that the anionic-ampoteric surfactant mixed system can produce a synergistic effect or an obvious compounding effect in reducing cmc. It is precisely because of this strong intermolecular interaction that the cmc value of the mixed micelles of soap and sulfobetaine amphoteric surfactant is reduced. The reduction of critical micelle concentration means that the monomers of soaps in the solution are reduced, that is, the probability of interaction between soaps and calcium and magnesium ions is reduced, so the calcium soap dispersion power of amphoteric surfactants is higher.

Table 3 lists examples of successful application of cocosulfopropyl betaine (CoSB) amphoteric surfactant as a calcium soap dispersant. Add CoSB to the soap with the brand name "Ivory" and observe the precipitation of calcium soap in 100 mgCaCO3/L hard water when the soap concentration is 0.075%. Experimental results show that a very small amount of CoSB amphoteric surfactant can effectively inhibit the precipitation of calcium soap and improve the foaming properties of soap in hard water. There are many similar application examples reported in the literature.

Table 3 Results of "Ivory" soap after adding CoSB in hard water

"Ivory" soap (w/%)

0.0750.0750.0750.075< /p>

CoSB(w/%)

Proportion

The result is precipitation, no bubbles

0.001500.003750.00750

50 ÷120÷110÷1

No precipitation, medium foam, no precipitation, large foam, no precipitation, large foam

In the medium, carboxybetaine loses soluble organic carbon approximately quantitatively, forming A large amount of CO2, so it is inferred that it has undergone complete biodegradation. According to the Sturm test and Fisher closed bottle test, the results of carboxybetaine are better than those of linear alkyl benzene sulfonate (LAS), which has been accepted as biodegradable. Betaine and amidopropyl betaine are easily biodegradable surfactants. The organic substances contained in this type of product have a BOD28/DOC value of at least 60% in the sealed bottle test, and at least 70% DOC can be removed in the improved cocamide OECD screening test.

The BOD28 value of propyl betaine reached 93% in the OECD301D test. Fernley[10] used Fischer, Sturm and OECD test procedures to study the biodegradability of alkyl betaine and sulfobetaine. In the OECD test, the primary biodegradation of hydroxysulfobetaine was very fast and complete, with a degradation degree of 96% and a verification experiment of 94.8%. However, sulfobetaine was not directly degraded in Fischer and Sturm experiments. The amount of CO2 produced by alkyl betaine in the Sturm test is 81% (C14~15 betaine) and 91% (C12 betaine) of the theoretical amount, while dodecyl sulfobetaine and cetyl sulfobetaine Betaine is 49% and 56% respectively. This may be due to the formation of rather stable intermediates. In the same test, betaine lost 93% to 99% of its initial DOC value, indicating its complete biodegradation without the formation of difficult-to-decompose intermediates. In the Fischer closed bottle experiment, the ratio of oxygen absorbed by betaine to theoretical oxygen was also higher than that of sulfobetaine and hydroxysulfobetaine, confirming the aforementioned results.

The test results using the BOD5/COD method prove that amphoteric imidazoline is a good biodegradable variety. The 20mg/L alkyl amphoteric carboxyglycinate salt solution was tested using the RiverDie test. According to its The reduction in surface activity to determine biodegradability also confirms the above conclusion. According to Re-wo Company's report, the biodegradability of amphoteric imidazoline measured by DIN38412 is 77%, which is an easily biodegradable substance. Henkel's report also believes that amphoteric imidazolines biodegrade rapidly. Test methods include: according to OECD classification, BOD28/COD is at least 60% in the closed bottle test, or at least 70% in the modified OECD screening test

Organic components that meet the above requirements are recognized as Easy DOC removal rate. Biodegradable.

All surfactants, including amphoteric surfactants, have similar aquatic toxicity, with approximately the same typical LC50 values ??(fish and Daphnia toxicity) of 1 mg/L to 15 mg/L. . Acute fish poisoning is reported in the form of LC50, which is 1 mg/L to 10 mg/L (goldfish: DIN38412T15 method, or zebrafish: ISO7346 method). The acute fish poison LC50 (goldfish: DIN38412T15 or spotted fish: ISO7346) of alkyl betaine ranges from 10 mg/L to 100 mg/L. The LC50 of amidopropyl betaine was determined to be 1 mg/L to 10 mg/L using the same method. The LC50 (96h, OECD203) of cocamidobetaine is 2.0mg/L.

The acute and chronic bacterial toxicity of amidopropyl betaine has been studied, and the acute toxicity EC50 (Ps.putida, oxygen consumption test) value is greater than

4 Hard water resistance

The structural characteristics of zwitterionic surfactants determine their strong resistance to electrolytes and therefore their resistance to hard water. The anti-hard water performance of surfactants is mainly reflected in two aspects, namely the dispersion of calcium soap and its own tolerance to calcium and magnesium hard ions. Many betaine amphoteric surfactants show very good stability to calcium and magnesium ions. The Lin-field research team investigated the calcium ion stability of betaine amphoteric surfactants and found that most of the sulfobetaine amphoteric surfactants The calcium ion stability of surfactants is above 1800mgCaCO3/L, which is among the surfactants with the best resistance to hard water. The corresponding secondary amine-based compounds have much lower calcium ion stability values. Fang Yun [8] reported that after introducing polyoxyethylene groups on the amide nitrogen of acylhydroxysulfobetaine, its calcium ion stability can still reach more than 1800 mgCaCO3/L, proving that this type of substance itself is not sensitive to water hardness. Literature reports that the calcium ion stability of C8~16 series N-(3-alkoxy-2-hydroxypropyl) betaine is also greater than 1800mgCaCO3/L, and it has good calcium soap dispersion properties.

5 Ecological properties

From the chemical structure of amphoteric surfactants, it can be inferred that they are varieties with good biodegradability. In the SturmCO2 test and DOC test

100mg/L, the EC50 (72h, OECDEC50 value is the same as the algae growth inhibition test of chronic toxicity (Ps.putida, growth inhibition test). 201) value is 3.3mg/ L.

Sodium tallow tripropylenetetramine pentacarboxymethyl (TN4A5) is a good amphoteric surfactant. Its ecological safety properties have been investigated. The results are shown in Table 4 and Table 5. . In Table 5, the test substance was exposed to the biodegradation products from the coupling test (OECD303A) (see Table 4). The starting concentration of TN4A5 at the beginning of the biodegradation test was 71 mg/L, and the total biodegradation rate reached about 80%. . Fish toxicity tests conducted directly with TN4A5 showed that the EC50 (48h, Daphnia) was 14mg/L and the LC50 (48h, river salmon) was 2.4mg/L.

Table 4 Biodegradability of TN4A5

Test method

1. Closed bottle test (OECD301D, 5 days) 2. Modified SCAS test (OECD302A) 3 .Coupled unit test (OECD303A)

Simulation test

>90.0

Primary biodegradation value measured by HPLC

Intrinsic organisms Degradation

80.0

Expressed as DOC value

Test properties Ready biodegradation

Test result (%) 72.5

The data listed in Table 6 can be seen that the total organic carbon (TOC) of the washing powder containing about 12% surfactant is 116g/kg, and the solid content is 46 The TOC of liquid detergents with about % is 336g/kg, so the high TOC value has become a major disadvantage of liquid detergents.

The recommended dosage of TN4A5 in liquid detergents is 10% to 15%. The TOC value of this amphoteric surfactant-based liquid detergent is only about 107g/kg, which is of great significance to the promotion of liquid detergents.

Table 6 TOC data

Laundry powder liquid detergent

TOC (g/kg)

116

336

Amphoteric surfactant-based liquid detergent

107

References:

[1] Fang Yun. Clough The relationship between point (KP) and cmc, PMAX [J]. Daily Chemical Industry, 1991(1):20-24.

[2]ParrisN.,WeilJ.K.,LinfieldW.M. ,Soapbaseddetergentformula-tion(V)[J].J.ofAmericanOilChemicalSoc.1973,50:509.

[3]ParrisN.,WeilJ.K.,LinfieldW.M.,Soapbaseddetergentformula-tion(XVIII) [J].J.ofAmericanOilChemicalSoc.1976,53:97.[4]ParrisN.,WeilJ.K.,LinfieldW.M.,Soapbaseddetergentformula-tion(XII)[J].J.ofAmericanOilChemicalSoc.1976,53:60.

[5]ParrisN.,PierceC.,LinfieldW.M.,Soapbaseddetergentformula-tion(XII)[J].J.ofAmericanOilChemicalSoc.1977,54:294.[6]Fang Yun.Wuxi Institute of Light Industry Master's degree thesis: Synthesis of new sulfobetaine amphoteric surfactants [D]. 1985.

[7] Zhu Shuixing, Xia Jiding, et al. Synthesis of new alkoxylated sulfobetaine amphoteric surfactants [J]. Daily Chemical Industry, 1995(1):4-8.

[8] Qin Shanmu. Master's thesis of Wuxi Institute of Light Industry: Synthesis and performance research of new sulfur-containing amphoteric surfactants[ D].1985.

[9] He Yuanjun. Master's thesis of East China University of Science and Technology: Research on new phosphate betaine amphoteric surfactants [D].1994.

[10] Fernleyg.W..Zwitterionicsurfactant:structureandperformence[J].J.ofAmericanOilChemicalSoc.1978,55:98.

Table 5 Fish toxicity test method for biodegradation products of TN4A5

1. Oral toxicity (OECD202) 2. Oral toxicity (OECD203)

Test subject Daphniamagna

Zebrafish (Brachydaniorerio)

EC50 (48h) (mg/L)

35.5>71

Excellent biodegradability and low fish toxicity make TN4A5 have good application prospects and can become a green chemical in detergents and personal care products Element. If combined with the low TOC value it brings to the formula, the above conclusion becomes more meaningful.

In recent years, the ecological effects of laundry detergents and liquid detergents have been extensively discussed, starting from

Amphoteric Surfactants IV

General Properties of Amphoteric Surfactants

FangYun　XiaYong-mei

(SchoolofChemicalandMaterialEngineering,WuxiUniversityofLightIndustry,Wuxi　214036,China)

Abstract: Generalpropertiesofamphotericsurfactantswereintroducedsuchasrheologicalproperty,hydrotropicproper-ty,limesoapdispersingabilityandhardwater-resistance.Therelationshipbetweenrhologicalpropertyandconcentrationofamph otericsurfactantswasdiscussed,andthemethodtoadjustrhoogicalpropertyofmixedsystemswasproposed,too. Keywords:amphotericsurfactant;rhologicalproperty;limesoapdispersingability;environmentaspect