CC BY
19
Раздел 02.00.13
Нефтехимия
УДК 661.1851 DOI: 10.17122/bcj-2021-1-51-55
И. М. Брудник (к.х.н., специалист-химик) 1, А. Г. Латыпов (к.т.н., доц.) 2
ОЦЕНКА НЕИОНОГЕННЫХ ПОВЕРХНОСТНО-АКТИВНЫХ ВЕЩЕСТВ КАК ПОТЕНЦИАЛЬНЫХ
ЭМУЛЬГАТОРОВ
Талмолдер Инк., отдел развития компании 325 Limestone Crescent, North York, ON M3J 2R1, Торонто, Канада; тел. +1(416)066486496 Уфимский государственный нефтяной технический университет, кафедра «Механика и конструирование машин» 450062, г. Уфа, ул. Космонавтов, 1; тел. (347)2431832; e-mail: aglat52@mail.ru
I. M. Brudnik 1, A. G. Latypov 2
EVALUATION OF NONIONIC SURFACTANTS AS POTENTIAL EMULSIFIERS
Talmolder Inc.
325 Limestone Crescent, North York, ON M3J 2R1, Canada; ph. +1(416)6485496 Ufa State Petroleum Technological University 1, Kosmonavtov Str., 450062, Ufa, Russia; ph. (347)2431832; e-mail: aglat52@mail.ru
Обсуждается способность неионогенных поверхностно-активных веществ (НПАВ) к эмульгированию минеральных масел в водной среде, т.е. образованию эмульсии прямого типа (масло в воде). На примере оксиэтилированных алкилфенолов установлено, что эмульгирующая способность НПАВ зависит не только от числа групп окиси этилена в их молекуле, но и от химического состава минерального масла (дисперсной фазы эмульсии). Для подбора эффективных и наиболее предпочтительных пар: эмульгатор (НПАВ) — дисперсная фаза (минеральное масло) предлагается использовать показатель «водное число». Установлены пределы изменения критерия, определяемого соотношением показателей «водного числа» НПАВ и минерального масла, которые соответствуют их физико-химической совместимости и образованию стабильной эмульсии.
Ключевые слова: «водное число»; гидрофиль-но-липофильный баланс; минеральное масло; оксиэтилированные алкилфенолы; поверхностно-активные вещества, эмульгатор; эмульсия «масло в воде».
The selection of an appropriate surfactant for emulsion stabilization is normally made through trial and error. It was a time-consuming procedure depending on the skills and experience of an individual formulator.
In order to rationalize the surfactant selection, a quantitative concept of the hydrophile-lipophile balance (HLB) in
Дата поступления 17.12.20
The emulsifiability of nonionic surfactants towards mineral oils is discussed. It was established that the emulsifiability of ethoxylated alkylphenols / alkyphenol ethoxylates (APEOs) as their compatibility with mineral oils (MOs) depend on the degree of ethoxylation and the chemical character of oil. The emulsifiability of APEOs as emulsifiers of oil-in-water (O/W) emulsions can be expressed through the relationship of the water number (WN) of APEO to the (WN) of MO. This relationship assists the selection of the most suitable pair (emulsifier-oil) for a stable o/w emulsion formation.
Key words: alkylphenol ethoxylates (APEOs); emulsifiability; emulsifier; hydrophile-lipophile balance (HLB); mineral oils (MOs); oil-in-water (o/w) emulsions; surfactants; water number (WN).
surfactant molecule has been introduced by William Griffin. According to Griffin 1, any surfactant may be characterized by HLB number considering its ability to form both straight and inverse emulsions. The more the HLB in surfactant molecule is shifted to the hydrophilicity side, the higher the HLB number.
However, as it has been noted by the author, the HLB value only gives a guideline to the surfactant function and has no information
of emulsifier efficacy. Although the HLB system is a function of the solubility of a given nonionic surfactant in both oil and water phases, it cannot take into consideration the interaction between potential emulsifier and oil in any single case.
Nevertheless, the HLB concept remains an important element in the development of the theory and practical application of surfactants 2-4.
A proposed method for evaluating the feasibility of nonionic surfactants as potential emulsifiers for o/w emulsions is described. For example, in the case of APEOs and MOs, it is shown that the emulsifiability of nonionic surfactants towards oils can be expressed numerically. It assists for the selection of the most suitable pair (emulsifier — oil) for the stable o/w emulsion formation.
The HLB system and emulsifier selection in application to alkylphenolethoxylates
Based on numerous experiments, Griffin established the certain ranges of HLB numbers for the evaluation of the feasibility of surfactants for every separate application (Table 1).
Table 1
The ranges of HLB numbers and recommended surfactant applications
HLB range Application
3 - 6 7 - 9 13 - 15 8 - 18 emulsifier, w/o emulsion wetting agent detergent emulsifier, o/w emulsion
He also proposed an empiric method for calculating the HLB value of certain types of surfactants 5. For several of nonionic surfactants, particularly for APEOs, the HLB number may be calculated by the following formula: HLB = E / 5,
where E — content of ethylene oxide (EO) groups in the surfactant molecule, wt.%.
The HLB numbers for APEOs with a various degree of ethoxylation have been calculated by the formula (Table 2).
Table 2
The values of HLB numbers and Water Numbers (WN) for APEOs
n 4 7 10 20
HLB number 8.67 11.45 13.13 15.86
Water Number 3.4 15.8 17.7 19.0
R—Ph—O(CH2CH2O)nH, where n is the degree of ethoxylation (the number of EO units).
The molecular weight of the initial alkylphenol mixture with R = C8—C12 is 230.
All of these surfactants have HLB numbers within 8—18 (Table 2) and, according to Griffin,
they should be employed as emulsifiers in o/w systems (Table 1), i.e. for the formation of straight emulsions.
The formation of emulsion through self-emulsifiable oil and verification of the HLB system applicability
Some experiments with these APEOs have been conducted to verify the above thesis.
The formation of o/w emulsions through self-emulsifiable oil is the more versatile method in emulsion technology. It consists of the following operations:
— mixing of emulsifier and oil,
— emulsifying the prepared mixture in water.
A considerable number of publications are focused on the study of the solubility of nonionic surfactants in water. In this case, the surfactant hydrophilicity increases with the number of EO units in the molecule increases.
Much less information on the solubility of the nonionic surfactant in hydrocarbon mediums.
Besides solubility in water, the solubility of APEOs in hydrocarbon solvents has been examined 6-8. Jelinek and Mayhew 6 studied solubility in the Stoddard solvent, Crook and Fordyce 7 in isooctane and Ultrasene, Lissant 8 in paraffinic kerosene, i.e. mainly in isoparaffinic hydrocarbons.
Ethylene oxide products with 4 and 6 moles of EO are completely soluble in the Stoddard solvent. The products from 10 moles and more of EO were insoluble. At the same time, it has been noted that none of these surfactants is soluble in MO 6.
Similar results have been reported in two other publications 7'8.
The solubility of nonionic surfactants in hydrocarbon mediums (including MOs) is a important factor in formulating self-emulsifiable oils, since the system should be thermody-namically stable and should not separate into layers (as well as not to form any turbidity and precipitation) for a long period of time.
Thereby, the compatibility of nonionic surfactants with MOs of different chemical composition has been explored.
APEOs with earlier calculated HLB numbers (Table 2) have been tested as potential emulsifiers.
MOs has been characterized and designated by aniline point. Aniline point (AP) is a critical temperature of the complete oil miscibility with aniline. AP reflects the chemical composition of oil. The more the aromatic character of oil, the lower the AP.
The AP values ( C) for the researched oils run in accordance with ASTM Test Methods
D 611-12 (2016) 10 are presented in Table 3, where for instance, M0-40 is a mineral oil with AP = 40.
Table 3
Characterization of mineral oils (MOs)
MO-AP MO-19 MO-28 M0-40 MO-81 MO-89
WN 5.1 4.5 4.2 2.2 1.5
The compatibility test has been performed by ASTM Standard Practice D 4054-93 (2003) recommendations 11.
Each one of the ready to test samples presented the mixture of APEO with MO in an optimized ratio.
As indicated in Table 4, the compatibility of APEOs with MOs depends not only on the degree of ethoxylation but also on the chemical composition of an oil. The compatibility is improved with the increase of the aromatic character of oil (AP).
The chemical structure of the lipophilic (oleophilic) segment of the molecule also has a substantial impact on the compatibility of nonionic surfactants with MOs. It may be illustrated by the following example.
The compatibility evaluation for ethoxylated fatty alcohol with the number of ethylene oxide units EO=(7) has been done for the comparison with APEO-(7). At this point, the number of carbon atoms in the oleophilic part remained the same. In other words, the surfactants were distinguished one from another just by the chemical structure of hydrocarbon segment.
R—Ph—O(CH2CH2O)7H APEO-(7)
R1-O(CH2CH2O)7H fatty alcohol ethoxylate-(7)
R1 is aliphatic hydrocarbon chain with the number of carbon atoms R+6.
An effort to incorporate fatty alcohol ethoxylate-(7) into MOs that were matched with APEO-(7) gave a negative result. Even initial unethoxylated fatty alcohol was incompatible.
With regards to incompatibility of APEO-(20) with MOs, it is the result of total predominance of the hydrophile character in the HLB of this surfactant molecule.
Thus, it is established that the compatibility of nonionic surfactants with MOs depends on the following 3 factors:
1) chemical composition of oil;
2) chemical structure of the hydrocarbon segment of nonionic surfactant molecule;
3) degree of ethoxylation, i.e. the number of EO groups in the nonionic surfactant molecule.
The emulsifiability examination for the matched pairs (APEO—MO) have been run after the compatibility test (Table 4). All the samples which have passed the examination had excellent / very good ratings of emulsion spontaneity and emulsion quality in accordance with ASTM E 1116-98 (2019), Standard Test Method 12.
Table 4
The results of compatibility test for APEOs and MOs
MO-AP\n 4 7 10 20
MO-19 + + + -
MO-28 + + + -
MO-40 + + - -
MO-81 + - - -
MO-89 + - - -
n — degree of ethoxylation (the number of EO units in the APEO molecule); «+» — compatible with oil; «—» —incompatible.
For incompatible pairs, the emulsifiability examination is not relevant due to the separation of the system into two initial phases (potential nonionic emulsifier and MO) after the compatibility test. Nevertheless, such attempt has been made where incompatible pairs have been tested but using the previous homogenization. All of the tested incompatible systems displayed a poor emulsion quality (stability under static conditions).
Therefore, the results of the conducted research (Table 5) show that only APEO-(7) and APEO-(10) in mixing with mineral oils (MO-19, MO-28, and MO-40) are able to form emulsions although all of the tested nonionic surfactants have HLB numbers within 8—18 (Table 2) and according to Griffin (Table 1) are recommended for the application as emulsifiers for o/w systems.
Table 5
The results of the emulsifiability examination for APEO/MO mixtures
MO-AP\n 4 7 10 20
MO-19 - + + x
MO-28 - + + x
MO-40 - + x x
MO-81 - x x x
MO-89 - x x x
«+» — mixture emulsifies; «—» — mixture doesn't emulsify; x — the emulsifiability examination for incompatible systems is not relevant due to the separation into two initial phases (potential nonionic emulsifier and mineral oil) after the compatibility test
Water number as an alternative method for evaluation of the hydrophile-lipophile characterization of nonionic surfactants and hydrophile character of oil: novel approach to emulsifiability evaluation
Water number (WN) is one more characterization related to the HLB of nonionic surfactants 9.
Water number is a volume (ml) of distilled water run for the titration of one-gram sample in 30 ml of the specially selected solvent (benzene— dioxane) until the first persistent turbidity.
The higher the WN, the more the hydrophile character is expressed.
In the series of APEOs (n = 4, 7, 10, 20) WN is increased with the increasing of the degree of ethoxylation (Table 2).
The hydrophile character of MOs can be evaluated in the same way 9. Particularly, the higher the WN, the more hydrophile and aromatic character of the MO and its AP is lower (Table 3). This corresponds to a fairly good correlation between WN and AP (Fig. 1).
Water number, ml
Fig. 1. Correlation between water number (WN) and aniline point (AP) of mineral oils (MOs)
Thus, WN, as well as AP, adequately reflects the chemical composition of oil and can be applied as a characterization of MOs.
Characterizing both nonionic surfactants and MOs through the WN enables to evaluate the emulsifiability of nonionic surfactants numerically. The relation between the water number of APEO (WNAPEO) and the water
Литература
1. Griffin W.C. Classification of Surface Active Agents by HLB // J. Soc. Cosmetic Chemists.— 1949.- V.1,№5.— Pp.311-326.
2. Becher P. Encyclopedia of Emulsion Technology. V.4.— New York: Marcel Dekker, 1996.
number of MO (WNMO) can be used as a universal indicator.
Thus, according to Table 5, the emulsifiability for the tested APEOs regarding MOs can be established via the following ratios: WNAPEO-(7) / WNMO-19 and WN APEO-(10) / WNMO-28 .
Otherwise, the range of the emulsifiability can be presented in such form:
3.01 < WNAPEO/WNMO < 3.93 .
At this point, the condition of the compatibility is followed automatically.
Hence, APEO-(4) a priori could not be an emulsifier for o/w emulsions although it is compatible with MOs and its HLB number is 8.67 (Table 2).
As a result of the conducted research, it is recommended to apply WN as a universal indicator for the preliminary evaluation of the hydrophile character of nonionic surfactants and mineral oils (MOs). Using the calculated relationships of their WNs to predict the emulsifiability and compatibility of APEOs towards MOs.
This approach can be extended to the other ethoxylated surfactants and oils, including carrier and essential oils, to form o/w emulsions for multiple purposes, such as chemical technology, cosmetics industry, and pharmaceuticals. Formulating emulsions on the base of biodegradable ingredients is another potential area of research.
To finalize, based on the above analysis the following findings have been established:
1. The compatibility of APEOs with MOs depends not only on the degree of ethoxylation but also on the chemical composition of the oil.
2. The emulsifiability of APEOs towards MOs can be evaluated numerically through the WNAPEO / WNMO relationship.
3. The range of the emulsifiability for APEOs and MOs is established.
4. The method described in this article is recommended for the evaluation of the other nonionic surfactants as potential emulsifiers for o/w emulsions.
References
1. Griffin W.C. [Classification of Surface Active
Agents by HLB]. J. Soc. Cosmetic Chemists,
1949, vol.1, no.5, pp.311-326.
2. Becher P. [Encyclopedia of Emulsion
Technology. V.4]. New York, Marcel Dekker,
1996.
3. Philip Haw. [The HLB System. A Time Saving Guide to Surfactant Selection] / Presentation to the Midwest Chapter of the Society of Cosmetic Chemists.- March 9, 2004.
4. [The HLB System. California Chapter of the Society of Cosmetic Chemists] / Presentation of Croda International Plc., 2015.
5. Griffin W.C. Calculation of HLB Values of Nonionic Surfactants // J. Soc. Cosmetic Chemists.- 1954.- V.5, №5.- Pp.249-255.
6. Jelinek C.F., Mayhew R.L. Nonionic Surfactants Their Chemistry and Textile Uses // Text. Res. J.- 1954.- V.24, no.8.- Pp.765-778.
7. Crook E.H., Fordyce D.B. Molecular Weight Distribution of Nonionic Surfactants. III. Foam, Wetting, Detergency, Emulsification and Solubility Properties of Normal Distribution and Homogeneous Octylphenoxyethoxyethanols // J. Am. Oil Chemists' Soc.- 1964.- V.41, №3.-Pp.231-237.
8. Lissant K.J. Uses of Glyphs to Organize Data in Multivariant Systems. Encyclopedia of Emulsion Technology. V.3.- New York: Marcel Dekker, 1988.- Pp.239-280.
9. Greenwald H.L., Brown G.L., Fineman M.N. Determination of the Hydrophile-Lipophile Character of Surface Active Agents and Oils by a Water Titration // Anal. Chem.- 1956.- №28.-Pp.1693-1697.
10. ASTM D 611-12 (2016), Standard Test Methods for Aniline Point and Mixed Aniline Point of Petroleum Products and Hydrocarbon Solvents.
11. ASTM D 4054-93 (2003), Standard Practice for Evaluating the Compatibility of Additives with Aviation-Turbine Fuels and Aircraft Fuel Materials.
12. ASTM E 1116-98 (2019), Standard Test Method for Emulsification Characteristics of Pesticide Emulsifiable Concentrates.
3. Philip Haw. [The HLB System. A Time Saving Guide to Surfactant Selection]. Presentation to the Midwest Chapter of the Society of Cosmetic Chemists, March 9, 2004.
4. [The HLB System. California Chapter of the Society of Cosmetic Chemists]. Presentation of Croda International Plc., 2015.
5. Griffin W.C. [ Calculation of HLB Values of Nonionic Surfactants]. J. Soc. Cosmetic Chemists, 1954, vol.5, no.5, pp.249-255.
6. Jelinek C.F., Mayhew R.L. [Nonionic Surfactants Their Chemistry and Textile Uses]. Text. Res. J., 1954, vol.24, no.8, pp.765-778.
7. Crook E.H., Fordyce D.B. [Molecular Weight Distribution of Nonionic Surfactants. III. Foam, Wetting, Detergency, Emulsification and Solubility Properties of Normal Distribution and Homogeneous Octylphenoxyethoxyethanols]. J. Am. Oil Chemists' Soc., 1964, vol.41, no.3, pp.231-237.
8. Lissant K.J. [Uses of Glyphs to Organize Data in Multivariant Systems. Encyclopedia of Emulsion Technology. V.3]. New York, Marcel Dekker Publ., 1988, pp.239-280.
9. Greenwald H.L., Brown G.L., Fineman M.N. [Determination of the Hydrophile-Lipophile Character of Surface Active Agents and Oils by a Water Titration]. Anal. Chem., 1956, no.28, pp.1693-1697.
10. ASTM D 611-12 (2016). [Standard Test Methods for Aniline Point and Mixed Aniline Point of Petroleum Products and Hydrocarbon Solvents].
11. ASTM D 4054-93 (2003). [Standard Practice for Evaluating the Compatibility of Additives with Aviation-Turbine Fuels and Aircraft Fuel Materials].
12. ASTM E 1116-98 (2019). [Standard Test Method for Emulsification Characteristics of Pesticide Emulsifiable Concentrates].
