DD274674A1 - METHOD FOR DETERMINING THE COALESCENCE STABILITY OF EMULSIONS - Google Patents

Abstract

The invention relates to a method for determining the coalescence Stability of emulsions, which finds application in a variety of industries, such. As crop protection, pharmacy, cosmetics, plastics. The object of the invention is to specify the measurement conditions of an easy-to-use method for characterizing the coalescence stability of emulsions. The object is achieved by bringing the emulsions to be examined into centrifuge cups or measuring cells and subjecting them to constant radial accelerations in speed-regulated centrifuges until constant layer heights of the dispersed phase and remaining emulsion are achieved.

Description

Inventor: Dr. Arndt Seifert

Dr * ge. Klaus Strength

Prof. Dr. se. Gerald Muschiolik Lothar Richter

Dr. Manfred Schultz

Method for determining the coalescence stability of emulsions Field of application of the invention

The invention relates to a method for determining the coalescence stability of emulsions by centrifugation.

Ivjdeutung possesses the invention in all fields in which the assessment of the stability of emulsions is necessary, for. In the following industries: crop protection, pharmacy, adhesives, food, cosmetics, oil, agriculture, detergents, lubricants, plastics, paints and varnishes, polishes, textile, paper, leather and photographic. Industry.

Characteristic of the known technical solutions

Emulsions are known to be distributions of liquid droplets in other liquids which are not miscible with the liquid droplets. Starting from these two liquid phases of an emulsion, the dispersed liquid droplets which form the so-called dispersed phase and the continuous phase surrounding the liquid droplets, methods for determining the stability by centrifugation are known, which relate to the coalescence of the emulsion droplets (coalescence) v / eiteren course may result in the separation of a liquid volume from the emulsion droplets.

So by R.D. Void, Kl. Mittal and A.U. Hahn in E. Matijevici: Surface and Colloid Science, Vol. 10, Plenum Press 1978, p 45 ff. In this regard, a kinetically oriented method described from which criteria for the coalescence stability of emulsions can be derived, such. For example, the severity of the separation and the amount of separated dispersed phase at time t. In these kinetically oriented methods, the in measuring cells

centrifugation in centrifuged, so-called analytical ultracentrifuges and registered during centrifugation, the separated amount of dispersed phase as a function of the Zentrifu? tionation time. The centrifugation is carried out only until reaching a mostly settable / range of the resulting from the measured values curve of the separated amount of dispersed phase over the centrifugation time.

A disadvantage is the frequent failure of these kinetically oriented methods, if several of the stated criteria are used to assess the stability of the emulsions simultaneously. Thus, even within a certain series of emulsions, even qualitative differences in stability are often obtained; H. this variant is not universally applicable. Another disadvantage of most variants of these kinetically oriented processes is that they can only be carried out with the expensive analytical ultracentrifuges.

Another method for determining the coalescence stability of emulsions is A.L. Smith and D.P. Mitchell in A.L. Smith: Theory and Practice of Emulsion Technology (Proceedings of a Symposium, Sept. 1974) Academic Press, London and New York 1976, pp. 61 ff.

A disadvantage of this process is the relatively large number of centrifugations to be carried out for determining the critical speed and the accuracy which deteriorates markedly as the number of centrifugations decreases.

The process is deficient in those cases where a separation of the dispersed phase is strongly delayed, z. B. in higher viscosity emulsions.

Object of the invention

The aim of the invention is the development of a method for determining the coalescence stability of emulsions, which is characterized by a greater scope, reliability and accuracy and proves to be less expensive.

Explanation of the essence of the invention

The object of the invention is e3 to specify the measurement conditions of an easy-to-use method for determining the Koalessenzstabilität of emulsions. The object is achieved by the method according to the invention for determining the coalescence stability of emulsions which can be separated by centrifugation on the basis of the separation of disperse phase from the emulsion in that the emulsions to be investigated are placed in centrifuge cups or measuring cells and subjected to constant radial accelerations in speed-regulated centrifuges. until constant layer heights of the dispersed phase and the remaining emulsion are reached, and the determination of the coalescence pressures characterizing the stability of the emulsions by the relationship for the pressure of the remaining emulsion (in Pa)

^P Em. * IS> ² «· Δ $. Cpd.P. · ^F < ^r ) <·) in which

(J) = the angular velocity of the rotor known by the given speed in s

= the known or experimentally determined density difference dispersed jhase (^ d ρ) ^land · continuous phase (^ p)

_ = the known or experimentally determined volume fraction of the dispersed phase

f (r) = factors given by the geometric shape of the centrifuge cells or cups used, which contain the distances of the lower (r _u ) and upper (r) limits of the leaded emulsion to the axis of rotation of the rotor in m

mean takes place.

It has surprisingly been found that in most emulsions under the influence of constant radial accelerations for the separated dispersed phase and the remaining emulsion after a corresponding centrifugation time layer height end values (constant layer heights) are achieved. The determination of this

Layer height end values are determined by known methods. The invention is based on the finding that the coalescence pressure according to the relationship (1) under the measurement conditions of the process according to the invention represents a quantitative, accurate measure of the coalescence stability of emulsions.

The invention can be realized by various Ausfiihrungsvarianten. A variant according to the invention consists in that the sample to be compared: a is centrifuged at a fixed radial acceleration (rotor speed) up to the final layer height values of the dispersed phase and the remaining emulsion.

A further variant of the method according to the invention consists in knowing, even at other, constant radial accelerations, which are above or below the first ones selected, that the mixture is centrifuged to the final layer height values of the separated dispersed phase and the remaining emulsion. The advantage of this variant is that, for the stability comparisons of the emulsions, the measured values are included in the various radial impressions. This results in comparison to the known methods - in which this is fundamentally not possible greater security and accuracy.

The last-mentioned variant can be carried out in a time-saving manner if two or more centrifuges are available, if possible of the same type.

In a further embodiment of the method according to the invention, the emulsion samples are first centrifuged at a constant speed up to the final values of the dispersed phase and the remaining emulsion. Thereafter, the rotor is accelerated to a higher, constant speed and, at this speed, in turn centrifuged to the final values, etc. (hereinafter referred to as graduated sentrifugation).

This variant is very time-saving, since experience shows that the second, third, etc. end values are set in shorter centrifugation times.

In this variant, too, the measured values are included in the different speed calculations for the stability comparisons. This variant makes it particularly advantageous to use centrifuges in which the change in layer height values can be registered during centrifugation »

With the aid of the process according to the invention, the influences of the material composition of emulsions and the production of emulsions, transport, storage are U3W. relevant physical parameters with higher reliability, sensitivity and accuracy determinable than with the known methods. The process according to the invention has a wider application range θ and is characterized by lower process costs. Furthermore, the long-term stability of emulsion-making materials, such as emulsifiers, concentrates, can be accurately assessed. A major advantage of the method is that it can be applied to ordinary centrifuges and ultra-centrifuge devices.

Exemplary embodiments Example 1

Four crop protection emulsions or blind formulations prepared from the concentrates of composition 5-0 (Table 1) were placed in measuring cells and in a

Tabo 1: Composition of concentrates for the preparation of pesticide treatment Bn and Blindformulierungen

Concentrate no. Composition of concentrates 5 40 wt -.% Acetic acid C, - ₈ alkyl esters 50 "XyIen 5" emulsifier ME 85 5 "active ingredient 6 like 5, but emulsifier ME 86 instead of ME 85 7 like 5, but without active ingredient 8th like 6, but without active ingredient

Speed-regulated centrifuge (Paom MOM, Budapest, Type 3170 / b) 4 different constant radial accelerations (rotor speeds) until slice-end values for the separated diaperged phase and the remaining emulsion were obtained With 998 kg / nr for _κ ρ and the experimentally determined values for 3 _di p and Cf> o | .p. And one f (r) of 1/2 (r _u - r _Q ) for the used ones sector-shaped measuring cells with the relationship (1) the coalescence pressures in Tab. 2.

Tab. 2: Centrifugation of emulsions prepared from concentrates 5-8 at different rotor speeds. Drlicke

the remaining emulsion (P

Em.).

number of revolutions

, 10 ³

Life time concentrate emulsion

und.Em. Pa. 10 ⁵

Phäsenvol. ^ see Vasser

a) Emulsions from concentrate 7 (ME 85, without active ingredient)

110 30 8th d 65 min 1.01 0.83 2: 5 32 1.04 0.82 34. 1.00 0.79 35 37 d 50 min 0.95 0.76 1 : 10 116 30 48 d 50 min 0.90 0.94 125 30 0.33 1.0

b) emulsions from concentrate 8 (ME 86, without active substance) 30 32 34 35 12 d 45 min 0.61 0.65 0.72 0.72 0.48 0.44 0.43 0.41 2: 5 111 30 55 d 55 min 0.41 0.26 130 30 55 d 7 d > 0.43 0.31 132 30 55 d 71/4 d 0.38 0.28 133

c) Emulsion off 2 30 the concentrate 65 5 (ME 85 , With active ingredient) , 92 2: 5 11 32 O, 83 0 90 35 13 d min O, 86 0 , 86 85 0

d) Emulsion off 3 30 the concentrate 50 6 (LlE 86 , With active ingredient) 49 2: 5 11 32 O, 58 O, 46 35 15 d min O, 61 O, 45 67 0

It can be seen that with a concentrate / V / aaaer phase volume ratio of 2: 5 and comparable residence times of the concentrates and emulsions, the drug-free emulsions with the ME 85 emulsifier emulsifier (v.110) show markedly better fluorescence-resistant (correspondingly higher coalescence pressures) than those with MB 86 (verse 111). For the active ingredient-containing emulsions the same trend applies (see also verse 112 with 113). The active ingredient has no influence on the coalescence stability of the ME 86 emulsions. The coalescence pressures of verse 111 do not differ. In the case of don ME 85 emulsions, the active agent slightly reduces stability. The coalescing pressures of verse 110 are about 20 % higher than those of verse 112.

A reduction in the ratio of 2: 5 to 1: 10 of the phase-yolumen ratio Concentrate / Was3 results in a decrease of the coalescence pressure to about one-third in the case of the ME85 emulsions without active ingredient (compare Vers. 110 with 125). The coalescer stability of the drug-free ME 85 emulsions decreases somewhat within concentrate lifetimes of from 1 to 5% (compare Vers. 110 with 116). The same trend applies for the ME 86 emulsions for concentrate lifetimes between 2 and 7 weeks (compare Vera 111 with 130). Service lives of the emulsions between 1 hour and 7 days have no influence on the coalescence pressures in the non-corrosive ME 86 emulsions (compare Verses 130, 132 and 133).

Example 2

Three O / W pesticide blends prepared from the concentrates of composition 1-3 (Table 3) were placed in measuring cells and subjected to two different, constant radial accelerations (rotor speeds) in a speed-controlled centrifuge until each of the final layer height values for the separated dispersed phase and the remaining emulsion were achieved. The final layer thickness values for the remaining emulsion are found to be 998 kg / m ³ for ^ ρ and the experimentally determined values for ⁰ ^ p _{1 and} CJ ^ p and f (r) of 1/2 (r _a - r _Q ) with the relation (1) the coalescing pressures in Tab. 4.

Tab ♦ 3? Composition of concentrates for the preparation of antifungal formulations

Ni concentrate.

composition

concentrates (% by weight)

Solvent (oil coreactant) Tensidmisahung

7.5 fatty amine, oxeth. 2.5 nonylphenol, oxeth.

90 n-decane 5.0 fatty amine, oxeth. 5iO nonylphenol, oxeth. 2.5 fatty amine, oxeth. 7.5 nonylphenol, oxeth.

Tab. 4:

Centrifugation of emulsions prepared from Concentrates 1-3 at different speeds. Driicke the ver

permanent emulsion P.

Verse.

Number of revolutions

Surfactant mixture. Fat amine / NP ¹ '

Service time conc./ months live voi. Ve rh.

Concentrate / water

em

Pa. 10 "

3 1

1.5 1.78 0.39

1.0 0.16

30

5.3 / 4 15: 5

0.38 0.76

0.16 0.26

3:

161/4

30 50 0.73 1.48

0.23 0.19

50

1 :

17 1/4 0.77 1.66

0.21 0.22

30

3 1

5 3/4: 10

0.96 1.77

1.0

1) NP = nonylphenol

It can be seen that, with a pot life of 1.5 months and a concentrate / water phase volume ratio of 2: 5, increasing the proportion of pettamine in the surfactant slurry from 1: 3 to 3: 1 significantly reduces the coalescence stability, correspondingly substantially lower coalescing pressures (see Verses 58 and 59) causes.

The same change in the surfactant mixture ratio leads to a significant increase in the coalescence stability with a pot life of 5 3/4 months and a phase volume ratio of 1: ¹ O (see "u-ra 64 with 65) / Water of 2: 5 and pot lives of 16 to 17 months, the increase of the fatty amine content from 1: 1 to 3: 1 results in only a slight decrease in the coalescence stability (see also paragraph 69 at 69) Concentrates of between 1.5 and 16 months, the coalescence stability of the emulsions from the concentrate of the 3: 1 surfactant mixture improves approximately twice (compare Ver 59 with 69) .The same trend results for the emulsions of the 1: 1 surfactant mixture for pot lives of 6 to 17 months (see paragraphs 66, 68 and 70).

Example 3

Of a n-decane-in-V / ater emulsion with sodium dodecyl sulfate as a stabilizer and a proportion of dispersed phase of about 71 vol .-%, emulsion samples NEN life of the emulsion were angegebe- by the in Tab. 3 • brought into measuring cells and in a Tab. 5 i demulsification of n-decane-in-0.1 m NaDS Lag.-emulsions. Influence of the life of the emulsion. (30,000 rpm) pressures of the sum of the transparent and opaque emulsion layers »

Verse. p transp. + and. Em. Life of the Sci.P. 39 Pa. 10 ⁵ emulsion 40 4.5 0 578 41 5.8 3 513 42 5.4 4 457 46 7.1 5 384 7.0 11 363

Centrifuged centrifuge centrifuged at 30,000 rpm until the final layer height values for the separated dispersed phase and the remaining emulsion were reached. The layer height end values for the remaining emulsion show 998 kg / m for J ^ p and the experimentally determined values fUrQtypo ^ 1.0 and J ₀ Jp ₁ and f (r) of 1/2 (r _u r; with the relationship (1) the coalescing pressure in Table 5 »This results in a significant increase in the coalescence pressure with increasing service life of the emulsions within 0 to 5 days after the preparation, after which the coalescence stability remains constant until 11 days after preparation.

Claims (1)

Patentanspruoh Method for determining the Koaleazenzatabilität Emulsions based on the separation of dispersed phase of the emulsion, characterized in that the emulsions to be investigated are placed in centrifuge cups or measuring cells and subjected to constant radial accelerations in speed-controlled centrifuges until constant heights of the dispersed phase and the remaining emulsion are reached, and the determination of the Coalescence pressures characterizing the stability of the emulsions by the relationship for the pressure of the remaining emulsion (in Pa) ^P Em. ^{Ö (} ° ² 'Μ -W · ^{f (r)}
wherein LO = the known by the predetermined speed angular velocity of the rotor in s ^s the known or experimentally determined density difference dispersed phase (^, f ») and continuous phase = the known or experimentally determined volume fraction of the dispersed phase f (r) β given by the geometric shape of the centrifuge cells or cup used factors that contain the distances of the lower (r _υ ) and upper (r) limit of the remaining emulsion to the axis of rotation of the rotor in m mean
he follows"