ORIGINAL ARTICLE

Detergency of Vegetable Oils and Semi-Solid Fats UsingMicroemulsion Mixtures of Anionic Extended Surfactants: TheHLD Concept and Cold Water Applications

Linh D. Do Chodchanok Attaphong

John F. Scamehorn David A. Sabatini

Received: 29 June 2014 / Accepted: 21 November 2014 / Published online: 14 December 2014

AOCS 2014

Abstract In spite of the increasing interest in cold tem-

perature detergency of vegetable oils and fats, very limited

research has been published on this topic. Extended sur-

factants have recently been shown to produce very prom-

ising detergency with vegetable oils at ambient

temperature. However, the excessive salinity requirement

(414 %) for these surfactants has limited their use in

practical applications. In this work, we investigated the

mixture of a linear C1018PO2EONaSO4 extended sur-

factant and a hydrophobic twin-tailed sodium dioctyl sul-

fosuccinate surfactant for cold temperature detergency of

vegetable oils and semi-solid fats. Four vegetable oils of

varying melting points (from -10 to 28 C) were studied,these were canola, jojoba, coconut and palm kernel oils.

Anionic surfactant mixtures showed synergism in deter-

gency performance compared to single surfactant systems.

At temperatures above the melting point, greater than 90 %

detergency was achieved at 0.5 % NaCl. While detergency

performance decreased at temperatures below the melting

point, it was still superior to that of a commercial detergent

(up to 80 vs. 40 %). Further, results show that the experi-

mental microemulsion phase behaviors correlated very

well with predictions from the hydrophiliclipophilic

deviation concept.

Keywords Microemulsion Vegetable oil Semi-solidfats Cold detergency Extended surfactant Hydrophiliclipophilic deviation

Introduction

It has been reported that heating water accounts for more

than 80 % of energy consumption during the laundry

process [1]. A reduction of washing temperature from 40 to

10 C is projected to result in 5065 % energy savings [1,2]. However, cold water detergency of vegetable oils and

semi to solid fats presents a critical challenge to the

laundry process. Vegetable oils are mixtures of triglyceride

oils which comprise to more than 95 % of the oil content.

Below their melting points, vegetable oils are semi-solid

fats, also known as waxy soils. These waxy soils are

mixtures of liquid oils and solid fats where the liquid oils

are entrapped in the crystalized structure of solid fats,

causing them to poorly interact with surfactants in solution

[3]. Further, above their melting points, vegetable oils or

oily soils are also difficult to remove due to their highly

hydrophobic nature and bulky triglyceride structure. Good

detergency with vegetable oils and fats generally requires

high temperature when using nonionic surfactants or high

salinity when using ionic surfactants [411]. While deter-

gency of oily soils has been studied by several research

groups, very limited information on detergency of semi-

solid fats or cold water detergency of vegetable oils is

found in the literature [4, 5, 12]. Therefore, the overall goal

of this research is first to investigate the cleaning efficiency

of extended-surfactant-based microemulsion formulations

L. D. Do C. Attaphong D. A. Sabatini (&)School of Civil Engineering and Environmental Science,

University of Oklahoma, Norman, OK, USA

e-mail: sabatini@ou.edu

L. D. Do C. Attaphong J. F. Scamehorn D. A. SabatiniInstitute for Applied Surfactant Research, University of

Oklahoma, Norman, OK, USA

J. F. Scamehorn

School of Chemical, Biological Engineering and Material

Science, University of Oklahoma, Norman, OK, USA

123

J Surfact Deterg (2015) 18:373382

DOI 10.1007/s11743-014-1659-1

on vegetable oils and fats at temperatures above their

melting points, and then to study detergency for these

formulations below the melting point, where microemul-

sions do not form.

Microemulsion-based formulations have been reported

to enhance the detergency of hydrophobic oily soil from

fabrics [4, 6, 1315], building on the early work of Miller

and Raney [810, 15]. These surfactant formulations can

effectively reduce the interfacial tension (IFT) between the

washing solution and the targeted oily soil to low values

(\0.1 mN/m), thereby lowering the work required toremove the soil through roll-up and snap-off mechanisms.

Extended surfactants have proven to be the most successful

class of surfactants to produce ultralow IFT and form

alcohol-free microemulsions with vegetable oils at ambient

temperature [1621]. These surfactants have an intermedi-

ate polypropylene oxide (PO) and/or polyethylene oxide

(EO) groups inserted between the head and tail of the sur-

factant molecule. This unique chemical structure allows the

surfactant tail to extend further into the oil phase,

enhancing the surfactant tail-oil interaction without losing

its aqueous solubility [17, 22, 23]. Phan et al. [4] reported

microemulsion formation with canola oil at ambient tem-

perature using a single branched extended surfactant,

C14,158POSO4Na. Very good canola oil detergency was

obtained at relatively low surfactant concentration

(500 ppm). However, the high salinity requirement (NaCl

concentrations of 414 wt%) limited the use of these

extended surfactants in practical applications. The high

salinity requirement was due to the very hydrophilic nature

of the extended surfactant. Minana-Perez et al. [24] reported

on phase behaviors and solubilization in microemulsions

containing mixtures of extended surfactants and conven-

tional non-ionic surfactants. The application of et al. the

mixture of extended surfactants and non-ionic surfactants

has also been reported in the literature [6, 25]. Tanthakit

et al. [13] studied palm oil detergency at 30 C using amixture of an extended surfactant (branched C14,153PO

NaSO4) with a nonionic secondary alcohol ethoxylated

surfactant having five ethylene oxide groups. It was repor-

ted that the studied anionic/nonionic surfactant mixture at

25/75 weight ratio showed synergism in palm oil deter-

gency performance compared to the use of a single sur-

factant. Optimum palm oil detergency (84 %) was reported

in the Winsor Type III region at 2,000 ppm surfactant

concentration and 2 wt% NaCl. While good detergency was

achieved, the surfactant and salinity concentrations were

relatively high for the laundry application.

In spite of increasing interest in cold water detergency

for vegetable oils and fats, very limited information on this

topic is published in the literature; therefore, the use of

further optimized extended surfactant mixtures for such an

application is of special interest in this study. The

objectives of this research were to (1) develop an extended

surfactant-based formulation with good detergency but

reduced salinity levels from previous research; (2) compare

the experimental microemulsion phase behaviors above the

melting points with the theoretical hydrophiliclipophilic

deviation equation; and (3) study the cold temperature

washing efficiency of mixed extended surfactant and

sodium dioctyl disulfosuccinate (SDOSS) surfactant both

above and below the melting point of select oils. Four oils

were evaluated in this study, including canola, jojoba,

coconut and palm kernel oils. These oils can be charac-

terized into two different groups of high melting temper-

ature oils (coconut and palm kernel oils) and low melting

temperature oils (canola and jojoba oils). They can also be

characterized into two different chemical structure groups,

triglyceride oils (canola, coconut and palm kernel oils) and

waxy oil (jojoba oil) [26]. Selected physical properties and

chemical structures of these oils are shown in Table 1.

The choice of extended surfactant was guided by pre-

vious work [18]. When comparing the optimum interfacial

tension (IFT*) values and optimum salinity (S*) among

three types of extended surfactants (linear PO extended

surfactant, branched PO extended surfactants and linear

POEO extended surfactants) with triolein oil, Do et al.

[18] reported that ultralow IFT* could be achieved with

linear POEO extended surfactants, specifically C10

18PO2EONaSO4, at the lowest S*. While the extended

chain of the surfactant lowers IFT values and enhances oil

solubilization, microemulsion formation using extended

surfactant alone took weeks to months to equilibrate due to

the high rigidity of the surfactant membrane [19, 27, 28].

High salinity also caused dehydration of the surfactant

headgroups, leading to close packing of the surfactant

micelles, higher rigidity of the surfactant membrane and a

slow coalescence rate [27, 28]. To overcome this problem,

we propose to use a mixture of C1018PO2EONaSO4extended surfactant and branched sodium dioctyl disulfo-

succinate (SDOSS) surfactant. It has been shown that a

mixture of two branching tail cationic/anionic surfactants

Table 1 Chemical structures and selected physical properties ofstudied oils

Oil Melting point

(C)Chemical structure

Canola -10 Triglyceride oil

Coconut 24.4

Palm kernel 28.6

Jojoba 9.7 Wax oila

(Z,Z)-CH3(CH2)7CH=CH(CH2)mCOO

(CH2)nCH=CH(CH2)7CH3 m = 7, 9,

11, 13 and n = 8, 10, 12, 14

a Adapted from [17]

374 J Surfact Deterg (2015) 18:373382

123

improved surfactant tail-oil interactions, enhancing limo-

nene oil solubilization [29, 30]. Witthayapayanon et al.

[19] reported that the use of SDOSS surfactant in a mixture

with a branched PO extended surfactant was able to reduce

the coalescence rate to form microemulsions with hexa-

decane from months to less than an hour while substan-

tially reducing the salinity requirement. While these studies

dealt with microemulsion formation and phase behaviors at

relatively high surfactant concentrations ([4 wt%), ourstudy here focuses on lower surfactant concentrations for

detergency application.

As stated in the objectives, we are also interested in

correlating the experimental microemulsion phase behav-

iors with those predicted by the theoretical hydrophilic

lipophilic deviation (HLD) equation. HLD concept was

first introduced and developed by Salager et al. [3133].

An extensive review on the HLD concept was recently

published by Salager et al. [22]. The general HLD equation

for anionic surfactant is described as follows [17, 22, 33

36]:

HLD ln S K NC;O f A Cc aTDT 1where S stands for the salinity concentration in the aqueous

phase (g/100 mL); K is a constant parameter, ranging from

0.1 to 0.16 depending on the surfactant headgroup [32, 34];

NC,O represents the number of carbon atoms in the oil

molecules, also known as alkane carbon number (ACN) for

alkane oils or equivalent alkane carbon number (EACN) of

other oils [17, 22, 34]; f(A) is a function of the co-surfactant

or alcohol; Cc is the characteristic curvature of the sur-

factant molecule [34] (also referenced to as r which wasdefined as a characteristic surfactant parameter in the ori-

ginal work of Salager et al. [33]; aT is the temperaturecoefficient and has a value of 0.01 for most ionic surfac-

tants [32, 37]; DT is the temperature difference between thestudied temperature and the reference temperature (25 C).For co-surfactant and alcohol free microemulsions,

f(A) = 0. The HLD value indicates the deviation of the

microemulsion phase from optimum Winsor Type III mi-

croemulsions where the surfactant interactions in the oil

and aqueous phases are balanced [27, 32, 34]. Thus,

HLD = 0 for optimum Winsor Type III microemulsions,

HLD \0 for Winsor Type I microemulsions and HLD [0for Winsor Type II microemulsions. It is important to note

that the Cc value also reflects the relative hydrophilicity

or hydrophobicity of the surfactant. It has been well

established that the HLD approach is preferred to the

hydrophiliclipophilic balance (HLB) approach for

microemulsion formulation, and that the Cc is preferred to

the HLB number as predicted from the group contribution

number in comparing the relative hydrophobicity/hydro-

philicty among surfactants, especially for extended sur-

factants [32, 38].

Applying the linear mixing rule for microemulsions

systems containing binary mixture of anionic surfactants,

the HLD equation can be written as [34]:

HLDmix X1HLD1 X2HLD2 2where X1 and X2 are the molar fractions of surfactants 1 and

2. Correlations between the experimental and predicted

microemulsions phase behaviors are discussed in this paper.

Experimental Procedures

Materials

The linear extended surfactant C1018PO2EOSO4Na

(22.55 %) was donated by Hunstman Chemical Co.

(Houston TX, USA), and the branched surfactant dioctyl

sodium sulfosuccinate (SDOSS, ?99 % anhydrous) was

purchased from Fisher Scientific. Sodium chloride (NaCl,

?99 %) and oil-soluble dye Oil-red-O were purchased

from Sigma-Aldrich (St. Louis, MO, USA).

Crisco pure canola oil (The J. M. Smucker Company,

Orrville, OH, USA) was purchased from a local market.

Pure jojoba oil was purchased from NOW Foods. Palm

kernel and coconut oils were purchased from Mountain

Rose Herbs (Eugene, OR). All materials were used without

further purification.

The fabric used in the detergency test was a white 65/35

polyester/cotton blend and was purchased from a local

market. A commercial detergent (Tide Liquid Laundry

Detergent, Clean Breeze) was also purchased from a local

market and was used for comparison purpose.

Methods

EACN Determination of Studied Oils

The use of an optimum formulation correlation method or

HLD method for determining the EACN or NC,O value of

an unknown oil has been well documented in the literature

[18, 32, 34]. The EACN and NC,O terms are used inter-

changeably in this paper. EACN values of studied oils were

determined using the surfactant C1018PO2EONaSO4 at

25 C. The HLD equation for C1018PO2EONaSO4 inthe absence of alcohol and at 25 C is [18]:

HLDC1018PO2EONaSO4 ln S 0:1042 NC;O 0:0314 3

Semi-solid coconut and palm kernel oils were mixed

with canola oil at a 1:1 weight ratio to form liquid oil

mixtures at 25 C in order to find their EACN values. TheEACN value of unknown oil can be calculated from a

mixture using the formula below [34]:

J Surfact Deterg (2015) 18:373382 375

123

EACNmix X1EACN1 X2EACN2 4where X1 and X2 are the mole fractions of each oil in the

mixture and EACNmix was found from the optimum

salinity for a given oil and Eq. (3).

HLD Calculations of Mixed Ionic Surfactants

Equation (2) was used to calculate HLDmix for binary

anionic surfactant mixtures of C1018PO2EONaSO4 and

SDOSS. The HLD equation for SDOSS in co-surfactant

free systems and at 25 C was reported in the literature asthe following [34, 38]:

HLDSDOSS ln S 0:17 NC;O 2:50 5Dynamic Interfacial Tension (IFTDyn)

Dynamic interfacial tension experiments were performed

using a spinning drop tensiometer (University of Texas,

Model 500). First, 13 lL of oil was injected into a 300-lLcapillary tube containing the aqueous surfactant solution.

Each IFTDyn sample was repeated in triplicate and recorded

at 20 min.

Microemulsion Phase Behavior Experiments

Phase behavior experiments were carried out by fixing the

total surfactant concentration at 1 w/v % and varying the

salinity concentration. For low melting point oils (canola and

jojoba oils), equal volumes of aqueous phase and oil at 5 mL

(or water to oil ratio, abbreviated as WOR at 1) were put into

a 15-mL glass vial. For high melting point oils (coconut and

palm kernel oils), due to the difficulty in mixing the semi-

solid fat with the aqueous surfactant solution, (i.e., the semi-

solid fat adhered strongly to the vial wall and did not suspend

into the aqueous surfactant solution at high WOR), a WOR of

4:1 (4 mL of water and 1 g of semi-solid fats) was used. The

solutions were shaken three times a day for three days and

left for two weeks to ensure equilibrium.

Detergency

Detergency testing was conducted following the proce-

dures documented in the literature [4, 5] and summarized

here. The 65/35 polyester/cotton blend fabric was pre-

washed in deionized water [39]. The fabric was then ironed

flat and cut into a 3 9 4 inch swatches in the warp and weft

direction. Studied oils were mixed with chloroform at 20

vol%. Coconut and palm kernel oils were heated above

their melting points prior to mixing with chloroform. The

swatches were completely submerged in the oil/chloroform

mixture for one minute. The soiled fabrics were then hung

to dry and allowed to equilibrate overnight prior to use.

The initial oil content in percentage of the soiled swatch

was determined gravimetrically by dividing the amount of

oil soiled on the swatch to the mass of pre-soiled swatch

times 100. The resulting swatches had an average oil

content to fabric mass of 25.5 1.7 % jojoba oil,

24.4 2.3 % canola oil, 25.1 1.3 % coconut oil and

24.2 1.6 % palm kernel oil.

Detergency experiments were conducted using a Terg-

O-Tometer (Model 7243; USA Testing Co., Inc., Hoboken,

NF). Three soiled swatches (triplicate samples) were

washed for 20 min in 1 L of surfactant washing solution.

The swatches were then rinsed twice with 1 L of deionized

water for 3 and 2 min, respectively (i.e., two rinse cycles).

All washing and rinsing cycles were conducted at 120 rpm

agitation speed. The treated swatches were hung to dry

overnight using laundry wooden hanging clips with the

temperature in the laboratory ranging from 21 to 24 Cprior to evaluating the detergency performance. It is

important to note that under high humidity condition, the

fabric could take up moisture from the air causing error in

detergency performance analysis; this was not found to be

an issue in our work as the humidity in the laboratory was

relatively low and consistent (ranged from 35 to 55 %).

Preliminary tests were conducted to determine if the oil

soluble dye Oil-red-O was suitable for evaluating the

detergency performance. According to Goel [7], a suitable

dye should be soluble in tested oils, but not soluble in fresh

surfactant solution. However, it was found that the O-red-

dye was partially soluble in the fresh C1018PO2EO

NaSO4 and C1018PO2EONaSO4/SDOSS surfactant

solutions. Thus, the use of O-red-dye was deemed unsuit-

able in this case [7]. Also from [7], it was found the

detergency performance on 65/35 polyester/cotton blend

fabrics evaluated gravimetrically gave consistent and valid

results. We also found that the fabric weight loss due to

washing was less than 0.4 %. Therefore, we decided to use

the gravity method to evaluate the detergency performance

in this study. The detergency performance was determined

gravimetrically by weighing the pre-soiled, soiled and

treated fabrics directly on the mass scale. The fraction of

oil removed in percentage was determined by dividing the

amount of oil removed by the initial amount of oil and

multiplying by 100. It is important to note that, to further

examine whether the use of Oil-red-O dye is suitable for

evaluating the detergency performance, one can test for the

preferentially solubilization in micelles by adding an

excess amount of an oildye mixture into a micellar solu-

tion and evaluate if the concentration of the dye in the

excess oil phase changes. If it changes, the dye is indeed

not suitable for evaluating the detergency performance.

However, if the concentration of the dye in the oil after

solubilization is the same as the initial concentration, then

the use of Oil-red-O dye is still a valid method.

376 J Surfact Deterg (2015) 18:373382

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Results and Discussion

EACN Determination

Figure 1 presents optimum salinity values (Table 2) for the

test oils as well as the HLD correlation for our surfactant

systems (lnS* vs. EACN developed using oils of known

EACN [18]). The EACN of the studied oils can be esti-

mated from the information using the Do et al. [18] cor-

relation as a calibration curve. The interfacial properties

(IFT values) and predicted EACN values of jojoba, canola,

coconut and palm kernel oils are summarized in Table 2. It

can be seen that ultralow IFT (\0.01 mN/m) were achievedusing the C1018PO2EONaSO4 extended surfactant. The

vegetable oils studied in this work had varying EACN

values, from a medium hydrophobic oil (jojoba,

EACN = 11) to a highly hydrophobic oil (canola,

EACN = 17). The hydrophobicity of the studied oils is in

the order of jojoba \ coconut \ palm kernel \ canola.

DetergencySingle Versus Mixed Surfactant Systems

Figure 2 shows canola oil detergency as a function of C10

18PO2EONaSO4 mole fractions in the mixture with

SDOSS using optimum salinity (S*) conditions predicted

by the HLD method (HLDmix 0) at 25 C. The S* valuespredicted from HLDmix 0 are also shown in Fig. 2. It canbe seen that mixture of these anionic surfactants showed

synergism in detergency performance compared to using a

single surfactant which is consistent with the literature

[40]. More than 90 % canola oil detergency efficiency

could be achieved using surfactant mixtures as compared to

68 % using SDOSS alone or 85 % using C1018PO2EO

NaSO4 alone. The detergency performance using an

extended surfactant alone (mole fraction of 1) was com-

parable to values reported in the literature using other

extended surfactants [4, 6]. While better oil solubilization

and IFT reduction is expected for longer chain length

surfactants [17], using an extended surfactant alone also

makes the surfactant membrane highly rigid, causing the

formation of undesirable phases like gel or liquid crystals

[28, 38]. Adding a shorter tail branched surfactant into such

a system helps the surfactant membrane to be more flexible

[28, 29], thereby enhancing the surfactant interaction with

the oil phase. Mixtures of a linear or branching cationic

surfactant and a branched anionic surfactant has been

reported to avoid liquid crystal or gel formation [29, 30].

Using mixed anionic surfactant formulations in this study,

more than 90 % detergency of canola oil could be achieved

at relatively low salinity (2 %) without encountering this

aqueous solubility problem. Thus, in subsequent experi-

ments, the C1018PO2EONaSO4 to SDOSS mole frac-

tion was fixed at 0.260.74.

Fig. 1 EACN values of studied oils and their mixtures predictedfrom the optimum formulation correlation for C1018PO2EO

NaSO4 at 25 8C. The optimum formulation correlation was adaptedfrom [18]

Table 2 Interfacial properties at optimum conditions and predictedEACN values of studied oils with C1018PO2EONaSO4 at 0.15

w/v% at 25 C

Oil MWa (g/

mol)

S* (w/

v%)

IFT*

(mN/m)

EACN

Jojoba NA 3.00 0.00052 11

Canola 880 6.00 0.0057 17

50 vol% Coconut/canola

mixture

NA 4.50 0.0024 14

50 vol% Palm kernel/

canola mixture

NA 5.35 0.0026 16

Coconut 646 NA NA 12

Palm kernel 756 NA NA 15

EACN for pure coconut and palm kernel oils were predicted from

Eq. (4)

NA not availablea Adapted from [13]

Fig. 2 Effect of C1018PO2EONaSO4 mole fraction in mixturewith SDOSS on detergency of canola oil at 25 8C at their optimumsalinity concentration predicted from HLDmix and compared to a

commercial detergent. All surfactant concentrations were at 1000

ppm. Agitation was at 120 rpm. Full procedure test consisted of 20

min wash-cycle, 3 min rinse-1 and 2 min rinse-2

J Surfact Deterg (2015) 18:373382 377

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Phase Behavior, Optimum Salinity and HLD

Figure 3 presents salinity (NaCl) scans for microemulsion

phase behaviors of coconut (Fig. 3a) and palm kernel oils

(Fig. 3b) at 25 C (above both their melting points). Thelower portion of the figure visually shows the phase

behavior versus NaCl concentration. The upper region of

the figure shows microemulsion phases versus NaCl con-

centration as predicted by the HLD equation. It can be seen

that the HLD equation correlates very well with the

experimental microemulsion phase behaviors; e.g., at low

NaCl the phase behavior and HLD both show Winsor Type

I systems while at higher NaCl both show Winsor Type II

systems. It is interesting to observe the microemulsion

formation consisted of an excess semi-solid phase with

normal micellar microemulsions in the Type I region and a

middle phase microemulsion in equilibrium with excess

semi-solid phase and the aqueous phase in the Type III

region. A middle phase microemulsion of coconut oil was

experimentally obtained at 1 % NaCl, which agreed very

well with that predicted by the HLD method. Similarly, a

middle phase microemulsion for palm kernel oil was

observed at 1.5 % NaCl experimentally versus 1.56 %

NaCl predicted by the HLD method. Similar agreement

was likewise observed for canola and jojoba oils (data not

shown). Thus, the HLD concept proved to be very useful in

predicting the microemulsion phase behaviors of vegetable

oils using the studied surfactant systems.

Canola Detergency Versus Salinity and Rinse/No Rinse

Figure 4 shows the effect of NaCl concentrations (or mi-

croemulsion type) and washing cycles on the detergency

performance of canola oil at 25 C with C1018PO2EONaSO4/SDOSS mixture at 0.24/0.76 mole fraction. The

total surfactant concentration was 1,000 ppm. All studied

formulations had IFT values with canola oil well below 1

mN/m. Using NaCl concentrations from 0.05 to 1 % pro-

duced Winsor Type I behavior and from 4 to 5 % produced

Winsor Type II systems with 2.5 % corresponding to

Winsor Type III microemulsions. Considering the deter-

gency performance from 20 min wash only cycle (no rinse)

with the surfactant formulation, it can be seen that the

highest oil detergency performance was achieved in the

Type I region approaching the Type III region. The trend in

increasing detergency efficiency as the microemulsion

phase approached the Type III region has also been

observed by other researchers [4, 14]. As the microemul-

sion phase approaches the Type III region, the IFT

decreases and the oil solubilized increases, thereby

enhancing the detergency performance [5, 14]. About 90 %

detergency was achieved in the Type I region at 0.5 %

NaCl. The detergency performance in the wash only (no

rinse) was slightly reduced in the Type III region and

dramatically reduced to about 45 % in the Type II region.

This trend is similar to what was observed before by Phan

et al. [4] using a single extended surfactant formulation.

Fig. 3 Correlations betweenexperimental microemulsion

phase behaviors and theoretical

HLD prediction for a coconutoil and b palm kernel oil versusNaCl scan. Phase behavior

experiments were conducted at

25 8C using 1 w/v% of totalsurfactant concentration

consisting of C1018PO2EO

NaSO4 and SDOSS at 0.26/0.74

mole fraction

378 J Surfact Deterg (2015) 18:373382

123

The dramatic detergency reduction in Type II region was

attributed to the hydrophobicity of the surfactant system

leading to the tendency to form reverse micellar micro-

emulsions. Thus the surfactants are more oil soluble and

tend to partition into the oil phase.

Considering the detergency performance of the full

washing cycle (20 min wash, 3 min for rinse 1 and 2 min

for rinse 2), also shown in Fig. 4, it can be seen that in the

Type I region, a slight increase in oil removal is realized

during the rinsing steps compared to the washing step

(wash ? rinse results are slightly higher than wash only in

Type I region, NaCl B1 %). However, in the Type II

region, the detergency increased substantially with the

rinse steps added, achieving more than 95 % oil removal,

surprisingly exceeding the detergency performance in both

Type I and III regions. Similar results have been observed

in previous research when using an extended surfactant

alone system; however, for such system, the NaCl

requirement was substantially higher (14 %) compared to

our formulation (4 %) [4]. One possible explanation for

good detergency performance in the Type II region is the

gradient effect in the rinsing step. In the washing step, the

Type II system favored surfactant partition into the oil on

the fabrics. Once the fabric was rinsed with deionized

water, the system presumably underwent phase transition

from Type II to Type I and in between transition to an

optimum Type III [4], thereby producing excellent

detergency.

Effect of Temperature on Detergency

Figure 5 presents the effect of washing temperature

(1030 C) on detergency of the four studied oils. The righty-axis in Fig. 5c and d is the solid fat index defined as the

solid to liquid ratio in fat. The SFI data was adapted from

[3]. The NaCl was fixed at 0.5 % for these tests, corre-

sponding to Winsor Type I for all systems. In all systems, it

can be seen that the detergency performance of our for-

mulation is superior to that of the commercial detergent,

especially at low temperature. For all systems, at temper-

ature above the melting points of the studied oils, our

formulation achieved more than 90 % detergency perfor-

mance at relatively low NaCl concentration of 0.5 %

(much lower NaCl levels than previous research with

extended surfactants [4, 6]). At temperatures below the

melting points of the coconut (Fig. 5c) and palm kernel

(Fig. 5d) oils, detergency performance using our formula-

tion gradually reduced, but still exceeded the performance

of the commercial detergent. When using our formulation

at temperatures well below the melting point of coconut

and palm kernel oils, the detergency performance gradually

increased as the temperature increased or SFI decreased

(the amount of solid fraction decreased with increasing

temperature). This trend was not observed when using the

commercial detergent. These results are thus quite

encouraging as they suggest that an extended surfactant

based system can show superior performance in cold water

detergency of triglyceride oils and fats; this should be

further explored in the future research.

We speculated that below the melting points, the IFT

reduction of our formulations for the liquid fraction of the

oil was sufficient to enhance the semi-solid fat (mixture of

liquid and solid) detergency. Another possible explanation

is based on the microemulsion phase behavior study of

palm kernel oil shown in Fig. 6. In Fig. 6, three surfactant

systems were investigated including commercial detergent

with no NaCl added (Fig. 6a), C1018PO2EONaSO4 at

0.5 % NaCl (Fig. 6b) and C1018PO2EONaSO4-/

SDOSS mixture at 0.5 % NaCl. It can be seen that Type I

bluish microemulsion phases were formed when using

extended surfactant alone or in mixture with SDOSS

(Fig. 6b, c, respectively), whereas no appreciable oil was

solubilized by the commercial detergent solution (Fig. 6a).

To our knowledge, we have not seen reported phase

behavior study with semi-solid fat in the literature.

Regarding the effect of temperature on the HLD value,

the HLD value of ionic microemulsions with conventional

surfactants (non-ethoxylated or propoxylated) is expected

to increase as the temperature decreases. In other words,

the conventional ionic surfactant systems become rela-

tively more hydrophobic as the temperature decreases.

However, the change in temperature will not have a sig-

nificant effect on the hydrophiliclipophilic balance of the

ionic surfactant system as the temperature coefficient has a

small value of 0.01. Thus, for a 10 C decrease in tem-perature, the HLD would only be expected to shift 0.1 and

thus have a negligible impact on performance. For sur-

factants with ethylene oxide groups [4144], and,

Fig. 4 Effect of microemulsion types and washing cycles on canolaoil detergency at 25 8C, 120 rpm agitation speed and 1000 ppm oftotal surfactant concentration. Surfactant mixture consisted of C10

18PO2EONaSO4 and SDOSS at 0.26:0.74 mole fractions

J Surfact Deterg (2015) 18:373382 379

123

somewhat surprisingly, for extended surfactants with pro-

pylene oxide (PO) groups [42], the temperature effect has

been shown to be the oppositeas the temperature decrea-

ses these surfactants become more hydrophilic. For

extended surfactants with PO groups this temperature

effect has been attributed to the first several PO groups

(first 23) being near the interface and thus somehow

hydrated (as for EO groups); with decreasing temperature

the hydration increases thus making the surfactant slightly

more hydrophilic [42]. Interestingly, for extended surfac-

tants temperature changes will have opposing effects on the

ionic head group and the EO/PO intermediate groups,

further minimizing the anticipated effect of a 10 C tem-perature decrease on the system HLD.

In summary, cold temperature detergency of semi-solid

fats is a complicated process. While this paper reports on a

very promising surfactant mixture for cold temperature

detergency application at relatively low salinity concen-

tration (0.5 % NaCl) which is competitive with or better

than commercial detergents, additional research needs to

be conducted to obtain good detergency at lower salinity

concentrations and gain fundamental understanding of the

detergency of solid to semi-solid fats. Ongoing research

work is evaluating the model methyl palmitate oil of high

melting point (30 C) to gain more fundamental insightsinto the detergency mechanism of semi-solid fats. Future

research should also study the detergency performance as a

function of the surfactant concentration. A surfactant

Fig. 5 Effect of temperature ondetergency of a canola,b jojoba, c coconut and d palmkernel oils. 1000 ppm total

surfactant concentration,

consisting of C1018PO2EO

NaSO4 and SDOSS at 0.26:0.74

mole fractions. NaCl was fixed

at 0.5 w/v% (Type I). Solid fat

index (SFI) was adapted from

the literature [3]

Fig. 6 Phase behaviors of palm kernel oil with different surfactantsystems: a commercial detergent, b C1018PO2EONaSO4 andc C1018PO2EONaSO4/SDOSS at 0.24/0.76 mole fraction, 0.5w/v% NaCl and 25 8C. Total surfactant concentration was at 1 w/v%

380 J Surfact Deterg (2015) 18:373382

123

concentration as low as 125 ppm would be more desirable

for practical applications. Finally, to our knowledge, select

extended surfactants are commercially available and can be

used to formulate in personal care and consumer products,

making this work of practical interest.

Acknowledgments The authors would like to thank George Smithfrom Huntsman Corporation (The Woodlands, TX) for providing the

extended surfactant sample. Funding for this work was provided by

industrial sponsors of the Institute for Applied Surfactant Research at

the University of Oklahoma: CESI Chemical, Church & Dwight,

Clorox, Conoco Phillips, Ecolab, GlaxoSmithKline, Haliburton Ser-

vices, Huntsman, InVia Westvaco, Novus, Procter and Gamble,

Phillips 66, Sasol, SC Johnson and Shell Chemicals.

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Linh D. Do received her B.Sc. (2004) and Ph.D. (2010) from theUniversity of Oklahoma, all in chemical engineering. She is currently

a Principal Chemist at Nalco ChampionAn Ecolab Company. Her

research interests include surfactant properties and their applications

in microemulsions, consumer products, oilseed extraction, biofuels

and enhanced oil recovery. Her research now focuses on developing

hydraulic fracturing fluid systems for unconventional oil and gas

reservoirs.

Chodchanok Attaphong received her B.Eng. (2005) and M.Sc.(2007) from Chulalongkorn University, Thailand and her Ph.D.

(2014) from the University of Oklahoma. She is currently a

postdoctoral researcher at the University of Oklahoma. Her research

interests include surfactant properties, surfactant adsorption, and their

applications in vegetable oil-based microemulsions (i.e., biofuels and

consumer products). Her research now focuses on formulating

microemulsions for detergent applications at low temperature and

surfactant characteristics of bio-surfactants for oil spill cleanup in

seawater.

John F. Scamehorn is Emeritus Director of the Institute for AppliedSurfactant Research at the University of Oklahoma where he is Asha

Glass Chair Emeritus in Chemical Engineering. He received his B.Sc.

and M.Sc. at the University of Nebraska and his Ph.D. at the

University of Texas, all in chemical engineering. Dr. Scamehorn has

worked for Shell, Conoco, and DuPont. His research interests include

surfactant properties important in consumer production formulation

and thermodynamics of surfactant aggregation processes.

David A. Sabatini is David Ross Boyd Professor and Sun OilCompany Endowed Chair of Civil Engineering and Environmental

Science, is Associate Director of the Institute for Applied Surfactant

Research and Director of the WaTER Center at the University of

Oklahoma. He received his B.Sc. from the University of Illinois

(1981), his M.Sc. from Memphis State University (1985) and his

Ph.D. from Iowa State University (1989). His research focuses on

surfactant-based environmental technologies, surfactant-based formu-

lations for vegetable oil extraction and biofuel production and

cleaning systems, and sustainable technologies for drinking water

treatment in developing countries.

382 J Surfact Deterg (2015) 18:373382

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Detergency of Vegetable Oils and Semi-Solid Fats Using Microemulsion Mixtures of Anionic Extended Surfactants: The HLD Concept and Cold Water ApplicationsAbstractIntroductionExperimental ProceduresMaterialsMethodsEACN Determination of Studied OilsHLD Calculations of Mixed Ionic SurfactantsDynamic Interfacial Tension (IFTDyn)Microemulsion Phase Behavior ExperimentsDetergency

Results and DiscussionEACN DeterminationDetergency---Single Versus Mixed Surfactant SystemsPhase Behavior, Optimum Salinity and HLDCanola Detergency Versus Salinity and Rinse/No RinseEffect of Temperature on Detergency

AcknowledgmentsReferences