1

PALM-BASED SODIUM DIHYDROXYSTEARATE DEODORANT STICK

Zahariah Ismail1, Salmiah Ahmad1, Rosnah Ismail1 ,Rigano Luigi2

1Advanced Olechemical Technology Division, Malaysian Palm Oil Board

Lot 9 &11Jalan P/14, Section 10, 43650 Bandar Baru Bangi, Selangor, Malaysia, 2ISPE Laboratory, Italy

ABSTRACT

Dihydroxystearic acid (DHSA) has been prepared from palm oleic acid via

catalytic reaction. In–vivo test confirmed that the use of DHSA at 5% and below

is non-irritant. With two vicinal alcohol groups positioning at C9 and C10, DHSA

has been found to be applicable in cosmetics as thickener or gelling agents.

Stearic acid is known to be used as stick-gel foaming agent. The aim of this

study was to find out the possibility to combine the potential stick forming

properties of DHSA with anti-microbial properties, at the same time to determine

its key physical properties and the deodorant efficacy of this raw material.

Ternary phase diagram of DHSA/propylene glycol (PG)/sodium hydroxide

solution was constructed at 80oC. The phase changes were observed visually

through polarizer film and polarizer microscope. Result showed that the

anisotropic properties changed from isotropic, lamella liquid crystals identified as

maltese crosses pattern and 2-phases. Deodorant sticks were developed based

on the maltese crosses pattern, showed the most stable network. Formulae D4

(anti-microbial active and perfume), D5 (anti-microbial active) D6 (perfume) and

D7 (without anti-microbial and perfume) were compared with C1 and C2

commercially available sodium stearate based deodorant sticks.

The sticks were characterised for pH, softening point, hardness, disintegration

time, weight loss by evaporation, synerisis upon three months’ storage and in-

vivo microbial test. The physicochemical properties remain unchanged after three

2

months storage. The screening for bacteria type was made using blood agar

media and the species identified was Staphyloccocus In manittol agar media, it

inhibited bacteria growth for at least 4 hours in D7. The same results were found

with the rest of the samples.

INTRODUCTION

Deodorants are chemicals that prevent or reduce axillary malodor, which results

from bacterial breakdown of perspiration from eccrine and apocrine sweat

glands. The sweaty odor is caused by the interaction between a variety of

substances including low-molecular-weight fatty acids (i.e caproic, caprylic,

isovaleric, butyric), lactates, urea and ammonia, cholesterol, and other steroid

compounds [1,2]. Odor control can be achieved by various means - basic

hygiene (washing with soap and water) is the most important but also by

antimicrobial agents, antiperspirant, fragrances or any combination of these.

Basically, deodorants and antiperspirants are two different ways to prevent odor.

Deodorants are perfumed preparation, which mask but do not actually affect

perspiration, whereas antiperspirants reduce perspiration with astringent

chemicals. There are many forms and formulations available in the market, i.e.

rolls-ons, deodorant and antiperspirant sticks, gel, cream etc. The market of

these product types is growing (Table I) According to information resources, Inc.

(IRI), Chicago, the sale of antiperspirants and deodorants rose 0.4% for the year

ended Dec. 31, 2000 [3].

Table I

Deodorant sticks are based on alcohol or propylene glycol gelled with sodium

stearate. Propylene glycol is often preferred as there is less shrinkage of the

sticks. It is also less flammable. The sodium stearate stick system is also

produced because of the ease of manufacture, economy, recognized safety,

physical and chemical stability [5,6,7].

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Dihydroxystearic acid and its derivatives have been successfully prepared from

palm oleic acid [8,9.10]. They have potential applications in cosmetics as

thickener or gelling agents. Recently, study on the properties of

dihydroxystearate soap has been carried out by Roila et al., [11]. In this study,

sodium dihydroxystearate sticks are prepared and compared with the sodium

stearate based deodorant sticks commercially available as standards.

MATERIALS AND METHODS Materials

Crude DHSA was obtained from Advanced Oleochemical Technology Division

(AOTD), Malaysian Palm Oil Board (MPOB). The DHSA characteristic was

shown in Table II. Glycerol at 98% purity was obtained from Cognis Sdn Bhd.

Sodium hydroxide (NaOH), propylene glycol (PG) and ethanol used were at 98%,

99% and 95% respectively.

Table II

Methods

(a) Phase diagram

A phase diagram using DHSA/ Propylene glycol (PG)/sodium hydroxide solution

was constructed at 80oC. The phase changed was observed through polarizer

film and while the optical pattern was confirmed with a heating stage.

b) Preparation of deodorant sticks

The ratio of DHSA / PG / NaOH solution (55/40/5) which is in liquid crystalline

region was selected for development of deodorant sticks with addition of

humectants, perfume, and anti-microbial agent. DHSA was heated until melted

prior to the addition of propylene glycol. The mixture was neutralized using NaOH

solution. Ethanol or/and glycerin was added into the neutralized mixture. The

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mixture was cooled at 45oC and poured into a deodorant casing, followed by

setting at room temperature.

c) The characteristic and performance of the palm-based DHSA deodorant stick

• Hardness

The stick hardness as described in DIN 5179, ASTM Standard Method

of Test D 1321-57 T and D937-58 was measured by penetrometer. A

greater distance indicates a softer stick whereas a smaller distance

indicates a stronger resistance to penetration and therefore it is harder.

• Softening point

This is the temperature at which the stick becomes unusable. In this

test, the stick was cut in half lengthways, mounted vertically in petri

dishes and put in incubator. It was then observed as temperature was

slowly raised until the sharp edges of the tip and slides began to melt

or round off [12]

• Disintegration time

The stick was placed in enough distilled water to make an 8% w/w

solution of the stick mass. The beaker containing the stick and water

(at 37 0C) was observed and the time needed for complete dissolution

of the stick was recorded [12].

• Weight loss by evaporation

A saturated solution of sodium nitrite was used to produce the required

humidity (60-70%) in the WTB-Binder oven at 30±0.1 0C. The sticks

were subjected to such conditions in their open containers. Calculation

of percentage of total loss was related to the amount of total solvent in

the sticks (dividing the percent total weight loss by 0.48 since ethanol,

PG and water constituted 48% of the weight of the sticks [12].

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• pH measurement

1% solution was prepared by dissolving 0.5 g sample in 49.4 g distilled

water. The sample solution was then measured with pH meter at

control temperature ( 21oC to 24oC)

• Stability

Stability test was carried out at room temperature (25oC) and 45oC for

three months. The samples were observed for sweating, and stick

deformation phase separation. When the stick was out of shape or oil

droplet could be seen on the surface of the deodorant stick, the system

indicated unstable and vice versa.

•• In vivo anti–microbial test

30 panelist men and women were selected and they were informed

not to use any deodorant or wash with soap a week before the test

was carried out. The prepared stick was applied to either left or right

axilla’s panelist and the one without the product as a control. The

bacteria was inoculated from underarm area using cotton bud starting

from 0 hr (with and without application) and followed by every 2 hours ,

i.e 2hr, 4hr, 6hr and 8hr and transferred into the media agar rich in

nutrient to let them grow. The number of bacteria growth was noted.

• Microscopy

Optical microscopy was carried out using an Olympus AX 70

microscope with a heating stage and microphotographs taken with a

Nikki camera. This microscope was used to identify the texture of

lamellar liquid crystals at various percentage of NaOH solution.

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RESULTS AND DISCUSSION

Ternary phase systems

Figure 1 showed that the anisotropic properties changed from isotropic, lamella

liquid crystals and 2-phase. From the ternary DHSA system, the liquid crystalline

region was observed at 90/10 and 100/0 DHSA and propylene glycol (PG) with

the NaOH solution ranged 27% to 50%.

The texture of the liquid crystalline phase at various compositions was recorded

(Figure 2). The typical pattern of maltese crosses and oily streak were observed

at various percentage of NaOH solution at 45/35/20 of DHSA/PG/ NaOH solution

at 80oC. The prominent maltese crosses structure at 40% NaOH solution was

selected to formulate deodorant stick.

Figure 1

Figure 2

Deodorant stick formulations

Four formulations were prepared based on the three components selected ratio

from the ternary phase diagram which exhibited liquid crystalline structure. The

anti-microbial active and perfume were added to the formulations. The

appearance of deodorant stick ranges from opaque, transparent to translucent,

depending on the crystalline network structure formation.

The deodorant sticks based on DHSA were coded as D4 (with active and

perfume), D5 (without active and with perfume), D6 (with perfume) and D7 as

shown in Table III.

Table III

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Deodorant sticks evaluation

According to Kassem et.al.,[12] the physical properties of deodorant sticks were

evaluated based on hardness, disintegration time, softening point and weight

loss at high humidity upon storage via evaporation. Besides, pH and color

changed were also monitored.

Hardness

The hardness is useful to evaluate the durability of the stick during packaging,

storage and usage upon application. Figure 3 showed the hardness of all the

samples at the initial and upon one month storage did not change much. D6 stick

containing perfume and solubilisant gama 2428 was found to be the hardest

while the rest of the sticks were comparable to the C2 (5.8 -6.2 mm) except D7

has similar hardness with C1.

Figure 3

Softening point

The softening point is of interest in hot climate especially during handling,

storage and display in pharmacy window. Figure 4 showed that the softening

point in D series were comparable to the commercials C1 and C2. However, all

the formulations showed practically an acceptable softening point and there were

not much changes in softening point upon one month storage.

Figure 4

Disintegration time

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Figure 5 showed that D4, D5, D6 and D7 had the lowest disintegration time

which are suitable for medicated stick. After one month storage, similar

disintegration time for all samples was observed..

Figure 5

pH measurement

The stick pH varied from 9.5 to 10.5 which is suitable for the human skin and

non-irritant upon application. D4, D5, D7 and D6 were comparable or higher

than C1 and C2.(Figure 6).

Figure 6

Rate of drying of the sticks by evaporation

Figure 7 showed the weight loss of deodorant sticks in 7,14, 21 and 28 days. D4,

D5, D7 indicated ≤ 5% weight loss which is not comparable to C2 but is better

than C1. This is due to C2 formulation contained PEG-400 beeswax while C1

contained alcohol. Therefore PEG-400 helps to stabilize the system.

Figure 7

Storage stability

Sweating is an excess of oil or solvent occurred onto the surface of deodorant

sticks. Sweating can be seen clearly if the sample is unstable. Table IV showed

that all the sticks were stable upon storage for 3 months at 28oC and 45oC except

for C1. C1 was found to be unstable because it contains alcohol.

Table IV

In vivo anti–microbial test

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To differentiate and selective of the growth of bacteria and mould /yeast,

mannitol salt and saboroud dextrose agar were used respectively. The mannitol

agar changed from reddish to yellowish color by staphylococcus aureus

indicating an acidic condition with pH ≤ 6.8. This bacterium gave bad odor.

Figures 8 and 9 showed the score given based on the number of bacteria/yeast

growth for every 2 hrs until 8 hrs. The score number 1 to 3 indicates less growth,

whereas 4 to 5 indicated more growth. Figure 8 showed that D4, D5 D6 and D7

gave the score ≤ 3.3 for a period of 6 to 8hrs which is acceptable growth

compared to 0hr (C) and 8hrs ( C ) giving higher score, i,e 5.0.

Figure 9 showed the fungus and yeast growth on the sabaroud dextrose agar

with the score versus the samples. D4 and D7 indicated ≤ 3.0 for 8 hrs when

compared to 0 hr and 8 hrs ( C ).

CONCLUSION

The optical pattern which showed maltese crosses is the most stable when

formulated into products. The appearance of deodorant sticks, ranges from

opaque, transparent to translucent is due to the crystalline network structure

formation. The physical properties of DHSA sticks i.e pH, softening point

hardness, and disintegration time remain unchanged after one month storage.

The DHSA deodorant sticks either with active antimicrobial or perfume, have

short disintegration time making them suitable for medicated type. D6 indicated

less evaporation and comparable to C2. After 3 months' storage, no sweating

was found in all samples and comparable to C2 . D7 was found to have anti-

bacterial properties.

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12. References

1. Motley C., WO 9604886 (1996). Procter & Gamble.

2. Smith J., US 5480637 (1996). Dow Corning.

3. Bahr B, Legrow G., Katsoulis, Smith J., US 5492692 (1996). Dow Corning.

4. Market report, Antiperspirant–deodorant Market Update, Soap, Perfumery &

Cosmetics, Happi 7, 2001, 21 5. Fox, C., (1984). Gels and sticks review and update, Cosmetics and Toiletries ,

99,19.

6. Barker G., et al., Versatile gelling agents for innovative stick, Product, Soap and

Chem. Spec., 58, (1982), 44a –44 b.

7. Barker G., et al., Solidified sodium stearate-based sticks, Cosmetics Toiletries ,

(1977), 92, 73-75.

8. Awang, R., Ahmad, S., and Kang, Y.B., Preparation of dihydroxyfatty acid from

oleic acid Malaysian Patent, PI 9804456,(1998)

9. Awang,R., Basri, M., Ahmad, S., and Salleh, A.B., Characterization of

dihydroxystearic acid from palm oleic acid. J. Am Oil Chem Soc., 78 (6)

(2001),1249-1252.

10. Awang,R., Basri,M. Ahmad, S., and Salleh, A.B., Enzymatic esterification of

dihydroxystearic acid, J. Am Oil Chem. Soc. 77(6) (2000), 609-612

11. Awang, R., Ahmad, S., and Ghazali, R., Properties of sodium soap derived from

palm-based dihydroxystearic acid, J..of Palm Oil Research , 13 (2), (2001). 33-

39

12. Kassem, A.A., Mattha, A.G., and El-Khatib, G.K. Influence of some humectants

on the physical characteristics of solidified sodium stearate-based sticks, Int. J.

Cosmet. Sci., 6, (1984),13-31.

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ACKNOWLEDGEMENTS

I would like to thank Y Bhg. Tan Sri Datuk Dr. Yusof Basiron (Director-General of

MPOB) for giving the opportunity to present this paper and Hajar Bilal for her technical

assistance.

PG

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NaOH solution DHSA

Figure 1 : Ternary Phase Diagram of DHSA/PG/NaOH solution at 80oC

35% 40% 43%

25% 27% 30% Figure 2 : Liquid crystalline structure at 45/35/20 of DHSA/PG/ NaOH solution. in 80oC

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Table I : Estimated growth of deodorant market, 2000-2005

Countries 2000 ( $ m) 2005 ($ m)

United Kingdom 700.1 732.6

Germany 521.2 552.4

France 461.3 541.5

Italy 357.5 383.5

Spain 201.9 252.5

Source : Information Resource-ces, Inc. (IRI),Chicago

Table II .Specification of crude DHSA

Parameter Crude DHSA

Iodine value (g I2/100)

Acid value (m KOH/g)

OHV (mg KOH/g)

Sap. Value (mg KOH/g)

Melting point (oC)

Form

10.2 ± 1.6

179.3 ± 0.4

196.0 ± 4.2

178.0 ± 0.2

61.9 ± 1.3

semisolid

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Table III: Palm-based deodorant sticks formulations

DHSA BASED

CODE D4 D5 D6 D7

DHSA/PG/NaOH solution Y Y Y Y

Humectant 2 Z Z Z Z

Active –antimicrobial activity

(Sandalwood)

2.7 2.7 - -

Perfume 0.5 - 2.7 -

Solubilisant gama 2428 1.0 5.4 -

Table IV : 3 months storage stability of palm-based deodorant sticks

Code RT (28oC) 45oC

S4 S5 S6 S7

S S S S

S S S S

D4 D5 D6 D7

S S S S

S S S S

C1 C2

US S

US S

0

2

4

6

8

10

Har

dnes

s (m

m)

D4 D5 D6 D7 C1 C2

Palm-based deodorant sticks initial 1 month

Figure 3 : Hardness of palm-based deodorant sticks

56

58

60

62

64

66

68

Soft

enin

g po

int (

o C)

D4 D5 D6 D7 C1 C2

Palm-based deodorant sticks initial 1 month

Figure 4 : Softening point of palm-based deodorant sticks

0

0.5

1

1.5

2

2.5

3

Dis

inte

grat

ion

time

(hrs

)

D4 D5 D6 D7 C1 C2

Palm-based deodorant sticksinitial 1 month

Figure 5 : Disintegration time of palm-based deodorant sticks

15

9

9.2

9.4

9.6

9.8

10

10.2

pH

D4 D5 D6 D7 C1 C2

Palm-based deodoranrt sticks initial 1 month

Figure 6: pH of palm-based deodorant sticks

0

5

10

15

D4 D5 D6 D7 S4 S5 S6 S7 C1 C2

Palm-based deodorant sticks

% w

eigh

t los

s (g

)

7 days 14 days 21 days 28 days

Figure 7 : Weight loss of deodorant sticks upon storage at high humidity

16

17

D4D5

D6 D7D5

D7

5

4

3

scor

e

2

1

0C(0hr) 0 hr 2hrs 4hrs 6hrs 8hrs C(8hrs)

D4 D5 D6 D7 C1

Figure 8: Bacteria growth rate on mannitol agar for palm-based deodorant sticks

D4

D7

0

1

2

3

4

5

Scor

e

C (0hr) 0hr 2hrs 4hrs 6hrs 8hrs C(8hrs)

D4 D5 D6 D7 C1

Figure 9: Fungus and yeast growth rate on saboroud dextrose agar for palm-based deodorant sticks

ranking : 0 1 2 3 4 5 < growth > growth