This document summarizes a study on determining the critical micelle concentrations of various biodegradable surfactants. Specifically, it analyzes sodium dodecyl sulfate (SDS), polysorbate 80 (Tween 80), and saponin extracted from soapnuts. The critical micelle concentration of each surfactant was determined by measuring the conductivity and pH of solutions with varying concentrations and plotting the results. The study found the CMC of SDS to be 8mM, Tween 80 to be 0.012mM, and extracted saponin by soaking soapnut pericarp in water and monitoring conductivity and pH over time.

1. A STUDY ON BIODEGRADEABLE
SURFACTANTS AND
DETERMINATION OF THEIR
CRITICAL MICELLE
CONCENTRATIONS
REPORT BY
Ritu Treisa Philip
Sengavi Thirupathy
(SSN College of Engineering, chennai )
UNDER THE GUIDANCE OF
Dr. Susy Varughese
Department of Chemical Engineering
Indian Institute of Technology, Madras
MAY – JULY 2016

2. ABSTRACT:
A detergent is a surfactant or a mixture of surfactants which possesses cleaning
properties in dilute solutions. These substances are usually
alkylbenzenesulfonates, a family of compounds that are similar to soap but are
more soluble in hard water (as the polar sulfonate(of detergents) is less likely than
the polar carboxyl (of soap) to bind to calcium and other ions found in hard
water). The detergents of today have few disadvantages like:
 Detergents are non biodegradable.
 Soil pollution and water pollution can be caused by soil pollution.
 Entry of non biodegradable substances into the food cycle and increase in
the concentration can result in bio magnification.
 Some detergents also contain inorganic phosphates which are dangerous to
the environment. They cause conditions like eutrophication.
In an attempt to solve this problem, the use of soapnuts as a natural bio-
degradable source of surfactants has come into existence. Soapnuts are
major source of a natural surfactant called saponin. It is a non-ionic
surfactant and a mild detergent which goes easy on the skin and the fabric.
In order to understand more about surfactants and their CMC value
determination, surfactants like SDS and Tween-80 and their micellar
characteristics have been studied. The critical micelle concentration of
Sodium dodecyl sulphate, polysorbate-80 and sapindus saponin have been
determined by plotting graphs between concentration of the solutions
against pH and conductivity. Sapindus Saponin was extracted from
commercially purchased soapnuts using method given by Rao et al.the
saponin hence obtained was used for further studies on their CMC. The raw
pericarp of the soapnuts were soaked in water and the pH and conductivity

3. of the water was recorded and a time against ph and conductivity plot was
obtained to study the characteristics of the saponin released during the
process over time.
WHAT ARE SURFACTANTS?
Surfactants are compoundswhich lower the surface tension between two
liquidsor between a liquidand a solid. Surfactants may act as detergents,
wetting agents, emulsifiers and dispersants. Surfactants are usually
organic compoundsthat are amphiphilic.They containboth hydrophobic
(water insoluble)and hydrophilicgroups (water soluble). These are the
tailsand headsthat form the surfactant structure. Surfactants will diffuse
in water and adsorb at interfaces between airand water or oil and water.
Most commonly, surfactants are classified according to polarhead group.
A non-ionicsurfactant has no charge groups in its head. The head of an
ionic surfactant carries a net charge. If the charge is negative, the
surfactant is more specificallycalled anionic;if the charge is positive, it is

4. called cationic.If a surfactant containsa head with two oppositely
charged groups, it is termed zwitter-ionic.
We distinguishbetween non-ionicsurfactants and ionic surfactants.
The ionic groups are much more hydrophilicthanthe non-ionicpolar
groups. The nonionicsurfactants are dissolvedas electroneutral
molecules, e.g. higher fatty alcoholsor cholesterol which have polar
hydroxyl groups. Ionic surfactants dissociate in aqueoussolutionsinto
pairs of 2 cationsand anions, but usually only one kind of these ionsare
surface active, and ions with the opposite charge are called counterions.
Based on the charge and the nature of the ion which generates surface
activity, we can divide the ionic surfactants into following classes:
1. anion-active(anionic)surfactants - e.g. sodium or potassium salts of
higher fatty acids (soaps), salts like sodium dodecyl sulfate, sodium
tetradecyl sulfate etc.
2. cation-active(cationic) surfactants - e.g. quaternary ammonium salts –
hexadecylpyridiniumbromide, carb ethopendeciniumbromide
(Septonex) etc.
3. ampholyticsurfactants – e.g. long-alkyl aminoacids, with pH
dependentcharges.

5. POLYSORBATE – 80(C32H60O10)
Polysorbate 80 is a non-ionic surfactant commonly used in the food
industry and cosmetics industry. It is an amber coloured, viscous and
water-soluble liquid.This surfactant provides formulating benefits in a
number of home care applicationsas well. Polysorbates or tweens are
hydrophilicin nature and or soluble or dispersible in water and dilute
solutionsof electrolytes. The solubilityof Tweens in acqueoussolutions
increases with the degree of ethoxylation.
Polysorbate- 80 is PEG-20 sorbitan monoleate. It is solublein water,
partiallysoluble in repressed oil and methyl oleate. It is insolublein
mineral oil, kerosene and Butyl stearate.

6. SDS – Sodium Dodecyl Sulphate
Sodium dodecyl sulfate (SDS or NaDS), sodium laurilsulfateor sodium
lauryl sulfate (SLS) is an organic compound with the formula
CH3(CH2)11OSO3Na. It is an anionicsurfactant used in many cleaningand
hygiene products. The salt is of an organosulfate consisting of a 12-
carbon tail attached to a sulfate group, giving the material
the amphiphilicproperties required of a detergent. Derived from
inexpensive coconut and palm oils, it is a common component of many
domestic cleaning products. Sodium laurylsulfate is probably the most
researched anionicsurfactant compound. Like all detergent surfactants,
sodium lauryl sulfate removes oilsfrom the skin, and can cause skin and
eye irritation. The critical micelle concentration (CMC) in pure water at
25 °C is 8.2 mM, and the aggregation number at this concentrationis
usuallyconsidered to be about 62. The micelle ionizationfraction (α) is
around 0.3 (or 30%).

7. SOAP NUTS AND SAPONIN:
Saponinsare a class of large number of saponaceoussubstances
produced by plants. Examples of plants, which have saponin,are soapnut,
soybean, Quillaja bark and Fagonia indica.Soapnutsare obtainedfrom
the trees of Sapindusmukorossi and Sapindusemarginatus, found in
India, Pakistan and other tropical and sub-tropical regions of the world.
The outer pericarp of soapnutscontains6–10 wt% of saponindepending
on the weight of the fruit. The outer pericarp of soapnutshas been
traditionallyused in India for fabric washing, bathing and in folk medicine
due to the formation of lather or foam in water. The saponin used in the
experiment has been extracted from soapnutsand are calledsapindus
saponin.
CRITICAL MICELLE CONCENTRATION:
This is the concentrationwhere surfactant will work as a micelle. Because
surfactants are absorbed mainlyon the surface of the solution, creating a
thin monolayer, they are called surface active substances.When they are
dissolved, after they reach a certain value of concentration, molecules or
ions of surfactants begin to associate and to organize themselves into
more complexunits, also called micelles. The characteristic concentration
value, where the association process begins, is calledthe critical micelle
concentration and is labeledwith abbreviation CMC.
The CMC is one of the most useful physicochemical characteristics of
many biologicallyactive substances and drugs. From the chemical point
of view, surfactants are mostly low-molecularcompounds, so when
dissolved, they form true solutionsin concentrationranges below the
CMC. Micelles aggregates are formed from larger number of simple
molecules or ionsof surfactants, so the resulting size of such structures is
in the colloidal range.

8. DETERMINATIONOF CMC:
The physicalmethods for CMC determinationincludesconductivity,
solubility,viscosity, light scattering, measuring the surface tension by
Wiebelmy slide method or by the method of maximum bubblepressure ,
measurement of ion activity and by dye incorporationmethod, Gel
filtration spectrophotometricallyandcounter-ion magnetic resonance.
Schematic representation ofthe concentrationdependence of some physical
properties ofsolutions ofa micelle-formingsurfactant. (Redrawn from Jönsson,
B., Lindman,B., Holmberg,K. and Kronberg, B., Surfactantsand Polymersin
Aqueous Solution),©1998 John Wiley & Sons Ltd., Chichester,Reprinted in April
2001,p. 36, Reproduced with Permission) [6]
The sharpness of the break in the physical properties dependson the
nature of the micelle and on the method of the CMC determination.
The CMC is a useful tool for the selection of surfactants for specific
applicationsor properties. The CMC can be determined by measuring the
changes in physicalproperties such as electrical conductivity,turbidity,
surface tension, interfacialtension, solubilisationandauto diffusion.
Detail evaluation ofdifferent methods for the determinationof CMC can
be found in (Mukherjee et al 1971).

9. EXPERIMENTAL STUDIES:
Determination of CMC of SDS, Tween- 80:
Tween 80 is a non-ionicsurfactant whose CMC is 0.012mM. Based on this
50ml solutionsof different concentrations aroundthat range of tween-80
were prepared. Following which, the pH of each concentration was
measured using a pH meter and tabulated.For each solution,the
conductivitywas also measured and tabulated.
The same procedure was carried out for SDS (Sodium Dodecyl Sulphate),
whose CMC is 8mM. Accordingly, 50ml solutionsof different
concentrationswere prepared. Followingwhich, the pH and conductivity
of each concentrationwere measured and tabulated.
Thus, CMC was determined by studying the variationof pH and
conductivitywith change in concentrationof the surfactant.
Studying the properties of saponin extracted from pericarp as a
function of time
Soap Nuts consist of 56.2 % pericarp and 43.8% seed. The outer pericarp
of the soapnuts were separated from the seeds. 100g of the pericarp was
measured and then taken in a beaker. To this 300g of water was added.
The beakerwas sealed and kept aside to rest. 20mL samples were
periodicallydrawn and their pH and conductivitywas measured at that
point of time. The values were tabulatedand a graph of pH/conductivity
vs. time was plotted to study its variationwith time.

10. Extraction of Sapindus Saponin precipitate from Soap Nuts
Saponinwas extracted from soapnut applyingthe method detailedby
Rao et al. Soapnutswere purchased from a local shop. The outer pericarp
of the fruits were separated from the seeds and weighed. (Fig. A &B)
Then the pericarp was dried at 400
C for 4 daysin a hot air oven. It was
ground to a fine powder (Fig. C)and the water-soluble matter was
extracted. Thissolution was centrifuged for 1 hour to separate water-
insolublematter. The extract was then treated with ammonium sulphate
to precipitate the saponin.The saponinthat separated on the top was
skimmed off and dried at 400
C. (Fig. D&E) [3]
(A)
(B)

11. (C)
(D)

12. (E)
Determination of CMC of Saponin:
From the extraction process of saponin from the dried pericarp, 0.577g of
saponin was obtained as precipitate. From this different weights of the precipitate
was measured and dissolved in 50g of water to prepare solutions of different
concentrations (ranging from 0.02% to 0.12% in weight percent). After which pH
and conductivity of each solution was measured and tabulated. A graph of pH vs.
concentration and conductivity vs. concentration was plotted to determine the
CMC value of saponin. [9]
RESULTS AND DISCUSSIONS:
From the pH metry and conductivityexperiments on the different
concentrationsolutions, pH vs concentrationand conductivityvs
concentrationwere plotted. By the literature followed, CMC was
identifiedto the point in the graph where is there is a change in slope.
The CMCs obtainedfrom the experiments closely fell within the range
specified by the literature.

13.  Determination of CMC of Tween- 80:
-0.002 0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016
5.0
5.2
5.4
5.6
5.8
6.0
6.2
6.4
6.6
pH
CONCENTRATION
pH
CMC
-0.002 0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016
1
2
3
4
5
6
7
CONDUCTIVITY(µSi)
CONCENTRATION (mM)
CONDUCTIVITY
CMC

14. After studying the variation of pH and conductivity with
concentration, the CMC of Tween 80 was found to be around
0.012mM.
The Literature states that the CMC of Tween 80 is found to be within
the range of 0.012-0.016 mM [1] [2]
 Determination of CMC of SDS:
-2 0 2 4 6 8 10 12 14 16 18
6.0
6.5
7.0
7.5
8.0
pH
CONCENTRATION (mM)
pH
CMC

15. -2 0 2 4 6 8 10 12 14 16
0
100
200
300
400
500
600
700
CONDUCTIVITY(µSi)
CONCENTRATION (mM)
CONDUCTIVITY
CMC
On studying the variation of pH and conductivity with concentration, we get the
CMC value of SDS as 8mM.
The CMC value of SDS generally lies between the range of 6-8 mM from
literature. [5]

16.  Determination of CMC of SAPONIN:
0.02 0.04 0.06 0.08 0.10 0.12
0.1
0.2
0.3
0.4
0.5
0.6
0.7
CONDUCTIVITY(mSi/cm)
CONCENTRATION (Weight Percentage %)
CONDUCTIVITY
pH
CMC
6.2
6.4
6.6
6.8
7.0
7.2
7.4
7.6
7.8
pH
Variation of conductivity and pH with Sapindus saponin at various
Concentrations

17. Fig. A – Reference paper (1)
The CMC of Sapindus Saponin was found to be 0.045 wt % from the above graph
[1]

18.  Extraction of sapindus saponin precipitate from Soapnuts:
The above mentionedpaper’s experimental method was followed and
from 40g of soapnut powder taken 0.577 g of saponinwas obtained.
 Extraction of saponin from soaked Pericarp
The trend of the experiment is rightly found to be pH decreasing with
time. The experiment was carried out for 4 days.

19. The trend of the experiment is rightly identifiedto be Conductivity
increasing with time. The experiment was carried out for 4 days.
FUTURE RESEARCHSCOPE:
 Newer methods of extraction of SapindusSaponin
 Further work on Bio-Remediationby detergents
 Biodetergents
 Compare the efficiency of saponinaobtainedfrom extraction
process and directly from the pericarp

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