Colloidal and Surface
Phenomena of
Liquid Laundry Detergent
CE 457-527
Dr. Alexandridis
April 9, 2002
Daniel Boek
Erika Indivino
Katherine Marso
Karey Smollar
Table of Contents
Page
History
3
Components
8
Soil Removal
16
Fabric Types
27
Processing
28
Packaging
28
Environmental Concerns
30
Market Sales
30
2
History and Background of Laundry Detergents
The method of cleaning clothes has changed greatly since its beginnings in ancient
history. The first form of laundering was purely mechanical. Clothes were beaten
against rocks to remove water-soluble stains. To remove the more difficult oily stains,
additional compounds needed to be added. This led to the first production of soap in the
15th century1.
By combining animal or vegetable fats with aqueous sodium hydroxide soap is made.
Soaps are advantageous because they are made from biodegradable renewable resources.
Therefore, soaps are not polluting the environment. These factors are outweighed by the
negative affects of hard water and the cost of the raw materials. Soaps react with calcium
and magnesium ions in hard water leading to the formation of precipitates. Increased
household use of alkylbenzene sulfonates (ABS), a former compound used in laundering
with soaps, resulted in large bodies of water covered in foam. The synthesis of ABS is
shown below in Figure 1.
Figure1: Synthesis of ABS2
These factors, as well as the commercialization of the Ziegler process leading to the
production of linear alkylbenzene solfonates, lead to the production of synthetic
detergents3.
3
The manufacture of synthetic detergents, commonly called laundry detergent, began in
1916 in Germany during WWI. The production of detergents in the United States took
off after WWII. The first detergents were used mainly for dishwashing and fine fabric
laundering. In 1946 the first all-purpose laundry detergent was produced using builders
with surfactants4. Surfactants and builders became increasingly more complex as the
demand for better soil removal grew. The use of sodium triphosphate (STP), a very
effective builder, was restricted in the 1960’s because it caused eutrophication in rivers.
Trisodium citrate, NaCit, is an effective, biologically degradable builder commonly used
in detergents today5.
Figure 2: Chemical Structures of STP and NaCit6
New additives are continually being introduced to the detergent industry to keep up with
customer demand.
Liquid laundry detergent became popular in the U.S. in the 1970’s. The USA holds the
largest market of liquid heavy-duty detergents (HDL) in the world. Liquid laundry
detergents usually do not contain bleaching agents and are best at removing oily stains at
low temperatures7. Liquid laundry detergent is a huge industry in the United Stated.
Research has continued to develop detergents that would provide people with efficient
cleaning agents that are safe for the environment. The sale of liquid detergent has soared
over powdered detergent in the last decade. The two types have reached a 50/50 market
split in the U.S., whereas liquid detergent only holds 13% of the market in Europe.
Consumers find liquid detergents more convenient to use while giving better results in
the U.S. Liquid detergents are easier to measure and easier to apply directly to stains.
The liquid laundry detergent industry will continue to grow in the coming years and
overtake that of powdered laundry detergents8.
4
An interesting development in the industry is the introduction of tablets first marketed in
2000. Tablets are marketed towards students and the elderly for their convenience factor.
Tablets dissolve within seconds of hitting the water. Although they are new and fairly
expensive, with continual improvements in efficiency and production, tablets will also
become a strong competitor in the market9.
There has been very little response to tablets in the U.S. In Europe, on the other hand,
tablets hold 25% of the market in some countries. This response lead to the introduction
of the sachet, or pouch, in April 2001. This new product delivers liquid laundry detergent
through a water-soluble polyvinyl alcohol skin. The pouch dissolves in minutes, leaving
behind no residue. These types of unit-dose products, such as tablets and pouches, are on
the very frontier of the detergent industry. It is a race to see which company can produce
the fastest dissolving, most easily dispensed detergent on the market10.
5
Design considerations
Laundry detergent is a basic necessity for every household. Liquid laundry detergents
must have specific properties that will meet the needs of the general public.
Excellent soil removal is the main feature that consumers look for when choosing a
detergent. This is the central reason that people need any cleaning agent, to remove the
dirt.
Low sensitivity to water hardness is another crucial property of detergents. Many homes
only have hard water available. Hard water that contains high concentrations of calcium
and magnesium greatly decreases the effectiveness of soaps. The minerals react with the
soap to form a precipitates that are left on clothes. Detergents were introduced to
laundering applications to remove soils without leaving precipitates. Since most people
cannot afford to have a water softening system their home, it is important that detergents
avoid the formation of precipitates. Liquid laundry detergents contain builders that
prevent calcium and magnesium deposits when using hard water. Detergents must also
have good dispersion properties to ensure that the entire load of clothing is sufficiently
cleaned. Liquid detergents dissolve and spread much faster than powder detergents do in
water. Soil antiredeposition capability is also very important. Surfactants in the
detergent must be decided upon according to how well they keep soil from redepositing
onto the clothing. The soil from the clothing must be kept in suspension in the water
until it can be rinsed away. It is important that detergent has a high solubility in water.
The purpose of using a detergent is to overcome the surface tension of water so that soils
can be removed. The surfactants need to overcome the surface tension of water to ensure
sufficient wetting power. Liquid laundry detergents dissolve in water more quickly than
powdered laundry detergents, especially in cold water.
The amount of foam during washing has a psychological affect on whether detergent is or
isn’t working. Too little foam indicates poor cleaning performance. Poor rinsing and
draining is also a result of too much foam. Liquid laundry detergents contain surfactants
that act as foaming agents to control this element of the detergent. Odor is another aspect
6
to be considered when thinking about consumer needs. Fragrances need to be added to
cover any chemical smell of the detergent. Perfumes are also added to differentiate one
brand from another. Detergents with low levels of fragrances are also produced for
people who are sensitive to perfumes. The color of the product should also be
considered, but not too excessively. On the other hand, the amount of toxicity to humans
should be a major concern. One cannot assume that every user of a household product
pays strict attention to warning labels or recommended safety precautions. Therefore,
exposure through skin, ingestion, and inhalation must be investigated whenever chemical
products are put on the market. Every compound included in liquid laundry detergents is
extensively investigated for its affects on humans.
Favorable environmental behavior is another important aspect that must be integrated
into liquid laundry detergent. Excess water containing additional energy (heat), soil from
the laundry, lint, dyes, finishing agents, and detergents is drained into the environment11.
The affects of these by-products on the environment need to be as minimal as possible.
The use of phosphates, one of the original compounds used in detergent, has been
severely limited due to their harmful affects on the environment. Companies continue
research in the area of environmental affects to ensure that detergents are not damaging
the environment.
Convenience is a very important design consideration for detergent companies.
Costumers find liquid detergents easier to pour with a cap as opposed to scooping dry
detergent out of a box12. All the above mentions aspects of detergent must be integrated
into product that can be sold in a very competitive market. There is a fine balance
between creating an efficient cleaning agent, keeping the costumers happy, and keeping
the environment safe.
7
Components
The components of liquid laundry detergent are listed in Table 113 below:
Table 1: Composition of liquid laundry detergent
Ingredients
Volume Percent
Anionic Surfactants
Nonionic Surfactants
Soaps
Builders
Solubilizers
Alcohols
Enzymes
Optical Brighteners
Stabilizers
Fragrances
Water
10 - 25
6 - 10
4-6
15 - 30
0-5
0-5
0 - 1.5
0.05 - 0.25
Trace amount
Trace amount
30-50
Surfactants
Surfactants are the most important components of liquid laundry detergents. Surfactants
are water-soluble surface-active agents that adsorb onto the surface of soil particles to
separate the soil from clothing. Surfactants remove oil by lowering the surface tension of
water, allowing the clothing surface to become wet.[1] Surfactants consist of a
hydrophilic and a hydrophobic portion. The hydrophobic component consists of an eight
to eighteen carbon hydrocarbon. Sources of these hydrocarbons are natural fats and oils,
petroleum fractions, synthetic polymers, and synthetic alcohols.
Surfactants are divided into three groups; anionic, nonionic and cationic. Anioinic
surfactants are the most abundant ingredient in liquid laundry detergent because they
have proven to show the most enhancing effects of removal of soil. Nonionic surfactants
are used primarily for their stabilization effects during detergency.
8
Surfactants are chosen based on their sensitivity to water hardness. Certain surfactants
such as Linear Alkylsulfonate (LAS) show good detergency despite water hardness. The
surfactants exhibiting more sensitivity to water hardness are less effective regarding their
absorbance to fabrics and an increased production of surface film. Not one single
surfactant is capable of effectively removing all soil types on different types of fabrics.
Therefore, surfactant mixtures are proven to be most effective when considering a wide
range of solvent conditions and soil types.
The effectiveness of surfactants is proportional to the length of the chain. A high number
of carbon atoms in the surfactant molecule correspond to an increase in the number of
surfactants adsorbed. The type of hydrophilic group determines the classification of the
surfactant as anionic, nonionic, or cationic. The characteristics of surfactants cause the
hydrophobic component to be drawn together to form micelles. This allows the
surfactants to form a coating around a suspended material. A surfactant used to suspend
a solid in water is called a dispersant.[2]
Liquid laundry detergents contain larger amounts of anionic surfactants than ionic
surfactants. Anionic surfactants ionize in solution and have a negative charge. They are
good cleaning agents and create high “sudsing”. Some examples of anionic surfactants
are linear alkylbenzene sulfate, alcohol ethoxysulfates, alkyl sulfates and soaps.
Nonionic surfactants do not ionize in solution and therefore have no electrical charge.
Cationic surfactants ionize in solution to give a positive charge.
Anionic Surfactants
Anionic surfactants are the main component of liquid laundry detergents and found to be
the most active ingredient for the soil removal process14. Some examples of the most
common type of anionic surfactants include sodium linear alkylsulfonate (LAS),
alkanesulfonates (SAS), and olenfinsulfonates (AOS).
9
The production of LAS originated from the former surfactant called
Tertrsproplynenbenzene sulfonate (TPS), which was used in the earlier stages of
detergency to replace the use of regular soaps. The structures of both molecules are
similar, but the LAS molecule eliminated the branching found on the TPS molecule. The
straight chain structure of LAS demonstrates more effective detergency due to its
increasing solubility, greater level of biodegradation, and less sensitivity to changing pH
levels. LAS is shown below in Figure 3.
n + m = 7–10
Figure 3: Sodium linear alkylsulfonate (LAS)
TPS is shown below in Figure 4.
Figure 4: Tetrapropylenebenzenesulfonate (TPS)
Another type of anionic surfactant, Sodium Alkanesulfonate, has high solubility, fast
wetting properties, and chemical stability of alkali and acids15.
10
The production of SAS is formed by sulfooxidation and sulfochloronation process.
Figure 5: Secondary Alkanesulfonates (SAS)
The third type of anionic surfactant, Olenfinsulfate (OAS) is produced using the alkaline
hydrolysis process. This surfactant is unique because it exhibits less sensitivity to water
hardness. This effect can be dependent on the chain length of the hydrophobic portion of
the surfactant.
R1–CH2–CH=CH–(CH2)n–SO3Na Alkenesulfonates
Hydroxyalkanesulfonates
R1 = C8 – C12
n = 1, 2, 3
R2 = C7 – C13
m = 1, 2, 3
Figure 6: Olefinsulfonates (AOS)
The characteristics of these surfactants offer several advantages over one another. Due to
the fact that detergents must maintain satisfactory ability for removing various types soils,
the most effective type of surfactant used has proven to be a surfactant mixture. The
advantages of using surfactant mixtures include reduction of amount of detergent needed
during the detergency process and the reduced size of packaging.
11
Nonionic Surfactants
Nonionic surfactants are also an essential ingredient for liquid laundry detergents, but are
often found in a much smaller quantity as compared to anionic surfactants.
Both types of surfactants play different roles in detergency but work well in conjunction
with one another. The anionic surfactant plays an active role in the removal of the soil
from the surface of the fabric. The nonionic surfactants are used for the stability of
solution. The nonionic surfactants, depending on their structure, are commonly attracted
to the outer most part of the micelle and are used to help stabilize the micelle formations
and reduce redeposition of the treated soil back onto the fabric.
Builders
Builders play an important role in the effectiveness of liquid laundry detergents by
enhancing the affects of surfactants. Builders help remove water hardness and keep soils
from redepositing onto the clothing. The most common types of builders are phosphates,
silicates, carbonates and oxygen releasing materials. Phosphates are no longer used due
to their negative affect on the environment.
Builders are also used to remove Ca2+ and Mg2+ ions which produce hardness of the wash
liquor. Calcium and magnesium form complexes with builders, diminishing the
surfactant interaction with calcium and magnesium. Trisodium citrate is the most
common builder used in today’s laundry detergent. Trisodium citrate is shown in Figure
7.
Figure 7: Trisodium Citrate (NaCit)
12
In the absence of builders, hardness ions form complexes with soil. The complex can
redeposit onto the negatively charged fabric and soil interfaces. Zeolites are waterinsoluble builders of 10m diameter and molecular formula Na2OAl2O3*4.5H2O.
Calcium and magnesium ions replace sodium ions from the zeolite crystals. Therefore,
hardness ions cannot form complexes in the wash liquor.
Redeposition Inhibitors
Micelles are negatively charged structures that can redeposit on neutral surfaces. For
example, synthetic fibers don’t acquire a strong negative charge in water. Therefore, the
surface needs an electrostatic charge to keep negatively charged detergent micelles from
redepositing their soils on the fabric. These additives are known as redeposition
inhibitors. Sodium carboxymethyl cellulose (SCMC) is a polymer of molecular weight
from 20,000 to 500,000 that attaches itself to the fibers and adds to the negative charge.
SCMC can be seen in Figure 8 below.
Figure 8: SCMC Diagram
13
The types of detergent builders have changed over the years with increasing
environmental awareness. With tighter environmental restrictions, the uses of phosphates
biulders in detergents have been diminishing.
Enzymes
Protein stains from sources such as milk, cocoa, blood, egg yolk, and grass are resistant
to removal from fibers by enzyme-free detergents, particularly after stains are dried-on.
Chocolate, starch-based food stains, and greasy/fatty stains are particularly difficult to
remove in low-temperature washing. Proteolytic, amylolytic, and lipolytic enzymes are
usually capable of eliminating such soil during washing.
Commercial production of detergent enzymes experienced rapid expansion in recent
years. For example, by 1969 nearly 80 % of the detergents marketed in the Federal
Republic of Germany contained proteases as enzyme additives to detergents. Today's
detergent enzymes are perfectly safe. As a result, nearly all detergents produced in
Europe, North America, Japan and many other countries worldwide contain enzymes
today. The effectiveness of proteolytic, amylolytic, and lipolytic detergent enzymes is
based on enzymatic hydrolysis of peptide, glucosidic, or ester linkages, respectively.
Whitening agents
14
Fluorescent whitening agents (FWA), or optical brighteners, are added to liquid laundry
detergents to give laundry a much whiter appearance. FWA’s are organic compounds
that convert invisible ultraviolet light into longer wavelength visible blue light. Optical
brighteners decrease the absorption of the blue radiation that gives clothes a yellowish
tint. Due to the fact that FWA’s also exhibit reflectance in the visible region, a build up
on the fabric may also leave marks. FWA’s are applied through a dyeing process.
Distyrylbiphenyl, stilbene, coumarin, and bis(benzoxazole) are the most common
brighteners. FWA’s are evaluated on their stability (resistance to chemical change} and
fastness (chemical change after adsorption).
15
Soil Removal
Removal of Oily/Greasy Soil by Detergents
The removal of soil from clothing is primarily due to the wetting properties and
interfacial tensions between the washing liquid and the deposited soil. During the
washing process, the most significant interactions occur between the liquid (water) and
the surfactant. Over the time clothes are worn, oily/greasy soils are deposited and spread
evenly on the clothing. The ability of water to be in contact with oil is referred to as the
measure of wetting. The measure of wetting is useful when describing the contact angles,
which are responsible for the removal of the soil from the fabric.
The physical properties of water and the ingredients of the detergent are essential. The
soil that is present on clothing is apolar and the washing liquid is polar. In order for the
removal of the soil from the clothing to occur, there must be some sort of medium, which
causes a strong attraction between the two surfaces. Anionic surfactants allow for the
formation of the droplets, but nonionic surfactants create the attraction between the
micelles.
Surfactants concentrate at water-liquid, water-gas, or water-solid interfaces because the
hydrophobic and hydrophilic properties of the surfactant are satisfied. One nonionic
surfactant molecule has an apolar hydrocarbon polymer tail and a polar head group. The
following diagram depicts a single surfactant. Another type of surfactant, ionic
surfactants, have static charges associated with their head groups.
polar head
group
apolar hydrocarbon polymer
Figure 9: Nonionic Surfactant Molecule
16
Figure10 below displays the alignment of surfactant molecules at an interface between oil
and water.
Oil
interface
Water
Figure 10: Oil-Water Interface
Before surfactants are added to the oil-water system, the oil-water interactions are very
weak. As the surfactant molecules replace water at the oil-water interface, the attraction
between water and the head group increases. Likewise, the attraction between the
polymer chain and oil also increase. The new attractions decrease the soil-water
interfacial surface tension.
The water, soil, and fabric interfaces are shown below in Figure 11.
Water
fabric-water
interface

Fabric
soil-water
interface
Soil
fabric-soil
interface
Figure 11: Contact Angle in Water-Soil-Fabric System
The Young equation describes the overall shape of a droplet of oil at the three-component
interface. The Young equation is
cos 
 FW   FS
 SW
(1)
where  is the surface tension at the corresponding interfaces and  is the contact angle in
Figure 11 above. After surfactants are added to the system the fabric-water and soilwater interfacial tensions approach zero (FW and SW = 0). The interfacial tension between
soil and fabric remains constant, therefore, FS  FW. The Young equation now gives
17
cos  0. Solving for the contact angle,   900. This contact angle means that the area
of contact between soil and fabric reduces to zero. Figure 1216 shows this mechanism of
detergency, called roll-up.
Figure 12: Complete Removal of Oil Droplets by Roll-up
Without surfactants, part of the soil droplet can be removed from the fabric by
mechanical agitation. The Young equation now yields a positive value for cos ,
resulting in a positive contact angle less than 900. As the area of contact is reduced, the
oil droplet pinches off and leaves some oil residue. This process is illustrated in Figure
1317.
Figure 13: Partial Removal of Oil Droplets by Agitation Without Surfactant
At high concentrations, detergents form micelles in aqueous solution. Micelles dissolve
the fatty stains. The inner section of the micelle contains hydrophobic polymer chains
and oil. Micellar size and shape can vary, depending on surfactant type, temperature, and
18
the presence of salts. The packing properties of surfactants are dependent upon crosssectional surface area of the headgroups (a0 ), the volume (v ) of the hydrocarbon chains,
and the maximum length, (lc ), of the chains. The packing parameter is dimensionless
where p=v/aolc. The packing parameter determines the geometry of the surfactants. The
possible shapes are shown in Figure 1418.
Figure 14: Geometry of Surfactants
As seen above in Figure 14, for p < 1/3, the surfactant forms a cone shape. Therefore, the
corresponding micelle is spherical. The truncated cone surfactant shape is valid for
1/3 < p < ½, forming a rod-like micelle. If ½< p <1, the surfactant is cylindrical in shape
and a bilayer is formed.
Spherical micelles in the presence of an aqueous salt solution form a multilamellar
structure. The multilamellar structure is formed because the salt ions are attracted to the
surfactant headgroups. The repulsive forces between headgroups are minimized. Figure
15 below shows the difference of headgroup area with and without salt ions present
19
water
oil
a) oil drop with water surrounding it
+
+
+
+
water and salt ions
oil
b) oil drop with water and ions surrounding it, thus decreasing surface area of the
headgroups
Figure 15: a) Oil with Water, b) Oil with Water and Salt Ions
The packing parameter now takes on the bilayer shape. A continuous lamellar phase of
bilayer aggregates is formed (shown in Figure 1619 below).
Figure 16: Continuous Lamellar Liquid Crystalline Phase
Several bilayers pack around each other to form multalamellar vesicles, or lamellar
droplets. Lamellar droplets form from the continuous lamellar liquid crystalline phase
even though they are metastable. Mechanical agitation dissolves sodium citrate and
induces the formation of lamellar droplets. Although the continuous lamellar liquid
crystalline phase is more thermodynamically stable, spontaneous curvatures of the
bilayers are favored in the presence of a surfactant mixture. Bilayers form multilamellar
20
vesicles to minimize interactions between hydrocarbon chains and solvent that would be
present at the edges of the crystalline structure.
The presence of bilayers within a salt solution gives rise to the formation of
multilameller (multi-bilayer) structures due to strong osmotic forces. Multibilayers are
thermodynamically favored within a salt solution (i.e. sodium citrate) when the area of
the hydrophilic head groups are reduced. Although the multilamellar bilayers are more
thermodynamically stable, spontaneous curvature of these bilayers is favored in the
presence of a surfactant mixture. This spontaneous curvature gives rise to the formation
of the multi-lamellar droplets. The Gibbs energy of a two-component bilayer is
minimized by the formation of the lamellar droplet. Figure 1720 shows a lamellar droplet.
21
Figure 17: Lamellar Droplets
Many multilamellar vesicles phase separate. In stable conditions interlamellar repulsive
forces are present. Flocculation occurs if interlamellar attractive forces are strong. Van
der Waals forces are present, causing lamellar droplet flocculation. Counterion
concentration increases in the intralamellar region. Osmotic flow of solvent into the
intralamellar region takes place to keep the bilayers separated. Poor solvents increase
flocculation unless decoupling polymer is present, thus causing steric repulsion.
22
Flocculation of lamellar droplets causes phase separation. In the presence of electrolytes
(salts) water is a poor solvent. The hydrophilic portion of the nonionic surfactant
decreases in length because of this poor solvency. Therefore, intralamellar droplet
volume decreases. Decoupling polymer, comprised of a hydrophilic backbone and
hydrophobic side chains, is added to the solution and attaches to the lamellar droplet
surface. The side chains attract to the oily portions of the exterior bilayers (of the droplet)
and the backbones dissolve in the water solvent. Figure 1821 displays three scenarios:
good solvent, bad solvent, and bad solvent with decoupling polymer. Steric repulsions
between the decoupling polymers causes the droplets to repel, and no flocculation occurs.
Figure 18: a) good solvent, b) poor solvent, c) poor solvent with decoupling polymer
23
Particulate Soil
The removal of particulate soil is based on the DLVO Theory. The potential energy must
be overcome in order to removal the soil from the clothing fiber. Potential Energy graphs
demonstrate the potential energy as a function of distance from the garment.
Calculated potential energy of
attraction PA and repulsion PR as a
function of the distance of a particle
from a fabric, along with the
resultant potential P; predictions
based on the DLVO theory
DLVO computational parameter
z=4
Figure 19: Potential Energy versus Distance
The smaller the potential energy, the easier it is to remove the solid particle. Although a
soil already in the washing liquor is less likely to be redeposited on the clothing if the
potential barrier is large.
Bi-layers are first created due to attractive Van der Waals forces when no electrical
double layer exists. The formation of bi-layer structures causes the free energy of the
system to be reduced. As a result of the greater stability of the bi-layer, it takes a
24
considerable amount of energy (mechanical energy) to introduce contact between the
lamellar droplet and the substrate. This is important when considering anti-redeposition
of the soil.
The presence of calcium ions in solution also is relevant to the potential energy theory.
The Schulze-Hardy rule discusses the how water hardness causes the compression of the
double layer. At high concentrations the calcium ions may induce more attractive forces
causing flocculation, which would lead to less efficient detergency.
In addition to surface potential, the electrical charge of the surfactant and the fibers of the
clothing are also important. Generally, the soil/pigment and fiber both have has a
negative charge, which can be altered depending on the pH of the solution. The
following diagram (Figure 20) shows that changes in pH and its effect on potential
energy of different fabric types.
Figure 20: Potential of various fibers as a function of pH [66]
a) Wool; b) Nylon; c) Silk; d) Cotton; e) Viscose
Although pH can enhance the performance of the detergency it is not good enough to
create repulsive forces for steric stabilization. As more and more anionic surfactants are
absorbed, the negative charge on the surface increases. Therefore the dispersing power
25
of the pigments is also increased, which results in reduction of redeposition of removed
soil.
The most effective soil removal therefore occurs at high surfactant concentrations where
there is the greatest negative charge. When the laundry goes through the rinse cycle,
charge reversal takes place creating a neutral environment. This environment of
electrical neutrality is avoided because it would enhance redeposition of the soil or
pigment. For this reason, anionic surfactants are used instead of cationic surfactant for
the effective detergency.
Complexing agents show similar effects to anionic surfactants. Complexing agents
undergo specific attraction to surfaces, which demonstrate a distinct delocalized charge.
The benefit of using complexing agents is that they can be specifically absorbed unlike
anionic surfactants, which are absorbed at all hydrophobic surfaces. By adding
complexing agents to the washing solution, the absorption of the anionic surfactant on the
metal oxides is diminished. Although the opposite is true at surface of the fiber, the
absorption is enhanced by the electrolyte nature of the complexing agent. Due to the fact
that multiple soil types exist on the surface of the soiled clothing, the specificity of the
complexing agent and the surfactant provide complementary functions to the fabrics.
The role of the nonionic surfactant for the removal of particulate soils is similar for other
soil types. The nonionic surfactant does not affect the surface charge but enhances
surface absorption. The nonionic surfactant shows significant absorption at the
hydrophobic surface. The hydration of the nonionic surfactants is important when
considering redeposition. As the amount of hydrated spheres that surround the substrate
increases, interference is created which reduces Van der Waals forces, thereby reducing
redeposition22.
26
Calcium-Containing Particulate Soil
Calcium containing particulate soils is common on textile fabric surfaces. The problem
with these soils is that they are not very soluble. As the hardness of the water increases,
the solubility is minimized. Although this is true, the calcium ions can show some
solubility when using distilled water as the washing solvent. This small amount of
solubility can cause the break up of the calcium-containing solid on the fabric until the
extent of the calcium is absorbed in the washing solution
Types of Fabrics
The type of fabric being washed determines the type of soil removal. One example can
be demonstrated between textile fabrics, which contain calcium ions, and synthetic fibers,
which have low calcium content. The major difference between these fabrics is their
“wettability” due to their degree of hydrophobic and hydrophilic nature.23 As a result, the
complexing agents also react differently with each type of soil. Sodiumtriphosphate, a
common complexing agent, shows enhancing effects to the removal of soil from both
synthetic and cotton garments. The efficiency is more dependent on the
hydrophilic/hydrophobic nature of the fabric. One example is that the effect of sodium
triphosphate enhancing the removal of soils from hydrophilic fibers such as poylamide or
polyacrylonitrile, but shows minimal effects when considering hydrophobic textile fibers.
Although soil removal is specific to the fabric type, these effects can complement each
other when considering the detergency of fabric blends in the presence of soil mixture.
27
Processing
The manufacturing process for liquid laundry detergent is very complex. First, the
surfactants, builders, and other additives are mixed and dried so that they form a compact
powder. The resulting dried powder is then added in particulate form to either a batch or
continuous reactor, where it comes into contact with the agitated liquid medium. This
liquid must be able to suspend not only the detergent particulate, but other additives that
may be desired such as bleaching agents, bleaching activators, and detergent builders24.
A schematic of the process follows.
Surfactants
STPP/Zeolite
Sodium Sulphate
Sodium Perborate
Sodium Carbonate
Sodium Silicate
Minors
Mixing and Homogenizing
Liquid
Detergent
Figure 21: Manufacture of liquid detergent25
Packaging
The three main purposes of packaging are to protect the product so that its quality does
not change between manufacture and purchase, to supply information about the detergent
to the consumer, and to make handling easier. There are many factors companies must
consider when packaging liquid laundry detergent. The selection of packaging materials
involves taking into account product compatibility, cost, safety, waste, and appeal.
Advances in plastics have made the goal of environmentally conscious packaging more
easily obtainable. Convenience is also a very important issue. The size and shape of the
bottle must be well thought-out so that consumers like the design and want to use the
product again. Cheskin Research conducted a telephone survey of 200 people, where
each person was asked to rate the importance of certain package features. The following
figure shows what consumers notice.
28
Most Useful Package Attributes
Percent Stating
Fun ctio nally
obv ious
32%
Reu seable /
recyclab le
23%
9%
Res ealable
Easy to
sto re
7%
29%
Other
0%
10%
20%
30%
40%
50%
(Sample Size = 200)
Figure 22: Important package features26
Typical bottles for liquid detergent are recyclable plastic. Companies such as Procter &
Gamble have been gradually adding recycled material to their plastic in order to cut down
on waste. These bottles generally contain 25% recycled plastic. Smaller bottles
containing a concentrated detergent solution are very popular. This results in less solid
waste because the same amount of laundry can be done with a smaller container.
Concentrated detergents use less chemicals per load of wash as well. Another way
detergent manufacturers reduce waste is by selling refillable containers. This concept
was introduced in the early 1990s. A consumer purchases a larger container initially, and
then buys refills that range 65-90% smaller than the original container.
29
Environmental Considerations
In order to create the most marketable product, the detergent industry must keep up with
changing societies. The trend toward more environmentally friendly washing machines
has forced detergent manufacturers to adjust and compensate for these changes. New
washing machines pose problems because they use less water, energy, and the
temperature of the water is lower. If the industry does not meet its past standards for new
technologies and concerns, consumers will be dissatisfied.
Water consumption is a major concern worldwide. This needs to be addressed by
detergent producers because laundry contributes to water usage. Niall Fitzgerald,
chairman of Unilever, voiced his concern: “By 2025, two-thirds of our village (the earth)
will be living with “water stress,” meaning that they won’t even have enough for safe
drinking water and sanitation-never mind enough for a wash load.”27 His priorities for
the future of detergents include minimizing the amount of water necessary for washing,
the ability to wash with poor water quality such as cold water, gray water, and salt water.
Market Sales
There are several types of laundry detergents on the market currently. There are powders,
tablets, liquids, and different types of fragrances, pre-treatments, and boosters. The
leading style of detergent is liquid, with sales surpassing that of powders for the first time
in 1998. According to Information Resources, Inc., Chicago, for the 52 weeks ending on
October 7, 2001, $3 billion of liquid detergent was sold, as opposed to $1.8 in powders.
The popularity of liquid detergent is attributed to its convenience. Dispensing and
measuring the liquid is thought to be much easier than using a cumbersome box of
powder. Additionally, liquids dissolve easier in water than powder detergents.
Speculators claim powder detergents have a market only because it is cheaper per load of
laundry to use powder. The top three manufacturers of liquid laundry detergent have
30
been the same for the past two years. In descending order, they are Procter & Gamble,
Lever Brothers, and Dial28.
The leading brand of liquid detergent is Tide®, and it has held this top position for
several years. The sales for the year until October 7, 2001 were $1 billion according to
Information Resources, Inc. This figure means that Tide® controls over 33% of the
entire liquid laundry detergent market in the United States29. Other top brands include
All®, Purex®, Wisk®, Xtra®, and Cheer®. There are virtually no middle-tier brands of
detergent because consumers either tend to buy for quality (more expensive liquid
varieties), or price (inexpensive powders). The following chart shows the market
breakdown by brand30.
Market Breakdown of Laundry Detergents
All (Unilever)
7%
Gain (Procter &
Gamble)
7%
Purex (Dial)
7%
Other
22%
Wisk (Unilever)
7%
Cheer (Procter &
Gamble)
6%
Arm & Hammer
(Church &
Dwight)
5%
Tide (Procter &
Gamble)
39%
Figure 23: Detergent Market31
31
Endnotes
1
http://www.ub.rug.nl/eldoc/dis/science/j.kevelam/c1.pdf
ibid
3
ibid
4
http://www.sdahq.org
5
http://www.ub.rug.nl/eldoc/dis/science/j.kevelam/c1.pdf
6
ibid
7
http://www.mrw.interscience.wiley.com/ueic/ull_search_fs.html
8
http://www.ub.rug.nl/eldoc/dis/science/j.kevelam/c1.pdf
9
http://www.happi.com/current/Jan024.htm
10
McCoy, Michael. “Soaps and Detergents.” Chemical &Engineering News 21
January 2002: 21-28
11
http://www.mrw.interscience.wiley.com/ueic/ull_search_fs.html
12
http://www.ub.rug.nl/eldoc/dis/science/j.kevelam/c1.pdf
13
ibid
2
14
http://www.mrw.interscience.wiley.com/ueic/ull_search_fs.html
15
http://www.mrw.interscience.wiley.com/ueic/ull_search_fs.html
http://www.ub.rug.nl/eldoc/dis/science/j.kevelam/c1.pdf
17
ibid
18
ibid
19
ibid
20
ibid
21
ibid
22
ibid
23
http://www.mrw.interscience.wiley.com/ueic/ull_search_fs.html
24
United States Patent number 6,277,804.
http://patft.uspto.gov
16
25
http://www.ballestra.com/ps_deter.htm#liquid
http://www.cheskin.com/who/press/release_19980929.doc
27
http://www.happi.com/current/Jan024.htm
28
ibid
29
ibid
30
McCoy, Michael. “Soaps and Detergents.” Chemical &Engineering News 21
January 2002: 21-28
26
31
ibid
32