Colloidal and Surface Phenomena of

Liquid Laundry DetergentCE 457-527

Dr. AlexandridisApril 9, 2002

Daniel BoekErika Indivino

Katherine MarsoKarey Smollar

Table of ContentsPage

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

6

that act as foaming agents to control this element of the detergent. Odor is another aspect

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 10 - 25Nonionic Surfactants 6 - 10Soaps 4 - 6Builders 15 - 30Solubilizers 0 - 5Alcohols 0 - 5Enzymes 0 - 1.5Optical Brighteners 0.05 - 0.25Stabilizers Trace amountFragrances Trace amountWater 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.

The production of SAS is formed by sulfooxidation and sulfochloronation process.

10

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.

12

Figure 7: Trisodium Citrate (NaCit)

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 water-

insoluble builders of 10m 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

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.

13

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

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).

14

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.

16

Figure 9: Nonionic Surfactant Molecule

apolar hydrocarbon polymer polar head group

Figure10 below displays the alignment of surfactant molecules at an interface between oil

and water.

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.

The Young equation describes the overall shape of a droplet of oil at the three-component

interface. The Young equation is

(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 soil-

water 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

Oil

Water

interface

Figure 10: Oil-Water Interface

Water Soil

Fabric

soil-water interface

fabric-waterinterface

fabric-soil interface

Figure 11: Contact Angle in Water-Soil-Fabric System

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.

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.

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

Figure 12: Complete Removal of Oil Droplets by Roll-up

Figure 13: Partial Removal of Oil Droplets by Agitation Without Surfactant

the presence of salts. The packing properties of surfactants are dependent upon cross-

sectional 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.

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

Figure 14: Geometry of Surfactants

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).

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

oil

water

+ + + +

a) oil drop with water surrounding it

b) oil drop with water and ions surrounding it, thus decreasing surface area of the headgroups

oil

water and salt ions

Figure 16: Continuous Lamellar Liquid Crystalline Phase

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

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

Figure 17: Lamellar Droplets

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.

1 http://www.ub.rug.nl/eldoc/dis/science/j.kevelam/c1.pdf2 ibid3 ibid4 http://www.sdahq.org5 http://www.ub.rug.nl/eldoc/dis/science/j.kevelam/c1.pdf6 ibid7 http://www.mrw.interscience.wiley.com/ueic/ull_search_fs.html 8 http://www.ub.rug.nl/eldoc/dis/science/j.kevelam/c1.pdf9 http://www.happi.com/current/Jan024.htm10 McCoy, Michael. “Soaps and Detergents.” Chemical &Engineering News 21

January 2002: 21-2811 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 14 http://www.mrw.interscience.wiley.com/ueic/ull_search_fs.html

15 http://www.mrw.interscience.wiley.com/ueic/ull_search_fs.html16 http://www.ub.rug.nl/eldoc/dis/science/j.kevelam/c1.pdf17 ibid 18 ibid 19 ibid 20 ibid 21 ibid

23

Figure 18: a) good solvent, b) poor solvent, c) poor solvent with decoupling polymer

24

Figure 14: a) Good Solvent, b) Poor Solvent, c) Poor Solvent with Decoupling Polymer

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.

 

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

25

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

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

26

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.

22 ibid

27

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.

23 http://www.mrw.interscience.wiley.com/ueic/ull_search_fs.html

28

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.

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

24 United States Patent number 6,277,804.http://patft.uspto.gov

25 http://www.ballestra.com/ps_deter.htm#liquid

29

SurfactantsSTPP/ZeoliteSodium SulphateSodium PerborateSodium CarbonateSodium SilicateMinors

Mixing and Homogenizing Liquid Detergent

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.

Most Useful Package AttributesPercent Stating

(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.

26 http://www.cheskin.com/who/press/release_19980929.doc

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31

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

27 http://www.happi.com/current/Jan024.htm

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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.

Figure 23: Detergent Market31

28 ibid29 ibid30 McCoy, Michael. “Soaps and Detergents.” Chemical &Engineering News 21

January 2002: 21-28

31 ibid

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Endnotes

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