Colloidal and Surface Phenomena Of

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

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 century[1].

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 ABS[2]

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 detergents[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 surfactants[4]. 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 today[5].

Figure 2: Chemical Structures of STP and NaCit[6]

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 temperatures[7]. 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 detergents[8].

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 market[9].

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 market[10].

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 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 environment[11]. 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 box[12]. 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.

Components

The components of liquid laundry detergent are listed in Table 1[13] below:

Table 1: Composition of liquid laundry detergent

Ingredients / Volume Percent
Anionic Surfactants / 10 - 25
Nonionic Surfactants / 6 - 10
Soaps / 4 - 6
Builders / 15 - 30
Solubilizers / 0 - 5
Alcohols / 0 - 5
Enzymes / 0 - 1.5
Optical Brighteners / 0.05 - 0.25
Stabilizers / Trace amount
Fragrances / Trace amount
Water / 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.

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 process[14]. Some examples of the most common type of anionic surfactants include sodium linear alkylsulfonate (LAS), alkanesulfonates (SAS), and olenfinsulfonates (AOS).

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 acids[15].

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.

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.