004.Chemistry Of Cleaning & Sanitizing


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004.Chemistry Of Cleaning & Sanitizing

  1. 1. DETERGENTS Detergents are composed of physical or chemical active ingredients such as surfactants, builders, solvents, chelators, preservatives, bleaches and enzymes. 1. Surfactants 2. Chelating/Sequestering Agents 3. Builders 4. Solvents 5. Preservatives 6. Bleaches 7. Enzymes 1. Surfactants The interaction between water, surfactant, and surface is called “surface activity.” In fact, the name surfactant comes from the phrase “SURFace ACTive AgeNT.” Surfactants are molecules that reduce the surface tension of water, helping it to spread out more uniformly. Basically, surfactants make water “wetter”. They also help penetrate, loosen and trap soils . In more technical terms: • Surfactants enable the cleaning solution to fully wet the surface being cleaned so that dirt can be readily loosened and removed. • Surfactants clean greasy, oily, particulate-based, protein-based, and carbohydrate-based stains. • Surfactants are instrumental in removing dirt and in keeping them emulsified, suspended, and dispersed so they don't settle back onto the surface being cleaned. Surfactants are one of the major components of cleaning products and can be regarded as the 'workhorses': they do the basic work of breaking up soils and keeping the dirt in the water solution to prevent re-deposition of the dirt onto the surface from which it has just been removed. Surfactants disperse dirt that normally does not dissolve in water. Each surfactant molecule has a hydrophilic (water-loving) head that is attracted to water molecules and a hydrophobic (water-hating) tail that repels water and simultaneously attaches itself to oil and grease in dirt. These opposing forces loosen the dirt and suspend it in the water. 17
  2. 2. Modern technology can produce many different types of surfactants by changing the chemical composition of the hydrophobic and hydrophillic ends of the molecule. By changing the chemical composition, surfactants have greater or lesser abilities in different areas: a. Detergency: the ability to break the bond between soil and the surface. b. Penetrating and wetting: allows water to surround soil particles that would otherwise repel the water. c. Foaming: creation of bubbles that lift dirt from the surface. d. Emulsifying: the ability to break up greasy petroleum soils into small droplets that can be dispersed thoroughly. e. Solubilizing: dissolving a soil so that it is no longer a solid soil particle. f. Dispersing: spreading the minute soil particles throughout the solution - to prevent them back onto the cleaned surface. Many surfactants will be used in combination to create a cleaner/detergent with just the right balance of detergency, foaming, wetting, emulsifying, solubilizing and dispersing properties. Each surfactant contributes its own special abilities to the cleaner formula. Surfactants can be natural or synthetic origin. Surfactants from natural origin (vegetable or animal) are known as oleo-chemicals and are derived from sources such as palm oil or tallow. Surfactants from synthetic origin are known as petro-chemicals and are derived from petroleum. Formulation scientists focus quite a lot on developing detergents that perform well at lower wash temperatures. This approach will continue to yield energy savings during the consumer use phase, hence a reduction of CO2 emissions. The surfactant lines up at the interface. The hydrophobic end of the molecule gets away from the water and the hydrophilic end stays next to the water. When dirt or grease is present (hydrophobic in nature) the surfactants surround it until it is dislodged from the boundary. Notice in diagram 4 that the dirt molecules are actually suspended in solution. 18
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  4. 4. The law of mass cleaning action expresses a relationship between time, action, concentration, and temperature in the process of removing soils. This laws states that if you decrease any one of these factors, we must increase one or more of the remaining factors in order to maintain equal cleaning ability. There is a broad range of different surfactant types, each with unique properties and characteristics. Detergents use a combination of various surfactants to provide the best possible cleaning results. There are four main types of surfactants used in cleaning products. Depending on the type of the charge of the head, a surfactant belongs to the anionic, cationic, non-ionic or amphoteric/zwitterionic family. Anionic surfactants In solution, the head is negatively charged. This is the most widely used type of surfactant for laundering, dishwashing liquids and shampoos. Anionic surfactants are particularly effective at oily soil cleaning and oil/clay soil suspension. They can react in the wash water with the positively charged water hardness ions (calcium and magnesium) , which can lead to partial deactivation. The more calcium and magnesium molecules in the water, the more the anionic surfactant system suffers from deactivation. To prevent this, the anionic surfactants need help from other ingredients such as builders (Ca/Mg sequestrants) and more detergent should be dosed in hard water. The most commonly used anionic surfactants are alkyl sulphates (AS), alkyl ethoxylate sulphates (AESs) and soaps. LAS (Linear Alkylbenzyne Sulphonate) O O CH3(CH2)11 S Na O 20
  5. 5. LABSA (Linear Alkylbenzene Sulphonic Acid) SO3 o Cationic surfactants In solution, the head is positively charged. There are 3 different categories of cationics each with their specific application: 1. In fabric softeners and in detergents with built-in fabric softener, cationic surfactants provide softness. Their main use in laundry products is in rinse added fabric softeners, such as esterquats (esterified quaternary ammonium compounds), one of the most widely used cationic surfactants in rinse added fabric softeners. An example of cationic surfactants is the esterquat. 2. In laundry detergents, cationic surfactants (positive charge) improve the packing of anionic surfactant molecules (negative charge) at the stain/water interface. This helps to reduce the dirtl/water interfacial tension in a very efficient way, leading to a more robust dirt removal system. They are especially efficient at removing greasy stains. An example of a cationic surfactant used in this category is the mono alkyl quaternary system. 21
  6. 6. CTAB (Cetyl Trimethyl Ammonium Bromide) CH3 CH3 N Cl CH3(CH2)15 CH3 3. In household and bathroom cleaners, cationic surfactants contribute to the disinfecting/sanitizing properties. Non-ionic surfactants These surfactants do not have an electrical charge, which makes them resistant to water hardness deactivation. They are excellent grease removers that are used in laundry products, household cleaners and hand dishwashing liquids. Nonionic surfactants , which do not dissociate when dissolved in water, have the broadest range of properties depending upon the ratio of hydrophilic/ hydrophobic balance. This balance is also affected by temperature. For example, the foaming properties of nonionic detergents is affected by temperature of solution. As temperature increases, the hydrophobic character and solubility decreases. At the cloud point (minimum solubility), these surfactants generally act as defoamers, while below the cloud point they are varied in their foaming properties. Most laundry detergents contain both non-ionic and anionic surfactants as they complement each other's cleaning action. Non-ionic surfactants contribute to making the surfactant system less hardness sensitive. The most commonly used non-ionic surfactants are ethers of fatty alcohols NPE (Nonyl Phenol (Poly)Ethoxylate) CH3(CH 2)8 O(CH 2CH2O)m H Amphoteric/zwitterionic surfactants These surfactants are very mild, making them particularly suited for use in personal care and household cleaning products. They can be anionic (negatively charged), cationic (positively charged) or non-ionic (no charge) in solution, depending on the acidity or pH of the water. 22
  7. 7. They behave as cationic surfactants under acid conditions, and as anionic surfactants under alkaline conditions. They are compatible with all other classes of surfactants and are soluble and effective in the presence of high concentrations of electrolytes, acids and alkalis. These surfactants may contain two charged groups of different sign. Whereas the positive charge is almost always ammonium, the source of the negative charge may vary (carboxylate, sulphate, sulphonate). These surfactants have excellent dermatological properties. They are frequently used in shampoos and other cosmetic products, and also in hand dishwashing liquids because of their high foaming properties. Dodecyl Dimethyl Sulphobetaine CH3 H2 O C N S CH3(CH 2)11 O CH3 O Dodecyl Dimethyl Amine Oxide CH3 CH3 OH O N H N CH3(CH 2)11 CH3 CH3(CH 2)11 CH3 It is a common practice to blend surfactant ingredients to optimize their properties. However, because of precipitation problems, cationic and anionic surfactants cannot be blended. 2.Chelating/Sequestering Agents Soil removal is a complex process that is much more involved than just adding soap or surfactant to water. One of the major concerns we have in dealing with cleaning compounds is water hardness. Water is made "hard" by the presence of calcium, magnesium, iron and manganese metal ions. These metal ions interfere with the cleaning ability of detergents. The metal ions act like dirt and "use up" the surfactants, making them unavailable to act on the surface we want to clean. A chelating agent (pronounced keelating from the Greek word claw) combines itself with these disruptive metal ions in the water. The metal ions are surrounded by the claw-like chelating agent which alters the electronic charge of the metal ions from positive to negative (see diagram below.) This makes it impossible for the metal ions to be precipitated with the 23
  8. 8. surfactants. Thus, chelated metal ions remain tied up in solution in a harmless state where they will not use up the surfactants. Some common chelating agents used in industrial cleaning compounds include phosphates, EDTA (ethylene diamine tetra acetate), NTA, gluconic acid, sodium citrate, and zeolite compounds. Organic chelating agents, which are used in formulation in water conditioners, are more efficient than are phosphates in sequestering calcium and magnesium ions and in minimizing scale buildup. Most organic agents are salts of EDTA. 3. Builders The chelating process, though very effective, is not always necessary and adds to the cost of formulating detergents. Builders are often a multifuctional alternative and they are cheaper. Builders are added to a cleaning compound to upgrade and protect the cleaning efficiency of the surfactant(s). Builders have a number of functions which help to reduce the hardness of the water, buffer the solution, and emulsify the soil. Builders soften water by deactivating hardness minerals (metal ions like calcium and magnesium. They do this through one of two ways: Sequestration - holding metal ions in solution. Precipitation - removing metal ions from solution as insoluble materials. Builders, in addition to softening, provide a desirable level of alkalinity (increase pH), which aids in cleaning. They also act as buffers to maintain proper alkalinity in wash water. Finally, builders help emulsify oily and greasy soil by breaking it up into tiny globules. Many builders will actually peptize or suspend loosened dirt and keep it from settling back on the cleaned surface. Below are three of the most common builders used in today's heavy-duty detergents. A short description of each follows. 24
  9. 9. EDTA Ethylene Diamine Tetra Acetate NTA Nitrilo Triacetic Acid Phosphates, usually sodium tripolyphosphate (STPP), have been used as builders extensively in heavy-duty industrial detergents. They combine with hardness minerals to form a soluble complex which is removed with the wash water. They also sequester dissolved iron and manganese which can interfere with detergency. Phosphates serve as builders in cleaning compounds by providing: ● Enhancement of the wetting effect and resultant cleaning efficiency of cleaning compounds. ● Sufficient alkalinity necessary for effective cleaning without being hazardous. ● Maintenance of the proper alkalinity in the cleaning solution through buffering ability. ● Emulsification of oily, greasy soil by degradation and subsequent release from the surface to be cleaned. ● Loosening and suspension of soil with the ability to prevent redeposition on the clean surface. ● Water softening by keeping minerals dissolved to prevent settling on what is being cleaned. ● Reduction in numbers of bacteria associated with a clean surface. Sodium tripolyphosphate (STPP) Na5P3O10 Sodium carbonate (soda ash) is used as a builder but can only soften water through precipitation. Precipitated calcium and magnesium particles can build up on surfaces, especially clothing, and therefore sodium carbonate is not used in laundry detergents. 25
  10. 10. Sodium carbonate / Na2CO3 Sodium silicate serves as a builder in some detergents when used in high concentrations. When used in lower concentrations, it inhibits corrosion and adds crispness to detergent granules. Sodium silicate is the common name for a compound sodium metasilicate. Sodium metasilicate / Na2SiO3 4. Solvents Solvents can be found in a wide variety of applications. Coatings, cleaners, personal care products, inks, adhesives, pharmaceuticals, and agricultural products all benefit from the performance advantages of modern solvents. Solvents are chemical substances that can dissolve, suspend, or extract other materials, usually without chemically changing either the solvents or the other materials. Solvents can be organic, meaning the solvent contains carbon as part of its makeup, or inorganic, meaning the solvent does not contain carbon. For example, "rubbing" alcohol (isopropyl alcohol) is an organic solvent, and water is an inorganic solvent. Hydrocarbon (aliphatic and aromatic hydrocarbons) and oxygenated solvents (alcohols, glycol ethers ketones, esters, and glycol ether esters) are examples of types of organic solvents that can effectively dissolve many materials. Water is a solvent that dissolves many things. But water cannot dissolve everything. For example, water will not dissolve oily/greasy substances. That is because solvents work on the principle of “like dissolves like.” Water has chemical characteristics that are very different from greases. In order to dissolve things that water cannot, other solvents are needed. These solvents are chemically much more similar to greases and, therefore, can effectively dissolve them. Water makes up a large percentage of most liquid cleaner formulas. It is not uncommon for water-based detergents to contain 50% water or more. Some ready-to-use formulations may contain as much as 90% to 95% water. Water can be considered an active ingredient that actually adds to the detergency of cleaners. It performs several very important functions in liquid cleaners. Most importantly, it adds to the "detergency" of a cleaner. Water acts as a solvent that breaks up soil particles after the surfactants reduce the surface tension and allow the water to penetrate soil (water is commonly referred to as “the universal solvent”). 26
  11. 11. Water also aids in the suspension and anti-redeposition of soils. Once the soil has been dissolved and emulsified away from the surface, we want to prevent it from being redeposited. Water keeps the soil suspended away from the clean surface so that it can be carried away easily during the rinsing process. It is clear that without this water, our cleaning formulas would be much less effective. In addition to water, other chemical solvents are often added to cleaners to boost performance. Compounds such as 2-Butoxyethanol (EGBE), isopropyl alcohol (rubbing alcohol) and d- Limonene are all considered solvents. Their main function is to liquefy grease and oils or dissolve solid soil into very small particles so surfactants can more readily perform their function. Solvents may be classified as polar and nonpolar types. Polar solvents, like water, have molecules whose electric charges are unequally distributed, leaving one end of each molecule more positive than the other. Usually polar solvent has O-H bond of which water (HOH), methanol (CH3OH) and acetic acid (CH3COOH) are examples. Propanol, butanol, formic acid, formamide are polar solvents. Dipolar solvents which contain a C-O double bond without O-H bond are acetone [(CH3)2C=O], ethyl acetate (CH3COOCH2CH3), methyl ethyl ketone, acetonitrile, N,N-dimethylformamide and diemthyl sulfoxide. Nonpolar solvents, like carbon tetrachloride (CCl4), benzene (C6H6), and diethyl ether (CH3CH2OCH2CH3), have molecules whose electric charges are equally distributed and are not miscible with water. Hexane, tetrahydrofuran and methylene chloride are nonpolar solvents. Polar Nonpolar Polar Nonpolar 27
  12. 12. 5. Preservatives A preservative is nothing more than a substance that protects soaps and detergents against the natural effects of aging such as decay, discoloration, oxidation and bacterial degradation. Synthetic detergents are preserved differently from soaps. In soaps, preservatives are used to forestall the natural tendency to develop rancidity and oxidize upon aging. Butylated hydroxdytoluene (BHT) and stannic chloride are commonly used in this application. Also used in small amounts is EDTA. BHT - Butylated hydroxdytoluene C15H24O BHT is a lipophilic (fat-soluble) organic compound that is primarily used as an antioxidant (E321) . Oxygen reacts preferentially with BHT rather than oxidizing fats or oils, thereby protecting them from spoilage. Stannic chloride pentahydrate (SnCI4-5H2O) Stannic chloride (SnCI4) is a caustic liquid used in soaps as a colour and perfume stabilizer and bacteria and fungi control. In detergents, preservatives are used to prevent bacteria from spoiling the solution. Methyl paraben and propyl paraben are very common for this application. Detergents would not be preserved if they weren't biodegradable. Bacteria found in air, waste treatment systems and in soil decompose the surfactants and other ingredients found in our cleaners once they enter into the environment. Methyl Paraben C8H8O3 Propyl Paraben C10H12O3 Methylparaben and Propylparaben are from the paraben family of chemicals. Due to their antimicrobial properties, the are used extensively as a water-soluble preservative in many foods, beverages, pharmaceuticals, detergents and personal care products. 28
  13. 13. 6. Bleaches – Oxidizing Agents A bleach is a chemical that removes colors or whitens, often via oxidation. Oxidizing agents used in detergent application are sodium hypochlorite (NaClO) (chlorine bleach) and perborate (oxygen bleach which contains hydrogen peroxide or a peroxide-releasing compound) Sodium hypochlorite (NaClO) There are several kinds of bleach, but the most widespread form is chlorine bleach, chemically known as sodium hypochlorite. Bleach eliminates stains because it breaks apart the bonds of the chromophores in molecules. Chromophores are the parts of molecules responsible for color. Through an oxidation reaction that breaks these bonds, bleaching makes the compounds colorless. Therefore, the stain can no longer be seen. A reducing bleach Works by changing the double bond in chromophores to a single bond, once again making the compounds that cause a stain colorless. The chlorine in bleach also helps kill bacteria because it disrupts their biological processes. When chlorine bleach is added to water, it forms many different chemicals, one example being hypochlorous acid (HOCl). This chemical and others work to kill microorganisms and bacteria. Due to its small size, the hypochlorite anion (ClO-) kills bacteria by diffusing through the bacteria's cell wall and disrupting its ability to function. The compound attacks lipids in the cell wall, causing destruction of enzymes and other parts of the cell, leaving the bacteria harmless . Although bleach can be a useful disinfectant and stain remover, it is a dangerous chemical that can inflict harm to human cells the same way it attacks unwanted bacteria. The process of bleaching can be summarized in the following set of chemical reactions: Cl2(aq) + H2O(l) H+(aq) + Cl-(aq) +HClO(aq) The H+ ion of the hypochlorous acid then dissolves into solution, and so the final result is effectively: Cl2(aq) + H2O(l) 2H+(aq) + Cl-(aq) + ClO-(aq) Hypochlorite tends to decompose into chloride and a highly reactive form of oxygen: ClO- Cl- + O This oxygen then reacts with organic substances to produce bleaching or antiseptic effects. 29
  14. 14. 7.Enzymes Enzymes are proteins, composed of hundred of amino-acids, which are produced by living organisms. They are responsible for a number of reactions and biological activities in plants, animals, human beings and micro-organisms. They are found in the human digestive system to break down carbohydrates (sugars), fats or proteins present in food. The most important reasons to use enzymes in detergents are I. that a very small quantity of these inexhaustible bio-catalysts can replace very large quantity of man made chemicals II. enzymes can work at very low temperature at which traditional chemistry quite often is no longer effective III. they are fully biodegradable. All these characteristics make enzymes - on top of their high efficiency - environmentally friendly ingredients. Proteases Proteases are the most widely used enzymes in the detergent industry. They remove protein stains such as grass, blood, egg and human sweat. These organic stains have a tendency to adhere strongly to textile fibres. The proteins act as glues, preventing the water borne detergent systems from removing some of the other components of the soiling, such as pigments and street dirt. The inefficiency of non enzymatic detergents at removing proteins can result in permanent stains due to oxidation and denaturing caused by bleaching and drying. Blood, for example, will leave a rust coloured spot unless it is removed before bleaching. Proteases hydrolyse proteins and break them down into more soluble polypeptides or free amino acids. As a result of the combined effect of surfactants and enzymes, stubborn stains can be removed from fibres. Lipases Though enzymes can easily digest protein stains, oily and fatty stains have always been troublesome to remove. The trend towards lower washing temperatures has made the removal of grease spots an even bigger problem. This applies particularly to materials made up of a blend of cotton and polyester. The lipase is capable of removing fatty stains such as fats, butter, salad oil, sauces and the tough stains on collars and cuffs. Amylases Amylases are used to remove residues of starch-based foods like potatoes, spaghetti, custards, gravies and chocolate. This type of enzyme can be used in laundry detergents as well as in dishwashing detergents. 30
  15. 15. Cellulases The development of detergent enzymes has mainly focused on enzymes capable of removing stains. However, a cellulase enzyme has properties enabling it to modify the structure of cellulose fibre on cotton and cotton blends. When it is added to a detergent, it results into the following effects: Colour brightening: When garments made of cotton or cotton blends have been washed several times, they tend to get a 'fluffy' look and the colours become duller. This effect is due to the formation of microfibrils that become partly detached from the main fibres. The light falling on the garment is reflected back to a greater extent giving the impression that the colour is duller. These fibrils, however, can be degraded by the cellulase enzyme, restoring a smooth surface to the fibre and restoring the garment to its original colour. Softening: The enzyme also has a significant softening effect on the fabric, probably due to the removal of the microfibrils. Soil removal: Some dirt particles are trapped in the network of microfibrils and are released when the microfibrils are removed by the cellulase enzyme. 31