002.Chemistry Of Cleaning & Sanitizing


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002.Chemistry Of Cleaning & Sanitizing

  1. 1. Soil Classifications There are 3 main classifications of soils: 1. Type of Soil 2. Solubility Characteristics of Soil 3. Types of Cleaning Compounds These classes are helpful about understanding cleaning processes. They are parts of one unit. 1. Type of Soil 1.1 Inorganic Soil Matter that was never "alive", and thus contain no carbon. a) Hard-water deposits such as water spots, calcium and magnesium carbonates (Scale and lime deposits ) b) Metallic deposits such as rust, corrosion, and oxidation. c) Alkaline deposits such as films left by improper rinsing after use of an alkaline cleaner. d) Minerals and rock formation. ( Sand, silt, clay ) Oftentimes acidic cleaners are used to remove inorganic deposits. Minerals are often cleaned with general purpose cleaners. 1.2 Organic Soil Matter that once “lived” and that does contain carbon. a) Fat & Grease ( Body oils and animal fat ) b) Carbonhydrates & Proteins ( sugar, honey, chocolate, jelly, chicken, milk, beef, … etc.) c) Living matter ( mold, yeast, bacteria) Most of the time organic soils are best removed using alkaline cleaners or solvents. 1.3 Petroleum Soils Motor oils, axle greases, wax, gums and other products made from petroleum. These soils contain no water - in fact they repel water - and thus do not have a pH. They often require another petroleum based solvent to remove them. 5
  2. 2. 1.4 Combination Soils These are soils that contain an organic plus an inorganic soil and/or a petroleum substances. These soils are difficult to remove because they are hard to identify. Proper identification is critical. Most combination soils are removed with a very concentrated, highly built combination type cleaners - alkalines and solvents or acids and solvents. It is important to select the appropriate solvent and the correct cleaning compound for removing a specific soil. An acid-cleaning compound is most appropriate for the removal of inorganic deposits. An alkaline cleaner is more effective in removing organic deposits. If these classes are subdivided, it is easier to determine the specific characteristics of each type of soil and the most effective cleaning compound. Table 1–1 gives a breakdown of soil subclasses Table 1-1 Classification of Soil Deposits Type of Soil Soil Subclass Hard-water deposits Inorganic soil Metallic deposits Alkaline deposits Food deposits Organic soil Petroleum deposits Nonpetroleum deposits 2. Solubility Characteristics of Soil 2.1 Water-soluble Soils These soils will dissolve in tap water and in other solvents that do not contain a cleaning compound. They include many inorganic salts, sugars, starches, and minerals. Soils of this type present no technical problem because their removal is merely a dissolving action. The greater part of food soil can either by suspended in water or can simply be removed from a surface by the force of a water spray. Any soils not directly soluble in water will be left behind as a thin film or as a deposit. 2.2 Acid-soluble Soils Acid-soluble soils are soluble in acidic solutions with a pH below 7.0. Deposits include films of oxidized iron (rust), zinc carbonates (ZnCO3), calcium oxalates [Ca(COO)2], metal oxides (iron and zinc) on stainless steel, waterstone (reaction between various alkaline cleaners and 6
  3. 3. chemical constituents of water having noncarbonate hardness), hard-water scale [Calcium carbonates (CaCO3) & Magnesium carbonates (MgCO3) ], and milkstone (a waterstone and milk film interaction, precipitated by heat on a metal surface). 2.3 Alkali-soluble Soils Alkali-soluble soils are basic media with a pH above 7.0. Fatty acids, blood, proteins, and other organic deposits are solubilized by an alkaline solution. 2.4 Insoluble Soils Soils insoluble in the cleaning solution are insoluble throughout the range of normal cleaning solutions. However, they must be loosened from the surface on which they are attached and subsequently suspended in the cleaning media. Table 1-2 Solubility Characteristics of Food Soils Surface Deposit Solubility Sugar Water-soluble Fat Alkali-soluble Protein Alkali-soluble Starch Water & Alkali Soluble Monovalent Salts Water & Acid Soluble Polyvalent Salts Acid Soluble 3. Types of Cleaning Compounds Soil deposits are characteristically complex in nature and are frequently complicated by organic soils being protected by deposits of inorganic soils, and vice versa. Therefore, it is important to identify correctly the type of deposit and to use the most effective cleaning compound or combination of compounds to effectively remove soil deposits. It is frequently essential to utilize a two-step cleaning procedure that contains more than one Cleaning compound to remove a combination of inorganic and organic deposits. Table 1–3 illustrates the types of cleaning compounds applicable to the broad categories of soil. Table 1-3 Types of Cleaning Compounds for Soil Deposits Type of Soil Required Cleaning Compound Inorganic soil Acid-type cleaner Organic soil Nonpetroleum Alkaline-type cleaner Petroleum Solvent-type cleaner 7
  4. 4. Cleaning Process The major functions of a cleaning compound are to lower the surface tension of water so that soils may be dislodged and loosened and to suspend soil particles for subsequent flushing away. To complete the cleaning process, a sanitizer is applied to destroy residual microorganisms that are exposed through cleaning. Cleaning process has three sub-processes. 1. Seperation of the soil from the surface Soil separation can occur through mechanical actions; through alteration of the chemical nature of soil; or without alteration of the chemical nature of the soil. The soil and surface must be thoroughly wet for a cleaning compound to aid in separating the soil from the surface. The cleaning compound reduces the energy binding the soil to a surface, permitting the soil to be loosened and separated. 2. Soil dispersion in the cleaning solution Dispersion is the dilution of soil in a cleaning solution. Soil that is soluble in a cleaning solution is dispersed if an adequate dilution of cleaning medium is maintained and if the solubility limits of the soil in the media are not exceeded. The use of fresh cleaning solution or the continuous dilution of the dispersed solution with fresh solution will increase dispersion. Some soils that have been loosened from the surface being cleaned will not dissolve in the cleaning media. Dispersion of insoluble soils is more complicated. It is important to reduce soil to smaller particles or droplets with transport away from the cleaned surface. A synergistic action of the energy reduction activity of the cleaning compound and the mechanical energy can break the soil into small particles and separate it from the surface. 3. Prevention of redeposition of dispersed soil. Redeposition can be reduced by removal of the dispersed solution from the surface being cleaned. Other reduction methods are continued agitation of the dispersed solution while still in association with the surface to stop settling of the dispersed soil; prevention of any reaction of the cleaning compound with water on the soil; elimination of any residual solution and dispersed soil that may have collected on the surface by flushing or rinsing the cleaned surface; and maintenance of soil in a finely dispersed condition to avoid further entrapment on the cleaned surface. Adsorption of surface-active agents on the surface of soil particles causes similar electrical charges to be imparted to the particles. This condition prevents aggregation of larger particles because like-charged particles repel each other. Surface redeposition is minimized because a similar repulsion exists between surfactant-coated particles and the surfactant-coated clean surface. 8
  5. 5. The best “rule of thumb” to consider when selecting a cleaning compound is that “like cleans like.” Therefore, an acid soil requires an acid cleaner, and an alkaline soil should be removed with an alkaline cleaning compound. Factors Affecting Cleaning Performance Time: contact time on the surface being cleaned Action: physical force exerted onto the surface (velocity or flow) Concentration: amount of cleaner used Temperature: amount of energy (as heat) used in the cleaning solution Water: used to prepare cleaning solution Individual: worker performing clean-up operation Nature: composition of the soil Surface: what material is being cleaned These factors spell out the acronym TACT WINS and describe important factors involved in cleaning. Energy Equation For Cleaning There’s actually an equation that determines the total amount of energy it takes to properly clean something: There are three types of energy that combine to create a clean surface. Mechanical energy comes from you, scrubbing away. It is Mechanical Energy external forces. While scrubing with sponge , you exert on soil to leave it on Thermal Energy Total Energy surfaces. Thermal energy comes from the (Cleaning) temperature of the cleaning solution. At the Chemical Energy optimum cleaning solution temperature alkali or acidic cleaning solutions are more effective. Their solubility and chemical activity increase. Chemical energy is what the chemicals in cleaning products bring to the equation. Mechanical and thermal energy vary with chemical energy. Detergents’ cleaning formulas provide chemical energy through : • Wetting of the surface and soil • Emulsification of oils • Saponification, or creating water soluble soaps with basic or alkaline compounds • Softening of water to neutralize the negative effects of calcium and magnesium • Adding enzymes and/or bleach to attack stains • Cleaning with solvents in combination with or in place of water These factors are often used together to maximize effects. There are 3 parameters that gets the dirty surface 100% clean which keeping the balance with each other. For example if you don’t want to scrub very hard, but still want the same Total Energy (cleaning), you need to raise either the Thermal energy or the Chemical energy. 9