Soaps Synthetic Surfactants And Polymers

7.1 INTRODUCTION

Soaps, surfactants and polymers are discussed together, following the discussion of petroleum, because most of the polymers and the surfactants in detergents are made mainly from chemicals derived from petroleum. Natural fats and oils are also used in the manufacture of surfactants (Figure 7-1). Soaps and surfactants contain segments of linear or lightly branched hydrocarbon chains that are, in the main, broken down to acetate up on metabolism by microorganisms in the environment. The biodegradation of petroleum occurs by the same pathway once a terminal carbon has been oxidized to a carboxyl grouping. The rate of degradation by other environmental reagents such as sunlight, oxygen, or water is much slower than that of microbial degradation.

Basic Starting Materials

Surfactants

»-Paraffins

Linear a-olefins

Natural fats & oils

Fatty acids

Ethylene

Detergent-range linear primary alcohols

Ethylene oxide

Linear alcohol ethoxylates

Raw Materials

Surfactants

Benzene

-►

Linear alkylbenzene

_^

-►

Linear alkylbenzene sulfonates

Secondary alkane sulfonates a-Olefin sulfonates

Fatty amine oxides a-Sulfo-methyl esters

Fatty alkanolamides

Alkyl poly-glucosides

Alkyl glyceryl ether sufonates

Alcohol sulfates

Alcohol ether sulfates

Linear alcohol ethoxylates

Principal Household Applications

Heavy-duty laundry powders Light-duty liquid dish detergents Heavy-duty laundry liquids Specialty cleansers

Light-duty liquid dish detergents

Liquid hand soap

Light-duty liquid dish detergents

Shampoos

Light-duty liquid dish detergents

Shampoos

Specialty cleansers

Heavy-duty laundry powders

Light-duty liquid dish detergents Shampoos

Light-duty liquid dish detergents

Toilet soaps Shampoos

Shampoos

Heavy-duty laundry powders

Light-duty liquid dish detergents ^ Heavy-duty laundry powders Heavy-duty laundry liquids Shampoos

Heavy-duty laundry liquids Heavy-duty laundry powders Specialty cleansers

FIGURE 7-1 Surfactants for household detergents: petrochemical raw materials and uses. Redrawn from "Soaps and Detergents," Susan Ainsworth, Chem. Eng. News, Jan. 24, 1994. Used by permission of SRI Consulting. Also see color insert.

7.2 SOAPS AND SYNTHETIC SURFACTANTS

Soaps and synthetic surfactants have similar structures, and their mechanisms of cleansing are similar. Both contain a hydrophobic portion (usually a hydrocarbon chain) to which a hydrophilic (polar) group is attached. Such materials are surface active: that is, they concentrate at the surface of an aqueous solution or form aggregates called micelles (Figure 7-2) within the solution. Surface-active materials lower the surface tension of the water so that the water better penetrates the surface and interstices of the object being cleaned. If the binding of the micelles of soap or synthetic surfactant to the substance being cleaned is greater than the binding of the soiling agent, the latter will then be transferred into the micelles upon agitation. Oils and greases will also be adsorbed by the hydrophobic end of the surface-active agent. The soiling agent can be washed away because the affinity of the polar group of the surfactant for water keeps the micelle-dirt complex suspended in the water.

The foam covering many otherwise scenic rivers and streams was a source of much public concern for many years. This environmental problem was caused by slowly degrading synthetic surfactants and was probably the first modern environmental problem to be solved as a result of public opinion.

FIGURE 7-2 A Simplified two-dimensional representation of a three-dimensional micelle. The hydrophobic hydrocarbon chains associate in the center of the micelle. Nonpolar substances associate with the hydrocarbon chains of the micelle, become solubilized, and are removed from the fabric.

FIGURE 7-2 A Simplified two-dimensional representation of a three-dimensional micelle. The hydrophobic hydrocarbon chains associate in the center of the micelle. Nonpolar substances associate with the hydrocarbon chains of the micelle, become solubilized, and are removed from the fabric.

Some indication of the nature of the problem was apparent as early as 1947 when the aeration tanks at the sewage disposal plant at Mount Penn, Pennsylvania, were inundated with suds. This spectacular effect was the result of a promotional campaign during which free samples of a new detergent had been distributed at local stores. Everyone used the new product at about the same time, but unfortunately the microorganisms residing at the disposal plant metabolized the synthetic surfactant in this detergent very slowly. Despite this early warning, slowly degrading surfactants were manufactured up to 1965 before the detergent industry responded to public pressure and voluntarily switched to the manufacture of surfactants that degrade more rapidly in the environment.

7.2.1 Soaps

Soaps are prepared by the saponification (base hydrolysis) of animal or vegetable fats as shown in reaction (7-1) (note, however, that the R groups are usually different). Hydrolysis converts the triglycerides in the fats to the sodium salts of carboxylic acids (soaps) and glycerol. The carboxylate group is the polar, water-soluble end of the soap.

O II

Healthy Chemistry For Optimal Health

Healthy Chemistry For Optimal Health

Thousands Have Used Chemicals To Improve Their Medical Condition. This Book Is one Of The Most Valuable Resources In The World When It Comes To Chemicals. Not All Chemicals Are Harmful For Your Body – Find Out Those That Helps To Maintain Your Health.

Get My Free Ebook


Post a comment