USC
About this Article
Written by: Rupesh Parbhoo
Written on: September 5th, 2005
Tags: chemical engineering, lifestyle
Thumbnail by: American Cleaning Institute
About the Author
In the spring of 2005, Rupesh Jayantilal Parbhoo was a junior majoring in Chemical Engineering, Nanotechnology with a minor in Mathematics in the Viterbi School of Engineering at the University of Southern California. He was born in New Orleans, Louisiana, and raised in El Paso, Texas.
Also in this Issue
Freeze! Engineering Frozen Vegetables and FruitsWritten by: Amy Lin
Security Versus Privacy: The Engineering of X-Ray Vision Written by: Farzana Ansari
Taking Off and Landing on an Aircraft CarrierWritten by: Jeff Moring
The TrebuchetWritten by: Christopher Carrillo
Stay Connected

Volume IX Issue II > A Chemical Engineer's Guide to Cleaning Just About Anything
When people kneel down to scrub the stains out of their bathtubs or struggle to remove the coffee grounds from their kitchen counters, they are probably not thinking about the complicated chemical reactions that are happening just beneath their hands. The cleaning supplies that we all use, from simple soaps to detergents to vinegars and bleaches, have all been carefully engineered and designed to break down various types of soil and keep our homes as clean and safe as possible.

Introduction

Have you sanitized your sponge today? Dr. Philip Tierno, the Director of Clinical Microbiology and Immunology at New York University Medical Center, found that the greatest amount of infectious bacteria in the home comes from dirty kitchen sponges [1]. Moreover, rotavirus, a virus causing severe diarrhea, contaminates remote controls, light switches, and door knobs [2]. Shockingly, Tierno's research also showed that fecal matter contaminates toothbrushes because toilets spray as much as 20 feet when flushed [1]. Cleaning these contaminants represents an essential part of our daily lives and allows us to live in a healthy environment.
The first step in deciding which cleaning agent to use is figuring out the category of the soil or dirt we want to remove. Once this is determined, options range from the first widely used cleaning agent, soap, to modern chemical creations, such as detergent, and finally to common household products, such as vinegar and bleach. The various chemical structures and properties of each of these agents will determine which is most appropriate for each situation.
Illumin
Figure 1: Simplified Soap Molecule.

Types of Soil

For our purposes, "soil" is defined as matter that makes a surface dirty or that is in an undesired place. For instance, pizza is a delicious food, but when it is rubbed into the carpet it becomes soil that needs to be removed [3]. Soil can be grouped into three categories: organic, inorganic, and a mixture of the two [4]. Organic soils are made up of two main groups: food and petroleum. Food soils include grease, fat, mold, and bacteria, while petroleum soils include motor oil and axle grease. Inorganic soils include hard water, rust, scale, minerals, sand, and clay [3]. Mixtures or a combination of organic and inorganic soil, like the ever-elusive soap scum, pose the greatest removal challenge for any cleaner. These soils require an ideal mixture of organic and inorganic cleaning agents.

Soap

Soaps, the most common cleaning agents, remove organic soils. Basic soaps are composed of water-soluble potassium fatty acid salts (see Fig. 2) [5]. They are made from fats and oils that are treated strongly with an alkaline solution [6]. In soap, three fatty acid molecules are attached to a glycerin molecule (see Fig. 2). The molecules in soap have two important components: the head and the tail. The head of the soap molecule is a negatively charged carboxylate anion (CO2-), which is hydrophilic, or "water loving." The tail of the soap molecule has a long hydrophobic, or "water hating," hydrocarbon chain (see Fig. 1). In water, the hydrophobic tails congregate together, while the hydrophilic ends attract other water molecules to result in the formation of a micelle structure (see Fig. 3).
American Cleaning Institute
Figure 2: Composition of Soap.
In the presence of soil, the hydrocarbon tail attaches to the organic soil as the polar carboxylate "head" pulls the dirt off the surface. Unfortunately, traditional soaps also react with minerals in water to produce soap scum, a combination of organic and inorganic soils that is difficult to remove.