Play-Doh Surfactants and Inhibitors
Amylose helps make Play-Doh compound sturdy and cohesive, but it has one drawback. As a starch-and-water mixture cools, the strands of amylose left in the water bind to each other. This is known as retrogradation, or set back. Retrogradation can cause dough to harden permanently.
For this reason, Play-Doh compound includes a retrogradation inhibitor -- a substance that keeps the amylose strands from sticking together. Play-Doh includes amylopectin or a waxy starch to act as a retrogradation inhibitor.
Extra amylopectin, though, can cause Play-Doh compound to become a sticky paste rather than a smooth gel. For this reason, Play-Doh includes ingredients to improve its texture and consistency -- a lubricant, like mineral oil or vegetable oil, and a surfactant.
You can find surfactants -- also called surface active agents -- in cleaning products in your home. Surfactants are artificially manufactured molecules whose jobs are to suspend substances in water. They can do this because of their unique molecular structure. One end of the surfactant molecule is hydrophilic -- it likes water. The other end is lipophilic -- it likes fats. The lipophilic end is also referred to as being hydrophobic.
If you add a solution of surfactant and water to a fat, the lipophilic ends of the surfactant molecules will bind to fat molecules. The hydrophilic end of the molecules will bind to nearby water molecules. In this way, the fat becomes suspended in the water. (With different proportions, water could also become suspended in a fat). In Play-Doh compound, surfactants bind to molecules of lubricant and suspend them in the starch-and-water solution. This reduces the compound's stickiness.
So, with this combination of ingredients -- starch, water, retrogradation inhibitor, surfactant and lubricant -- you get a pliable compound that's smooth instead of sticky. The rest of the Play-Doh ingredients fine-tune the dough and give it its color and fragrance. Salt adds some antimicrobial properties and reduces the number of free water molecules. Hardeners and humectants can make the compound harder or moister if needed. Preservative increases the shelf life, and fragrance and color add the final finishing touches. Manufacturing Play-Doh compound essentially requires mixing all of these ingredients together and placing the mixture into sealable containers.
We'll learn about several recipes for making homemade Play-Doh in the next section.