Putty Science: Family Fun with Polymers
Creating a batch of homemade putty puts polymers in the palm of your hand. This family science activity may inspire nostalgia, but your kids will have a blast exploring the tactile medium.
When you think of the comics from the Sunday paper, as they were during your childhood, what comes to mind? (If you are under 30, ask your parents or a teacher!) First, they were in color, a novel weekend change from the daily black and white. Even if newspaper comics are really targeted for the adult, sit-with-the-paper-and-a-cup-of-coffee crowd, there is a certain allure to them for kids, especially in the slightly washed tones that were once the colors de jour of the Sunday edition. If memories of a stretchy, slightly hard but malleable wad of flesh-colored putty piggybacks on your childhood memories of the Sunday paper, don't feel bad. I'm right there with you. For some reason, when I think of Silly Putty®, I think of the Sunday comics, and vice versa. The Silly Putty timeline puts things in a bit of historical perspective, with Crayola acquiring the rights to Silly Putty during my childhood, followed by a resurgence of interest in the stretchy, bouncy medium and its egg-shaped containers in the 80s. What I didn't know back then was that the stretchy putty is actually a great example of science and what can happen when molecules link together in long repeating chains.
What Came First
The story of Silly Putty is one with a take-to-heart moral for scientists and engineers of all ages: invention sometimes is the result of an accident or a failed experiment. Or, in science project terms, what you discover when your hypothesis is disproven might be even more exciting than what you were hoping to discover! The second-level moral surely has something to do with having one's eyes open to unexpected possibilities.
Silly Putty was first created during World War II by researchers who were trying to develop synthetic alternatives to rubber, an important commodity that was rationed during the war. While more than one researcher claims the initial discovery, Crayola lists James Wright, who worked for General Electric, as the inventor. What Wright (at GE) and another team (at Dow Corning) had separately discovered in their labs was that a combination of boric acid and silicone oil yielded a stretchy substance that bounced when dropped. Despite its unusual (and entertaining) properties, the putty wasn't a viable alternative to rubber. No good use for the putty was found, in fact, until a toy store owner saw it and realized its tactile potential—as a toy. The familiar egg-shaped container came later, along with more than a quarter million units sold in three days, and the rest, as they say, is history, although the putty's path from the lab into popular culture didn't happen overnight. Though Silly Putty didn't enjoy simple rocket-to-the-top success, it did shuttle to the moon with the crew of Apollo 8 in 1968. Today, the putty even has a spot at the Smithsonian Institute.
While Silly Putty, from the store, can be a fun and inexpensive diversion for the kids, putty is one of many DIY mediums you can mix at home for a quirky, crafty, scientific experience that's perfect for the family, spans a range of ages, and gives everyone something to play with afterwards. Other interesting tactile substances you can concoct at home include Ooblek and Gak. While different in nature, the three together make a powerful trio for summer fun and hands-on kid science. Be forewarned, however, that differences in printing and ink technologies may make it hard to replicate your childhood Sunday comics memories. The nostalgia you may have when working with the Elmer's® school glue, on the other hand, may more than make up for it. For your kids, you'll be highlighting some important science concepts that help explain how many materials we use every day are created. Plus, the outcome of the project is a wad of goo with a small amount of slime-factor that can stretch, bounce, and squoosh. For certain age groups, it doesn't get much better than that!
Substances like Silly Putty are part of a class of materials called polymers. Like other molecules, polymers are compounds, but they are large and may contain tens of thousands of atoms. Compare this, for example, to water, a compound of hydrogen and oxygen that contains three atoms. A good way to visual the difference between small molecules (like water) and polymers (also called macromolecules) is to think of the size difference between a crystal of salt (small) and a strand of spaghetti (larger and longer).* Like the strand of spaghetti, polymers are long chains of molecules strung together. These strands can also be tangled up to create a giant mess of polymer chains. Are you still envisioning a bowl of spaghetti?
Part of what makes polymers interesting is that each polymer has unique properties and behaviors defined by its molecules. Some polymers are stretchy. Some are sticky. Some are hard. Many familiar and commonly used polymers are synthetic, but there are also naturally occurring polymers, including cellulose, starch, proteins, silk, chitin, and rubber. What you want your putty-mixers to understand is that Silly Putty has its characteristic stretch and bounce because of the molecules from which it is made.
Bring on the Polymers
Using a combination of Elmer's white school glue, borax (a cleaner made from sodium tetraborate), and water, you can create a substance similar to Silly Putty. The polymer in DIY putty is not the same as in a commercially sold egg-container of Silly Putty, but glue and borax react to form a similar polymer structure. One of the ingredients in Elmer's glue is polyvinyl acetate—a polymer. When you combine Elmer's glue with borax, a chemical reaction occurs, and borax molecules create links between molecules of polyvinyl acetate in the glue. As more and more cross-linked molecules form, the polymer begins to take on new properties—and new substance. Since you wouldn't pick up and play with a handful of glue, you know that something has happened in the mixing because your putty isn't sticky like glue.
Figuring out the optimal ratio of glue to borax is a great science exploration for students. As you mix up separate batches with varying amounts of the two main ingredients, you can compare the differences in the resulting substances. If you want to focus on a single batch until you determine a formula that feels and works well, start with a single recipe from one of the sources below and add small amounts of the borax solution until you reach the desired consistency. Just be sure and work the borax into the glue solution well each time so that it mixes thoroughly before you add more! (Tip: have your students take the putty from the bag, feel it, stretch it, and manipulate it with their hands to evaluate the consistency. Is it too sticky? Is it too hard to squish? Does it break too easily?)
The following resources can help guide your exploration. The full Science Buddies Project Idea can be used during science fair season, but the general procedure gives you a blueprint for turning the project into an exciting family activity:
- Bouncy Polymer Chemistry
- Playing with Polymers (this adaptation of the Science Buddies Project Idea appears in Scientific American's Bring Home Science)
Be prepared for some experimental zaniness after the putty is mixed. Once students get past the initial sensation of how the putty "feels" in their hands, seeing what happens when you do "this" or "that" with the putty is part of the fun and part of the science-based observation the activity inspires. All you have to do to turn up the volume as they squish the putty around in their hands is ask: does it bounce?
Note: Dispose of your glue and borax waste in a trash bag, not down the sink.
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