STEAM Three Ways: Silly Putty

Cover Image via PaperPolaroid.

Library staff are often crunched for time, particularly in the youth services department (although I may be biased here). To that end, getting the supplies and planning for a single science activity that can be used in multiple age groups has a real, measurable time and budget savings. It’s important that these activities not only be adaptable in practice, but also in interest level. So to kick off this new occasional blog feature, I thought I should start with something everyone loves: silly putty.

I have a love of making silly putty. It’s fun, it’s easy, and you can change it up to suit the lesson you’re trying to convey. I tend to use the very simple glue/Borax mix. (I know, I know, it’s not actually silly putty. I’ll address the chemical difference in the “Teen Program” section.)

Basic recipe:

– 1 8 oz bottle of Elmer’s glue (brand is weirdly important here)

– 1/2 cup warm water, supersaturated with Borax (just mix in Borax until it starts to settle out of the solution)

– a plastic bag

NOTE: I don’t ever measure it out as they do here. I tend to put some glue and some supersaturated Borax solution into a Dixie cup and stir. If it’s too hard, add more glue, if it’s too soft and sticky, add more Borax solution.

Preschool Program:

I used this silly putty for part of my color mixing curriculum. This recipe creates a white silly putty, but with a few quick drops of food coloring into the glue before adding the Borax, the kids saw how adding a bit of yellow to the red completely changed the color of their silly putty. After mixing it up initially, children can take their finished silly putty and mix it together. Create a batch of blue and a batch of yellow? Try to play with them together until you get some green putty. I’ve used homemade playdough for the same exercise, but this BOUNCES!

School Age Program:

My school age programs run grades 2-4 and 5-7. There’s a huge range of science knowledge here, so I tend to keep my explanations pretty basic to allow for differences in school curriculum.

So let’s talk simple science. The FAQs on the Elmer’s Glue site and this excerpt from Steve Spangler Science both use the spaghetti model of polymers:

In simplest terms, a polymer is a long chain of molecules. You can use the example of cooking spaghetti to better understand why this polymer behaves in the way it does. When a pile of freshly cooked spaghetti comes out of the hot water and into the bowl, the strands flow like a liquid from the pan to the bowl. This is because the spaghetti strands are slippery and slide over one another. After awhile, the water drains off of the pasta and the strands start to stick together. The spaghetti takes on a rubbery texture. Wait a little while longer for all of the water to evaporate and the pile of spaghetti turns into a solid mass — drop it on the floor and watch it bounce.

Polyvinyl Acetate and Borax reaction
An illustration of the PVA (glue) and Borax reaction. © The University of Edinburgh

I haven’t ever actually used spaghetti to illustrate this point, but depending on the program, you may want to. The reason why Elmer’s glue is sticky are the polymer chains it contains, and this illustration really clearly demonstrates how these polymer chains behave when they are lubricated (the wet glue in the bottle) and when they are dry (the solid, bouncy lump of spaghetti).

It may take students a bit to understand this, depending on their grade level. Words like “molecule” and “element” might be beyond some of the younger students, so creating a glossary can be helpful.

For this age group, I often have them try to see if they can make a batch of “gak” – really stringy, liquidy putty, and a bouncy ball. Students can experiment with different ratios of glue to Borax solution, and might discover a few more tricks about how to make the solution more solid. For instance, the more you mix a batch of silly putty, the harder it will get. Want to know why, or have curious school age kids who do? Check out the teen program below.
Teen Program:

Silly putty is great for a low-key program or a planned science class. Low key allows them to just work out their over-scheduled lives with a toy they probably had as kids. It feeds into the maker mentality because they made the thing they used to have to buy, as well as reinforcing the engineering design process as they try to make the silly putty just the right consistency. If you want hard science though, here’s what makes our Elmer’s/Borax silly putty tick.

Louisiana State University has a great explanation (with graphics!) of what’s happening:

Elmer’s Glue is made up of polyvinyl acetate, which reacts with water to some extent to replace some of the acetate groups with OH (alcohol) groups. The B-OH groups on the borax molecules react with the acetate groups on the glue molecules (relatively long polymer chains) to eliminate acetic acid and form new bonds between the borax and two glue molecules. The linking of two glue molecules via one borax molecule is called polymer cross-linking and it makes a bigger polymer molecule, which is now less liquid-like and more solid.

A model of polyvinyl acetate, the reactive ingredient in the Elmer’s glue.           Copyright © Azim Laiwalla, UCLA SEE-LA GK-12 Program, University of California, Los Angeles

…Many of these borax cross-links occur to “glom” together many polymer molecules turning them into a pliable solid “silly putty”. This really isn’t the silly putty you buy in the store, since it will dry out. Real silly putty is an organosiloxane polymer that doesn’t have any water in it so it doesn’t dry out.

Polyvinyl Acetate crosslinking  with Borax
Illustration and structural formula for the crosslinked Borax/Polyvinayl Acetate result. Copyright © CSACNAS Student Chapter at Texas State University

Get all that? If not, don’t worry – this explanation is about on par with my high school organic chemistry class (and required a lot of refresher before I understood it myself. Essentially, the strings of PVA “spaghetti” get held together by the Boron molecule, holding them in place. The more places that the Boron connects PVA chains, the sturdier the structure and the more solid the silly putty.

Try this activity to give teens (and school age groups, if they’re advanced enough) a clearer picture of how the Borax binds the PVA, also from LSU:

Have about 6 groups of 4 students hold hands and form glue chains. Have them walk around the room. These are your PVA chains.

Then send out 6 individual students to act as borax molecules to grab onto two glue chains – one with each hand. Tell the glue chains that once they are grabbed onto by the borax students that they shouldn’t try to break free. This should result in all the glue chains being linked together by the borax molecules (students). Now that all the students are linked together they represent the more solid “silly putty” that was formed in the experiment. This is a rather good physical analogy to the chemistry going on.

Quick note: while I’ve used the term Polyvinyl acetate, the reaction with water in glue creates polyvinyl alcohol. Dr. Richard Barrans from the Dept. of Physics and Astronomy at the Argonne National Laboratory put the difference between the two like this: “Poly(vinyl alcohol) is a polymer with the repeating unit (CH2-CHOH). Polyvinyl acetate is similar, except that it has an acetic acid ester in the place of the alcohol group: (CH2-CHOCOCH3). Polyvinyl alcohol is actually made from polyvinyl acetate, by cleaving the acetate ester.”  Down to brass tacks, both PVAs make our silly putty.

Interesting to note that the side effect of this reaction is the creation of acetic acid, which, when diluted, is better known as white vinegar. This can lead to further experimentation with acids/bases in your silly putty. For instance, what happens if you mix baking soda into it? Will it bubble and fizz like a baking soda/vinegar volcano?

Wrap up

Have other ideas for making this silly putty recipe appeal to various ages? Let me know. My library does class structures for a lot of the STEAM programs, so explanations and iterative experimentation are important. How do you do STEAM at your library? Any STEAM activities you wish you had better explanation for, or knew how to use with other age groups?

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