Sharing chemistry with the community

Polyurethane foam smoothies

Polyurethane foam smoothies continue to be one our most popular hands-on, make-and-take activities. They are easy to do, safe to perform (with supervision), inexpensive, and useful for illustrating several chemical concepts for a wide range of audiences. Another plus, each participant can take his or her smoothie home and talk about the process of making it and the underlying chemistry with family and friends. It can also be scaled up as an impressive demonstration for larger audiences. We have used polyurethane foam smoothies as one of several hands-on activities designed to introduce the world of polymers to elementary-aged children and for Chemistry and Crafts. For middle school, we’ve used this as a hands-on activity to illustrate some of the indicators of chemical change. In high school, you can focus on the polymers and catalysts.

Concepts

• Polymers
• Cross-linking
• Evidence of chemical change
• Formation of a solid material
• Generation of a gas
• Generation of heat (exothermic process)

Materials (per smoothie)

• One 10-oz clear plastic drink cup (Hefty^® brand works well)
• Two 2.5-oz clear plastic cups
• One jumbo craft stick
• Paper towel
• Cafeteria tray (optional)
• Polyurethane Foam System (Flinn Scientific Inc. #C0335 ($32 for a kit — makes almost 50 smoothies)
• Permanent marker (used to write name on the cup)
• Food coloring, silver glitter, soda straw, sprinkles (all optional)

Safety

• Wear safety glasses/goggles
• Wear protective gloves and apron
• Perform activity in a well-ventilated area; avoid inhalation of fumes
• Avoid contact with the chemicals provided in the Polyurethane Foam System kit; both Part A and Part B are skin irritants
• Allow the resulting polyurethane foam to completely set before touching; it should be fully set in about 15-20 minutes

Advance preparation

• Both part A and part B of the Polyurethane Foam System can be pre-poured into separate 2.5-oz cups and stored in a fume hood or other well-ventilated area. I recommend doing this if you have a large group who will be performing this activity individually. Measure one-third of a cup of each part. Avoid using more than a third of a cup.
• I have the participants perform this activity on a cafeteria tray that has been covered with a paper towel. Trays can be covered and stacked in advance.
• I measure out small amounts of glitter and sprinkles in separate small weigh boats, enough for each participant. I save the weigh boats and reuse them for this activity.

Procedure

1. Write your name on bottom of the 10-oz drink cup.
2. Transfer Polyurethane Foam System Part A (1/3 of a 2.5-oz cup) to the 10-oz cup. Use the jumbo craft stick to scrape the small cup in order to get most of Part A transferred. Leave the jumbo craft stick in the large cup and discard the small cup immediately in the trash.
3. Add 5-6 drops of food coloring, if desired, and mix well.
4. Add the silver glitter, if desired, and stir well.
5. Transfer Polyurethane Foam System Part B (1/3 of a 2.5-oz cup) to the mixture. Use the jumbo craft stick to scrape the small cup in order to get most of Part B transferred. Discard the small cup immediately in the trash.
6. While holding the 10-oz cup, stir the contents vigorously for 10-15 seconds, until the mixture appears uniform, no longer marbled. Remove the jumbo craft stick, scrape any mixture adhering to the stick on the rim of the cup, and discard the stick in the trash.
7. Set the cup down on the paper towel and observe.
8. When the mixture has risen about halfway up the cup, insert the soda straw all the way to the bottom of the cup and add the sprinkles, if desired.
9. Carefully feel the outside of the cup and note the temperature.
10. Set aside to allow the material to set. Do not touch it.

Disposal

• Paper towels, craft sticks and used cups can be placed in the trash.
• Once set, the participant can take his or her polyurethane foam smoothie.

Erica learned the process of making the smoothies and appropriate methods of conveying the chemistry to others. She participated in two chemistry outreach events demonstrating the procedure and the chemistry behind these chemical smoothies. Not only did the audience benefit from her presentations, but Erica too learned much from these experiences. Here are her reflections:

Making a polyurethane foam smoothie for the very first time was truly a wonderful experience. I felt like a child again when I saw the mixture rise up and spill out of the cup. I could not wait to share this exciting demo with others. Through repeated practices I not only learned how to make the smoothies but also appropriate methods of engaging audiences and communicating the underlying chemistry. Last February, Duke Chemistry Outreach participated in the FEMMES (Females Excelling More in Math, Engineering, and Science) Capstone event (grade 4-6). I helped students make polyurethane foam smoothies and was very impressed with the girls’ enthusiasm, interest, and scientific reasoning skills. They made excellent observations and followed with “Why?,” wondering about the reaction, why the cup felt warm, and what was causing the liquids to become solid. The girls were able to describe the reaction in their own words so I knew they were on the right track. While the girls may not remember all the specifics, they gained knowledge about the chemistry and enjoyed the experience.

I presented polyurethane foam smoothies again in a totally different setting, the annual Science Night at a local elementary school. Unlike FEMMES, the kids constantly cycled through stations. I had no idea that our smoothie-making station would be so popular and the high demand caused me to struggle with multitasking the preparation, execution and explanation. At times, four children were preparing smoothies while numerous others watched eagerly, waiting their turn. I came to fully appreciate the value of teamwork, so crucial to the success of all our outreach events. Dr. Lyle pitched in by refilling the materials, enabling me to remain focused on the audience.

Again, the children’s high level of curiosity and intelligence amazed me. Without prompting, the children openly expressed their observation, noting bubble formation, the increase in cup’s temperature and the expansion of the mixture. I was impressed with their natural scientific curiosity and mindset to use their senses to understand this unfamiliar process taking place before their eyes.

Personally, one of my biggest challenges arose from the diverse backgrounds of the audience. In order for everyone to grasp the underlying chemical concepts, I needed to tailor my explanations to the individual. Initially this was a challenge but over the course of several outreach events, I became much better at fine-tuning my presentation.

With each new volunteer experience, I learn more about myself as a presenter and the ways to improve for the next event. One important feature of the chemistry outreach program is the wide range of formats tailored to the size, age and backgrounds of the audience, and the needs of our community partners. I believe I am now a better presenter because of the diverse nature of the chemistry outreach presentations.

Watching the kids’ faces light up with enthusiasm and comprehension is truly rewarding. Participation in chemistry outreach is much more than just sharing the chemical knowledge. I shared my enthusiasm for science and served as proof that chemistry is interesting and fun. To this very day, the polyurethane smoothie I made long ago sits on my bedroom windowsill. It reminds me that chemistry is one of the coolest things to do and sharing it with others is one of the greatest gifts.

*Erica Weinberg is a sophomore at Duke University majoring in Evolutionary Anthropology with a minor in Chemistry. She is considering a career in dentistry upon graduation.

**Dr. Kenneth Lyle, a lecturing-fellow in the Department of Chemistry at Duke University, serves as the lecture-demonstrator, chemistry outreach coordinator instructor of Chemistry Outreach Service Learning Course.

The Powell Family Trust, the Duke-Durham Neighborhood Partnership, and Biogen Idec – Research Triangle Park, fund the Duke Chemistry Outreach Program.

[Editor’s note: Flinn Scientific Inc. does not ship chemicals across the border to Canada. We have not fully investigated where a kit similar to Flinn's can be found in Canada. A place to start would be Sculpture Supply Canada which sells "Soft Expanding Polyurethane Foam". There are two parts, and it is used to make masks from molds for artists. We have not tried this, but it has potential. If you do try it, make sure you follow the manufacturer's safety guidelines. If you have a source in Canada, let us know.]