Reverse Spherification
Introduction & Motivation
In an earlier activity, we explored how to Turn Milk Into Plastic. It is an incredible technology most people use every day for things like grocery shopping, packing lunch, or getting a drink on the go. It’s so popular that we produce 300 million tons of plastic waste worldwide every year! Many of the items contributing to this amount of plastic waste are intended for single-use, meaning they are used for mere minutes and thrown away.
Despite how cool it is that we’ve been able to harness such a cool and versatile material, this is actually a huge issue. There is even an island in the Pacific Ocean that is entirely made up of garbage like plastics, called the Great Pacific Garbage Patch! You may know that plastics take a really long time to break down, sometime never breaking down in your whole life. Actually, plastics just get so small we can see them anymore. Through being out in the weather, plastics become microplastics, often no bigger than 5 mm in length. This causes many health issues for animals who live or feed in areas with microplastics.
Often, our first thought about plastics is that we should recycle them! Reduce, Reuse, Recycle is the phrase we see on a lot of recycling bins. This definitely handles some of the plastic, but unfortunately it’s not as effective as we think. Every town has access to a different recycling center, with different rules on what can and cannot be recycled. For example, in the town where Tufts is (Medford, MA), you cannot recycle small plastics, films, or black plastics because of the machinery which separates and processes them. Additionally, you cannot recycle anything with food residue on it! Adding these things which cannot be recycled often contaminate batches and render it unable to be recycled.
So, what can we do about this? For people who are not chemical engineers, you can switch to reusable bags, bottles, straws, and utensils when grocery shopping or taking food with you! Some stores that sell food or beauty products even ask that you bring your own reusable containers so they don’t have to individually package products in plastics. Some countries and cities have even banned single-use plastics, and companies like LUSH have programs which reward you for returning your clean packaging! Luckily, as a chemical engineer, you have a lot of power to usher in a future where we use less plastic.
We’ve witnessed the power of membranes for separations through other activities, and here is another area where they shine. You may have seen edible water bottles, which use edible membranes to contain water in an orb. That is exactly the science we will use to contain other products in this activity!
Materials
- Immersion blender
- Kitchen scale
- Calcium Chloride (salty, better texture)
- Calcium Lactate (no taste)
- Sodium Alginate
- Spoons
- Gatorade
- Chocolate Milk
- Apple Sauce
- Apple Juice
- Soap
- Lotion
- Bowls (2 per group)
- Plastic cups
- Measuring spoons
- Pipettes
- Syringe plungers (3 – 5 mL)
Procedure
Before starting the activity, consider showing the video linked below about edible water bottles to the students to get them excited. Ahead of time, prepare the solutions to be used in this activity accordingly:
SODIUM ALGINATE SOLUTION: Using an immersion blender, make a bath that is 0.5% sodium alginate solution (0.5 grams sodium alginate for 100 grams of water). For a group of roughly 20 girls, 3 – 4 L of sodium alginate solution was sufficient to start.
**Tip! Sodium alginate doesn’t like to dissolve, so either get an immersion blender or you’ll need to spend a good 5 – 10 minutes mixing. The alginate likes to hydrate (become gel-like) so mix immediately.**
PRODUCT (CALCIUM CHLORIDE) SOLUTION: Add 0.5 gram of calcium chloride and 50 grams of your chosen solution to a cup, and mix with a spoon. If you chose to do more or less than 50 grams of your solution, then add 1% of your solution’s weight in calcium chloride to it.
**Tip! Since this is salty, it is best used with cosmetic products such as lotion or soap.**
PRODUCT (CALCIUM LACTATE) SOLUTION: Add 1 gram of calcium lactate and 50 grams of your chosen solution to a cup, and mix with a spoon. If you chose to do more or less than 50 grams of your solution, then add 2% of your solution’s weight in calcium lactate to it.
- Give each group about 500 grams of the sodium alginate solution and small cups of products that they are interested in spherifying.
- Fill the second bowl with water. This is your rinsing bath for the spheres.
- Using a pipette, plastic spoon, or measuring spoon, slowly add your product solution to be spherified to the sodium alginate bath.
- Slowly stir the bath with a spoon to create a casing around all of your liquid. Stir the bath for about 30 seconds to 1 minute. Then remove the balled liquid, place it in the water bath, and stir the water bath for 10 seconds. Remove the balled liquid.
Discussion
- Which products worked best? Which do you think are the most viable or interesting for wide-spread use?
- Hooray! You’re on the way to solving one of the biggest environmental problems: single-waste plastic. Now, we have to consider how to scale this product up to commercial manufacturing. How might you store your orbs for transport between stores?
- Are there any parts of the process of making the orbs that seems particularly difficult for a machine or robot to do?