Materials by Design
A 5 to 1 ratio of PVA and sodium borate creates crosslinks with the polymer to produce a ball-like solid without compromising the desired ability to bounce, stretch and maintain shape through extreme temperature.
Polyvinyl alcohol is a polymer that when combined with sodium borate creates covalent crosslinking bonds between the polymers, which change the solution from a liquid into a jelly-like solid that can be formed into a ball. 2 A polymer is a chain made of units combined in the same linkage throughout the entire substance. 2 Polymers are used extensively in today’s world to create paper, bike tires, plastic, PVC and many other household common items. 3 The bonds in the polymer are cross-linked; therefore the ball should be flexible and have the ability to stretch considerably. 2 Due to the fact that the sodium borate is the solution that causes hydrogen bonds, which do not hold the ball together, we can assume that the greater amounts of sodium borate will cause the ball to have undesired properties and fall apart.⁵ By keeping the amount of borax used constant and changing the amount of PVA the experiment should show which ratio is better suited for the goal of creating a ball. The ball needed to be able to bounce, not fall apart, be flexible but come back to its original shape after stretching, be nontoxic, odorless, and easy to make in order to lower manufacturing costs. After finding the top two ratios they will be tested in cold and hot conditions that are similar to the areas in which the balls will be shipped. The ice bath represents Alaska and the hot bath represents New Mexico. The following picture shows the crosslinking between the PVA and sodium borate. The borate ion has bonded with the hydroxyl (OH) groups of the polymer and links them together. ¹ The molecular formula of PVA is [-CH2CHOH-]n and the chemical structure of sodium borate is Na2B4O7. 2
Borate ions crosslinking with the PVA chains. 6
While performing the experiment safety goggles should be worn at all times and gloves should be worn at all times while pouring the solutions and handling the gel. Do not taste the gel or get it on your clothes because it can stain. ¹ Procedure for Experiment 1:
1. In three separate 10 mL graduated cylinders measure out 10 mL PVA, 8 mL PVA and 6 mL PVA. 2. In three separate 10 mL graduated cylinders measure out 2 mL sodium borate, 2 mL sodium borate and 2 mL sodium borate. 3. In one 250 mL beaker combine 10 mL PVA and 2 mL sodium borate. 4. For a minute hold the beaker and swirl it so the contents can combine. Put to the side. 5. In a 250 mL beaker combine 8 mL PVA and 2 mL sodium borate. 6. For a minute hold the beaker and swirl it so the contents can combine. Put to the side. 7. In a 250 mL beaker combine 6 mL PVA and 2 mL sodium borate. 8. For a minute hold the beaker and swirl it so the contents can combine. Put to the side. 9. Taking the first beaker that is holding the 10 mL PVA and 2 mL sodium borate scoop out the contents with your hand and for 20 seconds roll your hands together to form a ball with the gel. 10. Test its bounce ability by dropping it on the table and using a ruler measuring how high it bounced. Record. 11. Test its ability to stretch by holding it between two fingers and dangling above the table. Use a ruler to record how long it stretches before breaking. Record. 12. Repeat steps 9-11 with the other two beakers and their contents. After seeing the result we decided to try one more ratio that had the lowest amount of sodium borate. 1. In a graduated cylinder measure out 6 mL PVA.
2. in a graduated cylinder measure out 1 mL sodium borate.
3. In a 250 mL beaker combine the 6 mL PVA with the 1 mL sodium borate. 4. For a minute hold the beaker and swirl it so the contents can combine. 5. Scoop out the contents by hand and for 20 seconds roll your hands together to...