THE EFFECT OF BORAX ON THE ELASTICITY OF SLIME

THE EFFECT OF BORAX ON THE ELASTICITY OF SLIME Mieke Jones (Year 10) Science Faculty, The Illawarra Grammar School, Western Avenue, Mangerton, 2500

Abstract

Slime is a toy that is enjoyed by children all over the world. In this work, PVA glue and borax solution was used to create the non-Newtonian fluid, slime. This experiment involved creating 3 separate slimes with different amounts of borax solution. The elasticity of slime was evaluated and in particular the effect of borax on the elasticity of the slime. To evaluate the elasticity each slime was stretched along a ruler until they snapped and the final length at breaking was recorded. The study found that the slimes with a lower amount of borax solution in them had a higher elasticity.

Introduction

Polymers are a class of natural or synthetic substances comprised of very large molecules which are made up of multiples of smaller units called monomers. When monomers join together to make polymer, they join by forming covalent bonds through sharing electrons (Evans, D & Watkins, S 2017). Polymers can be found in living organisms, minerals and many man-made materials. Polymers are used extensively in children’s toys (Polymer, 2021).

Polyvinyl acetate (PVA) glue is a vinyl polymer (Wikipedia 2021) which is made by chemically combining vinyl acetate monomers into long chain-like network molecules (Polymerisation, 2020). The PVA polymer is used in many applications. It can be found in paints, food additives and adhesives for wood, paper and cloth (Oksman, K 2017). Crosslinking is the process of joining long chain-like network polymer molecules together. This process can alter the overall structure of the polymer and change its properties, for example its elastic behaviour (Kuckling, D 2012). PVA can be cross-linked with different cross-linkers. One such cross-linker is sodium tetraborate, commonly known as borax. Many studies have been done on cross-linking PVA by using borax or boraxbased substances and cross-linking of solutions of PVA and water resulting in gellike materials has also been reported. Some studies also showed that borax type additives also cause the PVA to become more mouldable (Oksman, K 2017).

In 1976 Mattel Toys released a product called Slime that was designed to be a gross, oozing substance. It was a light green coloured and was supplied in a little green garbage can. Presumably during the development of this product by Mattel the effect of the cross-linker on the base polymer would have been studied to provide a product with the desired properties. This report investigates the cross-linking reaction between PVA glue and borax and the effect of increasing volume of borax on the properties of the final polymer. (The Science behind Slime, 2017.).

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Method

Three batches of slime were made using PVA glue, water and borax solution. The borax solution was made by adding 1 teaspoon of borax into half a cup of water and stirring until the borax is completely dissolved. Into three different cups a PVA and water solution was made in the ratio of 1:1; one spoon of PVA glue and 1 spoon of water. These PVA solutions were mixed carefully until the PVA glue was evenly mixed into the water. A single drop of food colouring was added to the PVA solution and mixed in thoroughly. To the first cup of PVA solution 25 drops of borax solution was added and mixed to make slime. A 1m ruler was laid on the bench. The slime was removed from the cup, moulded into a ball and by pinching gently between the fingers of each hand the slime was pulled apart above the ruler until it broke. The final length of the slime when it broke was measured on the ruler. The slime was collected, remoulded into a ball and stretched a further 2 times (3 times total). Each measurement of the stretched slime was recorded. This process was repeated for the remaining PVA solutions by adding 35 drops of borax to one and 45 drops of borax to the other. The results of all experiments were collated and graphed.

Results

The results for the stretched length of each slime recipe are collated in Table 1 and represented graphically in Figure 2.

In this work, the elasticity of the slime is being represented by the length achieved during the pull test, where a longer length equates to a greater elasticity. The three pull test results were averaged for each slime recipe. Based on the average length results from the pull test; the slime recipe with the greatest elasticity was the recipe with 25 drops of borax, and, the recipe with the least elasticity was the recipe with the 45 drops of borax.

The average elasticity increased by 176% when the volume of borax was reduced from 45 drops to 25 drops. The average elasticity increased by 24% when the volume of borax was reduced from 45 drops to 35 drops. The change in the elasticity based on the volume of borax did not follow a linear relationship. This can be seen in Figure 1 where the trend line is the liner relationship and the average length in the pull test for 35 drops of borax is below this line.

Table 1: Results of slime pull test for elasticity.

Slime Recipe Trial 1

Slime Elasticity (cm) Trial 2 Trial 3 Average

25 drops of borax 50 60 28 46 35 drops of borax 18 16 28 20.67 45 drops of borax 10 18 22 16.67

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Figure 1: Average elasticity for slime recipes with increasing amounts of borax.

Discussion

Making slime is a common experiment used in schools to discover and learn about monomers, polymers, bonding and crosslinking. Documentation on the experimental work done when slime was discovered by Mattel toys in the 1970s is most likely unavailable due to it being a company secret and to avoid direct copies. Many experiments have been done since then to create slime but few have complete documentation available. The science however is well known and this experimental work supported the hypothesis that the volume of borax will change the properties, in this case elasticity, of slime. This experimental work showed that as the volume of borax is increased the elasticity of slime is decreased. The PVA polymer solution consists of long molecules of the PVA polymer moving around in water. When the borax is added the borate, ions attach to the PVA molecules by the process known as cross-linking. Cross-linking reduces the ability of the PVA molecules to move and the PVA solution produces a less liquid substance known as slime. By adding more borax, more borate ions are available to attach to the PVA molecules and the number of crosslinks increases (Carnegie Mellon University, n.d.). which in turn further reduces the ability of the PVA molecules to move or slide relative to each other (American Chemical Society, 2021). For the PVA polymer solution to have elasticity it needs some crosslinking (to make it slime and not liquid) but not too many cross-links to stop it from being able to stretch far without breaking (Questacon, n.d.). The graph in Figure 1 shows that there was variability in the results of the pull test. There are several variables that could be the cause of this variability. Firstly, the original moulded shape of the slime could vary such that the slime is thinner or already stretched a little bit before starting the pull test. It is suggested that a more controlled and consistent method of measuring the elasticity of the slime would reduce the variability of the individual results.

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A second variable relates to the slime acting like a non-Newtonian fluid. For a nonNewtonian fluid, it’s physical behaviour can change depending on the nature of the applied force (Helmenstine, A 2019). For example, it was observed that if the speed of the pull test changed the results were different. For a faster pull speed, the slime broke at a shorter length (The Science Behind Slime n.d.). It was difficult to pull the slime at the same speed and force every time which likely contributed to the variability in the results.

By comparing the results for the average length of the pull tests for each slime recipe the increase in elasticity from 45 drops to 35 drops was only 24%, while the increase in elasticity from 35 drops to 25 drops, the same change in volume, was 176%. The change in elasticity did not follow a linear relationship. It is acknowledged that the number of results in this experiment are limited and it is recommended that more experiments be conducted with volumes below 25 drops and between 25 and 35 drops to better understand how the elasticity changes with borax volume and perhaps identify the optimum volume of borax for maximum elasticity. Looking at the individual results for the 45 drops and 35 drops recipes it is suggested that the difference in elasticity might not be significant because both recipes had results of 18cm and the other results were not very far apart. The variation between these two recipes might just be experimental variation. To explore this you could increase the number of individual tests from 3 to 10 to gain better understanding of the results (Accuracy, Precision, and Error n.d.). If the results are similar this could identify that for the PVA solution in this experiment there is a limit to the number of cross-links that can form and the extra borate ions available are not used.

References

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Questacon n.d., Borax Slime, Questacon, Canberra, viewed 17 November 2021, <https://www.questacon.edu.au/outreach/pr ograms/science-circus/activities/boraxslime>. Science Mom 2017, The Science behind Slime, online video, 9 December, viewed 15 November 2021, https://www.youtube.com/watch?v=4F9uk CQvP20. The Science Behind Slime n.d., viewed 16 November 2021, <https://littlebinsforlittlehands.com/basicslime-science-homemade-slime-for-kids/>. Wikipedia 2021, ‘Polyvinyl acetate’, wiki article, 2 November, viewed 12 November 2021, <https://en.wikipedia.org/wiki/Polyvinyl_a cetate>.)

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