Recycling plastics using switchable solvents

Methods

Summary

Part 1-(Mumladze et al. 2018) 

For safety, the entirety of the procedure will be carried out wearing a 3M 6052 QL Respirator fitted with 3M Multi Gas/Vapor Cartridges. Chemical resistant nitrile gloves and safety glasses will also be worn. All experimentation will also be performed in a fume hood.    First, MFP will be cut into 1cm by 1cm squares after washing the samples with distilled water and dried. DMCHA (dimethylcyclohexylamine) will be obtained and mixed in a 1:1 ratio of water to DMCHA to have a total volume of 15 mL in a 50 mL Erlenmeyer flask.  MFP will be added in a  1:3 g to mL ratio of 5 g MFP to 15 mL DMCHA solution. The mixture will be heated to 50℃ using a hot plate checking temperature with a thermometer. As layers of the packaging either dissolve or separate from one another, floating pieces of film or other parts of the MFP will be isolated. After all the film is recovered, the solution will be centrifuged (aluminum will settle). The liquid solution will be separated from the aluminum using a pipette. To the recovered liquid solution, 30 mL of water will be added, and the mixture will be placed in ice and CO2 added via an aquarium CO2 bubbling system (1 atm). Then this solution will be filtered. To regenerate solvent, the solution will be heated to 60 °C and when it separates from the water, only the SHS layer will be carefully extracted. For the final purification step, the film will be added to 15mL water in a 50 mL beaker and CO2 will be bubbled in to remove any excess solvent that is contaminating the film. After removing the film, the aluminum will be added to the carbonated water. Finally, the film and aluminum will be dried by a fan. 

Part 2- 

First, polystyrene (PS) will be cut into pieces approximately 1cm by 1cm by 1cm pieces. DMCHA will be mixed with water in a 1:1 ratio for a total volume of 15 mL in a 50 mL Erlenmeyer flask. The plastic will be added in a 1:3 g:mL ratio of plastic to SHS solution. Then the solution will be heated until the polystyrene dissolves into the solution, ensuring to check the temperature with a thermometer. If materials float, they will be removed from the solution. The solution will be centrifuged, and if materials settle to the bottom, the solution will be separated by pipette. To separate out apolar materials that dissolved in DMCHA, twice the volume of water will be added, and the mixture will be placed in ice. Then CO2 will be bubbled in. Finally, the solution will be filtered. To regenerate the solvent, it will be heated to 60 °C, and the DMCHA will be separated from the water by pipette. Finally, the recovered material will be put in 15mL of water in a 50mL beaker and CO2 will be bubbled in to remove excess solvent. After being removed from carbonated water, the materials will be dried by fan. The procedure described in this paragraph will be repeated for polyvinyl chloride (PVC), waxed paper, and mixed plastic waste.

Afterwards, the previous steps will be repeated using dimethylbenzylamine  and 2-(dibutylamino)ethanol. 

If the 1:3 g:mL ratio of material to solvent does not work, different ratios will be tested. Both ratios of 1:1.25 g:mL and 1:5 g:mL will be tested to see which mixture of material to solvent is optimal.

Sources:

“Approach to Recycling of Multilayer Flexible Packaging Using Switchable Hydrophilicity Solvents”

Challenges

Considering this experiment will be conducted in a high school setting, the lack of supplies and funding may be a challenge. Additionally, because there is not much prior research in this field, there is very little reference material to go to in case the experiment does not go as planned. 

Pre Analysis Plan

The plastic will be analyzed by H1 NMR and metal’s surface purity will be analyzed by scanning electron microscopy. The spectrum of the plastic sample will be compared to a spectrum of a pure sample of the same plastic found on a database to determine how good the separation by the switchable solvent treatment was. For analysis of the metal, both a control sample of the same metal and processed sample of the metal will be imaged using scanning electron microscopy and compared to test for purity of the surface of the metal.