Calculations

5 plastic water bottles were used for testing of the chopper and the interaction with ferrofluid.  Measurements were taken for the time to chop all bottles, the weights before and after chopping and sieving, and the amount of ferrofluid needed to separate efficiently.  The amount of ferrofluid needed per weight of chopped plastic was then calculated to determine the capacity of the system.

Testing Method 

5 plastic water bottles were cut in half and their caps removed for chopper functionality.  After weighing the starting amount of plastic, it was chopped and sieved using a 5.6mm sieve, in order to separate the big plastic pieces from microplastics.  The big plastic pieces and the microplastics were then each weighed.  The bigger plastic pieces were sent through the chopper for a second pass, and again separated to remove microplastics and each section weighed.  The microplastics were then put in water to test ferrofluid separation.

Measurements and Calculations

Time to chop 5 bottles: 2 minutes, 13 seconds = about 30 seconds per bottle 

Starting weight of plastic bottles: 22.4g 

Weight of chopped bottles, first pass through chopper: 20.8g 

Weight of microplastics (after sieving through 5.6mm sieve): 4.0g 

Weight of big plastics (unfiltered): 16.7g 

Loss from chopper: 0.1g

Weight of chopped plastic, second pass: 16.4g 

Weight of microplastics (after sieving through 5.6mm sieve): 6.9g 

Weight of big plastics (unfiltered): 9.5g 

Loss from chopper: 0g

Total weight of microplastics: 10.9g 

= 0.49g microplastics per 5 bottles = 0.1g microplastics per plastic bottle

Ferrofluid: 

2.5g of microplastics in 500mL of water + 1mL of ferrofluid (~15 drops from plastic pipette)

= 0.4mL ferrofluid per 1 gram microplastics

= 0.04mL ferrofluid per plastic bottle