Mass balancing is an age-old principle based on physics. It has been applied to everything from chemical engineering to financial accounting. These days, it is also being applied to sustainability. So much so that the mass balance approach to plastic recycling is a hot topic.
Plastic manufacturers view the mass balance approach as a way to significantly boost sustainability by increasing recycling efforts and simultaneously reducing the demand for virgin plastic. Of course, there are those who believe that mass balancing doesn’t deliver – despite the fact that it is utilized extensively throughout the broader sustainability movement.
The Basic Principle
In physics, mass balance is also known as material balance. It stipulates that the input of any material into a physical system should be identical to the output, even though form might change. For example, a slurry made up of water and sediment should exhibit the same volume and output as exhibited during input, despite the materials being separated. If the balance is off, accumulation has occurred somewhere within the system.
The principle has been applied to accounting as a way to more easily track inflow and outflow without necessarily having all of the details. Likewise, mass balancing has been applied to a number of different sustainability efforts to better quantify what was previously unknown.
Mass Balance and Cocoa
A frequently cited example of mass balancing in the sustainability space involves cocoa. Sustainability proponents would prefer that manufacturers purchase cocoa only from certified-sustainable farms. But such farms do not produce enough cocoa to meet the demand. Thus, manufacturers need to source cocoa from multiple providers.
The mass balance approach says that both certified and non-certified cocoa can be mixed in the supply chain at any point. The manufacturer doesn’t know the exact content of certified cocoa being purchased. But a baseline volume can be estimated based on the laws of mass balance.
Mass Balance in Plastic Recycling
If we apply the same mass balance principles to plastic recycling, we get a similar outcome. Both recycled material and virgin plastic can be combined to provide feedstocks to manufacturers. That does not mean that all the feedstock a manufacturer utilizes is identical.
A shipment delivered this month could be 50-50. But a shipment next month might be 40% recycled plastic and 60% virgin material. As long as a feedstock does not contain more recycled material than a manufacturer allows, the exact ratio isn’t so important.
Mass balancing is not applied so much to mechanical recycling. Why? Because mechanical recycling keeps materials separated in the supply chain. Consider Seraphim Plastics out of Tennessee. Seraphin purchases and mechanically recycles industrial plastic scrap in numerous states. What they recycle is transformed into regrind, a material that is sold to manufacturers.
Manufacturers combine the regrind with virgin feedstock. They know the exact formulation because they receive each type of material separately. They mix it on-site.
Applying It to Chemical Recycling
This sort of arrangement does not work well with chemical plastic recycling. Chemical recycling breaks plastic down into its individual components. Those components are then pulled out and used to manufacture new plastic. But exact volumes are difficult to track.
Mass balancing solves the problem by always guaranteeing that input and output match. As long as they do, the resulting material is suitable for new manufacturing. More recycled material can be used without jeopardizing final product quality.
The mass balance approach has its critics, at least in plastic recycling, but the concept has proven itself over the last few decades. If mass balancing works for cocoa, it also works for recycled plastic.