With controlled blending, recycled material is physically present in the product in a known proportion. Mass balance is a separate chain of custody model and should not be used as a synonym for physical blending.
How does controlled blending work?
Recycled material is physically combined with virgin plastic, additives, masterbatch or other materials. The proportion should be known and reproducible from the formulation, dosing and production data.
Example
If a formulation contains 60 kg of certified recycled material and 40 kg of other ingredients, the physical recycled material share in that mixture is 60%, provided all masses refer to the same product scope.
What is mass balance?
Mass balance is one of the chain of custody models describing how a specified characteristic is managed within a system. It does not require the declared characteristic to be physically present at the same proportion in every individual unit of product.
Why should these terms be kept separate?
When a customer receives information about a product's actual recycled content, it must be clear whether the figure follows from physical composition or another chain of custody model. Calling ordinary quantity accounting or controlled blending “mass balance” leads to misunderstandings.
What should be documented for controlled blending?
- qualification of the recycled material;
- the formulation and product version;
- actual dosing;
- batch numbers or other material links;
- production quantity;
- losses and material returned to the process;
- the quantity balance for the period examined.
Internal regrind
Material returned from an organisation's own process needs separate analysis. Reusing it does not automatically add a new share of recycled material, because grinding it again does not change its origin.
Key takeaway
Controlled blending describes a product's actual composition. Mass balance describes how a specified characteristic is allocated within the chain of custody. These are different mechanisms and should be communicated separately.