Meaning
Accounting methods that track and attribute the use of sustainable feedstocks through a complex chemical production process allow companies to claim recycled or bio-based content in finished polymers without physically segregating the materials. Implementing mass balance allocation enables chemical plants to mix recycled pyrolysis oil with fossil-based crude in the same cracker. This system governs the certified distribution of environmental attributes to specific output batches of resin.
The process ceases to apply when the physical polymer leaves the certified supply chain and enters non-audited distribution networks.
Co-processing Auditing
Recycled and fossil feedstocks are co-processed in the same industrial equipment to minimize energy use and avoid building separate production lines. Under mass balance allocation, the total mass of sustainable input is measured at the start of the chemical process. This input mass is then allocated to a corresponding volume of finished resin using a certified conversion factor.
The finished polymer is chemically identical to conventional plastic, meaning it holds the same datasheet values and processing characteristics as virgin resin.
Certifying System
Third-party organisations audit the chemical plant and the downstream moulders to ensure that the allocated volume does not exceed the physical input. A mass balance allocation requires a strict chain of custody certificate, such as those issued by International Sustainability and Carbon Certification. This certificate must follow each batch of resin through the distributor and the moulder to the final brand owner.
The audit trails prevent double-counting of the sustainable attributes and ensure that the environmental claims made on consumer packaging are legally defensible.
Process Window
Moulders can use these certified resins without modifying their injection parameters, rebuilding their tooling, or risking part performance failures. This benefit makes mass balance allocation highly attractive for medical and food-contact applications that face strict regulatory barriers to using mechanical recycled plastics. The processor can run the material on existing machines with the same cycle times and scrap rates as standard fossil-based polymers.
This approach eliminates the trial-and-error costs associated with adjusting processes for traditional recycled materials.
