Blog
Analyses with Circo® Recycled Plastics
February 13, 2026 at 12:00 PM
Mold‑filling analyses have long been standard practice, especially in the design of technical plastic components. Drawing on his deep expertise in plastics, Mikko Koivuniemi, Director of Plastics Recycling, explains how simulations based on a 3D model can predict filling and cooling behavior, product warpage, and gas venting. The purpose of simulation is to reduce production start‑up time, lower mold‑related costs, and optimize product quality.
Today, the necessary data is also available for recycled materials, enabling reliable filling simulations. Circo compounds are already used in numerous demanding applications and are available with several reinforcement options. When a base polymer is filled or reinforced, its mechanical and rheological properties change. Because these materials are often used in more advanced technical components, the need for—and the value of—simulation becomes even greater.
Traditionally, melt flow index (MFI) has been used to describe the flowability of a molten polymer. MFI represents a single point on a viscosity curve. However, polymer viscosity and flow behavior depend strongly on shear rate. This means that relying solely on MFI may give an incomplete or even misleading picture of a material’s actual flow characteristics.
Left image: Circo PP without reinforcement, melt flow index 22 (2.16 kg / 230°C)
Right image: Circo PP + 20% cellulose fiber, melt flow index 9 (10 kg / 200°C)
As images above show, the flow length achieved during injection molding with the lower‑MFI material (noting the different MFI test settings) is significantly longer than the melt flow index alone would suggest.
Shear‑rate ranges across different processes. The shear rate used in MFI testing is generally lower than that encountered in both extrusion and injection molding.
When material characterization data—such as viscosity curves, PVT data, and specific heat—is available, the material’s behavior during injection molding can be simulated accurately. Key simulation outputs include mold‑filling behavior and prediction of weld lines, which help optimize product quality. Simulation can also predict potential shrinkage and warpage of the part, which can be influenced by controlling the cooling process.
Melt‑front advancement in a technical plastic part simulated using Circo PP recycled material.
Filling analyses and simulation are not the exclusive domain of virgin plastics. Recycled materials can also be used for technical applications, and characterization can be performed for different recycled‑plastic compounds to support simulation.
The CircoLab service has been developed to support product development and testing. The properties of recycled plastics often need to be enhanced with additives or reinforcements. While simulations provide valuable insight, mechanical testing is also recommended to thoroughly evaluate material performance.
Mikko Koivuniemi
Director, Plastics
NG Nordic