Analysis of Two-Stage Supercritical CO₂ Foaming Process Principle

Supercritical CO₂ physical foaming is a low-carbon polymer processing technology supported by China’s Ministry of Industry and Information Technology. Compared with traditional AC chemical foaming, it produces no VOC residues and delivers a lower global warming potential (GWP). At present, the two-stage supercritical CO₂ foaming production line matched with the PET foam sheet extruder has become the top choice for mass-producing insulation substrates in new energy energy storage and aerospace lightweight sectors.

Conventional single-stage foaming equipment has unavoidable technical flaws. Gas dissolution and bubble expansion happen simultaneously inside one chamber. Once the polymer softens, its mechanical strength drops sharply. Instant pressure relief generates powerful expansion force, which easily results in oversized foam cells and unbalanced porosity. Slight fluctuations in process parameters will lead to large batches of defective products, failing to meet the production standards of high-end energy storage insulation board equipment.

Chinese university research teams have developed a two-stage separated foaming technology, which splits gas saturation and foaming into two independent phases with separate temperature and pressure control:

1. First stage: Low temperature & high pressure Supercritical CO₂ fully permeates and dissolves into polymers below the material softening point. The substrate maintains high rigidity to prevent premature bubble nucleation and growth.
2. Second stage: Slow heating under backpressure The polymer viscosity gradually falls into the optimal foaming window. Bubbles grow at a steady rate, forming uniform microporous and reentrant concave microstructures precisely.

(a) Schematic diagram of the preparation process of Si-PC foam and reentrant Si-PC foam
(b) Experimental control of temperature and pressure during two-stage supercritical CO₂ foaming

Different from ordinary chemical foaming, the two-stage supercritical CO₂ foaming process leaves no foaming agent residues and achieves low carbon emissions. Trimming scraps generated on the production line can be recycled in a closed loop with the PS foam recycling machine, satisfying the low-carbon production requirements of energy storage manufacturers. This technology supports flexible regulation of single-mode and dual-mode multi-level cell structures, making it a core manufacturing solution for battery heat insulation and aerospace lightweight materials.