Properties & Three Industrial Foaming Processes of PET Structural Foam

PET structural foam serves as the core sandwich core material for lightweight composite materials, mass-produced by PET Foam Sheet Extruders and Two-Stage Supercritical CO₂ Foaming Production Lines. This paper elaborates on the core performance of PET foam, three mature manufacturing processes, and the iterative trends of foaming technologies

Schematic diagram of PET (polyethylene terephthalate) structural foam cellular structure

1 Introduction

As the core sandwich layer of composite structures, core materials directly determine the rigidity, weight and service life of finished products. Traditional core materials such as balsa wood, PVC and PMI suffer poor recyclability and high carbon footprint. Driven by the dual-carbon policies and surging lightweight demand, PET structural foam has gained rapid popularity, integrating high strength, light weight and 100% recyclability. It is widely applied in wind power, rail transit, new energy vehicles and other sectors, with the global market size reaching USD 347 million in 2025.

2 Basic Definition & Five Core Properties of PET Structural Foam

PET structural foam is closed-cell thermoplastic foam fabricated via physical or chemical foaming with PET resin as the matrix. It can be composited with skins to bear bending, shear and compressive loads. Its core advantages are listed below:

(1) Independent closed-cell structure: ultra-low water absorption, excellent thermal and sound insulation performance;

(2) Thermoplastic processability: heat formable under high temperature, recyclable via melt re-granulation;

(3) Adjustable density: density ranging from 60 to 350 kg/m³ via foaming process control, adaptable to light and heavy load scenarios;

(4) Outstanding heat resistance: heat distortion temperature over 100°C, compatible with composite processes such as prepreg curing and resin transfer molding;

(5) Full closed-loop recyclability: unlike thermosetting foam that cannot be regenerated, waste scraps can be reprocessed with the PS Foam Recycling Machine.

3 Three Main Industrial Forming Processes

(1) Continuous Supercritical CO₂ Extrusion Foaming

PET raw materials, nucleating agents and modifiers are melt-blended in twin-screw equipment. Supercritical carbon dioxide is injected under high pressure, followed by precise segmented temperature and pressure control. Continuous PET foam sheets are extruded and cooled.

Supporting equipment: PET Foam Sheet Extruder, Two-Stage Supercritical CO₂ Foaming Production Line

Core advantages: no residual chemical foaming agents, uniform microcells, low carbon emission. Trimming scraps can be directly fed into the PS Foam Recycling Pelletizer to realize zero-waste closed-loop production.

(2) Intermittent Autoclave Foaming

PET sheets or pellets are saturated with supercritical fluid inside an autoclave, then foamed through rapid pressure relief. This method is only suitable for special-shaped prototypes and small-batch trials, limited by low production efficiency and incapable of mass supply.

(3) Integrated Reactive Extrusion Foaming

PET chain extension and foaming are completed simultaneously, eliminating pre-drying procedures for raw materials and cutting overall energy consumption. It is particularly suitable for direct production from recycled PET bottle flakes.

4 Four Development Trends of Foaming Technologies

(1) Microcellular refinement: cell size reduced to micron or nanometer level to simultaneously boost material strength and surface smoothness;

(2) Functional integration: flame retardant and phase change fillers added during foaming to integrate thermal insulation and fire resistance;

(3) Green production: 100% recycled PET raw materials matched with residue-free supercritical foaming system;

(4) Intelligent equipment: digital twin online monitoring enables automatic adjustment of temperature and pressure, stabilizing the finished product yield above 92%.

Conclusion

Continuous supercritical CO₂ extrusion foaming stands as the optimal mass-production route for PET structural foam. Matched with complete foaming and recycling equipment, it balances production capacity, product quality and environmental protection, becoming the mainstream manufacturing solution for lightweight materials.