What is The Science Behind the Reactive Extrusion Process of PET Foam?

As we all know, polyethylene terephthalate (PET) foam is the first structural core material to be produced continuously. It is a thermoplastic that produces a lower cost, yet structurally sound core product. And the most important feature is this kind of material can be recycled. Rising environmental concerns and sustainability are propelling the demand for recyclable materials across industries. Because of the advantages of PET foams, more and more clients prefer to choose this environmental material.

Importance of Polyethylene Terephthalate Foam (PET Foam)

In times when environmental safety is being more and more in danger, scientists are obliged to look for new ways of using waste materials. Thanks to the properties of polyethylene terephthalate foams, they are suitable for a variety of applications, including food packaging, water bottles, and pipe insulation. Besides, the growing demand for PET foam from the wind energy, marine, and packaging end-use industries in China, India, Japan, and Australia is driving the market growth of PET foam in the Asia Pacific region.

Compared to widely and the most commonly used PS foam, PET foams are safer and have lower toxicity, have higher temperature resistance, have good mechanical and thermal insulation properties, are economical and lightweight, are more easily recyclable, and have a lower carbon footprint. PET as a  foamed material possesses few limitation characteristics like unsatisfying viscosity that causes the collapsing of the foam structure during the stabilization phase of foam production. However, the production process of PET foam presents challenges that can prevent its adoption.

The Challenges in Reactive Extrusion Process of PET Foam

Extrusion foaming of the polyethylene terephthalate foam is still faced with many challenges.

Firstly, it requires the incorporation of additives, such as chain extenders, to the polymer in the process of polyethylene terephthalate’s foaming. And, the equipment used must be designed for high temperatures which must be high enough to cause decomposition of the gaseous products necessary to produce the porous structure in the melted polymer because the melting point of PET foams is around 250°C, but it must not be too high to cause degradation of the plastic material.

Secondly, the processing equipment in the reactive extrusion process of PET foam remains stable at the chosen temperature, as temperature overshooting can lead to thermal degradation of the polymeric chains, heavily affecting the final mechanical properties of the foam.

Thirdly, optimal foaming is achieved near the crystallization temperature of PET, and therefore temperature undershooting would lead to a solidification of the polymer inside the system and a stop of production.

Production of Polyethylene Terephthalate Foam (PET Foam)

Both recycled and virgin PET foam can be used as raw materials and supercritical fluid is used as a physical foaming agent.

In first, to avoid the strong hydrolysis of melt PET, all materials must be dried by hot air with a dew point of at least -40℃ for 4 hours to eliminate the humidity under 50ppm.

PET and additives are fed at constant rates through gravimetric dosing devices. The reactive extrusion of PET with a multifunctional agent increases the molecular weight, broadens the molecular weight distribution, and introduces a long-chain branch, which increases the melt foamability of PET and the product properties.

The blowing agent, injected into the extruder steadily, dissolves into the PET melts in the extrusion line, and the PET/SCF solution is then cooled and extruded through the foaming die, where cells nucleation and growth are initiated by the rapid depressurization.

The extruded PET foams are then calibrated, conveyed, edge cut, and surface planed to obtain the final PET products.

Advantages of Carbon Dioxide (CO2) as Foaming Agent for PET

Traditional PET foam uses fluoride as a foaming agent during production. However, Feininger has successfully used extrusion foaming with carbon dioxide (CO2) as a foaming agent for PET. What are the differences between these two kinds of materials?

1. Compared with fluoride, CO2 is safer. Fluoride as a foaming agent for PET takes a toll on health in our daily life. Because it exists in the bubbles of PET foams.  But carbon dioxide not. 

2. CO2 as a blowing agent of PET foams is more environmentally friendly which can achieve ZERO greenhouse gas emissions. 

3. CO2 as a extrusion foaming agent is more cost-efficient. 

Besides, the effects of the foaming temperature, screw revolution speed, gas input, and addition of nucleation agent have been carefully investigated on the extrusion foaming and the resulted polyethylene terephthalate (PET) foams properties.  

In conclusion, PET extruded foam is a kind of closed-cell thermoplastic structural foam that can be 100% recycled. This material has begun to gradually replace the use of other foam core materials, such as PVC, PS. The PET production line designed and constructed by the Feininger team could improve productivity efficiently, reduce the production cost, and regulate the PET properties easily. Any questions, welcome to contact us.