Closing the loop. Sustainable Raw Materials for Foaming PP with Twin-screw Extrusion Technology

Borealis and FAP are minimizing the environmental impact of foam applications
CO2 used as blowing agent in the extrusion process for physically foamed Daploy™ WB140HMS polypropylene.
Borealis and its long-standing partner FAP, a leading producer of equipment for the physical foaming of expanded polypropylene (EPP), set out to make low-density foam applications that are more easily recyclable. The performance properties that have ensured the popularity of polymer foams would have to be maintained - or even improved. By leveraging their expertise in polypropylene resins and foaming technology, respectively, the partners aimed to improve physical foaming processes in order to offer innovative material solutions that are affordable, resource efficient, and more environmentally compatible.
FAP and Borealis focused their collaborative efforts on achieving better process stability in the foaming process when using liquefied CO2 as the blowing agent along with the Borealis resin Daploy™ WB140HMS, a long chain-branched PP polymer developed for the PP foam extrusion process. In contrast to conventional PP, WB140HMS offers a combination of high melt strength and low melt viscosity due to the shear thinning effect caused by the branch structure. Its excellent foamability and consistency are complemented by its easy processing. This further enhances the efficiency of the closed-loop production of PP foam.
Having tested the use of CO2 as a foaming agent in the laboratory for many years, FAP was able to develop a new machine which was used on the FAP EXT 753-120 extrusion line with two screws. To foam EPP using CO2, the screws had to be designed in such a way as to maintain the necessary pressure in the gas injection zone at high temperatures. This ensured the high quality and controlled atomization of gas into melting. Further testing led to the development of suitable extrusion dies, as well as dies to control the expansion and crystallization of the polymer after leaving the extrusion head.
Closed-loop production: all material waste generated during production is immediately turned back into granules and fed back into the process, thereby reducing the use of virgin raw materials - with no compromise in mechanical performance.
“Borealis is proud to have joined with FAP to become the first to use low-cost and safe CO2 as a blowing agent in the physical foaming process to produce a low-density product with a lower carbon footprint. We see enormous market potential for HMS PP-based monomaterial foams used as composites and multilayer materials in the construction, automotive, aviation, and other vital sectors. Such endeavors are key to bringing about a circular economy of plastics and ensuring that all future foaming applications will be reusable and recyclable. In line with our EverMinds™ ambition, we are accelerating action on circularity together with our partner FAP.”
Florin Sabau
Borealis Global Commercial Director Consumer Products Rigid
“Our decades of experience in extrusion, and many years of laboratory testing in the field using CO2 as a foaming agent, have expanded our understanding of what is possible in the physical foaming of polymers. In this collaboration with our partner Borealis, we have further refined our unique counter-rotating twin-screw extrusion technology. The result is superior quality and an acceptable density of the finished foam product when made using Daploy WB140HMS and supercritical CO2.”
Francesco Poli
FAP CEO