New Spanish Project to Create Recycled Polypropylene Powder for 3D Printing

The Spain-based Andaltec Technological Centre is working on what it calls the RECYPPOWDER project, aiming to transform polypropylene (PP) into a powder bed fusion (PBF) material. Collaborating with partners Innomaq 21 and the University of Barcelona, the center, which boasts 156 employees and generates €6 million in revenue, seeks to create a circular product using the widely popular PP material. While there are some TPU and TPE powders available for PBF, and HP has introduced a PP material, this initiative would mark the first recycled PP material designed specifically for this PBF 3D printing. The company is targeting functional prototypes with this new material.

PP is known for its immense versatility, capable of being both soft and hard, and it is a very durable material that offers comfort. While its flame resistance is poor, it can withstand a wide range of chemicals and harsh conditions well. Generally, its UV resistance is not great, but it can handle service temperatures of around 110°C. PP is noted for its good impact resistance and toughness. It can serve as an alternative to TPU and TPEs and is generally lighter than TPUs. With a melting point of around 160°C and processing temperatures around 200°C, PP is well-suited for processing with powder bed fusion techniques.

The trio aims to explore different PP copolymers and work on defining the optimal particle sizes to enhance the material’s properties. They also plan to blend a proportion of virgin material with recycled powder to create an effective working mix. Typically, in PP applications, the mix comprises about half virgin and half recycled material. The implications for the leftover powder and its recycling rate within the machine itself remain uncertain at this stage. Generally, in PBF processes, unsintered powder remains after supporting the parts during their construction. This leftover powder cake is then sieved and recycled. Approximately half of this material is eventually discarded, but the specific proportion and the frequency of its reuse depend on the material, additives, machine settings, and usage. Powders with exceptionally high recyclability rates on the machine lead to favorable economics and a more environmentally friendly outcome.

PP is a widely used commodity or bulk plastic, with its cost ranging from as low as $0.10 to around $3 per kilo, significantly lower than the $4 to $6 per kilo typically seen for ABS and PLA. Estimates indicate that PP usage amounts to around 79 million metric tonnes per year, which is four times more than the volume of ABS and 40 times the volume of PLA. Given the vast volume of plastics in circulation, there is a compelling argument for minimizing the use of virgin materials in 3D printing. Certainly, virgin materials may offer advantages for medical devices and components under significant strain, but for many prototypes and a considerable number of end-use parts, the use of new material offers little value. The relatively small volumes required for 3D printing could easily be met by diverting some waste material for use in this technology for most applications. The absence of a $5 per kilo 3D printing material that could challenge existing niche and more expensive products remains a notable gap in the market.

I believe this product could find significant volumes in areas such as shoes, end-use cushioning parts, sports handles, and similar items. The high adoption of Arkema’s castor bean-derived PA 11 materials, which offer good properties coupled with a positive environmental message, is noteworthy. Similarly, Evonik has developed a PA 11 material from reused cooking oil. A recycled PP could convey a strong message to consumers, potentially serving as a persuasive tool for designers and firms aiming to encourage the use of recycled materials over new raw counterparts. Over recent years, brands have been keen to highlight their recycling credentials, and if this material performs well, it could become a successful choice for branded end-use parts made with 3D printing.

Creating powder bed materials, particularly achieving the correct morphology, grind, and additives, can be an expensive and tedious process. Although Andaltec has previous 3D printing expertise, demonstrated through a composites project in 2020 and another project on shape memory polymers, producing powders for 3D printing presents a unique challenge. While the company possesses extensive rheology knowledge and facilities such as dual and single screw extrusion lines for mixing compounds and creating master batches, it remains to be seen whether it can successfully produce the powder. However, let’s remain optimistic, as a relatively affordable 50% recycled PP powder could potentially lead to the development of very exciting 3D printed products.