US Researchers Create 3D Printing Filament from Recycled Cellulose Polypropylene

In this recently published study, ‘Recycled Cellulose Polypropylene Composite Feedstocks for Material Extrusion Additive Manufacturing,’ researchers from the US explain their findings in using not only composites but those made out of recycled material. Here, the focus is on using polypropylene reinforced with cellulose waste to create 3D printing filament for material extrusion additive manufacturing (MEAM).

With cellulose being more commonly used to strengthen thermoplastics, today, such composites can be helpful in applications such as decking, paneling, furniture, household goods, and more. Not only are they plentiful, but also affordable to use—and best of all, renewable. Such materials also offer strength, low-bulk density—along with less abrasion, meaning that products last longer. To date, many studies have centered around ABS and PLA composites; in fact, some have even included using materials like ground-up macadamia shells with ABS.

For this study, materials like wastepaper, cardboard, and wood flour were used for additives, with powders melted into filament and then printed into samples for testing, considering that mechanical properties could be affected due to filler, along with wettability.

“Strong particle–matrix interfacial adhesion can improve toughness due to efficient stress transfer between phases,” stated the researchers. “On the other hand, poor wetting can lead to debonding, plastic void growth, and shear banding mechanisms, which absorb energy and can improve toughness.”

The composites were created through pulverization, minimizing particles for better results in fabricating samples. The ingredients used for the composite were rather interesting too, in the form of Wegmans and Great Value yogurt containers, along with office printer paper, corrugated cardboard, and wood flour.

“Recycled polypropylene from yogurt containers was cleaned by rinsing with water, ethanol and drying in the air at room temperature. The labels were removed before cutting into pieces that could be fed into the paper shredder (Compucessory model CCS60075). Wastepaper and cardboard were fed through an identical cross-paper shredder,” explained the researchers.

While all the samples were 3D printed as planned, the researchers pointed out that clogging was an issue for some pieces when using the typical 0.5 mm nozzle. The team theorized that cellulose was responsible for the clogging due to some particles not ground finely enough. Cardboard and paper did not always remain sufficiently mixed either. 3D printing was performed on a Lulzbot Taz 6 3D printer, with a 100 °C bed temperature and a 220 °C nozzle temperature used.

“Sections along the length of a filament spool were examined by scanning electron microscope and thermogravimetric,” concluded the researchers. “The rPP/CB composites have a greater loading of cellulose compared to the commercial PP (cPP)/CB composites, but loading does not change significantly along the ca. 30 ft. examined. Further, weight percent remaining by TGA does not show significant differences in char along each respective filament.”

While 3D printing today offers a host of different materials to choose from as a whole, many are better when reinforced, meaning that composites are becoming increasingly more popular from copper metal to continuous wire polymers or continuous carbon, and more—even to include alternatives like wood and cork.

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[Source / Images: [‘Recycled Cellulose Polypropylene Composite Feedstocks for Material Extrusion Additive Manufacturing’]