Université de Lorraine team advances post-consumer mixed plastic direct processing for 3D printing
Group worked with compatibilizers to investigate possibilities around a process that would help significantly increase the amount of recyclable plastic that could be used in additive manufacturing
A team of researchers at the Université de Lorraine in Nancy, France, has conducted research that contributes to the development of sorting-free recycling strategies.
Working to advance the evolution of Distributed Recycling Additive Manufacturing (DRAM) as a pathway toward more localized, circular production systems, the group compared conventional processing with fused granular fabrication (FGF) using recycled PET and HDPE water bottles.
The team tested three styrene-based compatibilizers for recycling mixed post-consumer plastics, using large-format 3D printing, and published its results in Materials Today Sustainability.
By blending recycled polyethylene terephthalate (rPET) and recycled high-density polyethylene (rHDPE) at a 90/10 weight ratio, sourced from water bottles, the team set out to determine whether direct 3D printing could match conventional extrusion-injection molding methods.
The study tested two non-reactive compatibilizers, G1650 and G1652, plus one maleated SEBS called cirKular+ C1010, all added at 10% by weight. Lead researcher Cécile Nouvel from Université de Lorraine’s CNRS laboratory stated that the work addressed “the high costs and inherent inefficiencies of conventional processes” by bypassing sorting requirements in plastic recycling.
Samples processed through conventional twin-screw extrusion and injection molding exhibited tensile strength approximately 50% higher and impact strength 34% higher, in comparison to samples produced via FGF 3D printing.
The conventional method produced fully dense parts, while 3D printed samples contained voids due to layer-by-layer deposition. However, 3D printed samples showed less thermal degradation and more organized crystalline structures at elevated temperatures.
The addition of compatibilizers enhanced elongation at break by approximately 40% in conventionally processed samples. The G1652 compatibilizer reduced melt flow index by 10%, while G1650 reduced it by 47%, indicating increased viscosity. The reactive compatibilizer C1010 slightly increased melt flow index by 6%.
The 3D printing process used a modified Gigabot XL printer with a single-screw extrusion system and 2.2-minute residence time. Researchers noted that “a single mixing point often results in non-uniform shear distribution, which can hinder the effective breakdown of polymer domains”. The team concluded that future work should incorporate twin-screw or planetary roller extruder systems into 3D printers to improve blend homogenization.
The research involved collaboration with the Université de Lorraine’s ERPI and LRGP laboratories and Western University’s (Canada) Department of Electrical and Computer Engineering.
