HOUSTON—Local Motors, a motor-vehicle manufacturer, and SABIC, a chemical company, have completed a joint study on the feasibility of recycling scrap thermoplastic parts and shavings from the 3D printing process rather than send them to a landfill. The study included analyzing the printability and mechanical properties of SABIC’s LNP Thermocomp AM reinforced compound, used by Local Motors, after being printed, reclaimed, ground and reprocessed into pellet form.
The study determined that material from post-production parts and scrap can potentially be reused in large format additive manufacturing (LFAM) or other processes, such as injection molding or extrusion, at amounts up to 100 percent. These insights can help identify a feasible path to circularity and an extended lifecycle for materials used by the LFAM industry.
“As adoption of LFAM accelerates, it is essential to find sustainable alternatives to landfilling large, printed parts,” says Walter Thompson, senior applications development engineer at SABIC. “Our study showed great potential for reusing these materials and marks a first step in supporting reuse within the value chain.”
“Building next-generation vehicles means embracing next-generation manufacturing processes,” says Johnny Scotello, director of technical products at Local Motors. “Bringing value to scrap or end-of-life parts is a difficult challenge, but the results of this study point to a bright future for sustainable, circular products.”
Currently, no established value chain exists for reclaiming post-production LFAM parts and scrap. This complex sequence of steps includes managing the logistics of locating, collecting and transporting large parts to a facility capable of cleaning, cutting, regrinding and repurposing the material.
Another challenge of reusing LFAM materials is potential degradation from multiple heat cycles (grinding, re-pelletizing, re-compounding, etc.). Each step adds to the cumulative heat history, which tends to break down the polymer chains and reduce fiber length and can affect performance. These factors should be considered when identifying opportunities for material reuse.
The study included evaluations for printability, throughput and mechanical properties. In order to assess printability, six material samples of LNP Thermocomp AM compound were prepared, containing 0, 15, 25, 50, 75 and 100 percent reprocessed content, respectively. These samples were monitored for changes in throughput and melt flow rate on SABIC’s Big Area Additive Manufacturing (BAAM) machine from Cincinnati Inc., located in the company’s Polymer Processing Development Center in Pittsfield, MA.
Each sample was used to print a single-wall hexagon, which is SABIC’s typical test part geometry for processing and material characterization. All the samples printed well, with a smooth, shiny surface and straight, even layers that demonstrated no issues with material flow.
For the mechanical properties evaluation, specimens were cut from each hexagonal printed part. These were tested for tensile properties using Test Method D638 as a guideline, and for flexural modulus using a three-point bend test following a modified ASTM D-790 test method. Results showed excellent tensile properties in the part samples containing smaller percentages of regrind and only incremental declines in the samples that included larger percentages of regrind.
The 100 percent regrind sample experienced just a 20 percent reduction in tensile properties in the X direction and a 15 percent reduction in the Z direction. For flexural properties, the same gradual trend occurred, with flexural modulus declining by just 14 percent in the X direction and 12 percent in the Z direction for the sample containing 100 percent regrind.
As expected, tensile and flexural testing showed decreasing mechanical strength as the percentage of regrind increased. This finding is typical of regrind used in other processes such as injection molding and extrusion.