New study on recycling of scrap thermoplastic

Circular economy

United StatesSABIC and Local Motor have completed a combined feasibility study on the recycling of scrap thermoplastic components and shavings from the 3D printing process.

In preparation for the widespread deployment of big format additive manufacturing, the study investigated more sustainable options to landfilling massive, printed items (LFAM). It entailed testing the printability and mechanical properties of SABIC’s LNP THERMOCOMP AM reinforced material, which was used by Local Motors, after they were printed, reclaimed, ground, and reprocessed into pellet form.

According to the study, material from post-production parts and scrap can be reused up to 100 percent in LFAM or other processes such as injection molding or extrusion. These findings can help identify a possible path to circularity and a longer lifecycle for materials used in the LFAM industry.

Challenges of reusing LFAM materials

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.

Results of the study

The SABIC-Local Motors 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, Mass.

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.

To measure the mechanical properties, each hexagonal printed part was used. These parameters were measured with a tensile force using Test Method D638 as a reference, and with a flexural modulus using a three-point bend test. The tensile qualities of the samples with different percentages of regrind were tested, and the results revealed good to great results for all of them. The 100% regrind sample saw a 20% loss in tensile characteristics in the X direction and a 15% reduction in the Z direction. The flexural modulus decreased by just 14% in the X direction and 12% in the Z direction for the sample containing 100% 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.

Looking forward

Post-industrial LFAM shavings and pieces are useful again. Recycled materials hold a lot of potential, but existing holes in the recycling value chain need to be filled before this process becomes sustainable. As a result of the LFAM community’s collaborative effort, including resin makers, converters, 3D printers, and recyclers, an economical process for collecting scrap must be developed.

Conducting this study with Local Motors and presenting these results are SABIC’s first steps in finding a circular solution for the LFAM industry. The company will soon complete a report containing detailed data from the study.