Low-Cost Open-Source Melt Flow Index System for Distributed Recycling and Additive Manufacturing

Abstract

The increasing adoption of distributed recycling via additive manufacturing (DRAM) has facilitated the revalorization of materials derived from waste streams for additive manufacturing. Recycled materials frequently contain impurities and mixed polymers, which can degrade their properties over multiple cycles. This degradation, particularly in rheological properties, limits their applicability in 3D printing. Consequently, there is a critical need for a tool that enables the rapid assessment of the flowability of these recycled materials. This study presents the design, development, and manufacturing of an open-source melt flow index (MFI) apparatus. The open-source MFI was validated with tests on virgin polylactic acid pellets, shredded recycled poly(ethylene) terephthalate glycol flakes, and high-density polyethylene/poly(ethylene) terephthalate blends to demonstrate the range of polymer types and recyclability. The proposed MFI tool offers a user-friendly and cost-effective solution for evaluating the flow properties of materials from waste streams, thereby enhancing their viability for additive manufacturing applications.

Keywords: material extrusion; material properties; melt flow index; open hardware; polymers; recycling; rheology; thermal properties.

Figure A1

Part 1: Stand.

Figure A2

Part 2: linear support.

Figure A3

Part 3: motor mount.

Figure A4

Part 4: flange support.

Figure A5

Part 5: loadcell fit (left). Part 6: shaft loadcell coupler (right).

Figure A6

Part 7: cutter connector (left). Part 8: blade fix (right).

Figure A7

Part 9: extra frame (left). Part 10: extra frame b (right).

Figure A8

Part 11: foot support (left). Part 12: Housing (right).

Figure A9

Part 13: insulation housing (left). Part 14: cap band (right).

Figure A10

Part 15: piston guide (left). Part 16: piston tip guide (right).

Figure A11

Part 17: scale housing (left). Part 18: scale plate (right).

Figure A12

Part 19: calibration part.

Figure A13

Steps of the frame assembly: (a) Motor mount assembly; (b) linear support assembly; (c) flange assembly; (d) cutter assembly; (e) stand assembly; and (f) foot support assembly.

Figure A14

Steps of the piston assembly: piston tip assembly.

Figure A15

Steps of the piston assembly: coupler connection assembly.

Figure A16

Steps of the piston assembly: (a) linear rail assembly; (b) loadcell assembly; and (c) shaft coupler assembly.

Figure A17

Steps of the heating pipe assembly.

Figure A18

Steps of the cap assembly: (a) band heater tightening; (b) insulation cap assembly.

Figure A19

Steps of the heating pipe and cap ssembling: (a) flange assembly; (b–d) extra support assembly; (e) pipe assembly; and (f) cutting setup adjustment.

Figure A20

Steps of the scale assembly: HX711 board assembly (left); and load cell assembly (right).

Figure A21

MFI device assembly after the different parts’ assembly.

Figure A22

Operation instructions: using the serial monitor in Arduino IDE.

Figure A23

Operation instructions: setting the temperatures for the tests.

Figure A24

Operation instructions: moving the piston after the preheating procedure (left) and reaching the pressure set point to start the testing (right).

Figure 1

Overall hardware structure of the OS MFI device, highlighting the different parts of the assembly reported in the BOM (Appendix A, from top to bottom): motor mount; shaft loadcell coupler; load cell; loadcell fit; linear support; flange support; piston guide; extra frame; insulation housing; cutter-c; cap band; stand; foot support; and scale.

Figure 2

Steps of the assembly procedure followed before using the OS MFI device: (1) main frame assembly; (2) piston assembly; (3) heating pipe assembly; (4) digital scale assembly; (5) electrical wiring; and (6) first calibration.

Figure 3

Electronic schematic of the OS MFI device control board (from top left to bottom right): main control board (up left); force control system (up right); weight connection system (left); temperature control (right); low-dropout (LDO) regulator, power connector, servo connector, and connectors (bottom left).

Figure 4

Steps of the test procedure followed using the OS MFI device: (1) sample preparation; (2) calibration; (3) test parameter setting; (4) device preheating; (5) material sample load; (6) heating and piston load; (7) testing; (8) sample collection and weighing; (9) MFI calculation; and (10) device cool-down and cleaning.

Figure 5

Force control calibration: load cell calibration part to be 3D printed (left) [83] and its assembly for the calibration procedure (right).

Figure 6

Results of the MFI measurements (from left to right) obtained with the commercial equipment (left side bars, blue) and OS MFI devices (right side bars, orange): (1) virgin PLA (vPLA); (2) recycled PETG (rPETG) at 240 °C, (3) 230 °C, and (4) 220 °C; (5) rPET90/rHDPE10; and (6) and rPET90/rHDPE10/SEBS10.

Figure 7

Results of the virgin PLA measurement with the OS MFI device applied to four batches of samples (dot lines, a different batch measurement for each color) compared to rPETG measurement (straight line, green), where each batch corresponds to one measurement. Each sample, indicated by the different dots, was collected after a progressive interval of 30 s during the specific MFI measurement, which means 1 = 30 s, 10 = 5 min, and 20 = 10 min.

Figure 8

MFI values of virgin PLA changing through different pre-heating times from the tests with the OS MFI device, i.e., 8, 10, 13.5, 20, and 30 min; 8 min corresponds to the minimum preheating time, which means the complete melting of the tested material.