This PDF file includes:

• CNT/PLA hot-pressed films and electrical characterization
  
• Microwave heating thermometry for hot-pressed films
  
• COMSOL
  
• Heating response as a function of thickness
  
• Microwave bonding of thermoplastic interfaces
  
• Filament coating method
  
• Heating response of coated filaments
  
• 3D printing ASTM D1938 tear test coupons
  
• Microwave exposure of tensile coupons
  
• Mode III fracture strength (trouser tear) testing method
  
• Mode III fracture strength (trouser tear) testing results
  
• table S1. DC conductivity measurement details.
  
• table S2. Material properties used in COMSOL calculations.
  
• table S3. Material properties of PLA filament.
  
• fig. S1. Dielectric measurements using a sample holder placed between two coaxial transmission lines.
  
• fig. S2. AC dielectric properties including the real part of the relative permittivity, the loss tangent, and AC conductivity.
  
• fig. S3. FLIR thermal image screenshots of hot-pressed PLA films after 30 s of heating at 15 W.
  
• fig. S4. Max temperature versus time for various wt % of CNTs in waveguide, 15-W microwave power.
  
• fig. S5. Geometry used in COMSOL simulations.
  
• fig. S6. Differential scanning calorimetry data for PLA.
  
• fig. S7. COMSOL simulation predictions for temperature (average) versus time for all samples.
  
• fig. S8. Setup for spray coating PLA films outlined in the “COMSOL” section.
  
• fig. S9. The microwave response of 10 wt % MWCNT spray-coated PLA films (as quantified by the mean temperature of the film at 30 s) versus film thickness.
  
• fig. S10. Stress versus strain for lap-shear samples.
  
• fig. S11. Coating bath internal view.
  
• fig. S12. Microscope image of the 1.75-mm printer filament with CNT coating.
  
• fig. S13. Microscope image of the coated filament after being extruded from a 0.5-mm nozzle.
  
• fig. S14. Schematic for calculation of coating thickness.
  
• fig. S15. Coated PLA filament array glued to polymer film.
  
• fig. S16. FLIR image of coated filament bundle heating in waveguide and corresponding COMSOL simulation of filament bundle heating in a waveguide.
  
• fig. S17. Stacker 500 desktop 3D printer.
  
• fig. S18. Stacker printer nozzle showing heat sink.
  
• fig. S19. Slicing pattern and G-code preview of the rectangular tear specimens.
  
• fig. S20. FLIR camera positioned over the waveguide to directly measure sample temperature during exposure to microwaves.
  
• fig. S21. Microwave choke tube designed to attenuate and contain microwave energy yet still allow for direct viewing of sample.
  
• fig. S22. Maximum temperature versus time for all five LIRF samples.
  
• fig. S23. Instron 5944 load frame used for tensile and tear tests.
  
• fig. S24. Close-up view of sample gripped in the tensile load frame.
  
• fig. S25. Optical microscope image of a tear test sample viewed edge-on to determine the mean weld line thickness.
  
• fig. S26. Tear test fracture strength versus extension results for bulk PLA film.
  
• fig. S27. Tear test fracture strength versus extension results for neat printed PLA.
  
• fig. S28. Tear test fracture strength versus extension results for CNT-coated printed PLA.
  
• fig. S29. Tear test fracture strength versus extension results for CNT-coated, LIRF-welded printed PLA samples.
  
• fig. S30. Tear test fracture strength results for each sample type.
  
• fig. S31. Tear test fracture strength versus extension results for nozzle temperature sweep.
  
• fig. S32. Optical microscope image of tear test fracture surface for bulk hot-pressed PLA sample (necking and crazing are clearly visible).
  
• fig. S33. Optical microscope image of tear test fracture surface for neat 3D-printed PLA control sample (necking and crazing are absent; instead, a clean fracture surface is observed).
  
• fig. S34. Optical microscope image of tear test fracture surface for LIRF-welded sample (necking and crazing are clearly visible).
  
• fig. S35. Optical microscope image of tear test fracture surface for LIRF-welded sample (necking and crazing are clearly visible).
  
• fig. S36. SEM image of tear test fracture surface for neat PLA 3D-printed tear samples.
  
• fig. S37. SEM image of tear test fracture surface for neat PLA 3D-printed tear samples.
  
• fig. S38. SEM image of tear test fracture surface for neat PLA 3D-printed tear samples.
  
• fig. S39. SEM image of tear test fracture surface for neat PLA 3D-printed tear samples.
  
• fig. S40. SEM image of tear test fracture surface for LIRF-welded, 3D-printed PLA tear test samples (necking and crazing are clearly visible).
  
• fig. S41. SEM image of tear test fracture surface for LIRF-welded, 3D-printed PLA tear tests.
  
• fig. S42. SEM image of tear test fracture surface for LIRF-welded, 3D-printed PLA tear test samples (necking and crazing are clearly visible).

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