Thermal Properties of Composite Filaments for 3D Printers

Significance of the Topic

3D printing is rapidly expanding across industrial and hobbyist applications, relying on thermoplastic filaments that melt and solidify during fused deposition modeling. Understanding the thermal behavior of composite filaments is essential to optimize printing parameters, ensure dimensional accuracy, and achieve desired mechanical properties. Differential scanning calorimetry (DSC) provides critical insights into melting transitions, crystallinity, and glass transitions of these materials.

Objectives and Study Overview

This study evaluated the thermal properties of various composite filaments for 3D printers, including Nylon 6 and PEEK matrices reinforced with carbon or glass fibers in short or continuous forms. The primary goals were to demonstrate how DSC can guide filament selection and printing conditions, and to reveal differences in thermal behavior even among filaments based on the same resin.

Methodology and Used Instrumentation

Samples were prepared by cutting short fiber composites into round slices and trimming continuous fibers to 3 mm segments. Approximately 10 mg of each sample was analyzed under a nitrogen atmosphere. Key measurement parameters:

• Instrument: Shimadzu DSC-60 Plus differential scanning calorimeter
• Heating rate: 10 °C/min
• Temperature range: 0–245 °C for Nylon 6; 30–400 °C for PEEK
• Sample weight: ~10 mg

Complementary thermogravimetric analysis (TGA) was performed using a Shimadzu DTG-60 analyzer to assess moisture content and weight loss up to 200 °C.

Main Results and Discussion

Nylon 6 composites exhibited distinct melting endotherms around 200–220 °C for crystalline samples, while one amorphous sample showed a glass transition near 66 °C without a clear melt peak. All samples displayed a broad endothermic change from room temperature to 200 °C, attributed to adsorbed moisture. TGA confirmed approximately 2 % weight loss by 200 °C. DSC measurements after drying at 80 °C for 0, 1.5, and 18 h demonstrated that increased water content lowers the glass transition from 108.7 °C (dried) to 65.8 °C (undried), highlighting the need for proper filament pretreatment.

PEEK composites showed glass transitions at 143.1 °C and 146.8 °C, melting peaks at 340.2 °C and 336.6 °C, and an exothermic crystallization event at 189.5 °C for one sample. A second DSC run assessed post-molding crystallinity by comparing heats of fusion, revealing higher crystallinity in the sample with a greater fusion enthalpy (–46.8 J/g) versus –36.6 J/g.

Benefits and Practical Applications

DSC analysis enables:

• Accurate determination of melting and glass transition temperatures for setting printer nozzle and bed temperatures
• Assessment of filament drying protocols to control formability and prevent defects
• Evaluation of crystallinity to predict mechanical strength and dimensional stability of printed parts

Future Trends and Potential Applications

Advanced thermal analysis will integrate with real-time monitoring and predictive AI models to tailor filament compositions and printing parameters. New composite formulations, including hybrid fiber reinforcements and nano-additives, will require detailed DSC/TGA profiling to optimize performance. Online DSC modules may be developed for in situ quality control during filament extrusion.

Conclusion

The DSC-60 Plus effectively distinguished thermal transitions and crystallinity variations among composite 3D printer filaments. Even materials based on the same resin exhibited significant differences in melting points, glass transitions, and fusion enthalpies. Such thermal insights are vital for optimizing filament pretreatment, printer settings, and achieving reliable mechanical properties in printed products.

Reference

1. N. Jia and H. A. Fraenkel, Journal of Reinforced Plastics and Composites, 23(7), 729 (2004).