Additive manufacturing of CNTs/PLA composites and the correlation between microstructure and functional properties

doi:10.1016/j.jmst.2020.04.038

Abstract

Abstract:

Owing to the facile, low cost, rapid, personalization characters, 3D printing method has been one of the most attractive additive manufacturing processes in medicine, airplane, packaging and printing areas. In this work, a series of carbon nanotubes/polylactic acid (CNTs/PLA) composites were prepared through the combination of molten co-extrusion and 3D printing processes. The orientation and dispersion of CNTs in PLA matrix were investigated to explore the impact of 3D printing process on the morphology of CNTs/PLA composites via transmission electron microscopy, field emission scanning electron microscopy and Raman spectroscopy. X-ray diffractometer, differential scanning calorimetry, and thermal gravity analysis were employed to study the crystal structure and thermal properties of the composites. In addition, the electrical conductivity of the prepared specimen revealed that the orientation of CNTs in PLA might enhance the conductivity of the composite. It was found that 3D printing process was beneficial to increasing the purity of CNTs, electrical conductivity and mechanical properties of CNTs/PLA composites.

Key words: Carbon nanotubes, Microstructure, Polymer nanocomposites, Thermal stability

Xing Zhou, Jingrui Deng, Changqing Fang, Wanqing Lei, Yonghua Song, Zisen Zhang, Zhigang Huang, Yan Li. Additive manufacturing of CNTs/PLA composites and the correlation between microstructure and functional properties[J]. J. Mater. Sci. Technol., 2021, 60: 27-34.

Figures/Tables 12

Fig. 1. Scheme of 3D printing process with the prepared printing filament.

Table 1 Information of the samples and 3D printing parameters.

Sample	CNTs/PLA ratio (wt%)	Melt index (g/10 min)	Fixed parameters
			Build orientation (deg.)	Filament diameter (mm)	Envelop temperature (°C)	Filling rate (%)	Contours number
PLA	/	～32.4	0	1.75	50	100	5
CNTs/PLA-1	1%	～22.5
CNTs/PLA-2	1%	～22.3
CNTs/PLA-3	3%	～12.7

Fig. 2. SEM micro morphology of PLA and CNTs/PLA composites before and after 3D printing. (a) the pure PLA. (b), (c) CNTs/PLA-1 with CNTs loading of 1 wt% in composite after the extrusion process, the inset image shows individual nanotube dispersed in PLA matrix. (d), (e) CNTs/PLA-1 with CNTs loading of 1 wt% in composite after 3D printing, the inset image shows individual nanotube dispersed in PLA matrix. (f) The digital photo of the 3D printed matter for sample CNTs/PLA-3. (g)-(i) CNTs/PLA-3with CNTs loading of 1 wt% in composite after 3D printing, the inset image in (i) shows the high resolution microstructure and printing layer clearly.

Fig. 3. TEM photos for sample CNTs/PLA-3. (a), (b) The microstructures of the composite and CNTs dispersion in PLA matrix. (c), (d) The high-resolution TEM images showing the lattice of CNTs.

Fig. 4. Raman spectra of pure PLA and CNTs/PLA composites before and after 3D printing.

Fig. 5. XRD spectra of pure PLA and CNTs/PLA composites before and after 3D printing.

Fig. 6. DSC curves of pure PLA and CNTs/PLA composites before and after 3D printing.

Table 2 Summary of DSC heating curves of PLA and CNTs/PLA composites before and after 3D printing.

Samples	Heating process
	^aT_g (°C)					^bT_c (°C)		^cΔH_c (J/g)	T_m (°C)	^dΔH_m (J/g)	X_c (%)
	T₁	T₂	T₃	T₄	ΔC_p (J g^-1 K^-1)	T_c1	T_c2
PLA	67.5	69.1	70.7	70.9	0.308	/	/	/	171.5	34.4	/
CNTs/PLA-1	58.8	59.7	60.4	60.5	0.912	89.8	119.2	40.79	171.0	38.27	2.7
CNTs/PLA-2	55.7	58.1	58.4	60.2	0.572	107.4	126.7	23.31	144.3	21.8	1.6
CNTs/PLA-3	56.7	59.7	60.0	62.0	0.564	101.9	115.3	37.68	159.9	34.35	3.7

Table 3 Main decomposition and residual weight of the prepared samples.

Sample	T¹_onset (°C)	T²_end (°C)	Residual weight (wt%)
PLA	285	374	0
CNTs/PLA-1	284	372	1.3
CNTs/PLA-2	262	371	1
CNTs/PLA-3	255	370	2

Fig. 7. TGA thermograms of the of pure PLA and CNTs/PLA composites before and after 3D printing. (a) TG curves; (b) DTG curves.

Fig. 8. Surface resistivity of the prepared CNTs/PLA composites before and after printed. The inset photos show the resistance of the 3D printed matter and human body detected by avometer.

Fig. 9. The mechanical properties of PLA and CNTs/PLA composites: (a) tensile strength, (b) surface roughness.

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