Graphene/Carbon Nanotube Hybrid Nanocomposites: Effect of Compression Molding and Fused Filament Fabrication on Properties

Round 1

Reviewer 1 Report

This is a nice contribution to the literature on 3D printing of electrically conductive polymer-based filaments. The manuscript is well organized and clearly presented and a comparison of the results obtained with those reported in the literature was included. However, the study is limited to a fixed percentage of fillers, hence the general value of the conclusions is not obvious

The English language is adequate, but a global revision is required as a few errors and typos exist (for exemple, lines 17, 21, 58, 62, 89, 98, 151…)

Section 2.2.4 – please provide more information on the 3D printing conditions

Line 236- “It can be therefore inferred that, during extrusion and FFF process, the graphene nanoplatelets are forced to align along the layer plane” – the sentence is not clear. Do you mean the 3D printed layers?

Figure 3 - why is the comparison made using micrographs with different magnifications?

Author Response

Reply of Authors to Reviewer 1

This is a nice contribution to the literature on 3D printing of electrically conductive polymer-based filaments. The manuscript is well organized and clearly presented and a comparison of the results obtained with those reported in the literature was included. However, the study is limited to a fixed percentage of fillers, hence the general value of the conclusions is not obvious

- Abstract and Conclusions have been modified as follow

Line 24-26:

the hybrid composition of 50:50 of GNP:CNT was selected as the most suitable for the filament production suitable for the FFF process of 6 wt.% carbonaceous nanocomposites.

Lines 460-462-:

GNP:CNT hybrid composition of 6 wt.% carbonaceous nanocomposites showed a good compromise between processability and enhancement of properties

1.1 The English language is adequate, but a global revision is required as a few errors and typos exist (for example, lines 17, 21, 58, 62, 89, 98, 151…)

 

The authors acknowledge Reviewer 1 for the initial list of errors/typos. The number of Line changed.

- Line 17: were produced by melt compounding

- Line 21: a a positive

- Line 58 (59): lays downs or adds successive layers

- Line 62(63): relatively low amount of productions à relatively low-volume productions

- Line 89: no research has not been reported yet

- Line 98 (97-98): The incorporation of CNT provided not only a high increase of the electrical conductivity, but also a severe increase of the viscosity

- Line 150-151 ( ): Filaments of neat ABS, and GNP:CNT (100:0), GNP:CNT (50:50) and GNP:CNT (0:100) nanocomposites at 6wt.% of nanofiller

- Line 153: 3D-printed specimens were manufactured by a prototype 3D printer for high-temperature

- Line 233-234: SEM figures of compression moulded plates, see Figure 3(a1-a3), evidence a poor adhesion level between graphene and ABS.

- Line 241: oriented mostly perpendicular to the fracture plane, and therefore most likely oriented

- Line 258: GNP:CNT (50:50) specimen reveal the highest strain at break in comparison with the other nanocomposites.

- Line 261-262: our results suggest no evident synergistic effects on tensile modulus and strength, probably due to the higher concentration of nanofiller

- Line 269-281: modulus of hybrid nanocomposites of HC and H45 samples is further increased in comparison with the pure CNT nanocomposites; on the other hand, strength and strain at break of this material (50:50) are slightly reduced

- Line 284-285: Moreover,  it should be noted the more brittle behavior of all the PC samples, almost independently on the GNP:CNT composition, due to 1.2 Section 2.2.4 – please provide more information on the 3D printing conditions

- Line 300: Following the volume electrical measurements, the results of bulk resistivity

 

1.2 Section 2.2.4 – please provide more information on the 3D printing conditions

 

The text has been modified as follows.

 

“…as detailed in our previous publication [39]. In summary, all the specimens were 3D-printed following these printing parameters: object infill 100%; no raft; nozzle diameter 0.40 mm; bed temperature 110 °C; layer height 0.20 mm; raster angle [0°/0°] for HC and PC, and raster angle [+45°/-45°] for H45; infill speed 40 mm/s for HC and H45 and 16 mm/s for PC specimens. The 3D-printed parts were manufactured at a nozzle temperature of 280 °C for CNT nanocomposite, and 250 °C for ABS matrix, GNP and hybrid GNP:CNT nanocomposites.

 

1.3 Line 236- “It can be therefore inferred that, during extrusion and FFF process, the graphene nanoplatelets are forced to align along the layer plane” – the sentence is not clear. Do you mean the 3D printed layers?

The text has been modified as in the following (new Lines 242-246)

oriented mostly perpendicular to the fracture plane, and therefore most likely oriented along the loading direction of dumbbell specimens. It can be therefore inferred that, during extrusion the graphene nanoplatelets are forced to align along the extrusion direction of the filament, and during the following FFF process this orientation is then maintained in each single microfilament during the layer deposition.

 

Thanks to the Reviewer observation, these notes appear more interesting in view of the full process description/interpretation (filament production and FFF printing).

 

 

1.4 Figure 3 - why is the comparison made using micrographs with different magnifications?

The comparison of different magnifications was made in order to optimize the vision of the peculiar microstructure of different samples. In particular, in the low magnification images, we can observe the microvoids derived from extrusion and 3D printing (Figure 3b1-c1). In order to evaluate the morphology of nanofillers, medium magnification SEM images show mainly the micro size of graphene only (Figure 3a2-b2-c2), but not carbon nanotubes. And the reader can see the dispersion of carbon nanotubes at the highest magnification images (Figure 3a3-c3).

Hence, due to the different level of nanofiller size and defects, the magnifications have been properly adapted for each sample.

And following the Reviewer observation Figure 3b1 has been changed for a better vision of the filament fracture surface.

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript deals with the manufacturing of graphene-CNT- reinforced ABS composites and the effects of compression moulding and fused filament fabrication. The manuscript is interesting, systematic and scientifically sound. A minor revision is necessary based on the following comments.

Provide stress-strain plots. It is important to showcase the behaviour of the composites under stress. Is electrical conductivity is at the surface of the samples or through-thickness? If authors are referring to surface resistivity, they are asked to add some comments on through-thickness resistivity. Based on the nature of the work, I would suggest author revise the main title. The current one does not really reference the theme. May be specify something like ‘effects of compression moulding and FFF process on their mechanical and electrical properties”. Add some basic quality assessment data of GNP and CNT, such as Raman spectra and XRD. If possible, add the SEM of the both. Formatting errors: Wt% should be wt.% There are some typos here and there. Some occasional grammatical errors found. Particularly, tenses change abruptly. Please check them.

Author Response

Submission polymers-657022

Reply of Authors to Reviewer 2

The manuscript deals with the manufacturing of graphene-CNT- reinforced ABS composites and the effects of compression moulding and fused filament fabrication. The manuscript is interesting, systematic and scientifically sound. A minor revision is necessary based on the following comments.

 

2.1Provide stress-strain plots. It is important to showcase the behaviour of the composites under stress.

Representative stress-strain curves of all the samples have been added in Supplementary Materials, with the following Caption. Moreover, in the revised text Figure S1a and Figure S1b-e are properly mentioned in the caption of Figure 4 and Figure 5. At the end of the attached/uploaded document all the new Figures are also reported.

Figure S1. The stress-strain curves of neat ABS, and GNP:CNT (100:0), GNP:CNT (50:50), GNP:CNT (0:100) nanocomposites: (a) compression moulded samples, (b) filaments, (c) HC, (d) H45 and (e) PC.

 

2.2 Is electrical conductivity is at the surface of the samples or through-thickness? If authors are referring to surface resistivity, they are asked to add some comments on through-thickness resistivity.

At the end of paragraph 2.3.4 the following text has been added.

“All reported electrical conductivity and resistivity are volume electrical conductivity and volume resistivity, taking into account the thickness of samples.”

2.3 Based on the nature of the work, I would suggest author revise the main title. The current one does not really reference the theme. May be specify something like ‘effects of compression moulding and FFF process on their mechanical and electrical properties”.

The title has been modified

“Graphene/Carbon Nanotubes Hybrid Nanocomposites: Effect of Compression Molding and Fused Filament Fabrication on Properties”

 

2.4 Add some basic quality assessment data of GNP and CNT, such as Raman spectra and XRD. If possible, add the SEM of the both.

In paragraph 2.1 the following text has been added with also two new references.

“The basic quality assessment data of nanofillers are available in the technical data sheet of GNP [42] and CNT [43], respectively, and in some literature publications. In particular, Raman spectra and XRD characterization have been reported for GNP [42,45] and for CNT [46]. TEM images of both GNP and CNT, have been also illustrated in our previous publication [40]. Moreover, TEM micrographs of MWCNT-NC7000 in ABS nanocomposite evidenced a certain level of orientation in filaments [47].”

 [45] Shokrieh et al. Effect of graphene nanosheets (gns) and graphite nanoplatelets (gnp) on the mechanical properties of epoxy nanocomposites. Science of Advanced Materials 2013, 5, 260-266.

[47] Dul, S.; Pegoretti, A.; Fambri, L. Fused filament fabrication of piezoresistive carbon nanotubes nanocomposites for strain monitoring. Frontiers in Materials. Polymeric and Composite Materials 2019, Submitted/in press.

 

2.5 Formatting errors: Wt% should be wt.%

All the formatting corrections have been done (wt.%). Some have been evidenced in RED color.

2.6 There are some typos here and there. Some occasional grammatical errors found. Particularly, tenses change abruptly. Please check them

Many typos and sentences have been modified (and evidenced in RED). Particular attention has been spent for the tenses in the paragraph “Results and Discussion” (simple present and past perfect).

 

Author Response File: Author Response.docx