Mechanical and Shape Memory Properties of 3D-Printed Cellulose Nanocrystal (CNC)-Reinforced Polylactic Acid Bionanocomposites for Potential 4D Applications

Round 1

Reviewer 1 Report

In the manuscript, 3D printing of CNC reinforced PLA composites was performed for potential 4D applications. The present work is meaningful and interesting. However, the following questions should be considered before acceptance for publication.

1) The information in the introduction is poor, a comprehensive and systemative description on this research background should be presented. Also, the novelty should be emphasized. Please rewrite the introduction.

2) The properties of 3D-printed specimens should be compared to others by using a table.

3) Could 3D-printed PLA/CNCs bionanocomposite be tightly attached to nylon fabrics?

4) It is recommended that the authors can cite some related articles, such as ACS Appl. Mater. Interfaces 14 (2022) 7283; Small 17 (2021) 2101093; Chem. Eng. J. 423 (2021) 130304)

Author Response

• The information in the introduction is poor, a comprehensive and systemative description on this research background should be presented. Also, the novelty should be emphasized. Please rewrite the introduction.

As suggested by the reviewer, the background and novelty of this manuscript has reworked. Please see page 2 lines  53-58, 71-73 and 83-113…. In revised manuscript.

• The properties of 3D-printed specimens should be compared to others by using a table.

The authors have used a combination of tables, bar charts and figures to compare the properties based-on best practices (see Tables 2, 3 and 4) Pages 8, 10, and 12

• Could 3D-printed PLA/CNCs bionanocomposite be tightly attached to nylon fabrics?

Yes, a close visual and haptic inspection revealed excellent adhesion between the PLA/CNC bionanocomposite and the nylon spandex fabric. This indicates good compatibility between the two materials. The adhesion was further tested by subjecting the prototype (P2) material to stretching and bending deformations as shown in Figure 14a - d. See page 17 line 480 - 483.

• It is recommended that the authors can cite some related articles, such as ACS Appl. Mater. Interfaces 14 (2022) 7283; Small 17 (2021) 2101093; Chem. Eng. J. 423 (2021) 130304)

The references have been included in the revised manuscript – Page 2 lines 83 - 86

Reviewer 2 Report

In this article, Agbakoba et al. have reported the use of Cellulose Nanocrystal (CNC) as a reinforcing element of polylactic acid (PLA) for 3D printing shape memory applications. The authors have well-structured their manuscript and the results were discussed. The reviewer has some comments that should be considered as follows.

1. Under 2. Materials and Methods: It is nowhere said, what is the content of  plasticizer/chain extender in the composite.
2. Is there any reason why the authors stored the specimens at 45°C prior to DMA measurement and tensile testing (in sector 2.3 and 2.4)? Were the tensile testings done at 45°C as well?
3. Typo on line 305: "is" instead of "it"
4. Table 4: The Deviation for Tensile modulus and for Elongation at break of the sample PLACNC0.1% is really high compared to the others. What could be the reason for this? Could this be because of a not well dispersion of CNC in the PLA matrix?
5. Figure 10: Please re-check the caption of the figure. Which picture is showing which composition? What is shown in (d)? For comparison, it would be good to include a SEM-image of PLASCE in the figure as well. 
6. Line 425: the authors state, that bed temperature is 0°C, is this a mistake?

After the rework on these points, the reviewer believes that the manuscript can be published in Sustainability.

Author Response

• Under 2. Materials and Methods: It is nowhere said, what is the content of plasticizer/chain extender in the composite.

The actual loading of the additives has not been disclosed as it is part of a separate work submitted for patent review.

• Is there any reason why the authors stored the specimens at 45°C prior to DMA measurement and tensile testing (in sector 2.3 and 2.4)? Were the tensile testing done at 45°C as well?

Tensile analysis was performed at room temperatures, the sample conditioning was performed to mitigate moisture absorption and potential lubrication effects caused by the presence of moisture. This has been added in the revised manuscript – Page 5 Lines 181 - 183

• Typo on line 305: "is" instead of "it"

Correction has been effected.

• Table 4: The Deviation for Tensile modulus and for Elongation at break of the sample PLACNC0.1% is really high compared to the others. What could be the reason for this? Could this be because of a not well dispersion of CNC in the PLA matrix?

The porous microstructure negatively affected the mechanical properties of the 3D printed specimen. The porous microstructure also explains the large deviation recorded in the tensile modulus (E) and elongation at break (ε_b) of the specimen containing 0.1% CNCs

This observation and commentary were highlighted in section 3.6, page 13 and lines 407 – 410 (see revised manuscript)

• Figure 10: Please re-check the caption of the figure. Which picture is showing which composition? What is shown in (d)? For comparison, it would be good to include a SEM-image of PLASCE in the figure as well.

As suggested by the reviewer, the figure captions have been edited. Unfortunately, the SEM of samples containing CNC were only performed and hence we do not have SEM of PLASCE.

• Line 425: the authors state, that bed temperature is 0°C, is this a mistake?

Yes, that was a mistake, it has been corrected to reflect the temperature used (50°C).

Reviewer 3 Report

Line 92: Actual type and amount of 'green solvents' (polyethylege glycol, triacetin, and chain extender) should be described in detail.

It is also supposed that, during the filament formation, water is included in the polymer. The included water may also affect the processability during 3D printing and crystallinity and deformability of the processed biocomposite. Do the authors have any information about the amount of included water in the processed biocomposite?

Author Response

• Line 92: Actual type and amount of 'green solvents' (polyethylege glycol, triacetin, and chain extender) should be described in detail.

Information on the type and quantity of green solvents have been incorporated in the revised manuscript;  Lines 126 and 127 in the corrected manuscript. The optimized amounts of polyethylene glycol, triacetin and chain extender has not been disclosed as it is part of a separate work submitted for patent review.

• It is also supposed that, during the filament formation, water is included in the polymer. The included water may also affect the processability during 3D printing and crystallinity and deformability of the processed biocomposite. Do the authors have any information about the amount of included water in the processed biocomposite?

Water was not included in this study, the moisture in the cellulose nanocrystals (CNC) was removed via sublimation during freeze-drying. So, water was not added, instead the CNC was dispersed in polar protic and aprotic solvents (ethanol, acetone, and ethyl acetate). Meanwhile, the PLA biopolymer was dried for about 12hours prior to processing.

Reviewer 4 Report

The manuscript entitled, ‘Mechanical and shape memory properties of 3D printed cellulose nanocrystals (CNC) reinforced polylactic acid bionanocomposites for potential 4D applications’ reported preparation of polymer composites via 4D printing and its applications. I am mentioning some loopholes of this work which should be accounted before publication;

1.      What is the main objective of the work is not clarified. It will be better if the author put more emphasis on the novelty section.

2.      Why PLA has been chosen? Is it true for other polyesters or similar kind of thermoplastics? Please argue.

3.      As CNCs were loaded, how did the author ensure their compatibility with the polymer phase?

4.      How the filler affected the damping quality of the reinforced composites?

5.      Some articles related to such composites could be referred for better literature review: Ganguly, S., & Das, P. (2022). Synthesis and Production of Polylactic Acid (PLA). In Polylactic Acid-Based Nanocellulose and Cellulose Composites (pp. 29-50). CRC Press.; https://doi.org/10.1016/j.jclepro.2022.130749; https://doi.org/10.1016/j.progpolymsci.2022.101574; https://doi.org/10.1016/j.susoc.2021.09.004.  

Author Response

• What is the main objective of the work is not clarified. It will be better if the author put more emphasis on the novelty section.

Most of the studies in literature on shape memory applications focus on PLA alone or PLA reinforced with HA (see lines 70-80). There are few studies on the use of PLA-CNC system for shape memory applications. This has been included in the revised manuscript – see Page 2, lines 89 - 113

• Why PLA has been chosen? Is it true for other polyesters or similar kind of thermoplastics? Please argue.

Polylactic acid (PLA) was chosen as it is a viable shape memory polymer due to features such as semi-crystallinity, biodegradability, durability, biocompatibility, high stiffness, and 3D printability. This has been included in the revised manuscript. See page 2 lines 57 - 59

• As CNCs were loaded, how did the author ensure their compatibility with the polymer phase?

The food grade additives [polyethylene glycol (PEG), triacetin (TA) and an epoxy-based styrene-acrylic multifunctional chain extender] were added to improve compatibility between PLA and CNC. The actual loading of the additives have not been disclosed as it is part of a separate work submitted for patent review.

• How the filler affected the damping quality of the reinforced composites?

The PLA/CNCs bionanocomposites exhibited decreased tan delta (Tδ) curves compared to the specimen without CNCs. Also, the large area under the Tδ curves is indicative of improved damping properties associated with improved molecular mobility. Damping properties are discussed in Page 7 section 3.1, lines 240 - 243.

• Some articles related to such composites could be referred for better literature review: Ganguly, S., & Das, P. (2022). Synthesis and Production of Polylactic Acid (PLA). In Polylactic Acid-Based Nanocellulose and Cellulose Composites (pp. 29-50). CRC Press.; https://doi.org/10.1016/j.jclepro.2022.130749; https://doi.org/10.1016/j.progpolymsci.2022.101574; https://doi.org/10.1016/j.susoc.2021.09.004.  

As suggested by the reviewer, the references aligned to the topic have been included in the revised manuscript – Page 2 lines 71 and 73 .

Round 2

Reviewer 1 Report

accepted

Reviewer 4 Report

It can be accepted in its present form