Biofillers Improved Compression Modulus of Extruded PLA Foams

Round 1

Reviewer 1 Report

This manuscript focuses on poly(lactic) acid-based foams. This manuscript contains valuable results, but I recommend you accept it after major revision.

Remarks

• In affiliation, It seems the e-mail addresses are failed ([email protected])
• If this manuscript focuses on biodegradable materials, why do you refer to oil-based polyurethane as an example? It is very disruptive.
• Although the introduction is well-written, it does not contain sufficient relevant literature for:

Poly(lactic acid) foams prepared by supercritical CO2-assisted extrusion:

• Flame retardancy of microcellular poly(lactic acid) foams prepared by supercritical CO2-assisted extrusion https://doi.org/10.1016/j.polymdegradstab.2018.04.021
• Mastering the structure of PLA foams made with extrusion assisted by supercritical CO2 DOI: 10.1002/app.45067

Foaming of PLA with physical and chemical blowing agents:

• Characterization of different chemical blowing agents and their applicability to produce poly(lactic acid) foams by extrusion. 10.3390/app8101960
• Poly(lactic acid) foams reinforced with cellulose micro and nanofibers and foamed by chemical blowing agents https://doi.org/10.1177/0021955X17720155
• The aims are visible by the authors at the end of the introduction, which focuses on the PLA foaming with a physical blowing agent. In contrast, CBA and PBA were used. Please clarify!
• Why did you use talcum for the reference PLA materials?
• Why did not use talcum for the composites?
• Please insert Figure S1 into the manuscript! It very helps to understand the foam preparation.
• Please clarify the exact type of the PLA (for example, NatureWorks Ingeo 4032D)! Please add the D-lactic content to the description! This is useful information in terms of the maximum available crystalline fraction of PLA.
• Why did you use an endothermic type of CBA. What by-product was formed during the decomposition? If water, how could you manage under the processing to decrease the hydrolysis effect?
• The described parameters to produce PLA-based foam by extrusion does not enough! Please fill Table 2 with the temperature profile of the extruder, and use "bar" instead of "psi".
• Analyzing the achieved results, the following conclusion can be drawn:
• the average cell diameter is subjectively determined. It can be seen that the number of open cells increased and the shape of the cells became significantly distorted as the filler increased. The deviation of the cell sizes is significant, no clear conclusion can be drawn. Please increase the number of the measure cells!
• The reduction of the density is not significant despite PBA foaming. It could have been achieved using CBA alone.
• From crystallinity data, it can be seen increasing the filler content the crystallinity increases, which depends on the cooling speed also.
• In summary, it is strongly argued that the results achieved would be a good alternative to traditional rigid petroleum-based foams. It would be useful to compare them under the same measurement conditions to support this statement.

Author Response

Dear Reviewer,

Thank you for your thorough and thoughtful comments. Here are the steps we have taken to address your comments:

• Affiliation email addresses are added
• Polyurethane foams were referenced in the conclusion section as biobased polyurethanes are typically more expensive to produce than the industry standards. The biofillers could provide a route to reducing material cost. However, this reference is now removed for clarity.
• Additional literature on PLA foam produced with PBAs and CBAs are added to the introduction section.
• Talc and CBA were added to the PLA materials and not to the composites due to our hypothesis that the filler materials could act as nucleation agents. Talc is a known nucleation agent and the CBA used is designed specifically to also provide nucleation capability. Our nucleation agent hypothesis is included in the methods section.
• Figure S1 is now moved to the main manuscript.
• Details about the PLA (exact grade) and CBA (decomposition by-product) are added to the materials section.
• Table 2 is updated according to your suggestions.
• Additional cell size measurements were completed and incorporated into the data set bring the total measurements per sample up to 45. The cell size figure has been updated to include the new results. There are no statistically significant changes.
• Your suggestion to conduct direct comparisons with traditional petroleum based foams is added as potential future work.

Reviewer 2 Report

The submitted manuscript entitled ‘Biofillers Improved Compression Modulus of Extruded PLA Foams’ is dealing with the production of PLA foams with improved (enhanced) compressive modulus. The manuscript is interesting, it is basically well-written, the aims and the methods are clear, only a minor revision is suggested. The main weaknesses are: (i) please provide the compressive curves of the samples and explain graphically the determination of the modulus; (ii) please insert alternative methods to measure the effective modulus of the samples (scan the literature for modal analysis, Szlancsik et al., Dombóvári et al.). After the proper corrections reflecting the problems listed, the manuscript is ready for publication.

Author Response

Dear Reviewer,

Thank you for your thorough and thoughtful comments. Here are the steps we have taken to address your comments:

• Stress-strain curves are now included in addition to modulus data.
• Alternative methods to measure effective modulus are added to the compression testing section. 

Round 2

Reviewer 1 Report

The manuscript has been greatly improved with the corrections. I recommend accepting it.