Evaluation of the Circularity of Recycled PLA Filaments for 3D Printers

Round 1

Reviewer 1 Report

Line 2-3

Most of the work relates to the Material Circularity Indicator (MCI). Perhaps this should be reflected in the title of this paper.

Line 18-22

“Following this circular economics framework, the Polytechnic University of Madrid has adopted strategies aimed at improving the circularity of products and in particular, this article provides the result of obtaining recycled PLA filament from waste originating from university 3D printers and waste caused by “Coronamarkers” in the production of visors and parts for EPIS during the confinement of COVID 19.”

This sentence is too long. Please explain EPIS in the abstract.

Line 52-60

In my opinion, this paragraph is not complete. The presented description does not fully explain the diagram presented in Figure 1. Please complete the description or propose your own graphic, showing a biological cycle and a technical cycle.

Line 112-133

This paragraph should be rewritten. The authors emphasize the historical rather than functional aspect of the methodology.

Line 157-158

“The broken lines in Figure 4 indicate that this methodology does not necessarily require a closed loop.” I think this sentence is also true for Figure 3. Maybe it is worth combining or juxtaposing these two diagrams with each other (fig. 3 and 4).

Line 173-176

What kind of PLA filament is used here? What type of equipment was used to generate filaments and parts.

Line 252-253

Authors have been assumed a 2% loss in the process of creating the filaments formed by recycled PLA and virgin PLA. But what about losses in the 3D printing process e.g. connect with building rafts/brim/skirt, supports, cleaning extruder head?

Line 274

Is it necessary to presents the results (0.844781739) in Table 1 with such accuracy?

Line 282

Please remove the value (1.1)  from the y-axis in Figure 5. MCI can obtain a maximum of 1.0.

General comments

1. The authors made assumptions for the production of parts by 3D printing with PLA. Please specify which technology was used? FDM / FFF?
2. What is the scale of this activity? On how many variants of the 3D printed parts were the computational model verified? Authors inform only about the average mass of a piece.
3. What is the causal link with the coronavirus pandemic? Why this thread was highlighted by the authors of the paper.
4. The achieved MCI value of 0.844781739 does not give an idea of the meaning of this count very well and what the result is. We only know about the extreme conditions when the MCI is equal to 0 or 1. Can you give an example of a product production cycle that could be a certain reference to the results achieved? Or give a scale to which we can assign a qualitative interpretation.

Author Response

Dear reviewer:

Thank you very much for your comments. They are so valuable and they will enrich our paper.

Below you can find the correction made with your suggestions:

Line 2-3: The objective of the MCI is to know the circularity of the product; so we decide to keep the same title

Line 18-22: We short the sentence. EPIS was not translated; EPIs= PPEs (Personal Protective Equipment)

Line 52-60: We have made a wide description (lines 53-61) of picture 1

Line 112-133: We short this section and give more importance to the following paragraphs

Line 157-158: It was a mistake; It should be Figure 3 not 4.

Line 173-176 : We have made a wide description and include Figures of the recycled process.

Line 252-253 :We assume that waste in the general 2% loss. The geometry of the part is very important in the 3D printing waste and the preparation of the supports. We have to work deeply in this issue.

Line 274: It is not necessary; we have changed it in the document

Line 282: We have changed the Y axis value to 1

General comments

The authors made assumptions for the production of parts by 3D printing with PLA. Please specify which technology was used? FDM / FFF?:

****We used FFF 3d printers.  We have included in the abstract (line 22 ) and in the document (line 175).

What is the scale of this activity? On how many variants of the 3D printed parts were the computational model verified? Authors inform only about the average mass of a piece.

***The parts belong to a mechanical assembly; but we have used the mass average of the different components. Actually we are working to get enough recycled filament to work with it in a continuous way

What is the causal link with the coronavirus pandemic? Why this thread was highlighted by the authors of the paper.

****Conronamakers gave us enough defective PLA parts to start the recycled process. They pushed our project. They, due the pandemic, had parts with mistakes o incompleted parts that we can used to recycled. There were a lot of people working and producing parts in a short time. So we had PLA to start the process. Our main problem is to get enough PLA parts or PLA waste to start the recycled process.

The achieved MCI value of 0.844781739 does not give an idea of the meaning of this count very well and what the result is. We only know about the extreme conditions when the MCI is equal to 0 or 1. Can you give an example of a product production cycle that could be a certain reference to the results achieved? Or give a scale to which we can assign a qualitative interpretation.

***No, we can not find references, even we don’t have information about the MCI of other products or processes (they are not public). It shows that as much of recycled PLA is used, we are closer to 1.

Thank you very much for your time and suggestions.

Regards

M Luisa M Muneta

Universidad Politécnica de Madrid

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors proposed a method to evaluate the material circularity and demonstrated the material circularity of the recycled PLA filament from waste originating from university 3D printers and waste caused by “Coronamarkers” in the production of visors and parts for EPIS. The material circularity in that case was shown to be very high, even when taking into account the losses in the process of making PLA filament and the defects in the material detach due to blows and other causes. The establishment of such an evaluation method is a must for our future sustainable production of products and business, and is a globally important task. The proposed method for calculating material circularity and its demonstration and discussion in this paper may serve as a global guideline for the future. The global use of such evaluation methods will also drive more recyclable and environmentally friendly products to the market. Therefore, I recommend that this manuscript be published in this journal. My comments on this manuscript are as follows.

1. At present, there are many recyclable products in the materials mainly used in the market, even if they are not biological materials, and since there is more demand for products using materials such as engineering plastics, the MCI evaluation proposed by the authors may be possible in this regard as well. In other words, isn't it useful to apply this method to materials other than Principle #1 in MCI?

2. The text in lines 157 and 161 says Figure 4, but isn't that Figure 3?

3. I would like to see a clear description or table that shows which parameters used in the MCI calculations are related to which of the six MIC principles. This would make it easier to understand and discuss the parts not taken into account in the current calculation.

4. The authors say it is recommended that Fr should be between 60% and 80% in order to avoid affecting the quality of the part, but please add the references if you have.

5. Losses and efficiencies are shown for each parameter in the calculation, but anything that has a reference to them should be shown. If you don't have a reference, please explain why.

6. The subscripts of all the symbols used in the calculations, such as Lav, Uav, Ef, etc., should be subscripts (should be small). I also felt that all of these symbols and their meanings should be summarized in a table separate from Table 1 to understand their calculation easier.

7. How is a functional unit calculated? You need to be a little more specific.

Author Response

Dear reviewer:

Thank you very much for your comments. They are so valuable and they will enrich our paper.

Below you can find the correction made with your suggestions:

1. At present, there are many recyclable products in the materials mainly used in the market, even if they are not biological materials, and since there is more demand for products using materials such as engineering plastics, the MCI evaluation proposed by the authors may be possible in this regard as well. In other words, isn't it useful to apply This method to materials other than Principle #1 in MCI?

This MCI is proposed for technical cycles. It is difficult to evaluate how much waste is used as a nutrient in the biological cycle. Specifically we are focus in the 4^th principle “Reuse recycled components or materials after use”

2. The text in lines 157 and 161 says Figure 4, but isn't that Figure 3?:

You are right. We have changed in the paper.

3. I would like to see a clear description or table that shows which parameters used in the MCI calculations are related to which of the six MIC principles. This would make it easier to understand and discuss the parts not taken into account in the current calculation. :

We add the description of the variables in the table.

4. The authors say it is recommended that Fr should be between 60% and 80% in order to avoid affecting the quality of the part, but please add the references if you have.

We have information from professionals and in the following docs

1. Tanney, D., Meisel, N. A., Moore, J. Investigating Material Degradation through the Recycling of PLA in Additively Manufactured Parts. Solid Freeform Fabrication 2017: Proceedings of the 28th Annual International Solid Freeform Fabrication Symposium, Austin Texas.
2. Eduardo Moreno, Freddys R. Beltrán González , Marina P. Arrieta, Gerald Gaspar, María L. Martínez Muneta, Ruth Carrasco, Susana Yañez, David Hidalgo, María Ulagares de la Orden, Joaquín Martínez Urreaga Technical evaluation of mechanical recycling of PLA 3D printing wastes. The First International Conference on “Green” Polymer Materials 2020. CGPM2020. November 2020
3. Losses and efficiencies are shown for each parameter in the calculation, but anything that has a reference to them should be shown. If you don't have a reference, please explain why.

We have made a more extensive description of the recycling process followed as well as the description of different values.

6. The subscripts of all the symbols used in the calculations, such as Lav, Uav, Ef, etc., should be subscripts (should be small). I also felt that all of these symbols and their meanings should be summarized in a table separate from Table 1 to understand their calculation easier.

We have changed to subscripts and added a description in table 1

7. How is a functional unit calculated? You need to be a little more specific.

We add more information about that in lines 209-217

I hope the changes made are consistent with your suggestions.

Thank you very much for your time and suggestions.

Regards

M Luisa M Muneta

Universidad Politécnica de Madrid

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear Authors,

Thanks for the explanation. I accept the article in this form. If it is possible please change color of the filament in Figure 6 to orange from black. It will correspond with figure 5b and c.