Controlled and Accelerated Hydrolysis of Polylactide (PLA) through Pentaerythritol Phosphites with Acid Scavengers
Round 1
Reviewer 1 Report
The manuscript titled “Controlled and accelerated hydrolysis of PLA through pentae- 2rythritol phosphites with acid scavengers” is a very well written and informed document. Not only does it highlight pathways of hydolysing the biodegradable plastic, polylactic acid, it also critically scrutanises the use of phosphites. This manuscript should be considered for immediate publication have a couple of very minor points are considered.
General comments
Materials - PLLA – define as different to polylactic acid
Specific comments
· Although the different reaction parameters are followed, there is not clear direction at the overall reaction conversion and product selectivity. Is the major hydrolysis product the only one observed or are there other products formed?
o What is the mass balance for each reaction, to ensure no loss of carbon.
Author Response
Thank you very much for your very positive feedback and proposals. As suggested we added a phrase to define PLLA and why PLLA was used in the study. The products of the hydrolytic cleavage have still a polymeric character in the investigated time range and we don´t find any other low molecular weight byproducts. The degradation is exclusively through hydrolysis and abiotic. Therefore, for calculating the mass balance biodegradation is of importance, which is an additional topic of future investigations.
Reviewer 2 Report
Dear Authors
This manuscript is focused on the accelerated hydrolysis of the polyester PLA through the addition of phosphites based on pentaerythritol. To control hydrolysis and ensure processing stability different types of phosphites and combinations of phosphite with acid scavengers were studied.
The following suggestion and comments should be taken:
1. The authors could insert more numerical data into the Abstract for enhancement of the manuscript.
2. Could the authors include the standard deviation of the used methods?
3. Figure 2. Please correct this image for better quality (the inscriptions).
4. Figure 3. Please correct this image for better quality.
5. Figure 4. Please correct this image for better quality.
6. Figure 5. Please correct this image for better quality (the inscriptions).
7. Figure 9 and 11. Please correct this image for better quality (the inscriptions).
8. Authors are suggested to describe some future plans in conclusions.
9. Why authors used NMR but not XPS, TEM or SEM analysis? Please explain
Author Response
Thank you very much for your comments and suggestions. We added into the abstract some numerical data as proposed. The standard deviations of the MVR values are included in table 1 and standard deviations are included in the figures related to MVR measurements. For the other relevant analytical method in the paper (GPC) an information to the standard deviation is included now. The original figures were sent seperately together with the submission and are, therefore, already available to be included in the version to be published. We suppose that the picture quality is reduced through building the pdf document and the issue is solved through the original figures. Future plans have been included in the conclusions paragraph. NMR was used via 31-P for the investigation of the hydrolytic stability of the selected phosphites and not of the compounds or the final products. Therefore investigations of a phosphite solution via NMR was the best choice to identify the hydrolytic stability. XPS, TEM and SEM would have been more suitable for investigations of potential plastics parts and their morphological changes which were not the target of the paper.
Reviewer 3 Report
Biobased and biodegradable polymers are considered as a vital component of arising circular economy and there is an urgent need to reduce waste.
This study provides insight into the accelerated hydrolysis of the polyester
PLA through addition of phosphites based on pentaerythritol.
The investigations are useful and the paper could be published after revision. *Why phosphites based on pentaerythritol were chosen for the investigations ? *Hydrolysis experiments were performed at 23 °C, 35 °C and 58 °C.
How the temperatures were selected ? *Twin-screw extruder was used for preparation of composites.
Was a simple extruder not suitable ? *Extrusion process for preparation of samples was rather complicated.
This would be a disadvantage for planning an industrial process
for PLA waste ? *Efficiency of the described process should by compared in conclusions
with other methods used for hydrolysis of PLA and already published.
Author Response
Thank you very much for the comments and questions. Phosphites based on pentaerythritol can be based on natural resources and are commercially available. This explanation has been added to the paper.The reasons for the selection of temperatures were: 58 °C is the typical composting temperature in industrial composting facilities, the temperature is as well above the glass transition temperature of PLA, 35 °C is an average temperature of home composting and 23 °C is the comparison to room temperature behavior. An explanation for the selection of temperatures has been added to the paper. For compounding purposes a twin screw extruder is preferred through better mixing capabilities as we have to guarantee a homogeneous compound, of course for e.g. an additional film preparation a single screw extruder would be sufficient. Other methods to accelerate the hydrolysis of PLA are already described in the introduction, some results from literature have been added there additionally. In general a real comparison between literature data is very difficult due to different materials and methods used in the publications.
Round 2
Reviewer 2 Report
The authors have addressed all comments and the manuscript can be published as is.
