Forest by-Product Valorization: Pilot-Scale Pinus radiata and Eucalyptus globulus Bark Mixture Extraction

Round 1

Reviewer 1 Report

The manuscript is focused on the investigation and evaluation on the feasibility of forest by-products (P. radiata and E. globulus bark) valorisation. In this respect, the manuscript is within the scope of the Forests journal. In general, the manuscript is very well-written, structured and informative, but needs some minor improvements before acceptance for publication. Please, see below my comments on your work:

In general, the title (lines 2-3), the abstract (lines 22 to 40) and the keywords (line 41) correspond to the scope, aims and objectives of the manuscript. The abstract is well-written and informative, and contains the main findings of the article.

In the keywords, I’d suggest adding also “tree bark”.

Line 31: please revise to (0-100%).

Line 59: Although tannins are still the only bio-based feedstock that have found industrial application as wood adhesive (mainly in particleboards), there are many studies reporting the efficient valorisation of technical lignins in wood adhesives, mostly as a partial or complete replacement of phenol in phenol-formaldehyde resins, please consider.  

In line 74 you stated petroleum-based resins are cheap, and in line 76 “…the rising prices of all the oil-based resins..” which is a bit contradictory, please revise. Of course, the economic costs are a main factor, but the main drivers for the increased academic and industrial interest in bio-adhesives is the transition towards a circular bioeconomy, environmental concerns, and strict legislation related to the emission of harmful VOCs, including formaldehyde from the finished composites.

Line 107: “similar behaviour” is repeated, please revise.

Overall, the Introduction part is very well-written and informative, and provides relevant information and references on the research topic. However, I’d recommend to further elaborate it based on the minor comments given above.

Line 128: Figure 1 is not of a very good quality, please replace it, if possible. In addition, in the figure caption, there is no need to specify the software used (AutoCAD). Instead, please provide a clear description of the different elements.

Line 190: “one week” is duplicated, please revise.

Lines 199-200: please provide information on the equipment used (company producer, city, country).

Line 219: please provide pressure value in MPa (SI unit).

Lines 222-224: please add the standards used in the references of your work.

Overall, the Materials and Methods section is well written and detailed, but can be further elaborated based on the comments above.

Figure 5 is very difficult to read, please replace it, if possible.

Line 500: particleboard performance – have you investigated other mechanical properties of the particleboards bonded with the developed bio-adhesive, e.g. MOR or MOE? What about the dimensional stability in terms of water absorption and thickness swelling?

In general, the results of the study are very detailed, informative and properly discussed with relevant research works in the field.

The Conclusion part (lines 523-548) clearly reflects the main findings of the manuscript.

 

The References cited are appropriate for the topic of the manuscript. 

The English language and style used in the manuscript are fine, only some minor technical issues should be addressed, please see my comments. 

Author Response

Responses to reviewer 1.

The manuscript is focused on the investigation and evaluation on the feasibility of forest by-products (P. radiate and E. globulus bark) valorisation. In this respect, the manuscript is within the scope of the Forests journal. In general, the manuscript is very well-written, structured and informative, but needs some minor improvements before acceptance for publication. Please, see below my comments on your work:

In general, the title (lines 2-3), the abstract (lines 22 to 40) and the keywords (line 41) correspond to the scope, aims and objectives of the manuscript. The abstract is well-written and informative, and contains the main findings of the article.

Thanks for your comments.

In the keywords, I’d suggest adding also “tree bark”.

Thank you for the suggestion. We added tree barks sentence in the keywords section

Line 31: please revise to (0-100%).

Thank you for the suggestion. We revised the phrase and added the percentage symbol

Line 59: Although tannins are still the only bio-based feedstock that have found industrial application as wood adhesive (mainly in particleboards), there are many studies reporting the efficient valorisation of technical lignins in wood adhesives, mostly as a partial or complete replacement of phenol in phenol-formaldehyde resins, please consider.  

Of course, the applicability of lignin and lignosulfonates in adhesive formulation is a highly studied topic. We have included the application of adhesives for the possible applications of lignin.

 

In line 74 you stated petroleum-based resins are cheap, and in line 76 “…the rising prices of all the oil-based resins..” which is a bit contradictory, please revise. Of course, the economic costs are a main factor, but the main drivers for the increased academic and industrial interest in bio-adhesives is the transition towards a circular bioeconomy, environmental concerns, and strict legislation related to the emission of harmful VOCs, including formaldehyde from the finished composites.

To clarify, the sentence was changed: “These components have a very good performance as an adhesive resin, which makes it difficult to replace them with natural products more difficult”

Line 107: “similar behaviour” is repeated, please revise.

Thanks for your commentary we reviewed the mistake.

Overall, the Introduction part is very well-written and informative, and provides relevant information and references on the research topic. However, I’d recommend to further elaborate it based on the minor comments given above.

Thank you for the commentary. Based on your comments the introduction text was changed

Line 128: Figure 1 is not of a very good quality, please replace it, if possible. In addition, in the figure caption, there is no need to specify the software used (AutoCAD). Instead, please provide a clear description of the different elements.

Thanks very much for you suggest. figure 5 has been improved and updated according your comments.

Line 190: “one week” is duplicated, please revise.

Thanks for your commentary we reviewed the mistake.

Lines 199-200: please provide information on the equipment used (company producer, city, country).

Thanks for your commentary, the company producer, city and country was added

Line 219: please provide pressure value in MPa (SI unit).

Thanks for your commentary; the pressure unit value was changed

Lines 222-224: please add the standards used in the references of your work.

The standards used were added in the references section. 

Overall, the Materials and Methods section is well written and detailed, but can be further elaborated based on the comments above.

Thank you for the commentary. Based on your comments the Materials and Methods  text was changed

Figure 5 is very difficult to read, please replace it, if possible.

Thanks for your comments, figure 5 has been improved and updated

Line 500: particleboard performance – have you investigated other mechanical properties of the particleboards bonded with the developed bio-adhesive, e.g. MOR or MOE? What about the dimensional stability in terms of water absorption and thickness swelling?

In this case, these properties were not evaluated because the objective of this section of the work was only to compare the reactivity of the extracts obtained from 100% Pine Bark and the mixture of Pine Bark and Eucalyptus. Furthermore, these tests are not required to pass the rule to be classified as class P1 particleboard. Of course, future work will study these and other bioadhesive formulations and their impact on the properties of particle boards produced with these bioadhesives.

In general, the results of the study are very detailed, informative and properly discussed with relevant research works in the field.

Thanks for your comments

The Conclusion part (lines 523-548) clearly reflects the main findings of the manuscript.

 Thanks for your comments

The References cited are appropriate for the topic of the manuscript. 

Thanks for your comments

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript “Forest by-products valorization: Pilot-scale Pinus radiata and Eucalyptus globulus bark mixture extraction” treats an actual problem (valorisation of forest by-products (bark) as a source of tannin rich extracts for bio-adhesive formulation for further particleboard production. The aim highlights the importance of this study: for obtaining of tannin rich extracts not common pine bark will be used, but its mixture with E. globulus bark (deciduous tree with significant lower application in tannin field). The manuscript definitely matches the aims and scope of the Forest Journal.

The title and abstract are appropriate for the content of the text. The article is well constructed, the experiments were well conducted, and analysis was well performed.

The poor quality of Figures 1 and 5.

In the Line 135 the weight is calculated on dry bark. However, the moisture content of initial bark is not specified. Theoretically, the moisture content could be up to 70%.

The authors several times emphasizes that bark extracts are mainly composed of condensed tannins, or rich in proanthocyanidins. But there is no pointed out the content of this compounds. The content of condensed tannins could be calculated from the Stiasny number. It will be useful to add this value in Table 3.

Proanthocyanidins (Lines 341 and 349) (synonym condensed tannins (Lines 25, 80, 91… etc))- use one of them in the whole manuscript

The titles of the subsection 3.1; 3.2.; 3.3.; 3.4 is confusing by similarity Characterization of … I suggest to specify them... 3.3 to Spectral Analysis instead of Characterization of ...

The Figure 5 must be updated with compounds identified in Table 5 to visually see the balance between identified and unidentified compounds.

Author Response

The manuscript “Forest by-products valorization: Pilot-scale Pinus radiata and Eucalyptus globulus bark mixture extraction” treats an actual problem (valorisation of forest by-products (bark) as a source of tannin rich extracts for bio-adhesive formulation for further particleboard production. The aim highlights the importance of this study: for obtaining of tannin rich extracts not common pine bark will be used, but its mixture with E. globulus bark (deciduous tree with significant lower application in tannin field). The manuscript definitely matches the aims and scope of the Forest Journal.

The title and abstract are appropriate for the content of the text. The article is well constructed, the experiments were well conducted, and analysis was well performed.

The poor quality of Figures 1 and 5.

Thanks for your comments, the quality of the Figures 1 and 5 were upgraded

In the Line 135 the weight is calculated on dry bark. However, the moisture content of initial bark is not specified. Theoretically, the moisture content could be up to 70%.

In the industrial process, the bark is dried and, of course, the moisture content of the initial bark samples was measured to assess the extraction yield and the amount of bark used as raw material in the extraction process.

The authors several times emphasizes that bark extracts are mainly composed of condensed tannins, or rich in proanthocyanidins. But there is no pointed out the content of this compounds. The content of condensed tannins could be calculated from the Stiasny number. It will be useful to add this value in Table 3.

The Stiasny number measures the reactivity of the extracts with formaldehyde, and the authors do not believe that it can be a good method to evaluate the content of proanthocyanidins.

Proanthocyanidins (Lines 341 and 349) (synonym condensed tannins (Lines 25, 80, 91… etc))- use one of them in the whole manuscript

Thank you for your comment. As mentioned in line 341, proanthocyanidins can indeed be considered a synonym for condensed tannins. In line 349 we specify that pine bark has a higher content of procyanidins and a lower content of prodelphinidins. For this reason, the definition of "condensed tannin" is not used in this last point.

The titles of the subsection 3.1; 3.2.; 3.3.; 3.4 is confusing by similarity Characterization of … I suggest to specify them... 3.3 to Spectral Analysis instead of Characterization of ...

Thank you for your suggestion. However, the authors have reviewed the titles and they seem appropriate.

The Figure 5 must be updated with compounds identified in Table 5 to visually see the balance between identified and unidentified compounds.

Thanks for your comments, figure 5 has been improved and updated

Author Response File: Author Response.docx