Hardness of Densified Wood in Relation to Changed Chemical Composition

Round 1

Reviewer 1 Report

Specific Comments:

Line 45-49: Please rewrite sentence for clarity. Perhaps use 2 sentences.

Line 55: Chang Stama and Seborga to Stamm and Seborg.

Line 61: Change Sanberg to Sandberg.

Introduction: The goal of this research is missing. The novelty of this research is missing. Both the goal and the novelty should be mentioned in the introduction.

Line 82-84: Is there some evidence that syringyl lignin is more reactive than guaiacyl lignin?

Line 88: 0.1mm accuracy seems not very good. Is this correct? After reading results, this really doesn't matter. No change needed.

Line 152: Change cramps to clamps.

Figure 2: The screws on the top plate do not appear centered from front to back. Please change.

Table 2: In addition to lignin, cellulose, and hemicelluloses, there are some other minor components. Therefore, the summation of the percent chemical component will be somewhat less than 100%. The control samples summation was about 98 to 99%. However, the chemically treated samples had cumulative percent components of about 66 to 69%. What is the basis and why is the summation not approximately 100%? One expects the percent of cellulose would increase after the chemical treatment, but Table 2 indicates a reduction of cellulose percentage. Perhaps I don’t understand Table 1. Is the term “m” in equations 1, 2, and 3 the same? I think somehow the basis of the percent composition is the original mass of the specimen before chemical treatment.

Table 3: I am surprised that the MC for all sample types are approximately the same. One would expect that chemically-treated sample to have a lower equilibrium MC because the hemicellulose content is low.

Line 205: Bulnesia sarmienti  or Lignum vitae? Include scientific name.

Equation 5: This equation assumes the density of the cell wall is 1.5 g/cm3 regardless of the chemical treatment. One expects the cell wall density to be reduced after some of the lignin is extracted. Not important for the comparison, but should be mentioned.

The calculation of porosity for the chemically treated samples does not exactly follow the concept of porosity. Perhaps it would be possible to recalculate the cell wall density after chemical treatment.

Line 219: Are you referring to the vessel cells when you imply the larger diameter pores? Please rewrite this sentence. I recall that the vessels in poplar and birch are about the same diameter. The difference in density is due to the frequency of vessels, and perhaps the cell wall thickness of the longitudinal fibers.

Line 221: Do you mean “degree of density” or “degree of densification”?

Conclusion: Start by restating the goal of the experiment. This was lacking in the introduction. I believe the goal was to reproduce the results of Song et al [27] and determine the change in chemical composition. Furthermore, the goal was to determine if reducing the lignin and hemicellulose components increase density and improve hardness of compressed material. Look at the abstract.

General comments:

It is surprising that the authors did not compare results to previous publications using Populus sp and densification. The citations below (and there are others) all include thermo-hydro-mechanical (THM) compression of poplar. Another term synonymous with THM is VTC (viscoelastic thermal compression).  The Standfest article includes information of porosity change of VTC wood compared to native poplar wood.

Hornicek, S; P Rademacher; R Rousek, A Kutnar; FA Kamke. 2015. Selected physical and mechanical properties of viscoelastic thermal compressed wood from fast growing poplar. Pro Ligno 11(4):324-329.

Kamke, F.A. and A. Kutnar. 2014. Comparison of transverse compression creep of Pseudotsuga menziesii and Populus sp. in high temperature steam environments. Wood Materials Science & Engineering 9(2):84-91.

Gabrielli, C. and F.A. Kamke. 2008. Treatment of chemically modified wood with VTC process to improve dimensional stability. For. Prod. J. 58(12):82-86.

Kutnar, A.; F.A. Kamke and M. Sernek. 2008. The mechanical properties of densified VTC wood relevant for structural composites. Holz als Roh- Werkst. 66(6): 439-446

Standfest, G., A. Kutnar, B. Plank, A. Petutschnigg, F.A. Kamke, and M. Dunky. 2013. Microstructure of viscoelastic thermal compressed (VTC) wood using computed microtomography. Wood Science and Technology, 47:121-139.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Referee comments

This research paper seems sound, clearly written and a simple nice protocol is described to test the effects of modification on wood of two selected species.

I would comment shortly some points:

• Introduction has a good presentation of current literature. However, Aims of the current study has been left out. Please, add Aims of the study to the end of introduction part.
• Line 30: "it formation"?? sould it be "its formation"?
• Lines 200-201: Numbers presented in the text are not exactly the same as in Table 3. Please, correct.
• In results and discussion, the comparison of presented results to current literature is poor. Please, add some text with discussion and comparison to relevant literature.
• Conclusions are compact and sound, but some discussion concerning the importance of the presented methods and results related to commercial wood applications, could be also presented. Please, add some text.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Please find all my comments directly written into the pdf.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf