Study on the Effect of Acrylic Acid Emulsion on the Properties of Poplar Wood Modified by Sodium Silicate Impregnation

Round 1

Reviewer 1 Report

This paper is well written. The subject is the impregnation of fast growing poplar wood with inorganic silicate agent and to improve this impregnation they used an acrylic acid emulsion/sodium silicate solution. This study showed good results on the dimensional stability and the thermal stability was still higer than the non-modified poplar wood. The explanation of the reactivity in the wood is well explained.

Introduction:

The introduction shows all the background on this research. However, the last paragraph is generally to present the study and not telling the results. It will be best to remove at the end of the introduction the results and just present what was done/evaluated in this study.

Materials and method:

2.1 (l82-83) you wrote 'with several samples of each', plesase add the exact number of samples for each test or remove this sentence and add the exact number of specimens/replicates tested for each series in each test you've done.

2.2 You repeate yourself twice with the 2 first sentences, please reduce in one.

The tests were well explicated with all the parameters needed. Just the number of replicates for each series are missing for each test. Please add this information.

Results:

Could you describe me how the error bars were made please? Small and similar variation for all the series whereas generally wood is a variable material.

Could you rewrite the first paragraph of your results on the TG/DTG please? I think heat resistance is not the word to what you describe.

3.2 Please rewrite the first sentences, words are missing (l191)

Is it really the swelling rate that is presented in figure 3b? Please rewrite either the figure or the text.

Figure 3e please add the title and unit for both vertical axes

Conclusion:
It summarizes the results of the study. 

 

Author Response

Responds to the reviewer 1:

Dear reviewer,

Thank you very much for your comments concerning our manuscript entitled “Study on the effect of acrylic acid emulsion on the properties of poplar wood modified by sodium silicate impregnation” (ID: Forests-2394464). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the paper. The main corrections in the paper and the responds to the your comments are as follows.

 

Comments 1: Introduction:

The introduction shows all the background on this research. However, the last paragraph is generally to present the study and not telling the results. It will be best to remove at the end of the introduction the results and just present what was done/evaluated in this study.

Reply: Thanks for your comments, we have revised this section in the manuscript. The revised content is as follows.

Based on the excellent water resistance and weather resistance properties of acrylic emulsion and its adhesion to wood substrates, a waterborne acrylic resin and sodium silicate were used in this study to modify poplar wood by co-mixing and immersion. The good film-forming property and water resistance of the acrylic emulsion improved the hygroscopicity of silicates and enhanced the impregnating agent's adhesion. This study explores the modification of poplar wood via immersion in inorganic sodium silicate, improving its properties.

 

 

Comments 2: Materials and method: 2.1 (l82-83) you wrote 'with several samples of each', please add the exact number of samples for each test or remove this sentence and add the exact number of specimens/replicates tested for each series in each test you've done.

Reply: Thanks for your comments, we counted all samples in the experiment. Since each test requires at least 12 samples for a total of 4 groups, the number of samples per size is 48.

 

Comments 3: 2.2 You repeat yourself twice with the 2 first sentences, please reduce in one.

Reply: Thanks for your comments, we apologize for the distress caused by our presentation. We have revised this section in the manuscript.

 

Comments 4: The tests were well explicated with all the parameters needed. Just the number of replicates for each series are missing for each test. Please add this information.

Reply: Thanks for your comments, we have added to the manuscript on the number of test pieces. The number of physical and mechanical properties tests for each group of modified wood is 12.

 

Comments 5: Could you describe me how the error bars were made please? Small and similar variation for all the series whereas generally wood is a variable material.

Reply: Thanks for your comments, we have added data analysis methods in the manuscript. We have recalculated and recalculated the data as shown in the figure below.

Statistical Analysis

The type of ANOVA test was Least Significant Difference (LSD). According to the minimum significant difference standard of 95 % confidence level, the results of ANOVA-test showed significant difference (p < 0.05).

 

Comments 6: Could you rewrite the first paragraph of your results on the TG/DTG please? I think heat resistance is not the word to what you describe.

Reply: Thanks for your comments, we have revised in the manuscript as you requested.

Fig 2d and 2e. According to the TG results, the thermal stability of AA/SS modified poplar was much lower than that of SS modified poplar due to the addition of acrylic emulsion. The addition of organic filler reduced the thermal stability after modification, but it was still greater than that of the natural poplar wood. The acrylic acid cured material almost completely decomposed at 700 °C, with only 1.48% residue, which could not provide it with heat-resistant substances to improve the thermal stability of the modified poplar wood.

 

Comments 7: 3.2 Please rewrite the first sentences, words are missing (l191)

Reply: Thanks for your comments, we have revised this phrase in the manuscript. The revised content is as follows.

The water absorption rates of the samples of various modified poplar woods after soaking in pure water for 60 h are shown in Fig 3a. Due to the different degrees of internal void filling, the water absorption rates of modified materials significantly decreased. Natural poplar wood has more space to accommodate water due to its voids, resulting in the highest water absorption rate of 145%.

 

Comments 8: Is it really the swelling rate that is presented in figure 3b? Please rewrite either the figure or the text.

Reply: Thanks for your comments, we showed the most pronounced change in tangential in Figure 3b. We have added labels to the figure 3b.

 

Comments 9: Figure 3e please add the title and unit for both vertical axes

Reply: Thanks for your comments, we have revised Figure 3e in the manuscript as you requested.

 

Author Response File: Author Response.docx

Reviewer 2 Report

The paper is relevant, with various experiments but  very briefly presented.

 The additional comments are given below.

 2.1. Materials

Line 28- Introduce the Latin name of the poplar species. Please, generally write what means processed because the reader probably is not familiar with Chinese standards. A test procedure or relevant information could be added.

Line 82-83- What means several samples? You should detail the method and present the number of the samples used for each test.

Line 98- What means aged for 24h? Maybe the appropriate word is “conditioned”?

Line 114-118- When you present the methods for testing, I assume “Should be” is “was”. Please specify the FTIR equipment.

Line 146-149- the affirmation must be argued by SEM. You didn’t present any image, except fig 3e, where seems to be a macroscopic picture. Instead of fig 3e, maybe will be more interesting to present the impregnation layers of the treated samples visualized on SEM.

Indicate in the text the standard deviation for presented tests.

The results from Chapter 3.2. should be completed with microscopic images to correlate with comments  in the text. Maybe some results of other researchers will help you in interpretation and validation of the results.  

Line 216- Where is presented the weather resistance and corrosion in your text?

 The statistical interpretation is minimal, the number of samples/tests is not indicated in the manuscript.

Where do you recommend using this modified wood in relationship to its improved properties?

 The paper is rejected in this stage.

Author Response

Responds to the reviewer 2:

Dear reviewer,

Thank you very much for your comments concerning our manuscript entitled “Study on the effect of acrylic acid emulsion on the properties of poplar wood modified by sodium silicate impregnation” (ID: Forests-2394464). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the paper. The main corrections in the paper and the responds to the your comments are as follows.

 

 

Comments 1: 2.1. Materials

Line 28 Introduce the Latin name of the poplar species. Please, generally write what means processed because the reader probably is not familiar with Chinese standards. A test procedure or relevant information could be added.

 

Reply: Thanks for your comments, we have added the Latin name of the poplar species in the manuscript. I'm sorry I didn't find test procedure or relevant information about this. The revised section is shown below.

Due to its fast growth, low weight, and moderate hardness, poplar (Populus L.) is widely used in construction, furniture, and papermaking applications.

 

Comments 2: Line 82-83 What means several samples? You should detail the method and present the number of the samples used for each test.

Reply: Thanks for your comments, we counted all samples in the experiment. Since each test requires at least 12 samples for a total of 4 groups, the number of samples per size is 48.

 

 

Comments 3: Line 98 What means aged for 24h? Maybe the appropriate word is “conditioned”?

Reply: Thanks for your comments, we are placing the specimens at room temperature and pressure to allow the modified poplar wood to become stable. We apologize for the error caused by our misrepresentation, which we have corrected in the manuscript. The revised content is as follows.

Then, the modified poplar wood surface was cleaned and air dried for 24 h.

 

Comments 4: Line 114-118 When you present the methods for testing, I assume “Should be” is “was”. Please specify the FTIR equipment.

Reply: Thanks for your comments, we have revised this section in the manuscript. The revised section is shown below.

The sample was loaded at a constant speed, and the failure time should be between 1.5 and 2.0 min.

The FT-IR test equipment is the Thermo Fisher iS50.

 

Comments 5: Line 146-149 the affirmation must be argued by SEM. You didn’t present any image, except fig 3e, where seems to be a macroscopic picture. Instead of fig 3e, maybe will be more interesting to present the impregnation layers of the treated samples visualized on SEM.

Reply: Thanks for your comments, we have added SEM images of the modified poplar wood to the manuscript.

 

Comments 6: Indicate in the text the standard deviation for presented tests.

Reply: Thanks for your comments, we have added this to the MATERIALS AND METHODS.

Statistical Analysis

The type of ANOVA test was Least Significant Difference (LSD). According to the minimum significant difference standard of 95 % confidence level, the results of ANOVA-test showed significant difference (p < 0.05).

 

Comments 7: The results from Chapter 3.2. should be completed with microscopic images to correlate with comments in the text. Maybe some results of other researchers will help you in interpretation and validation of the results.

Reply: Thanks for your comments, we have added SEM images of the modified poplar wood in Fig 3e.

 

Comments 8: Line 216 Where is presented the weather resistance and corrosion in your text?

Reply: Thanks for your comments, we have removed this section from the manuscript. We would like to express that the probability of mold and mildew infestation can be reduced due to the reduction of moisture absorption rate. We will include it in the follow-up study. The revised section is shown below.

By adding acrylic acid emulsion, the moisture absorption and stability of sodium silicate impregnated modified poplar wood were improved, increasing its water resistance and ultimately improving its service life and quality.

 

Comments 9: The statistical interpretation is minimal, the number of samples/tests is not indicated in the manuscript.

Reply: Since each test requires at least 12 samples for a total of 4 groups, the number of samples per size is 48.

 

Comments 10: Where do you recommend using this modified wood in relationship to its improved properties?

Reply: The modified poplar wood has greater strength and water resistance and can be considered as a material for outdoor utilities.

Author Response File: Author Response.docx

Reviewer 3 Report

This manuscript explains and describes experimental work to document and study on the effect of acrylic acid emulsion on the properties of poplar wood modified by sodium silicate impregnation.  This study presents a study in combining an-organic and organic material to improve low-density wood.  The findings are significant contribution to its field and suitable with the scope of the journal.   Therefore, I respect authors very much. 

 

So that, I expect the Editorial Board to accept this article with minor revision. 

 

I have some comments on the article as the following:

 

TITLE:

In my opinion, the title has represented contain of the manuscript

 

ABSTRACT:

In my opinion, since TG, FTIR and XPS were only mentioned once in abstract, they should not be written as abbreviations.

 

INTRODUCTION:

Introduction contains vast literature study concerning the topics.

 

MATERIALS AND METHODS

The schematic of Figure 1 is a result of this study?

Since the title of Fig 1 is preparation process, so that the figure should elaborate how the samples were made, which part of poplar wood the samples came from, the sample dimension etc

 

RESULTS

Authors statement: The acrylic emulsion penetrated the poplar cell cavities, and after the water evaporated, the components only needed to infiltrate and adhere to the cell walls, where they played a binding role in the original structure during lateral force loading, helping it withstand greater loads. Therefore, its improvement relative to the natural poplar wood was worse when subjected to longitudinal stresses. After sodium silicate cures, it becomes brittle, so the compressive strength of poplar modified by sodium silicate was significantly improved, but the bending strength was reduced.

 

Do the authors have SEM/TEM images to verify the above statements?

I think if the materials have filled the cavities in the cell walls, it should improve the bending properties also.

 

Fig 3e, the illustration, based on what? are there SEM/TEM images to verify that. Since all the components are mixed and put inside the wood. How do we know that acrylic will stay only on the surface of the cell wall or wood surface?

 

Based on your results of FTIR, there were some changes especially in hemicellulose, so that the impregnation solution not only acted as bulking agent but also built a bond between cell wall components. However, in the above statements, the authors only explain the material fill the cavities of poplar wood.

The degradation of hemicellulose also the reason why dimensional stabilities of AA/SS was improved. Please elaborate more the correlation of the hemicellulose degradation with dimensional stability of modified poplar wood.

 

CONCLUSIONS

The conclusion has answered the objectives clearly.

Author Response

Responds to the reviewer 3:

Dear reviewer,

Thank you very much for your comments concerning our manuscript entitled “Study on the effect of acrylic acid emulsion on the properties of poplar wood modified by sodium silicate impregnation” (ID: Forests-2394464). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the paper. The main corrections in the paper and the responds to the your comments are as follows.

 

Comments 1: ABSTRACT

In my opinion, since TG, FTIR and XPS were only mentioned once in abstract, they should not be written as abbreviations.

Reply: Thanks for your comments, we have changed the abbreviation to full name in the manuscript. The revised section is shown below.

The thermogravimetric analysis (TG) results showed that the addition of organic components reduced the heat resistance of modified wood, but the thermal stability was still higher than unmodified wood. Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) results showed that acrylic esters in acrylic acid emulsion reacted with hydroxyl groups on sodium silicate and wood to form covalent bonds that improved the impregnating agent's resistance to loss and reduced the moisture absorption of the wood.

 

Comments 2: MATERIALS AND METHODS

The schematic of Figure 1 is a result of this study? Since the title of Fig 1 is preparation process, so that the figure should elaborate how the samples were made, which part of poplar wood the samples came from, the sample dimension etc.

Reply: Thanks for your comments, Figure 1 mainly showed the preparation process of modified poplar wood and the resulting effect. Sections 2.1 and 2.2 of the manuscript described the detailed process of preparation and issues such as the sample dimension.

 

Comments 3: RESULTS

Authors statement: The acrylic emulsion penetrated the poplar cell cavities, and after the water evaporated, the components only needed to infiltrate and adhere to the cell walls, where they played a binding role in the original structure during lateral force loading, helping it withstand greater loads. Therefore, its improvement relative to the natural poplar wood was worse when subjected to longitudinal stresses. After sodium silicate cures, it becomes brittle, so the compressive strength of poplar modified by sodium silicate was significantly improved, but the bending strength was reduced. Do the authors have SEM/TEM images to verify the above statements? I think if the materials have filled the cavities in the cell walls, it should improve the bending properties also.

Reply: Thanks for your comments, we have added SEM images of the modified poplar wood to the manuscript. Although the modified poplar wood cells were filled, the filler was not tightly bonded to the cell walls and thus did not exhibit increased strength when subjected to lateral forces.

 

Comments 4: Fig 3e, the illustration, based on what? are there SEM/TEM images to verify that. Since all the components are mixed and put inside the wood. How do we know that acrylic will stay only on the surface of the cell wall or wood surface?

Reply: Thanks for your comments, we have added SEM images of the modified poplar wood in Fig 3e. When we impregnate wood with acrylic emulsion alone, a film is formed on the surface of the wood. The surface of the filler was rough when we impregnated the wood with the sodium silicate solution alone, but became smooth when the acrylic emulsion was added. Therefore, we reasonably infer that acrylic emulsions will be coated with sodium silicate when the curing reaction occurs.

 

Comments 5: Based on your results of FTIR, there were some changes especially in hemicellulose, so that the impregnation solution not only acted as bulking agent but also built a bond between cell wall components. However, in the above statements, the authors only explain the material fill the cavities of poplar wood.

Reply: Thanks for your comments, we have mentioned in the manuscript the formation of a chemical bond between the agent and the cell wall. The revised section is shown below.

As shown in Figure 5c, the Si-O-C structure was formed inside both SS and AASS modified poplar, which proved that sodium silicate was able to form a chemical bond with wood and acrylic emulsion in the presence of sodium silicate

 

Comments 6: The degradation of hemicellulose also the reason why dimensional stabilities of AA/SS was improved. Please elaborate more the correlation of the hemicellulose degradation with dimensional stability of modified poplar wood.

Reply: Thanks for your comments, we have added relevant content to the manuscript. The revised section is shown below.

Hemicellulose is the main component of moisture absorption in wood, and degradation of hemicellulose reduced the moisture absorption of modified poplar wood.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

I agree with the corrections made. I agree to publish the document

Author Response

Responds to the reviewer 1:

Dear reviewer,

Thank you very much for your recognition of our research work. Thank you for your valuable suggestions for our paper.

Reviewer 2 Report

I appreciate the authors improved the quality of the manuscript. They followed the reviewer recommendations. 

I still have some observations:

"Processed" for wood means to be planed, no defects, etc...

The microscopic image from fig. 3e is still not clear, even if it is exemplified by the large images to the right of figure.

Author Response

Responds to the reviewer 2:

Dear reviewer,

Thank you very much for your comments concerning our manuscript entitled “Study on the effect of acrylic acid emulsion on the properties of poplar wood modified by sodium silicate impregnation” (ID: Forests-2394464). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the paper. The main corrections in the paper and the responds to your comments are as follows.

 

 

 

Comments 1: "Processed" for wood means to be planed, no defects, etc....

Reply: Thanks for your comments, we have revised this section in the manuscript. The revised content is as follows.

The preparation procedure is shown in Fig 1.

The key procedure parameters were a vacuum degree of -0.095 MPa and a retention time of 5 min.

Fig. 1 The preparation procedure of modified poplar

 

Comments 2: The microscopic image from fig. 3e is still not clear, even if it is exemplified by the large images to the right of figure.

Reply: Thanks for your comments, we have replaced the image with a larger magnification in fig. 3e. 

Author Response File: Author Response.docx