Physico-Mechanical and Biological Durability of Citric Acid-Bonded Rubberwood Particleboard

Round 1

Reviewer 1 Report

The manuscript studies how citric acid content affects the performances of woodparticle board. Although control sample is used for comparison, I am not sure what is the essential properties and requirements for the applications of woodparticle board; thus it is hard to conclude whether the adoption of citric acid is suitable for woodparticle boards. The authors should provide a clear and quantitative target or requirement. Also, if 20wt% citric acid shows the best properties, how about higher content? My other comments are listed below:

1. Line 207: Table 2?
2. Tables 1 and 2, what is the meaning of letters a, b, c, and d?
3. For the definition of WA, should it be (W2-W1)/W1 instead of (W1-W2)/W2?
4. Lines 182-184: The authors state that citric acid has reacted with the hydroxyl groups of rubberwood, could authors show the IR spectra of CA samples before and after hot pressing treatments?
5. Line 200: It should be lower WA24h. Could authors provide photos or images for CA10 and CA15 before and after water soaking for 24h?
6. Lines 241-242: Since the rubberwood (RW) particles were dried to 3% moisture content at 103 ± 2 °C prior to particleboard fabrication, what is the meaning of pre-drying?
7. Lines 253-254: I am confused, should less weight loss indicate better resistance?
8. Figures 2 and 4: Scale bar should be provided.

Author Response

Reviewer 1 : The manuscript studies how citric acid content affects the performances of woodparticle board. Although control sample is used for comparison, I am not sure what is the essential properties and requirements for the applications of woodparticle board; thus it is hard to conclude whether the adoption of citric acid is suitable for woodparticle boards. The authors should provide a clear and quantitative target or requirement. Also, if 20wt% citric acid shows the best properties, how about higher content? My other comments are listed below:

√ All the results have been compared with the requirements stipulated in JIS A 5908. Particles sprayed with higher resin content (>20 wt%) were failed to be formed into boards due to extremely high moisture content.

Comment 1: Line 207: Table 2?

√ It has been revised to Table 1 (Line 229).

Comment 2: Tables 1 and 2, what is the meaning of letters a, b, c, and d?

√ The meaning of letters a, b, c and d has been added as footnote in Table 1 and Table 2. 

Question 3: For the definition of WA, should it be (W2-W1)/W1 instead of (W1-W2)/W2?

√ The formula for both TS and WA has been revised. We would like to thanks the reviewer for pointing it out (Line 112 & 123).    

Comment 4: Lines 182-184: The authors state that citric acid has reacted with the hydroxyl groups of rubberwood, could authors show the IR spectra of CA samples before and after hot pressing treatments?

√ Figure 1 showed the IR spectra of control and rubberwood particles sprayed with 10, 15 and 20 wt% citric acid and were dried in an oven at 103 °C for 3 h before subjected to FTIR analysis. The changes in peak intensity has proved the formation of ester linkages (Line 102-103). 

Comment 5: Line 200: It should be lower WA24h. Could authors provide photos or images for CA10 and CA15 before and after water soaking for 24h?

√ The photo has been provided as in Figure 2 (Line 204-210).  

Comment 5: Lines 241-242: Since the rubberwood (RW) particles were dried to 3% moisture content at 103 ± 2 °C prior to particleboard fabrication, what is the meaning of pre-drying?

√ The meaning of pre-drying has been added (Line 275-278).    

Comment 6: Lines 253-254: I am confused, should less weight loss indicate better resistance?

√ Yes, thank you very much for pointed it out, we have revised it (Line 292).    

Comment 7: Figures 2 and 4: Scale bar should be provided.

√ We are sorry that we don’t have the scale bar when we take the photo of the samples. The samples have already been discarded. To make up for that, we indicate the size of the samples so that the readers are able to get a better image on the dimensions of the photo (Figure 3 and 5).

Reviewer 2 Report

Physico-mechanical and biological durability of citric acid-bonded rubberwood particleboard

Zhou Huaxu, Lee Seng Hua1, Paridah Md Tahir, Zaidon Ashaari, Syeed SaifulAzry Osman Al-Edrus, Nor Azowa Ibrahim and Siti Fatahiyah Mohamad

The overall assessment of work.

The authors decided to evaluate the effects of different citric acid content on rubberwood particleboard's physico-mechanical and biological durability. Citric acid bonded particleboard had inferior physical properties like water absorption and thickness swelling. Mechanical properties like internal bonding strength, modulus of rupture and modulus of elasticity compared to UF-bonded particleboard. The authors concluded that citric acid is a suitable green binder for particleboard. However, some improvement is needed during the particleboard production process.

Specific remarks:

• 67-69:. The work's aim is laconic and sounds more like the goal of an expert opinion than a scientific work. I propose to formulate a research hypothesis and then present the cognitive goal of scientific work.
• 190-202, 206-220:. The authors should clearly explain why citric acid bonded particleboard characterized significantly higher WA and TS than that of control particleboard.
• 206-207:. Should be Table 1
• 222-242:. The density of the new chipboards is similar (not much higher) to the reference boards. So why does the use of citric acid reduce strength (MOR) and stiffness (MOE)? Does citric acid corrode wood? Does it reduce adhesion forces?
• Conclusions correspond to the scope of the work. But some sentences (conclusions) seem speculative because not come from the research investigations. Therefore, the fragment 317-319 can be treated as a suggestion for further research. However, they propose to use it in the introduction to a new publication.

The work is interesting, new, cognitive, and after minor improvements, suitable for publication.

Author Response

Reviewer 2

Physico-mechanical and biological durability of citric acid-bonded rubberwood particleboard

Zhou Huaxu, Lee Seng Hua, Paridah Md Tahir, Zaidon Ashaari, Syeed SaifulAzry Osman Al-Edrus, Nor Azowa Ibrahim and Siti Fatahiyah Mohamad

The overall assessment of work.

The authors decided to evaluate the effects of different citric acid content on rubberwood particleboard's physico-mechanical and biological durability. Citric acid bonded particleboard had inferior physical properties like water absorption and thickness swelling. Mechanical properties like internal bonding strength, modulus of rupture and modulus of elasticity compared to UF-bonded particleboard. The authors concluded that citric acid is a suitable green binder for particleboard. However, some improvement is needed during the particleboard production process.

Specific remarks:

Comment 1 : 67-69:. The work's aim is laconic and sounds more like the goal of an expert opinion than a scientific work. I propose to formulate a research hypothesis and then present the cognitive goal of scientific work.

√ Research hypothesis has been added (Line 67-74).  

Comment 2 :190-202, 206-220:. The authors should clearly explain why citric acid bonded particleboard characterized significantly higher WA and TS than that of control particleboard.

√ Explanation to the findings has been added to the text (Line 243-247).

Comment 3 : 206-207:. Should be Table 1

√ It has been revised to Table 1 (Line 229).  

Comment 4 : 222-242:. The density of the new chipboards is similar (not much higher) to the reference boards. So why does the use of citric acid reduce strength (MOR) and stiffness (MOE)? Does citric acid corrode wood? Does it reduce adhesion forces?

√ Explanation of the findings has been added to the text (Line 271-273).

Comment 5 : Conclusions correspond to the scope of the work. But some sentences (conclusions) seem speculative because not come from the research investigations. Therefore, the fragment 317-319 can be treated as a suggestion for further research. However, they propose to use it in the introduction to a new publication.

√ The conclusion has been revised (Line 354-360).  

Comment 6 : The work is interesting, new, cognitive, and after minor improvements, suitable for publication.

Round 2

Reviewer 1 Report

The manuscript has been properly revised. My further comments are listed below:

1. Some typos, such as 700 kg/m3 in abstract, the number 3 should be superscript; also, 340 × 340 × 12 mm should be 340 mm× 340 mm× 12 mm. Please check the whole text to correct these typos.
2. Line 188-189: The authors state that the peak at 1200/cm increases at higher CA content. In my opinion, we could compare the relative intensity changes of two peaks, or the peak intensity should be compared based on external or internal standard peak. The authors should provide extra evidence for this statement.
3. Line 205-210: If some particles fall off, the WA values would be meaningless without considering these falling parts. I would suggest to leave these values blank in the tables.
4. When CA content is higher than 20%, I am wondering that why moisture becomes too significant to form a particle board with good structural integrity?
5. It is better to include the requirements included in JIS A 5908 to understand the advantages, shortages and further improvements of CA bonded particle boards.

Author Response

Reviewer 1

1. Some typos, such as 700 kg/m3 in abstract, the number 3 should be superscript; also, 340 × 340 × 12 mm should be 340 mm× 340 mm× 12 mm. Please check the whole text to correct these typos.

√ We have checked the entire manuscript carefully and corrected all the typos.   

2. Line 188-189: The authors state that the peak at 1200/cm increases at higher CA content. In my opinion, we could compare the relative intensity changes of two peaks, or the peak intensity should be compared based on external or internal standard peak. The authors should provide extra evidence for this statement.

√ Internal standard where peak ratio approach has been used to normalized the spectra (Figure 1). The observation was made based on the change of peak intensity and the relevant text has been revised (Line 187-189).

3. Line 205-210: If some particles fall off, the WA values would be meaningless without considering these falling parts. I would suggest to leave these values blank in the tables.

√ We have put the word “disintegrate” in Table 1 and we have revised the relevant text that describing this finding (Line 203-205).

4. When CA content is higher than 20%, I am wondering that why moisture becomes too significant to form a particle board with good structural integrity?

√ For every boards, we used 1000 g of oven-dried rubberwood particles. For CA content of 10% (60% solid content), 166.67 g CA solution is needed. For 15% and 20% CA content, the amount needed is 250 g and 333.33 g.

That said, for every increment of 5% CA, an additional of 83.33 g CA solution is required and that is a significant amount of water incorporated into the particles during blending process. 

5. It is better to include the requirements included in JIS A 5908 to understand the advantages, shortages and further improvements of CA bonded particle boards.

√ The requirements stipulated in JIS A 5908 has been mention in the text for comparison to the obtained results. Further improvement has also been suggested (Line 230-231, Line 247-248, Line 253-256 & Line 348-351).   

Author Response File: Author Response.docx