Determination of Strength Improvements in the Acacia Hybrid Through the Combination of Age Groups at the Air-Dry Conditioning Stage

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article presents the results of studies on obtaining a new wood hybrid material. The physical and mechanical properties of the material were assessed. The article lacks scientific justification for the studies conducted. The article must be radically revised in accordance with the remarks provided.

Remarks:

1. The abstract must be redone. Clearly define the problem, methods for solving the problem, why it is necessary to conduct this research.
2. Why it is necessary to conduct this research, what the problem is, indicate in the "Introduction" section.
3. Please indicate the "Objective of the work" at the end of the "1. Introduction" section.
4. How was the selection of combinations of wood age groups (7 + 10, 10 + 13 and 7 + 13 years) carried out. It is necessary to provide a justification for the choice of wood age groups. Why older wood cannot be used.
5. What is the scientific novelty of the study. What new things did the authors do? Combining different wood groups is not new.
6. What is the adhesion between different boards (between a 7-year-old board and a 10-year-old board). How was the adhesion determined? Please indicate in the text of the article.
7. How does the chemical interaction between boards (between a 7-year-old board and a 10-year-old board) occur in a hybrid.
8. It is better to combine Figure 1 and Figure 2.
9. It is necessary to provide a photograph of the joint of two boards (between a 7-year-old board and a 10-year-old board, etc.) with a higher resolution. Preferably on a microscope.
10. It is necessary to provide the values ​​of compressive strength for hybrid boards of different ages.
11. What are the values ​​of relative deformation and absolute narrowing of hybrid plank under different loads? What is the maximum value of relative and absolute deformation for hybrid boards? At what stress values ​​is it achieved?
12. It is necessary to describe in detail the technological process of obtaining hybrid material. Give the main technological parameters of the process. How do the main technological parameters of the process of obtaining the material affect its physical and mechanical properties?
13. The article lacks mathematical equations that establish fundamental connections of the conducted research. Can the authors of the article present mathematical equations describing the influence of different composition of planks on the structural parameters and properties of the obtained hybrid wooden material?
14. What bending loads (stresses) can the obtained material withstand?
15. How do temperatures (low and high) affect the physical and mechanical properties of the obtained composite material? What are the maximum low and high temperatures the developed material can withstand without changes in its structure and properties?

    16. Conclusions also need to be adjusted.

Author Response

Dear Sir / Mdm,

First of all, thank you for your comments and suggestions. Here is my answer to your comments.

The abstract must be redone. Clearly define the problem, methods for solving the problem, why it is necessary to conduct this research.

Change had been made as suggested.

Why it is necessary to conduct this research, what the problem is, indicate in the "Introduction" section.

Please indicate the "Objective of the work" at the end of the "1. Introduction" section.

Change had been made as suggested.

How was the selection of combinations of wood age groups (7 + 10, 10 + 13 and 7 + 13 years) carried out. It is necessary to provide a justification for the choice of wood age groups. Why older wood cannot be used.

It has been stated that 7 years as a juvenile wood, 10 years are considered transitional, and 13 years are considered mature, as well as saving resources by using wood of various ages. Additional information had been put in the text where for Acacia wood, survival had been reported by Le Dinh Kha et al. (2012) to decline to 68.7% at age 9 years. In a similar study by Jusoh et al. (2017), the survival rate of Acacia hybrid decreased at the age of 10.3 years, with only 41% of the planted trees of Acacia hybrid surviving. Meanwhile, Afifi Nazeri et al. (2021) also reported that for the parent species of Acacia hybrid, the survival rate on the 12.7-year-old stand was only 27.4%, and they concluded that the survival rate and stem density decreased as stand age increased due to environmental impact.

 

What is the scientific novelty of the study. What new things did the authors do? Combining different wood groups is not new.

Although the use of age group combination techniques in laminated wood products is not an entirely new approach in the field of wood technology, this study introduces several significant original contributions in the context of local hybrid species. First, this study is among the first efforts to conduct a comprehensive quantitative assessment of specific age combinations of Acacia hybrid wood, namely 7, 10 and 13 years, in laminated form. This approach enables a deeper understanding of the physical and mechanical interactions between juvenile and mature wood in various configurations.

Second, this study stands out in terms of the depth of statistical analysis used. In addition to analysis of variance (ANOVA) to identify significant differences between age groups, a complementary approach using the Garrett rank method was applied to evaluate the composite performance holistically. The use of this combination of statistical methods provides greater accuracy and transparency in interpreting the relative strength between age variants.

Finally, a significant contribution of this study is the proposed strength classification for Acacia hybrid wood, based on the mechanical test results obtained. Currently, there is no formal classification for Acacia hybrid species in the Malaysian standard MS544:2017. This study suggests that laminated timber of a combined age of 10+13 years can be classified under strength group SG5 based on the obtained parallel compressive strength and modulus of rupture (MOR) values. This proposal presents a preliminary database that can be used for consideration in the classification of national standards.

What is the adhesion between different boards (between a 7-year-old board and a 10-year-old board). How was the adhesion determined? Please indicate in the text of the article.

How does the chemical interaction between boards (between a 7-year-old board and a 10-year-old board) occur in a hybrid.

This study did not conduct adhesion and chemical study because it is a constant variable in this study, and the preparation of the sample is according to the American Society for Testing and Materials (1999) Standard Specification for Adhesive Used for Laminate Joints in Non-structural Lumber Products, and Japanese Agricultural Standards (2003), MAFF, Notification No. 234 Japanese Agricultural Standard for Glued Laminated Timber.

 

It is better to combine Figure 1 and Figure 2.

Change had been made as suggested.

 

It is necessary to provide a photograph of the joint of two boards (between a 7-year-old board and a 10-year-old board, etc.) with a higher resolution. Preferably on a microscope.

I would like to thank you for your suggestion for microscope images of 7 and 10-year-old wood joints. However, I would like to inform you that these images are not available at this time. The sample is not broad, but it is a small clear stick sample.

 

It is necessary to provide the values ​​of compressive strength for hybrid boards of different ages

It is provided in full in Table 7.

 

What are the values ​​of relative deformation and absolute narrowing of hybrid plank under different loads? What is the maximum value of relative and absolute deformation for hybrid boards? At what stress values ​​is it achieved?

The answers were translated into MOR, MOE and compression values.

 

It is necessary to describe in detail the technological process of obtaining hybrid material. Give the main technological parameters of the process. How do the main technological parameters of the process of obtaining the material affect its physical and mechanical properties?

It has been well described in the text under “Preparation of Material”.

 

The article lacks mathematical equations that establish fundamental connections of the conducted research. Can the authors of the article present mathematical equations describing the influence of different composition of planks on the structural parameters and properties of the obtained hybrid wooden material?

Regression analysis was also carried out to analyse the data to see if there is any correlation and to generate mathematical equations.

What bending loads (stresses) can the obtained material withstand?

Already provided in MOR form in the text.

 

How do temperatures (low and high) affect the physical and mechanical properties of the obtained composite material? What are the maximum low and high temperatures the developed material can withstand without changes in its structure and properties?

Sorry, this sample is not prepared in composite material; it is prepared as a glue-laminated timber (glulam) product from a small clear stick sample. Low or high temperature effects are not carried out in this study.

 

Conclusions also need to be adjusted.

Change had been made as suggested.

 

Reviewer 2 Report

Comments and Suggestions for Authors

Line 31 – what is basic density in terms of physical properties of wood?

Line 32 – “7+10-year-old specimens etc.“ not very neat way to describe a series of samples

Lines 56-57 – the sentence is debatable

Lines 53-75 - Text includes several general statements about engineered wood products (EWP), but it lacks some important elements that would provide a more complete and informative overview. Below are the main points that are currently missing or could be expanded:

1. Although glulam is mentioned, there’s no broader overview of different types of EWP.
2. Limited discussion of EWP applications (other than glulam)
3. No mention of limitations or drawbacks of EWP
4. Lack of data or quantitative comparisons – wood vs EWP

Lines 76-88 – not relevant to the topic

Line 109 -  The assumption that combining timber from trees of different ages enhances the mechanical strength of a composite raises some important questions. It is not immediately clear whether this effect is truly attributable to the age diversity of the raw material. An alternative explanation could be that the mechanical enhancement observed is primarily due to the contribution of the adhesive layers, which act as reinforcement zones within the structure.

Line 122- Dry – means at 0% MC?

Line 156 – how long this process lasted?

Figure 1 – Is it truly necessary?

Figure 3 – “Samples were sorted/visually graded” – Was this a binary (0/1) sorting method, or was there a classification into quality grades? How was this taken into account in the preparation of the samples and the definition of the experimental variants? To assess the methodological rigor, it would be helpful to clarify whether the timber was sorted using a simple accept/reject (binary) approach, or if it was categorized into quality classes based on specific grading criteria (e.g., visual grading, density, knots, or mechanical properties). Additionally: How these quality levels influenced the grouping of material for composite production. Whether the sorting/classification affected the allocation of timber to different variants. If and how this classification was statistically accounted for in the analysis. Understanding this is crucial for evaluating the consistency and comparability of the sample sets used in the experiments.

Line 217 – what defects were taken into account ?

Line 267 - order of presentation of results should be in line with the methodology

Line 268 – statistical analysis was performed in any software? It is a methodology and should be moved into this section

Line 326 – are there statistically important differences between obtained results? Please specify directly

Line 279 - I don't quite understand the need for such a long discussion of the obtained moisture results. The aim of the moisture test was to show that the moisture content of all samples is the same and lower than 19%. So, there are far-fetched considerations here about the state of fiber saturation or the effect of moisture on mature and young wood...

Line 333 – Again, are there statistically important differences in mean values?

Lines 361- 365 - completely unnecessary information

Do you plan to test other age combinations or include older trees (e.g., 15+ years) to see if there's an upper performance threshold?

Will future research investigate long-term durability, creep, or bonding performance of these age-mixed composites under real-life environmental conditions?

Have you considered evaluating other properties, such as dimensional stability, swelling/shrinkage, or resistance to biological degradation?

Author Response

Dear Sir / Mdm,

First of all, thank you for your comments and suggestions. Here is my answer to your comments.

Line 31 – what is basic density in terms of physical properties of wood?

For Acacia hybrid, basic density is around 0.40 - 0.65 g/cm³

 

Line 32 – “7+10-year-old specimens etc.“ not very neat way to describe a series of samples

Change had been made as suggested.

 

Lines 56-57 – the sentence is debatable

Change had been made as suggested.

 

Lines 53-75 - Text includes several general statements about engineered wood products (EWP), but it lacks some important elements that would provide a more complete and informative overview. Below are the main points that are currently missing or could be expanded:

1. Although glulamis mentioned, there’s no broader overview of different types of EWP.
2. Limited discussion of EWP applications (other than glulam)
3. No mention of limitations or drawbacks of EWP
4. Lack of data or quantitative comparisons – wood vs EWP

Change had been made as suggested.

 

Lines 76-88 – not relevant to the topic

Change had been made as suggested.

 

Line 109 -  The assumption that combining timber from trees of different ages enhances the mechanical strength of a composite raises some important questions. It is not immediately clear whether this effect is truly attributable to the age diversity of the raw material. An alternative explanation could be that the mechanical enhancement observed is primarily due to the contribution of the adhesive layers, which act as reinforcement zones within the structure.

This has been explained in the findings of the research.

 

Line 122- Dry – means at 0% MC?

In this study, the moisture content was < 12% based on one year of drying. A zero MC value can only be achieved by oven drying and is not practical in real applications.

 

Line 156 – how long this process lasted?

The total time from cutting to testing is approximately 12 months (natural drying), 24 hours of lamination pressure, and 7 days of glue curing. More than 1 year.

 

Figure 1 – Is it truly necessary?

Yes.

Figure 3 – “Samples were sorted/visually graded” – Was this a binary (0/1) sorting method, or was there a classification into quality grades? How was this taken into account in the preparation of the samples and the definition of the experimental variants? To assess the methodological rigor, it would be helpful to clarify whether the timber was sorted using a simple accept/reject (binary) approach, or if it was categorized into quality classes based on specific grading criteria (e.g., visual grading, density, knots, or mechanical properties). Additionally: How these quality levels influenced the grouping of material for composite production. Whether the sorting/classification affected the allocation of timber to different variants. If and how this classification was statistically accounted for in the analysis. Understanding this is crucial for evaluating the consistency and comparability of the sample sets used in the experiments.

Preparation of materials is strictly according to Testing Methods for Plantation Grown Tropical Timbers.  ITTO Project on Improving Utilisation and Value Adding of Plantation Timbers from Sustainable Sources in Malaysia; FRIM[26], Methods of Testing Small Clear Specimens of Timber, BS 373:1957 [27], and ASTM International. Standard Test Methods for Small Clear Specimens of Timber, ASTM D143-14.

 

Line 217 – what defects were taken into account ?

Referring to Testing Methods for Plantation Grown Tropical Timbers [26] and to BS 373:1957 [27], where all types of defects have been ignored because the experiment was carried out using the small clear method (defect-free sample).

 

Line 267 - order of presentation of results should be in line with the methodology

Change had been made as suggested.

 

Line 268 – statistical analysis was performed in any software? It is a methodology and should be moved into this section

Change had been made as suggested.

 

Line 326 – are there statistically important differences between obtained results? Please specify directly

Change had been made as suggested.

 

Line 279 - I don't quite understand the need for such a long discussion of the obtained moisture results. The aim of the moisture test was to show that the moisture content of all samples is the same and lower than 19%. So, there are far-fetched considerations here about the state of fiber saturation or the effect of moisture on mature and young wood...

Change had been made as suggested.

 

Line 333 – Again, are there statistically important differences in mean values?

Change had been made as suggested.

 

Lines 361- 365 - completely unnecessary information

Change had been made as suggested.

 

Do you plan to test other age combinations or include older trees (e.g., 15+ years) to see if there's an upper performance threshold?

Yes, it is in our plans to conduct studies for other age combinations to gain as much research information as possible.

 

Will future research investigate long-term durability, creep, or bonding performance of these age-mixed composites under real-life environmental conditions?

Yes, it is in our plans to conduct other studies as intended.

 

Have you considered evaluating other properties, such as dimensional stability, swelling/shrinkage, or resistance to biological degradation?

We have already conducted several other studies, such as evaluating biological degradation properties, which we know as durability tests, and plan to continue with studies for other ages and species.

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Everything is fine.