Three Adhesive Recipes Based on Magnesium Lignosulfonate, Used to Manufacture Particleboards with Low Formaldehyde Emissions and Good Mechanical Properties

Round 1

Reviewer 1 Report

The authors present a mediocre study on wood-adhesives, based on magnesium lignosulfate. The research is very basic and includes only a low amount of samples which are compared without any references. Also, the language of the manuscript is not very good.

The most pressing concerns:

• Why magnesium? This is not rationalized. What are the expected advantages against e.g. ammonium linosulfate?
• The results are not compared to any references (except the one minimum value of EN312.
  • It must be shown how magnesium compares to other (already known) types.
  • It must be shown how the recipes compare to conventional systems. I suppose they are still a lot weaker unless proven otherwise.
• There is no real explanation on "why?" the cross-linked recipes are better in terms of emissions. This need to be defined and proven analytically.
• I would recommend to include a few pictures to visualize the results in a better way.

 

Concluding, I cannot recommend publication at this state.
Especially the missing reference experiments need to be conducted before a potential resubmission.

Author Response

Reviewer 1

The authors would like to thank the reviewer of the paper for his enormous work, for his detailed study of the paper and especially for his contribution to increasing the value of the work and its reading by journal readers. The authors also appreciate the pertinent observations, recommendations and conclusions made on the paper. The authors have modified profoundly the text and below are presented the basic modifications and answers:

1. Reviewer: The research is very basic and includes only a low amount of samples which are compared without any references.

Authors answer:

1. For each test and work stage the number of specimens used was specified.
2. 8 new bibliographic references were introduced, as a basis for comparison with the results of the paper. Many analyses and comparisons between the results of the paper and those of other authors have been inserted in the paper.  

    Explanations: The paper is modestly written, which is why in the following rows we try to express the enormous workload. The research contains extensive activities related to formaldehyde emissions, modulus of strength and elasticity, internal cohesion, cutting and conditioning of samples, moisture content and density, the chipboard density profile, and the particle size and granulometry of the chips. All these activities required about 25 units of equipment, tools, work devices and specialized personnel. Only the preliminary research part for the establishment of the 3 gluing recipes required the realization of over 30 boards from wood chips and other such glued test pieces in order to obtain the resistance to the gluing shear. Also, in establishing the manufacturing recipes, proportions of 10, 15, 20 and 25% lignosulfonate were used in relation to the amount of chips, finding that the value of 15% lignosulfonate is the most efficient and had acceptable physical and mechanical results (this is why the 15% lignosulphonate is used).

 

2. Reviewer: Also, the language of the manuscript is not very good.

Authors answer: Whole paper was changed. All typos from paper were eradicated. Some grammatical expressions have been completely removed and other new grammatical constructions have been introduced. See new version of paper.

 

3. Reviewer: The most pressing concerns: Why magnesium? This is not rationalized. What are the expected advantages against e.g. ammonium linosulfate?

Authors answer:

1. A lot of sentences were added. We add on page 4 the next paragraph: “There are 5 types of lignosulfonates, that are soluble in water: magnesium lignosulfonate, calcium lignosulfonate, sodium lignosulfonate, potassium lignosulfonate and ammonium lignosulfonate. They are differentiated according to the method of cellulose extraction (sulphite, kraft, basic, acid, etc.) and contain small amounts of magnesium, calcium, sodium, potassium or ammonia; the most used from them are ammonium and magnesium sulphonate with no differences on formaldehyde emission for obtained composites”;  
2. Also, for a better highlighting of the characteristics of this material, a new table was drawn up, with its features on page 4.
3. Magnesium is a good option. Magnesium is the eighth most abundant element in the Earth's crust and fourth most common element in the Earth (after iron, oxygen and silicon).

 

Mg is one of the metals with the lowest energy demand for production and generates the lowest amount of CO₂ during production (according to: https://www.eurekalert.org/news-releases/745590).

607. Low cost and eco-friendly nature of lignosulfonates have increased popularity of lignosulfonates in numerous applications, such as agriculture, animal feed, concrete additives, dust control, metallurgy, oil & mining, gypsum board, chemical processing, and others. The global lignosulfonates (sodium lignosulfonate, calcium lignosulfonate, magnesium lignosulfonate, ammonium lignosulfonate, others) market size was valued at $607.2 million in 2019 and is projected to reach $741.22 million by 2026, registering a CAGR of 2.89% from 2020 to 2026 - according to: https://www.marketresearch.com/Gen-Consulting-Company-v4078/Global-Lignosulfonates-Forecast-13122805/
608. Magnesium lignosulfonate has similar characteristics with ammonium lignosulfonate regarding: density, pH, lignosulfonates % etc. Magnesium lignosulfonate is recommended to be used as a filler and binder in ceramic tiles, resins to fiber boards, casting sand and in fodder pellets, while ammonium lignosulfonate, is mainly used agriculture as irrigation and spray fertilizer. (https://www.lignosulfonate.com/ ; https://www.chinalignin.com/products/magnesium-lignosulfonate ; https://greenagrochem.com/wp-content/uploads/2013/11/Magnesium-Lignosulfonate-Technical-Data-Sheet-1.pdf )
609. In this context, magnesium lignosulfonate was a good option for our research. There are several recent research works made with magnesium lignosulfonate for wood bio-composites manufacturing and also with ammonium (these were introduced in the paper), as can be seen below:

   -Klapiszewski, L.; Jamrozik, A.; Strzemiecka, B.; Matykiewicz, D.; Voelkel, A.; Jesionowski, T. Activation of Magnesium Lignosulfonate and Kraft Lignin: Influence on the Properties of Phenolic Resin-Based Composites for Potential Applications in Abrasive Materials. Int. J. Mol. Sci. 2017, 18, 1224

   Hu, J.-P.; Guo, M.-H. Influence of ammonium lignosulfonate on the mechanical and dimensional properties of wood fiber biocomposites reinforced with polylactic acid. Ind. Crop. Prod. 2015, 78, 48–57. [CrossRef]

   Bekhta, P.; Noshchenko, G.; Réh, R.; Kristak, L.; Sedliaˇcik, J.; Antov, P.; Mirski, R.; Savov, V. Properties of Eco-Friendly Particleboards Bonded with Lignosulfonate-Urea-Formaldehyde Adhesives and pMDI as a Crosslinker. Materials 2021, 14, 4875. https:// doi.org/10.3390/ma14174875 Magnesium lignosulfonates

   Antov, P.; Savov, V.; Krišt’ák, L’.; Réh, R.; Mantanis, G.I. Eco-Friendly, High-Density Fiberboards Bonded with Urea-Formaldehyde and Ammonium Lignosulfonate. Polymers 2021, 13, 220. [CrossRef]

   Antov, P.; Jivkov, V.; Savov, V.; Simeonova, R.; Yavorov, N. Structural Application of Eco-Friendly Composites from Recycled Wood Fibres Bonded with Magnesium Lignosulfonate. Appl. Sci. 2020, 10, 7526

   Antov, P.; Mantanis, G.I.; Savov, V. Development of Wood Composites from Recycled Fibres Bonded with Magnesium Lignosulfonate. Forests 2020, 11, 613.

   Hemmilä, H.; Adamopolus, S.; Hosseinpourpia, R.; Ahmed, S.A. Ammonium Lignosulfonate Adhesives for Particleboards with pMDI and Furfuryl Alcohol as Crosslinkers. Polymers 2019, 11, 1633

   Yuan, Y.; Guo, M.; Liu, F. Preparation and Evaluation of Green Composites Using Modified Ammonium Lignosulfonate and Polyethylenimine as a Binder. BioResources 2014, 9, 836–848

   Antov, P.; Savov, V.; Krišt’ák, L’.; Réh, R.; Mantanis, G.I. Eco-Friendly, High-Density Fiberboards Bonded with Urea-Formaldehyde and Ammonium Lignosulfonate. Polymers 2021, 13, 220.

1. Reviewer: The results are not compared to any references (except the one minimum value of EN312.

Authors answer:

1. The paper was extensively completed with many referenced comparisons, as follows.  The following new comparisons with other specialized and referenced papers have been introduced in the paper, referring to all aborded problems of paper (without the minimal value of European standard EN 312):

  -At Discussion chapter, a new paragraph was introduced referring to particle dimensions: “Referring to granulometry analysis, large differences were observed between coarse and fine particles in terms of participation rate. The participation rate analysis for particles with diverse geometry is justified by the fact that the biomass particles are mostly in inhomogeneous in terms of size and shape. As a result, two particles going through the same sieve with the same mesh size may differ in shape [17]”.

Etc.

1. Other comparisons were already in the research.   

  -At page 14: …with ultra-low formaldehyde emission, close to that of natural wood [20].

  -At page 15: the introduction of pMDI crosslinker is beneficial… [29]; …the PMDI-glucose crosslinkers combination strongly decreases formaldehyde emissions…[20]; if the length is much larger than the width and thickness [45]; a clear separation was made between the two categories of chips (coarse and fine), as other authors have specified before [44,45];

  -At page 16: Some authors [63, 64] observed that, in order to obtain high strengths, the peaks of the density profile must be around 900 kg/m³,..; Other authors [15,18] have established that the optimal density of chipboard could be 680 kg/m³; . This is given by the different standard deviation … as other authors have stated before [15];

  -At page 17: Static bending strength is…, along with internal bond [29-31]; Many studies [3,13] have shown a decrease in formaldehyde emission when using lignosulfonates ….; in order to obtain the emission class E1 [14]

Etc.    

1. Reviewer: It must be shown how magnesium compares to other (already known) types.

Authors answer:

1. At page 17 we add the next text: “Also, all research using lignosulfonates, whether based on magnesium or ammonium [25,29,33], has had a beneficial effect on reducing formaldehyde emissions from composite boards. It is shown in this way that the small differences between the two lignosulfonates, respectively percentages of less than 6% of magnesium or ammonium, do not have an influence on the formaldehyde emissions.”
2. Also, at page 4 some general aspects about lignosulphonates were aborded (see point 3)

etc.

1. Reviewer: It must be shown how the recipes compare to conventional systems. I suppose they are still a lot weaker unless proven otherwise.

Authors answer: At page 3, a new paragraph was introduced: “The most used adhesive in the boards is the urea-formaldehyde adhesive UF, it has the highest mechanical strength (well above the minimum required), which is why in the recipe of this adhesive are included fillers to reduce the costs of adhesion. This adhesive also has the highest formaldehyde emissions, requiring formaldehyde traps, which greatly increase the cost of adhesion. This is why bio-adhesives are the cheap solution to replace UF adhesive, even if the mechanical strength of the boards is weaker, but it falls within the minimum limits [10]”. 

 

1. Reviewer: There is no real explanation on "why?" the cross-linked recipes are better in terms of emissions. This need to be defined and proven analytically.

Authors answer:

     -At page 3 a new sentence was introduced. “Lignin from lignosulphonate keeps its capacity for adhesion, as the native lignin has in time of tree growth”.

Others are seen in the revised paper.

General statements: Wood is generally made up of cellulose, hemicellulose and lignin. Cellulose and hemicellulose have the role of skeleton and strength, and lignin has the role of gluing and adhesion. In the technology of cellulose, pulp and paper, wood is broken down into the two main compounds holocellulose and lignin, in order to take up cellulose for processing. It will thus remain lignin, as a by-product, maintaining its adhesion capacity under certain conditions. Other processes, such as briquetting and pelletizing of sawdust, are based directly on lignin's adhesion capacity.

 

1. Reviewer: I would recommend to include a few pictures to visualize the results in a better way.

Authors answer:

1. A new figure (Fig. 10) has been introduced, showing the flow of activities and results from the entire paper, on the base of some visual pictures. This figure was also introduced properly in the text of the research.
2. Another new figure (Fig. 11) has been introduced, showing the cross microscopic picture for the 3 experimental boards. Necessary analysis was presented.

 

1. Reviewer: Especially the missing reference experiments need to be conducted before a potential resubmission.

Authors answer: Other new 8 references were added, for a properly comparison. A lot of corelation between the results of research and other authors were made. Many referencing aspects were made in the revision paper.  As examples:

   -“Referring to granulometry analysis, large differences were observed between coarse and fine particles in terms of participation rate. The participation rate analysis for particles with diverse geometry is justified by the fact that the particles are mostly inhomogeneous in terms of size and shape. As a result, two particles going through the same sieve with the same mesh size may differ in shape [17]”.

   - “Addition of pMDI and glucose as crosslink agents, improved the internal cohesion of particles [13]”.

   -“Lower value of IB (of 0.18 N/mm² and below 0.16 N/mm²) was obtained also by Da Silva et al. [44] in case of using solely calcium and magnesium lignosulfonates as adhesives for particleboard manufacturing…”.

Authors

Author Response File: Author Response.docx

Reviewer 2 Report

Manuscript titled " Three adhesive recipes based on magnesium lignosulfonate, used to manufacture chipboards with low formaldehyde emission and good mechanical properties " has been well-written with a good scientific value. Following points can be considered to increase the readability and value of the manuscript:

1. Abstract seems to be short of few information. It can be suitably rewritten.
2. Introduction section contains sufficient literature survey results, but most of the papers are almost a decade or half-a-decade old. Authors are suggested to refer and cite some of the following recent literatures. https://www.mdpi.com/2073-4360/14/3/589, https://www.mdpi.com/1999-4907/11/6/613, https://www.mdpi.com/1999-4907/12/5/641, https://onlinelibrary.wiley.com/doi/abs/10.1002/9781119655053.ch7.
3. Kindly merge the objectives with the running text. Separate subsection can be removed.
4. It is recommended to represent the constituents of the raw materials in the form of a table. Readability of such contents in textual form is poor.
5.  All equations can be included in the manuscript through a dedicated equation typing software like MathType etc.,
6. What is unit of sieve sizes used in granulometry? Kindly mention the same.
7. There are many typos in the manuscript. Kindly eradicate them before submitting the revised version.
8. Prefixes and suffixes of most of the terms in the equation is not represented properly. Kindly check all and correct.
9. It is recommended to include the version of all the software like AutoCAD, MS Excel etc., used in the study.
10. All the graphs can be drawn in a dedicated graph drawing software for better visibility.
11. Conclusion section can be rewritten to portray the essential results of experiments.

Author Response

Reviewer 2

The authors would like to thank the reviewer of the paper for his enormous work, for his detailed study of the paper and especially for his contribution to increasing the value of the work and its reading by journal readers. The authors also appreciate the pertinent observations, recommendations and conclusions made on the paper. The authors have modified profoundly the text and below are presented the basic modifications and answers:

 

Manuscript titled " Three adhesive recipes based on magnesium lignosulfonate, used to manufacture chipboards with low formaldehyde emission and good mechanical properties " has been well-written with a good scientific value. Following points can be considered to increase the readability and value of the manuscript:

1. Abstract seems to be short of few information. It can be suitably rewritten.

Author answer: The abstract was extended, highlighting a series of technical data from the paper. In this way it expresses in more detail the content of the whole paper.

 

1. Introduction section contains sufficient literature survey results, but most of the papers are almost a decade or half-a-decade old. Authors are suggested to refer and cite some of the following recent literatures. https://www.mdpi.com/2073-4360/14/3/589 , https://www.mdpi.com/1999-4907/11/6/613 , https://www.mdpi.com/1999-4907/12/5/641 , https://onlinelibrary.wiley.com/doi/abs/10.1002/9781119655053.ch7 .

Author answer: All 4 proposed papers were introduced in the bibliography and cited accordingly in the paper. Proper repositioning of the citation numbers has been done. Moreover, 4 other new researches were also introduced in the paper.

1. Kindly merge the objectives with the running text. Separate subsection can be removed.

Author answer: The subsection of objectives was removed and became one simple paragraph of introduction chapter.

 

1. It is recommended to represent the constituents of the raw materials in the form of a table. Readability of such contents in textual form is poor.

Author answer: A new table (Table 2) was introduced. This table expresses features of magnesium lignosulphonate.

 

1.  All equations can be included in the manuscript through a dedicated equation typing software like MathType etc.,

Author answer: Initially, all the equations were made with Microsoft equation Editor, but they were changed in Word, because when editing the paper on the journal page, these equations cannot be worked and can appear in the form of photos (depending on the age of the software used) (see Instruction of authors). That's why I recommend that the equations remain in this form, so as not to have problems with the journaling page.

 

1. What is unit of sieve sizes used in granulometry? Kindly mention the same.

Author answer: Units of sieve sizes was introduced in the paper, on page 5, namely mm.

 

1. There are many typos in the manuscript. Kindly eradicate them before submitting the revised version.

Author answer: Lots of typos were eradicated. Whole paper was investigated from this point of view. Also, many grammatical constructions have been changed.

 

1. Prefixes and suffixes of most of the terms in the equation is not represented properly. Kindly check all and correct.

Author answer: All equations were checked and a lot of changes were made.

 

1. It is recommended to include the version of all the software like AutoCAD, MS Excel etc., used in the study.

Author answer: The necessary data was introduced on page 7 of statistical analysis.

 

1. All the graphs can be drawn in a dedicated graph drawing software for better visibility.

Author answer: The authors made efforts in this regard, transferring some graphs such as those from the density profile from those with poor visibility taken from the installation-machine in Microsoft Excel, for superior clarity and visibility. The diagrams made with the statistical program Minitab 18 have probably become more obscure, but this is due exclusively to the transformation of the Word document into PDF.

 

1. Conclusion section can be rewritten to portray the essential results of experiments.

Author answer: Chapter of Conclusion was rewritten, by completing it with some new aspects of research and completing others.

Authors

Author Response File: Author Response.docx