Application of Polyvinyl Acetate/Lignin Copolymer as Bio-Based Coating Material and Its Effects on Paper Properties

Round 1

Reviewer 1 Report

Please take into consideration the recommendations from the attached file.

Comments for author File: Comments.pdf

Author Response

Response to the reviewer: 1

Response summary: We have to thank the reviewer for the valuable comments on our manuscript; your super detailed comments and suggestions are constructive in improving our manuscript. Hence, based on the significant suggestions, we have corrected all typing mistake, The abstract was re-editing to be clear and understandable for readers. In the same way, the introduction was also enhanced, and all the mistakes which were mention have been amended. Thanks again and hope our responses to your comment are satisfactory.

1. Overall, the abstract is not clear, please try to rearrange the sentences and be careful to typographical and grammatical errors, e.g.: Lignin is an organic waste of pulp and paper industries was used to enhance polyvinyl acetate properties via copolymerized technique by adding a varying amount of lignin, viz. 5%, 10%, 15% and 20%.

Response: thank you so much for pointed this out. So, The abstract was re-editing to be clear and understandable for readers. Hopefully, the amended abstract is acceptable.

Abstract: In this work, lignin-vinyl acetate copolymers containing different fractions of lignin was synthesized by copolymerization technique. The synthesized copolymer was successfully applied to coat the paper for enhancing its properties and performance. The effects of the lignin-vinyl acetate copolymer on the physicochemical, air permeability, and mechanical properties of paper were investigated. The mechanical strength, hydrophilic, and air permeability properties of coated paper were improved with the increasing content of the lignin. Lignin-vinyl acetate copolymer containing 15% lignin coated paper exhibited a 1.86 times increase in the tensile index, 45 times increase in the water contact angle, and a 41.1% reduction in the air permeability compared with uncoated paper. Scanning electron microscopy was applied to study the morphology of the coated and uncoated paper. The results showed that paper surface porosity structure was decreased, while the surface smoothness was enhanced, considerably with increasing lignin fraction in the copolymer. Therefore, the successful fabrication of such an enchanting coated paper may afford new potential and great applications in the packaging paper.

 

2. There is a lot of textbook/Wikipedia-style writing. The information is enumerated in sentences that are not connected. The text is confusing to readers. Please reorganize the whole introduction.

Response: in this point, we in agreement that the introduction was written with some rush with multi mistakes and contraction in some sentences.  However, the introduction part has been rewritten and amended to avoid these mistakes.

3. . Lines 73-81: The authors forgot to delete the indications from the template.

Response: thanks for mention the mistake which was not intended. The missed paragraph from the template was removed.

 

 

4. Line 133: Fourier transform infrared spectrsocopy (ATR-FTIR).

Response:  the missed word (spectroscopy) was mentioned and highlighted with yellow

Fourier Transform Infrared Spectroscopy (ATR-FTIR)

5. Line 234-250: These data must be moved to section 2. Materials and Methods.

Response: The data on lines 234 – 250 were summarized and moved to the materials and methods section

The surface free energy (SFE) for coated papers was determined by measuring the contact angles (ϴ) between the solid surface (coated papers) and the test liquids, with known surface tensions (water), free surface energies of the coated papers were calculated using automatic Owens, Wendt, Rabel & Kaelble (OWRK) calculation method [22,23]. The OWRK method is the most frequently used method for the determination of SFE (γ) of polymer surfaces, along with their polar (γ ^p) and dispersive (γ^d) part. The liquid was a droplet on the surface with a volume of 1 μL. The contact angles of the droplet were captured by CCD camera and measured after the initial contact of the droplet with the surface [24].

 

 

6. The manuscript needs extended proofreading because there are a lot of typographical and grammatical errors.

Response: Thank you for your sincere comments. We have carefully checked the manuscript language Word™ program. We hope that the reviewer and editorial office finds our responses satisfactory and convincing.

7. - Lines 26-27: such as repeats twice and it’s annoying; try to reformulate.

Response: the repeating of such as has been removed

8. - Line 31: use the full word for viz.

Response: the full name of viz was substituted with namely.

 , namely at molecules, fibrils, fibers, and fiber mat (paper)

9. - In subsection: 2.1. Materials the authors used different times. Please correct this aspect:

Response: all mistake in materials part

Sodium lignosulfonate was purchase from Shanghai Xushuo Biotechnology Co., Ltd. Formaldehyde was supplied by Laiyang Kangde Chemical Co., Ltd. Acetone was purchase from Yantai Far East Fine Chemical Co., Ltd. Filter paper was provided from Fushun Civil Administration Filter Paper Co., Ltd.. Whereas the vinyl chloroacetate (CVAc), vinyl acetate (VAc), diethylenetriamine (DETA), benzyl peroxide (BPO), Polyvinyl alcohol (PVA) 1799 were provided from Shanghai McLean Biotechnology Co., Ltd. Isopropanol was purchased from Tianjin Fuyu Fine Chemical Co., Ltd.

 

Author Response File: Author Response.docx

Reviewer 2 Report

Manuscript is poorly written and is filled with instrumentation data and pictures. Proper scientific explanations are necessary to support data obtained from instruments.

At least briefly discuss and specify the polymerization method from [16]. Your TGA shows onsets at 100 oC. DSC was necessary for your work to support your statement on lines 40-42.

Your statement mentioned on line 35 completely contradicts your statement on lines 40-42. Which defeats the purpose of this manuscript, indicating that your work is not anything new or a step up to what is already known in the industry.

Interestingly, there appears to be what looks like a copy paste of a review comment given to the authors previously from other reviewers ( possibly of another journal). This should not have  happened!

Author Response

Response to Reviewer 2

 

Response summary: We have to thank the reviewer for his valuable comments on our manuscript; the comments were very helpful for the sake of improving our manuscript. Based on the significant suggestions, we have carefully revised the whole manuscript in terms of language mistakes, discussion, and scientific explanation. Besides, a brief description of the preparation of the copolymers, and the DSC analysis was performed to confirm the assumption and investigate the thermal properties of coated papers. The contradiction of some sentences removed, and the originality of the manuscript was checked with a plagiarism checker software. We hope that the reviewer finds our responses satisfactory and convincing. The detailed responses to your comments are listed below:

• The manuscript is poorly written and is filled with instrumentation data and pictures. Proper scientific explanations are necessary to support data obtained from instruments.

Response: Thank you for your sincere comments, we are totally in agreement that the manuscript needs hard polishing in term of writing quality. Hence, We have carefully checked the manuscript language Word™ program. And also double-checked by a foreigner colleague.  We hope that the reviewer and editorial office finds our responses satisfactory and convincing.

• At least briefly discuss and specify the polymerization method from [16].

Response: A brief description of the preparation of copolymers was noted and highlighted with yellow.

In short, synthesis was done in two-steps; firstly, lignin-vinyl acetate monomer (LVAc) monomer was prepared by simple grafting reaction of chlorovinyl acetate with animated lignin. Secondly, as-prepared LVAc and the acetate (VAc) monomers were polymerized in different ratios for purpose of obtaining PVAc copolymer containing different fractions of lignin.

• Your TGA shows onsets at 100 ^o DSC was necessary for your work to support your statement on lines 40-42.

Response: As suggested, the DSC analysis was performed to confirm the assumption and investigate the thermal properties of coated papers.

Figure 8 shows the DSC curves of coated paper with PVAc and its copolymer containing different fractions of lignin, all these samples of coated papers displayed a well-defined glass transition (T_g). The coated paper with PVAc showed a clear T_g at 43 oC, while all the coated papers with copolymers showed an obvious increase in their T_gs which reached 56 ^oC when the fraction of lignin in the copolymer was 20%. Thus, arguably the fractions of lignin on the PVAc copolymer have a significant impact on the thermal properties of PVAc, which leads to increases in the range of enthalpy relaxation and T_gs. These increases of T_gs are attributed to the changes in the structure and crystallization behavior of the PVAc with the introduction of lignin molecules in its copolymers, as similarly reported by Nana Zhang [3]. Notably, the increase of T_g values was directly proportional to the amount of lignin fractions in the copolymers. Interestingly, the DSC results are in good agreement with those obtained by thermogravimetric analysis and the previous literature [4,5].

• Your statement mentioned on line 35 completely contradicts your statement on lines 40-42. Which defeats the purpose of this manuscript, indicating that your work is not anything new or a step up to what is already known in the industry.

Response: Thank you for pointing out this mistake. Accordingly,  the contradiction of the statement on line 35 with the statement on line 40-42 was removed.

• Interestingly, there appears to be what looks like a copy paste of a review comment given to the authors previously from other reviewers ( possibly of another journal). This should not have happened!

Response: Thank you so much we appreciate your precious comment on this point. Firstly we have to apologize for in intention mistake which was based on a lag of experiences of young researchers. However,  the originality of the manuscript was checked with a plagiarism checker software.    

 

Reviewer 3 Report

See my attached comments.

Comments for author File: Comments.pdf

Author Response

Comments:

In this paper, the authors investigated the application of polyvinyl acetate/lignin copolymer as bio-based coating material and its effects on paper properties. The effects of the polyvinyl acetate/lignin copolymer on the physicochemical, air permeability and mechanical properties of paper were studied. The authors found that the mechanical strength, hydrophilicity, and air permeability of coated paper improved with the increasing content of lignin. This paper requires major revisions before publication in Coatings.

Addition minor comments:

1. Figure 2 must-have scale bar.

Response: Thank you for your sincere comments. The scale bar has been added to the SEM photographs.

Figure 2. Electron micrographs of the surface of the blank paper (A) and coated paper with PVAc (B), and coated papers with copolymers containing different fractions of lignin (C, D, E, and F).

2. The authors used organic solvent-based coating instead of water-based coating.  Emulsified polyvinyl acetate and is commonly used in water-based adhesives and coatings. I understand that the PVAc/lignin is not water-soluble, but for application, it will be very hard to use organic solvent-based coatings in the industry. Water-based coating is cheaper and environmentally friendly.

Response: in this point, we are in agreement that, and although lignin-based copolymer is inexpensive the use of organic solvent-based coating is very hard in the industry. However, the current part of this project is being to produce lignin-based PVA polymer, which is expected to dissolve in hot water easily.

3. Why the coating was applied on only one surface side of the paper?

Response: Thank you so much. Actually, we applied coating from one side thinking for two reasons which are economical issues, and the end-use of coated paper (for food packing).

4. How the coating affects the printing quality of the paper?

Response: thank you so much for pointed this out. We didn’t investigate this yet.

5. The DSC showed two Tgs for the blends with 10, 15, and 20 wt. % lignin. The authors have not explained this important observation.

Response: Thank you so much. The changes in Tg values of the coated paper has been explained.

Figure 8 shows the DSC curves of coated paper with PVAc and its copolymer containing different fractions of lignin, all samples of coated papers displayed a well-defined glass transition (T_g). The coated paper with PVAc showed a sharp T_g at 43 ^oC, while all the coated papers with copolymers showed an obvious increase in their T_gs which reached 56 ^oC when the fraction of lignin in the copolymer was 20%. Besides, the TgS peaks became broader thanks to the introduction of the phase change component of lignin molecules. These changes referred to the segment motion of the copolymer chains restricted as a result of the interaction between the copolymer and the surface of the paper [41]. The increases of T_gs of coated paper with the copolymer are attributed to the changes in the structure and crystallization behavior of the PVAc with the introduction of lignin molecules in its copolymers, as similarly reported by Nana Zhang [4]. Notably, the increase of T_g values was directly proportional to the amount of lignin fractions in the copolymers, this is due to the lignin molecules acting crosslinker which lead to enhance the thermal stability as was suggested by Yao et.al[42], and Wang et.al [43]. Moreover, the DSC results are in good agreement with those obtained by thermogravimetric analysis (TGA) and the previous literature [5,6]. Thus, arguably the fractions of lignin on the copolymer have a significant impact on the thermal properties of PVAc, which leads to increases in the range of enthalpy relaxation and T_gs.

6. Table 2 has a very large size, bold symbols, and units that must be corrected.

Response: Thank you so much, the size of data in table 2

Coated paper	Contact angle
	θ1	θ2
0%	14.2	86.4	3.83	28.02	31.85	0.1365
5%	23.1	85	5.19	26.63	31.82	0.1948
10%	23.2	92.8	2.18	26.61	28.79	0.0818
15%	15.7	80.0	6.41	27.83	34.25	0.2305
20%	14.4	107.4	0.01	28.00	28.01	0.0005

 

Round 2

Reviewer 1 Report

The manuscript looks better now. Overall, the authors tried to address my comments and suggestions, but I think there it’s still place for improvements, so I think they should consider the following aspects:

Abstract and Introduction

1. Overall, the abstract and the introduction are better now.

Materials and Methods

2. Line 108: Please add the full name for this analysis technique: UV spectrophotometry; UV is to general.
3. Please be careful to add the full name of a word when is first used in the text and then the abbreviation. E.g. TGA, DTGA. Maybe it will be useful to add an Abbreviation section.

In general, the manuscript still needs a careful proofreading. E.g.:

- Line 53: Moreover, lignin was used to improve the physical and chemical properties of PVAc in several studies. it has been blended with PVAc in different ratios to improve UV resistance.

Author Response

Response to reviewer 1 (second round)

 

Response to the reviewer: 1

Response summary: We appreciate the reviewer for his precious comments on the second round of the manuscript. According to your suggestions, we have carefully revised the whole manuscript in terms of language mistakes and typing mistakes, and abbreviations were explained. Thanks again and hope our responses to your comment are satisfactory.

1. Overall, the abstract and the introduction are better now.

Response: Thank you for your considerations. We do believe that this progress these parts were regarding your valuable comment.

1. Line 108: Please add the full name for this analysis technique: UV spectrophotometry; UV is too general.

Response: Thank you for pointing out this misunderstandable abbreviation. Accordingly, the UV was replaced with UV spectrophotometry.

1. Please be careful to add the full name of a word when is first used in the text and then the abbreviation. E.g. TGA, DTGA. Maybe it will be useful to add an Abbreviation section.

Response: Thank you for figuring out this. Accordingly, all the abbreviations were defined well.

1. Line 53: Moreover, lignin was used to improve the physical and chemical properties of PVAc in several studies. it has been blended with PVAc in different ratios to improve UV resistance.

Response: Thank you for your sincere comments. The whole manuscript was double, and mistakes were corrected. The error in line 53 was corrected and highlighted with yellow color as seen below.

Besides, lignin has been also used to enhance the physical and chemical properties of the PVAc polymer in several studies. For example, but not limited to, it was blended with PVAc to enhance or add new properties, such as the UV resistance [6], to enhance the mechanical properties

 

 

 

Reviewer 2 Report

I admire your effort in patching the manuscript in this short time, but I personally believe it is not sufficient.  The introduction is not adequate, the manuscript needs to be prepared again to correct several errors.

Your introduction should go from general to pin-pointed discussions of the state of the art of copolymers used as paper coatings then identify what some of those commercial copolymers or products are. Then, discuss shortcomings of the available products in the industry (supported by TGA, DSC, etc). Finally, propose and discuss scientific methodology to solve the problem. The solution can only be novel not a repeat of what is already being done in the industry.  Hence, the crux of the work is, is it new? well, the introduction does not convince me otherwise.

• PVAc and corresponding copolymers are already used in the industry as paper coating additives.

For example, there are blends, cross-linked system, copolymers, etc .

• Your data for your copolymers should have been compared to a control (possibly to a well-known industrial product).
• PVAc has several thermal decomposition stages, the first occurs around 250 ^oC NOT from 35 ^oC all the way to 100 ^o You are probably seeing acetone or other residual solvent.
• The applications of such coated papers usually are under air and hence, the thermal degradation should be done under air NOT under inert atmosphere (nitrogen).
• Paper should be written again and can possibly be submitted to a calorimetric or characterization type journal.

Author Response

Response to reviewer 2 (round 2)

• I admire your effort in patching the manuscript in this short time, but I personally believe it is not sufficient.  The introduction is not adequate; the manuscript needs to be prepared again to correct several errors.

Response: Thank you so much for the compliment. The introduction was reconstructed to be clearer, detailed and the novelty and aim of this work were pointed out. Besides, the whole manuscript was double checked to avoid grammatical and spelling mistake as possible as.

• Your introduction should go from general to pin-pointed discussions of the state of the art of copolymers used as paper coatings then identify what some of those commercial copolymers or products are. Then, discuss shortcomings of the available products in the industry (supported by TGA, DSC, etc). Finally, propose and discuss the scientific methodology to solve the problem.

Response: Thank you so much, we appreciate your comments which were helped too much to increase the quality of the introduction.

• The solution can only be novel, not a repeat of what is already being done in the industry.  Hence, the crux of the work is, is it new? well, the introduction does not convince me otherwise.

Response:  The solution of PVAc-lignin copolymer consider a novel solution that applied in the field of paper coating.

• PVAc and corresponding copolymers are already used in the industry as paper coating additives. For example, there are blends, cross-linked systems, copolymers, etc .

Response:  Thank you so much for explaining this point. This part has been mentioned in the introduction and highlighted with yellow color.

• Your data for your copolymers should have been compared to a control (possibly to a well-known industrial product).

Response: In this work, we tried to investigate the possibility of the synthesized Poly(VAc-co-lignin acetate) for paper coating.  In order, the study the effect of lignin fraction on the performance of paper coating pure PVAc was used as control.

• PVAc has several thermal decomposition stages, the first occurs around 250 ^oC NOT from 35 ^oC all the way to 100 ^o You are probably seeing acetone or other residual solvents.

Response: The TGA results of blank and coated papers were rewritten in a scientific way.

The TGA and DTGA of the blank paper and coated paper with PVAc and its lignin copolymers containing different lignin concentrations were carried out to investigate the effects of coating on the thermal properties of coated papers. As shown in the TGA curves (Figure 7(a)) all samples were shown three stages of loss in weight. In the first stage, a common behavior observed for all samples is the dehydration process, in which 8 – 12 wt. % of water was removed in the temperature range between 35 °C and 130 °C. The loss of mass in this stage depends on the initial moisture content of the samples. It was observed that there was a slight decrease in the amount of loss in weight after coating the papers. Besides, the blank paper has shown the ability to absorbed more water than coated one, this possibly due to it had a more porous structure, as it was seen early in the SEM photographs. The main thermal decomposition (in the second stage) was happening at the range of 240 – 420 ^oC. The blank paper showed a narrow range of thermal decomposition with maximum degradation at thermal degradation at 391°C[1]. While the coated papers depicted a wide range of thermal decomposition and their maximum degradation temperature slightly decreased. This is due to the thermal degradation of vinyl acetate in PVAc and co-polymers take place early [2]. Besides, the presence of lignin molecules in copolymers creates a new inter-chain interaction with neighbor PVAc molecules (cross-linking) which restrict the motion of the main-chain [2,3]. Notably, the decomposition in this stage is due to the thermal-cracking reaction of C–C, and C–O–C bonds (chain scission). The last phase of thermal decomposition happened at a temperature range of 420 °C to 600 °C, unlike the blank paper, the coated papers showed a higher loss in weight. The decomposition is due to the carbonization and evaporation of some volatiles compound (CO and CO₂)[4]. Worth mention at the end of thermal degradation, the ash (carbon) content of the coated papers was higher than that of the blank paper.

• The applications of such coated papers usually are under air and hence, the thermal degradation should be done under air NOT under inert atmosphere (nitrogen).

Response: Thank you so much for this comment. I am totally agreed with your suggestion and wouldn’t mind doing it again, but unfortunately, we are on vacation till end of February (the Chinese spring holiday). 

• The paper should be written again and can possibly be submitted to a calorimetric or characterization type journal.

Response: Thank you so much, your advice is considered. In fact, this work is part of project lignin beneficiations: lignin-based monomers. We already succeed to prepare lignin-based monomers and their copolymers [5,6]. Currently, we are figuring out suitable applications for these products.

Finally hope that our responses are satisfactory.

 

1. Mousavioun, P.; Halley, P.J.; Doherty, W.O.S. Thermophysical properties and rheology of PHB/lignin blends. Industrial Crops and Products 2013, 50, 270-275, doi:10.1016/j.indcrop.2013.07.026.
2. Panesar, S.S.; Jacob, S.; Misra, M.; Mohanty, A.K. Functionalization of lignin: Fundamental studies on aqueous graft copolymerization with vinyl acetate. Industrial Crops and Products 2013, 46, 191-196, doi:https://doi.org/10.1016/j.indcrop.2012.12.031.
3. Silva, M.F.; Pineda, E.A.G.; Hechenleitner, A.A.W.; Fernandes, D.M.; Lima, M.K.; Bittencourt, P.R.S. Characterization of poly(vinyl acetate)/sugar cane bagasse lignin blends and their photochemical degradation. Journal of Thermal Analysis and Calorimetry 2011, 106, 407-413, doi:10.1007/s10973-011-1475-z.
4. Chelazzi, D.; Chevalier, A.; Pizzorusso, G.; Giorgi, R.; Menu, M.; Baglioni, P. Characterization and degradation of poly(vinyl acetate)-based adhesives for canvas paintings. Polymer Degradation and Stability 2014, 107, 314-320, doi:https://doi.org/10.1016/j.polymdegradstab.2013.12.028.
5. Zhang, N.; Wang, S.; Gibril, M.E.; Kong, F. The copolymer of polyvinyl acetate containing lignin-vinyl acetate monomer: Synthesis and characterization. European Polymer Journal 2020, 123, 109411, doi:https://doi.org/10.1016/j.eurpolymj.2019.109411.
6. Liu, P.; Zhang, N.; Yi, Y.; Gibril, M.E.; Wang, S.; Kong, F. Effect of lignin-based monomer on controlling the molecular weight and physical properties of the polyacrylonitrile/lignin copolymer. International Journal of Biological Macromolecules 2020, 164, 2312-2322, doi:https://doi.org/10.1016/j.ijbiomac.2020.08.119.