PONE-D-19-35172

Properties of Wood Composite Plastics Made from Predominant Low Density Polyethylene (LDPE) Plastics and Their Degradability in Nature

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Reviewer #1: No

Reviewer #2: Yes

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Reviewer #1: No

Reviewer #2: Yes

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Reviewer #1: No

Reviewer #2: Yes

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Reviewer #2: No

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: While variation of WF content is linear, variation of properties is not linear; this aspect is not discussed. Authors marginally discussed about extractives from wood dissolved in solvent and then dispersed in PE matrix. Therefore the final WPC material consists of PE matrix, dispersed WF particles and dispersed extractives from WPC. Actually the presence of extractives dispersed in PE is the key factor in this system, since this strongly affect the properties of final material. Therefore, a complete study should consist of four types of samples: 1) PE alone; 2) PE and extractives only (WF in xylene until complete extraction – residual WF in new xylene shows no coloration – , filtration, PE in xylene containing extractives); 3) PE and residual WF (PE and WF remained after complete extraction from sample 2; 4) PE and WF (samples presented in this paper). Analysis of extractives in xylene is needed (e.g. FTIR). Careful language check is absolutely needed.

- Materials: sieved sawdust is wood particulates, not wood fibers.

- Dissolution/re-precipitation technique: Dissolution temperature (115 oC) is close to boiling point of xylene (144 oC); how was evaporation of xylene avoided, in order to maintain the 1:20 ratio? What was the mixing time after addition of WF? How was the liquid mixture transformed into pellets?

- Composite processing: Weight of 15 kg is for entire surface of the board? This is much lower than 30 kgf/cm2 for hot press. Why is cold press used after hot press?

- Physical properties: How many samples have been tested in order to perform statistical analysis? Moisture content depends on the storage conditions, since just after preparing moisture content is virtually zero. Therefore, without describing storage conditions, moisture content is meaningless. Considering the strong hydrophobicity of PE, major component, swelling, if any, might occur only at the margins of the specimen, therefore dimensional change will manifest mainly at the margins, and less inside; was this considered? Thickness of specimens was not mentioned. Figure 1: Why 90:10 mixture had highest density? Agglomeration of WF, as described by authors, is expected since no compatibilizer was used. Final material has low homogeneity thus large variation in properties, which can induce misleading interpretation of results, and made them unsuitable for practical purpose. What means a, b, c, d in Figure 2 and Figure 3? Why 90:10 mixture had highest swelling and water absorption at 2 hours since it also had highest density?

- Mechanical testing: Size of specimens or standard used is not mentioned. Without using PE alone as references, discussion on addition of WF is meaningless. Replace OF with OR in “Bending strength of modulus of rupture”. Which parameter is “MOE strength”? Should be either MOE, either strength. Delete “dimensions” from were determined in “mm dimensions”. Please introduce values of MOE and MOR for neat LDPE in Figures 5 and 6. What type of device has been used for internal bond (IB) testing? Please specify if bending tests were performed on vertical or horizontal position of the samples.

- Degradation: Without describing the exposure condition (e.g. sample size/mass, soil temperature, humidity, pH, graveyard test is meaningless). Since adding WF could increase degradability of plastics, PE alone should be considered as reference, for all tests, as in Figure 9. How many samples have been buried in the soil for degradation testing?What means the values in brackets in Table 3? Why the 90:10 mixture had highest mass loss? Please provide a reference for equation 8 and upgrade the reference Hunter Lab. 2008 (is just direct link to Hunter Lab webpage) – e.g. https://support.hunterlab.com/hc/en-us/article_attachments/201439655/an07_96a.pdf

Table 4: It is not clear what is the reference sample in color analysis. Change in colour could be only an effect of leaching the extractives into soil, not of degradation of WF itself. From all information that DTA analysis can provide, it is not clear what is the meaning of temperature in Table 5. The values are by far over the alteration of crystalline structure of PE or melting. They are in the range of thermal degradation, which is a complex process, especially in the case of WF, therefore careful interpretation is needed. DTA curves should be given. Figure 11: Normaly, preparation of WPC should assure that xylene solvent is totally removed from the system. Replace ENCAPSULATED with INCORPORATED in “…termites have no choice in feed sources except from wood sawdust particles encapsulated in the matrix plastics in WPC systems. Authors mentioned “acclimatization to the termite was conducted for 10 days after collecting termites from the native habitat.”, but how long were the termites in contact with WPC samples?

Reviewer #2: Dear Editor,

The paper is related to “Properties of Wood Composite Plastics Made from Predominant Low Density Polyethylene (LDPE) Plastics and Their Degradability in Nature”. The paper fits within the scope of the journal. I think the contribution of the data in the article to the research community will be limited. The study has to go under major language sub editing. Work can be published after language editing.

Best regards.

Assistant Professor Dr.Timucin BARDAK

Bartin University

Furniture and Decoration Program, Bartin Vocational School,

74000, Bartin - Turkey

E-mail: timucinb@bartin.edu.tr

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Reviewer #1: No

Reviewer #2: No

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Properties of Wood Composite Plastics Made from Predominant Low Density Polyethylene (LDPE) Plastics and Their Degradability in Nat ure

PONE-D-19-35172R1

Dear Dr. Nuryawan,

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Kind regards,

Deniz Aydemir, PhD

Academic Editor

PLOS ONE

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