Review Reports - Drag Reduction Performance and Mechanism of Hydrophobic Polymers in Fresh Water and Brine

Round 1

Reviewer 1 Report

The manuscript by Tan et al. entitled "drag reduction performance and mechanism of hydrophobic polymers in fresh water and brine" describes the use of three synthetic polymers as drag reducers under various conditions. The work is somehow interesting but would benefit from the addition of tables to summarise the content.

The manuscript is overall easy to read, with only minor spell checks needed. The introduction is interesteing and sets up well the field and the challenges.

The authors do not discuss why they have chosen these quantities of the different monomers. Indeed there is no "synthesis" section in the "results and discussion" section.

The proton NMR characterisation does not seem accurate nor complete. For example, protons d should not be a triplet as written in Figure 2, as they do not have any proton neighbours. These same protons are also expected to have the same chemical shift than protons d' and d'', which is not the case at the moment. All the signals above 5 ppm are not assigned for PHWAM-2 and PHWAM-3. This is missing.

Regarding the characterisation of the polymers, have the authors been able to do some size exclusion chromatography to determine the dispersity of their materials. How such a dispersity would affect the rheological properties.

Do the authors expect 100% of the monomers to react? Can the conversion be monitored? Are there the same ratios as in the starting monomers?

All the DR sections could benefit from having a table to summarise the main results. This is nicely done in the conclusion but it would increase the readibility of the paper if it was also done in the resuls/discussion section.

Figure 5a: I believe the polymer used should be PHWAM-1.

The references do not seem to have been formatted as they should. The style is inconsistent as well as the information provided.

Author Response

(1)The work is somehow interesting but would benefit from the addition of tables to summarise the content.

Reply: In the description of the last part of the paper, we mainly explained the reasons for the different DR characteristics of three different drag reducers with different molecular structures that can be shown by corresponding DR curves, so there is no table in the first half of this paper to show the corresponding content. In the second half of this paper, we supplemented the corresponding tables to compare the impact data of inorganic salt on DR when we analyzed the performance of inorganic salt ions on drag reducers.

(2) The manuscript is overall easy to read, with only minor spell checks needed. The introduction is interesting and sets up well the field and the challenges.

Reply: Some errors on language and spell were revised.

(3) The authors do not discuss why they have chosen these quantities of the different monomers. Indeed there is no "synthesis" section in the "results and discussion" section.

Reply: It wasn’t described in this paper that the amount of monomers in the process of polymer synthesis was the best proportion. In fact, in the long-term study of the polymerization, we found that the best reaction ratio differs from different monomers. Thus we adopted the same molar ratio of monomers in order to control the initial reaction conditions.

(4) The proton NMR characterisation does not seem accurate nor complete. For example, protons d should not be a triplet as written in Figure 2, as they do not have any proton neighbours. These same protons are also expected to have the same chemical shift than protons d' and d'', which is not the case at the moment. All the signals above 5 ppm are not assigned for PHWAM-2 and PHWAM-3. This is missing.

Reply: The chemical shift of proton d has been revised in Figure 2, as we agree with that these same protons have same chemical shift. Besides, δ3.79 ppm for ethanol solvent peak. All the signals above 5 ppm for unreacted hydrophobic monomer proton peak and other impurities.

(5) Regarding the characterisation of the polymers, have the authors been able to do some size exclusion chromatography to determine the dispersity of their materials. How such a dispersity would affect the rheological properties.

Reply: It is very meaningful to comment on the reviewer's suggestions for describing the dispersion of polymers drag reducers. However, we regret that we can’t do this experiment now due to the impact of the recent epidemic, but we will accept your suggestions in the next work.

(6) Do the authors expect 100% of the monomers to react? Can the conversion be monitored? Are there the same ratios as in the starting monomers?

Reply: We have measured monomers conversion of these inverse emulsion polymerizations. These polymers were weighed after the emulsion was repeatedly soaked in ethanol solvent and dried in a vacuum box. and monomers conversion of the inverse emulsion polymerization was calculated by comparing the dosages of initial monomers. The results showed that monomers conversion of the three polymerization reactions were 97.8%,93.3%, 91.8% respectively.

(7) All the DR sections could benefit from having a table to summarise the main results. This is nicely done in the conclusion but it would increase the readibility of the paper if it was also done in the results/discussion section.

Reply: In order to express the effect of Ca²⁺ and Mg²⁺ on drag reducer, two tables are used to describe the drag reduction results of samples under different conditions.

(8) Figure 5a: I believe the polymer used should be PHWAM-1.

Reply: Figure 5a is used to describe DR mechanism of the polymer without a hydrophobic group, as the polymer in PHWAM-1 reducer.

(9) The references do not seem to have been formatted as they should. The style is inconsistent as well as the information provided.

Reply: several errors on reference section were revised to stay same style as well as the information provided.

Reviewer 2 Report

The work by Tan et al. analyzes the synthesis and performance of different drag reducers. The work os detailed and the results seem to be sound. However, the work is presented in such a way that makes it difficult to follow. Author should address the following aspects:

-authors should present the polymerization method in a clearer and concise way

-a short scheme including the characteristics of the samples studied will help on the understanding the work.

-authors claim that they use Dynamic light scattering for the characterization of the emulsions. However, no information about the characteristics of the samples are included.

-the discussion should be made in a more concise way, authors present manu data and in many cases it is difficult to follow

Author Response

-authors should present the polymerization method in a clearer and concise way.

Reply: The newly added Table 1 has been used to summarize the polymerization test scheme more succinctly.

Table 1. the synthetic scheme of drag reducers.

Samples	Water Phase (110 g, pH=7)						Oil Phase (110 g, HLB=6)
Samples	AM (mol)	AA (mol)	AMPS (mol)	C¹²AM (mol)	DiC¹²AM (mol)	SDS (mol)	White Oil (g)	Tween-60 (g)	Span-80 (g)
PHWAM-1	0.4	0.14	0.03	\	\	0.01	100	1.6	8.4
PHWAM-2	0.4	0.14	0.03	0.001	\	0.01	100	1.6	8.4
PHWAM-3	0.4	0.14	0.03	\	0.001	0.01	100	1.6	8.4

-a short scheme including the characteristics of the samples studied will help on the understanding the work.

Reply: The newly added Table 1 has been used to summarize the similar physical characteristics of some three drag reducers.

Table 2. The characteristics of the drag reducers samples.

Samples	Intrinsic Viscosity (mPa·s)	Solid Content (%)	Stability coefficient
PHWAM-1	16.6	20.0	0.91
PHWAM-2	15.6	19.1	0.87
PHWAM-3	15.4	18.9	0.84

-authors claim that they use Dynamic light scattering for the characterization of the emulsions. However, no information about the characteristics of the samples are included.

Reply: The purpose of DLS is to prove that DR performance of polymers in drag reducers in clear water or salt water differs from molecular chain morphology in aqueous solution, and the different polymer molecular structures in three drag reducers in salt water have different DR performance. Therefore, DLS is only the theoretical basis for Figure 10.

-the discussion should be made in a more concise way, authors present manu data and in many cases it is difficult to follow

Reply: Some tables has been added to describe the data of discussion in more detail, for example, the newly added Table 3 and 4 were used to briefly summarize the effect of high valence inorganic salt on drag reducers, making the data clearer.

Author Response File: Author Response.docx