Degreasing Efficiency of Electroplating Pretreatment Process Using Secondary Alcohol Ethoxylate as Nonionic Surfactant
Round 1
Reviewer 1 Report
The ethoxylate surfactants have been known for a long time, most of the publications concerning that (web of science) have been published in the 1980s. There are also reports of the high harmfulness of these surfactants [Biodegradability and aquatic toxicity of glycoside surfactants and a nonionic alcohol ethoxylate https://doi.org/10.1007/BF02517997 ]. There are really difficult to find in this publication the arguments for usefulness of such surfactant and advantages of them, especially that their efficiency in degreasing process are not compared with standard commercial degreasing solution or even the same solution but without of ethoxylated surfactant –(NaOH present in this solution with high concentration can catalyzed hydrolysis of removing oil and theoretically in solution appear fatty acid sodium salt as good surfactants ). The results of contact angle measurements are not compared with clean steel specimen and with steel specimen totally covered by oil. I do not understand the action mechanism of insoluble surfactant. I do not see clearly why there are the comparison of surface tension of diluted solution while as surface tension of degreasing solution is the same.
Author Response
We would like to thank you for your kind comments. We carefully considered your comments and modified our manuscript accordingly. Please find our point-to-point response below. We also corrected the content following the reviewers’ comments and the revised parts are shown in blue in the manuscript.
Reviewer #1
- The ethoxylate surfactants have been known for a long time, most of the publications concerning that (web of science) have been published in the 1980s. There are also reports of the high harmfulness of these surfactants [Biodegradability and aquatic toxicity of glycoside surfactants and a nonionic alcohol ethoxylate https://doi.org/10.1007/BF02517997 ]. There are really difficult to find in this publication the arguments for usefulness of such surfactant and advantages of them, especially that their efficiency in degreasing process are not compared with standard commercial degreasing solution or even the same solution but without of ethoxylated surfactant –(NaOH present in this solution with high concentration can catalyzed hydrolysis of removing oil and theoretically in solution appear fatty acid sodium salt as good surfactants ). The results of contact angle measurements are not compared with clean steel specimen and with steel specimen totally covered by oil. I do not understand the action mechanism of insoluble surfactant. I do not see clearly why there are the comparison of surface tension of diluted solution while as surface tension of degreasing solution is the same.
Reply 1-1: Degreasing process using solution without surfactant would be prolonged for a long duration to obtain surface totally eliminated oil. In production, it is unrealistic to obtain a steel specimen without oil on surface before degreasing process. Moreover, our objective in this study was to investigate the effect of HLB and CP of surfactant on degreasing efficiency. Therefore, we do not recommend the comparison with samples relating to solution without surfactant, and steel specimen without oil.
Reviewer 2 Report
The paper has significant contribution to knowledge. However, there are some points to improve:
1. Abstract should add the research gap, objectives, and methodology
2. Eq (2) must supported by reference. It is define in line 79 ratio of hydrophilic to hydrophobic yet in Eq. (2) hydrophobic to total
3. Add characteristic and properties of cloud point in the introduction section since it does affect the results
4. add references for the time and temperature chosen (line 106) and Du Nouy Ring method (line 164)
5. The first para of section 3.1 should elaborate on the degreasing efficiency process as describe in Eq. (3)
6. Figure 1-3 should be combine as to see the comparison and the discussion should be done as a whole as temperature increases from 30-80 C. The significant findings should be highlighted rather than just re-stating the percentage variations. Why degreasing efficiency at 60 C is more optimum compare to the other temperatures? Why SE-20 perform better at higher temperature compare to lower temperature? Both HLB & CP increase with SE#
7. In sect 3.2 & 3.3, explain why comparing 40 C and 80 C are necessary?
8. Explain the behaviour of Hogaboom results differ to the degreasing efficiency, e.g. at 40 C SE7-SE20 specimens reach 100% degreasing efficiency at 5 min, however this is not reflect in hogaboom result (fig 4) for SE20; and SE20 should have better hogaboom result compare to SE3.
9. Explain why contact angle at 40C does not directly proportional to the HLB number as at 80C?
10. Similarly to the form height, why SE12 outperforms SE20?
11. the surface tension results must relate to all other results obtained in sections 3.1-3.4 and how this can help electroplating performance
12. All references are too old. References should at least 50% in the year 2018-2022.
Author Response
We would like to thank you for your kind comments. We carefully considered your comments and modified our manuscript accordingly. Please find our point-to-point response below. We also corrected the content following the reviewers’ comments and the revised parts are shown in blue in the manuscript.
Reviewer #2
- 1. Abstract should add the research gap, objectives, and methodology.
Reply 2-1: Abstract was edited as follows.
In this study, the effect of the hydrophilic–lipophilic balance (HLB) number and cloud point (CP) of a secondary-alcohol ethoxylated nonionic surfactant on the degreasing efficiency was investigated. Degreasing process was conducted for steel samples with difference surfactants in degreasing solution. The HLB number and CP increased with increasing n of the hydrophilic ethylene oxide (OCH2CH2)n group. For a constant temperature of the degreasing solution (30–80 °C), the degreasing efficiency was investigated as a function of degreasing time. The highest degreasing efficiency was observed near the cloud point of the surfactant, and the degreasing efficiency decreased significantly at temperatures lower and greater than the cloud point. Hogabom test was carried out to observe oil strain on the surface of samples. Additionally, the contact angle of surface with water droplet was measured after degreasing with various surfactants.
- Eq (2) must supported by reference. It is define in line 79 ratio of hydrophilic to hydrophobic yet in Eq. (2) hydrophobic to total.
Reply 2-2: The reference was added, and the definition was correct as below.
Several methods have since been proposed to calculate the HLB from the chemical structure of an emulsifying agent; however, the equations are all based on the proportion of hydrophilic groups that constitute the molecules of an emulsifying agent as below.
(1)
where M0 is the molecular weight of the hydrophobic portion and M is the total molecular weight [7].
- Add characteristic and properties of cloud point in the introduction section since it does affect the results.
Reply 2-3: The description was supplemented as follows.
One other critical factor affect degreasing efficiency is cloud point, which refers to the temperature transforming an isotropic micellar state into a two-phase state of surfactant solution. The cloud point of an alcohol ethoxylate is influenced by HLB, the number of ethylene oxide, and hydration state [17].
- 4.add references for the time and temperature chosen (line 106) and Du Nouy Ring method (line 164).
Reply 2-4: References were added.
- The first para of section 3.1 should elaborate on the degreasing efficiency process as describe in Eq. (3).
Reply 2-5: The description was supplemented as follow.
Using the variation of samples before and after degreasing, the degreasing efficiency was calculated by equation 3 as mentioned in Section 2.2.
- Figure 1-3 should be combine as to see the comparison and the discussion should be done as a whole as temperature increases from 30-80 C. The significant findings should be highlighted rather than just re-stating the percentage variations. Why degreasing efficiency at 60 C is more optimum compare to the other temperatures? Why SE-20 perform better at higher temperature compare to lower temperature? Both HLB & CP increase with SE#.
Reply 2-6: The significant findings were mentioned as follows.
Figure 1: Apparently, the degreasing efficiency increased along with the extension of duration.
Figure 2: Overall, when the temperature increased over 50 °C, the degreasing efficiency significantly increased for all surfactants, and reached maximum after 2 min.
Figure 3: It could be observed that the degreasing efficiency was reduced for SE-3, 7, 9, and 12 as the temperature was above CP of these surfactants. Moreover, the degreasing efficiency could achieve maximum value at 1 min due to the activation at high temperature.
The explanation was supplemented as below.
The reason for the differences in the degreasing efficiency between the degreasing solution temperatures was related to the CP. A nonionic surfactant becomes soluble when hydration occurs at the oxygen position of ether groups bonded to the EO chain, which is a hydrophilic group. The number of ether bonds increases as the length of the EO chain increases; therefore, the solubility in water improves as the degree of hydration increases. Precipitation occurs at the Krafft point related to the hydrophobic part of surfactant molecule, and at the cloud point system which separates into a concentrated and dilute surfactant phase. The temperature at which emulsification occurs is referred to CP, where the CP of nonionic surfactants is higher because the percentage of hydrophilic part CP is higher [14]. The degreasing efficiency decreases at temperatures above the CP as the solubility of the surfactants in water is reduced, while it is optimal when temperature approach the CP. Therefore, temperatures of 50 and 60 °C yielded higher degreasing efficiency than temperatures of 30 and 40 °C, as these temperatures was closer to CP of most surfactants, except SE-3.
- In sect 3.2 & 3.3, explain why comparing 40 C and 80 C are necessary?
Reply 2-7: The explanation was supplemented as below.
The Hogaboom test was conducted at 40 and 80 °C, which is represent for low and high temperature ranges.
- Explain the behaviour of Hogaboom results differ to the degreasing efficiency, e.g. at 40 C SE7-SE20 specimens reach 100% degreasing efficiency at 5 min, however this is not reflect in hogaboom result (fig 4) for SE20; and SE20 should have better hogaboom result compare to SE3.
Reply 2-8: The explanation was supplemented as below.
Although most of oil weight was removed from the surface relating to SE-20 after 5 min (Figure 1), oil stain was observed on the surface of sample after the Hogaboom test. This could be explained that the temperature of 40 °C was lower than CP of SE-20, and hence, oil stain still remained on the surface.
- Explain why contact angle at 40C does not directly proportional to the HLB number as at 80C?
Reply 2-9: The explanation was supplemented as below.
As 40 °C was close to CP of SE-7 and SE-9, the surfaces involved SE-7 and SE-9 showed better the hydrophilic property than other ones.
The surfaces involved SE-12 and SE-20 showed better the hydrophilic property than other ones, because 80 °C was near CP of these surfactants.
- Similarly to the form height, why SE12 outperforms SE20?
Reply 2-10: To the best of our knowledge, there is no relation between surfactant characteristics and foam formation. However, as mentioned in Section 3.4, the existence of foam significantly affect degreasing. Therefore, we conducted measurement of foam height to explore the optimal surfactant for foam formation. Meanwhile, higher foam height means worse degreasing efficiency. The foam height obtained by SE-12 was higher than that of SE-20. Thus, SE-12 was inferior to SE-20.
- 11.the surface tension results must relate to all other results obtained in sections 3.1-3.4 and how this can help electroplating performance
Reply 2-11: Section 3.5 about surface tension was deleted.
- All references are too old. References should at least 50% in the year 2018-2022.
Reply 2-12: References were modified as suggested
Author Response File: 
Author Response.docx
Reviewer 3 Report
Son et al. reported on the “Degreasing Efficiency of Electroplating Pretreatment Process using Secondary Alcohol Ethoxylate as Nonionic Surfactant”. The presented results are within the scope of the journal and could be of interest to the scientific community of the respective area. The presented manuscript needs improvements. The author needs to work on some aspects and areas before the manuscript is published. Some points are given below
1. Please give a clear novelty statement in the introduction section about why this work is important considering the existing study on the concerned topic.
2. In table 1 no need to write a,b,c, and d in superscript. The term itself gives clear meaning just state the abbreviations.
3. Write equation 3 in the equation writer.
4. In figures, temperature should be written within the figures rather than on the top of the figure.
5. In figure 2, a and b are explained in the caption, but it is not given in the figure. Please rewrite SE20 again in figure 2 a.
6. Maintain the harmony in figure captions either a, b, or right/ left.
7. Add some reasoning to the degreasing efficiency & Hogaboom results.
8. In figure 8 author wrote S.E.- in other figures, it is SE-. Please follow the same notation.
9. Please add some comparison at the end of the results, how and why your systems are better than others.
1The conclusion should be to the point and crisp. Please refine it.
The Paper can be published after revisions.
Author Response
We would like to thank you for your kind comments. We carefully considered your comments and modified our manuscript accordingly. Please find our point-to-point response below. We also corrected the content following the reviewers’ comments and the revised parts are shown in blue in the manuscript.
Reviewer #3
- Please give a clear novelty statement in the introduction section about why this work is important considering the existing study on the concerned topic.
Reply 3-1: The clear novelty statement was added as follow.
Many studies of the HLB of surfactants have been actively conducted in the pharmaceutical, paint, cosmetic, and food industries, but no research on HLB is sufficient in the electroplating field, especially for pretreatment process. Meanwhile, to the best of our knowledge, there has been no study focused on the influence of cloud point on degreasing efficiency.
- In table 1 no need to write a,b,c, and din superscript. The term itself gives clear meaning just state the abbreviations.
Reply 3-2: These superscripts were deleted.
- Write equation 3 in the equation writer.
Reply 3-3: Equation 3 was rewritten in equation form.
- In figures, temperature should be written within the figures rather than on the top of the figure.
Reply 3-4: Figures were edited as suggested.
- In figure 2, a and b are explained in the caption, but it is not given in the figure. Please rewrite SE20 again in figure 2 a.
Reply 3-5: Figure was edited as suggested
- Maintain the harmony in figure captions either a, b, or right/ left.
Reply 3-6: Figure captions were corrected as pointed out.
- Add some reasoning to the degreasing efficiency & Hogaboom results.
Reply 3-7: The explanation was added as follow.
The reason for the differences in the degreasing efficiency between the degreasing solution temperatures was related to the CP. A nonionic surfactant becomes soluble when hydration occurs at the oxygen position of ether groups bonded to the EO chain, which is a hydrophilic group. The number of ether bonds increases as the length of the EO chain increases; therefore, the solubility in water improves as the degree of hydration increases. Precipitation occurs at the Krafft point related to the hydrophobic part of surfactant molecule, and at the cloud point system which separates into a concentrated and dilute surfactant phase. The temperature at which emulsification occurs is referred to CP, where the CP of nonionic surfactants is higher because the percentage of hydrophilic part CP is higher [14]. The degreasing efficiency decreases at temperatures above the CP as the solubility of the surfactants in water is reduced, while it is optimal when temperature approach the CP. Therefore, temperatures of 50 and 60 °C yielded higher degreasing efficiency than temperatures of 30 and 40 °C, as these temperatures was closer to CP of most surfactants, except SE-3.
Although most of oil weight was removed from the surface relating to SE-20 after 5 min (Figure 1), oil stain was observed on the surface of sample after the Hogaboom test. This could be explained that the temperature of 40 °C was lower than CP of SE-20, and hence, oil stain still remained on the surface.
As 80 °C was above CP of SE-7, and SE-9, oil strain could not completely eliminate from the surface. Meanwhile, 80 °C was approaching CP of SE-12, and SE-20, and thus, the clean surface without oil strain was obtained.
- In figure 8 author wrote S.E.- in other figures, it is SE-. Please follow the same notation.
Reply 3-8: Figure was edited as suggested
- Please add some comparison at the end of the results, how and why your systems are better than others.
Reply 3-9: As mentioned in Introduction, most of previous works studied about HLB of surfactants in the pharmaceutical, paint, cosmetic, and food industries. To the best of our knowledge, our study is the first one reporting the influence of HLB and cloud point on degreasing efficiency in electroplating pretreatment process. Therefore, it was hard to find out the relevant points of previous studies for comparison.
- The conclusion should be to the point and crisp. Please refine it.
Reply 3-10: The conclusion was modified as follows.
In this study, the effects of the HLB number and cloud point (CP) of SE nonionic surfactant on degreasing efficiency was explored. For the same concentration of surfactant, the hydrophilicity of the solution increased with increasing number of hydrophilic EO groups as the HLB number increased. The degreasing efficiency of the solutions was temperature-dependent because of the different CPs of surfactants. The Hogaboom test confirmed that SE-9 and SE-7 exhibited cleaner surfaces at 40 °C, and SE-20 and SE-12 showed less oil strains at 80 °C, than other ones. Based on contact angle of surface with water droplet, it could be concluded that the hydrophilic property decreased in the order: SE-9, SE-7, SE-12, SE-20, and SE-3, while at 80 °C, it decreased in the order: SE-20, SE-12, SE-9, SE-7, and SE-3. Excluding SE-3, which is an insoluble surfactant that generates almost no foam, the tendency to foaming increased in the order of: SE-7, SE-9, SE-20, and SE-12.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Thank you for your response, I can agree that comparison with steel specimen completely degreasing is maybe unrealistic, but comparison that one with not undertaken of process of degreasing and covered by oil without degreasing, give us the range of contact angle which we compare. Without this frame with so small differences in contact angle, it is not clear if ca =65 is really good degreasing results I think that making clear what exactly means R, R1, R2, R3, R R in equation 2 could be helpful. Thank you for your response, I can agree that comparison with clear steel specimen is maybe unrealistic but that one wit nod undertaken of process of degreasing and covered by oil without degreasing give us the range of contact angle which we compare. I think that making clear what exactly means R , R1, R2, R3, R R ' could be helpful.Additionally I would like to know the relation between cmc and cloud point in given temperature. In other words my question is: if this wt 1% concentration is below of above cmc, and if cloud point allow for reaching cmc.
Additionally I would like to know the relation between cmc and cloud point in given temperature. In other words my question is: if this wt 1% concentration is below of above cmc, and if cloud point allow for reaching cmc.
Author Response
When a steel specimen is completely degreased, the contact angle ca = 65 to 70, and the contact angle covered with oil without degreasing is lipophilic exceeding ca = 90[22].
In Equation 2, R, R1, R2, R3, and R represent the alkyl group of RCOOR'.
Also, the cloud point is the measured temperature when each surfactant is 1 wt %, and it is also true that the cloud point changes as the concentration changes. In fact, SE-7 has a cloud point of 37 °C in Table 1, but in this experiment, it was confirmed that the concentration of 0.5 mL/L has a cloud point at 35~36 °C. Therefore, cmc will also decrease partly, but the purpose of this experiment is to compare the degreasing efficiency of each nonionic secondary alcohol ethoxylate as surfactant under the same concentration condition, and it seems that it will not matter even if it does not have exactly the cmc and cloud point of this surfactant mentioned in Table 1.
Reviewer 2 Report
Remove chap 2.6 as chap 3.5 has been removed.
Author Response
Chap 2.6 was deleted.
