Maleic Anhydride Modified Dicyclopentadiene Resin for Improving Wet Skid Resistance of Silica Filled SSBR/BR Composites

Round 1

Reviewer 1 Report

Authors introduced MAH modified DCPD resin to increase wet traction of the SSBR/BR/silica vulcanizates. They suggested the mechanism of the increase of wet traction. However, there are a lot of unclear points. Detail questions are attached.

1. Page 2: Need more information for DCPD. Is DCPD resin? If so, need the information of chemical structure, molecular weight, and glass transition temperature, etc. If not, please show the polymerization mechanism.
2. Page 2, Table 1: What does the data of AR(%) mean? This value is large that the ratio of MAH/DCPD.
3. Page 3, Fig. 1: What is Norborlylene (M1)? Show the chemical structure of RM1M1• and RM1M2•.
4. Page 3: Show the mixing procedure and dump temperature of the compounds by using another Table.
5. Page 4, line 133: What does it mean the “copolymerization”? Need detail explanation.
6. Page 5, Fig. 2: In the GPC data, molecular weight of M2 – M8 were increased. Explain the reason.
7. Page 6, Fig. 3(a) & (b): (a) According to Fig 3(a), compound’s Tg looks like that R0<R6<R2<R4R4>R2>R8. When the silica is well dispersed, the peak values of tan δ is increased because of the increase of rubber volume fraction. This means tan δ at 60 ℃ should be decreased. In Fig. 3(b), the values of tan δ at 60 ℃ of R2 – R8 compounds are higher than that of R0 compound. This means that silica dispersion became worse when the M2 – M8 is added. Payne effect data should be more helpful to discuss the dispersion of silica in the compounds.  (c) Show the data od the compound which is not applied DCPD.
8. Page 7, Fig.4: This schematic figure has no meaning. Refer to comment 7. The R0 compound shows the highest value of the peak value of tan δ.
9. Page 7, Fig. 5: Need explanation of the figure in the figure caption
10. Page 7, line 188-198: “M-DCPD facilitate the movement and latter exposure of silica” cannot be agreed. The reduction of contact angle should be due to the increase of polarity of the vulcanizate by the increased amount of MAH.
11. Page 10, Table 3: E300 was increased by increasing the amount of MAH. Please show the mechanism.

#    Need correction English by a native speaker.

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Author Response

Response to reviewer 1's comment

Authors introduced MAH modified DCPD resin to increase wet traction of the SSBR/BR/silica vulcanizates. They suggested the mechanism of the increase of wet traction. However, there are a lot of unclear points. Detail questions are attached.

Response: We thank the reviewer for the comments.

1. Page 2: Need more information for DCPD. Is DCPD resin? If so, need the information of chemical structure, molecular weight, and glass transition temperature, etc. If not, please show the polymerization mechanism.

Response: We adjusted Fig.1 in revised manuscript, which clearly described that DCPD resin was an oligomer that obtained by thermal polymerization and Diels-Alder reaction of dicyclopentadiene and pentadiene. “DCPD resin is obtained by thermal polymerization and Diels-Alder reaction as shown in Fig.1, whose molecular weight and softening point are measured 3387 g·mol^-1 and 108.9 ^○C, respectively.” was added to introduce DCPD resin in detail in Page 12.

2. Page 2, Table 1: What does the data of AR (%) mean? This value is large that the ratio of MAH/DCPD.

Response: AR refers to the weight ratio of MAH in the modified M-DCPD, which is measured by titrating with potassium hydroxide/ethanol standard solution. Equation and detailed measurement were explained in 2.4.1.

Thanks for your reminder. We made a mistake for the previous values. Now the AR was recalculated carefully according to equation (1) in our revised version, and the values are listed in table 1. It seems that all the MAH has reacted with DCPD resin, the values of AR slightly higher than the ratio of MAH/DCPD probably due to the acid-base titration error.

3. Page 3, Fig. 1: What is Norborlylene (M1)? Show the chemical structure of RM1M1• and RM1M2•.

Response: we have revised the synthetic mechanism of M-DCPD from copolymerization to grafting reaction after serious discussion. We redrew the reaction equation in Fig.1.

4. Page 3: Show the mixing procedure and dump temperature of the compounds by using another Table.

Response: the specific mixing procedure and dump temperature of the compounds were shown in Table.1 in the revised manuscript.

5. Page 4, line 133: What does it mean the “copolymerization”? Need detail explanation.

Response: as is explained in response 3, the copolymerization was corrected to grafting reaction.

6. Page 5, Fig. 2: In the GPC data, molecular weight of M2 – M8 were increased. Explain the reason.

Response: There are two reasons for the slight molecular weight increase. First, some M-DCPD resins with small molecular weight dissolved in the xylene during purification of the M-DCPD resins. Second, small amount of MAH may act as chain extender to enhance the molecular weight during grafting.

7. Page 6, Fig. 3(a) & (b): (a) According to Fig 3(a), compound’s Tg looks like that R0<R6<R2<R4R4>R2>R8. When the silica is well dispersed, the peak values of tan δ is increased because of the increase of rubber volume fraction. This means tan δ at 60 ℃ should be decreased. In Fig. 3(b), the values of tan δ at 60 ℃ of R2 – R8 compounds are higher than that of R0 compound. This means that silica dispersion became worse when the M2 – M8 is added. Payne effect data should be more helpful to discuss the dispersion of silica in the compounds.  (c) Show the data on the compound which is not applied DCPD.

Response: (a) After further amplified the tan δ curve around 0 ℃ in the revised version, we can clearly observe that the tendency of curves consistently matched with the data of tan δ at 0 ℃. (b) Tan δ is obtained by dividing the loss modulus with the storage modulus, which affected by rubber volume fraction, elastic modulus of resin, and intermolecular force. “Although extended rubber volume fraction by released rubber chain enhanced viscidity, elastic modulus of vulcanizates increased as the polar interaction enhanced due to addition of M-DCPD, resulting in the decline of peak value of tan δ of R8 at glass transition zone” was added to explain why the peak values of tan δ was decreased as the increase of MAH content. (c) Since the curve of tan δ of compound which is not applied DCPD is much different from others with much lower peak value, we didn’t show the curve to confuse the readers.

8. Page 7, Fig.4: This schematic figure has no meaning. Refer to comment 7. The R0 compound shows the highest value of the peak value of tan δ.

Response: Please refer to response 7. The peak value of tan δ was affected not only by rubber volume fraction but also elastic modulus of vulcanizates that is obviously increased as the addition of M-DCPD resin.

9. Page 7, Fig. 5: Need explanation of the figure in the figure caption

Response: The explanation of patterns was added on the Fig.5 (Fig.6 in our revised version) as “Fig.6. Interaction mechanism of vulcanizates and water affected by M-DCPD resins with anhydride and silica with polar group”.

10. Page 7, line 188-198: “M-DCPD facilitate the movement and latter exposure of silica” cannot be agreed. The reduction of contact angle should be due to the increase of polarity of the vulcanizate by the increased amount of MAH.

Response: We rewrote the deduction as “As a result, the ease with forming asperity could be deduced from the interfacial polar interaction of water with silica that is close to the interface”, because “The surface polarity of vulcanizates could reflected by water contact angle that shown in Fig. 7, which had a negative relationship with the content of MAH (Fig. 8), making it clear that content of hydrophilic groups on the surface of the vulcanizates increased with increasing MAH content. Obviously, the differences in hydrophilicity among different samples are caused by the quantity of silica on which a large number of hydroxyl groups exist, as well as that of M-DCPD resins that grafted with anhydride”.

11. Page 10, Table 3: E300 was increased by increasing the amount of MAH. Please show the mechanism.

Response: “As is discussed in 3.2 and 3.3, intermolecular force was enhanced by the addition of M-DCPD resins due to improved polarity of vulcanizates, resulting in increase of 300% modulus. But the 300% modulus of R8 was lower than that of R6 due to the relevantly poor dispersion of M8” was added in Page 9 to discuss the change of E300.

Author Response File: Author Response.docx

Reviewer 2 Report

I have the following comments that need to be addressed before this paper is accepted for publication:

1. Table 1: Please define AR.
2. Section 3 is written in the present tense while section 4 is written in the past tense. Please be consistent. 
3. Spelling mistake in Line 141.
4. Figure numbers are wrong after Figure 2. 
5. Please explain how you used GPC curves to conclude that MAH reacted with side chains and not cross-linking?
6. How did you calculate μ for equation 2?
7. Please rewrite Section 8. I cannot understand what you are trying to say in this paragraph.
8. Please explain the Sem images. How do the images support your conclusion?

Author Response

Response to reviewre 2's comments

I have the following comments that need to be addressed before this paper is accepted for publication.

Response: We thank the review for the comments. We have conducted suggested experiments and following please find our detailed responses.

1. Table 1: Please define AR.

Response: AR refers to the weight ratio of MAH in the modified M-DCPD resins, which is measured by titrating with potassium hydroxide/ethanol standard solution. Equation and detailed measurement were explained in 2.4.1.

2. Section 3 is written in the present tense while section 4 is written in the past tense. Please be consistent. 

Response: The tense of section 4 (section 2.3 in the revised manuscript) was corrected to past tense.

3. Spelling mistake in Line 141.

Response: Line 141 (Line 149 in revised version) was rewrote as “DSC was conducted accordingly to characterize the resins. Fig.3a shows that the more MAH added…”.

4. Figure numbers are wrong after Figure 2. 

Response: Figure numbers have been all adjusted in the revised version and uniformly used “Fig.”.

5. Please explain how you used GPC curves to conclude that MAH reacted with side chains and not cross-linking?

Response: Because either DCPD resin or M-DCPD resins can totally dissolved in tetrahydrofuran, and the molecular weight of M-DCPD resins is slightly increased according to GPC. We deduced that most MAH reacted with the side chain and small part of MAH acted as chain extender.

6. How did you calculate μ for equation 2?

Response: According to the reference [10], friction coefficient between rubber and rigid material is far bigger than that between rigid materials since there is great deformation of rubber under shear stress, so μ is a particular constant once the measuring material was selected, which is 3.09 in our BPST test.

7. Please rewrite Section 8. I cannot understand what you are trying to say in this paragraph.

Response: Section 8 (section 3.4 in the revised manuscript) was rewrote as “Table 4 summarizes the physical-mechanical properties of the vulcanizates. Cross-linking density, the 100% modulus and 300% modulus increase, whereas the elongation at break decreases slightly from R0 to R6. R8 shows the opposite trend. Meanwhile, hardness, tensile strength and tear strength fluctuate in a narrow range, resilience as well. As is discussed in 3.2 ana 3.3, intermolecular force was enhanced by the addition of M-DCPD resins due to improved polarity of vulcanizates, resulting in increased 300% modulus. But the 300% modulus of R8 was lower than that of R6 due to relevantly poor dispersion of M8”.

8. Please explain the Sem images. How do the images support your conclusion?

Response: The SEM images was used to study the resin phase, whose particle sizes corresponded to their dispersion. As discussed in 3.2, the dispersion of resin closely influenced the dispersion of silica through polar interaction. The bad dispersion of M8 thus resulted in the poor performance of M8 in wet skid resistance.

Author Response File: Author Response.docx

Reviewer 3 Report

Maleic anhydride modified…

The implementation in tire tech in the wet skid resistance (WSR) and rolling resistance the authors have presented in the following paper is interesting but requires major revision.

First of all, the authors could specify the type of SBR and PB used in terms of molecular weight by weight and the molecular weight distribution and in particular for PB the structure as % cis, % trans and 1,2 vinyl.

In relation to the vulcanization reactions that has an important effect on all mechanical and elastic characteristics of all items as tires produced, the reviewer suggests to the authors to consider the following up to date papers in the field of tire technology and the blend between different rubbers

• 2018: Quasi analytical kinetic model for Natural Rubber and Poly-Butadiene rubber blends. Reaction Kinetics, Mechanisms and Catalysis, 123, pp. 351–365.
• 2018: Rubber blends: kinetic numerical model by rheometer experimental characterization. Journal of Mathematical Chemistry, 56, pp. 1520–1542. 
• 2018: Optimal vulcanization of tires: Experimentation on idealized NR-PB natural and poly-butadiene rubber blends, phenomenological smoothed numerical kinetic model and FE implementation. Polymer Testing, 72, pp. 63-85.
• 2019: Optimal production of tires through an integrated experimental, kinetic and finite element FE modelling approach. Chemical Engineering Transactions 74, pp. 1177-1182.
• 2019: Numerical kinetic model with regularization for NR–PB natural and poly-butadiene rubber blends: implementation and validation against experimental data. Journal of Mathematical Chemistry, 57(4), pp 1019–1034. 

Also the authors could add the size and the size distribution of the highly dispersed silica.

In the preparation of M - DCPD. The authors write: “..DCPD was completely melt in a 500ml…” What does it mean? In the reviewer opinion the DCPD is liquid and with a specific boiling point.

In the paper the authors write: “In this study, the modified DCPD was prepared by alternating copolymerization of DCPD with maleic anhydride .”, but in the figure 1 there is not represented this alternating copolymer. Could the authors explain in detail this apparent disagreement?

The reviewer has not understood in which phase of the tire production this copolymer is added.

Then, the authors write in the conclusions: “the addition of DCPD modified with MAH in 4% wt. and 6% wt., the BPST index and than? increased respectively, as well as a decrease in contact angle by more than 4%”.

The authors could explain why these little increases and reduction have significant importance in the practical point of view.

Author Response

Responde to reviewer 3's comments

The implementation in tire tech in the wet skid resistance (WSR) and rolling resistance the authors have presented in the following paper is interesting but requires major revision.

Response: Thanks for all the comments, the modified parts in the revised manuscript are as follows.

1. First of all, the authors could specify the type of SBR and PB used in terms of molecular weight by weight and the molecular weight distribution and in particular for PB the structure as % cis, % trans and 1,2 vinyl. The authors could add the size and the size distribution of the highly dispersed silica.

Response: “(styrene content: 23%, vinyl content: 53%)”, “(Cis 1,4-polybutadiene content:96%-99%)” and “(surface area:170 m²/g, grain size: 14 nm)” was added to specify the type of SSBR, BR and silica in section 2.1, respectively.

• In relation to the vulcanization reactions that has an important effect on all mechanical and elastic characteristics of all items as tires produced, the reviewer suggests to the authors to consider the following up to date papers in the field of tire technology and the blend between different rubbers2018: Quasi analytical kinetic model for Natural Rubber and Poly-Butadiene rubber blends. Reaction Kinetics, Mechanisms and Catalysis, 123, pp. 351–365.
• 2018: Rubber blends: kinetic numerical model by rheometer experimental characterization. Journal of Mathematical Chemistry, 56, pp. 1520–1542. 
• 2018: Optimal vulcanization of tires: Experimentation on idealized NR-PB natural and poly-butadiene rubber blends, phenomenological smoothed numerical kinetic model and FE implementation. Polymer Testing, 72, pp. 63-85.
• 2019: Optimal production of tires through an integrated experimental, kinetic and finite element FE modelling approach. Chemical Engineering Transactions 74, pp. 1177-1182.
• 2019: Numerical kinetic model with regularization for NR–PB natural and poly-butadiene rubber blends: implementation and validation against experimental data. Journal of Mathematical Chemistry, 57(4), pp 1019–1034. 

Response: Thanks a lot for your recommendation and guidance. We can learn more about blending between different rubber.

3. In the preparation of M - DCPD. The authors write: “..DCPD was completely melt in a 500ml…” What does it mean? In the reviewer opinion the DCPD is liquid and with a specific boiling point.

Response: DCPD is liquid, but the DCPD resin is solid. It was revised to “..DCPD resin was completely melt in a 500ml…”.

4. In the paper the authors write: “In this study, the modified DCPD was prepared by alternating copolymerization of DCPD with maleic anhydride.”, but in the figure 1 there is not represented this alternating copolymer. Could the authors explain in detail this apparent disagreement?

Response: In our revised version, we amended the synthesis mechanism of M-DCPD resin from copolymerization to grafting reaction after serious discussion. We redrew the reaction equation in Fig.1.

5. The reviewer has not understood in which phase of the tire production this copolymer is added.

Response: Table.2 was added to describe the mixing procedure and dump temperature in detail. The resin was added after the addition of silica in HAAKE mixer.

6. Then, the authors write in the conclusions: “the addition of DCPD modified with MAH in 4% wt. and 6% wt., the BPST index and tan increased respectively, as well as a decrease in contact angle by more than 4%”.

The authors could explain why these little increases and reduction have significant importance in the practical point of view.

Response: We have recalculated the number for improvement. With the addition of DCPD modified with MAH in 4 wt% and 6 wt%, the BPST index and tanδ increased by around 16% and 15%, respectively. Although the increases are not huge, it’s already a great success in improving wet skid resistance of green tires. The enhancement of WSR is valid to improve driving safety and desirable duration of tire. We added “Consequently, with the addition of DCPD modified with MAH in 4 wt% and 6 wt%, the BPST index and tanδ increased by around 16% and 15%, respectively, as well as a decrease in contact angle by more than 11% and 9%, respectively, indicating that both external and internal friction are obviously improved, and the surface polarity of vulcanizates are also enhanced. As a result, the modification of DCPD resin with appropriate dosage of MAH could give a great improvement in WSR of silica filled SSBR/BR. Moreover, the enhancement of WSR is valid to improve driving safety and desirable duration of tire. Our work proposes a detailed strategy to use modified DCPD resin as antiskid resin by introducing polar groups, and we anticipate further efficient methods to explore more multifunctional resins” in page 10.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Authors improved the manuscript in the revised version.

However, I did not agree with the authors for the analysis of the data of Fig.2 (revised manuscript).

Authors did not explain the reason of the increase of tan δ at 0 ℃ by the addition of M-DCPD. This data is important for the evaluation of wet grip. My opinion is that this is mainly due to the increase of Tg of the compound. Authors should suggest the value of Tg of each compound. Also show the E” data at 0 ℃. This data also should be helpful to evaluate wet grip.

According to the data of tan δ at 60 ℃, silica dispersion became worse by addition of M-DCPD. This trend is well consistent with the data of peak tan δ. However, authors did not agree. So Payne effect data are needed to evaluate silica dispersion.

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Author Response

Response to Reviewer 1 Comments

Authors improved the manuscript in the revised version.

Response: thanks for all your professional suggestions. There were some adjust according to your opinion.

However, I did not agree with the authors for the analysis of the data of Fig.2 (revised manuscript).

Authors did not explain the reason of the increase of tan δ at 0 ℃ by the addition of M-DCPD. This data is important for the evaluation of wet grip. My opinion is that this is mainly due to the increase of Tg of the compound. Authors should suggest the value of Tg of each compound. Also show the E” data at 0 ℃. This data also should be helpful to evaluate wet grip.

According to the data of tan δ at 60 ℃, silica dispersion became worse by addition of M-DCPD. This trend is well consistent with the data of peak tan δ. However, authors did not agree. So Payne effect data are needed to evaluate silica dispersion.

Response: The mechanism of how resin improve wet skid resistance was restated in our revised version. “The effect of resin on tanδ is closely related to the compatibility between resin and rubber compounds, which results from the changes of glass transition temperature. The closer the peak value to 0 ^○C, the better improvement of the wet skid resistance of the vulcanizates [23].Fig.2 shows that with increasing MAH content in the M-DCPD resins, the T_g of vulcanizates increases from -17.5 ^○C to -11.7 ^○C, values of tanδ at 0 ^○C increases from 0.51 to 0.58 as well. The WSR performance of R8 was limited by inferior solvability of M8 in the rubber compounds due to its high glass transition temperature” was added. Reference [23] was added to demonstrate our analysis. The E” data at 0 ℃ shown below presents that in correspondence with our statement, the addition of M4 enhanced the hysteresis of vulcanizate.

[23] Mark T.Arigo (2019) Using Impera performance resins to expand the”magic triangle”for tire tread compounds. Rubber World. 260(6):24-30

We totally agreed with your point and have measured the Payne effect that shown in attached file. The Payne effect is related not only to rubber-rubber and silica-rubber interaction, but also plastification, which was weaken under the test temperature as the T_g of M-DCPD increases from 48.2 ^○C to 91.1 ^○C. We thus considered that the Payne effect was insufficient to prove the dispersion of silica without further research in detail, such as filler dispersion by SEM and rheological property. In addition, filler dispersion affects 300% modulus directly. “the enhanced 300% modulus also indicates improved dispersion of silica since uniform dispersion is beneficial for more chemical bonding between silica and rubber chain and ulteriorly higher intermolecular force” was added in 3.4 to explain the good dispersion of silica.

Author Response File: Author Response.pdf

Reviewer 3 Report

In the first round of the review I explicitly asked the authors to improve the discussion on rubber blends with proper reference of the state of the art, but the authors did not. For this reason, the paper is rated as not acceptable for publication in its present form.

Author Response

Response to Reviewer 3's comments

In the first round of the review I explicitly asked the authors to improve the discussion on rubber blends with proper reference of the state of the art, but the authors did not. For this reason, the paper is rated as not acceptable for publication in its present form.

Response: thanks for your comment.

“For one thing, the type and curing process of rubber blend influence directly on performance, stimulating research on stimulation study of how rubber compound affect properties” was added in Introduction. Reference [10] was added as well.

[10] Milani G, Milani F (2019) Numerical kinetic model with regularization for NR-PB natural and poly-butadiene rubber blends: implementation and validation against experimental data. J. Math. Chem.57(4):1019-1034

Author Response File: Author Response.pdf

Round 3

Reviewer 1 Report

Authors answered what I had questions.

I agree with author's opinion.

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Reviewer 3 Report

The paper can be now accepted