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. 2020 Dec 24;13(1):39.
doi: 10.3390/polym13010039.

Alleviating Molecular-Scale Damages in Silica-Reinforced Natural Rubber Compounds by a Self-Healing Modifier

Bashir Algaily  1   2 , Wisut Kaewsakul  3 , Siti Salina Sarkawi  4 , Ekwipoo Kalkornsurapranee  1
Affiliations

Alleviating Molecular-Scale Damages in Silica-Reinforced Natural Rubber Compounds by a Self-Healing Modifier

Bashir Algaily et al. Polymers (Basel). .

Abstract

The property retentions of silica-reinforced natural rubber vulcanizates with various contents of a self-healing modifier called EMZ, which is based on epoxidized natural rubber (ENR) modified with hydrolyzed maleic anhydride (HMA) as an ester crosslinking agent plus zinc acetate dihydrate (ZAD) as a transesterification catalyst, were investigated. To validate its self-healing efficiency, the molecular-scale damages were introduced to vulcanizates using a tensile stress-strain cyclic test following the Mullins effect concept. The processing characteristics, reinforcing indicators, and physicomechanical and viscoelastic properties of the compounds were evaluated to identify the influences of plausible interactions in the system. Overall results demonstrate that the property retentions are significantly enhanced with increasing EMZ content at elevated treatment temperatures, because the EMZ modifier potentially contributes to reversible linkages leading to the intermolecular reparation of rubber network. Furthermore, a thermally annealing treatment of the damaged vulcanizates at a high temperature, e.g., 120 °C, substantially enhances the property recovery degree, most likely due to an impact of the transesterification reaction of the ester crosslinks adjacent to the molecular damages. This reaction can enable bond interchanges of the ester crosslinks, resulting in the feasibly exchanged positions of the ester crosslinks between the broken rubber molecules and, thus, achievable self-reparation of the damages.

Keywords: composite; filler; intermolecular reparation; polymer failure; rubber crosslink.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Scheme 1
Scheme 1
Preparation of the self-healing modifier used in this study and the possible ester and ionic crosslink structures generated through the hydrolyzed maleic anhydride after the modifier underwent a vulcanization process [14,15].
Figure 1
Figure 1
Mixing fingerprints based on (a) torque and (b) temperature of silica-filled NR compounds with various EMZ contents added via either extra addition (E05-E15) or blending (B05-B15).
Figure 2
Figure 2
Dump temperatures and final mixing torques of the silica-filled NR compounds as a function of EMZ content added via either extra addition (Set A) or blending (Set B).
Figure 3
Figure 3
Correlations among final mixing torques, dump temperatures, and Mooney viscosities of silica-filled NR compounds with different amounts of EMZ added via either extra addition (E05–E15) or blending (B05–B15).
Figure 4
Figure 4
Influence of EMZ content on chemically bound rubber contents and Payne effect of silica-filled NR compounds. EMZ was added via either extra addition (Set A) or blending (Set B).
Figure 5
Figure 5
Effect of EMZ contents on the apparent crosslink density of silica-filled NR vulcanizates. EMZ was added via either extra addition (Set A) or blending (Set B).
Figure 6
Figure 6
Effect of EMZ content on tensile strength, elongation at break, and reinforcement index of silica-filled NR vulcanizates. EMZ was added via either extra addition (Set A) or blending (Set B).
Figure 7
Figure 7
Stress relaxation curves as a function of EMZ loading levels of silica-filled NR vulcanizates. EMZ was added via either extra addition (Set A) or blending (Set B).
Figure 8
Figure 8
(a) Stress–strain curves of the reference sample (Ref.) and B-15 vulcanizate under a cyclic tensile deformation for 10 cycles. Integral area of hysteresis loop as a function of cycle number of the vulcanizates from (b) Set A, with extra addition of EMZ, and (c) Set B, with blending of EMZ. (d) Schematic illustration of how to calculate the values of hysteresis from the loading and unloading stress–strain curves.
Figure 9
Figure 9
Examples of stress–strain cyclic curves of (a) the reference and (b) B-15 vulcanizates from the first cycle of a cyclic tensile test. The pristine sample of each vulcanizate after its first-round test was thermally treated at different temperatures prior to the repetition of the stress–strain cyclic test.
Figure 10
Figure 10
Recovery of the hysteresis after a tensile cyclic test (10 cycles) of silica-filled NR vulcanizates with different contents of EMZ modifier added via either extra addition (Set A) or blending (Set B).
Scheme 2
Scheme 2
Postulated intermolecular interactions in silanized silica-filled natural rubber compounds with the presence of the self-healing modifier EMZ.
Figure 11
Figure 11
The recovery ratio of silica-filled NR vulcanizates with different EMZ loading levels treated at (a) room temperature and (b) 120 °C for three rounds of the cyclic test.
Scheme 3
Scheme 3
Plausible self-reparation mechanism of molecular damages of rubber network through the transesterification reaction of the thermochemically exchangeable ester crosslinks.
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References

    1. Awaja F., Zhang S., Tripathi M., Nikiforov A., Pugno N. Cracks, microcracks and fracture in polymer structures: Formation, detection, autonomic repair. Prog. Mater. Sci. 2016;83:536–573. doi: 10.1016/j.pmatsci.2016.07.007. - DOI
    1. Hernández M., Grande A.M., Dierkes W., Bijleveld J., Van der Zwaag S., García S.J. Turning vulcanized natural rubber into a self-healing polymer: Effect of the disulfide/polysulfide ratio. ACS Sustain. Chem. Eng. 2016;4:5776–5784. doi: 10.1021/acssuschemeng.6b01760. - DOI
    1. Forrest M.J. Introduction to recycling and the re-use of rubber. In: Forrest M.J., editor. Recycling and Re-use of Waste Rubber. 2nd ed. De Gruyter; Berlin, Germany: 2019. pp. 1–8.
    1. Coran A.Y. Vulcanization. In: Mark J.E., Erman B., Roland C.M., editors. The Science and Technology of Rubber. 4th ed. Elsevier Academic Press; Boston, MA, USA: 2013. pp. 337–381.
    1. Asaro L., Gratton M., Seghar S., Aït Hocine N. Recycling of rubber wastes by devulcanization. Resour. Conserv. Recycl. 2018;133:250–262. doi: 10.1016/j.resconrec.2018.02.016. - DOI

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