Design of “Zn²⁺ Salt-Bondings” Cross-Linked Carboxylated Styrene Butadiene Rubber with Reprocessing and Recycling Ability via Rearrangements of Ionic Cross-Linkings

Abstract

Constructing a reversible supramolecular network cross-linked by noncovalent bonds is an effective approach to realize self-healing as well as reprocessing and recycling for rubbers. Unfortunately, in most case the resultant noncovalent cross-linked rubbers cannot hold enough forces to meet the routine applications. In this paper, our strategy was based on a simple reaction between carboxy groups in carboxylated styrene butadiene rubber (XSBR) and zinc oxide (ZnO), where the formed Zn2+ salt bondings connect separate XSBR molecules. The further self-aggregation of ion pairs of Zn2+ salts resulted in an ionic cross-linked network, whose rearrangements brought XSBR excellent reprocessing/recycling ability. Additionally, the reclaimed XSBR exhibited valuable mechanical properties due to the compensation of additional formed new Zn2+ salt bondings during recycling. The fresh XSBR with 5 wt % zinc oxide showed a tensile strength of 6.7 MPa, and it was further increased to 10.3 MPa after 3 recycles, which was far higher than most reported noncovalent supramolecular rubbers. This study thus opens up an avenue to further extending the recyclable cross-linked XSBR with considerable mechanical properties to various engineering applications.

Tough and Multi‐Recyclable Cross‐Linked Supramolecular Polyureas via Incorporating Noncovalent Bonds into Main‐Chains

“…[20] Besides dynamic covalent bonds, various noncovalent bonds have been used as cross-linking points to construct recyclable networks. [21][22][23][24][25][26][27][28][29][30][31] Compared with dynamic covalent bonds, the binding strength of noncovalent bonds is weaker and therefore noncovalent bonds are more likely to break and reform reversibly under facile conditions without catalysts. [32][33][34][35][36][37][38][39][40][41][42] More importantly, no cleavage and formation of the chemical bonds are involved during the dissociative and associative process of noncovalent bonds, hence there are few side reactions in the exchange process.…”

Shape memory and self‐healing behavior of styrene–butadiene–styrene/ethylene‐methacrylic acid copolymer (SBS/EMAA) elastomers containing ionic interactions

“…For rubbers with functional groups, such as carboxylated styrene‐butadiene rubber (XSBR), the ionic interactions can be introduced by adding metal oxides or amino compounds, to enable self‐healing and simultaneously improve the mechanical properties. For saturated rubbers, the ionic interactions can be introduced by blending with functional polymers or ionomers, such as acrylic acid‐based copolymers.…”

Enhanced thermo‐physical properties of nitrile‐butadiene rubber nanocomposites filled with simultaneously reduced and functionalized graphene oxide

“…As observed from Fig. b, tan δ of rubber composites, which represents the ratio of the viscous part to the elastic part, is an indicator of how efficiently the material loses energy due to molecular rearrangements and internal friction . As can be seen, a glass transition region is observed in the curves of tan δ as a function of temperature.…”