Effects of Alkalinity of Ionic Liquid on Catalyzed Silanization in Rubber/Silica Composites

The silane coupling agent has been used for ages to improve the performance of silica-filled rubber composites. To improve the degree of silanization of silica, ionic liquids (ILs) as a catalyst are incorporated to the styrene–butadiene rubber/silica composites. The reaction between bis­[3-(triethoxysilyl)­propyl]­tetrasulfide and silica with different basic ILs is investigated. The results show that the ILs with stronger alkalinity exhibit higher catalytic efficiency. The silanization occurs at lower temperature with the incorporation of ILs. The parameters characterizing interfacial interactions show that the interfacial adhesion is gradually improved with increasing alkalinity of ILs. Consequently, the resulting composite with ILs possessing strong alkalinity exhibits excellent whole performance compared with the composites without ILs. Especially, the energy loss of the rubber wheel in the rolling process is gradually decreased. The composites exhibit excellent abrasion resistance and heat build-up

New Design Strategy for Reversible Plasticity Shape Memory Polymers with Deformable Glassy Aggregates

Reversible plasticity shape memory (RPSM) is a new concept in the study of shape memory performance behavior and describes a phenomenon in which shape memory polymers (SMPs) can undergo a large plastic deformation at room temperature and subsequently recover their original shape upon heating. To date, RPSM behavior has been demonstrated in only a few polymers. In the present study, we implement a new design strategy, in which deformable glassy hindered phenol (AO-80) aggregates are incorporated into an amorphous network of epoxidized natural rubber (ENR) cured with zinc diacrylate (ZDA), in order to achieve RPSM properties. We propose that AO-80 continuously tunes the glass transition temperature (<i>T</i>_g) and improves the chain mobility of the SMP, providing traction and anchoring the ENR chains by intermolecular hydrogen bonding interactions. The RPSM behavior of the amorphous SMPs is characterized, and the results demonstrate good fixity at large deformations (up to 300%) and excellent recovery upon heating. Large energy storage capacities at <i>T</i>_d in these RPSM materials are demonstrated compared with those achieved at elevated temperature in traditional SMPs. Interestingly, the further revealed self-healing properties of these materials are closely related to their RPSM behavior

Integrating Sacrificial Bonds into Dynamic Covalent Networks toward Mechanically Robust and Malleable Elastomers

Vitrimers are a class of covalently cross-linked polymers that have drawn great attention due to their fascinating properties such as malleability and reprocessability. The state of art approach to improve their mechanical properties is the addition of fillers, which, however, greatly restricts the chain mobility and impedes network topology rearrangement, thereby deteriorating the dynamic properties of vitrimer composites. Here, we demonstrate that the integration of sacrificial bonds into a vitrimeric network can remarkably enhance the overall mechanical properties while facilitating network rearrangement. Specifically, commercially available epoxidized natural rubber is covalently cross-linked with sebacic acid and simultaneously grafted with N-acetylglycine (NAg) through the chemical reaction between epoxy and carboxyl groups, generating exchangeable β-hydroxyl esters and introducing amide functionalities into the networks. The hydrogen bonds arising from amide functionalities act in a sacrificial and reversible manner, that is, preferentially break prior to the covalent framework and undergo reversible breaking and reforming to dissipate mechanical energy under external load, which leads to a rarely achieved combination of high strength, modulus, and toughness. The topology rearrangement of the cross-linked networks can be accomplished through transesterification reactions at high temperatures, which is accelerated with the increase of grafting NAg amount due to the dissociation of transient hydrogen bonds and increase of the ester concentration in the system

Polyphenol-Reduced Graphene Oxide: Mechanism and Derivatization

In this work, tea polyphenols (TPs) were employed as an environmentally friendly and highly efficient reducer and stabilizer for graphene oxide (GO). The results from XPS, Raman, and conductivity studies of reduced graphene indicated the efficient deoxidization of GO. The adsorption of oxidized TPs onto graphene supplies steric hindrance among graphene sheets to keep them individually dispersed in water and some solvents. To investigate the reduction mechanism, epigallocatechin gallate (EGCG), the primary component of TPs, was used as a model. Characterization by ¹H NMR and FTIR spectroscopies indicated that the gallic units in EGCG were converted to galloyl-derived orthoquinone and the flavonoid structure survived during the reduction. To further enhance the organosolubility of the resultant graphene, derivatization of the graphene was conducted by galloyl-derived orthoquinone–thiol chemistry. The successful derivatization was found to greatly improve the organosolubility of graphene in solvents with low boiling points

Elastomer Reinforced with Innate Sulfur-Based Cross-Links as Ligands

Although the incorporation of sacrificial bonds into an elastomer is an effective way to provide a combination of high strength and high fracture toughness, this method normally involves complicated chemical processes. The coordination between metal ions and polysulfides has been documented. However, the potential of polysulfide structures in vulcanizates as ligands has long been neglected. Using innate sulfur-based cross-links, we show how weak and nonpolar elastomers achieve significant reinforcement without modification of the backbone. By simply soaking vulcanizates into solutions containing metal ions, dual ions are simultaneously introduced into the vulcanizate to generate coordinations with different bond strengths, resulting in an unprecedented high modulus. Overall, this work presents a universal yet high-efficiency reinforcing strategy to prepare high-performance elastomers without additional chemical modifications, which should promote comprehensive research and industrial application of sacrificial bond strategies for elastomers

Sustainable Carbon Nanodots with Tunable Radical Scavenging Activity for Elastomers

The application of polymers as an essential class of material was greatly inhibited due to the aging failure of these versatile materials during normal use. Hence, it is generally recognized that stabilization against thermo-oxidative aging is indispensable to extend the service life of polymers for long-term applications. However, toxicity and pollution of the state-of-the-art antiaging technologies have long been puzzles in the polymer industry. Herein, sustainable carbon nanodots (CDs), synthesized by facile and cost-effective microwave-assisted pyrolysis, are used for first time as radical scavengers to resist the thermo-oxidative aging of elastomers. We have demonstrated that incorporation of the resultant CDs could be green and generic radical scavengers toward highly aging-resistant elastomers. Furthermore, by controlling the photoluminescent quantum yield of the CDs with various passivated agents, tunable radical scavenging activity was achieved. We established for the first time that the aging resistance originates from the prominent reactive radical scavenging activity of the CDs, which was rationally controlled by their photoluminescent quantum yield

Enabling Design of Advanced Elastomer with Bioinspired Metal–Oxygen Coordination

It poses a huge challenge to expand the application gallery of rubbers into advanced smart materials and achieve the reinforcement simultaneously. In the present work, inspired by the metal–ligand complexations of mussel byssus, ferric ion was introduced into an oxygen-abundant rubber network to create additional metal–oxygen coordination cross-links. Such complexation has been revealed to be highly efficient in enhancing the strength and toughness of the rubbers. Significantly, such complexation also enables the functionalization of the rubber into highly damping or excellent multishape memory materials. We envision that the present work offers an efficient yet facile way of creating advanced elastomers based on industrially available diene-based rubber

Generic Mechanochemical Grafting Strategy toward Organophilic Carbon Nanotubes

Although carbon nanotubes (CNTs) have been produced in industrial scale, their poor dispersibility in organic solvents still imposes a huge challenge for their practical applications. In the present work, we propose a generic mechanochemical grafting strategy to prepare the organo-soluable CNTs, which is facile, efficient, and scalable. Significantly, the solvent spectrum of the CNTs suspension can be simply extended by changing the chemical composition of the grafted elastomer chains. The prospect of the organo-solubale CNTs is demonstrated by the free-standing buckypapers by direct filtration of the CNT colloids. Such buckypapers exhibit great potential as robust and ultraflexible conductors due to the combination of high toughness and stable conductivity under cyclic bending and twisting. Furthermore, this facile surface modification strategy of CNTs also enables remarkable improvement in mechanical properties of CNT-based rubber composites. We envision that the present work offers a facile yet efficient strategy for scalable production of organosoluable CNTs and other nanoparticles, which is of great scientific and technological interest

Facile Strategy for the Biomimetic Heterogeneous Design of Elastomers with Mechanical Robustness, Malleability, and Functionality

It remains challenging to simultaneously realize mechanical robustness, malleability, and functionality in elastomers via facile yet efficient methods. Herein, a simple strategy for the biomimetic heterogeneous design is proposed to achieve mechanically strong, malleable, and functionalized elastomers. We demonstrate the strategy by straightforward mechanical mixing of a highly cross-linked vitrimeric elastomer with a homogeneous gum and subsequent curing, resulting in heterogeneous vitrimeric elastomers (hetero-VEs). The hetero-VEs comprise two phases: a hard phase with dense cross-links and a soft matrix with few cross-links, with excellent interface between the two phases. The hard phases can be deformed upon loading, dissipating energy, which significantly improves the overall mechanical performance of the hetero-VEs. When conductive fillers are incorporated into the soft matrix, due to the volume exclusion effect of the hard phases, the resultant hetero-VEs exhibit high conductivity with a small fraction of fillers. In view of the facile and generic preparation process, this strategy should be a promising way to reinforce and functionalize many vitrimeric elastomer systems