Recyclable Rubber Research Articles

4D printable and recyclable two-way shape memory butadiene rubber as ultrasensitive, longer-lasting, and lower-cost fire warning sensors

4D printable and recyclable two-way shape memory butadiene rubber as ultrasensitive, longer-lasting, and lower-cost fire warning sensors

Self‐healing, low oil leakage and recyclable thermally conductive Al2O3/boron nitride@siloxane composites based on reversible dynamic network

AbstractIn order to overcome the commercialized silicone‐based thermal interface materials' issues such as oil leakage and mechanical damage, we developed a thermoset silicone rubber matrix (SR) achieved through the condensation reaction of hydroxyl silicone oil and tetraethyl silicate. Additionally, we constructed a self‐healing and recyclable silicone rubber matrix (SCNR) by incorporating heat reversible ionic and hydrogen bonds between carboxyl and amino functionalized polydimethylsiloxane. Finally, the flexible, low oil leakage, self‐healing, and recyclable composites Al2O3/BN@SR/SCNR was prepared by adjusting the ratio of SR/SCNR and the spherical alumina and boron nitride (BN) fillers. The results indicated that with SR/SCNR mass ratio of 1/0.075 and filler content of 70 wt%, the thermal conductivity of the composite reaches 1.866 W m−1 K−1, 646% increasing over the SR/SCNR matrix. The self‐healing efficiency reaches 97% and the thermal conductivity remains essentially unchanged after being recycled for three times. The composites can be bent and twisted multiple times and still return to their original shape. Notably, the oil leakage of the Al2O3/BN@SR/SCNR composites is significantly lower than that of additive silicone composites. Therefore, the recyclable thermal conductivity composite developed in this study provides a promising solution for improving the durability of heat dissipation materials in electronic devices.

Recyclable Rubber Flooring in Farrowing Crates and Its Influence on the Development and Welfare of Piglets in the Maternity Phase

To boost productivity in pig production, it is essential to improve the litter size per sow. However, achieving this goal requires reducing newborn mortality rates and increasing their weight gain. In this regard, prioritizing animal welfare and adopting practices that promote sustainability in the activity is crucial. The study aimed to evaluate the sustainable flooring coverage of farrowing crates, considering piglet adaptation, thermal comfort, animal development, and increased productivity. Three types of flooring treatments were defined: T1—wood shavings; T2—solid rubber mat; T3—perforated rubber mat, for 12 litters (±50 animals/treatment). Behavior, physiology, piglet production indices, and facility microclimate were assessed. The facility’s microclimate indicated the possibility of cold stress. There was a greater preference for the mat treatments among the animals, as they remained on them for longer periods and showed increased activity in the farrowing crates. The presence of mats resulted in lower mortality due to crushing, positively contributing to production. These findings suggest the potential of using recyclable rubber mats in pig production and encourage the exploration of new designs and installation locations.

Chemically Recyclable and Biodegradable Vulcanized Rubber.

The cross-linked nature of vulcanized rubbers as used in tire and many other applications prohibits an effective closed-loop mechanical or chemical recycling. Moreover, vulcanization significantly retards the material's biodegradation. Here, we report a recyclable and biodegradable rubber that is generated by the vulcanization of amorphous, unsaturated polyesters. The elastic material can be broken down via solvolysis into the underlying monomers. After removal of the vulcanized repeat units, the saturated monomers, constituting the major share of the material, can be recovered in overall recycling rates exceeding 90%. Respirometric biodegradation experiments by 13CO2 tracking under environmental conditions via the polyesters' diol monomer indicated depolymerization and partial mineralization of the vulcanized polyester rubbers.

Dynamic co‐ordination networks in carboxylated nitrile rubber and development of self‐healing and recyclable rubber composites

AbstractMetal–ligand coordinated cross‐linked polymeric composites that can alter the network topology via a dynamic bond‐exchange mechanism have been recognized as very promising candidates to address the shortcomings of conventional cross‐linked composites, such as poor recyclability and self‐healing ability. This has led to much interest in the cross‐linking of elastomers via non‐covalent interactions with suitable metal ions. In this report, we present a simple but efficient approach to ferric ions (Fe3+) assisted crosslinking of carboxylated nitrile rubber (XNBR) in the presence of an aliphatic amine (Et3N). The dynamic coordination reaction via carboxylate functional group of nitrile rubber (XNBR) is employed to fulfill the coordination requirements of the central Fe3+ metal ion. This is confirmed by x‐ray photoelectron spectroscopy and Fourier‐transform infrared spectroscopy. The crucial role of Et3N in partially hindering and regulating the extent of crosslinking is investigated and mechanistically interpreted by swelling, differential scanning calorimetry, and rheological study. The tensile strength of ferric crosslinked XNBR could be enhanced up to four times than that of pure XNBR. Furthermore, the dynamic coordination‐driven network of XNBR offers excellent self‐healing (90% efficiency) and recyclability features (80% efficiency) for a composite of appropriate formulations.

Reprocessable and Recyclable Self-Healing Natural Rubber/Carbon Black Composite Based on Metal Thiolate Ionic Network

Reprocessable and recyclable self-healing rubber composites were fabricated by mixing natural rubber (NR) with carbon black (CB) filler in the presence of zinc thiolate (ZT) to form the ionic association in the rubber system. This work investigated and compared the unfilled and natural rubber filled with 5phr of carbon black. The recycling process was repeated three times, and the mechanical performance was measured each time. Tensile strength was increased by more than 430% for unfilled rubber and 520% for NR/5CB composites after the third recycling process. Tear strength was also increased with the number of the recycling process. According to a welding test ability, the developed materials showed potential for repair. Scanning electron micrographs revealed that as the recycling number increased, the white spot of ZT responsible for generating the ionic network reduced as more ZT was converted into Zn2+ salt bonding.

Reinforced, self-healing, recyclable rubber materials based on multiple dynamic bond constructs crosslinked with chemical groups

Enhancing the mechanical attributes of traditional rubber, while simultaneously imparting superior self-healing and recyclability, remains a formidable task within the realm of polymer science. In this study, we introduce, for the inaugural time, the utilization of metal–ligand interactions to amalgamate chemical cross-linking sites within a styrene-butadiene rubber matrix. This approach facilitates the creation of a fortified, self-healing, and recyclable rubber composite, interconnected by an array of dynamic bonds within a singular chemical entity. This chemical assembly engenders a microphase-separated architecture that exhibits reinforcement and resistance to creep. In addition, the presence of reversible oxime-carbamate and metal–ligand bonds bestow the rubber composites with remarkable self-healing and recyclability. Notably, the self-healing efficiency reached an impressive 87%, while the recyclability retention hovered between 85 and 91% (in terms of tensile strength) post multiple reprocesses. This research paves a novel avenue for the fabrication of rubber composites that are robust, self-healing, and recyclable.

Recyclable microcellular rubber foams with superior photothermal performance via constructing Fe3+ heterodentate coordination between epoxidized natural rubber and polyaniline

Developing recyclable microcellular rubber foams with excellent photothermal conversion ability can reduce resource waste and harvest solar energy to alleviate environmental pollution and the energy crisis simultaneously.

Enhanced design of dual dynamic cross-linked rubber composites: Achieving self-healing and recyclability through imine and metal-ligand bonding

The quest to confer self-healing and recyclable properties to conventional rubber is a prominent research area in the rubber industry. This study presents the novel construction of a self-healing and recyclable rubber composite by employing imine bond and Cu2+-imine cross-linking the polybutadiene rubber matrix and Cu2+-imidazole groups cross-linking at the silica-rubber interface. The introduction of imine bonded cross-linked imparts high elasticity to the rubber, while the Cu2+-imidazole complex serves as a bridge, enhancing the interfacial interaction between the silica and rubber matrix. The Cu2+-N (Cu2+-imidazole and Cu2+-imine) complexes not only improves silica dispersion but also acts as a sacrificial unit, thereby enhancing the mechanical properties of the rubber composites. The addition of 0.2 mmol anhydrous copper (II) chloride (CuCl2) results in a significant increase in tensile strength and Young's modulus of the samples (1.04 and 3.91 MPa), with improvements of 181 % and 407 %, respectively, compared to the pure samples. Additionally, the highly dynamic nature of the imine bond and the Cu2+-N (Cu2+-imidazole and Cu2+-imine) complexes imparts excellent self-healing and recyclable properties to the material, exhibiting repair efficiency and recycling recovery of up to 90 % (tensile strength). Therefore, this work opens a new avenue for the design and development of self-healing, recyclable rubber composites.

Seismic performance of mechanically stabilized earth walls with Sand-Crumb rubber backfills of varying proportion

The applicability of crumb rubber mixed with sand as alternative fill material in mechanically stabilized earth (MSE) walls is investigated in the current study. Shaking table tests have been conducted to analyze the dynamic response of model geogrid reinforced earth walls subjected to three different base input motions. Eight different sand-crumb rubber mixture combinations were used as backfill. The outcomes of this study provide quantitative results on how base excitation amplitudes could influence the seismic behavior of the MSE walls in the presence of sand-rubber backfill. The results have been analyzed in terms of deformation and rotation of the wall, settlement of backfill, acceleration amplification, and earth pressure response. Wall displacement and backfill settlement was found to reduce with the addition of rubber in the sand. The maximum displacement at the top of the wall was found to reduce by 45% at a rubber content of 30% for high peak ground acceleration (PGA) input motion. Two-wedge failure was observed with the failure envelope inclined at an angle of 49° from the vertical. Apart from this, the strain in the geogrid was decreased with an increase in the rubber content. Hence, the rubber content of 30% mixed with sand can be considered an optimum percentage to control the dynamic performance of MSE walls. In the end, a cost-benefit analysis was conducted, and it was found that using rubber as a partial substitute for sand backfill reduces the overall cost of the project. This research will also promote the use of recyclable rubber as a construction material in highway construction.

Self-healing and recyclable elastomer based on epoxidized natural rubber and carboxylated-chitosan

Rubbers are strategically important due to their high elasticity in transportation, military, and daily life. However, traditional rubbers are difficult to remanufacture and self-heal due to its irreversible crosslinking network, which imposes a great burden on the environment. Therefore, the development of a form of self-healing and recyclable rubber would provide a sustainable approach to reduce the environmental problems produced by cross-linked conventional vulcanized rubbers. In the current study, a simple and promising way is demonstrated to incorporate the β-hydroxyl ester bond into the epoxidized natural rubber/maleic anhydride modified chitosan. The ensuing samples are covalently cross-linked and possess self-healing and recyclable performance which can be conveniently tailor-made via various maleated chitosan content.

A long-lived self-healable and recyclable rubber composite via biomass Zn2+-polyphenol bonds and plasticizer-like proton donors

It is significant to fabricate lasting self-healing polymers to repair product mechanical damage in industries. In this letter, a novel self-healing rubber composite is prepared by introducing Zn2+-polyphenol complex and proton donors of diethylene glycol (DEG). The rubber composite exhibits high ductility of beyond 500 %, good reprocessable, simply reshaping and a fast heating-triggered self-healing property with 90 % healing efficiency. More importantly, it sustains the long-lived self-healing capability after being thermally aged.

Engineer a controllable hierarchical dynamic cross-linked network

The overall performance of rubber is largely governed by its internal cross-linked network structure. However, it remains a major challenge to probe into cross-linked networks associated with their fascinating hierarchy and dynamic characteristics. Herein, we propose a strategy for developing “hierarchical dynamic cross-linked networks (HDCs)” in rubber composites to circumvent the inherent trade-off between stiffness and toughness while accelerating the dynamic properties of the networks. The robust HDCs enabled by networks union enhances the stiffness, and at the same time improves the toughness by dissipating energy in motion and dissociation of multiple interactions. Moreover, the strong diffusivity of the polymer chains and the dynamic reversibility of the cross-linking sites ensure that the rubber composites can be readily healed and recycled, restoring the original mechanical properties under heating. By means of a model system of carboxylate nitrile rubber (XNBR) material, a healable, recyclable and intelligent responsive rubber composite with simultaneously enhanced stiffness (modulus = 3.20 ± 0.12 MPa) and toughness (40.9 MJ m−3) is fabricated. The clever design of the HDCs in rubber composites conciliates the stubborn contradiction between reinforcement, self-healing/recycling and functional application, which is expected to impact many fields in elastomer science and engineering.

Renewable Vanillin-Based Thermoplastic Polybutadiene Rubber: High Strength, Recyclability, Self-Welding, Shape Memory, and Antibacterial Properties.

The vast majority of traditional vulcanized rubber products are insoluble and infusible, which is difficult to reprocess and biodegrade, resulting in black pollution. In addition, although most rubber materials based on covalent adaptive networks (CANs) can achieve structural reconstruction, the lack of traditional vulcanization system leads to a decline in strength. In this study, biobased vanillin derivatives (PV) were synthesized to cross-link the commercially available 1,2-polybutadiene rubber precursor to construct imine-based CANs, thereby fabricating a resource-renewable, recyclable, and degradable high-performance rubber material. Due to the rigid tripod structure of the PV, the tensile strength of the material can achieve as high as 16.24 MPa, ranking among the best in the field of recyclable polybutadiene-based materials. Benefiting from the dynamic imine unit, the "dynamic covalent bridge" can be re-established to repair the damaged network and endow the material with excellent weldability. And, shape memory faculty of the material was proved and depicted. Moreover, this material displayed excellent antibacterial property originates from the introduced Schiff-base structure. By mixing with graphene, the application of action sensors can also be achieved.

Carbonate nanophase guided by terminally functionalized polyisoprene leading to a super tough, recyclable and transparent rubber

The interplay between polymer microstructures and vulcanization method has rarely been investigated for rubbers. Herein a terminally hydroxyl functionalized polyisoprene is crosslinked by ring opening of bis(6-membered cyclic carbonate) (bCC), generating uniformly dispersed carbonate nanophase in the polyisoprene matrix. The carbonate phase not only performed as nanofillers to reinforce the rubber and accelerate the strain crystallization behavior of polyisoprene, but also imparted the recovery property and recyclability into the rubber. In contrast, the copolymer without the terminal block showed disorderly carbonate nanophase and much inferior properties. The mechanical strength and toughness could be finely tuned by the content of bCC crosslinkers, which are even superior to those of vulcanized natural rubber. In addition, the crosslinked polyisoprene exhibits notable transparency, which is not common to vulcanized rubber and could meet the requirements for transparency of rubber products in some fields.

A facile strategy for high mechanical performance and recyclable EPDM rubber enabled by exchangeable ion crosslinking

Endowing rubber with excellent recycling ability is of great significance for energy conservation. It is still a huge challenge to obtain high-performance recyclable commercial rubber to satisfy practical applications. Herein, a facile strategy of incorporating exchangeable Zn2+-carboxyl crosslinks into commercial EPDM system was developed through reaction of zinc acetate and EPDM grafted maleic anhydride (EPDM-g-MAH) to obtain EPDM-g-MAZn. The constructed exchangeable crosslinking networks as sacrificial unit significantly enhanced mechanical properties of EPDM, much higher than EPDM cured by covalent bonds (tensile strength: 2.00 MPa and fracture toughness: 6.75 MJ/m3). The dynamic crosslinking was reversibly broken and reformed by hot pressing, endowing EPDM-g-MAZn with good recycling ability. The promising mechanical properties of EPDM-g-MAZn can be tailored by incorporation of carbon black (CB) or zinc dimethacrylate (ZDMA), and recycled EPDM-g-MAZn/CB exhibited good mechanical properties to meet industrial applications. Additionally, multiple crosslinking networks were constructed for EPDM-g-MAZn/ZDMA with fine dispersion of ZDMA due to Zn2+-carboxyl interactions. Such effective strategy exhibits a promising perspective in industrial applications of high-performance recyclable rubber field.

Healable, recyclable, and adhesive rubber composites equipped with ester linkages, zinc ionic bonds, and hydrogen bonds

This study reports healable, recyclable, and adhesive rubber composites equipped with ester linkages, Zn2+ ionic bonds, and H-bonds based on carboxylic styrene butadiene rubber (XSBR), nano-ZnO, and diglycidyl ether of bisphenol A (DGEBA). Zn2+ ionic cross-links are introduced into XSBR networks through the acid-base reaction between nano-ZnO and carboxyl groups of XSBR. The in-situ generated Zn2+ is thus evenly dispersed in the rubber matrix to serve as transesterification catalyst, which promotes the healing and reprocessing of the rubber composites at a higher temperature. The healing efficiency of the rubber composites can realize 75% and further improved to 90% after introducing additional hydroxyl groups. The rubber composites can reprocess at least 5 times. Moreover, the rubber composites are easily disintegrated to recycle neat XSBR due to the dissociation of ester linkages in the alkaline solution. Interestingly, the rubber composites show a surprising reversible adhesion property under water stimulation.

Self-Strengthening, Self-Welding, Shape Memory, and Recyclable Polybutadiene-Based Material Driven by Dual-Dynamic Units.

A covalent adaptable network can endow rubber materials with recyclability and reprocessability and is expected to alleviate black pollution caused by end-of-life rubber. However, the loss of traditional vulcanization systems severely sacrifices their strength, and the tensile strength in the current study rarely exceeds 10 MPa unless fillers are added. In this work, we proposed a self-strengthening process based on dual-dynamic units (imine and disulfide), briefly, under heating, phenylsulfur radicals generated from aromatic disulfide bonds can react with double bonds (mostly vinyl) and/or couple with allyl sites, thus reforming a stronger cross-linked network. The neighboring imine unit is not affected and provides excellent thermal reprocessability and chemical recyclability. The result shows that the tensile strength can reach 19.27 MPa via self-strengthening without adding fillers or any other additives, and this ultra-high-strength is much higher than those of all known recyclable polybutadiene-based rubber materials. In addition, the material also has malleability, shape memory, and self-welding properties. By doping carbon nanotubes, a recyclable conductive composite can also be achieved. In general, we envision that this enhanced strategy has great potential to be generalized for all elastomers containing double bonds (such as styrene-butadiene rubber, nitrile rubber, isoprene rubber, and their derivatives). The reprocessability and self-welding are practical for on-site assembly or repair of composite parts and extend the service life of materials.

Self‐healable and recyclable nitrile rubber based on thermoreversible ionic crosslink network

AbstractIn this work, commercial carboxylated nitrile butadiene rubber (XNBR) was ionically crosslinked with zinc thiolate forming reversible ionic salt bonding between carboxy groups (COOH) in XNBR chains and Zn2+ ions from zinc thiolate. The reversible nature of the ionic crosslinks allows rearrangement of rubber molecular chains under an external heat and provides self‐healing capability to the materials. The amount of zinc thiolate was varied at five levels (10, 20, 30, 40, and 50 per hundred rubber (phr) to assess the maximum reaction between COOH and Zn2+ ion for the formation of ionic crosslink networks. Evidence that ionic crosslinks formed within the materials was determined by the increased of curing torque and the chemical interaction was identified by Fourier transform infrared spectroscopy. An equilibrium swelling testing quantitatively measured the ionic crosslink density within the material and XNBR with 30‐phr zinc thiolate showed the highest ionic crosslink density. The results revealed that, damaged XNBR with 30 phr zinc thiolate able to recover 98% of its initial properties under thermal healing at 150°C for 10 min. Furthermore, the material can be reprocessed and recycled for three times without compromising its initial properties. Perhaps, the tensile strength increased 360% at approximately 23 MPa, after third recycling process. In addition, the self‐healing XNBR also have excellent weldability on the damage sample, which shows high potential for repairing of existing rubber products installed in heavy engineering applications.

Novel Crosslinking System for Poly-Chloroprene Rubber to Enable Recyclability and Introduce Self-Healing.

The introduction of dynamic bonds capable of mediating self-healing in a fully cross-linked polychloroprene network can only occur if the reversible moieties are carried by the cross-linker itself or within the main polymer backbone. Conventional cross-linking is not suitable for such a purpose. In the present work, a method to develop a self-healable and recyclable polychloroprene rubber is presented. Dynamic disulfide bonds are introduced as part of the structure of a crosslinker (liquid polysulfide polymer, Thiokol LP3) coupled to the polymer backbone via thermally initiated thiol-ene reaction. The curing and kinetic parameters were determined by isothermal differential scanning calorimetry and by moving die rheometer analysis; tensile testing was carried to compare the tensile strength of cured compound, healed compounds and recycled compounds, while chemical analysis was conducted by surface X-ray Photoelectron Spectroscopy. Three formulations with increasing concentrations of Thiokol LP-3 were studied (2, 4, 6 phr), reaching a maximum ultimate tensile strength of 22.4 MPa and ultimate tensile strain of 16.2 with 2 phr of Thiokol LP-3, 11.7 MPa and 10.7 strain with 4 phr and 5.6 MPa and 7.3 strain with 6 phr. The best healing efficiencies were obtained after 24 h of healing at 80 °C, increasing with the concentration of Thiokol LP-3, reaching maximum values of 4.5% 4.4% 13.4% with 2 phr, 4 phr and 6 phr, respectively, while the highest recycling efficiency was obtained with 4 phr of Thiokol LP-3, reaching 11.2%.