Key Takeaways & Executive Findings
- •• • Achieved direct upcycling of unmodified waste BIIR via SiO2-Py nanoparticles, yielding composites with tensile strength ~14 MPa and toughness ~60 MJ m−3, outperforming original inner tube material and enabling high-performance reuse. • • The dual interpenetrating network (sulfur-vulcanized + bromine-pyridinium crosslinked silica-rich) provides exceptional mechanical properties, with air permeability as low as 8.78×10−15 cm3 cm/(cm2 s Pa), critical for tire and seal applications. • • Strategy circumvents energy-intensive desulfurization or pyrolysis, preserving the polymer backbone and original sulfur network, reducing environmental impact and processing costs. • • Demonstrated scalability using discarded bicycle inner tubes, showing potential for industrial adoption in rubber recycling without chemical modification of waste.
Abstract
Brominated butyl rubber (BIIR) is widely used in tires and biomedical products due to its excellent elasticity and gas barrier properties, but recycling end-of-life BIIR remains challenging because of its covalent cross-linked network. Here, we report a direct upcycling strategy for unmodified waste BIIR via nanoparticle-mediated interfacial crosslinking, avoiding chemical modification or degradation of the polymer structure. Pyridyl-functionalized silica nanoparticles (SiO2-Py) were synthesized and used to crosslink bromine atoms in waste BIIR with those of fresh BIIR, reconstructing the crosslink network without altering the original sulfur-vulcanization network. The resulting composites exhibit a dual interpenetrating network comprising the sulfur-vulcanized network and a bromine-pyridinium crosslinked silica-rich network, providing exceptional strength and toughness. Using discarded bicycle inner tubes as waste BIIR source, the upcycled composites achieved a tensile strength of ~14 MPa, toughness of ~60 MJ m−3, and ultra-low air permeability of 8.78×10−15 cm3 cm/(cm2 s Pa), significantly outperforming the original inner tube material. This work presents a scalable and effective solution for BIIR waste recycling, advancing sustainable development in the rubber industry.
1. Introduction
Brominated butyl rubber (BIIR) is indispensable in tire inner liners, pharmaceutical stoppers, and protective apparel due to its impermeability and damping characteristics. Yet its thermoset nature, arising from sulfur vulcanization, renders conventional recycling futile: grinding yields low-value crumbs, while devulcanization or pyrolysis degrades the polymer backbone and emits volatile organic compounds. Existing reprocessable rubbers rely on dynamic covalent or non-covalent crosslinks introduced during synthesis, but these require chemical modification of virgin polymer, altering mechanical performance and complicating integration with established manufacturing lines. Consequently, waste BIIR—amounting to millions of tons annually—accumulates in landfills or incinerators, representing both a resource loss and an environmental liability.
This work introduces a nanoparticle-mediated interfacial crosslinking strategy that directly upcycles unmodified waste BIIR. Pyridyl-functionalized silica nanoparticles (SiO2-Py) react with bromine atoms on both waste and fresh BIIR chains, forming a new crosslinked network that interpenetrates the original sulfur-vulcanized network. This approach avoids any chemical modification or degradation of the waste polymer, preserving its intrinsic properties while enabling reconstruction of a robust network. The resulting composites exhibit a dual-network architecture that synergistically enhances strength and toughness, as evidenced by tensile strength of ~14 MPa and toughness of ~60 MJ m−3. Moreover, the silica-rich network imparts ultra-low gas permeability (8.78×10−15 cm3 cm/(cm2 s Pa)), surpassing the performance of the pristine inner tube material. This strategy offers a scalable, industrially viable route to upcycle waste BIIR into high-performance composites, addressing a critical bottleneck in rubber sustainability.
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Changwei Wu, Jie Wen, Meijuan Jiang, Xinyuan Bi, Zhengtian Xie, Jinrong Wu (2026). Direct Upcycling of Unmodified Waste Brominated Butyl Rubber via Nanoparticle-Mediated Interfacial Crosslinking Strategy. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3681-6
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Frequently Asked Questions
What is the mechanism by which SiO2-Py nanoparticles crosslink waste BIIR without altering the sulfur-vulcanized network?
SiO2-Py nanoparticles bear pyridyl groups that undergo nucleophilic substitution with bromine atoms on BIIR chains, forming bromine-pyridinium linkages. This reaction occurs at the interface between waste BIIR and fresh BIIR, creating a new crosslinked network that interpenetrates the existing sulfur-vulcanized network. The sulfur network remains intact because the reaction targets only bromine sites, not sulfur crosslinks, preserving the original network structure.
How do the mechanical properties of the upcycled composites compare to those of the original BIIR material from bicycle inner tubes?
The upcycled composites exhibit a tensile strength of approximately 14 MPa and toughness of about 60 MJ m−3, significantly outperforming the original inner tube material. This enhancement is attributed to the dual interpenetrating network structure, which combines the resilience of the sulfur-vulcanized network with the reinforcing and crosslinking effects of the silica-rich network.
What is the air permeability of the upcycled composites, and why is it important for applications?
The upcycled composites show an ultra-low air permeability of 8.78×10−15 cm3 cm/(cm2 s Pa), which is critical for tire inner liners and airtight seals. This value is lower than that of the original BIIR material, indicating improved gas barrier properties, which can enhance tire performance and reduce air loss over time.
What are the scalability and environmental advantages of this upcycling strategy compared to conventional recycling methods?
This strategy avoids energy-intensive processes like desulfurization or pyrolysis, which degrade the polymer backbone and emit VOCs. By directly crosslinking waste BIIR with SiO2-Py nanoparticles, the process is simpler, more energy-efficient, and preserves the polymer structure. The use of discarded bicycle inner tubes demonstrates scalability, and the resulting high-performance composites can be used in demanding applications, offering a sustainable alternative to landfilling or incineration.
How does the dual network structure influence the mechanical performance, and what are the underlying mechanisms?
The dual interpenetrating network consists of the original sulfur-vulcanized network and a new bromine-pyridinium crosslinked silica-rich network. The sulfur network provides elasticity and resilience, while the silica-rich network imparts rigidity and energy dissipation. This combination results in exceptional strength and toughness, as the rigid network distributes stress and the elastic network maintains flexibility, preventing catastrophic failure.
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