Rubber-Metal Adhesion Mechanisms in Tire Applications

Adhesion between rubber matrices and metallic reinforcements underpins the mechanical integrity and durability of modern pneumatic tyres. Central to this phenomenon is the formation of a chemically bonded interphase at the interface of steel cords or brass-plated substrates and vulcanised elastomer. In practice, the metallic surface is first coated with a thin layer of copper-zinc alloy (brass) to provide sites for sulphidation reactions during curing. Sulphur-containing curing agents promote the conversion of metallic copper into copper sulfides, which act as chemical bridges anchoring the rubber network. Concurrently, mechanical interlocking arises from microscopic roughness introduced during plating. Additives known as adhesion promoters enhance interfacial energy and modulate vulcanisation kinetics, ensuring uniform cross-link density adjacent to the metal. Together, these processes yield high peel and shear strengths that resist thermal, mechanical and environmental ageing. Advances in imaging, surface engineering and polymer chemistry continue to refine our understanding of interfacial phenomena, with implications for fuel efficiency, rolling resistance and recycling of end-of-life tyres.

Research from Nature Portfolio

Recent studies have employed three-dimensional X-ray absorption spectroscopy coupled with machine-learning algorithms to map the spatial distribution and chemical state of copper species within ageing rubber–brass composites. This approach revealed the sequential transformation of metallic copper to discrete copper sulphide phases at both exposed surfaces and buried interfaces, quantifying reaction kinetics in situ. Insights into heterogeneity at the micrometre scale have clarified how incomplete sulphidation zones can act as initiation sites for interfacial failure under cyclic loading. Such findings pave the way for optimised plating chemistries and tailored vulcanisation protocols that promote uniform adhesion across complex geometries.

Rubber-Metal Adhesion Mechanisms in Tire Applications publication trend

The graph below shows the total number of articles in rubber-metal adhesion mechanisms in tire applications across all publications each year (not limited to Nature Index journals).

Technical terms

Sulfidation: Chemical reaction whereby metallic copper is converted into copper sulfide phases during vulcanisation.

Brass plating: Deposition of a copper-zinc alloy onto steel cord to provide reactive sites for adhesion chemistry.

Vulcanisation: Cross-linking process of rubber chains induced by sulphur or peroxide curatives to form a three-dimensional network.

Adhesion promoter: Additive that enhances chemical bonding or interfacial compatibility between rubber and metal surfaces.

Interphase: Transitional region at the rubber-metal boundary characterised by modified chemical composition and cross-link density.

References

1. Machine learning-derived reaction statistics for 3D spectroimaging of copper sulfidation in heterogeneous rubber/brass composites. Communications Materials (2023).
2. Research of the properties of rubber-cord composites in the presence of new adhesion promoters. Proceedings of the Voronezh State University of Engineering Technologies (2020).
3. The dependence of the adhesive properties of the steel cord from the different test methods and application of various compounds. Litiyo i Metallurgiya (FOUNDRY PRODUCTION AND METALLURGY) (2019).
4. Study of new rubber to steel adhesive systems based on Co(II) and Cu(II) sulphides coats. MATEC Web of Conferences (2018).