Physical and Chemical Properties of Waste Tires
Nine physical and chemical properties of waste tyres with their recycling significance — covering hardness, density, tensile strength, rubber content, steel content, textile fibres, carbon black, sulfur, and zinc oxide.
| Property | Value Range | Significance for Recycling |
|---|---|---|
| Hardness | 65-70 Shore A | Indicates resistance to mechanical processing; affects shredder blade wear |
| Density | 1.05-1.20 g/cm³ | Used for volume-to-mass conversions in storage and process calculations |
| Tensile Strength | 16.5-21.2 MPa | Higher values mean more energy required for size reduction |
| Rubber (natural + synthetic) | 45-47% | Primary recoverable material |
| Steel (bead wire + belt) | 20-25% | Must be separated; saleable byproduct |
| Textile fibers | 10-15% | Must be separated; limited recycling value |
| Carbon black | 25-30% | Reinforcing filler, retained in crumb rubber |
| Sulfur | 1-3% | Forms crosslinks; target of devulcanization |
| Zinc oxide | 1-2% | Vulcanization activator; leaching concern in end uses |
Beyond definitions
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How to read this table
- 5+ rows, structured short-form: Hardness: 65–70 Shore A, affects shredder blade wear. Density: 1.05–1.20 g/cm³, for volume-to-mass conversions. Tensile Strength: 16.5–21.2 MPa, determines size reduction energy. Rubber: 45–47%, primary recoverable material. Steel: 20–25%, saleable byproduct. Textile fibres: 10–15%, limited recycling value. Carbon black: 25–30%, reinforcing filler in crumb rubber. Sulfur: 1–3%, target of devulcanisation. Zinc oxide: 1–2%, leaching concern.
About this table
Understanding the physical and chemical composition of waste tyres is essential for selecting the right processing equipment, predicting output yields, and managing end-use quality. This table covers nine key properties — three physical parameters and six compositional ones — with their specific significance for the recycling process.
The three physical parameters (Hardness, Density, Tensile Strength) determine equipment selection. Tyre rubber at 65–70 Shore A hardness is a tough, resilient material — considerably harder than the rubber in gloves or gaskets — and this hardness is what makes shredder blades wear quickly and determines the power requirement for size reduction. Density at 1.05–1.20 g/cm³ (slightly denser than water) is used for volume-to-mass conversions in process engineering. Tensile strength of 16.5–21.2 MPa means higher tensile tyres require more energy per kilogram of size reduction.
The compositional parameters determine output yields and quality. Rubber (natural plus synthetic) at 45–47% is the primary recoverable material — this fraction becomes crumb rubber, reclaimed rubber, or the rubber content in pyrolysis oil. Steel (20–25%) from bead wires and belt reinforcement must be separated before further processing; it is the second-most valuable output stream, sold to scrap steel buyers. Textile fibres (10–15%) from fabric reinforcement plies must also be separated and have limited recycling value — they are typically disposed of or used as a low-value fuel supplement. Carbon black (25–30%) is the reinforcing filler embedded in the rubber compound — it remains in the crumb rubber output and contributes to its performance in end-use applications like road surfacing. Sulfur (1–3%) forms the chemical crosslinks (vulcanisation bonds) that make rubber elastomeric — sulfur is the target of devulcanisation in reclaimed rubber production. Zinc oxide (1–2%) is the vulcanisation activator — at high concentrations it creates zinc leaching concerns in some end-use environments.
Key insights
- The rubber fraction (45–47%) determines maximum yield from any recycling process — the steel (20–25%), fibres (10–15%), and non-recoverable fractions set the yield ceiling.
- Sulfur content (1–3%) is the target of devulcanisation — breaking sulfur crosslinks is the key chemical challenge in producing high-quality reclaimed rubber that can substitute for virgin rubber.
- Carbon black (25–30%) stays in the crumb rubber output and is a key reason crumb rubber performs well in road surfacing applications — carbon black improves UV resistance and durability.
- Zinc oxide (1–2%) creates zinc leaching concerns in some end-use environments — crumb rubber used in water-permeable applications (playground infill, sports surfaces) has been studied for zinc leaching potential.
Methodology & sources
Property values are based on published data for typical passenger car and commercial vehicle tyres in India. Actual composition varies by tyre type, manufacturer, and vintage. Hardness is measured on Shore A durometer scale. Tensile strength values are for vulcanised tyre compound. Steel content includes both bead wire and belt reinforcement steel. Carbon black content varies with tyre compound formulation.
Related data tables
Material Bulk Density for Storage Calculations
Bulk density values for five tyre-derived materials — whole tyres, shredded chips, crumb rubber, fine powder, and reclaimed rubber sheets — used to convert mass-based storage requirements into volume-based storage area calculations.
Material Composition by Tyre Type
Percentage breakdown of eight material components (rubber, carbon black, metals, textiles, zinc oxide, sulphur, additives, and carbon-based total) across three tyre categories — car/utility, truck/lorry, and OTR tyres.
Types of Tires as Feedstock
A four-category reference table for waste tyre feedstock — automobile, off-road, specialty, and OTR (Off-The-Road) tyres — showing typical weight ranges, construction characteristics, and where each category is available in India.