Physical Parameters Relevant to Pyrolysis
A four-parameter reference table for waste tyre physical properties relevant specifically to pyrolysis — covering hardness, density, tensile strength, and elongation — with the impact of each parameter on pyrolysis reactor design and operation.
| Parameter | Value Range | Impact on Pyrolysis |
|---|---|---|
| Hardness | 65–70 Shore A | Harder tyres need more shredding energy; influences temperature profiles |
| Density | 1.05–1.20 g/cm³ | Higher density = more feedstock mass per reactor volume, affects throughput |
| Tensile Strength | 16.5–21.2 MPa | Shredders must handle high resistance from steel wires and reinforced rubber |
| Elongation | 136–142% | Strong polymer chains need higher thermal energy to crack, affects oil-to-char ratio |
Beyond definitions
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How to read this table
- Each row is one physical parameter; Value Range gives the typical range for waste tyres; Impact on Pyrolysis explains what that parameter means for the pyrolysis operation specifically.
- These parameters apply to the pre-processed feedstock entering the pyrolysis reactor — the shredded chips, not whole tyres.
- Elongation is the least commonly cited parameter but arguably the most relevant to understanding oil vs char yield distribution in pyrolysis.
About this table
Designing a tyre pyrolysis process requires understanding how the physical properties of the feedstock affect reactor behaviour, shredding requirements, and output distribution. This table covers four tyre physical properties and their specific implications for pyrolysis plant design and operation — going beyond the generic recycling relevance to the specific pyrolysis context.
Hardness at 65–70 Shore A means tyre rubber is a tough, resilient material that resists mechanical cutting. For pyrolysis, this matters in the pre-processing stage: harder tyres require more shredding energy per tonne and cause faster blade wear in primary shredders. Hardness also influences the temperature profile needed inside the reactor — harder rubber (which has more crosslinks) requires more activation energy to initiate thermal cracking. Density at 1.05–1.20 g/cm³ is the feedstock packing factor in the reactor. A higher-density feedstock packs more mass per cubic metre of reactor volume — meaning a reactor of given volume processes more tonnes per batch (for batch reactors) or per unit time (for continuous reactors). Accurate density data is essential for reactor throughput specification.
Tensile strength of 16.5–21.2 MPa is a measure of how strongly the rubber matrix resists being pulled apart. In a pyrolysis context, higher tensile strength correlates with stronger polymer chain networks that require more thermal energy to crack — reflected in the reactor needing more energy input per tonne of feedstock to achieve the same conversion rate. Tensile strength also affects the shredder specifications: shredders handling high-tensile feedstock (truck tyres, OTR tyres) need higher torque specifications than those handling lower-tensile passenger car tyres. Elongation at 136–142% measures how far the rubber stretches before breaking — it reflects the degree of polymer chain crosslinking. Higher elongation correlates with more crosslinks (from vulcanisation), which means more thermochemical energy is needed to break those crosslinks during pyrolysis. High-elongation feedstocks (particularly OTR and truck tyres with high natural rubber content) tend to produce higher char yields in pyrolysis because the more highly crosslinked rubber structure converts less efficiently to liquid oil at standard operating temperatures.
Key insights
- High elongation (136–142%) reflects a high degree of vulcanisation crosslinks — high-elongation feedstocks produce more char and less oil in pyrolysis because the crosslinked structure resists full thermal cracking at standard reactor temperatures.
- Density (1.05–1.20 g/cm³) directly determines reactor throughput — a denser feedstock pack produces more tonnes of oil and char per reactor cycle, which is the primary driver of batch reactor economics.
- High tensile strength tyres (truck, OTR) require higher-torque shredders and more reactor energy per tonne — this operational cost difference must be factored in when evaluating truck or OTR tyre as a feedstock relative to passenger car tyres.
- Hardness at 65–70 Shore A positions tyre rubber as significantly harder than soft rubber (30 Shore A) but softer than hard rubber (90 Shore A) — most standard tyre shredders are designed for this hardness range.
Methodology & sources
Physical parameters are based on published data for typical waste tyres. Values vary with tyre type (car vs truck vs OTR), manufacturer, and age. Elongation data in particular varies significantly between natural rubber-dominant (OTR, truck) and synthetic rubber-dominant (passenger car) tyre compounds. For reactor design purposes, laboratory testing of the specific feedstock available at the plant site is recommended.
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