Volatile matter (VM) in recovered carbon black (rCB, tire pyrolysis carbon black) refers to low-molecular pyrolysis oil residues, residual bound rubber fragments, light hydrocarbon organics and trace moisture adsorbed on carbon black aggregates, tested via thermogravimetry (ASTM D8474) or furnace proximate analysis (DIN 51720) under inert atmosphere at high temperature. Its value varies drastically based on pyrolysis temperature, post-treatment purification and commercial grade, with clear segmentation between raw crude char and finished processed rCB.
1. Volatile range of raw unprocessed pyrolysis char
Direct solid output from tire pyrolysis reactors without grinding/thermal devolatilization holds high residual organics:
- Low-temperature pyrolysis (350–450 °C): 10–18 wt% volatile matter
Incomplete cracking leaves abundant heavy tar and bituminous residues wrapped around carbon aggregates, causing severe particle agglomeration, poor dispersion and reduced iodine number. - Medium pyrolysis (450–520 °C): 7–11 wt% volatile matter (most common crude char baseline)
- High-temperature pyrolysis (>550 °C): 4–6 wt% volatile matter
Excess heat cuts organics but triggers aggregate sintering, lowering DBP absorption and reinforcing performance.
2. Standard volatile ranges for commercial processed rCB
After ultra-fine grinding, air classification and thermal desorption de-oiling, industrial-grade rCB falls into three mainstream specifications adopted by rubber compounders and tire manufacturers:
General semi-reinforcing grade (tire sidewall, hoses, mats)
Volatile matter: 5–8 wt%
Balanced cost and processability; compatible with partial replacement of N550/N660 virgin carbon black, the largest-volume rCB market product.
Premium low-volatile grade (high-performance rubber, conveyor belts)
Volatile matter: 3.0–4.5 wt%
Strictly controlled for consistent curing behavior, minimal mold fouling and stable mechanical properties; required by many tire OEM procurement standards.
Super-low volatile purified rCB (masterbatch, high-end sealing parts)
Volatile matter: <3 wt%
Requires secondary thermal devolatilization or mild oxidative cleaning to strip surface organics; performance closest to medium virgin carbon black, higher production cost.
3. Benchmark comparison with virgin carbon black
Virgin furnace carbon black has extremely low volatile content, typically 0.5–2.0 wt%, because feedstocks are fully cracked under precise continuous thermal control with no residual rubber/tar organics. This gap in volatile content is one core reason rCB cannot fully replace virgin carbon black at high loading without formulation adjustments.
4. Key factors affecting rCB volatile content
(1) Pyrolysis operating conditions
Lower reactor temperature and shorter residence time retain more tar, raising VM; overheating reduces volatiles yet damages carbon black aggregate structure.
(2) Post-processing devolatilization
Integrated thermal desorption in rCB grinding/classification lines strips surface light organics, cutting VM by 30%–60% versus raw char. JACAN’s complete rCB processing system includes low-temperature hot air stripping to stabilize volatile matter within target ranges without sintering aggregates.
(3) Feedstock tire type
Passenger car tires carry more soft polymer and plasticizers, producing rCB with higher volatiles; truck tire feedstock yields char with naturally lower residual organics.
(4) Storage and moisture absorption
Moisture is counted as part of total heating loss in quick oven tests (ASTM D1509). Humid storage slightly elevates measured volatile values, so rCB must be sealed for quality stability.
5. Industrial impact of excessive volatile matter
If VM exceeds 9 wt% in finished rCB:
- Severe agglomeration, poor dispersion in rubber compounds, visible black specks on finished goods
- Excess smoke and volatile emissions during mixing/extrusion, mold staining
- Interference with vulcanization: delayed cure rate, lower crosslink density, reduced tensile and abrasion resistance
- Blocked carbon black micropores, lowering iodine adsorption number and reinforcing capacity
Conclusion
- Raw tire pyrolysis char: volatile matter ranges 7–18 wt%, depending on pyrolysis temperature.
- Standard commercial processed rCB mainstream target: 5–8 wt% VM for general rubber applications.
- Premium low-volatility rCB for high-demand formulations: controlled at 3.0–4.5 wt%.
Super-low VM grades below 3 wt% require extra thermal purification for high-end substitution scenarios. Optimized grinding, classification and thermal devolatilization processing are essential to lower volatile residues while preserving the intrinsic reinforcing structure of recovered carbon black.
