The optimal temperature of rCB surface treatment is process-dependent. There is no single universal value; the target temperature is determined by your treatment goal: devolatilization/PAH removal, wet chemical oxidation, dry oxidative functionalization, or high-temperature steam/CO₂ activation for high-end rubber, masterbatch and new-energy applications.
1. Thermal devolatilization (most common pre-surface treatment for mining tire rCB)
Optimal range: 800–950 °C (inert / low-oxygen atmosphere, rotary kiln or fluidized bed)
This step burns off residual tar, heavy hydrocarbons and PAH contaminants coated on crude pyrolysis char surfaces without severely destroying the original carbon-black aggregate microstructure.
- Below 800 °C: tar and polycyclic aromatic residues cannot be fully stripped, leading to poor dispersion and high PAH content, disqualifying rCB for tire-grade or high-performance rubber.
- Above 950–1100 °C: excessive thermal sintering shrinks pore structure, reduces BET surface area and weakens reinforcement performance, raising energy consumption sharply.
For standard high-end rubber rCB, 850 °C is widely accepted as the sweet spot for continuous industrial devolatilization.
2. Mild dry oxidative surface functionalization (add oxygen-containing groups: -COOH, -OH)
Optimal range: 300–380 °C, controlled low-concentration air/oxygen
This process grafts polar functional groups onto rCB surfaces to improve compatibility with rubber and polymer matrices.
- <300 °C: reaction kinetics are too slow; few functional groups are formed.
-
385 °C: runaway oxidation occurs, causing mass loss, over-etching and uncontrolled burnout of carbon framework.
Best industrial setpoint: 350–370 °C with precise oxygen concentration control.
3. Wet chemical surface modification (nitric acid, alkaline leaching, silane coupling)
- Acid oxidative modification (HNO₃): optimal 45–65 °C. Temperatures above 70 °C cause aggressive over-oxidation and carbon etching.
- Silane coupling / wet functionalization for polymer composites: 80–120 °C. This improves silane grafting on rCB surface for better filler-matrix bonding.
4. High-temperature physical/chemical activation (for ultra-high surface area rCB / activated carbon grade)
Steam or CO₂ activation to boost BET surface area: 800–900 °C.
KOH chemical activation for maximum porosity: target 800 °C.
This route is only used for special high-value applications such as adsorbents or conductive fillers, not standard tire rCB, because it breaks the reinforcing aggregate structure required for rubber reinforcement.
Key operational notes for rCB from mining tire pyrolysis char
- Atmosphere is as critical as temperature. Devolatilization and activation must run under nitrogen or low oxygen to prevent bulk carbon loss.
- Heating rate and holding time must match temperature. Too fast heating causes localized hot spots and uneven surface treatment.
- Sequence matters: magnetic separation → ultrafine grinding & classification → thermal devolatilization → mild surface functionalization. Grinding before high-temperature treatment prevents agglomerate re-fusion.
Quick summary table
| Treatment Purpose | Optimal Temperature | Atmosphere | Typical Application |
|---|---|---|---|
| Tar / PAH devolatilization (tire-grade rCB) | 800–950 °C, sweet spot ~850 °C | N₂ / low O₂ | OTR tire, heavy-duty rubber |
| Dry oxidative functionalization | 350–370 °C | Controlled dilute air | Engineering plastic, masterbatch |
| Wet acid oxidation | 45–65 °C | Aqueous | Surface polarity increase |
| Silane wet grafting | 80–120 °C | Aqueous / ethanol | Polymer composite |
| Steam / CO₂ high-activation | 800–900 °C | Steam / CO₂ | High surface-area specialty materials |
