Pyrolysis char (crude recovered carbon black, rCB) from waste tire thermal cracking consists of fused hard agglomerates. The original primary aggregates of carbon black are nanoscale (20–80 nm), but high-temperature pyrolysis causes irreversible sintering to form large secondary agglomerates ranging from tens to hundreds of microns. Simply applying ordinary grinding equipment cannot isolate native nano carbon units; most equipment only reduces the size of agglomerates to micron level.
Based on ultra-fine processing technology from rcb-mill.com, this article explains the mechanism, technical route, equipment selection, critical process parameters, limitations and industrial implementation guidelines to obtain nano-dispersed pyrolysis char.
Important definition clarification
Two different concepts:
- Nano-sized primary particles: Inherent native carbon black aggregates (20–80 nm, cannot be further broken mechanically).
- Nano-dispersed powder: Destroy sintered pyrolysis agglomerates to release primary nano aggregates, achieving D50 < 1 μm, with discrete nano-scale carbon units in liquid or polymer matrix. Mechanical grinding cannot split carbon primary aggregates into smaller individual nanoparticles. It can only perform de-agglomeration.
1. Core Barriers to Obtain Nano-Scale Pyrolysis Char
- Hard sintered agglomerates
During pyrolysis, carbon aggregates bond together under thermal action to form rigid clusters. Low-shear milling only reduces lump size without separating primary nano units. - Surface tar & viscous contaminants
Unremoved pyrolysis tar acts as adhesive, making agglomerates resilient; mechanical shear bounces off rather than breaking clusters. - Impurity interference
Metal debris, ash minerals increase abrasion and hinder uniform de-agglomeration. - Re-agglomeration risk
Once nano carbon aggregates are exposed with high specific surface energy, particles rapidly re-cluster without proper dispersion medium or surface treatment.
2. Complete Technological Route for Nano De-Agglomeration of Pyrolysis Char
Step 1: Pre-Treatment (Mandatory Front-End Process)
2.1 Magnetic separation
Remove steel wire fragments and ferromagnetic impurities to avoid equipment wear.
2.2 Thermal desorption & drying
- Remove tar, volatile hydrocarbons and adsorbed moisture (moisture ≤0.25%).
- Heating temperature: 130–180°C (avoid >220°C to prevent carbon surface oxidation).
Eliminates sticky binders inside agglomerates, greatly improving subsequent de-agglomeration efficiency.
2.3 Coarse crushing
Break large bulk pyrolysis char into <200 μm feed for stable feeding into ultra-fine grinding system.
Step 2: Dry Ultra-Fine Grinding + Classification (Primary De-Agglomeration)
The JACAN dry grinding and air classification system (rcb-mill.com core equipment) implements high-intensity shear to split sintered agglomerates.
- Working principle: High-speed rotor generates impact, friction and shear force to separate fused carbon aggregates.
- Air classifier continuously extracts fine material; coarse agglomerates circulate back for repeated grinding.
- Target after dry processing: D97 ≤ 3–5 μm, most agglomerates partially opened.
Limitation: Dry grinding alone cannot achieve fully nano-dispersed state. Dry powder still exists as loose agglomerates. Dry processing is suitable as pretreatment before wet nano-grinding.
Step 3: Wet Media Milling (Key Step to Achieve Nano Dispersion)
If you need fully separated nano carbon aggregates for conductive ink, water-based coatings, slurry materials, horizontal bead milling is the standard industrial solution.
Recommended process parameters
- Medium: 0.1–0.3 mm zirconia beads (smaller beads deliver higher shear for nano de-agglomeration)
- Solid content: 15%–30% pyrolysis char slurry
- Dispersant: Polymeric dispersant matched with solvent/water system (critical to prevent re-agglomeration)
- Circulation grinding time: 2–6 hours, controlled temperature <45°C
- End-point target: D50 ≤ 300–800 nm (primary nano aggregates fully released)
Note: If dispersant dosage or type is incorrect, particles re-agglomerate immediately after milling.
Step 4: Optional Post-Treatment
- Spray drying: Convert nano slurry back into free-flowing powder for plastic and rubber applications.
- Surface activation: Improve compatibility with polymers after nano de-agglomeration.
3. Equipment Comparison for Pyrolysis Char Nano Processing
| Equipment | Fineness Limit | Working Mode | Suitability |
|---|---|---|---|
| Raymond mill / Ordinary hammer mill | D97 > 20 μm | Dry | Coarse crushing only, cannot reach nano dispersion |
| Jet mill | D97 2–8 μm | Dry | Limited de-agglomeration; high energy cost; difficult to fully open sintered rCB clusters |
| Vertical dry ultra-fine mill + air classifier (JACAN system) | D97 1–5 μm | Dry | Pre-de-agglomeration for pyrolysis char; ideal upstream process before wet milling |
| Horizontal bead mill | D50 300–1000 nm | Wet | Best choice for nano dispersion of pyrolysis char for ink, coating, slurry |
4. Critical Process Control Rules
4.1 Do not over-grind
Excessively long milling time will not reduce primary carbon particle size. Instead, it generates excessive heat, degrades dispersant and triggers severe re-agglomeration.
4.2 Inert atmosphere option (High-end conductive material grade)
Long-time high shear in air may cause mild surface oxidation of rCB. For battery and high-conductivity applications, adopt nitrogen-sealed closed milling.
4.3 Avoid premature drying of nano-dispersed wet powder
Once nano carbon slurry is dried without anti-caking treatment, irreversible hard agglomerates form again.
5. Common Misunderstandings
Misunderstanding 1: Jet mill can make pyrolysis char nano powder
Jet mill relies on particle collision. It works well for brittle minerals, but pyrolysis char agglomerates are elastic. Jet milling only breaks large lumps; it cannot fully separate sintered carbon aggregates into nano dispersed units.
Misunderstanding 2: Mechanical grinding can produce smaller nano carbon primary particles
The 20–80 nm primary carbon aggregates are formed during original tire carbon black manufacturing. Mechanical force cannot break the carbon aggregate structure; grinding only separates connected agglomerates.
6. Application-Oriented Process Selection
Scenario A: Rubber, plastic masterbatch (dry powder required)
Process flow: Pyrolysis char → magnetic separation → drying → JACAN dry ultra-fine grinding & classification.
Output: D97 ≤ 3–5 μm (de-agglomerated powder. Further nano dispersion is completed later via twin-screw extruder or Banbury internal mixer).
Scenario B: Conductive ink, water-based coating, electrode slurry (nano dispersion required)
Process flow: Pretreated refined rCB → solvent/water + dispersant premixing → horizontal bead mill circulation grinding → nano carbon slurry.
7. Challenges & Solutions After Nano Grinding
- Strong re-agglomeration tendency
Solution: Optimize dispersant; maintain stable slurry viscosity; avoid overheating. - Poor powder flow after spray drying
Solution: Add trace anti-caking agent; control spray drying temperature curve. - High energy consumption
Solution: Complete primary de-agglomeration via dry grinding first to shorten wet bead milling cycle and reduce overall cost.
You cannot grind pyrolysis char into smaller nano primary particles via mechanical force. The achievable target is de-sintering fused agglomerates to release inherent nano carbon aggregates:
- For dry powder products: Adopt integrated dry ultrafine grinding and air classification system from rcb-mill.com to achieve preliminary de-agglomeration; final nano dispersion takes place in polymer compounding equipment.
- For liquid ink, coating and slurry: Combine dry pre-processing + horizontal bead wet milling with matched dispersant system to realize stable nano dispersion.
Pretreatment (tar removal, drying, impurity removal) is the prerequisite. Skipping pre-treatment leads to low de-agglomeration efficiency, high equipment wear and failure to reach nano dispersion effect.
