Application of AO168 in Recycled Plastics: Problem Analysis and Solutions
With the development of the circular economy and environmental regulations, PCR (Post-Consumer Recycled) plastics are increasingly used in:
- Packaging materials
- Appliance housings
- Automotive parts
- Construction materials
- Cable sheaths
- Consumer products
Compared to virgin plastics, recycled materials often have:
- Oxidation and chain scission
- Higher moisture content
- Metal contaminants
- Poor thermal stability
These factors make recycled plastics more prone to yellowing, black specks, odors, and melt instability during processing, affecting both appearance and performance.
1. Role of AO168 in Recycled Plastics
AO168 is a phosphite secondary antioxidant. Its main function is to:
- Decompose hydroperoxides (ROOH) in polymers
- Prevent further thermal oxidative degradation
AO168 can improve:
- Yellowing
- Black spots
- Odor
- Smoke formation
- Melt instability
- MFI fluctuations
- Thermal aging resistance
AO168 mechanism illustration
2.1 Yellowing
Most common problem in PCR materials, especially:
- White or light-colored plastics
- Appliance housings
- High-temperature extrusion materials
Cause
Recycled materials are partially oxidized. During processing:
- AO168 is consumed quickly
- Residual oxidation products continue reacting
→ Resulting in yellowed material.
Yellowing defect photo
- Increase AO168 to 0.08–0.15%
- Combine with AO1010 (0.05–0.10%)
- Lower processing temperature
- Shorten melt residence time
- Ensure raw material is fully dried
Recommended Parameters to Prevent Yellowing
| Item | Recommended Parameter |
|---|---|
| AO168 dosage | 0.08–0.15% |
| AO1010 dosage | 0.05–0.10% |
| PP processing temperature | ≤230℃ |
| Melt residence time | ≤6 min |
| Raw material moisture | ≤0.1% |
2.2 Black spots and carbonized particles
Appearance: Black specks, carbonized particles in extrudate.
Causes
- Severely oxidized old material
- Metal contamination
- Extruder build-up or excessive shear
- AO168 degradation leading to further oxidation
Black spot defect photo
- Increase screen mesh count
- Regular equipment cleaning
- Reduce screw shear
- Use AO168 in combination with primary antioxidants
Optional: add metal deactivators or processing lubricants.
Black spot troubleshooting table
| Source | Symptoms | Suggested Action |
|---|---|---|
| Extruder build-up | Random black specks | Regular cleaning |
| Metal contamination | Hard black particles | Increase filtration |
| AO168 depletion | Black specks with yellowing | Add primary antioxidants |
| Excessive shear | Increased carbonized material | Reduce screw speed |
2.3 Odor and smoke
Recycled plastics often contain:
- Oils
- VOCs
- Residual organics
- Degradation byproducts
These accelerate AO168 decomposition at high temperatures → smoke, odor, irritant fumes.
Smoke and odor photo
- Pre-wash recycled materials
- Use vacuum vented extrusion
- Reduce processing temperature by 10–20℃
- Minimize idle or dead time
Optional: add adsorbents, odor removers, or vacuum devolatilization.
VOC Control Parameters
| Item | Recommended Value |
|---|---|
| Vacuum pressure | -0.08~-0.095 MPa |
| Extrusion temperature | Reduce 10–20℃ |
| Recycled material cleaning | ≥2 times |
| VOC limit | <1000 ppm |
| AO168 dosage | 0.1–0.2% |
2.4 Melt flow index (MFI) fluctuations
Symptoms: Unstable MFI → dimensional variation, melt fracture, reduced mechanical properties.
Causes
- Chain scission in recycled polymer
- Insufficient AO168 → continued oxidative degradation
Melt degradation photo
- Increase AO168 dosage
- Combine with AO1010
- Control processing temperature
- Reduce screw speed and melt residence time
MFI Improvement Reference Table
| Material | Without AO168 | With AO168 |
|---|---|---|
| PCR PP | ±35% MFI fluctuation | ±10% MFI fluctuation |
| PCR PE | Melt fracture | Stable melt |
| PCR ABS | Many black specks | Black spots reduced |
| PCR HIPS | Significant yellowing | Color improved |
3. Recommended AO168 Dosage in PCR Materials
| Material | AO168 Dosage |
|---|---|
| PCR PP | 0.08–0.15% |
| PCR PE | 0.05–0.12% |
| PCR ABS | 0.10–0.20% |
| PCR PET | 0.15–0.25% |
| PCR engineering plastics | 0.10–0.30% |
4. Recommended Processing Guidance
1. Dry raw materials
AO168 is moisture-sensitive. Typical drying conditions:
| Material | Drying Temp | Drying Time |
|---|---|---|
| PCR PET | 120–160℃ | 4–6 h |
| PCR PA | 80–120℃ | 4–8 h |
| PCR PP | 80–100℃ | 2–4 h |
| PCR PE | 80–100℃ | 2–4 h |
| PCR ABS | 80–90℃ | 2–3 h |
2. Do not use AO168 alone
AO168 is a secondary antioxidant. Must be combined with primary antioxidants:
- AO1010
- AO1076
3. Control processing temperature
- PP ≤230℃
- PE ≤220℃
- ABS ≤240℃
Avoid long melt residence, repeated recycling, and dead spots in equipment.
4. Use vacuum venting
Significantly reduces:
- VOC
- Odor
- Smoke
- Oxidation risk
5. Conclusion
AO168 is essential for stabilizing PCR recycled plastics. It effectively mitigates:
- Yellowing
- Black spots
- Odor
- Melt instability
However, due to the complex nature of recycled materials, challenges such as moisture, metal contamination, oxidative residues, and high processing temperatures remain.
By optimizing:
- Formulation
- Primary/secondary antioxidant synergy
- Temperature control
- Vacuum venting
- Raw material drying
AO168 can deliver maximum stability in recycled plastics.
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Ecochem China
Website: www.ecochemchina.com
Email: info@ecochemchina.com
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