AO168 Application Precautions: Which Additives Should Not Be Mixed? What Problems Can Incorrect Formulations Cause?
In the plastic modification and polymer processing industry, Antioxidant 168 (AO168) is one of the most widely used phosphite secondary antioxidants.
AO168 offers:
- Excellent processing stability
- Good thermal resistance
- Low volatility
- Outstanding color retention
Therefore, it is widely used in:
- PP
- PE
- ABS
- PC
- PA
- PET
- PBT
- Elastomers
and many other polymer systems.
The primary function of AO168 is:
Decomposing hydroperoxides generated during polymer processing
thereby preventing thermal oxidative degradation of polymers.
However, many plastic manufacturers eventually realize that:
AO168 is not a “universally compatible” additive
If the formulation design is improper,
or if it is incorrectly combined with certain additives,
it can easily cause:
- Yellowing
- Smoke generation
- Increased odor
- Black specks
- Melt instability
- Increased acid value
- Reduced mechanical properties
and in severe cases, lead to complete product failure.
Therefore, understanding the application precautions and compatibility limitations of AO168 is extremely important for polymer processing stability.
1. Why Is AO168 Easily Affected by Other Additives?
AO168 belongs to:
Phosphite antioxidants
Its molecular structure contains:
P–O bonds
Although this structure efficiently decomposes hydroperoxides,
it also means that AO168 is relatively sensitive to:
- Moisture
- Acidic substances
- Oxidative environments
Therefore, the stability of AO168 in formulations strongly depends on:
- Additive compatibility
- Processing conditions
- Temperature
- Moisture
- Acidity and alkalinity
2. The Most Problematic System for AO168: Strong Acidic Additives
1. Incorrect Combination with Acidic Flame Retardants
Many flame-retardant systems are inherently acidic.
Examples include:
- Acidic phosphorus flame retardants
- Certain DOPO systems
- Acidic phosphate flame retardants
These substances can:
Catalyze AO168 hydrolysis
leading to:
- Rapid antioxidant failure
- Processing yellowing
- Smoke generation
- Increased acid value
In severe cases, it may even cause:
Heavy smoke from the extrusion line
Typical Consequences of Incorrect Formulation
Common symptoms include:
- Yellowing of flame-retardant PP compounds
- Strong irritating odor during extrusion
- Darkened product surfaces
- Brittleness after long-term heat aging
Product Photos of Yellowing and Thermal Oxidation
Many newcomers to the plastics industry mistakenly assume that:
“AO168 can be used in all plastics”
In reality:
PVC systems are not compatible with AO168
because PVC releases:
HCl (hydrochloric acid)
during high-temperature processing.
Hydrochloric acid rapidly attacks:
The P–O bonds in AO168
causing rapid phosphite decomposition.
Common Problems After Incorrect Use
These may include:
- Rapid product yellowing
- Reduced thermal stability
- Smoke generation
- Increased odor
- Severe discoloration over time
Therefore, PVC systems more commonly rely on:
- Ca-Zn stabilizers
- Organotin stabilizers
- β-diketone stabilizers
rather than depending solely on AO168.
PVC Processing Defects and Discoloration
AO168 is essentially a:
Reductive stabilizer
Therefore, it is not suitable for use with strong oxidizing systems.
Typical Incompatible Systems
Examples include:
- DCP (Dicumyl peroxide)
- Benzoyl peroxide
- Crosslinking initiators
These systems rapidly consume AO168.
Consequences of Incorrect Combination
Possible issues include:
- Rapid antioxidant depletion
- Abnormal color changes
- Melt instability
- Poor processing consistency
This problem is especially obvious in:
- XLPE cable compounds
- Crosslinked polyethylene
- Foaming materials
Product Photos of Crosslinking and Oxidation Defects
Many engineers overlook the fact that:
Metal ions significantly affect AO168 stability
Especially:
- Copper
- Iron
- Manganese
These metal ions can:
Catalyze polymer oxidation reactions
and accelerate AO168 degradation.
Typical Problematic Systems
Examples include:
- Copper wire cable compounds
- Copper-containing pigment systems
- Metal-filled composite materials
Consequences of Incorrect Combination
These may include:
- Increased black specks
- Reduced long-term heat aging performance
- Material embrittlement
- Color instability
Product Photos of Black Specks and Thermal Degradation
Certain pigments contain:
- Metal ions
- Acidic residues
- Heavy metal catalysts
which may also affect AO168 stability.
This is especially common with:
- Copper phthalocyanine pigments
- Certain inorganic pigments
- Low-quality color masterbatches
Common Problems
These include:
- Color shift
- Gray discoloration
- Yellowing
- Reduced long-term stability
Therefore, high-end polymer systems often add:
Metal deactivators
such as:
- AO1024
- Copper inhibitor systems
to protect AO168 stability.
Product Photos of Pigment Instability and Color Defects
Although AO168 is one of the most important secondary antioxidants in the plastics industry,
it is not a “universal stabilizer” suitable for every formulation system.
Because its phosphite structure is sensitive to:
- Moisture
- Acidic environments
- Metal ions
- Strong oxidizing systems
special attention must be paid to additive compatibility during formulation design.
Incorrect additive combinations may lead to:
- Yellowing
- Smoke generation
- Black specks
- Increased odor
- Reduced thermal stability
- Long-term aging failure
Only by properly controlling:
- Additive combinations
- Processing temperature
- Raw material drying
- Metal contamination
can AO168 deliver its excellent processing stabilization performance.
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