During high-temperature processing, long-term outdoor service and humid aerobic environments, polymer materials continuously undergo thermo-oxidative aging and free radical chain reactions, resulting in yellowing, embrittlement, deteriorated mechanical properties, viscosity loss and other defects. Single-type antioxidants have inherent protective limitations and cannot satisfy comprehensive requirements including processing stability, long-term aging resistance, anti-yellowing performance, hydrolysis resistance and high-temperature tolerance.
Commercially mainstream antioxidants fall into three major categories: primary antioxidants (hindered phenols), secondary antioxidants (phosphites, thioesters) and specialty antioxidants. Each type has complementary strengths and weaknesses, and synergistic blending can deliver a protection effect greater than the sum of individual components, which is the core logic for formula optimization of polymer additives.
I. Pros and Cons of Single Mainstream Antioxidant Types
- Primary Antioxidants: Hindered Phenols (Free Radical Scavengers for Long-Term Protection)
Hindered phenols are the only primary antioxidants usable alone. Their core mechanism is capturing active free radicals in oxidative chain reactions to terminate aging cycles, focusing on long-term anti-aging protection during storage and service of finished products, serving as the fundamental component in all formulas.
Core Advantages
Excellent long-term stability: Stable molecular structure and outstanding persistent antioxidation, effectively preventing post-production embrittlement, cracking and mechanical degradation throughout the product service life.
Wide compatibility and universal applicability: Compatible with most polymers such as PE, PP, ABS, PC, nylon and rubber; low migration and blooming risk.
Good basic high-temperature resistance: High-molecular-weight hindered phenols (1010, 1098) feature high thermal decomposition temperature, suitable for conventional and medium-to-high temperature processing.
High chemical stability: No hydrolysis risk, applicable to humid and water-containing systems.
Core Drawbacks
Weak processing stability: Incapable of decomposing hydroperoxides generated under high processing temperature; insufficient to suppress instantaneous thermal degradation, leading to unstable melt flow.
Slight yellowing at high temperature: Quinone by-products form upon reaction, accumulating under prolonged heat and darkening the base tone; single use causes yellowing in highly transparent, white and light-colored products.
Limited heat resistance of low-molecular-weight grades: Grades like 1076 have low melting point and high volatility, prone to loss and failure under ultra-high processing temperatures.
Representative Grades & Characteristics
1010: High molecular weight, low volatility, superior heat resistance and long-term performance, universal first choice with mild yellowing tendency.
1076: Fast acting and clean base color, yet low molecular weight with poor heat resistance.
1098: Amide-modified, specially designed for nylon with excellent performance under nylon high-temperature processing and long-term aging; low cost-effectiveness for other polymers. - Secondary Antioxidants: Phosphites (Processing Stabilization & Anti-Yellowing Focus)
Phosphites are the most widely used secondary antioxidants in industry. They cannot terminate free radical chain reactions independently and must be blended with primary antioxidants. Their core function is decomposing hydroperoxides formed under high processing temperature to block instantaneous thermal degradation.
Core Advantages
Top-tier processing protection: Targets melt degradation and viscosity fluctuation during extrusion, injection molding and fiber drawing, stabilizing melt fluidity.
Outstanding anti-yellowing performance: No yellowing by-products under heat, offsetting slight yellowing caused by hindered phenols, ideal for transparent, white and light-colored articles.
Fast activation: High efficiency at high temperature, instant antioxidation to restrain oxidation during processing.
Core Drawbacks
No long-term protective effect: Only functions during high-temperature processing, losing antioxidation capacity at room temperature and leading to rapid aging failure of finished products if used alone.
Poor hydrolysis resistance: Most phosphites hydrolyze rapidly in moisture and humid environments, releasing trace acidic substances that corrode resins and damage product stability.
Limited compatibility for certain grades: High-phosphorus grade 626 delivers premium color retention yet suffers extremely weak hydrolysis resistance, forbidden for harsh humid conditions.
Representative Grades & Characteristics
168: Cost-effective, excellent compatibility and widest applicability, moderate heat resistance, preferred for general-purpose scenarios.
626: High phosphorus content and top-grade anti-yellowing property for high-end transparent products, with poor hydrolysis resistance as its main defect.
PEP-36: Superior heat resistance versus 168 and 626, suitable for engineering plastics processed above 280°C. - Secondary Antioxidants: Thioesters (Long-Term Aging Reinforcement with Low Cost)
Thioesters are secondary antioxidants that cannot be applied separately. They decompose peroxides and mainly enhance long-term thermal aging resistance, forming scenario complementarity with phosphites.
Core Advantages
Remarkable long-term anti-aging reinforcement: Greatly extends thermal oxidation service life, especially for thick PP products, pipes and injection molded parts enduring long-term high temperature.
Low cost: Far more cost-efficient than high-end phosphites, reducing formulation cost for bulk general plastic products.
Stable high-temperature performance: High thermal decomposition temperature without volatile loss at low temperatures.
Core Drawbacks
Poor anti-yellowing capability: Discolors easily under heat, strictly prohibited for white, transparent and light-colored products.
No processing stabilization effect: Cannot mitigate melt degradation and viscosity fluctuation during high-temperature processing.
Multiple formulation incompatibilities: Must not be blended with lead-based heavy metal stabilizers or acidic additives, triggering redox reactions and performance failure.
Representative Grades & Characteristics
DLTDP and DSTDP; DSTDP boasts better heat resistance and stability than DLTDP as the mainstream preferred grade. - Specialty Antioxidants (For Segmented Special Scenarios, Covering Performance Blind Spots of General Grades)
Developed for high-end and special applications unfit for conventional antioxidants, making up for performance gaps of general types:
Antioxidant CA: High heat resistance, low volatility and minimal yellowing, suitable for PS and special plastics with good compatibility; downside: moderate antioxidation strength, prone to blooming with excessive dosage.
Antioxidant 136: Low migration, extraction resistance, long-term contamination-free performance, applicable to high-end engineering plastics and food-contact products; downside: high price and narrow applicability, only for premium applications.
II. Core Complementary Principles of Different Antioxidant Categories
The core blending logic of antioxidants: primary antioxidants secure long-term protection, secondary antioxidants stabilize processing, specialty antioxidants fill performance gaps. Blending different categories offsets individual defects, covering full-cycle protection including high-temperature processing, long-term service and extreme environments to achieve synergistic enhancement. - Hindered Phenol + Phosphite (Industry Standard Golden Combination)
Complementary Logic
Hindered phenol drawbacks: insufficient processing stability, slight yellowing; advantage: long-term aging resistance.
Phosphite drawbacks: no long-term protection, poor hydrolysis resistance; advantages: processing stabilization, anti-yellowing, fast activation.
Synergistic Effects
Phosphites decompose peroxides, stabilize melt and suppress yellowing during high-temperature processing; hindered phenols capture free radicals to provide long-term anti-aging protection throughout product service life, covering both processing and service cycles. This is the standard formula for transparent plastics, light-colored articles and general polymers.
Common Mixing Ratios
1:2 or 1:1 (1010:168) for general applications; 2:1 (1010:626) for high-end anti-yellowing requirements. - Hindered Phenol + Thioester (Low-Cost Long-Term Aging Reinforcement Formula)
Complementary Logic
Thioesters compensate phosphites for high cost and insufficient long-term aging reinforcement.
Hindered phenols offset thioesters’ defects including no free radical scavenging capacity, poor processing stability and easy discoloration.
Synergistic Effects
Dual reinforcement of high-temperature and long-term aging resistance, drastically extending service life of thick PP/PE industrial products while lowering formulation cost.
Applicable Scenarios
Black and dark industrial plastic products, pipes, sheets and structural injection molded parts; forbidden for light-colored and transparent articles. - Hindered Phenol + Phosphite + Thioester (High-Performance All-Round Formula)
Complementary Logic
Integrates core strengths of three types: phosphites stabilize processing and resist yellowing, hindered phenols provide basic long-term protection, thioesters deliver secondary aging reinforcement, eliminating all single-component weaknesses.
Applicable Scenarios
High-demand outdoor products, high-temperature resistant engineering plastics and modified plastics enduring long-term sunlight exposure, delivering optimal comprehensive antioxidation performance.
III. Blending Incompatibilities & Avoidance Guidelines (Prevent Antagonism and Negative Complementation)
Phosphites incompatible with alkaline additives: Alkaline lubricants such as calcium/zinc stearate neutralize phosphites, directly deactivating the antioxidant system.
Thioesters incompatible with heavy metal stabilizers: Reacts with lead-based stabilizers to trigger discoloration and material degradation, completely losing protective performance.
Restrained use of 626 in high-temperature & high-humidity conditions: 626 suffers severe hydrolysis in humid and water-containing processing systems, rapidly losing efficacy and releasing acidic substances that damage resins.
1098 is application-specific, not universal: Delivers outstanding protection only for nylon systems with low cost-effectiveness and negligible synergistic effects when used with other plastics.
Controlled dosage of specialty antioxidants: Excessive CA or 136 causes blooming and impaired surface gloss of finished products, requiring strict dosage control.
IV. Summary: Mnemonic for Category Complementary Characteristics
Phenol alone: Excellent long-term protection, poor processing stability, slight yellowing.
Phosphite alone: Stable processing, anti-yellowing, no long-term protection.
Thioester alone: Strong aging resistance, low cost, easy discoloration.
Phenol + Phosphite complementary: Full-cycle protection, low yellowing, universal all-purpose formula.
Phenol + Thioester complementary: Superior aging resistance, low cost, only for dark-colored products.
Triple-component blend: High performance, full coverage, suitable for high-end applications.
Rational utilization of complementary advantages and disadvantages among antioxidant categories can specifically resolve core pain points including polymer degradation during processing, post-production aging, yellowing & gloss loss and mechanical performance attenuation, while optimizing formulation costs. It serves as a key technical point for formula upgrading in modification, injection molding and extrusion industries.