Application of Antioxidant 168 in EVA Photovoltaic Encapsulation Film

August 5, 2026

Application of Antioxidant 168 in EVA Solar Photovoltaic Encapsulation Film

As photovoltaic modules continue to evolve toward higher power output, longer service life, and greater reliability, EVA solar encapsulation film must provide more than excellent transparency, adhesion, and flexibility. It must also withstand extrusion processing, module lamination, and long-term exposure to sunlight, heat, oxygen, and moisture.

During the production of EVA film, the resin undergoes compounding, melt extrusion, film formation, and subsequent high-temperature lamination. Heat, shear forces, and oxygen may promote the formation of peroxides and hydroperoxides in EVA. These reactions can lead to polymer chain scission, uncontrolled crosslinking, color changes, melt-flow fluctuations, and an increase in gels and crystal spots.

As an efficient phosphite secondary antioxidant, Antioxidant 168 decomposes hydroperoxides generated during polymer oxidation. It is therefore an important processing stabilizer in stabilization systems for EVA photovoltaic encapsulation film.

Antioxidant 168 in EVA Photovoltaic Encapsulation Film

What Is Antioxidant 168?

Antioxidant 168, also known as AO-168, has the chemical name tris(2,4-di-tert-butylphenyl) phosphite. Its CAS number is 31570-04-4, its molecular formula is C42H63O3P, and its relative molecular weight is approximately 646.9.

AO-168 is a phosphite secondary antioxidant. Its primary function is not to provide all long-term aging protection by itself. Instead, it converts unstable hydroperoxides formed during high-temperature processing into less reactive, non-radical products, thereby interrupting or slowing the oxidative degradation process.

It can also reduce the premature consumption of primary antioxidants during processing. For this reason, Antioxidant 168 is commonly used together with hindered phenolic primary antioxidants such as Antioxidant 1010 and Antioxidant 1076.

Physicochemical Properties of Antioxidant 168

Item	Typical Information
Product name	Antioxidant 168 / AO-168
Chemical type	Phosphite secondary antioxidant
CAS number	31570-04-4
Molecular formula	C42H63O3P
Relative molecular weight	Approx. 646.9
Appearance	White free-flowing powder
Melting range	Approx. 183–187°C
Bulk density	Approx. 480–570 g/L
Solubility in water	Practically insoluble
Main characteristics	Low volatility, good hydrolytic stability, excellent processing stabilization, and low discoloration tendency

According to the EcoChem product page, AO-168 is a white free-flowing powder with a melting range of 183–187°C and a bulk density of approximately 480–570 g/L. It has low solubility in water and ethanol but shows a certain degree of solubility in organic media such as cyclohexane and n-hexane.

Although Antioxidant 168 offers good hydrolytic stability, phosphite antioxidants should still be stored in sealed packaging and protected from moisture and heat. Once the original package has been opened, prolonged exposure to humid conditions should be avoided to preserve product activity and formulation consistency.

Why Does EVA Photovoltaic Encapsulation Film Need Antioxidant 168?

1. Improved Extrusion Processing Stability

During EVA film extrusion, the resin is exposed to heat and shear for an extended period. Without sufficient antioxidant protection, the polymer may undergo chain scission or abnormal crosslinking.

These reactions may result in:

Fluctuations in melt pressure
Changes in flow behavior
Increased odor
Yellow discoloration
Reduced production stability

Antioxidant 168 decomposes hydroperoxides formed during processing, reducing the likelihood that oxidation reactions will continue to propagate. This helps maintain a more stable melt condition, molecular weight, and processing window.

2. Reduced Risk of Yellowing and Light-Transmittance Loss

Photovoltaic encapsulation film is positioned directly between the front glass and the solar cells. It therefore requires high light transmittance and excellent color stability.

Chromophoric substances generated through thermo-oxidative degradation may gradually cause the film to yellow. This can increase haze and reduce the amount of effective light reaching the solar cells.

AO-168 has a low discoloration tendency and can reduce initial color changes caused by oxidation during processing. It provides a stable foundation for producing EVA film with low yellowing and high transparency.

However, Antioxidant 168 cannot replace a UV absorber. For long-term outdoor light-aging protection, it should be used together with suitable UV absorbers, light stabilizers, and primary antioxidants.

3. Fewer Gels, Crystal Spots, and Surface Defects

During EVA oxidation, both chain scission and localized crosslinking may occur. These reactions can produce gel particles, crystal spots, fisheyes, and uneven film surfaces.

For transparent photovoltaic encapsulation film, such defects may affect:

Film appearance
Lamination quality
Module consistency
Finished-product reliability

By controlling oxidation during processing, Antioxidant 168 can help reduce the risk of abnormal gels and unstable crosslinking.

However, the final results will also depend on several other factors, including:

EVA resin grade
Vinyl acetate content
Extrusion temperature
Screw shear intensity
Filtration system
Type and dosage of peroxide crosslinking agent

4. Greater Synergy within the Overall Stabilization System

EVA photovoltaic encapsulation film is exposed not only to heat and oxygen but also to ultraviolet radiation, damp heat, and long-term electrical operating conditions.

A mature formulation therefore normally uses a combined stabilization system:

Hindered phenolic primary antioxidants capture free radicals.
Antioxidant 168 decomposes hydroperoxides.
UV absorbers reduce polymer damage caused by high-energy ultraviolet radiation.
Light stabilizers suppress photo-oxidative chain reactions.

When Antioxidant 168 is used together with a primary antioxidant, it can reduce the premature depletion of the primary antioxidant and help balance processing stability with long-term aging resistance.

Performance Comparison Before and After Adding Antioxidant 168

Comparison Item	Without AO-168 or with Insufficient Stabilization	After Appropriate Addition of AO-168
Extrusion processing	Melt pressure and flow behavior may fluctuate	More stable processing window
Initial color	More likely to yellow as thermal history increases	Lower risk of thermo-oxidative yellowing
Molecular structure	Higher risk of chain scission or abnormal crosslinking	Reduced abnormal molecular-weight changes
Film appearance	Greater risk of crystal spots, gels, and fisheyes	Helps reduce processing defects
Consumption of primary antioxidant	Faster depletion during processing	Synergistic protection with the primary antioxidant
Transparency after aging	Weaker retention of light transmittance and color	Better retention within a complete stabilization system
Batch consistency	More sensitive to temperature and residence time	Improved processing tolerance

The above comparison represents typical formulation trends rather than guaranteed performance values.

Customers should determine the actual degree of improvement through testing, including:

Melt flow rate
Yellowness index
Light transmittance
Haze
Oxidation induction time
Gel count
Crosslinking degree
Damp-heat aging
UV-aging performance

Recommended Dosage of Antioxidant 168 in EVA Photovoltaic Encapsulation Film

EcoChem’s general recommended dosage range for AO-168 is 0.05%–0.20% of the total formulation, equivalent to approximately 500–2,000 ppm.

The optimum dosage should be determined experimentally according to the resin grade, processing conditions, stabilization system, and target performance.

In publicly available EVA photovoltaic encapsulation film formulations, the total antioxidant dosage may range from 0.1 to 0.5 parts per 100 parts of EVA resin. Some formulations include 0.1 part of tris(2,4-di-tert-butylphenyl) phosphite.

These values may be used as a reference for establishing a laboratory evaluation range, but they should not replace formulation validation under the customer’s actual production conditions.

For transparent EVA solar encapsulation film, a stepwise dosage trial within the range of 0.05%–0.20% can be used as a practical starting point.

The following factors should be considered when determining the final dosage:

Vinyl acetate content and melt flow index of the EVA resin
Extrusion temperature, residence time, and screw shear intensity
Type of peroxide crosslinking agent and co-agent
Combination of primary antioxidant, UV absorber, and light stabilizer
Film transmittance, haze, yellowness index, and lamination requirements
Damp-heat aging, UV-aging, and long-term reliability targets

An insufficient dosage may not provide adequate control of processing oxidation. However, increasing the dosage without proper evaluation may raise costs and affect formulation compatibility, migration behavior, blooming risk, or the crosslinking system.

The most reliable approach is to optimize the dosage gradually through laboratory trials, pilot-scale testing, and commercial production validation.

Why Choose EcoChem Antioxidant 168?

EcoChem specializes in polymer additives and plastic stabilization solutions. The company offers Antioxidant 168, hindered phenolic primary antioxidants, UV absorbers, hindered amine light stabilizers, and other complementary additives.

This product range allows manufacturers of EVA photovoltaic encapsulation film to simplify product selection and source multiple stabilization additives from one supplier.

For EVA solar encapsulation film projects, EcoChem can communicate with customers according to their specific:

EVA resin grade
Processing temperature
Film structure
Crosslinking system
Performance targets
End-use requirements

EcoChem can also support customers with TDS, COA, MSDS, samples, and export documentation.

For customers evaluating both Antioxidant 168 and UV absorbers, obtaining coordinated support from the same supplier can reduce the time required for specification matching, technical document review, and supplier communication.

EcoChem also understands the practical requirements of international customers concerning packaging, lead time, destination ports, and technical documentation. Product and export support is available for manufacturers of photovoltaic encapsulation film, plastic film, and modified polymers in India, Southeast Asia, the Middle East, Europe, and other global markets.

Conclusion

Antioxidant 168 is an important processing stabilizer for EVA solar photovoltaic encapsulation film.

By decomposing hydroperoxides, it helps reduce thermo-oxidative degradation during compounding, extrusion, film production, and module lamination. When incorporated into a properly designed stabilization system, it can contribute to improved color stability, processing consistency, film appearance, and long-term performance retention.

For most formulations, 0.05%–0.20% may be used as an initial AO-168 evaluation range. The final dosage should then be optimized together with the primary antioxidant, UV absorber, light stabilizer, crosslinking agent, and other formulation components.

For manufacturers developing EVA, POE, or EPE photovoltaic encapsulation films, EcoChem can provide the TDS, COA, MSDS, samples, and quotation for Antioxidant 168.

To receive a more targeted product recommendation, please provide your current resin grade, processing temperature, estimated consumption, and destination port.

EcoChem Contact Information

Mobile / WhatsApp: +86 18921308539
Email: ecochemchina@gmail.com
Email: qin@ecochemchina.com

Frequently Asked Questions

Can Antioxidant 168 Be Used Alone in EVA Photovoltaic Encapsulation Film?

Antioxidant 168 can provide processing antioxidant protection when used alone. However, it is generally recommended to combine it with a hindered phenolic primary antioxidant, UV absorber, or light stabilizer.

A combined stabilization system provides broader protection against both thermo-oxidative degradation during processing and long-term photo-oxidative aging during outdoor service.

Will Antioxidant 168 Affect the Transparency of EVA Film?

At an appropriate dosage and with good dispersion, AO-168 generally has a low discoloration tendency.

However, the actual light transmittance and haze of the film will also depend on product purity, dosage, dispersion quality, EVA resin properties, and the other additives used in the formulation.

What Is the Recommended Dosage?

EcoChem’s general recommended dosage range is 0.05%–0.20%, equivalent to approximately 500–2,000 ppm.

The specific dosage should be determined through stepwise testing based on the formulation, processing conditions, crosslinking system, and performance requirements.

What Precautions Should Be Taken When Using Antioxidant 168?

Antioxidant 168 should be stored in sealed packaging and protected from moisture and heat. It should be evenly dispersed in the formulation, and its compatibility with peroxide crosslinking agents and other stabilizers should be evaluated.

The final formulation should be confirmed through tests such as: