Anti-yellowing agent for soles: a secret weapon in sandal production

In the fashion industry, sandals are not only a seasonal necessity, but also an art form that expresses personality and taste. However, in daily use, the appearance of sandals may change irreversibly over time, especially the yellowing problem of the sole. This phenomenon not only affects the aesthetics of the product, but also may reduce consumers' willingness to buy. In order to solve this problem, anti-yellowing agents in the sole came into being and became the "secret weapon" in sandal production. This article will conduct in-depth discussions on the basic principles, application methods, product parameters, and domestic and foreign research results of anti-yellowing agents to help readers fully understand how this magical chemical can make sandals shine for a lasting brilliance.

1. Causes and impacts of yellowing soles

(I) Definition and expression of yellowing

Yellow change of soles refers to the phenomenon that the sole material gradually changes in color under the long-term exposure to external factors such as light, heat, and oxygen. This change is usually manifested as the gradual yellowing of the white or light soles, and in severe cases, dark yellow or brown spots may appear, seriously affecting the appearance quality of the product. Yellowing is particularly prominent in common sole materials such as rubber, TPU (thermoplastic polyurethane), EVA (ethylene-vinyl acetate copolymer).

(II) The main reasons for yellowing

1. Photooxidation
   Unsaturated bonds in sole materials will undergo photooxidation reaction under ultraviolet irradiation, resulting in a carbonyl compound with yellow characteristics. For example, aromatic isocyanate groups in TPU are very sensitive to ultraviolet rays and are prone to yellowing.

2. Thermal aging effect
   During production and storage, high temperature environments can accelerate the aging process of sole materials, causing molecular chains to break and form yellow by-products.

3. The Effect of Oxygen
   Oxygen acts as a catalyst for free radical reaction, which will cause oxidation and degradation of unstable structures in sole materials, thereby causing yellowing.

4. Addant migration
   Plasticizers, stabilizers, or other additives used in certain sole formulations may migrate to the surface during use, reacting chemically after contact with air, resulting in yellowing.

(III) The impact of yellow change on sandals

The yellowing not only destroys the overall aesthetic of the sandals, but may also lead to consumers' doubts about their durability and quality. For manufacturers, the yellowing problem not only increases the cost of rework, but also may damage the brand image. Therefore, solving the problem of yellowing has become an urgent need for the sandal industry to overcometechnical difficulties.

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2. Principles and mechanism of anti-yellowing agent for soles

(I) Definition of anti-yellowing agent

Sole anti-yellowing agent is a class of chemical additives specially used to inhibit the yellowing of sole materials. They effectively extend the service life of sole materials and maintain their original color and performance by blocking or slowing down reaction channels such as photooxidation and thermal aging.

(II) Mechanism of action of anti-yellowing agent

1. Absorb UV rays
   The UV absorber in the anti-yellowing agent can capture UV energy and convert it into harmless thermal energy to release it, thereby preventing the occurrence of photooxidation reactions.

2. Catch free radicals
   Free radicals are important intermediates that cause yellowing. The antioxidant components in the anti-yellowing agent can neutralize free radicals by providing electrons, preventing the further development of chain reactions.

3. Stable molecular structure
   Certain anti-yellowing agents can chemically react with unstable groups in sole materials to form a more stable structure and reduce the possibility of yellowing.

(III) Classification of anti-yellowing agents

Depending on the mechanism of action, anti-yellowing agents in the sole are mainly divided into the following categories:

Category	Features	Application Scenario
Ultraviolet absorber	Absorb UV rays to prevent photooxidation	Commonly used in outdoor sandals
Free Radical Scavenger	Neutectic radicals and slow down oxidation reaction	Sandals suitable for use in high temperature environments
Light Stabilizer	Improve the light stability of the material	Widely used in various sole materials
Antioxidants	Stop oxidation and degradation, protect material properties	Most used in indoor sandals

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3. Product parameters of sole anti-yellowing agent

In order to better understand the practical application effects of anti-yellowing agents, the following lists some common product parameters and their significance:

Parameter name	Description	Reference value range	Unit
Add ratio	Recommended dosage of anti-yellowing agent in sole materials	0.5% – 2.0%	Percent Mass
Heat resistance temperature	Stable properties of materials under high temperature conditions	80°C – 150°C	Celsius
Photostability	The material's yellowing resistance under ultraviolet rays	≥90%	Percent
Antioxidation Index	The ability of materials to resist oxidative degradation	≥85%	Percent
Compatibility	The degree of compatibility between anti-yellowing agent and sole material	Excellent/good/poor	Level

These parameters provide scientific evidence for manufacturers to help them choose anti-yellowing agents suitable for specific application scenarios.

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IV. Application methods of anti-yellowing agents

(I) Adding method

The method of adding anti-yellowing agent directly affects its effect and uniformity. Commonly used methods of adding include:

1. Direct mixing method
   The anti-yellowing agent is added directly to the sole material in powder or liquid form, and uniform dispersion is achieved by stirring or extrusion equipment.

2. Masterbatch premix method
   Pre-made masterbatches for anti-yellowing agent and then mix them with the sole material in a certain proportion. This method can improve dispersion uniformity and operational convenience.

3. Spraying treatment
   The surface of the molded sole is subjected to anti-yellowing agent spraying, which is suitable for occasions where local protection is required.

(II) Notes

1. Control the amount of addition
   Excessive use of anti-yellowing agents may lead to decreased material properties such as increased hardness or reduced flexibility. Therefore, it must be strictly followedRecommended ratios are added.

2. Ensure uniform distribution
   Uneven distribution will lead to poor anti-yellowing effect and even local yellowing.

3. Avoid conflicts with other additives
   Some additives may have adverse reactions with anti-yellowing agents, affecting their performance. This should be fully considered when designing the formula.

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5. Progress in domestic and foreign research

(I) Foreign research trends

In recent years, European and American countries have made significant progress in research on anti-yellowing agents in the field of soles. For example, BASF, Germany has developed a new light stabilizer that can effectively inhibit the yellowing of TPU soles under extreme conditions. DuPont, the United States, has launched a high-performance antioxidant that can greatly extend the service life of EVA soles.

In addition, Japan Toyo Textile Co., Ltd. proposed a composite anti-yellowing scheme, combining the advantages of ultraviolet absorbers and free radical scavengers to achieve comprehensive protection against various yellowing factors.

(II) Current status of domestic research

my country's research on anti-yellowing agents in soles started late, but has developed rapidly in recent years. The School of Chemical Engineering of Zhejiang University has successfully developed a nanotechnology-based anti-yellowing agent, which is superior to traditional products in dispersion and stability. At the same time, the team of South China University of Technology has developed a highly efficient antioxidant for EVA sole materials, which significantly improves the yellowing resistance of the product.

(III) Comparative Analysis

Research Direction	Foreign progress	Domestic Progress
Ultraviolet protection	New Light Stabilizer	Nanoscale anti-yellowing agent
Oxidation Protection	High-efficiency antioxidants	Compound antioxidant
Comprehensive Protection	Compound anti-yellowing agent	Functional Modified Materials

It can be seen that domestic and foreign research has its own emphasis, but it gradually becomes consistent in functional improvement and practical application effects.

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6. Economic benefits and environmental considerations of anti-yellowing agents

(I) Economic benefits

Using anti-yellowing agents can not only improve the appearance quality of sandals, but also extend the service life of the product, thereby reducing theRepair rate and complaint rate. According to statistics, the rational use of anti-yellowing agents can increase the market competitiveness of sandals by about 20%, bringing considerable economic benefits to the company.

(II) Environmental protection considerations

With the increasing global environmental awareness, the greening of anti-yellowing agents has become an important trend in the development of the industry. Many companies are working to develop low-toxic, degradable, environmentally friendly anti-yellowing agents to reduce negative impacts on the environment.

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7. Conclusion

The wide application of anti-yellowing agents in soles has injected new vitality into the sandal industry. It not only solves the long-hacked yellowing problem, but also provides reliable guarantees for the appearance and durability of the product. In the future, with the continuous advancement of science and technology, anti-yellowing agents will make greater breakthroughs in functionalization and environmental protection, bringing consumers more high-quality sandals choices. As the saying goes, “Details determine success or failure”, and anti-yellowing agents are the key to the details.

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