The application of anti-yellowing agent in the manufacturing of rain boots: Ensure that long-term use does not change color

1. Introduction: A battle to defend “appearance”

Sole, this seemingly inconspicuous little component, carries every step we walk. It is not only a key part of the contact between the shoes and the ground, but also an important factor in determining whether a pair of shoes is durable. However, under the erosion of time, the color of the sole often changes quietly – the originally flawless rubber sole may gradually turn yellow due to oxidation, ultraviolet rays or chemical reactions. This phenomenon is called “yellow change”, just like an old photo stained with mottled traces by time.

For ordinary shoes, yellowing is regrettable, but it is acceptable; for products such as rain boots with extremely strong functional properties, yellowing not only affects the appearance, but may also weaken its performance. Just imagine, when you put on a pair of brand new black rain boots and step into the muddy street confidently, you find that the soles of your shoes turned ugly yellow in a few days. That mood may fall to the bottom in an instant, right? Therefore, how to prevent the soles of rain boots from turning yellow has become an urgent problem that needs to be solved in the shoemaking industry.

In recent years, with the development of technology and the increase in consumer demand, a magical substance called “sole anti-yellowing agent” has emerged. It is like a loyal guardian, protecting the “appearance” of rain boots, allowing them to maintain their original colors and quality even after experiencing wind, sun and rain. This article will deeply explore the application of anti-yellowing agents in the manufacturing of rain boots, and analyze its mechanism of action, product parameters, and domestic and foreign research progress to help us better understand the mysteries of this field.

So, let’s enter this battle to defend “appearance” together!

2. Analysis of the reasons for yellowing of the sole: Who is the culprit?

To understand the importance of anti-yellowing agents in the sole, you must first understand why the sole changes yellow. Behind this is actually a series of complex chemical reactions, which are like “destructive molecules” lurking inside the sole. Once the conditions are ripe, they will act quickly and turn the originally beautiful sole into pieces of “yellow land”. The following is a detailed analysis of the causes of yellowing of the sole from three perspectives: material characteristics, environmental factors and usage habits:

(I) Material characteristics: “Character defects” of the rubber family

Rubber is the main raw material for rain boot soles, divided into two categories: natural rubber (NR) and synthetic rubber. Although rubber has excellent elasticity and wear resistance, it is not perfect in itself and is particularly susceptible to oxygen, ultraviolet rays and other chemicals. Here are several common types of rubber and their reasons for yellowing:

Natural Rubber (NR)
Natural rubber is made of latex.It contains rich double bond structures. These double bonds are like fragile “chains” and are easily attacked by oxygen, which triggers a free radical reaction. This reaction causes the rubber molecules to break and recombinate, eventually forming a yellow quinone compound.
Styrene Butadiene Rubber (SBR)
Styrene butadiene rubber is a widely used synthetic rubber, but because there are double bonds in its molecular chains, it is also prone to oxidation reactions. In addition, SBR may also have side reactions with certain additives (such as vulcanizers), further aggravate the yellowing problem.
Neoprene Rubber
Neoprene is popular for its excellent oil resistance and elasticity, but its molecular structure contains a large number of chlorine atoms, which are easily decomposed under light conditions, resulting in a yellowish-brown intermediate product.

Material Type	Reasons for easy yellowing	Common Application Scenarios
Natural Rubber	Double bond structure is prone to oxidation	Sports shoes, outdoor shoes
Styrene Butadiene Rubber	The free radical reaction is significant	Tyres, industrial products
Neoprene	Chlorine atom decomposition under light	Diver Wear, Rain Boots

(2) Environmental factors: Nature’s “invisible killer”

In addition to the limitations of the material itself, the external environment is also an important driving force for yellowing of the sole. Whether it is direct sunlight or humid air, it can become a catalyst for accelerating yellowing:

Ultraviolet radiation
Ultraviolet rays are a powerful “colorist” in nature. When rubber is exposed to ultraviolet light, photon energy will stimulate electron transitions in the molecule, thereby breaking the stability of the molecular chain and promoting the occurrence of oxidation reactions. This phenomenon is similar to the process of plant leaves turning yellow in autumn, except that the “yellowing” of the soles appear more abrupt and unpopular.
High temperature and high humidity environment
High temperatures will accelerate the movement of rubber molecules, making the oxidation reaction easier; while humidity provides sufficient chemical reactionsmoisture support. Especially in rainy season or coastal areas, if the rain boots are in a humid environment for a long time, the risk of yellowing on the soles is naturally higher.
Contaminant Impact
Pollutants such as sulfur dioxide (SO₂) and nitrogen oxides (NOx) in the air will also react chemically with the rubber to produce colored substances. This phenomenon is particularly obvious in industrial cities, and some people even jokingly call it “the color of the city.”

(III) Usage habits: Human factors cannot be ignored

After

, the user’s own usage habits may indirectly lead to yellowing of the sole. For example:

Improper cleaning: Cleaning rain boots with detergent containing bleach may damage the protective layer on the rubber surface, making it easier to absorb oxygen.
Incorrect storage method: Stacking rain boots at will in direct sunlight, or storing them in a closed and humid space for a long time will increase the possibility of yellowing.
Overwear: The sole surface becomes rough due to friction, increasing the area in contact with the air, thereby speeding up the oxidation reaction.

From the above analysis, we can see that yellowing of the sole is the result of a joint action of multiple factors. To completely solve this problem, we must start from the root and introduce a “protective shield” that can effectively inhibit these reactions – this is the mission of the anti-yellowing agent in the sole.

3. The mechanism of action of anti-yellowing agent in soles: How does the power of science fight yellowing?

Since you know the reason for the yellowing of the sole, the next question is: How can you prevent this phenomenon from happening? The answer lies in the anti-yellowing agent of the sole. This is a chemical additive designed specifically to delay or suppress the yellowing of rubber, which acts like a strong line of defense, firmly guarding the color of the soles.

(I) The basic principle of anti-yellowing agent: Cut off the reaction chain

The core function of sole anti-yellowing agents is to interfere with and terminate chemical reactions that may cause yellowing through a variety of mechanisms. The following are its main functions:

Catch free radicals
During the aging of rubber, free radicals are active “destructors”. They will constantly attack the rubber molecular chain, triggering a chain reaction, and eventually leading to yellowing. The antioxidant components in the anti-yellowing agent can quickly capture these free radicals, converting them into stable compounds, thus breaking the reaction chain.
Absorb UV rays
In order to deal with the harm of ultraviolet rays, some anti-yellowing changesThe agent also has ultraviolet absorption capacity. They can form a “invisible barrier” inside the rubber, converting harmful ultraviolet light into heat energy and releasing it, preventing rubber molecules from being photolysis.
Stable molecular structure
Anti-yellowing agents can also reduce the possibility of double bond breaking by enhancing the stability of rubber molecular chains. This method is equivalent to putting a “protective suit” on the rubber molecule, making it more difficult to be harmed by external factors.
Nertize acid and alkaline substances
For rubber products that may be affected by air pollutants, anti-yellowing agents can also play a certain neutralizing role to prevent adverse reactions between acidic or alkaline substances and rubber.

Mechanism of action	Specific Functions	Common Ingredients
Catch free radicals	Stop oxidation reaction	Antioxidants (such as BHT)
Absorb UV rays	Prevent photoresolvation	UV absorbers (such as BP-1)
Stable molecular structure	Reduce double bond fracture	Stabilizers (such as phosphites)
Nethering acid and alkaline substances	Prevent pollution and corrosion	Buffer (such as calcium carbonate)

(II) Classification of anti-yellowing agents: each showing its magical powers

According to different mechanisms of action and scope of application, anti-yellowing agents in the sole can be divided into the following categories:

Antioxidants
Antioxidants are a common class of anti-yellowing agents, mainly used to inhibit oxidation reactions caused by free radicals. Among them, hindered phenolic antioxidants (such as BHT) and amine antioxidants (such as DNP) are typical. They can intervene in time before the rubber molecular chain breaks, nipping the danger in its bud.
Ultraviolet absorber
UV absorbers focus on resisting the threat of ultraviolet rays. They are usually dominated by aromatic compounds, such as benzophenones (such as BP-1) and benzotriazoles (such as TINUVIN). These substances can absorb ultraviolet light efficiently and convert it into harmless forms of energy.
Light Stabilizer
Photo stabilizers are a special class of anti-yellowing agents that can reduce photosensitive by regulating the electron distribution of rubber molecules. Halogenated hydrocarbon light stabilizers (such as CYASORB) are among the best ones.
Comprehensive Anti-yellowing Agent
There is also a comprehensive anti-yellowing agent later, which combines the above functions and is suitable for all-round protection in complex environments. For example, some high-end anti-yellowing agents have both antioxidant, ultraviolet absorption and molecular stability functions, and are called “all-round players”.

(III) Practical application case: The power of anti-yellowing agent is emerging

In order to more intuitively demonstrate the effect of anti-yellowing agents, we can refer to an actual experimental case. An internationally renowned shoe company conducted a one-year comparison test on the rain boots it produced, and the results are shown in the table below:

Sample number	Whether to add anti-yellowing agent?	Initial Color	Color after test	Yellow Index (ΔE)
A	No	White	Light yellow	7.8
B	Yes	White	Slightly yellow	3.2

From the data, it can be seen that after a year of natural aging, the degree of yellowing of Sample B with the addition of Anti-Yellowing agent is much lower than that of Sample A without adding. This fully demonstrates the excellent effect of anti-yellowing agents in extending the service life of rain boots.

IV. Product parameters of anti-yellowing agent for soles: Complete analysis of technical details

If the anti-yellowing agent is a “magic key”, then its parameters are the specific conditions for opening this door. Only by deeply understanding these parameters can you truly master the application skills of anti-yellowing agents. The following are several key indicators and their meanings:

(I) Active ingredient content

The active ingredient content of the anti-yellowing agent directly determines its protective ability. Generally speaking, the higher the content, the stronger the protection effect, but the cost will increase accordingly. The following are the effective ingredients ranges of several common anti-yellowing agents:

Anti-yellowing agent type	Active ingredient content (wt%)	Recommended dosage (phr)
Stealed phenolic antioxidants	95-98	0.5-1.0
Benzophenone UV Absorbent	90-95	1.0-2.0
Halogenated hydrocarbon light stabilizers	85-90	0.5-1.5

Note: PHR represents the number of parts per 100 parts of rubber.

(Bi) Thermal Stability

The thermal stability of the anti-yellowing agent refers to its ability to maintain activity in high temperature environments. This is especially important for the rain boot production process, as rubber vulcanization usually needs to be carried out at temperatures above 150°C. If the anti-yellowing agent fails during this process, its subsequent protective effect will be greatly reduced. The following are the thermal stability data of several anti-yellowing agents:

Anti-yellowing agent type	Decomposition temperature (℃)	Update temperature (℃)
Stealed phenolic antioxidants	>260	200
Benzophenone UV Absorbent	>220	180
Halogenated hydrocarbon light stabilizers	>240	190

(Three) Compatibility

The compatibility between the anti-yellowing agent and the rubber substrate is also an important consideration. Good compatibility means that the anti-yellowing agent can be evenly dispersed inside the rubber to fully exert its function. On the contrary, local concentrations may lead to unevenness and even precipitation.

Anti-yellowing agent type	Compatibility level	Improvement method
Stealed phenolic antioxidants	High	No processing required
Benzophenone UV Absorbent	in	Add cosolvent
Halogenated hydrocarbon light stabilizers	Low	Parcel processing

(IV) Environmental protection performance

As the increasing global attention to environmental protection, the environmental protection performance of anti-yellowing agents has also become a factor that cannot be ignored. Many countries and regions have issued relevant regulations to limit the use of certain toxic and harmful substances. Therefore, when choosing anti-yellowing agents, it is necessary to ensure that they comply with new environmental standards.

Anti-yellowing agent type	Environmental Certification	Special Requirements
Stealed phenolic antioxidants	REACH Compliance	No heavy metal
Benzophenone UV Absorbent	FDA certification	Phenyl-free
Halogenated hydrocarbon light stabilizers	RoHS Compliance	Low Volatility

5. Research progress at home and abroad: Standing on the shoulders of giants

The research on anti-yellowing agents in soles was not achieved overnight, but it took decades of hard work to achieve today’s results. The following is a brief review of the progress of relevant research at home and abroad:

(I) Current status of foreign research

As early as the mid-20th century, European and American countries began to pay attention to the anti-yellowing problem of rubber products. DuPont, the United States, took the lead in developing the first generation of antioxidants and successfully applied them to the tire industry. Subsequently, the German BASF Group launched a benzotriazole-based ultraviolet absorber, opening a new era of anti-yellowing agents.

In recent years, Japan’s Mitsubishi Chemical Company has made breakthrough progress in the field of anti-yellowing agents. They have developed a new composite anti-yellowing agent that can not only effectively prevent yellowing, but also significantly improve the mechanical properties of rubber. This innovative product has been widely used in many international brands.

(II) Domestic research trends

my country’s research in the field of anti-yellowing agents started late, but developed rapidly. Through years of hard work, the Institute of Chemistry, Chinese Academy of Sciences has successfully synthesized high-performance anti-yellowing agent with independent intellectual property rights. This product is not only cheap but also has excellent results. It has been exported to many Southeast Asian countries.

At the same time, the School of Materials of Tsinghua University has cooperated with many well-known companies to develop an intelligent anti-yellowing agent. This product can automatically adjust protection strategies according to environmental changes, greatly improving its adaptabilitysex.

Country/Region	Main research results	Application Fields
USA	First generation antioxidants	Tire Industry
Germany	Benzotriazole UV Absorbent	Auto Parts
Japan	New composite anti-yellowing agent	Sports soles
China	High-performance domestic anti-yellowing agent	Rain boots manufacturing

VI. Future Outlook: A New Chapter of Anti-yellowing Agent

With the continuous advancement of science and technology, anti-yellowing agents in the sole will usher in a broader development space. Future anti-yellowing agents may move in the following directions:

Multi-function integration
Integrate various functions such as antioxidant, ultraviolet absorption and molecular stability into a single product, simplify production processes and reduce costs.
Intelligent response
Develop intelligent anti-yellowing agents that can automatically adjust protective strength according to environmental changes to achieve true “on-demand protection”.
Green and environmentally friendly
Further optimize the formula, reduce or even completely eliminate the negative impact on the environment, and promote sustainable development.

In short, anti-yellowing agents in the sole are not only a technological innovation, but also a reflection of the pursuit of a better life. It makes our rain boots shine in the wind and rain, adding a sense of peace and joy to every trip. As the old saying goes, “Be down to earth and look up at the stars.” Only with the help of anti-yellowing agents can we go further and see higher!