TPU yellowing agent: a key technology to extend the service life of thermoplastic polyurethane elastomers

Introduction

In the vast world of materials science, thermoplastic polyurethane elastomer (TPU) is like a shining pearl, attracting great attention for its outstanding performance and wide application fields. However, just like any beauty who coexists with beauty and wisdom will eventually face the test of time, TPU cannot escape the impact of time on its color and performance - the problem of yellowing is one of its biggest enemies. Yellowing not only affects the appearance of the product, but also may weaken its mechanical properties, thereby shortening its service life. In order to protect this "pearl" from outside harm, scientists have developed a magical weapon - TPU yellowing agent.

What is TPU?

Let's get to know this protagonist first. TPU is a polymer material prepared by polymerization reaction of polyols, polyisocyanates and chain extenders. It has excellent wear resistance, flexibility, tear resistance and chemical corrosion resistance, so it is widely used in shoe materials, films, cable sheaths, medical devices, automotive parts and sports equipment. However, because its molecular structure contains aromatic isocyanate groups that are easily oxidized, TPU is prone to degradation reactions when exposed to ultraviolet rays, oxygen or high temperature environments for a long time, resulting in yellowing or even blackening of the color. This is the so-called "yellow change" phenomenon.

The hazards of yellowing

Yellowing is not just a superficial problem. When the color of the TPU product changes, it often means that the internal structure has been damaged to a certain extent. This damage may reduce the key performance indicators of TPU such as tensile strength, elongation at break and hardness, thereby affecting its normal use. For example, in car interior parts, if the TPU loses its original flexibility due to yellowing, it may cause the parts to crack; in sports soles, yellowing will make the shoes look old and seriously affect the consumer's purchasing experience.

To solve this problem, scientists invented TPU yellowing agent. These additives are like a strong protective shield, which can effectively delay the aging process of TPU and keep it bright and bright. Next, we will conduct in-depth discussion on the working principle, type and application of TPU yellowing agent, and analyze its importance based on actual cases.

The working principle of TPU yellowing agent

To understand how TPU yellowing agents work, we first need to understand the root cause of TPU yellowing. Simply put, the yellowing of the TPU is due to the irreversible change of certain chemical bonds in the material under certain conditions. Here are some of the main yellowing mechanisms:

1. Photooxidation: UV irradiation will cause the decomposition of aromatic isocyanate groups in TPU molecules, forming carbonyl compounds and other colored substances.
2. Thermal Aging: In high-temperature environments, TPU may undergo cross-linking or chain breakage reactions, resulting in changes in molecular structure.
3. Oxygen Free Radical Attack: Oxygen in the air interacts with TPU molecules to form peroxides or other unstable intermediates, further accelerating the yellowing process.

In response to the above problems, TPU yellowing agent protects TPU materials through the following methods:

1. Absorb UV rays

Some yellowing agents are UV Absorbers, which can convert UV rays into harmless heat and release them, thereby avoiding the direct damage to TPU molecules by UV rays. Such substances usually contain benzotriazoles or hydroxybenzophenone compounds, and their molecular structure has a strong UV absorption capacity.

2. Capture free radicals

Another type of yellowing agent is antioxidants, whose main function is to capture the free radicals generated by TPU molecules during the oxidation process and prevent the occurrence of chain reactions. Common antioxidants include phenolic compounds (such as BHT) and amine compounds (such as hindered amine light stabilizers, HALS). Among them, HALS has become the first choice for high-end TPU products due to its excellent stability and long-term effectiveness.

3. Inhibit carbonyl formation

In addition to the above two methods, there are some special types of yellowing agents specifically used to inhibit the formation of carbonyl compounds. These substances are chemically reacted with the carbonyl group to convert them into a colorless and stable product, thus eliminating the source of yellowing.

Comprehensive Effect

In fact, most commercial TPU yellowing agents are compound formulas of multiple ingredients, designed to deal with multiple aging factors such as ultraviolet rays, oxygen and high temperatures at the same time. This comprehensive protection strategy not only significantly slows down the yellowing speed, but also improves the overall durability of the TPU.

Classification of TPU yellowing agents

According to chemical composition and functional characteristics, TPU yellowing agents can be roughly divided into the following categories:

Each type of yellowing agent has its unique advantages and limitations. The specific choice needs to be weighed based on actual application scenarios and budget requirements.

Status of domestic and foreign research

In recent years, with the increasing demand for TPU market, research on yellow-resistant agents has also become increasingly in-depth. The following are important discoveries from some domestic and foreign scholars:

Domestic research progress

A study by the Institute of Chemistry, Chinese Academy of Sciences shows that by introducing functional monomers containing silicon elements, the yellowing resistance of TPU can be significantly improved. This method not only simplifies the production process, but also reduces production costs and has high industrialization value.

In addition, the Zhejiang University team has developed a new nano-scale ultraviolet absorber, which has better dispersion and has a smaller impact on TPU transparency, and is especially suitable for optical-grade TPU products.

International Research Trends

DuPont (DuPont) has always been in the leading position in the field of TPU yellowing agents. Their Hyperform series of light stabilizers has been proven to provide protection for more than a decade in extreme environments.

BASF, Germany, focuses on the development of environmentally friendly yellowing agents. Its products comply with the requirements of the EU REACH regulations and are favored by more and more green manufacturing companies.

Citation of literature

• Zhang, W., et al. (2020). "Enhanced Yellowing Resistance of TPU via Functional Monomer Incorporation." Polymer Engineering & Science, 60(5), pp. 789-796.
• Smith, J., & Brown, M. (2019). "Long-Term Stability of TPU with AdvancedLight Stabilizers." Journal of Applied Polymer Science, 136(12), Article ID: 47123.

Application Case Analysis

In order to more intuitively demonstrate the actual effect of TPU yellowing agent, we have selected several typical application cases to explain:

Case 1: Automobile interior parts

A well-known automaker uses TPU material with yellowing agent-resistant TPU on the dashboard of its new model. After three years of actual testing, the component has not shown any obvious yellowing, and user satisfaction has increased significantly.

Case 2: Sport soles

A sporting goods company launched a high-performance running shoe with a sole made of TPU material containing composite yellowing agents. Even under high-intensity training conditions, the soles still maintain good elasticity and aesthetics, winning unanimous praise from the market.

Conclusion and Outlook

TPU yellowing agents are the key technology to extend the service life of TPUs, and their importance is self-evident. Whether from the perspective of theoretical research or practical application, this technology has shown great potential and room for development. In the future, with the continuous emergence of new materials and new processes, I believe that TPU yellowing agents will become more efficient, economical and environmentally friendly, bringing more surprises to human society.

Later, I borrow an old saying: "If you want to do a good job, you must first sharpen your tools." For TPU, yellowing agent is the sharp tool that helps it shine with charming light throughout the river for a long time!

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