Analysis of the causes of rubber frosting

nalysis of causes of rubber frosting in English and optimized version

Rubber blooming refers to the phenomenon that during the processing, storage, or use of rubber products, the internal compounding agents migrate to the surface, forming a layer of frost-like substance in white or other colors. This phenomenon not only affects the appearance quality of rubber products but may also reduce their physical properties, adhesion, etc. In severe cases, it can cause the products to lose their use value. Conducting an in - depth analysis of the causes of rubber blooming is crucial for improving the quality and extending the service life of rubber products.

I. Factors Related to Compounding Agents

(1) Vulcanizing Agents Vulcanizing agents are key compounding agents in the rubber vulcanization process. Taking sulfur as an example, during the vulcanization of rubber, sulfur undergoes a cross - linking reaction with rubber molecules to form a three - dimensional network structure, endowing the rubber with good physical and mechanical properties. However, when the amount of sulfur used exceeds the stoichiometry required for cross - linking with rubber molecules, the excess sulfur will be in an unstable state within the rubber. Over time and under the influence of environmental factors, this excess sulfur is prone to migrating to the rubber surface, thereby forming a blooming phenomenon. Studies have shown that in natural rubber formulations, when the amount of sulfur used is too high, the blooming phenomenon is significantly aggravated.

(2) Accelerators The function of accelerators is to speed up the vulcanization reaction, lower the vulcanization temperature, and reduce the amount of vulcanizing agents used. However, different types of accelerators have different solubilities and migration characteristics in rubber. For instance, some ultra - accelerators have high chemical activity and react rapidly during the rubber vulcanization process. However, if their dosage in the formulation is inappropriate, their stability within the rubber after vulcanization is poor, and they are prone to migration. In some rubber formulations, when the dosage of dithiocarbamate accelerators exceeds a certain limit, it may lead to blooming. This is because their dispersion state within the rubber changes over time and gradually migrates to the surface.

(3) Antioxidants Antioxidants are used to prevent rubber aging and extend the service life of rubber products. However, the solubility of some antioxidants in rubber is limited. For example, amine antioxidants have reduced solubility in rubber under high - temperature or long - term storage conditions. When the content of antioxidants exceeds their solubility in rubber, they will precipitate onto the rubber surface in the form of crystals, forming a blooming phenomenon. Moreover, there may be interactions between some antioxidants, which affect their solubility and stability in rubber, further increasing the possibility of blooming.

(4) Softeners Softeners can improve the processing performance of rubber, reducing its hardness and viscosity. However, the compatibility of some softeners with rubber is poor. For example, paraffin - based softeners have a significantly different molecular structure from rubber molecules and form a relatively independent phase in the rubber system. Over time, paraffin - based softeners are prone to migrating from the inside of the rubber to the surface, forming a blooming phenomenon. This migration is more pronounced in low - temperature environments because low temperatures reduce the interaction force between the softener and rubber molecules.

(5) Reinforcing Fillers Reinforcing fillers can enhance the strength, hardness, and other properties of rubber. However, if the surface treatment of the fillers is improper, the interfacial bonding force between them and the rubber is weak. For example, inorganic fillers such as calcium carbonate, if not properly surface - modified, are difficult to disperse uniformly during the rubber mixing process. Around these non - uniformly dispersed filler particles, the distribution state of rubber molecules is different from other parts, which affects the diffusion and migration of compounding agents in the rubber. When rubber products are affected by external environmental factors, compounding agents are more likely to migrate from around these filler particles to the surface, triggering a blooming phenomenon.

II. Process Factors

(1) Mixing Process Mixing is a crucial process for uniformly dispersing various compounding agents in rubber. If the mixing time is too short, the compounding agents cannot be fully dispersed in the rubber matrix, resulting in a high local concentration of compounding agents. For example, during the mixing process, if compounding agents such as sulfur are not uniformly dispersed, in areas with a high local sulfur concentration, blooming is likely to occur during subsequent vulcanization and storage. Conversely, if the mixing time is too long, the rubber molecules may undergo excessive shear degradation, affecting the physical properties of the rubber and also potentially disrupting the interaction between the compounding agents and rubber molecules, making the compounding agents more prone to migration and increasing the risk of blooming. Additionally, the mixing temperature also has an important influence on the dispersion and dissolution of compounding agents. If the temperature is too high, some compounding agents may react prematurely or volatilize, causing a change in their effective content in the rubber and further affecting their stability, which can lead to blooming.

(%1) Vulcanization Process The vulcanization temperature and time are key parameters in the vulcanization process. If the vulcanization temperature is too high or the time is too long, the rubber will be over - cross - linked, resulting in an increase in the rigidity of the rubber molecular chain and a decrease in the free volume. This will affect the diffusion coefficient of the compounding agents within the rubber, reducing the resistance of the compounding agents to migrate to the surface. For example, in some high - temperature and rapid vulcanization processes, if the process parameters are not properly controlled, the vulcanized rubber products are more likely to experience blooming. On the contrary, if the vulcanization temperature is too low or the time is too short, the degree of rubber vulcanization is insufficient, the cross - linking network between rubber molecules is incomplete, and the binding force of the compounding agents within the rubber is weak, making them also prone to migration and causing blooming.

III. Storage Condition Factors

(1) Temperature Temperature has a significant impact on rubber blooming. In a high - temperature environment, the thermal movement of rubber molecules intensifies, and the diffusion speed of compounding agents within the rubber accelerates. This makes the compounding agents, which are relatively stable at room temperature, more likely to migrate to the rubber surface, thereby accelerating the blooming process. For example, when rubber products are stored in a high - temperature warehouse, the blooming phenomenon will occur faster and be more severe than in a normal - temperature environment. In a low - temperature environment, although the thermal movement of rubber molecules weakens, the solubility of some compounding agents decreases. As mentioned earlier, paraffin - based softeners have a reduced solubility in rubber at low temperatures and are more likely to crystallize and precipitate onto the rubber surface, forming a blooming phenomenon.

(2) Humidity Humidity also has a certain influence on rubber blooming. When the environmental humidity is high, the rubber surface may absorb moisture. The presence of moisture changes the physical and chemical properties of the rubber surface, affecting the adsorption and desorption equilibrium of compounding agents on the rubber surface. On one hand, moisture may act as a carrier for the migration of compounding agents, promoting their migration to the surface; on the other hand, the interaction between moisture and the rubber surface may damage the micro - structure of the rubber surface, making it easier for the compounding agents to diffuse from the inside to the surface, thereby increasing the possibility of blooming.

(3) Light High - energy rays such as ultraviolet rays in light can initiate photochemical reactions in rubber, leading to structural changes such as the breakage and cross - linking of rubber molecular chains. These changes affect the interaction between the compounding agents and rubber molecules within the rubber. For example, ultraviolet irradiation may change the molecular structure of rubber, resulting in a decrease in the solubility and stability of compounding agents and promoting their migration to the surface, thereby triggering a blooming phenomenon. Additionally, light may also increase the surface temperature of the rubber, further accelerating the migration process of compounding agents.

IV. Conclusion

Rubber blooming is a complex phenomenon caused by the combined action of multiple factors. The type, dosage, and interaction of compounding agents, the control of process parameters such as mixing and vulcanization, and environmental conditions such as temperature, humidity, and light during storage all have important effects on rubber blooming. In the production process of rubber products, it is necessary to comprehensively consider these factors. By reasonably designing the formulation, optimizing process parameters, and improving storage conditions, the occurrence of rubber blooming can be effectively reduced or avoided, improving the quality and performance of rubber products and meeting the requirements of different application fields for rubber products. In the future, with the continuous development of rubber material science, the research on the rubber blooming phenomenon is expected to be further deepened, providing stronger technical support for the development of the rubber industry.