Thermoplastic elastomer (TPE), a polymer material combining the elasticity of rubber and the processing properties of plastics, is widely used in the automotive, industrial, and consumer electronics industries. However, its oil resistance is often limited by its molecular structure and composition design. To address this issue, modification techniques, through optimizing material formulations, adjusting processing techniques, and introducing surface treatment technologies, can significantly improve the stability of TPE in oily environments. This can be explored from the following dimensions:
Material formulation optimization is the core strategy for improving oil resistance. The choice of matrix resin directly affects oil resistance. For example, SEBS (styrene-ethylene-butene-styrene block copolymer), with its higher degree of hydrogenation, effectively resists the penetration of non-polar oil molecules due to its high molecular chain saturation, resulting in significantly improved oil resistance compared to unhydrogenated SBS. Regarding additives, the polar fluorine atoms of fluoropolymers (such as PVDF resin) have a large polarity difference from non-polar oil molecules; their addition can form a physical barrier, reducing the oil penetration rate. The combination of polyester plasticizers and antioxidants can improve oil resistance while maintaining the material's mechanical properties. Furthermore, the addition of inorganic fillers such as calcium carbonate and talc can enhance the material's density, reduce oil molecule penetration channels, and further optimize oil resistance.
The introduction of cross-linking technology can construct a three-dimensional network structure, suppressing swelling. Chemical cross-linking uses peroxides or silane cross-linking agents to form covalent bonds within the material, increasing the connection strength between molecular chains; radiation cross-linking utilizes high-energy rays (such as gamma rays) to induce molecular chain cross-linking, forming a more stable three-dimensional network. Both methods effectively limit the diffusion of oil molecules within the material, especially suitable for applications exposed to high-temperature oil environments for extended periods. For example, cross-linked TPE seals, after immersion in engine oil, show a reduction in volume swelling rate of over 50%, significantly extending their service life.
Precise control of the processing technology is crucial for oil resistance. Temperature management is a key factor; excessively high processing temperatures can lead to thermal degradation of the material, causing additive leaching and molecular chain breakage, thereby reducing oil resistance. Taking SEBS-based TPE as an example, its processing temperature must be strictly controlled within the range of 180-220℃ to ensure sufficient plasticization and prevent degradation. In mold design, a uniform cooling channel layout can reduce internal stress in the product, avoid microscopic defects caused by uneven cooling, and thus reduce the risk of oil molecule penetration. Optimization of injection parameters (such as injection speed, holding pressure, and time) ensures that the material fully fills the mold cavity, improves the dimensional stability of the product, and indirectly enhances oil resistance.
Surface modification technology provides new ideas for building an oil-resistant barrier for thermoplastic elastomer (TPE). Oil-resistant coatings are a direct and effective method; highly oil-resistant coatings such as fluorocarbon coatings and polyurethane coatings can form a physical isolation layer on the TPE surface, preventing oil molecules from contacting the matrix. For example, after applying a fluorocarbon coating, the contact angle of the material in specific oils increases, and the amount of oil penetration is significantly reduced. Surface chemical treatments (such as plasma treatment) introduce polar groups by bombarding the material surface with high-energy particles, enhancing surface oleophobicity and further improving oil resistance. This treatment method is particularly suitable for applications with high requirements for friction performance, such as automotive transmission system components.
Improved material density can be achieved through filler modification. The addition of inorganic fillers (such as calcium carbonate and talc) not only enhances material rigidity but also fills the gaps between molecular chains, reducing the penetration path of oil molecules. The particle size distribution of the filler is just as important as surface treatment. Nanoscale fillers, due to their large specific surface area, can form a denser barrier layer after uniform dispersion. Fillers treated with silane coupling agents can form a stronger interfacial bond with the matrix resin, further improving oil resistance.
Environmental control is an auxiliary means of ensuring oil resistance. Avoiding prolonged exposure of TPE products to high-temperature and high-oil-pressure environments can slow down the diffusion rate of oil molecules. For example, in automotive fuel systems, optimizing component layout to reduce the direct contact time between TPE and fuel can significantly reduce the risk of swelling. Furthermore, storage should be kept in a dry and cool environment to prevent the material's oil resistance from decreasing due to moisture absorption or thermal aging.
Through multi-dimensional modification technologies such as material formulation optimization, introduction of cross-linking technology, processing control, surface modification, filler modification, and environmental management, the oil resistance of TPE can be systematically improved. These methods can be used individually or in combination. For example, in automotive fuel lines, a composite modification scheme involving hydrogenated SEBS matrix, the addition of fluorinated additives, chemical cross-linking, and coating with a fluorocarbon coating can achieve long-term stable operation of the material in extreme oily environments. In the future, with advancements in materials science, more innovative modification technologies (such as bio-based oil-resistant additives and smart responsive coatings) will further expand the application boundaries of TPE under harsh conditions.
