In the hydraulic systems of the aviation and heavy-duty industries, while phosphate ester fire-resistant hydraulic fluids offer exceptional flame retardancy, they pose a rigorous challenge to the oil resistance of sealing materials. Conventional silicone rubber is highly susceptible to molecular chain solvation within such environments, leading to volume swelling rates exceeding 15%—a phenomenon that triggers seal failure and system leakage. Phenyl raw rubber, leveraging its unique mechanisms of "enhanced molecular rigidity" and "polar repulsion," serves as the "volume stability anchor" of hydraulic systems, constructing a three-dimensional barrier at the microscopic level to resist fluid erosion.

The core of phenyl raw rubber's ability to inhibit volume swelling lies in the "steric hindrance effect of its phenyl groups" and its "polarity matching characteristics." Phosphate ester hydraulic fluid molecules possess strong polarity, whereas the non-polar methyl side chains of conventional silicone rubber are easily penetrated and swollen by them. By introducing bulky phenyl groups into the siloxane backbone, phenyl raw rubber not only significantly enhances the rigidity of the molecular chains but—more critically—generates a "repulsion effect" between the weakly polar phenyl groups and the polar phosphate ester molecules; this effectively cloaks the molecular chains in a "fluid-repellent coat." This structural configuration makes it difficult for hydraulic fluid molecules to intercalate into the gaps between the molecular chains, thereby locking the volume swelling rate within a limit of 5%.

Furthermore, the superior "crosslink network density" of phenyl raw rubber enables it to maintain a stable three-dimensional structure even when immersed in hydraulic fluids. The rigid structural support provided by the phenyl groups effectively suppresses the " disentanglement" and "slippage" of molecular segments under the influence of the fluid, thereby preventing the degradation of mechanical properties typically associated with swelling. Moreover, its exceptional thermal-oxidative stability ensures that, even within high-temperature hydraulic environments reaching 150°C, the rubber compound will not develop new fluid-ingress pathways resulting from aging-induced degradation.

Ranging from polar repulsion at the molecular level to macroscopic volume stability, phenyl raw rubber—through its synergistic mechanism of "rigid fluid-repellency and dense solvent-resistance"—successfully resolves the long-standing swelling challenge faced by silicone rubber in phosphate ester hydraulic fluid environments. It serves not only as a critical sealing material for the reliable operation of hydraulic systems, but also as an invisible safeguard for the safe functioning of industrial equipment under extreme operating conditions.