Aging Behavior of Rubber Materials in Marine Environments

1. Introduction

Due to its high elasticity, excellent air tightness, and resistance to various media, rubber is widely used in oil and gas sealing systems for aerospace, aviation, and naval weaponry.
With the rapid development of China’s national defense industry, vulcanized rubber components have become increasingly important in aerospace equipment, marine vessels, and deep-sea engineering.
In particular, under the complex marine environment, rubber sealing materials must withstand high humidity, salt spray, and mechanical stress simultaneously, placing higher demands on the material’s long-term stability and service life.

At present, most studies on rubber aging focus on the thermal-oxidative aging behavior of vulcanized rubber, mainly investigating the effects of temperature and oxygen on its properties.
However, in the marine environment, factors such as oil media, corrosive gases, and salt spray coexist, which significantly affect the sealing performance and service lifespan of vulcanized rubber components.

In contrast, non-vulcanized rubber parts (such as partially crosslinked protective pads, rubber coatings, and temporary seals used on-site) exhibit poorer aging resistance due to the lack of a stable crosslinked network.
These materials are prone to surface softening, deformation, and performance degradation under marine exposure.

2. Causes and Effects of Rubber Aging

The causes of rubber aging can be divided into intrinsic and extrinsic factors:

Intrinsic factors include the chemical composition of the polymer structure, molecular conformation, crystallinity, chain entanglement, and chain scission or oxidation introduced during processing.

Extrinsic factors include oxygen, ozone, temperature, humidity, salt mist, mold, and ultraviolet radiation in the environment.

For vulcanized rubber components, a three-dimensional crosslinked structure provides good stress-relaxation resistance and chemical stability.
However, prolonged exposure to marine environments can still cause crosslink bond breakage, surface cracking, or hardening.

Non-vulcanized rubber parts, on the other hand, lack vulcanization treatment. Their loose molecular chains and large free volume make them more susceptible to marine ions, oxidizing agents, and UV radiation, leading to accelerated aging.

Aging-induced performance changes include:

Appearance changes: surface hardening, cracking, stickiness, and discoloration.

Physical and chemical degradation: reduction in density, hardness, tensile strength, compression set, viscoelasticity, and electrical properties.

Therefore, in practical applications such as aerospace oil seals, naval protective pads, and deep-sea sealing rings, it is essential to establish distinct aging evaluation standards for vulcanized and non-vulcanized rubber products.

3. Accelerated Aging Tests and Service Life Prediction

In engineering practice, rubber products—especially vulcanized rubber components—often have a service life of over ten years.
To simulate long-term use, high-temperature accelerated aging tests are commonly employed.

Early studies used oxygen absorption as an indicator of aging rate, later evolving into methods such as oven aging, oxygen bomb, air bomb, and artificial weathering tests.
The most widely used approach today is based on the Arrhenius empirical relationship and the time–temperature superposition principle, which assumes that for every 10 °C rise in temperature, the reaction rate doubles.

However, in marine environments, traditional accelerated aging prediction models show deviations due to:

different reaction mechanisms at varying temperature zones,

antioxidant migration or precipitation,

polymer morphology evolution, and

oxygen diffusion limitations related to specimen thickness.

Therefore, for vulcanized rubber components operating in marine service conditions, it is advisable to lower the accelerated aging temperature, extend the test duration, or develop multi-factor coupling models involving humidity, salt spray, and microbial activity to improve lifetime prediction accuracy.

For non-vulcanized rubber parts, due to the absence of a stable crosslinked network, softening or failure occurs rapidly during accelerated aging.
Thus, traditional Arrhenius-based extrapolations are unreliable, and only short-term stability evaluations are generally conducted.

4. Marine Environment Simulation for Accelerated Testing

Given the complexity of the marine environment, single-factor tests such as humidity–heat, salt spray, or mold exposure cannot fully replicate actual service conditions.

In this study, an improved humidity–heat aging apparatus was employed, replacing distilled water with artificial seawater, and conducting tests at 90 °C and 98% humidity to simulate multi-factor accelerated aging.
This method increases the aging rate by approximately eightfold, allowing for rapid evaluation of vulcanized rubber components under marine exposure.

The experimental results provide valuable guidance for selecting sealing materials in naval vessels, diving equipment, and submarine cables, while also helping to optimize the short-term stability of non-vulcanized rubber components in protective structural applications.

Due to its high elasticity, excellent air tightness, and resistance to various media, rubber is widely used in oil and gas sealing systems for aerospace, aviation, and naval weaponry.