Rubber, a versatile polymer, plays an integral role in countless everyday products, from vehicle tires and industrial seals to household goods and footwear. Its unique flexibility, durability, and resilience make it indispensable across various applications. Despite these inherent properties, rubber is not impervious to the passage of time or the influence of its surroundings. Over time, rubber materials can lose their original characteristics and degrade. This process is influenced by environmental conditions, chemical interactions, and physical and biological factors.
Environmental Factors Affecting Rubber
Oxygen in the air reacts with rubber through a process known as oxidation, causing changes to its chemical structure. This reaction leads to the material becoming brittle and developing cracks over time. The presence of oxygen can significantly accelerate the aging process of rubber, diminishing its mechanical properties.
Ozone, a highly reactive form of oxygen, specifically targets the double bonds within the rubber’s polymer chains. This attack results in surface cracking, commonly referred to as “ozone cracking,” which is particularly noticeable on rubber products exposed to the atmosphere. Equipment that generates electric sparks or discharge can produce ozone, making such environments detrimental to rubber.
Ultraviolet (UV) radiation from sunlight initiates photochemical reactions within rubber, breaking down its polymer chains. Prolonged exposure causes discoloration, hardening, and a loss of elasticity. This weakening and breaking of monomer chains reduces flexibility, forms cracks, and leads to eventual disintegration.
Elevated temperatures accelerate the chemical reactions occurring within rubber, leading to premature aging. Depending on the type of rubber, sustained heat exposure can cause it to soften excessively or become hardened and stiff. Storing rubber products at temperatures exceeding 50°C can be particularly harmful, as high temperatures accelerate deterioration.
Chemical and Solvent Damage to Rubber
Certain organic solvents, such as gasoline, oils, greases, and various cleaning agents, can significantly degrade rubber materials. These solvents can penetrate the rubber’s structure, causing it to swell, soften, lose strength, or even dissolve. Gasoline, a complex mixture of hydrocarbons, interacts with the rubber’s molecular structure, breaking its chemical bonds and leading to a loss of flexibility and durability.
Different types of rubber exhibit varying levels of resistance to specific solvents. For instance, while most rubbers degrade upon contact with gasoline, materials like Nitrile rubber (NBR) and Viton (FKM) are engineered to resist hydrocarbons and are commonly used in fuel systems. Conversely, EPDM rubber, known for its weather resistance, has poor resistance to oils, gasoline, and other hydrocarbon solvents.
Strong acids and bases can also chemically attack and degrade rubber, fundamentally breaking down its polymer structure. Selecting rubber types with appropriate chemical resistance is important, as degradation can occur rapidly if the material is not suited for its environment.
Physical and Biological Breakdown of Rubber
Repeated physical stress, such as flexing, stretching, or constant friction, can lead to the physical breakdown of rubber. This mechanical stress can cause tearing, fatigue cracking, and general wear. Abrasion, which is wear caused by friction from physical contact, can result from processes like scuffing, scraping, sliding, and grinding.
The ability of rubber to withstand abrasive wear is known as its abrasion resistance, which is a critical property for products like tires. Fatigue abrasion, for example, occurs when rubber products are subjected to continuous cyclic compressions, shear, and tensile deformations, eventually leading to surface fatigue and crack formation.
Certain microorganisms, including bacteria and fungi, can degrade rubber under specific environmental conditions, such as in soil or damp environments, by utilizing rubber components as a food source. For example, some Actinobacteria contain genes that produce enzymes like latex clearing protein (Lcp), which cleaves the double bonds in rubber’s isoprene units, breaking them down for energy. Fungi, such as Aspergillus niger and Phlebia radiate, have also been shown to degrade natural rubber, with Aspergillus niger demonstrating a significant capacity for weight reduction.
Preserving Rubber Products
Proper storage is an effective way to extend the lifespan of rubber products. Storing rubber away from direct sunlight, strong artificial light with high UV content, and extreme temperatures (ideally below 25°C) helps prevent degradation. It is also beneficial to store rubber in airtight containers or in wrapping to protect it from circulating air and ozone, as ozone is particularly harmful.
Regular cleaning and maintenance contribute significantly to the longevity of rubber. Using mild soap and water to clean rubber surfaces helps remove dirt and debris, but harsh chemicals, strong solvents, or abrasive cleaners should be avoided as they can damage the material. After cleaning, thoroughly rinsing and drying the rubber is important to prevent moisture buildup.
Applying protective coatings can further safeguard rubber products, especially those exposed to harsh conditions. UV protectants, for instance, can shield surfaces from harmful UV rays, preventing fading, cracking, and premature aging. Silicone-based products or specialized dressings can also be used to maintain flexibility and prevent drying and cracking.
Selecting the appropriate type of rubber for a given application is crucial for its long-term performance. Material selection should consider environmental conditions, temperature range, and chemical exposure to ensure the product withstands its intended operating environment. For example, choosing Nitrile rubber or Viton for exposure to oils or fuels, due to their excellent chemical resistance, prevents premature degradation.