Rubber aging is irreversible degradation (tackiness, embrittlement, cracking, powdering) after storage or use. It has five trigger-based categories, with causes and failure features below:
1. Oxygen & Ozone Aging (Failures: surface cracking, fracture)
Causes: Oxygen in air and environmental ozone (ozone far more aggressive); rubbers with C=C bonds (NR, NBR, etc.) are highly sensitive.
Symptoms: Fine surface cracks; under tension, cracks propagate perpendicular to stress, leading to fracture. Oxygen causes either chain scission (softening/stickiness) or excessive crosslinking (hardening/brittleness). Ozone specifically attacks deformed rubber surfaces, creating irreversible cracks.
2. Thermal Aging (Failures: high-temperature hardening, melting/tackiness)
Causes: Sustained high heat in engine compartments or high-temperature environments.
Symptoms: Two opposite effects – NBR and BR undergo crosslinking, becoming hard and brittle like plastic, breaking easily when bent; NR network disintegrates under heat, becoming soft and sticky like melted adhesive. Heat accelerates molecular motion, breaks polysulfide bonds, and significantly reduces tensile strength and resilience.
3. Light & Weathering Aging (Failures: powdering, fading, cracking)
Causes: Outdoor UV, rain, and alternating temperature/humidity cycles.
Symptoms: Gloss loss, fading (black turns grayish, colored turns white), surface powdering and flaking, accompanied by fine cracks. UV cuts polymer chains; combined with rain-soaking and thermal cycling, the surface layer rapidly loosens and loses toughness.
4. Mechanical Fatigue Aging (Failures: internal heat melting, localized cracking/chunk loss)
Causes: Long-term repeated tension, compression, and high-frequency vibration on mounts, tires, drive components, etc.
Symptoms: Friction between polymer chains and carbon black generates heat. Poor compounding or high heat-generation formulas, combined with inadequate heat dissipation, cause internal heat accumulation and self-accelerated aging, greatly shortening service life.
5. Medium-Induced Aging (Failures: swelling, exudation-induced hardening/shrinkage)
Causes: Long-term contact with oils, hydraulic fluids, acids/alkalis, water, and other liquid media.
Symptoms: Seals swell and soften in oils; additives and plasticizers are leached out, causing hardening and shrinkage, leading to complete seal failure. Media penetrate molecular gaps, disrupt the crosslinked network, and ultimately cause leakage and material damage.
