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.

I. It’s No Coincidence That Your Car Windows Haven’t Let in Any Wind for 15 Years Ever wondered why your car’s decade-old door/window rubber seals stay crack-proof and leak-free, while new wiper blades wear out and squeak quickly? The secret lies in materials: factory seals use EPDM rubber, while wipers are mostly natural rubber or neoprene, which age easily under ozone and sunlight. Known as durable long-life rubber, EPDM has been widely used since the 1960s with an annual global demand over 1.5 million tons. It tolerates temperatures from -50°C to 150°C and resists sun cracking for up to 20 years. This article covers EPDM’s wide industrial sealing applications and its unsuitable usage scenarios. Molecular Code: Why Is EPDM Naturally Resistant to Aging? It is composed of three monomers working together: Ethylene + Propylene: These form a highly saturated hydrocarbon backbone. Saturation means the material is “unlikely to cause trouble,” so ozone, UV rays, and oxygen do not affect it. Non-conjugated diene (commonly ENB): Added in small amounts (2%–9% by mass), it provides several cross-linkable “anchors” on the main chain, facilitating vulcanization and shaping. The main chain of ordinary natural rubber contains many double bonds, which act like “openings” that ozone can easily cut through. The main chain of EPDM is almost entirely saturated, making it 5 to 10 times more durable than general-purpose rubber.   III. Hardcore Performance: Just How Durable Is It? Excellent Resistance toAging Outdoor Service Life: Over 20 years. Ozone Resistance: Tested per ASTM D1149, shows no cracking at 50 pphm ozone. Elasticity Acrossa Wide Temperature Range Conditions Temperature Long-term use -50°C to +150°C Short-term heat resistance (for several hours in air) ≤175℃  (For temperatures exceeding this limit, use SIR or FPM) Embrittlement temperature Approx. -60°C (remains flexible)   Excellent electricalinsulation properties Volume resistivity can reach 10¹⁵ Ω·cm, making it one of the top choices for high-voltage cable insulation. Good abrasion resistance, though not the best EPDM offers better abrasion resistance than silicone rubber and most thermoplastic elastomers, but is inferior to NR and SBR. Therefore, it is not used in tire treads, but it is more than adequate for sealing strips and gaskets. Key Parameters of EPDM Performance Typical values Notes Density (g/cm³) 0.85～0.87 Unfilled Hardness (Shore A) 30～95 Adjustable Tensile Strength (MPa) 7～21 Can exceed 20 after reinforcement Elongation at Break (%) 100～600 High-resilience formulation: 800% Compression Set (%) 15～60 Peroxide curing as low as 15% Resistance to Mineral Oil/Fuel Oil Poor Critical flaw EPDM vs. Other Rubbers Performance EPDM SIR CR NBR Ozone Resistance / Weather Resistance ★★★★★ ★★★★ ★★★ ★ Long-Term Heat Resistance (°C) 150 200 100 120 Low-Temperature Flexibility ★★★★★ ★★★★ ★★★ ★★★ Resistance to Mineral Oils / Fuels ★ ★★ ★★★ ★★★★★ Price / Cost Medium High Medium Medium Typical Applications Sealing Strips/ Roof Waterproofing High-Temperature Gaskets Oil-Resistant Hoses Oil Seals, Fuel Lines   Where Is EPDM Used? Automotive (top market): Door/window/sunroof seals, coolant hoses, brake diaphragms. Each car consumes 8–12kg EPDM. EVs need more EPDM for battery seals, cooling pipes and high-voltage cables. Construction waterproofing: Roof sheets for airports, stadiums and malls, with a 25-year service warranty. Cables: Insulation for mining, nuclear and underground urban power cables. Industrial parts: Hydraulic seals, pump/valve diaphragms, steam hoses. New sectors: Athletic tracks, playground flooring, TPV raw materials. Pitfalls to Avoid: These Three Mistakes That 90% of People Make When Choosing EPDM 1.EPDM contact with mineral oil/fuel Result: Swell, soften & lose strength fast, cause leakage. Solution: Use NBR or FKM instead. 2.Sustained temp over 150°C / short spike over 175°C Result: Harden, crack, seal failure. Solution: SIR/FPM for constant >150°C service. 3.Mismatch with specific adhesives & chemicals Result: Bond separation, tackiness, material degradation. Solution: Run compatibility tests prior to application. VII. The Market and the Future: An Industry Approaching $10 Billion Year Global Consumption/Market Size Note 2023 Approx. 1.5 million metric tons Actual figures for the past three years 2030 1.8–1.9 million metric tons Annual growth rate of approximately 3.5% 2025(Market Size) Approx. $3.3 billion Conservative forecast 2035 (Optimistic) $8.4 billion Requires a growth rate of 6–7%, driven by electric vehicles and green buildings Regional Landscape: The Asia-Pacific region accounts for more than half of the global market, with China being the largest single market. In Europe, high-end EPDM sheet growth is accelerating due to building energy efficiency regulations. New Trends: In 2024, Dow Chemical launched a bio-based EPDM with a carbon footprint reduced by more than 40%. Sealing for electric vehicle battery packs and liquid-cooling piping have emerged as new growth areas. VIII. Conclusion: Choose the Right Material to Save Millions in Maintenance Costs No universal rubber，only the right one works. EPDM boasts outstanding weather resistance and wide-temperature elasticity, vital for auto seals, construction waterproofing and cable insulation. But it poorly resists oil and high heat, and improper use shortens product service life greatly. That solid car door closing sound and elastic playground tracks all rely on durable EPDM.

Ⅰ.What Is Post-Curing? In the production workshop, the process of heating, pressurizing, and shaping the finished product in a mold is called “first-stage curing” (also known as primary curing or initial curing). “Secondary vulcanization” (commonly referred to in the workshop as “second-stage vulcanization” or “post-cure”) refers to the process of neatly stacking rubber products that have already been demolded and shaped into a large industrial oven equipped with forced-circulation hot air, and continuing to bake them at atmospheric pressure for several hours at a specific temperature (typically 150–200°C). Ⅱ.Which Rubbers Require Secondary Vulcanization? Not all rubbers require secondary vulcanization. Common types such as natural rubber (NR), styrene-butadiene rubber (SBR), and butadiene rubber (BR) are generally fully cured after the initial vulcanization stage in the mold and are shipped directly from the factory. Those requiring secondary vulcanization are often “high-end specialty rubbers” that are expensive, subject to extremely strict performance requirements, or made with special vulcanizing agents:   Ⅱ.Which Rubbers Require Secondary Vulcanization? Not all rubbers require secondary vulcanization. Common types such as natural rubber (NR), styrene-butadiene rubber (SBR), and butadiene rubber (BR) are generally fully cured after the initial vulcanization stage in the mold and are shipped directly from the factory. Those requiring secondary vulcanization are often “high-end specialty rubbers” that are expensive, subject to extremely strict performance requirements, or made with special vulcanizing agents: 1.Silicone Rubber (MVQ / Silicone) — Over 95% require secondary vulcanization Reason: During compression molding or injection molding, silicone rubber uses peroxide-based curing agents (such as Di-25, Di-24, and odorless Di-25 curing agents). After these curing agents complete their reaction in the mold, they produce large amounts of acidic byproducts and volatile substances. Unless these are removed through a secondary curing process in an oven, silicone products will become brittle, yellow, or even develop a white bloom on the surface after just a few days. 2.Fluorocarbon Rubber (FKM / Viton) — 100% mandatory Reason: Fluorocarbon rubber reacts relatively slowly. During the brief few minutes spent in the mold (the first stage of curing), it actually forms only about 70% of its chemical cross-linking network. The remaining 30% must be transferred to a high-end oven set at 200–230°C and thoroughly cured for 8 to 24 hours to fully transform into its ultimate “oil- and heat-resistant” state. 3.Acrylate Rubber (ACM) and Hydrogenated Nitrile Rubber (HNBR) Reason: These two types of rubber are commonly used in high-end automotive oil seals and engine gaskets. Similar to fluorocarbon rubber, their reactions within the mold rarely reach full saturation. To achieve extremely low compression set, they must undergo secondary post-curing in an oven. 4.Automotive interior rubber parts with ultra-low odor and low VOC requirements (e.g., EPDM pedal covers, gaskets) Reason: Automakers enforce extremely strict standards for in-cabin air quality (odor testing per VDA 270). Ordinary EPDM products retain pungent amine and mercaptan odors after vulcanization, so they must be placed in an oven where high-intensity hot air is used to “squeeze out and bake away” the odors in a single pass. III. What Are the Core Benefits of Secondary Vulcanization? Given that it is labor-intensive and energy-consuming, secondary vulcanization must offer four irreplaceable, miraculous benefits:   The Four Core Benefits of Secondary Vulcanization 1.Fills the cross-linking network (eliminates under-vulcanization, doubling rebound and tensile strength) 2.Evaporates small molecules (removes residual cross-linking agents through heating, completely eliminating odors and white bloom) 3.Eliminating Internal Stress (Prevents later issues such as curling edges, distortion, and deformation) 4.Enhancing Durability (Maximizing resistance to pressure changes at high and low temperatures)   1.Making the Cross-Linked Network More Dense: Truly “Baking” the Rubber Through Many specialty rubbers are in a “half-baked” or “barely passable” state after the first stage of compression molding. Secondary vulcanization is like placing rice in a rice cooker for the final “steaming” process. Effect: It allows unreacted molecular chains within the rubber to continue linking together, exponentially increasing the cross-linking density. The resulting cured rubber experiences a qualitative leap in tear strength, tensile strength, and resilience. 2.Eliminate low-molecular-weight volatiles: Purify the product, eliminate odors, and remove bloom Toxins and odors generated by curing agents inside the mold are forcibly vaporized and extracted by the high-temperature hot air in the oven. Effect: Completely removes the fishy, kerosene, and pungent VOC odors from new products; simultaneously, it prevents curing agent residues from migrating to the surface, thoroughly eliminating the problem of “blooming” or “whitening” on the surface. For products such as medical-grade silicone and baby pacifiers, secondary vulcanization is a mandatory requirement for obtaining food-grade certification (FDA). 3.Stabilizing Product Dimensions: Eliminating “Trapped Internal Stress” When rubber compound is forced into the mold under high pressure, its molecular chains accumulate “internal stress” from being constrained. If shipped directly from the factory, the products will gradually shrink, deform, and warp over time. Effect: The high temperature in the oven allows the molecular chains to relax freely, releasing all the pent-up tension (eliminating internal stress). As a result, the finished products maintain extremely stable dimensions and will not lose their shape no matter how they are positioned. 4.Quality Enhancement: Pushing Compression Set (Creep Resistance) to the Limit High-end oil seals and O-rings, in particular, are most vulnerable to failing to rebound after being compressed. Effect: Secondary vulcanization creates a seamless chemical network, reducing the high- and low-temperature compression set of EPDM, fluorocarbon rubber, and hydrogenated nitrile rubber to half or even one-third of their original values. This not only extends the service life of the seals but also prevents premature oil and gas leaks.