This paper analyzes the causes of shortened service life of rubber performance from perspectives such as raw rubber selection, vulcanization deviation, and filler ratio—including possibilities like molecular chain breakage or shrinkage deformation—and proposes solutions such as "molecular modification" and "gradient temperature control." Based on the service environment of automotive seals, it further examines potential safety hazards that may arise from the attenuation of rubber elasticity.
Rubber, a polymeric material, exhibits high elasticity, impact resistance, and sealing properties, performing on par with metal structures in fields such as automotive components and industrial equipment. However, under long-term complex environments and dynamic loads, rubber is highly prone to molecular chain scission, cross-linking failure, and interface debonding, resulting in elasticity attenuation, cracking, chalking, or even functional loss.
When rubber products degrade in performance, they may show surface cracking, whitening, and chalking; after losing elasticity, they feel hardened and embrittled, with local deformation. Reduced elasticity of seals leads to leakage; tires develop uneven wear with fine cracks; and under high temperatures, they emit odors. During movement, there is a high risk of fracture, delamination, edge curling, and debonding, with a sharp drop in fatigue resistance. After aging, they shrink in volume and lose their original functionality.
Product performance is largely determined by raw material composition. Currently, rubber product enterprises modify raw materials and add components according to specific performance requirements during production. Due to the complex ingredient systems, there are numerous factors affecting the degradation of rubber performance. According to data provided by rubber manufacturer Pexxon, common causes of rubber performance degradation are as follows:
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Inappropriate selection of raw rubber types and differences in molecular chain flexibility: Rubbers with high shrinkage tend to retract due to stress release after molding.
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Imbalanced ratio in the vulcanization system
- Excessive sulfur/cross-linking agent: Over-crosslinking increases material hardness but may cause uneven internal stress after vulcanization, exacerbating shrinkage during cooling.
- Insufficient accelerators/activators: Incomplete vulcanization (under-vulcanization) results in a loose rubber network structure, prone to continuous shrinkage afterward.
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Type and dosage of fillers
- Insufficient inert fillers: Reinforcing agents such as carbon black and silica can inhibit shrinkage; insufficient dosage increases shrinkage rate.
- Filler particle size and dispersibility: Large particles or unevenly dispersed fillers easily form local defects, leading to uneven shrinkage.
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Volatilization or migration of plasticizers/softeners
- Low-boiling plasticizers: Such as phthalates, which volatilize under long-term use or high temperatures, causing rubber volume reduction.
- Poor compatibility between plasticizers and rubber: Migration to the surface forms precipitates, leading to internal volume shrinkage.
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Lack or failure of anti-aging agents
- Insufficient antioxidants: Free radical attack on molecular chains causes main chain breakage (oxidative degradation), with materials thinning or 碎裂 (volume shrinkage).
- Lack of antiozonants: Ozone environments cause surface cracks in rubber, accelerating volume loss.
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Residues of moisture or volatile components
- Moisture residues due to insufficient mixing: Moisture vaporizes during vulcanization to form micropores, which collapse during cooling, causing volume shrinkage.
- Incomplete volatilization of solvents: Processing solvents (e.g., toluene) not fully volatilized before molding, with residual portions volatilizing later to cause shrinkage.
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Incompatibility of blended materials
- Imbalanced rubber/plastic blending ratio: For example, when EPDM is blended with PP, excessive PP ratio leads to warpage due to differences in crystallization shrinkage during cooling.
- Blending of polar/non-polar rubbers: Blending rubbers with different polarities (e.g., NBR and NR) may cause phase separation, with differences in shrinkage rates leading to deformation.
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Mismatched resin systems: Resins are key carriers for ink film formation; incompatibility with substrate polarity (e.g., BOPP, PET) results in insufficient affinity. For instance, polypropylene films require chlorinated polypropylene resin inks, while using general-purpose inks may cause adhesion failure.
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Unreasonable solvent systems: Insufficient solvent dissolving power or irrational volatilization gradients hinder resin wetting and anchoring on the substrate surface, even causing whitening or flocculation.
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Precipitation and uneven dispersion of additives: Poor pigment dispersion reduces resin's ability to encapsulate particles, while precipitation of additives such as slip agents and antistatic agents in films forms a barrier layer on the surface.
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Inadequate substrate surface treatment: Substandard surface tension of films (e.g., without corona treatment), moisture absorption, or contamination (oil stains, dust) directly weaken ink adhesion.
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Defects in printing processes: Operational issues such as excessively thick ink layers, incomplete drying, or mixing of different inks may damage ink film cohesion.
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Uncontrolled environmental temperature and humidity: High humidity easily causes ink to absorb moisture and emulsify, while low temperatures inhibit molecular movement and solvent leveling.
Solutions
Based on the above causes, the following solutions can be adopted from the perspectives of raw material quality control and formula optimization:
Based on the above causes, the following solutions can be adopted from the perspectives of raw material quality control and formula optimization:
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Raw rubber optimization: Blend low-shrinkage natural rubber with synthetic rubbers (e.g., styrene-butadiene rubber) to balance elasticity and anti-retraction ability through complementary properties. Introduce graft copolymerization or hydrogenation processes to improve molecular chain heat resistance and structural stability while maintaining elasticity.
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Adjustment of vulcanization system: Adopt a multi-stage vulcanization acceleration system, combining primary accelerators with auxiliary activators (e.g., thiurams + sulfonamides) to complete cross-linking reactions in stages and form a uniform network. Monitor vulcanization processes: Closely track microscopic data such as cross-linking degree and vulcanization ratio at each stage for dynamic optimization.
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Multi-scale reinforcement strategy: Synergistically use micron-sized carbon black and ultra-fine mineral fillers to fill molecular chain gaps and reduce internal stress concentration. Coupling agent-assisted dispersion: Add silane coupling agents to enhance interfacial bonding between fillers and rubber, reducing local shrinkage defects caused by agglomeration.
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Plasticizer optimization:
- Long-chain polymer plasticizers: Use high-boiling polyester or polyether plasticizers to reduce high-temperature migration and volatile loss through macromolecular chain entanglement.
- Self-healing encapsulation technology: Embed plasticizers in thermally responsive microspheres to release repair factors when rubber is damaged, simultaneously inhibiting volume shrinkage.
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Anti-aging upgrading: Construction of composite anti-aging barriers: Combine free radical scavengers and ultraviolet shielding agents to form a multi-level anti-aging protection chain from matrix to surface. Bionic coating for longevity: Spray lotus leaf-like hydrophobic coatings to reduce moisture and ozone penetration, delaying surface crack propagation and volume shrinkage.
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Blending compatibility optimization:
- Molecular polarity adaptation modification: Graft polar functional groups (e.g., carboxyl, epoxy groups) onto non-polar rubbers to improve compatibility with engineering plastics.
- Gradient temperature-controlled mixing: Adjust mixing temperatures step by step according to material properties to gradually eliminate thermal stress differences and inhibit shrinkage warpage at blending interfaces.
Conclusion
The long-term service performance of rubber products depends on precise design of material systems and process synergy. Based on data provided by rubber manufacturer Pexxon regarding raw rubber selection, vulcanization ratios, filler optimization, etc., innovative solutions such as molecular modification and multi-level reinforcement are proposed. However, in actual application scenarios and R&D production processes, limited by material analysis experience and high-precision analytical instruments, manufacturers often struggle to accurately identify the bottlenecks affecting rubber lifespan, thereby impacting large-batch product quality and subsequent issues.
The long-term service performance of rubber products depends on precise design of material systems and process synergy. Based on data provided by rubber manufacturer Pexxon regarding raw rubber selection, vulcanization ratios, filler optimization, etc., innovative solutions such as molecular modification and multi-level reinforcement are proposed. However, in actual application scenarios and R&D production processes, limited by material analysis experience and high-precision analytical instruments, manufacturers often struggle to accurately identify the bottlenecks affecting rubber lifespan, thereby impacting large-batch product quality and subsequent issues.