The aging of ABS plastic (Acrylonitrile Butadiene Styrene Copolymer) is caused by a combination of environmental factors and inherent characteristics of the material, mainly including the following reasons:
1. Thermal oxidative aging
High-temperature accelerated degradation: long-term exposure to high temperatures (> 60 ° C), the butadiene phase (rubber phase) in ABS is easy to react with oxygen, resulting in molecular chain breakage, the material becomes brittle.
Performance: yellowing of the surface, loss of gloss, significant reduction in mechanical properties (e.g. impact strength).
2. Ultraviolet (UV) radiation
Photo-oxidation: UV light triggers free radical reactions in styrene and butadiene chain segments, destroying the polymer structure.
Performance: surface chalking, color fading (especially dark ABS), cracks ("cracking" phenomenon).
Protection: need to add UV stabilizers or carbon black and other shading agents.
3. Hydrolysis
Moisture sensitivity: The acrylonitrile component in ABS is easy to absorb moisture, long-term exposure to high humidity environment (especially high temperature and high humidity) will trigger hydrolysis.
Performance: molecular weight decrease, tensile strength and modulus decrease, silver grain may appear.
4. Chemical corrosion
Solvent erosion: ABS is not resistant to strong polar solvents (such as ketones, esters, some halogenated hydrocarbons), which can lead to swelling or stress cracking.
Performance: sticky surface, deformation, or even localized dissolution.
5. Mechanical Stress Fatigue
Dynamic loading: Repeated bending or impact will trigger microscopic cracks, especially in the butadiene phase expansion, accelerated aging.
Performance: Stress whitening, brittle fracture.
6. Environmental Stress Cracking (ESC)
Stress + medium synergy: Even weakly corrosive mediums (e.g. detergents, alcohols) may initiate cracks under stress.
Performance: sudden brittle cracking without warning.
7. Microbial degradation (rare cases)
Certain microorganisms (e.g. molds) may attack additives (e.g. plasticizers) in ABS, leading to surface degradation.
Aging Characterization Methods
Appearance changes: yellowing index (ΔYI), surface roughness.
Mechanical properties: Impact strength, tensile strength reduction rate.
Molecular weight analysis: GPC to measure molecular weight distribution.
FTIR: Detection of oxidation products such as carbonyl (C=O).
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