After 10 years, will the fiber optic skin become brittle like an aged plastic bag that crumbles when squeezed?
Under normal design and standard service conditions, optical fiber coatings will not degrade to the point of crumbling when rubbed after 10 years, unlike weathered plastic bags. However, in harsh environments that exceed the material’s tolerance limits, coatings can indeed undergo severe physical and chemical aging, leading to embrittlement, cracking, or even pulverization and peeling.
I. Material Science Mechanisms of Coating Aging
Conventional communication optical fibers (e.g., G.652D, G.657) typically feature dual-layer, UV-cured acrylate coatings with an outer diameter ranging from 245\ \mu\text{m} \sim 255\ \mu\text{m}:
- Primary Coating (Inner): Low Young’s modulus, providing cushioning against mechanical shock and reducing microbending losses.
- Secondary Coating (Outer): High Young’s modulus, offering abrasion resistance, scratch protection, and mechanical integrity.
Under the influence of specific environmental factors, polymers undergo several primary aging processes:
- Thermal-Oxidative Aging
When operating temperatures consistently approach or exceed the long-term temperature limit for acrylates (typically +85\ \text{℃} ), molecular chains undergo thermal degradation and secondary cross-linking. Excessive cross-linking density drastically reduces the material’s elongation at break, resulting in the coating becoming harder, more brittle, and yellowed. - Hydrolytic Degradation
Prolonged exposure to high humidity and heat, or immersion in water, allows water molecules to penetrate the coating and degrade ester bonds. This simultaneously weakens the adhesion between the coating and the silica ( \text{SiO}_2 ) cladding, leading to delamination of the coating or a significant reduction in stripping force. - Photo-Oxidation
If the bare fiber coating is continuously exposed to solar ultraviolet (UV) radiation, UV energy can break polymer covalent bonds, rapidly causing surface micro-cracking, powdering, and embrittlement.
II. Performance Differences: Normal vs. Extreme Environments
| Service Environment | Coating Condition After 10 Years | Will It “Crumble When Rubbed”? |
|---|---|---|
| Standard Environment (Indoor, data centers, within compliant outdoor cables; temperature -40\ \text{℃} \sim +70\ \text{℃} ) |
Slight degradation of physical properties (e.g., minor changes in stripping force), but overall good elasticity and toughness remain. | No. The designed service life for typical communication optical fibers is 20 to 25 years. |
| Extreme Environment (Long-term direct sun exposure without UV-resistant jacketing, temperatures >85\ \text{℃} , strong acid/alkali corrosion, or prolonged waterlogging) |
Severe degradation of acrylate polymer chains (breakage or excessive cross-linking), loss of elasticity, powdering, and cracking. | Yes. Highly prone to crumbling and detachment when subjected to mechanical rubbing. |
III. Hazards of Coating Aging to the Optical Fiber Core
The quartz glass ( \text{SiO}_2 ) of the optical fiber itself is chemically very stable. However, it possesses microscopic surface cracks. The hazards posed by aged coatings are:
- Loss of Stress Corrosion Protection:
When the coating cracks or peels, environmental moisture directly contacts the stressed surface of the quartz glass, inducing stress corrosion. This drastically shortens the fiber’s mechanical failure lifetime. - Additional Attenuation (Microbending Loss):
Uneven aging-induced shrinkage or localized debonding creates irregular lateral stress on the glass cladding surface, leading to a significant increase in optical signal transmission loss.
IV. High-Weatherability / Harsh Environment Coating Solutions
For industrial, high-temperature, or harsh sensing environments that exceed the capabilities of standard acrylates, specialized coating materials with superior weather resistance are typically employed:
- Standard Single-Mode Optical Fiber (Acrylate Coating):
OFSCN® G.652D Optical Fiber
Suitable for standard communication and typical temperature ranges ( -40\ \text{℃} \sim +85\ \text{℃} ).
- High-Temperature Polyimide-Coated Optical Fiber:
OFSCN® 300℃ SM Polyimide Optical Fiber
Polyimide possesses exceptionally high thermal and chemical stability, enabling long-term service in extreme temperatures ( -200\ \text{℃} \sim +350\ \text{℃} ) and complex environments. Its resistance to thermal-oxidative aging is far superior to traditional acrylates.
