Does the optical fiber jacket become brittle over time?

OFSCN Global Technical Center OFSCN Technical Knowledge Base
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Will the fiber optic jacket crack if exposed to the sun for too long or frozen in a cold storage for too long?

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Yes, the plastic outer jacket (i.e., protective sheath) of ordinary optical fibers is very susceptible to physical and chemical degradation when exposed to prolonged sunlight or long-term freezing in cold storage. This can lead to hardening, embrittlement, and even cracking. This phenomenon is determined by the inherent physical and chemical properties of polymer materials.

I. Photo-oxidative Degradation Under Sunlight Exposure (UV and Thermal Aging)

The sheaths of most conventional fiber optic patch cords or cables are made from polymer materials such as Polyvinyl Chloride (PVC), Polyurethane (PU), or Low Smoke Zero Halogen (LSZH).

  1. Photochemical Reactions: Ultraviolet (UV) radiation in sunlight possesses high photon energy. When these UV rays strike the plastic sheath, they can break chemical bonds within the polymer molecular chains, generating free radicals and triggering photodegradation reactions.
  2. Loss of Additives: Plastic processing typically involves adding plasticizers to ensure flexibility. The continuous high temperatures generated by outdoor solar radiation accelerate the volatilization and degradation of these elastic additives.
  3. Cracking Mechanism: As the molecular chains break and plasticizers are lost, the sheath material gradually loses its elasticity, and its surface may discolor, harden, and become brittle. Under external mechanical stress (such as cable sway caused by wind or micro-vibrations) and thermal expansion/contraction cycles due to diurnal temperature variations, micro-cracks form on the sheath surface, eventually expanding into macroscopic cracks and shedding.

II. Low-Temperature Embrittlement in Cold Storage (Cold Brittleness)

All polymer materials have a critical physical property called the Glass Transition Temperature (T_g).

  1. State Transition: When the temperature is above T_g, polymer chain segments can move freely, and the material exhibits good elasticity and flexibility (rubbery state). However, when the ambient temperature drops below T_g, the movement of internal molecular chain segments is