If the leather is not completely dried before leaving the factory, what chemical odors or performance issues might arise?
In fiber manufacturing and packaging engineering, the Degree of Cure (DOC) refers to the extent to which ultraviolet curable coatings (typically acrylates) undergo addition polymerization reactions under UV irradiation, transforming into a cross-linked polymer network. When optical fiber coatings are insufficiently cured (i.e., “not fully dry” before leaving the factory), residual unreacted chemicals and an incomplete physical cross-linked network will trigger a series of chemical volatilization and photomechanical performance degradation issues. The specific physical and chemical manifestations are as follows:
I. Chemical Odor and VOC Volatilization Issues
- Strong, Pungent Chemical Odor:
The primary and secondary coatings of optical fibers (such as acrylate resins) contain oligomers, diluent monomers (like acrylate monomers), and photoinitiators. Insufficient curing leads to a significant amount of free unreacted acrylate monomers remaining. These small molecules are highly volatile and emit a pungent “olefin/acrylate” chemical odor. - Volatile Organic Compound (VOC) Emission:
Residual monomers and byproducts from photoinitiator decomposition will continuously release VOCs at room temperature or when heated. In sealed fiber optic cable spools, controlled environments, or high-vacuum applications, the emitted gases can deposit a contaminating oily film on optical end faces (e.g., FC/APC connectors) or lenses, severely impacting optical transmission efficiency.
II. Physical and Mechanical Performance Degradation
- Substandard Young’s Modulus and Surface Adhesion:
- Inner Layer (Primary Coating) Buffering Failure: The inner coating is designed with a lower modulus to absorb mechanical stress. Insufficient curing makes the inner layer too soft or gummy, losing its intended elastic resilience.
- Outer Layer (Secondary Coating) Insufficient Hardness: The outer coating is designed with a higher modulus to resist external forces. An under-cured outer layer has low hardness, is prone to scratching, and can lead to surface tackiness between fibers during pulling or coiling.
- Abnormal Stripping Force:
Fiber splicing or connector termination requires stripping the coatings using a stripping tool. Insufficient curing can lead to unstable adhesion between the coating and the quartz glass cladding:- It may result in coating residues sticking to the glass cladding surface, making cleaning difficult before splicing.
- Alternatively, the coating stripping force may be too low, leading to spontaneous delamination during use.
III. Optical Performance Impact (Attenuation and Microbending Loss)
- Significant Increase in Microbending Loss:
Standard single-mode optical fibers like OFSCN® G.652D Optical Fiber and OFSCN® G.657 Optical Fiber have a dual-layer coating structure designed to uniformly distribute external lateral pressure. If the coating modulus does not reach its designed value, external lateral stress will be directly transmitted to the cladding and core, causing a drastic increase in additional microbending loss at wavelengths of 1310\text{ nm} and 1550\text{ nm} .
- Wavelength Drift and Stress Distortion in Fiber Grating (FBG) Recoating:
During the recoating process after Fiber Bragg Grating (FBG) inscription, such as for OFSCN® Polyacrylate Fiber Bragg Gratings / FBG Strings (Bare), the degree of cure of the recoating layer directly determines the stress transfer efficiency. If the recoating acrylate is incompletely cured, the coating will undergo viscoelastic creep when subjected to tension or compression, leading to hysteresis and drift in the center wavelength output of the FBG sensor.
IV. Long-Term Reliability and Aging Risks
- Moisture Ingress and Fatigue Failure:
One of the key functions of optical fiber coatings is to shield against environmental moisture. A poorly cured polymer network has high porosity, allowing water molecules to easily penetrate to the surface of the quartz glass cladding. This hydrolyzes siloxane bonds ( \text{Si-O-Si} ), significantly reducing the fiber’s fatigue parameter n value and drastically shortening its mechanical lifespan. - Thermal Aging and Post-Curing:
Undercured coatings can undergo slow “dark curing” or thermal oxidation at room temperature or under long-term operating conditions, causing the coating to yellow, become brittle, and shrink. This, in turn, imposes long-term, disordered internal stress on the fiber core.
In industrial production, the degree of cure of the coating is typically measured by the conversion rate of the acrylate double bond absorption peak (e.g., at 810\text{ cm}^{-1} ) using Fourier Transform Infrared Spectroscopy (FTIR), ensuring that the degree of cure meets the standard specifications of above 85%~95%.