Biobased coating material for optical fibers

Purpose and goal

The project aims to develop a new coating material with physical / chemical characteristics that conventional polymers cannot offer. The vision is to modify a known carbon fiber process to be used as a process for deposition of coatings on optical glass fibers. For example, this can lead to extended use of fiber-optic sensors in hostile environments and elevated temperatures. The concept was tried experimentally and the objective of the project was fulfilled through measurements on the final product and identification of necessary further investigations.

Expected results and effects

We demonstrated a process for manufacture of optical fibers coated with a carbonaceous material using lignin from wood as the precursor. The process is based on solution application followed by thermal curing, and is fully compatible with optical fiber production. More work is needed for instance to develop thicker coatings (multilayers) but also to perform more extensive mechanical and optical tests. The preliminary results however support that a commercial process can be reached within 2-5 years, with potential use for special optical fiber applications such as fiber sensors.

Planned approach and implementation

The experiments started at Innventia with screening of various lignin fractions by thermal gravimetric analysis. Materials were mapped with regards to carbonization, melting, foaming , etc. Next, coating experiments were carried out by applying lignin-solutions on fiber pieces followed by thermal treatment. Visual inspection and SEM- and EDS-analysis provided a guideline for a first trial in Acreo´s fiber draw tower. Fibers were produced with time, temperature and atmosphere as primary parameters and optical, mechanical and thermal characterization was carried out.