Plastic coating of glass fibers and its influence on strength

Sodium borosilicate glass fibers pulled from the melt were plastic coated “on-line” to preserve the fiber strength. By the use of tapered nozzles within the coating applicator the coating could be made concentric around the fiber, and a 40-μm concentric coating was found to be sufficient for the fiber to withstand a mild abrasion test with no deterioration in strength. Strength measurements made in ambient conditions showed that the fiber had a uniform breaking strain of 4% elongation. The same fiber measured at liquid nitrogen temperatures had a breaking strain of 14%, even after extensive handling, which is close to the theoretical glass cohesive strength.