Phenolic Fibers
Properties
Phenolic fibers, also knonw as Novoloid, are a class of extremely heat-resistant synthetic fibers that are made by cross-linking a melt-spun novolac resin with formaldehyde.1,2 The cured fiber typically contains at least 85% by weight cross-linked novolac. Unlike most other fibers, Novoloid fibers do not melt. Instead, they gradually char until fully carbonized when exposed to extreme heat.
Due to the 3-dimensional cross-linked structure and high degree of aromaticity, fibers made from novolac resins have outstanding heat resistance,3 good UV stability, very low flammability, and excellent chemical resistance to most organic solvents as well as acids and alkalines. In addition, Novoloid fibers possess excellent electrical and thermal insulation properties. On the downside, they have poor abrasion resistance and only low to fair tenacity and low tensile modulus and strength when compared to other heat resistant high-performance fibers such as aramids, polyimides, and modacrylics.
COMMERCIAL Aramid Fibers
The only producer of commercial Novoloid fibers is Gunei Chemical Industry Co. based in Japan which sells the fiber under the trademark Kynol®. Important distributors in the US and Europe are Fiberline, and Kynol Inc.
Applications
Novoloid fibers and textiles are used for demanding and diverse applications. This includes flame resistant fabrics such as seat linings, curtains and carpets for aircrafts, ships, submarines, hotels, hospitals, night clubs, theatres, etc.; thermal insulation for shoe soles, ventilation ducts, military vehicles, etc.; electric arc protection such as wrapping tapes in high performance communication and power cables; spark and metal splash protection (welding), and chemical resistant garments and gloves. Novoloid fibers and fabrics are also used for various mechanical applications such as gaskets, disk brake pads, brake linings, reinforcement for composites, and as a precursor to carbon fibers that are used for similar applications.
1Melt-spun phenol-aldehyde resins can be cured in a solution of formaldehyde and hydrochloric acid. Alternatively, they can be cured by exposing them to an acidic gas (HCL). In this case, the phenolic resin is blended with a (latent) curative such as hexamethylenetetramine.2
2US Patent 4076692, Process for Manufacturing Novaloid Fiber, H.D. Batha & G.J. Hazelet, American Kynol Inc. (1976)
3According to the manufacturer/supplier, Novoloid fibers can withstand long-term heat exposure up to 150°C in air and 200 - 250°C in the absence of oxygen. In the case of short-term heat exposure, the fiber is stable at temperatures > 1000°C. However, the fiber will char and lose strength.