Polyacrylonitrile: a concurrent development

While researchers in the United States were reveling in rayon, scientists overseas were busy creating their own carbon fiber industries based on polyacrylonitrile, or PAN, which had been passed over by U.S. producers after unsuccessful attempts at making high modulus fibers.

A quiet study by Japanese researchers in 1961 — largely unknown to Western scientists — demonstrated high strength and high modulus fibers from PAN precursors. Akio Shindo of the Government Industrial Research Institute in Osaka, Japan, made fibers in the lab with a modulus of more than 140 GPa, about three times that of rayon-based fibers at the time. Shindo’s process was quickly taken up by other Japanese researchers, leading to pilot-scale production in 1964. In that same year, just a few months before Bacon and Schalamon debuted their hot-stretching method, William Watt of the Royal Aircraft Establishment in England invented a still higher-modulus fiber from PAN. The British fibers were rapidly put into commercial production.

The secret behind these developments was better precursors. In both Japan and England, researchers had access to pure PAN, with a polymeric backbone that provided an excellent yield after processing. The continuous string of carbon and nitrogen atoms led to highly oriented graphitic-like layers, eliminating the need for hot stretching. Chemical manufacturers in the United States, however, generally inserted other compounds in the polymer backbone that could account for up to 20 percent of the product, making them totally unsuitable for carbonizing.

The Japanese eventually took the lead in manufacturing PAN-based carbon fibers, effectively beating the British at their own game. Japan’s Toray Industries developed a precursor that was far superior to anything seen before, and in 1970 they signed a joint technology agreement with Union Carbide, bringing the United States back to the forefront in carbon fiber manufacturing.

PAN-based fibers eventually supplanted most rayon-based fibers, and they still dominate the world market. In addition to high modulus fibers, British researchers in the mid-1960s also developed a low modulus fiber from PAN that had extremely high tensile strength. This product became widely popular in sporting goods such as golf clubs, tennis rackets, fishing rods, and skis; it is also extensively used for military and commercial aircraft.

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