A new publication is being offered by G. M. Naul that offers a printed history of plastics and reminiscences of people that have been associated with the industry. The Newsletter of the American Plastics History Association is published 4 times a year and has had interesting articles regarding phenolics, acrylics, molded shellac, vulcanized fiber and many other interesting materials and processes.
The following is an article from the newsletter:
There are natural plastics such as gutta percha and shellac and synthetic ones such as nylon, phenolics and all the rest. There is at least one which seems to be between the two and this is known as "vulcanized fiber." Processed cellulose is vulcanized fiber. Fibers made from regenerated cellulose include viscose rayon and Cellophane.
Thomas Taylor of England patented vulcanized fiber in the U.S. in 1871. The title of the patent is "Improvement in the treatment of paper and paper-pulp." The process of "vulcanization" used zinc chloride to gelatinize cellulose fibers. Zinc chloride is the specific chemical for this process and is still the only one used to produce vulcanized fiber.
This material is now pretty much obsolete but in the past was used in athletic articles such as shoulder protectors, shin guards, etc. This was also used in cylindrical form for the body of large electrical fuses, and for large "cans" for yarn in textile operations. It was most commonly seen as the black insulating discs in electrical appliance plugs. It has excellent electrical properties, as long as it is dry. Its high moisture absorption is a detriment in athletic protection and for exposed electrical uses.
In the production of this material, the paper was saturated with zinc chloride solution which penetrated the cellulose molecule and "gelatinized" or converted it to a "sticky" state. In that condition, the paper was laminated into cylinders so that the contact between layers assisted in bonding one layer with adjacent ones. As soon as the bonding was accomplished, the zinc chloride was no longer needed. After cutting the cylinders and flattening them to form flat sheets, these were immersed in water to absorb the zinc chloride within the sheet. Unless the zinc chloride was eliminated, the vulcanized fiber would have very poor electrical properties.
In thickness to one-sixteenth of an inch, vulcanized fiber could be made in continuous lengths but required a machine at least one thousand feet in length. In the case of thick sheets, the leaching of the zinc chloride had to be done in steps of more and more dilute zinc chloride. A thick sheet immersed directly in pure water would blister due to the high osmotic pressure within the sheet. Following the leaching, the sheets were oven dried then pressed to flatten.
Normally this material was available in only three colors: bone (off-white), gray and a dull red. Vulcanized fiber was readily post-formed after heating with steam. Among products of this postforming were face shields for electrical welders and baseball catchers' shin guards.
The producers of vulcanized fiber were centered around Wilmington, Delaware. The companies included Continental Fibre Co., Diamond State Fibre Co. (the two united as Continental-Diamond Fibre Co.), National Vulcanized Fibre Co., Franklin Fibre Co. and others. Most of these companies later branched out into high-pressure thermoset laminates. At the present time, most of this business has vanished due to modern technology.
For more information, contact G. Marshall Naul, American Plastics History Association, 534 Stublyn Rd., Granville, OH 43023-9554, 614-587-3121.