The British patent for vulcanized fibre was obtained in 1859 by Thomas Taylor, an Englishman.
This patent came after the introduction of celluloid (Thermoplastic made from nitrocellulose and Camphor) in 1856 and before the invention viscose rayon (reconstituted cellulose) in 1894. In 1871 Thomas Taylor obtained the United States Patent for vulcanized fiber. The first organized industrial company, The Vulcanized Fibre Company, to make vulcanized fiber was incorporated in Delaware in 1875. Its factory was at Tenth, Wilson, and Walnut in Wilmington, Delaware. Cesar A. Rodney and Frank Taylor were principle managers. The rag paper used in the process at this plant was made nearby at the Marshall Paper Mill in Yorklyn, DE. The water power of the piedmont streams in Northern Delaware lead to a proliferation of companies in the vulcanized fiber business there. Over the years these companies reorganized and merged until in 1922 National Vulcanized Fibre Company emerged as the main competitor to Spaulding Fibre who had begun developing its vulcanized products a quarter century after the activities commenced in Delaware. Some of the companies involved in vulcanized fibre development in the Wilmington Delaware region were the Nunsuch Fiber Company, American Hard Fiber Company, American Vulcanized Fibre Company, Continental Fibre Co., Diamond State Fibre Co., and Franklin Fibre Company. In the 1965 Post’s Pulp and Paper Directory, National Vulcanized Fibre Co. was listed as having two mills producing rag paper for vulcanized fiber. They were Newark, DE producing 15 tons a day and Yorklyn, DE producing 18 tons a day. This compares with Spaulding Fibre’s Tonawanda plant shown as making 40 tons a day in the same Post’s directory. It is hard to say how much of the rag paper stock at either competitor was then going into bakelite production as Spaulding’s entry in bakelite was Spauldite and National’s entry was Phenolite. But clearly they were 1 and 2 in vulcanized fibre production, competitors tooth and nail.
Zinc chloride is highly soluble in water and the solution used in saturating the paper was 70 Baume in density (1.93 specific gravity) and about 110°F. This is roughly a 70% percent zinc chloride solution. Zinc chloride is a mild Lewis acid with a solution pH of about 4. An interesting property of Zinc chloride is that it can dissolve cellulose, starch, and silk. The zinc chloride used in the making vulcanized fibre swelled and gelatinized the cellulose in the cotton rag fibers. The fiber swelling explains why paper filters cannot be used to filter zinc chloride solutions and explains why a number of paper plies were used to build up to the desired vulcanized fibre thickness rather treating a single paperboard thickness. For instance the practice was to use 8 paper plies of 4 mils thickness as opposed to a single paperboard ply of 32 mils.
Once the paper plies were saturated with the gelatinizing zinc chloride they were pressed together. The pressing allowed intimate contact of the cellulose surfaces of cotton rag fibers thus promoting bonding between the cellulose chains. Once the bonding was established the process of leaching out the zinc chloride from the vulcanized fiber could begin. The leaching out (removal by diffusion out) of the zinc chloride was accomplished by subjecting the vulcanized fibre to successively less concentrated baths of zinc chloride. The rate at which this could occur was constrained by osmotic forces. If the rate at which the vulcanized fiber was subjected to lower and lower concentrations of zinc chloride solution were too rapid the osmotic forces could result in ply separations. The final leaching bath concentration was 0.05% zinc chloride. For thicknesses up to 0.093” can be made on continuous lines that stretch up to 1000 feet in length. For thickness above 0.093” and up to 0.375”thick, a discrete laminated sheet (similar in size (l x w) to plywood) was produced by the cutdown process. The cutdown sheets were racked and moved from vat to vat by overhead tracked cranes. Each vat was successively less concentrated until the desired 0.05% was reached. The thicker the material the longer it took to leach the zinc chloride to 0.05%. For the thickest products times of 18 months to 2 year were needed. The zinc chloride used in these processes was for the most part not consumed in achieving the desired bonding. Indeed any dilution of the zinc chloride resulting from the leaching was dealt with by using evaporators to bring the zinc chloride solution back to the 70 Baume needed for using it again for saturating. In a sense, zinc chloride can be thought of as a catalyst in the making of the vulcanized fibre.
Once the vulcanized fiber is leached free of the zinc chloride it is dried to 5 to 6 percent moisture and pressed or calendared to flatness. The continuous process made vulcanized fibre could then be sheeted or wound up into rolls. The density of the finished vulcanized fibre is 2 to 3 times greater than the paper from which it starts. The density increase is the result of 10% machine direction shrinkage, 20% cross machine direction shrinkage, and 30% shrinkage in thickness. The final product is a homogenous nearly 100% cellulose mass free from any artificial glues, resins, or binders. The finished vulcanized fibre has useful mechanical and electrical properties. It offers high tear and tensile strength while in the thinner thicknesses allowing flexibility to conform to curves and bends, and in thicker thicknesses it can be molded to shape with steam and pressure. One application for vulcanized fibre that attests to it physical strength is that it is the material of choice for heavy sanding discs. The electrical properties exhibited by vulcanized fibre are high insulating value, and arc and track resistance with service temperature of up to 110 to 120°C. Some typical electrical applications are fuse tubes, and insulation in winding electrical motor armatures. Vulcanized fibre shows high resistance to penetration by most organic solvents, oils, and petroleum derivatives
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