Volume 3, Number 6
Dec 1990

Fluorescent Brighteners

There are about 250 fluorescent brighteners listed by the [British] Society of Dyers and Colourists and the American Association of Textile Chemists and Colorists in the third edition of the Colour Index (CI), of which only 27 are commercially available today. They are listed, along with their CI number, chemical class, application (e.g., cellulose, nylon, paper, protein fibers) and properties (e.g., fastness to chlorine, peroxide and light).

This Colour Index list shows what a great variety of brighteners there are, each with its own capabilities and drawbacks. Most of them fluoresce colors: yellow, bright blue, greenish blue, bluish violet, reddish blue, greenish yellow, bright reddish violet. These must be what give "Day-Glo" colors their eye appeal (or shock value), and brighten ordinary colors in both textiles and papers. A few fluoresce white or "neutral"; these must be the brighteners used in laundry soaps and white paper.

You can easily tell whether fluorescent brighteners have been used in a given paper or textile by taking it into a dark room and shining ultraviolet (black) light on it. All issues of this newsletter since December 1989 have a bright eerie glow, showing that they have been printed on paper containing fluorescent brighteners. The glow comes from light absorbed in the UV range and re-emitted in the visible range. The November 1989 issue, on the other hand, was brightened with titanium dioxide--you can tell because it looks dark red under the UV light.

The introduction to the section of the Colour Index on fluorescent brighteners says, "Colourless compounds which fluoresce under ultraviolet radiation were first used by the British firm of security printers, Waterlow & Sons Ltd.... and later by Imperial Chemical Industries Ltd.... primarily to prevent forging of banknotes or other securities. Their use for imparting a whitening effect to textiles seems to have been first recorded by P. Krais (Melliant, 10 (1929) 468).... They made their general appearance in the early part of the 1939-45 war and their use is now firmly established particularly for paper and textiles, and large quantities are now incorporated into soap and proprietary household detergents. They are used not only to impart improved whiteness, for which purpose they have largely replaced Ultramarine, Methyl Violet and the other older blueing agents, but also to improve the colour of white discharges and to add brightness to delicately coloured dyeings and prints...."

A brochure on Du Pont Paper White SP Solution says it can be added either in the beater or in the size press, and a pH of 7 to 8 is suggested. The section headed "Lightfastness and Storage Stability" says "Fluorescent white dyes are not considered permanent to light or to storage, but are sufficiently durable on most grades of paper. White bond and writing papers show about the same degree of lightfastness and storage stability as the various colored grades, provided the pulps used possess good lightfastness and storage stability."

Even though paper's brightness fades in time as the brighteners deteriorate, the effect is not serious enough to worry the committees working on permanence standards in ISO, ASTM or NISO, which have merely set a minimum brightness (75 or 80). Other things, after all, affect brightness: kind of fiber used, pulping and bleaching methods, type and amount of filler, storage conditions, and aging behavior of lignin and hemicelluloses.

Most of the above information was sent in, on request, by John A. Burt of Mobay Corporation (PO Box 2855, Rock Hill, SC 29730, 803/329-3937). He also sent some historical information, including the fact that lawn bleaching of linen was facilitated 200 years ago with the help of an extract from the inner bark of the horse chestnut tree, which contained esculinic acid, a natural fluorescent agent.