MARKETS
Consumer Demand Spurs Brightener Use Steady growth pattern in detergents and softeners spreads to thermoplastics and man-made fibers A continuing demand for brighter products has been partially responsible for the steady growth in the sale of optical brighteners to the detergent industry. Now, this same demand has spilled over into the plastics industry —not to the extent it has in the detergent industry, but still to a fairly signincânt Volume. For example, consumer demand for brighter synthetic fibers is the reason for the quiet and partially successful efforts of a number of firms rich in photochemistry technology to develop better and cheaper optical brighteners. About $24.5 million worth of optical brighteners for all uses were sold in the U.S. in 1964. More than 50% went into soaps and detergents and another 25% into paper products. About 22% of the total went into textiles and the remainder into thermoplastics and miscellaneous products. However, many of the basic formulations used in man-made fibers are also used (with some modification) to brighten thermoplastic products. Thus the actual volume of optical brighteners that is used for synthetic fibers and thermoplastics is difficult to ascertain. Output. Production of optical brighteners is substantially higher abroad than in the U.S. About 200 to 250 products are offered on a world-wide basis by 30 to 40 manufacturers. Research in recent years has yielded compounds which are potentially suitable as brighteners because of their whitening effect. However, only a small number have found practical use. Optical brightening agents are essentially colorless, fluorescent organic substances which absorb invisible ultraviolet radiation and emit this radiation (or energy) as visible radiation. The brightening effect stems from the absorption of yellow and retransmission of visible blue light, which masks the yellow. The use of optical brighteners in detergents is straightforward—certain
Detergents, Textiles, Paper, and Plastics Boost Brightener Consumption Value (millions of dollars)
1958
1959
1960
1961
1962
1963
1964
1965
Source: U. S. Tariff Commission and C&EN estimates
chemical combinations are known to give a "whitening" efiFect to cloth by masking yellow and retransmitting reflected light into the blue range of the spectrum. The number of such brightener structures are many and compounding them into detergent formulations is a relatively simple procedure. For the plastics industry, the problem is more complex, because the performance of the brightener depends on the polymer substrate and brightener properties can vary from polymer to polymer. Plastics are most often brightened in the melt. The brightening agent is thus dispersed throughout the plastic to minimize migration to the surface which causes blooming—an uneven retransmission of the reflected light. As used in plastics, the brighteners
must not contain functional groups which react with plastics in a way to degrade them. The brighteners must also not affect the properties of other additives or the plastic. Since a brightener's function in a plastics formulation is to retransmit light it must resist light degradation, but must not give initial or aging color to the plastic. Wide Use. It's practically impossible to find a general-use classification for optical brighteners. This condition exists primarily because optical brighteners are used in a variety of fields such as detergents, paper, textiles, furs, and plastics. Within each field, a single brightener may find wide use through variations of the basic structure. For example, derivatives of diaminostilbene disulfonic acid are used to brighten cellulosics. APRIL
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A considerable number of optical brighteners are derivatives of 4,4'diaminostilbene-2,2'-disulfonic acid. Using the same basic stilbene-sulfonic acid arrangement, a whole series of brighteners have been patented by Switzerland's Geigy, Ciba, and Sandoz; Germany's Bayer; Britain's Imperial Chemical Industries; and in the U.S. by American Cyanamid and General Aniline & Film. Coumarin derivatives also exhibit the type of variability found in stilbene-sulfonic acid brighteners. For example, 7-aminocoumarin derivatives are used to brighten wool and nylon fibers. Derivatives of 3-phenyl-7aminocoumarin retransmit in neutral shades, and significantly improve brightness. This type of brightener is used with both synthetic fibers and plastics. Derivatives of 5-memberedring heterocycles, such as monoazoles, were developed by Geigy in an effort to find compounds with neutral fluorescence for use with fibers. With water-solubilizing groups, these types of brighteners are suitable for brightening cellulosic materials and nylons. Water-insoluble derivatives of this family with sulfamyl, aryl sulfonate, or nitrile groups are suitable for brightening synthetic fibers and resins. Brighteners which are especially suited for use with polyvinyl chloride are found in groups with structures such as bisbenzoxazolylethylenes and derivatives of 7-amino-3-phenylcoumarin. Water-insoluble products of naphthotriazolylstilbene derivatives are also used. In addition to PVC, plastics based on polystyrene, polyethylene, polypropylene, polyacrylates, polymethacrylates, and cellulose acetate are also brightened with variations of these compounds. Comparison. Eastman Kodak asks consumers to make color comparisons with its Kodel fiber. Consumer studies have shown that Du Pont's Dacron and Orion fibers are successful because of their brightness retention on repeated washing. Celanese has its Fortrel 410, an optically white polyester staple. All contain optical brighteners as part of their basic formulations. While the use of optical brighteners in fibers is clearly pitched to consumer demand, the use of these materials in plastics takes on a functional use also. For example, some plastics formulations, such as styrene-acrylonitrile compounds, develop a slight yellow cast on exposure to heat during 38
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processing. The addition of an optical brightener eliminates this cast, making extruded products using this formulation more acceptable. Geigy Industrial Chemicals in the U.S. makes and markets a line of optical brighteners under the trade name Tinopal. Two specific products, SFG and PCR, in the line are aimed at plastics and synthetic fibers. However, the same basic compound can be used with such items as emulsions, varnishes, lacquers, plastisols and organisols, and waxes. Fibers. Other companies also use basic compounds to make optical brighteners for several end uses. Ciba, for example, makes and markets its optical brighteners under the trade name Uvitex. While the group is primarily used in fibers, variations in the formulation can make them suitable for use in plastics as well. American Cyanamid's Calcofluor products are used in both. In addition to Geigy, Ciba, and American Cyanamid, General Aniline & Film (Blancophor), Verona-Pharma (Phorwhite), and Carlisle Chemical (MDAC, a coumarin derivative) make and market brighteners for plastics and fibers. Foreign manufacturers include Hickson and Welch (Photine) in England and ICI (Fluolite), also in England. ICI Organics (formerly Arnold Hoffman) is the U.S. outlet for ICI's line. Sandoz, a Swiss company with interests in several U.S. firms, markets its line of optical brighteners for plastics and fibers under the trade name Leucophor. Not all of the optical brighteners sold in the U.S. are made here. However, over the last several years the volume of imported brighteners for all end uses has declined. For example, in 1961 a total of 423,559 pounds with a value of $935,771 were imported. This level was maintained in 1962 when 438,520 pounds with a value of $1,182,511 were processed through U.S. customs. The volume of imported optical brighteners dropped sharply in 1963 to 82,383 pounds with a value of $425,480. Import figures for 1964 are not available from the U.S. Tariff Commission. More than half of the imported brighteners originate from companies located in Switzerland. They are followed by those firms which operate in West Germany although not all of these companies market brighteners in the U.S. Brighteners used in plastics cost
up to $30 to $35 per pound (compared to those used in detergents which cost about $1.95 per pound of
active material). They are used at concentrations from 0.001 to 0.05%. At much higher concentrations their use becomes uneconomical unless the consumer is willing to pay for the added brightness of the product. There are also other means to brighten plastics which don't materially increase the cost of the product. This works to the disadvantage of optical brighteners. For example, titanium dioxide, already used to a large extent in the paper industry and in small amounts in plastics, can be increased in concentration to whiten a yellow plastic at less cost than can an organic brightener. However, T i 0 2 can only be added to a level which will not affect other properties of the plastic. All plastics are degraded by ultraviolet radiation. For this reason UV absorbers are added to plastics as basic protection against photodecomposition. The absorber compounds absorb ultraviolet radiation and do not retransmit energy. There are conditions where both an absorber and an optical brightener are used to protect a plastic material against photodecomposition and discoloration. However, the absorber and the brightener are added separately to the plastic and not as a single compound. The absorber and the brightener compete for the available light energy and, to a degree, offset the effectiveness of each other. Combination. An ideal compound would combine both the absorber and the brightener. While such a compound isn't yet available commercially (and is considered technically impractical by some), a combination compound would have the advantage of offering both color retention and color brightness for long periods. The problem which must be solved is to find a neutral atomic linkage which will take the energy held by the absorber and pass it through the linkage to the brightener for retransmission in the visible range of the spectrum. The future for optical brighteners is assured regardless of the type ultimately used. Some industry estimates foresee a possible $80 to $100 million market within the next five years. Others, less optimistic (or possibly more reserved) see about $40 million as the plateau on which optical brighteners will rest.
