Modern Developments in Synthetic Resiris CARLETON ELLIS,Ellis-Foster Company, RIonLclair, N. J.
1he syntlletic resin indusIry uias originally concerned almost eritireiy wi/,/t,findingan oullrl for its producls in the ,form of molded articles and coatings. The lurgrsl oiiIput .f the products slill i s for molded articles, but deidoprnents J’oresh.udoiD (in eUen inore extemiw uIiiiraIion us structural muleruds. Newer upplicafioris qf the synthelic resiris embraw rnany d i w s e I,
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iii tiii: -yiitlii:t,ic rcsiii iiidustry i i i the last can be said to have t.akr:ii ~ I R Will two tlirwtions: (1) Tiierc lms been 11 r:ontinual d new types of resins, and ( 2 ) new applications Imve hccn nirrrlr of tlic iietter knowd materials. To adapt the niorc or lms standiinl resinous products to I ~ uses V has ncces&:itwl, i i i some cases at least, modificntioi~sof various kintls. nee in the i n i r t l i o i l s of utilization of syntlietic resps the most interesting and imiiortant phase of opnients. Natur:dly, incr production enii take pliicr only with n tcrials. The iiossilh snbstitot.ioii ul synthetic plastics fur w i o d h i s ived iiiucli consideration iii rccent years. TIE ndvaiit,:*gi~s of phstics liavc been rcpeatmlig einplianized atid nio only too obvious. Clieap resins, its mcll as elieap metli Fslxicatiorr, itre essential, however, before we can c q seeany extensive replaceruerit of wood as a structural n by molded or laminntcrl products. Some large radio r & nets, lavatories, arid tanks liavc already been niolilail of various materials, arid laminated board has limn ii table t,ops and n:ill-paneiing. Also, synthetic rosins Imve been u e < lt o provide w~terjrrorilglurs for the \wiwring irrdustry. IIowever, the possibility of phenolic and nldeliy~lic substances from petriilerini sources at very low cost Itads to the view that synthetic resiris at some time mag r~mkhigh as structural materials. To produce a resin which promises any hope of coriiiiit,rciai success, the eliernist is liiiiit~cilt o the lire of relat.ively clieap raw materials-for exiiiiijdi?, phenol, urea, formaldehyde, glycerol, piitlialic anhydridc, acetylene, rubber, and lietroleurn. For his laboratory prqiaration t o remain other th;m a curiosit,y, it must haw MJiilP properties superior to tliow of alri~:arlyexisting prodiirts. It lias been estiinatcd rouglily that there arc a.lrnoat as iiiniiy jlatixits on syntlri!t.ic resins and their applications :is f.lmc are mcrnhers of the Asrc.rric,+s CHEZ~SCAI. Socicra. For this it is not difiicrilt to acroriiit, since in imng ernes tlir: wily iippnrat,iis required to niake a iynthetic rc.sin is rl irst, tiilr. l‘liese figures do not appear quite ns ~lisiiesrteriing,lion I,, when it is realized t,liat none of ihc kiioim comntcr,,ial iyittliitic resins is without il l a n k
Adv:inecs iii jilier~ol-forrnali~e~~y~le resins iii tlie 1a.t fcw yearn liarn I~cenin clirerse fields and include siicb new developments its light-stable rcsiris for casting, acid-proof industri:LI eqnipmeiit of large size, arid tlic produrtion of oil-
soluble piienolic resins for varnislies. I’licnol resins can be cart in large pit liquid resin irito molds and allowing it to harden umler heat. Properly modified, tlie resins forming the east irloek or rod can be worked into finished articles of any shape hy the ordinary tooling operations applicable to brass or hardwood. However, the question of color, or rather, jiermanencc of color, has always been important. Froin the earliest days of the plienol-formaldelij~dc resin industry, there has been hope that colors of light amber could be proiliseed, but the first resins, while transparent and beautifully colored vhen fresh from the mold, ~ I T T . R darkened ~S n.ith age. Satisrally, this change militated agninst the decorative possibilities of tliese resins. As means of control of the reaction developed, and as the general knowledge of the effect of modifiers hecanre better understood, the ability t o produce light shades y e w to snch a11 extent that. r e have the lactic acid-modified
38
INDUSTRIAL AND ENGINEERING CHEMISTRY
phenol-formaldehyde resin (21). Cast resin has had a remarkable commercial growth in the last few years, and such products as Catalin, Marblette, and Joanite are being used in considerable volume for knife handles, beads, bracelets, etc. The resin produced can be so clear and transparent that many articles previously impossible can now be simulated to a remarkable degree. The lack of color and its stability to light permit the dyeing of the resin by the addition of organic
Vol. 26, No. 1
drying varnishes. The films deposited from these varnishes are highly resistant to moisture, alkalies, and sunlight. Another modification of phenol-aldehyde resins which was the result of an effort to impart oil solubility was that formed by reaction with tung oil (6). When these tung oil-modified resins were hardened by baking, a flexible film remained. A material which has recently made its appearance is the so-called Revolite, a cloth made waterproof by calendering with a phenolic resinoid product in such a manner that only minute penetration of the fabric occurs (18). This resinous coating, after hardening by heat treatment, is flexible. The cloth has been used for the production of adhesive plaster and surgical dressings of various kinds and may probably appear in larger sized colored sheeting. As a potential rather than existing source of cheap phenolic resins, low-temperature carbonization of coal, although commercially unsuccessful so far, would seem to offer possibilities for expansion of this field. Morgan and his collaborators (80) have ,indicated the enormous economic results which would ensue if the low-temperature process should ever be perfected.
UREA-FORMALDEHYDE RESINS
Courtesy, Bakelite Corporation
BEDSTEAD WITH INSERTS OF PHENOL-ALDEHYDE RESIN LAMINATED BOARD coloring matters, so that such shades as clear jade and rose quartz can be made, and the effects obtainable run from opaque or translucent to transparent. Even the highlights of opal and onyx can be imitated. Another development in phenol-formaldehyde resins has been the introduction of the material known as Haveg. The acid-proof nature of these resins was a properg. which manufacturers early sought to utilize, but until recently this advantage was only available by the use of coatings which were unsatisfactory, particularly on large vessels. The development of the Wirth patents (%), under which it has been possible to fabricate asbestos-filled phenol-formaldehyde resins so that molded vessels as large as 9 feet in diameter can be made, has opened up a large field, and these materials are finding a place in the industries where acid-resisting requirements must be met. Temperature changes up to 265" F. have no effect. Haveg is strong and durable and has about one-fifth the weight of iron. Although phenol-aldehyde resins have for some time been used as coatings which set on baking, a considerable advance was made when the resins were modified with rosin, rosin ester, or other natural resins to form the so-called Albertols and Amberols (4). These modified phenol-aldehyde resins when used with tung oil or other drying oil were the basis of the modern 4-hour varnishes. However, it has always been felt that the modifying materials necessary for conferring oil solubility to the phenol-aldehyde component detracted from the durability, toughness, and other qualities of the final film. Recent developments have resulted in phenol-aldehyde resins which are soluble in drying oils without the necessity of fist fluxing with rosin (26). Phenols such as 0- and p phenylphenol (3) (also called hydroxydiphenyls and for which the shorter name "xenols" has been proposed) and p-tertbutylphenol (16),and p-tert-amylphenol (Pentaphen) form the basis of these oil-soluble resins. The products obtained from these and other alkylated phenols and formaldehyde are readily soluble in tung oil and permit the making of rapid-
The use of urea-formaldehyde resin molding compositions is increasing both in volume and in importance on account of the wide range of available colors of the moldings and their fastness to light. Three large companies are now producing this type of material, known, respectively, a s Unyte, Plaskon, and Beetle. Urea molding compositions are widely used a t the present time for tableware, including cups, saucers, plates, tumblers, and even complete luncheon sets. Articles molded in bright colors have been offered as premiums with breakfast foods, tooth paste, and other commodities (1). The main problem of urea resin manufacture today is the matter of cost. Although the raw materials-urea and formaldehyde-are no more expensive than the materials used in phenol-formaldehyde resins, the great variety of colors demanded and the care required to keep the lighter colors clean and exact in shade call for close supervision and entail heavy additional labor charges. For the same reason the molder has to take special precautions against dirt, and rejects due to slight imperfections add materially to the cost of the finished molded piece. A recent development in the use of urea resins, because of their resistance to darkening under light, is the treatment of cotton and artificial silk fabrics to render them noncreasable (IO). The fabric is first swollen in a caustic soda bath and is then impregnated with the resin by immersion in an aqueous solution of it. The cloth is dried and then heated for a short time to about 170' C. (338" F.) in order to cure the resin. Subsequently the cloth is washed and dried. Urea resins have also been used to improve the hardness, flexibility, and gloss of nitrocellulose films (2). A resin of this type known as Plastopal, which can be incorporated with nitrocellulose, is an acid-free product, soluble in alcohols and glycol ethers. It becomes insoluble on heating. Another field that is growing rapidly is the button industry. Urea resin buttons offer distinct advantages over those of casein or vegetable ivory since they are very strong and are practically unaffected by washing. Also, because urea resins are odorless and considerably stronger than molded phenolic resins, they are finding increasing use as caps and closures for jars and bottles.
VINYLRESINS Vinylite, a tough, permanently thermoplastic resin made by co-polymerization of vinyl chloride and vinyl acetate, is used commercially for phonograph records (12) and dentures.
I t is available as a molding powder in various colors and lids been used for wall panels and doors, which are probably tlie largest single-piece press nioldings ever made (8) from a synthetic resin. The compositions have been tried experimentally for many articles, including molded jars, automobile steering wheels, and translncent panels for lamp shades and for indirect lighting fixtures. In the sound record industry, a 4uunce Vinylite record for niotion picture theaters was brought out about the middle of 1931 to replace a shellac record weighing 20 ounces. Tire reduction in size from 16 to 12 inches in diameter was made possible by tire greatly increased strength and flexibility of the new materizl as well as by its finer texture. Other types of records Lave been made from this rosin. The versatility of vinyl resins in this field is illustrated by the successful substitution of noninHammablo Vinylite for celluloid in records for iiomc-recording. Yinylite can be handled on the same equipment used for shellac compositions, with only minor changes in technic. The total production to date, including home recording, motion picture, and all special Viny1it.e records, is probably about a million records. Artificial dentures have been made from a nuniher of uiaterials, particularly hard rubber, celluloid, and Bakelite. Denture compositions of vinyl resin containing only a small amount of pignient and having a very natural appearance have been prepared which are adapted for this application. They are tasteless, odorless, and unaffected by continuous exposure to moisture, dilute acids, and alkalies. Dentnro blanks of this inaterial are distributed by two large dental inanufacturing companies under the names ltesovin and Vydon. Co-polymers high in vinyl chloride content are the ones which are better suited for molding. On the other hand, copulymers containing less vinyl chloride, OF even the pd~mier of vinyl acetate alone, are used as coating materials. Their chief points of interest in this connection are their pale color and tough, flexible nature. Vinyl acetate polymers are sold under the names Mowilith and Gelva. Treated with aldch y d e s they are converted to harder resins, known as Mvar. Polystyrene, a resin related to vinyl polymers, shows great possibilities, but at present its cost of production is too high to warrant any extensive use. The resin is w a t e r - w h i t e in color and has the highest insulating power of any a v a i l able s y n t h e t i c resin. higher even than shellac (17). Some samples of polystyrene which have been e x a m i n e d are so tough as to require a hammer and anvil t o b r e a k t h e m . Polystyrene is sold under the trade names Trolitul, Resoglaz, and Victron. A denture made from it is known as Tepperite.
REZYL~ The principal application of polyhydric alcohol-polybasic acid (alkyd, glyptal, or phthalic glyceride) resins has been in the coating field, especially for the manufacture of b a k i n g enamels (e). These r e s i n s have been modified so as to be
Ixttcr adapted to coatings and other applications. Momobasic acids have been used to change the characteristics of phthalic glycerides, such products being known, for instance, as Rezyls. Alkyd resins modified with natural resin acids, called Teglacs, are hard and brittle. Fatty oil acids when used to modify these phthalic glycerides yield softer and more guimny products. These modified polyhydric alcohol-polyacid resins are used with nitrocellulose in lacquers to ivliicli they impart exceptional durability, flexibility, and good adlicsion. Another type of akyd resin which has a wider range of utility is that modified by a d r y i n g 4 component. These products, wliich are varnish bases, dry in part by oxidation. They thus combine the qualities of both lacquers and varnishes. i'ermanent flexibility is an important feature of this type of resin. PLasrics
FROM
ACETYLENE
Under the iiiHiience of catalysts (particularly rnetallic copper), acetyierre forms an insoluble light-brown voluminous powder called "cupreiie" which has been suggested as a filler in molded articles, linulenrn, explosives, and paints (15). IIowever, in tlie presence of aqueous solutions of cuprous compounds, acetylene produces liquid materials, including mono- and divinylacetylene. Monovinylacetylene, treated with hydrochloric acid, forms cliloroprene whicli polymerizes to DuPrene, a substance which comes nearer to natural rubber in its physical properties than any other synthetic material. It is even better than rubber i n i b resistance to softening by gasoline (6). l)ivinylacetylene, anotlrer liquid derived from acetylene, gradually tliickens w h heated. A solution of the thickened liquid I,el,avcs like a drying oil and gmdually hardens to a Hrm acid-resistant coating when applied to a surface. Solutions of divinvlacetvlene sirup are sold under the name SD-Q (Syiitliotiii drying oil) (Id).
PETROLEUM RESINS Brown, neutral r e s i n s are being made by treating unsaturated petroleum fractions with a l u m i n u m c h l o r i d e @4). These resins, p r o d u c e d b y Dayton Synthetic Chemicals, dissolve readily in drying oils to form varnishes which can be thinned w i t h p e t r o l e u m spirits. They accelerate the drying of tung oil and are of i n t e r e s t b e c a u s e of their potential low cost and availability. CHLORINATED
PRODUCTS
Chlorinated rubber, which is m a r k e t e d as T o r n e s i t e or Pergut, is i n c r e a s i n g i n importance as a coating material for iron pipes, concrete, and wood (19). C o a t i n g s from t h i s m a t e r i a l are no more e x p e n s i v e than those of the usual good paints and have better a d h e s i v e qualities. In a d d i t i o n , the noninffammahle films are resistant to water, acids, and alka-
