-Siliconesreasons for this are evident. Silicones are often selected for an application solely on the basis of their heat stabilily. , When methyl and phenyl groups are the organic substituents on silicon the best heat stability is obtained, and this stability results from proximity to the siloxane bond. Longer alkyl groups and larger aryl groups are more readily affected by heat, but many uses are being developed that demand little in the way of high temperature stability. The presence of silicon and the siloxane bond in larger or more complicated units may be expected to influence the properties sufficiently to make them desirable for applications that are totally different from any developed so far. The basic structure of silicones is responsible for properties that can be stated in a negative fashion. The usefulness of silicones is often not due to what they do, but to what they do not do. They do not oxidize readily; they do not hydrolyze readily; they do not show the conventional reactions to temperature changes; they are not good adhesives, they are not good solvents. This negative attitude has been turned to advantage in many applications such as mold release and electrical insulation. In the former case they do not dissolve in the molded article and do not adhere. I n the latter case they do not oxidize and they do not absorb water, two of the primary requirements of a good insulator. Within the last few years, the pharmaceutical and medical professions have been considering the possibilities of using this type of material, largely because it is inert, as a component of dermatological creams, and even as an agent for the treatment of lobar pneumonia. Silicones appear to be inert to metabolib processes and are such poor solvents for vitamins that there is little danger of vitamin depletion if they are ingested (1).
So the properties of a silicone product, be it fluid, resin, or rubber, stem from the properties of the siloxane bond-its large bond angle, its ionic character, and its dipole effects--the size of the silicon atom, the degree of functionality chosen, and the types of organic substituents on silicon. Each of these factors may be altered a t will. The siloxane bond may be substituted in whole or in part by bondings such as silcarbane or silazane; silicon itself may be exchanged for carbon; functionality may be from 0 to 4; the entire wealt,h of organic radicals is available for altering properties. This astonishing breadth of possible properties is the exciting thing about silicone chemiptry and is the reason for the confidence that further investigating of silicone structure will be rewarded by finding values greater than those yet seen. ACKNOWLEDGMENT
Acknowledgment is made to Dow Corning Corp. and Corning Glass Works who Rponqored the multiple fellowship a t the Mellon Institute, Pittsburgh, Pa., under n-hich this work was done. LITERATURE CITED
(1) Barondes, R. de R., Judge, W. D., Towne, C. G., Baxter, M. L., The Military Surgeon, 106, 381 (1950). (2) Fox, H. W., Taylor, P. W.,and Zisman, W. A,, IND.ENG CHEM., 39, 140’3 (1947). (3) Hunter, RI. J., Warrick, E. L., Hyde, J. F., and Currie, C. C. J . Am. Chem. Soc., 68, 2290 (1946). (4) Wilcock, D. F., and Hurd, D. T., U. S. Patent 2,547,678 (April 3, 1951). R E C E I V Efor D review March 25, 1954
ACCEPTED June 4 , 19.54
ilieone Resins in Textiles FRED FORTESS Celanese Corporation of America, S u m m i t , N . J .
Apparel fabrics require finishing treatments to enhance their general performance and to overcome specific shortcomings for special end uses. The silicone resins based on liquid methylsiloxane polymers containing reactive groups for subsequent cross linking on the fabric have been found to impart durable water repellency, resistance to aqueous-borne stains, increased tear strength and abrasion resistance, and improved sewability, as well as recovery from wrinkling. The relationship of the resin structure to the properties imparted to the fabric is described. Optimum application conditions and sources of difficulties are outlined.
I
7S GENERAL, the textile industry depends on a careful se-
lection of the fiber or fiber blends and on fabric construction to achieve optimum fabric performance for particular apparel end uses. Finishing treatments of the dyed fabrics with a variety of chemicals are frequently required to enhance important fabric properties and to minimize secondary fabric deficiencies. The application of silicone resins as fabric finishing treatments has been found to improve many functional and esthetic properties of a large variety of fabrics. A description of some of the useful properties imparted to textile materials has been recently discussed in the literature (1, 3, 6, 6 ) . As a fabric finish, the unique contribution of the silicones applied to the surface of fibers is their effectiveness a t lower levels of application and their durability, especially on the relatively unreactive hydrophobic fibers such as acetate, Dacron (Du Pont November 1954
polyester fiber), nylon, and the acrylics. The achievement of durable water repellency, improved abrasion resistance and tear strength, increased recovery from wrinkling, resistance to aqueous-borne stains, improved sen-ability, and the modification and improvement of the drape and hand or feel of the fabrics, has resulted from 10 years of intensive study of special silicone polymers and their adaptation to the complex processes of the textile dyeing and finishing industry. I n general these improvements in fabric properties can be related to the hydrophobic, tough, resilient film of silicone resin formed around each fiber. Many difficulties were experienced in developing a satisfactory silicone finish during the early investigations in commercial dyeing and finishing mills due to improper selections of resin structures, poor choice of catalyst and curing conditions, inadequate preparation of fabric and poor emulsification of the silicone. The current
INDUSTRIAL AND ENGINEERING CHEMISTRY
2325
sful practices, to be brieH1, outlined in this paper, have rein the large scale producation of a wide variety of fabrica with optimum properties. (;EVE:RAL STRUCTURE OF .\ SlLiCONE RESIN REQIJIKED FOR Y,\RKI(: FIYISHING
utilized by the dyeing and iiiiisliiiig :iud thi. structure and properties of \voven fabrics have put defiriitc' clic~niicaland phj-sicd specifiviit,ions on the type of silicone resin+ that, may be applied. Such fabric properties as n - a t ~ i ,i~~pelleiicy and improved sPwnliility require that t,he chemical finish be applied as a fine cmulsioii to facilitate its uniform dist,ributioii on the surface, preferably around each individual fiixr. Subsequent high temperature treatment or curing should cwiivr'r't thp liquid silicone into il flcsihle film.
I n general silicone structures which have found greatest, us as textile finishes have been described in a number of patents ( f ) . By a careful selection of the monomeric alkyl eilane halides in proper portion, the polysiloxanes produced from hydrolytic poly merization can result in a & l e range of physical properties from volatilr liquids to britt,le solids. The number of silane hydrogen atoms present influences the subsequent. ease of further polyriierizat,ion by oxidative cross linking.. The monomers gcneridly used are CH3 CH, \ /'
Si A
CH, CI monofunctional chain stopper
CH, CHS \/ Si
/\
c1
c1
difunctional linear polymer
CHd C1
v Si /\
c 1 I€
,
trifunctional cross linked polymer
Figtile 1. Phidual Silicone Skins from 1 and 2% Sili(wnc Treated i c e t a t e Fabrics Extracted for 2 %T t n i i v s with
95 5 Acetone-Water
l'hc' general clieniical pi,operties and structure of thc. silic.ouo monomeric and polymeric mate&& have been descvibrd 11). ltochow ( 7 ) . In this paper thc trrm ',silicone" will refer to alkyl:it ~d siloxane polymers either linear or partly cross linlted. .?ti c~xcc~llent sympoyium on the chemistry and applications ot t h c oi,ganic silicon compounds apprared in 1947 (4). .\I) uureactive silicon(. fluid bawd on a high molecular wiglit litiwr ulkylnted siloxane structure applied from a solvent will rewlf in a surface distribution qf an oily film.
i
The textile finishiiig appliaatioii requires t,hat L: relatively h i d iiilicone polymer be applied to the fabrics, prcferably as an aqueous emulsion. Subsequent drying results in t.he formation of a, thin, cont,inuous film of tmhesilicone around eitcli fiber, and thc heat treatment or curing t>henresults in sufficient oxidative cros8 linking to insolubilize the silicone in intimate contact with the fibers with the forrnat,ion of a tough, flexible skin wound each fiber in t,he fabric. 4 minimum bonding together of the intlividual fibers is desirable; otherwise t h e hbric will he R t i f f and display poor mechanical properties. Where silanic hydrogen i s present, for the purpose of providing rros8 links under oxidizing conditions. Lhe resin Eormecl may kw represented 1))-
I,~.Y10'=10,1
~. .
K = CH, l'tiis fluid ij-iil impart water repellency and improved se\vabilii y I Ion-ever. it ie nondurahlc to detergent washing and dry cleaning. 'I'hc1 application of a high molwular weight, highly cross linked, iolid siloxane polymer dispersion. n-hich dries to a britt!e powder, w u l t s in a supeificid, noncontinuous stiff surface coating on t'lie f'a1)ric. A structure ~f thir 1y;)(.is represent,ed by ')
Si
2326
trilunctional linear polymer oxidative C ~ O S Rlinking
RR Si
Si
The two relatively h e a r mo1ecult:s are W O R F linked 1~5-the {orimition of an oxygen bridge resulting from thc oxidation of Bilanic> hydrogen. On such fibers as acetate and Dacron no evidence is availnlilc~ Lvhich would indicate a significant degree of reactmionof the silironc~ with the fiber substratum. On acetate exhaustive acetonci oxtraction of fibers treated Jvith 0.9Syo of a commercial silicmric> (calculated from silicon aunl-sis) resulted iii :I residue 01 i ,0574. The durability of the silicwnc resin rc~sultsfrom oheiniral fixation which requires effective oxidation condition[
