Plioform-A
New Molding Resin
Chemical Reactions of Rubber and Plioform H. R. THIESAND A. ht. CLIFFORD,T h e Goodyear Tire & Rubber Company, Akron, Ohio
F
It is of interest to note that OR many years the attenT h i s paper reviews ihe various chemical for the preparation of synthetic tion of chemists has been reactions clf the rubber hydrocarbon other than rubbers as well as certain resin$ drawn to the considerathose which accomplish oxidation and culcan i m and plastics, there h a v e been tion of rubber as a ram material lion. Particular atlention is given those reacutilized as the starting materials upon which to effect transforniations leading to the formation of resinoils and compounds possessing a cl o s e tion into substances possessing b t r u c t u r a1 relationship to the the properties of resins. Harries thermoplastic products, and finally the decelopstructural unit of rubber, and (20) in 1910 attempted t o transment of Plioforni. containing the vinyl g r o u p i n g form r u b b e r into gutta-percha Some of the outstanding properfies of these -C=CH2. I n all cases prodby means of sulfuric acid and newly deleloped rubber derivatices are: (1) obtained an inelastic p r o d u c t I T h e y are odorless, tasteless, and resistant to R which he c o n s i d e r e d a more ucts of high molecular weight are highly p o l y m e r i z e d f o r m of all alkalies and to a large majority of acids. obtained by p ol y m e r i z a t i o n rubber. He followed a logical ( 2 ) They are thermoplastic, do not cure i n the processes. This will be underprocedure because nature promold, and have a fairly narrow molding temstood b y c o m p a r i s o n of the vides the hydrocarbon ( C ~ H S ) ~ perature range; this operation simply involnes vinyl compounds t a b u 1a t ed in a variety of forms, of which working within a temperature range of 100" F . below. rubber is the most c o m m o n . I n the recent investigations of Balata and gutta-percha, em(3) N e w und attractive color effects are a i d a b l e (36) and Carothers Sieuwland pirically the s a m e a s r u b b e r , in a tough, nonshatterable resin. ( 4 ) They (91,intermediate polymerization closely resemble resins in being offer a wide field as a plastic molding material products of vinylacetylene and thermoplastic. I n a l l t h e s e and as a substitute f o r hard rubber. d e r i v a t i v e s are found to be f o r m s of t h e h y d r o c a r b o n viscous liquids, or. as in the case (C5HJ),the simple building unit of chloroprene, rubber-like, while apparently products of still nature has chosen is isoprene (P-methyldivinyl) : higher molecular weight may be formed which possess the CH3 properties of resins. Rubber itself, as pointed out previously, may be transCH,=C-CH=CHz I formed into hydrocarbons of distinctly different character, but By some unknown processes of nature, hydrocarbons of high of the same empirical composition. These transformations, molecular weight are built from this unit group; such whether of rubber or of the other vinyl derivatives leading hydrocarbons possess relatively fewer double bonds and are to the formation of resinous products, are accompanied by therefore less unsaturated than isoprene. I n rubber there a decrease in the unsaturation of the molecule involved. VINYLCOMPOCND Isoprene (methyldivinyl)
FORMULA
CHz
1
Butadiene (divinyl) 8,yDimethylbutadiene (dimethyldivinyl)
CH~=~-CH=CH~ CHs=CH-CH-CHz CH?=C-C=CHz
Vinylacetylene ( 3 6 ) Divinylacetylene Chloroprene (9)(chlorodivinyl)
HC=C-CH=CHI CH~=CH-C=C-CH=CH-CH=CHI CH*=C-CH=CHz
Chloro-2-methyl-3-butadiene( 8 ) (methylchlorodivinyl)
CHn=C-C=CH
Vinyl bromide (5'7) Vinyl chloride Vinyl alcohol Styrene (vinyl benzene)
~ H J CHz=CH-Br CHz=CH-Cl CHz=CHOH CHz=CH--CoHs,
i
~ H ~ & H J, ~
bl
bl
exists one double bond for each CsHg group, but up to the present time the number and manner in which these groups are united is not precisely known. It has been shown in recent investigations by Pummerer and his co-workers (41) that up t o 95 p3r cent of the carbon skeleton of rubber has been accounted for in the ozone cleavage products; yet these authors feel their results are still insufficient to prove whether the rubber molecule exists as a long chain or a large ring. I n any case the rubber hydrocarbon can be expressed simply as: CH3
POLYMERIZATION PRODCCT Synthetic rubbers Drying oils, hard resins Viscous liquid, brittle resins Polychloroprene resembles soft vulcanized rubbers
.
Rubber-like polymers
i
Thermoplastic vinyl resins
The reactions of the rubber hydrocarbon leading to the formation of resinous and thermoplastic products, and finally t o the development of Plioform, are, in the main, addition reactions, and the intermediate or final product< generally are amorphous substances of high molecular weight which range from colorless to dark brown. Their solubility bshavior, as well as other physical properties, depends on the type of reagent used and often on the conditions under which the reaction is effected as well. ADDITIONOF HYDROGEN TO RUBBER The successful hydrogenation of rubber is a relatively recent accomplishment. Berthelot ( 2 ) claimed by the action 123
124
I N D U S T R I A L A N D E 1v G I N E E R I N G C H E M I S T R Y
Vol. 26, No. 2
of hydrogen iodide to have obtained paraffinic hydrocarbons ether, benzene, and carbon disulfide. The solutions on evapoboiling above 350" C. (662" F.). Unsuccessful attempts ration deposit tough, transparent films. The hydrochloride a t catalytic hydrogenation with platinum black were made has a tendency to lose hydrogen chloride, a change which by Harries (63) and Henrichsen (65). Pummerer and Burk- can be brought to completion by heating with pyridine under hard (40) successfully hydrogenated purified rubber hydro- pressure (12). The resulting product, called "alpha-rubber," carbon over activated platinum black. They operated with a is less elastic than natural rubber. dilute solution of 0.2 to 0.6 per cent concentration in hexane Zinc dust reacts with rubber hydrochloride (14, 50) to or methylcyclohexane. The hydrorubber analyzed for form a white, hard thermoplastic material much less unG H d , . It w a s saturated than rubber but still analyzing satisfactorily for colorless and formed (CsHs),. It is presumed to be a polycyclorubber. With colloidal solutions the zinc alkyls Staudinger and Widmer (0) obtained from in ether. the hydrochloride, alkyl hydrorubbers: Staudinger a n d CHa re- I) F r i t s c h i (,@ I ported almost simul4Hz-CLCHz-CH2taneously with alkyl Pum m e r. e r . a n d .. Burkhard the hyFIQURE1. SHORE HARD RUBBER REACTIONS OF RUBBERWITH ORGANIC HALIDES DUROMETER HARDNESS us. TEMPERA- d r o g e n a t i o n Of TURE rubber w i t h platiKirchhof (SO) obtained by treatment of a solution of num black incorpo- rubber and benzyl chloride in an inert solvent with aluminum rated without a solvent. The reduction was carried out at chloride (cooled) a reaction liberating hydrogen chloride and about 270" C . (536"F.) with 100 atmospheres pressure. Their forming a white, brittle, amorphous solid. The product is product also analyzed for (C~HIO),.Staudinger showed that, insoluble in organic solvents. It is thermoplastic at 100" C . on heat decomposition, hydrorubber yields 5 per cent of CHF and inert toward halogens and oxygcn. Analysis indicates C H - C H Z - C H , , along with other olefins. Staudinger and the formula (C26H26),.
I
CH3 Feisst (47) hydrogenated purified rubber of molecular weight 70,000 over active nickel a t 180" to 200" C., and 100 atmospheres in methylcyclohexane. The product showed a molecular weight of 32,000 to 35,000 (viscosity measurements) , and was completely saturated and somewhat elastic. The properties of the hydro rubbers vary according to the treatment given the rubber and the conditions of hydrogenation. They are generally much less elastic than rubber, form colloidal solutions in benzene, ether, or chloroform, and behave chemically as saturated hydrocarbons,
REACTIONS OF RUBBERWITH OXYCHLORIDES
The acid-forming oxychlorides react generally with rubber by addition. Chromyl chloride gives a definite compound, (C,HsCrO2Cl2),, analogous to the types formed by the action of chromyl chloride on the terpenes (4,45). The product is a dark brown powder, insoluble in organic solvents and decomposed by water. Phosphorus oxychloride reacts with rubber in inert solvents. The product is thermoplastic and its solutions leave transparent films (67) on evaporation of the solvent. REACTIONSOF RUBBER WITH HALOGENS AND DERIVATIVES Selenium oxychloride was shown by Lehner (31)to react The halogens react readily with rubber. I n the case of with rubber. Frick (17) undertook a quantitative study of chlorine the reaction is so vigorous that substitution as well the reaction of both natural and synthetic rubbers. The as addition occurs, in an uncontrolled temperature reaction products are insoluble, amorphous, .yellowish white substances, devoid of elasticity. Analysis shows 23 to 27 per (35). Ostromislenski (S9), using a 9 per cent solution of chlorine in carbon tetrachloride, chlorinated purified rubber cent combined selenium and 24 to 26 per cent chlorine. a t 0" C. and claims to have obtained a compound (C5Hr REACTIONS OF RUBBER WITH KITROGEN COMPOUNDS C12)8. The rubber hydrocarbon reacts with nitric acid, nitrous Bromine adds to rubber without substitution when the temperature is kept low. The product, (CsHsBrz),, is a acid or nitrogen trioxide (Nz03),nitrogen tetroxide (Nz04),or white amorphous solid, soluble only in the simple halogenated various nitroso compounds such as nitrosobenzene, and tetranitromethane. solvents. It is stable toward mineral acids. Nitric acid reacts vigorously with rubber, forming a soluIodine reacts with rubber, but the products are less definite. Iodine chloride (28), as well as bromine, has been used for tion which on dilution with water yields a yellow precipitate. Both Ditmar (10) and Harries (19) have studied the reaction. quantitative estimation of the rubber hydrocarbon. The halogen addition compounds of rubber have been found The products are somewhat unstable; hence, nothing definite capable of reacting with phenols, forming ring substitution is known a t present concerning their structure. Among the products (15, 18, 56). The products form colloidal solutions oxidation products always formed are various acids, inin benzene with no depression of the freezing point; x-rays cluding oxalic. Fisher (14) has likewise obtained a product which he suggests may be a nitropolycyclorubber. exhibit characteristic amorphous rings. Nitrogen trioxide yields an unstable yellow powder, soluble REACTIONSOF RUBBERWITH HYDROGEN HALIDESAND in acetone and ethyl acetate, and insoluble in benzene. DERIVATIVES Harries' "Nitrosite C" (26) has been adapted to quantitaReaction of the hydrohalides on rubber results in definite tive estimation of rubber hydrocarbon. Nitrogen tetroxide converts rubber into products similar addition products, (C6HSHal),, (21, 51). Hydrogen chloride is the most reactive. The reaction can be accomplished under to Harries' Nitrosite C. Investigations by Emden (11) anhydrous conditions in chloroform or carbon tetrachloride indicate that oxidation and addition both occur, yielding a solution. Rubber hydrochloride is white and, after stand- product agreeing with the composition C I O H I ~ N ~ O ~ . A reaction involving the addition of nitroso compounds to ing, becomes hard and brittle. It is soluble in chloroform and halogenated solvents but relatively insoluble in alcohol, the rubber hydrocarbon was discovered by Allesandri (1)
INDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1934
and studied by Bruni and Geiger ( 3 ) . Nitrosobenzene was added in benzene solution to a solution of rubber in benzene, in the ratio of 3 moles per C ~ H group. B The product precipitated by petroleum ether is a powder, decomposing at 135-40" C. The solutions are colloidal. It may be represented aa : CHz I1 -CHB--CCCHI
(
"0 CBH~
125
aliphatic sulfonic acids as well as the diallcyl sulfates (16) react regularly. The benzene-soluble type of product, called "Thermoprene SL" (shellac type), upon purification was found to analyze properly for (CsH8),, and to be 55 to 60 per cent as unsaturated as rubber. Fisher believes this change to a lesser degree of unsaturation is due, as pointed out by Ostromislenski (38), Kirchhof (go), and Staudinger (46) to cyclization. REACTIONS OF RUBBERWITH STANNIC CHLORIDE,FERRIC CHLORIDE, BORONFLUORIDE, CHLOROSTANNIC ACID, ETC.
Bruson, Sebrell, and Calvert (7) obtained direct addition products of rubber when anhydrous solutions of the latter were treated with stannic chloride, titanium tetrachloride, ferric chloride, or antimony pentachloride. The addition --cc products are highly colored and fairly stable in dry nitrogen, but split off the metal halide when treated with alcohol or O = N J acetone, yielding the hydrocarbon (CsH& as a white amorThe products from various rubbers are insoluble, amor- phous powder. The addition products from stannic chloride phous powders turning yellow a t 150' C., brown a t 175", analyze properly for (C,H&oSnCL. Two products are formed in approximately the same ratio as the two phases of the and finally charring. original rubber, the benzene-soluble product being derived from the ether-diffusible portion of rubber. The soluble DERIVATIVES OF RUBBERAND THIOCYANOGEN AND THIOconversion product is a white, amorphous powder. Solutions GLYCOLIC ACID evaporated deposit transparent, colorless films. The soluble It has been shown by Bruson and Calvert (6) that thio- isomer softens a t 220" to 225" C. and melts (decomposes) cyanogen, (SCK)z, adds directly one mole to isoprene or di- a t 280". The insoluble isomer is a white, fibrous, inelastic methylbutadiene, yielding nicely crystalline derivatives. substance. It sinters a t about 255" and decomposes above The same reaction has been applied to rubber by Pummerer 300" C. The product is much less readily oxidized in air than the soluble isomer. Both products possess the capaand Stark (43) as a method of determining unsaturation. bility of recombining with stannic chloride to reform the Holmberg (26) reacted rubber with thioglycolic acid in the hope of obtaining water-soluble addition products. A water- intermediate addition compounds. soluble sodium salt of acid, the composition of which corresponds closely with (CsH&CH2COOH)z, was obtained. From the aqueous sodium salt solution, hydrogen chloride precipitates a white, plastic, somewhat elastic mass. After drying, the product is a vitreous mass, convertible by heating to 75-80" C. (167-176" F.) into a tough, viscous material. The product dissolves in warm alcohol, from which by evaporation a sticky rubber-like residue is obtained. With tetranitromethane, Pummerer and Pahl (42) obtained a stable addition product of rubber which they indicated partially by:
REACTIONS OF RUBBERWITH SULFURICACID, CHLOROSULFONIC ACID,ORGANIC SULFONIC ACIDS
It has been known for many years that sulfuric acid has a profound effect upon the properties of rubber. As early as 1781 Leonhardi (33) observed the formation of a tough, brittle, nonelastic substance. Mention has already been made of Harries' observations (80). Marquis and Heim (34) obtained conversion products by operating in chloroform solution. The product was a white amorphous powder soluble in chloroform and benzene. Kirchhof (31) has shown that the sulfuric acid rubbers are less unsaturated than rubber itself and postulated internal ring formation or cyclization. Much work has been done by Fisher (13) on transformation of rubber into thermoplastic, moldable products by treatment with sulfuric acid and sulfuric acid derivatives. The rubber is treated on a mill with concentrated sulfuric acid or sulfonic acids, and the mixture is heated. Partial oxidation occurs. The products vary in their solubility in benzene, depending upon the reagent and the manner of treatment. Numerous compounds were tried, including chlorosulfonic acid, toluene sulfonyl chloride, and other sulfonyl chlorides, including aliphatic types, toluene sulfonic acid, phenol sulfonic acid; generally, aromatic sulfonic acids were effective except those containing amino groups (sulfanilic, etc.). Also,
FIGURE 2. STRESS-STRAIN CURVESFOR PLIOFORM AND TWICAL TREAD COMPOUND
A
Boron fluoride and fluoboric acid (5) may be added directly to rubber and worked on a mill at elevated temperatures to yield thermoplastic, moldable, conversion products, Finally, halogenated acids of tin, such as chlorostannic acid (HzSnC16.6Hz0) or chlorostannous acid (HSnCla.3Hz0) react readily with rubber, as shown by Bruson (4). The reaction may be accomplished by direct addition of approximately 10 per cent of the reagent to rubber on a mill or to a solution of rubber in benzene. The products contain a certain proportion of bound chlorine, depending upon temperature of the reaction and other conditions. The conversion products from these reagents may be made to vary from balata-like substances to exceedingly hard materials resembling ebonite. With certain adaptations these are the essential features of the process by which rubber is converted into Pliofonn resin.
I N 1) U S T R I A 1, A N U IS N G I N E I? 13 I N G C H E M I S T I1 1
I26
c
.A
.4. 13.
D
\lo1 26.No 2
E
43 per cent nitric acid 50 per cent nitric ocid
E.
C . 5s per cent nitria acid D . 65 per ce‘est nitric acid 72 per cent (cumnmrrial euiwentiotuii n i i ~ i oncid
CnAaacrrEniwics OF I’uoFom KESINB
I t is possible to product? a miniher of grades of rmiu iii so iar as tlie physical properties are concerned. Almost all (if these grades have ccrt.ain properties which are (~omiiiori to the whole group, with variation in only a few cluwactpristics. These resins, as a whole, are true tliermoplastics; t,liey are iiiiierently r -tant to most acids, all alkrilier, and solvents of the acetolie type; tlioy are universally soliililc in solvents of tlie gasoline or i i e n z ~ i i etype. Their to moisture arid their rscelleiit electrical proper to tlie whole poiip. T h i s gmup of materials is I odorless and tastcless. Tlie varhiiis resins differ, in the temperatore a t wliicli they Oecomc rleformable and in such properties as impact strength and flesural strengtli. It is iiniformly true that. resins w h i c l i lie in tlie lower range of softening points are tough nnd noiilirittle, while the resins which lie in the higher range oi soSteiiinl: points tend to bccome brittle and e a d y breakahlc. Experiment,ally, this raiige of temperature rims from 120” to approximately 220“ F. It bas been found that most cornmercial applications for this type of molding resin can bo filled with two grades of the inaterial. III applications wlicre a tough, nonbrittle product i s wanted, Pliaform (the coiiirnerciill name for these resins) is iurnished in a grade wliich shows distortion under heat at approximately 175“ F. In applications wlicre heat rcsistance ahove the boiling point of water, sueli as sterilization, is desired, a second grade is furnished which possesses a distortion point of approximately 220” F. Using these two grades as raw material, the method of fabricating articles from tlieiii is that comnion in the wellknown use of m y thermoplastic. The molding powder, or preform, is introduced into the heated mold and formed to the rlosired shape under pressiirt:. Depending iipoii the type of resin employed, tlic mold temperatores may vary irom 260” to 310” F., and the molding pressure from 1000 to 3000 pounds per square ineh. 8.;soon as tlie article i s formed, the mold is cooled and, wlien the suriace temperature of the molded art,icle is approximately 100” 5’. tielow that of tlie molding temperature, it is possible to open the mold and remove the piece.
atriiiglit-line functioii iintil qiiite high twuperatures are
renelred; that is, the iinrclness of the stock uniformly dzcn!ases as tho tt:iriperatitrc is ruiserl. Tihe beliavior of l’lio-
form i n this r q m t is quite different in that t,here is nn marked decrease in liardness during the initinl rise of t.einpratures until one rcachcs blie region of the softening point. Wlicn this regioii lias heen reached, time is a sliarp decreari. in durtrnieter iiardness with small teiiiperature rise. 111 otlier words, the beliavior of l’liofism resin more nearly tipproximates the behavior of a clienrical compound possessing a niclting point than does ordinary rulcaniaed soft or hard rubtier (Viguure 1 ) . h o t . h e r interesting differeiiee in behavior between these resins and tlie usual products witlr wliich a rubber teciinologist is familiar is the behavior in milling. In the proces.? of manufacture, Plioforin resin is milled just as rubber is milled, but there is a remarkable difference in belravior between tlie two substances during this milliug operation. Pale crepe rubbcr mills at a teinperature somewhat. under 212” IC., and factory practice lins sliown that the power consumption of crude rubber is approxiniately one horsepower per iiicti of mill; that is, a 60-iueh mill requires 60 liorsepower to mill a batch of riililw, xhile an 80-inctl mill requires 80 horsepower for the same operation. Wlren I’lidorm is milled, tile milling temperatures arc exceedingly Iiigh, sometimes reaching 325“ F., and power consumptioii studies Iiave sliown that n figure of 5 liorsepowrr per inch of mill length under these coiidit.ions is more nearly rcpresentative of its ~mwerconsumption. This behavior gives an idpa of the toughness of tlie resins of this type. It is also interesting to compare the physical properties of a Plioform resin with those of a first grade, rubber tread stock. Assimiing that both have an ultimate tensile streiigtli of SO00 pounds per square inch, the stress strain curve of the two, of coi~rse,is vastly iiiffereiit. Tread stock will possess an elongation of some 500 or 600 per cent before rcaciiing its breaking point, while the Plioform stock possesses practically no eloneation. Tlie curves of Figure ., 2 illustrate this remarkable difference. A fourtli coinoarison hetween I’lioform resins arid the betber known rubber products is presented in Figure 3. In making this t.est, bars of Plioform and hard rubber (specific gravity, C ~ M P A K I wm: S ~ X lZuen~~{ 1.29) were made 0.5 x 0.5 x 2 iiiclies iri size, and were fiioform’s behavior is intercsting in so fitr its its softening immersed in various concentrations of nitric acid, 8 s sliomi point is concerned. If one iises the Shore hard-rubber in Figure 3, after 24 hours of immersion nit.ric acid of 43 durometer reading as an indication of softening of the material per cent concentration had no effect, upon the Plioform and s t i n k s the behavior of Plioform over a range of tem- bar hut had caosed the hard rubber liar to soften and distort peratures, it is found to differ from the usual vulcanized to approximately twice its originai dimensions. Increasing rubber product in that the softening point appears sliarply concentrations of acid iurtlier broiight out this difference. ani1 at a lower temperature than with vulcanized r111iIier. At 58 per cent there was some effect upon tlie surface of the Io ordinary vulcanized rubber practice, one considers tlie l’lioform bar, in that it was sliglitly discolored, but there ratio between durometer reading and temperature as a fairly was no evidence of action by acid on the resin. Sitric acid
v6!l,l.,LaQ, 1034
1 3 D U S 1'11 I A L A N D E N G I N E E R I N G C H E M I S T K Y
Oi 65 per cent coirc,entrai,ion sliowed diglit action arid can-
I J ~ O C ~ Sgives S tiiorougli itiiprcgnation of fibers arid dfieient resin 01) the surface to accomplish a11excellent metliod of fiber covering. Sheets so prepared van th(?n be stacked, one on top of t,lie other, arid rookled iii tire manner coiiiiiioii to thennoplast.ic materials, t,o iht:tin a laminated sheet of the ilesird tlrickliess.
sidcralilr riiseolorntion, wliile tbe coinrnercial coriceiitrated nitric acid sli~\\-eda pitting action on tlie surface of the I%Eorm bar. Tliese tests inay not he of pract,icid valiio I m a i i s c the aubhor. are not, 5s yet, ready to recoinriietid tho use oi I'lioionn in ,513per cent concentrated nitric acid, but tlie rrsiilts of tile t,csts arc given to show t i l e decided i1ifEermec iii behavior lietween Plioform arid liard rulher iiivler t,liese 'evere conditions. himt,la:r inheresting coiirparisiin oS l'lioform with Iiaril nihlier viis in cold flow. The 2illImdhk limit iiil liard riiiiber ior clcctrical pirpo , as irieasureil by om: large telqhone roiiipany's latiimtories, is 0.001 inch per half-iricli Iciigtli iiiiil~rZ(M0 p ~ i i i ~ l pressurc .; per sqnare iiicli with tlic tcst
l,AlllX.h'~Ell SllEETs
A large noiiiber of highly decorativc panels iias been prepared iii this rriaiiiicr. Aside from the decorative purpose it wield sewn tlint iliese jia~iclsslroiikl he of considerable iritercst lominercinlly Iiccaore id tlicir low riioisture absorptitin and their ability to sti~iid up in acid and alkaline solutions. The regular A. S.T . tpst comist.s of utilizing a slali oS laiiiiiititccl Iiiaterkt~1 inch Iiy 3 iiiclics in diameter, filing t.he ridges of this slab, and iiiiiixming it in water flJr a giver1 ptxioil or tiiio. h i:oriiliarisoo oi this sort made oil a Sourply, 8-ounce, fabric-larrrinatcrl strip of l'lioform shows ajrproxiiiiataly one per cwt inoiitiire absorption in 24 liours OS iiimicrsioii, as coinpareti i a corrwponding phenolic a nioisture absorption of lairiinntcd strip, w4iicir poss ovcr 4 per cent. Figure I SI the moisturc absorption of Pliofrrrm niolded in sheet foriii. The aiidit,ional ahsorption oE the lariiiiiated products in escess of this wrvc is due to moisture alJsorbed by tlie fibers oi the ialsic. Another interesting applicntioii of these materials utilizes iiie lainiiiated fabric i n connection with tlie regular inoldiiig powder. If tlie pearlescerit molding powdrrs are used in eoiijuiictioti with the impregnat.ed fabric, some striking effects caii be obtained. I n this operation the fabric is inipregiiated in tlie useal manner and molded, using properly granulated poiviler in equal amounts oii both sides of the fabric. This composite iriixtrire is then pressed and coded. Tlie resulting slieet.~possess a pleming finish in that they have a decided ilept,li uf iiirfnce and luster.
1. ABsorrETrON OF WATER I1Y h O F O K M l00krmn (8.5-ounee)sample, '/r inel? ti+k
RGrlaF.
piew at IXJ"I?. for 24 liours. Under tliesc test coiiditioiis PlioEorm So. 40 ~ O ~ S ~ : S aS cold ~ S flol~ oE 0.00035 inch per iiieli a 200 per cent factor oi safety ovcr liard siihlrcr. It iias lorig tieen the hope of rubber incn to protluw a colored hard rubber. These resins seein to be the answr to this ambition. Although they contain 110 suliur or siilfrirlieitring ingredients, Lliey rriiglit well he taken for liard r u l h r in so far as their lieiiavior is concerned in a number oE applications. They differ froin liard rubher ill that, they arc thermoplastic and that there is a wide range of c ~ l ~ o availrs .es slight liiniting effect upon the color imssihilitiee. 1h.i light aniber C l i k J r can Re utilized
tains one pound per gallon of tliorouglily iriilleti ruhber. This hrhnvior is just as true in the case ~ K X J J W 5 of l'liofrrrm rcsii1,S. ~
