April 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
The formation of amylose film on the surfaces of irregular ubjects by dip-coating or spraying should be facilitated by the rapid gelation of concentrated solutions of amylose of moderate inolecular weight, and these procedures are receiving attention :it this time. .\lthough many properties of amylose film including low temperature flexibility, gas and water vapor permeability, variation of properties with relative humidity, as well as the effect of nioistureproofing lacquer coatings and other plasticizers, remain to be further investigated, comparison of the known properties of amylose film with those of presently available commercial filnis suggests t h a t uses will be found for this material if economical production can be achieved. ACKNOWLEDGMENT
T h e authors are indebted t o R. J. Dimler and W. Z. Hassid tor several of the amylose samples used, t o Nison Hellman for niaking and interpreting the x-ray diffraction patterns of the films, and t o E H. Melvin for the ultraviolet absorption curves of the films. T h e authors also wish t o thank R. de S. Couch of General Foods Co., Hoboken, N. J., for his report on resistance of amylose film t o coconut oil.
919
(3) Lansky, S., Kooi, Mary, and Schoch, T. ,J., J . Am. Chem. Soc., 71, 4066-75 (1949). (4) Meyer, K. H., Bernfeld, P., and Hoheiiemser, H., Hela. Chim. A c t a , 23, 885 (1940). ( 5 ) Modern Plastics Encyclopedia, pp. 1189-91, New York, .. Plastics Catalogue Corp., 1949. (6) Rundle, R. E., Daasch, Lester, and French, Dexter, J . Am Chem. Soc., 66, 130-4 (1944); Rundle, R. E., and French Dexter, Ibid., 65, 558-61 (1943).
(7) Scherer, P. C., and Rouse, B. P., R a y o n and Synthetic TestdC\ 30, NO. 11, 42-4; KO.12, 47-9 (1949). (8) Schoch. T. J., in “Advances in Carbohydrate Chemistry,’ Vol. 1, TV. W. Pigman and M. L. Wolfrom, editors, p. 25‘1
New York, Academic Press, Ino., 1945. (9) Sohoch, T. J., Cereal Chem., 18, 121-8 (1941). (10) Sookne, A. M., and Harris, Milton, J . Research SatZ. B u r Standards, 30, 1-14 (1943). (11) TTeissberger, Arnold, ed., “Physical Methods of Organic Chemistry,” Vol. 1, pp. 491-3, S e w York, Intersciencc Publishers. Inc.. 1945. (12) Whistler, R.’ L., and Hilbert, G. E., IND.ENG. CHEM.,36 796-8 (1944). (13) Khistler, R. L., and Kramer, H. H., Agronomy J . , 41, 409-11 (1949). (14) Wilson, E. J., Schoch, T. J., and Hudson, C. S., J . Am. Chert. SOC.,65, 138@3 (1943); Bates, F. L., French, Dexter, and Rundle, R. E., Ibid., 65, 142-8 (1943). (15) TTolff, I. A., Gundrum, L. J., and Rist, C. E., J . Am. Chem S o c . , 72, 5188 (1950). (16) Wolff, I. A , , Olds, D. W., and Hilbert, G. E., IND.EKG.C H X Y . . 43, 911 (1951).
LITERATURE CITED
(1) Hilbert, G. E., and MachIasters, 31. bf., J . B i d . Chem., 162, 229-38 (1946). (2) Kerr, R. W.,ed., “Chemistry and Industry of Starch,” pp. 116-17. 334, New York, Academic Press, Inc., 1944.
RECEIYEDOctober 23. 1950. Work performed a t Northern Regional Research Laboratory, one of t h e laboratories of t h e Bureau of Agricultural a n d Industrial Chemistry, Agricultural Research Administration, U. R Department of Agriculture. Report of a s t u d y made under t h e Research a n d Marketing Act of 1946.
Removal of Stearic Acid from Surfaces by Alkaline Detergents FRED HAZEL I’riiaersity of Pennsylcaniu, Philadelphia, P a .
WM. STERICKER Philadelphici Qtcartz Co.,Philadelphia, Pa.
Commercial stearic acids are used as carriers for ahrasives in buffing and polishing compounds. If good adhesion is desired, these compounds must be cnnipletely removed from nietals hefore plating w-ith nickel or chromium. Various alkaline chemicals used as cleaners were tested as to their ability to remove “stearic acids” of different melting ranges from zinc, aluminum, steel, and, for comparison, glass surfaces. The more strongly alkaline chemicals w-ere the most effective cleaners at intermediate concentrations. . i t high concentrations they salted out sodium stearate. The more weakly alkaline chemicals %-eremuch less effective at all concentrations. Zinc appeared to react somewhat with the fatty acids, making them more difficult to remove. Higher temperatures improved the cleaning. A phase change in the hydrous soap formed was observed between 60” and 75” C. The results should be helpful in formulating polishing and buffing compounds and in setting up conditions for their removal from die castings.
B
U F F I N G compositions consist, functionally, of mild at i ~ i sives dispersed in solid, greasy vehicles. They are ai)plied to the metal surface indirectly through the agency of buffing wheels, which are made from cloth or other pliable ninterials ( 4 ) . Under operating conditions the wheel impinges a t high velocity on the surface and heat is generated by the frictioii. Adam (1) has discussed the changes that may he produced i l l surfaces as a result of the stresses that are set up and the tcmperature rise during polishing. T h e increase in temperature liquefies the vehicle and promotes intimate contact betm-een the buffing composition and the metal surface. This aids in accomplishing the objective of thc procedure-the smoothing out of irregularities of the surface. The buffing operation, however, increases contamination by leaving a deposit of the buffing composition; accordingly, the surface must be cleaned after it is buffed. The physical properties of stearic acid are such that it has been used as a vehicle in bufKng compositions. I n alkaline cleaning the acid is converted t o a soap whose solubility, like that of many other colloidal electrolytes, is affected markedly hy the presencc:
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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Figure 1. Effect of Sodium Ifetasilicate at Different Concentrations on Stearic .4cid I 1. 2. 3.
1
3
A t 90' C., rinr surfaces 4 . 0 . 4 8 0 7 ~\a@ (220) 5 . 0.625% NalO (203) 0.295% YarO (230) 6 . 0.738% h a 2 0 (217)
of l o x concentrations 11f electrolytes. Soaps a r c Eorined ill alkaline cleanirig. and by s:ipoiiificatioii of esters of fatty w i c k when hvdrogenntrd oil5 :it'e faiiil)lo!-ed :I:: vehiclw iri huffing compositions. B ~ C I I Uthe S Ceodiuni coinpourids used lkalirie cle:iiirr.s a l G o are elect,rolytes, it was thought tieuirable t,o investig:it4e the efficiency of several of these coinpoutids in removing ste;ii,ic acid from surfaces. T h e cleanel,?; \\-ere Pt,udied :it tliffeiwit r o i i c w trations arid temperatures. Thrse coiitiitioiis wet^^ found t,o xffeet the removal of the sodium ste:itxtr formed in plncr iiy lieutralization of t h r x i d . SURFACES STCJDIED
Zinc,, aluminum, steel. and glass served as bases for the ctenric acid (Table I ) . T h e effects of the various alkaline materials ori aluminuni and zinc have k e n studied and reported (3,7 ) .
3
6
1
Figure 2. Effect of Socliilni Siesquisilicate at 0,48OC,& NaiO .\lone and w-ith Sodium Compounds I O Increase Concentration to 0.88576 NarO
Blank
0.184% Y a r O (223)
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i t 90' C. stearic arid I, zinc surfaces SeaquiailicaLe, 0.480% Nan0 (201) Se$quisilicate, 0 . 8 8 5 7 ~KazO (170) Sesquisilicate. 0.480% Na?O and SaOH. 0 . 4 0 5 % NarO ( 2 5 2 ) Sesquirilicate. 0.(80%' Na?O and SaaP04.12H20, 0.405% Nag0 (246) Sesquisilicate. 0.48070 NaTO and Na?SOd, 0.405% Nag0
6.
St-cqui*iliratr. 0.480% Ua?Oand UaCI. 0. &0,5% Xa!O (21.3)
1. 2. 3. 4.
(244)
11F:I'H 01)
Pariela of the various matr.rialc \v(st'e ( u t to iiieasurr 2 . 5 7.5 m i . .-i~i>.surface coatings were rtlriioyod prior t o coating them \vith stearic acid I)? hantl-lnppiiig x i t h S o . 240 Pinery cloth or, in t h e case of strrl, piclcliiig in d f u r i c acid ( 1 6 ) . T h e stearic acid was applied t o t h r p r e p u m l panels by immcming theni to a depth of about 5 em. iii tlir molteii acid at 105' * 5" C. T h e panels ~ v e allon-ed r~ t o rcTni:iin it1 contact rvith t,he liquid until the solid acid, which frozc on thrir w r f : i c ~ swhen first immersed, melted. This usually rcquirrd 10 t o 20 seconds. Tlic panels then were draiiiril h y suspi~titlingiri :Lir. .\I 4TERl.4 LS
dodiuni hydroxitic,, t1,icotliutii orthophosphate, sodiuiii carbonate. aiitl several soiliuin silicates xere used a s cleaners. The
92 1
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April 1951
2
1
4
3
8
5
Figure
:{.
9
k:ffecl o f \ a r i o t l i ill,alit:t~ Socliurn Cornpouds at 0.480% S a 1 0 on Stearic i c i d 1. 2. 3.
4 1 90'
Blank .\Ietaeiliratr ('378) Sesquiailiratr (210) 2. Orthorilicute (400) a. 11, dratcd di.;iIirstt. (283)
(:.. zinr
I
surfaces 6 . N silicate (262) 7. Carhonate (297) 8 . Trisodium orthophosphate ( 3 9 5 ) 9. Hydroxide (258)
Coniiiit~rcial stearic acid is a niisturr of fatty acids prepared froin talloiv or other fats b y heating and prtvsing t o remove the low nielting fatt,p acids. I n addition to true etcmic acid, it con-
latter were conmierc~iulproducts oi k t i u i w characteristics (Tu1)le TI). The other compounds were J. T. Baker ;inalyzed grade. I n order to reduce the results to a common hasis for the different compounds. their effectiveness in removing 3te:iric n c , i c l was compared a t t,he same ,codiuni nsitie cwncentrations.
tains jialmitic acid, more or lees oleic acid, and smaller amouiit~ of othci. acids. I n these experimiJnts tKo grades of acid were used. The first ( I ) !vas a purified product with a melting range of 65" to 70" C., containing probably 85 to 90% stearic acid. This product was considrrahly purer than would normally he used in huffing compounds. Thv second sample (11)was a product nieeting the requiwnierits of the I-. 9. Pharmacopoeia S I I I . The nielting range on this sample was from 54' t o 57" C. and the iodine numher was supposed t o Lo lrss t h m 4. This would correspond to a good gradr of double-pressed stearic acid containing perhaps 55 to 60y0 of actu:iI stearic acid. Products of this kind are used in the manufacture of huffing compounds. Results ir-ith the purer material ( I )emphasizr the pffects produced by t h e higher melting fatt), acids.
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Figure 4. Effect of Sodium Metasilicate at Different Concentrations Steel and glass surfaces, 90' C., stearic acid I On Glass 0.014% Na2O (451) 2. 0.885% NalO (430) On Steel 3. 0.0295% S a 2 0 (441) 0.184% NarO (432) 4. 0.074% Ua,O (444) 1. 0.885% NazO (425) 5. 0.148% \a20 (437) 1.
6.
(:LE \ \ I \ < ;
PROCEDURE
T h e panele were iiiiiiiersed for 10 minutes in 811 upright p s i tion in distilled water solutions of various alkaline clearie:~ contained in 1-liter Frencli Iw:ilcets. A 100-ml. beaker resting iriFidr each of the larger healcers s e ~ ~ v cas ~ da prop for the pancla. T h e experiments were conducted at !)O ' C. uriless othernisc iridic.ntcd. The ratio of cleaner bath volunie t o panel area was 1500 tci 1, as recommended in the .4.S.'1.11. procedure (2). The appearnncr of thv p:iiiels !vas noted after 10 minutcs \\-hilo in the cleaner bath. Thr!- were then rciiioved carefully with the aid of crucible tongs, ciippcd in distilled water a t room tcmperature for 1.5 t o 20 seconds without stirring, and photographed a f t e r drying at rooni temperature. RESULTS
T h e efficacy of the alkaline cleaners in removing stearic acid from various surilil.c-. ~ I I I ~ C ' Itiiffei,ent, . conditions is shown in Figures 1 t o 11. Figure 1 s h o w the, c,ffwt o f the coiicc~ntr:itionof sodiuni oxide,
.-oiliuiii iiic%nrilicate, Tvit,li stcaric acid I o n sheet zinc. The ii\term~tii:iteconcentrations of sodiuni oxide-O.295 tu 0.480%--were more effective thaii either higher or lower concentrations. Siiiiihrly, an optimum cleaning concentration \vas found for a11 the compounds tried except sodium cai,bonate and the mow siliceous silicates. -411 the latt,er gavr poor results a t all concen tr:i tioris. T h e deposit's remaining on the metal surface a t the higher concentrations of the alkaline electrolytes were due to the salting o u t of the soap. The removal of stearic acid from solid surfaces by alkaline substances may be considered to consist of the followiiig stcps: :I-
St,enric acid-solid surface
--+ hydrated
soap-anlid surface --f soap solution solid surface
+
The higher concentrations of t h e electrolytes reduce the solubility of t h e soap by increasing the size and proportion o f micelles (11) and thus oppose t,he second step. In Figure 2, the h s t two zinc panels show t h e effect on stearl(wid I of sodium sesquisilicate a t a n optimum concentration of
INDUSTRIAL AND ENGINEERING CHEMISTRY
April 1951
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1
Figure 5 .
4
sodium metasilicate in r e m o v i 11 g stearic acid I is s h o m in these figurrs. Although sodium metasilicate at a c o n c e n t r a t i o n corresponding t ( J 0.184% sodium oxide failed to remoic. the acid from a zinc surface, concentrations of 0.0148, 0.074, and 0.148% sodium oxide removed i t from p h i s . aluminum, and steel, respectively, These results suggest strong bondiiig to the metal in the case of zinc anti steel and weak bonding in the w w of glass. With aluminum, the ni+ chanical effect of the mild gassing :it the lowest concentration of sodiriiii oxide aided in the removal of the acid. This metal showed some attack a t it concentration of 0.0295% sodiuni oxide with metasilicate, but highri concentrations left a specular surfaccb Yonsiliceous alkaline cleaners carinot he used for cleaning aluniinuiir (S, 6). T h e attack caused \,y lo\\ concentrations of sodium cai l>oiixtt sodium hydroxide, and triaodiuiil orthophosphate is shown in Figure (i. The stewic acid x a s removed in all cases, owing to the strong gassing.
Kffect of Sodium Jletasilicate at Different Concentrations
Aluminum surfaces, 90' C., stearic acid 1 1. 0,0295 % NaiO (449) 4. 0.625% >azo (601) 2. 0.074% NazO (604) 5. 0.885% NaiO (600) 3. 0.480% Naz0 (602)
0 480% sodium oxide and a t a salting out concentration o t 0.885% sodium oxide. T h e other panels in this figure were obt.1ined by immersing panels coated with stearic acid I in mixtures ( i f sodium sesquisilicate with other sodium compounds. The total concentration of sodium oxide in each of the mixtures was 0.885%, or the same as shown in Figure 2, panel 2, for the sesquisilicate alone. The mixture contained 0.480% sodium oxide a s the sesquisilicate, as with panel 1, and 0.405% sodium oxide eauivalent in the form of other sodium compounds Sodium hydroxide (a strong base), trisodium phosphate (an alkaline salt), and sndiuni sulfate and sodium chloride (two neutral salts) -were employed in the preparation of the mistures. The results clearly shorn t,he iniportance of the sodium ion concentrtrtion in reducing the soluhilit,y of the wap. Figure 3 shows the results ob1,ained xit.h t,he various alkaline cleaners a t concentrations corresponding to 0.480'% sodium oxide ~ ~ zinc i i panels coated wit,h stearic xcid I. Sodium carbonate and the >ilicates with the higher silica ratios irere least effective in removing the acid. This can be at.t,ributed to t,he lower pH of the solut,ions of thesc substances. Much lower concentrations of cleaners were found to be effective i n removing stearic acid from other surfaces than from zinc. Salting out of soap occurred a t the higher concentrations of cleaners with all surFigure 6 . Effect of faces, however. These results are shown in Figure 4 for both steel and glass surfaces and in Figure 5 for sluminum alloy 25. T h e efficacy of
923
EXPERIIIENTS WITH STEARIC AClD 11
The l o i r melting point of stearic acid 11, 54' to 57" C., iiitlicatt~l the presence of acids of lower riiolecular weight, due either to it uhorter chain or to unsuturatiou. Soaps formed from thew acids are more soluble and, accordingly, more difficult t < Ja:ilr out (9, I S ) . .1 correlation is known to exist between soluhility m d critical micclle concentration (8, 1 2 ) . Figure 7 s h o m the effect of solliuni nieta.-ilicate at conceiitrations ranging from 0.883 to 1.77% sodium oxide on steel coated
2
3
Nonsiliceous Alkaline Cleaners on Aluminum Surface?
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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The I)eiietic.ial effect of increase in temperature is not surprising, because it is a matter of frequent experience that most solid substauces show enhanced solubility a t high temperature9 due to thrir nrgative heats of solution (14). T h e fact that, soaps are involved, however, intruduces coiiiplicatiori~because of phase change9 n-hich occur tvitli change iti temperature of the hydrated sonp (,5, 10). The critical micelle csnric,eiitrution increases with increase in temperature ( 8 ): hence the composition of the ~ o l u t i o n iii equilihriuni x i t h the undissolved mal) :ilw changes with temperature. At 60" C., the wdiuni stearate formed i i i situ fri)iii the i t c ~ r r i ~ i w c *i d 1)y neutralization x i t h the :ilk:iliiie clwtiws w:is in t8he form of xhite, hyrlt,ous, swoll[lri * i m p curd. The curd was in~ o I u l i l (in ~ wlutions o f thc alkalino cleaner3 at this tenipct,:iturc. Slorcover, it is dissolved itic~oiiiljlct~ely ivheii plungecl either into distilled iwtt'r or i i i t o s d r i n i chloride solution, c o n ( , i , t i t t , : i t i i i i i 0,48070 dotiiuni ositle, :it 90" (:. S o
4
1
Hydrated sodium disilicate Soiution of siliceous silicate
2i.5 h 9
.?I;.@
17.i
1:.'.00
PL'OG
2i 8
(i2.4
1:s.L"
1 ::i:il' 1.
L('
~~~~
with stearic acid 11. S o deposit was ol)t,ainetl i i i thc l r c w l i t case with concentratioria which yielded R heavy depi)ait ivith til(, acid of higher melt.ing point (Figure 4). It n-as found that, the acid of lo\wr iiielt,iiig point c i i u l t l I!? I('riiovcd from other surfacer :it, c1e:iner coricent,l.ritions \vhic,li out the acid o f higher melting point. The g1:iss panel,* irt I 8, when compared n-ith t,how in Figure 4, d i o t~h i s to lie tlie (':i>i> wit,h sodium nietasilicatr. Figure 8 d s o s l i o ~ st1i:it sotliutii 111.droside had a greater salting out cffcct than thc. nic~t:i-jlic.:ito under the cwnditiona tiesct~ilmi.
Figure 8. Effect of Sodiitnl AIetasilicate and Sodiiiiii Hydroxide at Different Concentrations Glass c u r f a r r c , 90' C . ? stearic acid I1 Sodium %Ieta*ilicatc Sodium IT\droridr 0.0148% NatO (.i63) a. 0.88S% Nag0 (R68) 6 . 1 . 1 8 % Na2O ( W O )
1. 0.0148% NwO (564) 2. 0.8857~Na9O (ii6i) 3. 1.18% Na?O (569)
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INDUSTRIAL AND ENGINEERING
CHEMISTRY
925
phase change occurred under these conditions. T h e panels shown in Figure 10 were treated in the above manner after the soap curd had been formed a t 60" C. in a solut,ion of the sesquisilicate of 0.480% sodium oxide concentration. .Lt 75' C., the stearic acid was converted into a liquid crystalline, nearly t'ransparent soap phase hy the more alkaline cleaners a t concentrations corresponding t o 0 , 4 8 0 ~ osodium oxide or higher. lliich of the soap diffused into the solution under these conditions. When t h e panels treated a t 75" C. were removed froin the alkaline cleaner? rid plunged into distilled ivat'er a t room temperature, the liquid crj-stalline soap remaining 011 the surfaces was converted into white, fineytzincd soap curd. At4 60" C., the sodium stearate did not undergo the liquid phase transitit,ri and t h e curd appeared to have a coarser testure. This contrast, i s s h o r n in Figure 11 R S 1 2 3 4 i ~ e l las in the first two panels in Figure 9. Figure 9. Effect of 0.480$7"NalO, as Sodium Yesqiiisilicate, a t Difi'ererit The w:ip remaining o n the panels u t 90" C'. i i i Tempera tures tht. pre~enceof salting out concentrations of the ciwriers \vas a liquid crystalline phase. This is Zinc surfares, 3tearic aoid I 1. 60" (367) 3. 80°$(369) further evidence t h a t the solubilit,y of the soap 2. 75' (368) 1. 850 (370) d ~ ~ i e n dgreatlv s on the nature o f the Jolution with which i t is in equili1)rium. T h e chief conclusions which can tie draivir from the d a t a preThis umi,k on the factors ;tffecting metal cleaning is Iioirrg sented here are: ?onti nuw !.
__
Stearic acid is removed from metal surfaces most readily at iiit?rmedi:ite concentrations of alkaline cleaners. l'oorer removal at higher concentrations is due to reduced solubility of t h e soap formed. Higher temperatures ar? helpful. F a t t y acids of lower melting points are more readily removed fi,oni various surfaces. Strwic w i d is more difficult to remove from zinc than from the i)ther surfacies tested.
L I T E R \ T L R E (:ITED
"Physics anti C'hernistry of Surfnres," I ~ ~ i t d ~ ~ r i , Oxford L-niversity Press. 1041 ( 2 ) .Im.Soc. Testing Materials. ,\.S.T.hI. Specification D 9:30 --47T ( 3 ) Baker. P. L., ISD. Esr:. PHEM., 27, 1358 (1935). , 14) Eurns, K. hI., and S r h u h , A . E , , "Protective C'witings 1Iet:ils." S e w To~.lc,Reinholtl Publishing Cory.. 1939. (33 Doseher. T. h i , , and I-olci, 11, AI,, .J. P h j / a . & Colloid (7hCru.. 52. 97 (194s). (6) Hari.is. .J. C.. and Mcars. R. B.. A . . P . 2 ' J f , ( 1 ! .idam, S . K.,
I l $ ! / / , 120, , 3 3 ; 121. 33 (1943).
S1111181-
Figure 10. Effect of Temperature on Soap Curd Formed At 60' C., zinc surfaces. First trcatwl with 0,48070 Vag0 as sodium besqui3ilicate a t 60' C., t h c n dipped in 1. Water at 90° (389) 2. YaCl solution (Q.480% RasO) at 90' (390)
Figure 11. Effect of 0.623% Sad). as Sodium 3Ietasilicate
RK..CEII.ED .$pirl 1i. lY30. Presented liefore the I3ivision of Irrdiistrial a n d Engineering Chemistry a t t h e 117th >leetirig of the . $ M E R I ~ , A Y C H t . 3 1 I C h L ~ O C I I . S Y , T)etroit. l l i c h .
