Preparation of Films from Amylose IVAN A. WOLFF, H. A. DAVIS, J. E. CLUSKEY, L. J. GUSDRUJI, AND CARL E. RIST .\-orthPrn
Regional Research Laboratorr, Peoria, I l l .
In order to eialuate the potential utility of self-supporting films from am?lose, the linear starch fraction, techniques were devised for the laboratory preparation and tcsting of such filnis. The physical characteristics, chemical resistance, and mechanical properties of the films were studied, including t h e relation of properties to filni thickness, varying aniounts of added amylopectin, nioleciilar size of the ani?lose, heat treatmcnt, and amounts of gl) cero1 added a- plasticizer. The general mechanical behavior of the films is good, niost Talues of their properties lying within the range of common plastic films. Industrial applications can he expected if economical xiicans arc found for obtaining amylose either by starch fractionation or from starches of high amylose content. i m ) lose film should find unique applications in the food and pharmaceutical fields based on its digestibility and lweahdown to sugars absorbable in the animal body.
MYLOSE, the linear fraction of starch, would appear, by virtue of its structure, molecular size, and similarity to cellulose, to be a raw material useful for the preparation of selfsupporting films. Although films have previously been prepared from some of its aliphatic triesters ( 4 , I d , 16), only fragmentary films of amylose itself, in the form of the surface skins resulting from slow evaporation of an amylose solution, have been reported ( 6 ) . The optical properties and x-ray diffraction patterns of such rudimentary films have been described (6). In the present work techniques were devised for the batchwise preparation of sheets of high quality film from amylose by a solvent-casting procedure. Detailed study was made of such films, including appraisal of their mechanical properties and of those other characteristics which enable comparison with commercial films (6) or are related to specific uses. Several variables, including film thickness, addition of amylopectin, molecular size of the amylose, heat treatment, and incorporation of glycerol were investigated to determine their effects on the properties of amylose film. In general, amylose film has a combination of properties which places i t in the range of commercial usefulness. Exploitation of such use is, of course, dependent on the economical production of amylose. This may be achieved by the development of better methods for fractionating starch or by the development or discovery of plant varieties with starch containing a high percentage of amylose (1, IS).
solutions containing butanol were usually mottled in sppe:trance, it was desirable to remove this complesing agent prior to casting the film. This was done by distillation, l a v i n g :in aqucious solution of amylose which was stable at the reflux temperature but which quickly gelled on cooling t o about 00" ( ' . (depending on concentration and molecular w i g h t of the aniylose). The concentration may be adjusted its desired with hot water. For preparation of the film, the filtered, hot solutiori as poured onto a flat glass or chrome surface and immediately spread uniformly with a doctor blade set the desired distancme above the plate. The solution set rapidly to a white, opaque p l which became clear on drying. These filnis were usually XIlorn-ed to dry at 70" F. and a t 65% relative humidity. - i t unpredictable times amylose film was found to adhere 80 tightly to the chromium plated casting surfaces that strippinK without damage to the film was not possible. Sticking to glaw plates mas even more pronounced. Pretreatment of the surfaw with a very dilute solution of Dow-Corning silicone fluid (claimrvt to be odorless, colorless, and nontoxic) obviated this difficult,y. T h e dried amylose film was easily peeled from the plates a f k r a n edge was loosened with a razor blade. Complexing agents such as Pentasol, ethanol, and pyridine work equally as well as butanol. Aqueous methylamine (25y0 I was also a useful dispersion medium. However, films obtaineli when amylose a a s dissolved in boiling water in the absence of' :I secondary agent were usually grainy, indicative of less complete solution of the amylose. Previous reports that. amylose (or the A fraction of starch) is completely soluble in boiling water (.5) apparently do not apply to solutions of the concentrations used in this work. B typical preparation of amylose film is as follows:
A clean glass plate 18 inches wide and 4 feet long W M treat,c:ti with 15 ml. of 0.01% Dow-Corning 200 silicone fluid (viscosity grade 350 cs. a t 25" C . ) in carbon tetrachloride, spread with t: piece of cheesecloth, and polished. To a stirred mixture of 200 ml. of water and 30 ml. of n-butanol were added 20 grams (airdry basis) of corn amylose [iodine sorption = 190 mg. per gr:i 111 ( 1 4 ) ; intrinsic viscosity [ q ] a t 25" in 1 N potassium hydroxide = 1.30 ( 1 5 ) l . The mixture was heated and refluxed for 10 minutw:, with stirring, then distilled until only a single phase was present in the distillate. Hot water was added to replace that lost i n the azeotrope. The hot solution was then filtered by suct,irlri through a heated, coarse-porosity fritted-glass funnel into a prcheated flask kept in a steam bath. The filtered amylose solutiori was poured onto the treated plate and promptly spread with :t doctor blade 16 inches wide, having a clearance of 0.030 incxh (0.762 mm.). The film was then dried a t 70" F. and 65% relative humidity. The dried, clear film from such a preparatio~~ is approximately 0.030 mm. thick.
PREPARATION O F FILMS
CHARACTERISTICS OF AMYLOSE FILM
T h e amylose for these film studies was prepared by the butanol-precipitation procedure (8). Pondered amylose as usually obtained is soluble in hot water saturated with n-butanol or with other chemical agents known to form a complex with the amylose (8). Solutions containing from 10 t o 20% of unmodified corn amylose are not highly viscous. Since films cast from
Amylose film when cast as described is isotropic, odorless, tasteless, colorless, nontoxic, and biologically absorbable. (Floyd D e Eds and A. Ambrose of the pharmacology laboratory, Bureau of Agricultural and Industrial Chemistry, Albany, Calif., are making studies of possible applications of amylose film based on these properties.) Although transparent, amylose film often
915
INDUSTRIAL AND ENGINEERING CHEMISTRY
916
retains a slight haze which, as nil1 be shown, is related to the composition of the film-forming raw material. This haze is apparently a surface effect since thick and thin amylose films have the same percentage haze (measured by A.S.T.M. test D 6 7 2 4 5 T , Haze of Transparent Plastics by Photoelectric Cell) and since a nitrocellulose lacquer coating materially decreases the haze of the film.
Vol. 43, No. 4
being chcniically inert, it,s resistance to organic solvents as very good t o excellent, resistance to strong acids and alkalies as poor, ~ n resistance d to Rater and weak acids and alkalies as fair. The grease resistance of amylose film is excellent. In 36 hours, using the standard ThPPI test T454m-44 (turpentine lest for grease resistance of paper), there was no penetration of dyed turpentine through the film. Another laboratory found amylose film impervious to coconut oil a t 100" F. for 1 ncek. .\mylose film has excellent transparency t o ultraviolet light, a film 21 microns thick transmitting over 60% a t 2200 A. Unplasticized cellophane is somcwhat more opaque a t this bvave length (Figure 1 ).
4 IIECHASICAL PROPERTIES O F CORN ARIYLOSE FILZI
E
p
4'
eo
g 4000 '
O
AZ IN A
O
O
Figure 1. Ultraviolet Transparency of Amylose Film as Compared with Unplasticized Cellophane = A m y l o s e film, unplasticized X = PUT-0 300 Du P u n t cellophane, unplasticized
Amylose film as formed is not thermoplastic or heat-sealing.
It burns slowly with a luminous flame and with sputtering. It is not appreciably discolored when heated for 4 hours a t 170" C., b u t fiome dextrinization takes place. T h e film is enibrittled by such heat treatment even after being re-equilibrated t o replace the moisture lost in the oven. T h e film has a refractive index (11) of 1.52 a t 22" C. and 65% relative humidity. Its density, obtained by direct measurement and weighing, is 1.45, giving it an area factor (square inches per pound of film in 1 mil (0.001 inch) thickness) of 19,100. T h e equilibrium moisture content of amylose film is 15 and 18% at, 50 and 65% relative humidity (70" to i 2 " F.),respectively. Amylose film may be considered to be a nonhelical (21, retrograded (9) form of amylose. It does not sorb iodine vapor and is not soluble (grossly) in boiling water, boiling water-butanol mixture, or water-butanol a t 120" C., although it breaks into smaller pieces owing t o its low wet strength. Solution of a small amount of amylose is indicated by a blue color in the supernatant liquid on the addition of dilute iodine-potassium iodide solution. T h e film is not soluble in 0.5 X potassium hydroxide but' dis' potassium hydroxide in 7 hours at 0" c. solves completely in 1 h T h e insolubility of the film in water-butanol, the solvent from which it was originally cast, indicates that a crystallization of some type has occurred. rimylose film shows the starch B t,ype x-ray diffraction pattern ( 2 ) . T h e resistance of amylose film to various chemical reagents was evaluated in the following way: The outsides of 16 X 150 mm. test tubes were conted by dipping the tubes in a hot 10% aqueous solution ot amylose prepared as described, and the tubes were inverted until the films were dry. T h e tubes were then immersed in reagents suggested in A.S.T.RI. test D 543-43, Resistance of Plastics to Chemical Reagents. After 5 days in distilled water, 10% sodium chloride solution, 50y0ethanol, or 3y0 sulfuric acid the films were softened and weak but showed no wrinkling or loosening from thc tub:: in toluene and ethyl acetate there was no visible change; 111 acetone and 95% ethanol the film was easier to scrape from the glass, and there appeared t o be some embrittlcment, probably due to dehydration; in 30% sulfuric acid the film became very tender in 24 hours but was not dissolved in 7 days; in 10% sodium hydroxide the film dissolved in 1 hour, anti in 1% sodium hydroxide it wrinkled, swelled, and loosened in an hour but w m not dissolved in i days. Generally one might class the film as
.ill films were allowed to equilibrate a t 72" F. and 50% rrlative humidity for a t least 4 days prior t o testing. Tensile Strength. Stress-strain diagrams were obtained for most of the films on the Scott IP2 incline plane serigraph, a machine providing conqtant rate of loading, with the jaws set 40 mm. apart at, zero load. .\ carriage providing for a maximum capacity of 2000 grams was used for the dry films and one of 250-gram capacity for the weaker wet films. For the thickest films, d i o s e strength exceeded the capacity of the Scott machine, a pendulum type tensile-testing machine with a total capacity of 5 kg. was used. All tensile strength calculations are based on the original cross section of the dry film. The stress-strain diagram of unplasticized amylose film has an init,ial portion which is approximately a straight line, indicating an elastic region in which the stress is proportional to the strain. Calculated from this region of low stress, the modulus of elasticity of dry amylose film is 450 kg. per square mm. ( a t 50% rehtive humidity). A small region of plastic flow precedes the rupture. The dry tensile strength of these amylose films averaged from 6.5 to 7.2 kg. per square nim. (9200 to 10,200 pounds per square inch) although values well almve 8 kg. per square nun. (11,400 pounds per square inch) have been obtained. Such variations are due partly- to nonuniformity of the film and partly t o unknown factors. The tensile strength values given here are averages of 10 test strips. T h e elongation a t the time of break averaged approximately 13%. JVet tensile strengths were measured on film strips immersed for 5 minutes in distilled water. During immersion the films swelled, became more cloudy, and decreased in tensile strength to 0.2 kg. per square mni. T h e ultimate elongation of these wet strips !vas 15%. Amylose film immersed in Tvater for 2 hours a t room temperature absorbs 225% of its weight of water (based on the dry weight of the film-A.S.T.M. D 570-12, Water Absorption of Plastics). X o loss due t o solubles occurred during such a time period. Other Mechanical Properties. The flexibility of amylose film, measured on the Schopper folding endurance tester, was gcod. The unplasticized film (0.025 to 0.030 nim. t,hick) underwent from 650 to 900 double folds before breakiug, with occasional values over 1500. The bursting strength of amylose film averaged 21 points 'approximately pounds per square inchi on the LIullen tester for film 0.025 nim. thick. The internal tearing resistance, measured on the Elmendorf tearing tester varied from 6 to 10 grams as the force required for a single sheet. However, these latter values are considered approximate since the test values all fell within the lowest 10yG of the capacity of the standard size Elmendorf tester. Both the dry tensile strength and the flexibility of amylose film are on the average superior to thoie of amylose triacetate. EFFECT O F F I L I I THICKNESS ON PROPERTIES
By varying the concentration of the casting solution from 7 to 15% slid the clearance of the casting blade from 380 to 1 2 7 0 , ~amylose ~ films ranging in thickness from 11 to 17011 were successiullj- prepared. Tensile strengths, both wet and dry, were found t o he independent of thickness, as was the haze of the filiii. Film below 2 0 in ~ thickness was hard to handle I)+
INDUSTRIAL AND ENGINEERING CHEMISTRY
April 1951
EFFECT O F MOLECULAR SIZE OF AMYLOSE ON FILM PROPERTIES
TLBLE I. PROPERTIES OF FILXJ FRO\f
1IIXTURES O F C O R N Ak%fYLOSE.LXD COKV A h Y L O P E C T I N
(50% relative humidity a n d 72' F.)
70
%
Tensile Stlength, .\Irn.Dry Wet
92 86 77 68 59
14 13 13
6.0
inislose Content
of Film=, Haze,
22 27 26 36
6.2
5.1 5.0
24
11 16 10
1.5
16
30 42 29 24'
6.4
6.0 4.9
5.3
5,5
0.15 0.13 0.20 0.14 0.16 0.14
0.07 0.05
... , . . ... ...
rE$: :&'
Ult imate Elongation, c7
Ii&/'q.
Dry 23
Wet 18
8
13 16 14 19
11 15
10 6 6 6 7 a
17
11 11
, , .
.. ..
Folds,
No
960 530 450 350 140 100 63
28
21 19 21 14
Elmenh ~ ~ ld o lr b ~ Burst Tear , Points* Grams 22 6 15 5 13 18
17 15 12 10 8 8 8
+ 7
6 5 6 8 J
5 J 9 4 6 3 5.0 'I Based on iodine affinities of amylose and amylopectin used and assuming :hat pure amylose sorbs 200 mg. of iodine per gram and aniylopectin no .o ine. Corrected to thickness of 0.025 Inin. assuining direct proportionality. Unfractionated corn starch in which granules had been disrupted b, xgitation of hot paste in Waring Blendor for 1: minutes.
4'
cause of low total strength and sensitivity to skin moisture Optimum ease of handling was noted for f i l m in the range 20 t o :30p thick. Folding endurance decreased when the filni thickness was either above or below this range. For example, a film 11p thick lacked the general toughness needed in the Schopper fold tester and broke as soon as tension was applied t o the specimen (zero folds) whereas films 60, 7 5 , 115, and 1iOp thick gave respective folding endurance3 of 135, 122, 18, and 4 Bchopper double folds. Bursting resistance was directly proportional to film thickness; internal tearing resistance increased a t a eoniewhat greater rate than thickness. CT O F ADDED 4IlYLOPECTIN ON F I L I I PROPERTIES
~
To promote uniformity of processing operations and to achieve uniformity and quality of products, it is conimercial practice t o control, where possible, the degree of polymerization of filmand fiber-forming materials within certain desired ranges. Therefore, variation in the properties of amylose films, resulting from difference in the molecular weight of t,he amylose, was investigated. Films were cast by the standardized procedure given, from amyloses varying in intrinsic viscosity ( a t 25.1" C. in 1 N potassium hydroxide) from 0.38 (degraded corn) t o 3.52 (tapioca), representing degrees of polymerization of approsimately 230 to 2100. These degrees of polymerizat,ion were crtlculated from the Staudinger equation [ q ] = k M , in which the constant was derived froin three amylose samples, the molecular weights of whose triacetates had been measured osmotically by W.Z.Ilassid. Since there was appreciable variation in the c:tlculated value of I;, an average value was used, and the given degrees of polymerization should be considered significant only in a relative sense. Data on the properties of films from the various arnylo3-e samples are summarized in Table 11. Properties most sensitive to changes in molecular weight &-erehaze, folding endurance, wet tensile strength, and wet ult,imate elongation. Although the haze of films from amylose of a degree of polymerization greater than 600 [7] (approximately 1.00) averaged from 8 to 9%, those films from lower molecular weight amylose were much Icss transparent. When maximum film clarity is desired, it is thercfore important t o select an amylose which has not been too cstensively degraded. ' Folding endurance remained generally high for films prepared from amyloses with intrinsic viscosities greater than unity, and a decline in film flesibility occurred with more degraded amyloses. Wet tensile strengths were low, ninking the wet films difficult t o handle and the measurements IWS esact. However, a trend toward deterioration below a degree of polymerization of 600 can be noted. .imylose film prepared from inaterial of a degree of polymerization of 230 had so littlib wet strength that the gel critcked during d -ing, and a coherent' sheet could not be obtained. The dry teri le strength reported (1.9 kg. per square mm.) +as determined on a fragment of sufficient size for the purpose. The wet ultimate elongation showvcd the most regular and consistent variation with degree of polymerization of any property tested. This factor may be of particular importance in contemplat.ed esperiments on the spinning of fibers from amylose, where drawing of the n-et gel may be ncci:psary. I n contrast n-ith the forcgoiiig propcrtics the dry tensile streiigt 11. burst strength, and tear resistance n-ere less affected by niolrc~\ilm.
L-nlike amylopectin triacetate ( l a ) corn amylopectin itself iornietl a self-supporting film of brilliant clarity, good tensile strength ( a t 50% relative humidit,y), and immediate solubility in water. It was, therefore, of interest to prepare films with varying proportions of nniylose to amylopectin. Test. results on these films which were cast as previously described are summarized in Table I. Flesibility, burst resistance, x e t and dry tensile $trengths, and elongation decreased with decreasing amylosr content, indicating the inherently poorer mechanical properties of the branched chain amylopectin. Tear resistance was variable and did not, show a definite trend. Haze reached a niasiinum a t approyimately 40% amylose content. The reason for the increased haze of. films containing intermediate amounts of amylosr is not known. Unfractionated corn 3tarch film. ureoared from starch in whiah the granule T-LBLL IT. PROI'ERTIES O F Frr.\ia FRO\[ . i \ i Y l ~ ) S k ; S \-ARIISG IS structure had been completely ( 5 0 z relative huinidity and 72' I'.) broken down by honiogenization of its hot paste in :L i'il at Strength, Tensile Iodine 2 5 O C. \Taring I3lendor, had the prophffinity. in 1 N Haze. Kg./%. ~ m . Tb erties espected of a film con-iniylose .\Ig./G. KO11 DP' % Dry Ket Dry Wet taining about one fourth amyTapioca 18i 3.52 2110 4 G.2 0.13 13 138 ti-liite pntato 197 2.69 1610 11 .1.9 0.21 9 5i loFe and three fourths amyloKheat 193 LO5 1230 5 6 6 0.15 13 19 S5reet potato 191 2.03 1215 6.4 0.22 14 42 pectin Tapioca 189 2.01 1203 J i.0 0.18 18 38 Films containing lees than Tapioca 190 1.53 91.5 12 7.2 0.19 14 18 Corn 184 10 7.3 0.20 13 13 82G 1.37 4070 of amylose adhered more Corn 191 0.84 50.1 26 6.8 0.10 6 6 CornC 198 0.73 433 43 ,.I 0.02 7 3 tightly to the casting eurfacc Cnrnd 183 0.70 420 2i 7.4 0.06 8 3 Corn e 163 0.67 -100 :33 7.6 0.10 10 6 and could not be removed from Cornd "02 0.52 310 58 5 . 3 0.05 6 4 glass even when the latter hat1 CornC 197 0.44 265 51 6.6 ,.. 9 . been treated with stripping Cornd 180 0.38 230 87 1.9 , . . 1 .. ' Demree of polymerization calculated f r o m the eqllation [ V I = 1.67 X 10 3 D P agent as described. Such films CoFrected t o a thickness bf 0.025 mm. assuming direct proportionality. are removable from silicone;Fractionated Fractionated a t acid pH. after thinning of paste with a-amylase. treated chrome plated sure From 70 fluidity commercially acid-modified starch. faces. A
917
A
\IOI.F;Cl-l, \It S I Z l , :
& ~ & ~SDouble ~c h o&i ) i ~ r .\lullen
Kliiiendorfh Tear ,
So.
Burst Pointah
770
15
8
710 700
19
10 10 I)
~oldu,
690
1G 20
830
16
660
17
800 640
21 19 14 28
io0 490 830 120 R?
..
10 12
..
Graills
8
e
;
; 5 3
..
918
INDUSTRiAL AND ENGINEERING CHEMISTRY
1800 weight rhanges and shon et1 no great decline in values uni 11 I the degree of polymerization 1600 1 was in the range 230 to 266 The chief differences noted in the solutions of low molecular weight amyloses (besides reduced viscosity a t equivalent concentration) were their greater rapidity of gelation and higher turbidity. DependinK on the intended purpose the, former property may be i i i i advantage or a handicap The, gels from the lower molecu1:ir Reight amyloses had a mole granular appearance and feel, properties which are proha\,l\ related to their lover wet tensile strengths. It is of practical 200 importance that nmj lose from unmodified corn starch, the. most readily available coni0 100 200 ELONGATION , PERCENT mercial starch in the United States, is of sufficiently high F i g u r e 2. Stress-Strain Curves of Corn .iin>-lose degree of polymerization to Films Containing Indigive films as strong and flexible cated Amounts of as any prepared in this study. Glycerol I n the amylose series, the degree of polymerization (230) re. . quired for coherent film forniation 11as higher than i n the ceilulose nitrate series (about 30) ( 7 ) or the cellulose acetate series ( 3 0 , (10). Similarly, curves in which physical properties are plotted against degree of polymerization show plateaus a t higher drgree of polymerization values in the amylose series. Ho~vcver,astated above, degree of polymerization values may requirt, rhangc, as further data become availahle.
EFFECT OF ULTR4VIOLET LIGHT ON PROPERTIES Ob AMYLOSE FIL\I
.illiylose hlm, unplasticized cdlophane, and a sample 01 powdered corn amylose were placed 20 inches from a Type -4 Hanovia high pressure, quartz mercury arc lamp operated withnut a filter. The tube had a luminous length of 4.5 inches, dianieter of 20 mm., and operated at 550 watts. T h e films decreased in flexibility during the irradiation, as follows:
4oor;y.l ;
EFFECT O F HEAT TREAT.IlENT IN PREPARATION Ok' AMYLOSE FILM
The preparation of aiiiylore film by a cont,inuous c a e h g procedure would, of course, involve drying a t elevated temperature. Preliminary study indicated that heat. when applied in the presence of moisture caused distinct increases in the wet strength and flexibility, and a decrease in the haze of films prepared from both niotlified and uiiinodified amyloses. Comparative values of' films dried (a)a t 70" F., and ( B ) in a steam autoclave a t 120" C. for 15 ininut,es followed by an air stream introduced into the :tutorlave for ,5 to 10 iiiintite.s arr its follotvs:
Haze,
%
Unmodified corn amylosc Treatment A Treatment 13 Amylose f r o m a-amylase modified starch paste Treatment A Treatment B
51-10 4
58 4
\\-et lensile Strength Kg /Sa hlm.
Xo.
Schopper Folds
Time, Hours 0 1 2 8 16
30
0.50
0.05 0.37
600-900 2700 124
630
-
No. Schopper Double Folds D u Pont 300 PUT-0 cellophane 960 660 8.3 0 500 200 "0 19 110 0 1
A iiiylose
n
1
lfter 8 hours' exposure. the sample o r pondered am) low not only decreased in intrinsic viscosity froin 1.31 t o 0 58 but also had its iodine number lobrered from 190 to 166, indicating the possible formation of branched molecules Both of these factors ere probably involved in the observed emhrittlenient of the film. The resistance of the amylose film to ultraviolet light was of the same order of magnitude a i that of the unplasticized ccllophane. EFFECT O F GLYCEROL A S PLhSTICIZEK OX PROPERTIES O F A l l Y L O S E FILM
'rhe flexibility and ultimate elongation of unplasticized amylose tilm ( a t 50% relative hnniidityj appear sufficient to make added ~~lasticizer unnecessary for many purposes. If greater ultimate clongat,ion or a softer "fecl" is desired, the addition of glycerol, iiiixed with the hot solution iniinediately before casting, n-ill wcomplish this, of course wit,h t,he loss of some tensile strclitgth ~'l'ahle 1111. The increased aniount of plastic flow befor63 rupture, which apparently occurrcd xithuut any tendency for t lie film t o btzcome oriented in the direction of the test, is show11 in E'iyurti 2. The folding endurauce of the plasticized film^. lis rticwured on the Schopper machin?. showed a decline tvhicti may l)e rcalateii to lowering of the tensile strength. Burst anti rear rwistancca of the plasticized filnis were affected to a lesser extent, rvhereiis the haze was unchanged by the varying amounts of glyc(8rol. Other plast,icizcrs which tn:i>, prow, more effiriciii are Iwiiig r i , . G t n l .
\\ ater 4 bsorption.
,-
~
0.2
Vol. 43, No. 4
'23 130
.. , . .
Although some improvemerit was noted when n-et ireshly cast gels were subjected t o dry heat. the change was not so marked. D r y tensile strength appeared to be improved by steaming but t o a lesser extent than the properties noted. The autoclaved film from unmodified amylose retained a B type x-ray pattern with somewhat sharper rings than the original untreated film.
~
~~~~
~
~~~~~~
~~~~
~
. w I ~ L i c . ~ m os. x
K e ~ vfilm compositions can rnsily be prepared by the addition of water-dispersible substances to the amylose solution prior t o casting. For example, if pharmaceutical uses materialize, based on the biological absorbability of amylose film, any medicament stable to hot water for short time periods could easily be incorporated. For such uses, it is noteworthy that amylose film is stable under typical sterilizing conditions-immersion in '70% ethanol or autoclaving a t 15 pounds per square inch gage steam pressure. Colored amylose films for achieving decorative effects are also easily prepared by the addition of suitable dyes and pigments.
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
The authors are indebted to R. J. Dimler and W. Z. Hassid tor several of the amylose samples used, to Nison Hellman for niaking and interpreting the x-ray diffraction patterns of the films, and to E H. Melvin for the ultraviolet absorption curves of the films. The authors also wish to thank R. de S. Couch of General Foods Co., Hoboken, N. J., for his report on resistance of amylose film to coconut oil. 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.
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). RECEIYEDOctober 23. 1950. Work performed a t Northern Regional Research Laboratory, one of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. R Department of Agriculture. Report of a study made under the Research and 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
UFFING 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. The 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 to a soap whose solubility, like that of many other colloidal electrolytes, is affected markedly hy the presencc:
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