INDUSTRIAL AND ENGINEERING CHEMISTRY
430
help of F. H. Wright and C. L. Thiele of the Jet Propulsion Laboratory of the California Institute of Technology isacknowledged in connection with the measurements of the axial fluctuating velocities. The constructive criticisms and suggestidas of H. W. Liepmann and W. N. Lacey in connection with the review of this manuscript are acknowledged. NOMENCLATURE
isobaric heat capacity, B.t.u. per (pound) ( ” F.) = differential acceleration of gravity, feet per square second distance from center linemormal to flow, feet = distance from center line to boundary of channel, feet thermal flux, B.t.u. per (square foot) (second) = weight rate of flow, sounds per second pressure, pounds per square foot = temperature, ” F. = velocity, feet per second = velocity parameter, u/u* p feet per second = friction velocity, m = maximum velocity, feet er second = distance along channel, Peet = distance from lower wall normal to axis of flow, feet = distance from nearer wall = distance between channel walls, feet = distance parameter, YdUL / v = distance from side of channel, feet = eddy conductivity, square feet per second K, square feet per second 3 total conductivity, cc = eddy viscosity, square feet per second total viscosity, srn Y , square feet per second = time, seconds thermometric conductivity, square feet per second = = kinematic viscosity, square feet er second = density, pounds (square seconds7 per (foot)4 specific weight, pounds per cubic foot = shear, pounds per square foot = shear a t boundary of channel, pounds per square foot = turbulent Prandtl number = Reynolds number
CP =
d
f -:
l o
Q =
L t u u+ u* Urn
x
Y vd
yo
2/+
z 4
-e,
“= em
e K
v P 0
r 70
Pn Re
+
+
LITERATURE CITED
(1) Bakhmeteff, B. A,, “The Mechanics of Turbulent F l o ~ , ” Princeton, N. J., Princeton University Press, 1941. (2) Bridgman, P.W., “Dimensional Analysis,” New Haven, Conn., Yale University Press, 1937. (3) Corcoran, W. H., Page, F., Jr., Schlinger, W. G., and Sage, B. H.. IND.END.CHEM..44. 410 (1952). (4) Corcoran, W.H., Roudebush,‘B., and Sage, B. H., Chem. Erie. Progress, 43, 135-42 (1947). (5) Deissler, R. G.,Natl. Advisory Comm. Aeronaut., Tech. Note 2138 (1950). (6) Gebelein, H., “Turbulens,” Berlin, Julius Springer, 1935. (7) Jakob, M., “Heat Transfer,” Vol. 1, New York, John Wiley & Sons, 1949. (8) von K&rm&n,Th., J. Aeronaut. Sci., 1 No. 1, 1-20 (1934). (9) von KBrm&n,Th., Mech. Eng., 57, 407-12 (1935). (10) von K&rm&n,Th., Trans. Am. Soc. Mech. E m s . , 61, 706-10 (1939). (11) Laufer, J., Natl. Advisory Comm. Aeronaut., Tech. Note 2123 (1950). (12) McAdams, W. H., “Heat Transmission,” New York, McGrawHill Book Co., 1942. (13) McAdams, W. H.,Nicolai, L. A., and Kennan, J. H., Z ’ T ~ ~ O . Am. I w l . Chem. Engrs., 42,907-25 (1946). (14) Nikuradse, J., Forsch. Gebeite Ingenieurw., 3, supplement, FOTSChUWShej?, NO. 356, 1-36 (1932). (15) Page, F., Jr., Corcoran, W. H., Schlinger, W. G., and Sage, B. R., IND.ENG.CHEM.,44, 424 (1952). (18) Page, F., Jr., Schlinger, W. G., Breaux, D. K., and Sage, B. R., Washington, D. C., Am. Doc. Inst., Doc. No. 3294 (1951). (17) Prandtl, L.,Physik. Z . , 29, 487-9 (1928). (18) Rouse, H., “Fluid Mechanics for Hydraulic Engineers,” New York, McGraw-Hill Book Co., 1938. (19) Sherwood, T. K.,and Woertz, B. B., Trans. Am. I w t . Chem. Engrs., 35, 517-40 (1939). (20) Skinner, G., thesis, Calif. Inst. of Technology, 1950. (21) Wattendorf, F. L., and Kuethe, A. M., Physice, 5, 153-64 (1934).
.-
-
~
I
RECEIVED November 7, 1950. For material supplementary to this article order Document 3294 from American Documentation Institute, 1719 N St., N.W., Washington 6, D. C., remitting $1.00 for miorofilm (images 1 inch high on standard 35-mm. motion picture film) or $3.60 for photocopiea (6 x 8 inches) readable without optical aid.
Subscripts 1 = lowerplate u = upperplate
EngFnering
Vol. 44, No, 2
Precoat Filter Filtration of Phosphate-
Process development
Defecated Affination Sirup I
L. E. WEYMOUTH
AND
R.
S. MONTGOMERY’
JOHNS-MANVILLE RESEARCH CENTER, MANVILLE, Ne J.
W
HILE the use of diatomite filter aids in the clarification of affiation sirup is widely adopted in the sugar refining industry, i t is a relatively difficult type of filtration, because of the character and amount of colloidal impurities present. In the treatment of afEnation sirup generally, filtration rates are low, filter cycles short, and filter aid consumption relatively high. The treatment of a f i a t i o n sirup has been considered as a possible useful application of the Oliver Precoat filter, since this type of filter is adapted to the handling of many liquids that are difficult to filter. I n this filter, a precoat of straight diatomite filter aid is formed on a rotating drum under vacuum until a layer Present address, The Daw Chemical Co., Midland, Mich.
of as much as 2 inches in thickness is formed. In use, the turbid liquid to be clarified is passed through this rotating precoat layer, from the surface of which a scraper, automatically advancing with each revolution of the drum, removes the accumulated solids plus a very thin layer of the precoat itself, and thus presents a fresh filtering surface to the sirup. A preliminary study of the Oliver Precoat filter filtration of affination sirup in this laboratory was described by Cummins and Morris (1). This earlier work indicated definite advantages for the use of this filter in the processing of afKnation sirup with use of phosphate treatment. The phosphate-defecated sirup showed both better clarification and faster flow rate than was obtained
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
February 1952
in preooat filter filtration O S untreated sirup, and wlor removal was approximately 25% with 0.10% phosphorus pentoxide treatment. Filtration rates of treated sirup st 2 minutes per revolution drum speed (IZinch diameter drum) were 2 to 3 gallons per square foot pcr hour, clarities 20 to 30 fookandlos ( d ) , and filter Rid consumption 1.71 to 1 . 9 C ~ oon Brix solids. In view of the favorable preliminary results, it was considered that further study of the filtration of phosphatedeiecated affination sirup was warranted in order to investigate more thoroughly the possible merit of such operation and to establish the most favorable conditions for treatment. EQUIPMWYT AND MATERIALS
cloth together with l0-mevh Monel backing screen was used as the filter aid support. Submergence of filter drum wns upproximately 55%. It was equipped with a variable speed drive, so
431
difficulty WBB experienced in obtaining uniform samples from these &gallon wntainers because of solids separating out of the sirup. Far this r e w n Sirup I1 was diluted to 67' Brix belore heing placed in the refrigerator and better results were obtained hy this procedure EXPERIMENTAL
PILOSPIUTE TREATMENT. A representative sample of siru
was taken from a &gallon contsiner and heated to ahout 60'
dl
with mechanical stirring. At this time the calculated amount of dilute orthophosphoric acid (50 grams of phosphorus pentoxide per liter) was added and then a dilute suspension of calcium hydroxide ( 10 grams of calcium oxide per liter) was added until a pH of 7.2 was reached. Water was then added to reduce the density to 55" Brix. Generally very little water was added a t this time. hour a t low heat with the The sirup then was allowed to stand mechanical stirrer running at low speed to avoid dispersing of the phosphate fioc. Before startins the filtration, the Brix was again adjusted by adding more n'ater If required. In the runs where there was no phosphate treatment, the prooedure was the same except that water was added instead of dilute phosphoric acid and calcium hydroxide. A small amouut of calcium hydroxide was required to bring the wtreated sirup to pH
7.2. I'RUCOAT FILTGR FIL~TION The . Blter drum was prewated water (8 grams per liter) starting of 20 inches of 6ercurv when aDo;oxhatelv 1.2-in-c was obt&ned. The steam on filier pan jacket was tmned &only
which period the preeoat had almost stopped shrinking, thd te& perature had been adjusted to 82' C., and a steady state had been reach&. At this time the run was started. During the first 15 LFFiWATIOH SlRUP I . HlFlO SUPER-CEL. 0.008' CUT, DRUM SPEED 80 SEC/RfV
Figure 1.
Laboratory Rotary Vacuum Precaat Filter
thrd any devired drum speed within reasonable limits could be obtained. The knife cut could also be changed by changing the sprockets which advance the knife. The temperature was maintained by means of a steam jacket on the filter pan and the supply tank was heated by means of a steam coil. The sup ly tank was equipped also with a meohanical stirrer running a t a?ow s eed to maintain a uniform suspension with minimum breaking&wn of the calcium phosphate floc. The lnboratory service line provided the vacuum for the filter. The vacuum line wasnot connected dwectly to the filter but p e d through a 10-gdlon sur e tank fitted with a gage for reading vacuum and a eontrolldi leak for its adjustment to constant 20 inches of mercury. The filtrate waa collected in two 1-liter oalibrated glass receivers that were wed alternately. The pressure filtrations were carried out OD a 4 u n i t bomb-typefilter(z?). Regular Sounee cotton duck filter cloth was used. Clarity readings were made on the Johns-Manville Research Tyndallmeter (e),and are erpreqsed as footcandles extrapolated to zero depth of liquid. The Brlx of samples wm determined by means of an Abbe refractometer, the pH hy means of a lass eleetrode Beckman pH meter, and the color on a Coleman%odel 14 npectrophotometer using cells with a 1-mm. effective depth of I,nnirl __l._l_
Tests were run on two 50-gallon lots of affinstion sirup ohtained a t different times from a nearby refinery snd desi nated here 88 Sirup I and Siru 11 Although the two lots showei some differencesin color, in egeciof phosphate treatment, and in filtering characteristies, they were believed to he in the range of a typical affination sirup. Sirup I gave an apparent purity wefficient of 85.3 by Home's dry lead method. Sirup 11 gave un a p parent purity coefficientof 88.2. The second lot waa darker ID wlor than the first. Both sirup were of approximately 78" Brix when obtained. Sirup I was mured thoroughly with addition of 2 mi. of formaldehyde per gallon and divided into 5-gpll?n quant.;t,iaq
ahbh
a-1-
d,,rarl
in " - - C ~ - - - - L
)'.
I
v i
I
I
I 0 I$
0
*I
0
I
I
,I
PzOI TREATMENT
Figure 2.
Effect of Varying Phosphate Treatment Affinstion Sirup 1, HyRo Svpa~eel 0.805inch cut Drum a&. 95 Iremnde por nroiution
or 20 minutes of the run, the mechanical advance of knlie was supplemented by some hand advance, hecause of a slight further shrinkine of the DPeN1Rt. After this time onlv " mn.hanical knife a d v e n c e k use& The temnerature of the sirun in ttLP trouph was maintained a t 82' C. hy'controiling the steak to &e ste-& ~
~~
~
to the sirup in the supply-tank as required. Tbk vaeuu"m w? maintainedat20inohesofmPrritrv + 1 inrh h . r * * - - - P ---.--a*
INDUSTRIAL AND ENGINEERING CHEMISTRY
432
,
I t
50
II ' t1
d 2
I
COLOR REWOVAL
FILTER A I 0 CONSUMPTION
1.00
I
60
80
DRUM SPEED
-
x
40
2 0: w
1
I
w -I n = U
95
Vol. 44, No. 2
treatment-namely, 0.20% phosphorus pentoxide. Results are shown in Figure 5. Hyflo and Celite 503 (a higher flow-rate grade) gave practically equivalent results, with no advantage indicated for the 503. Celite 512 (a lower flow-rate grade than Hyflo), however, gave a somewhat lower filtration rate with slightly better clarification than Hyflo or 503. A number of runs With Celite 535 (a faster flow-rate grade than 503) under comparable conditions were triedibut no satisfactory run was obtained. The 535 precoat showed a tendency to develop leaks and holes and to permit penetration of the phosphate floc into the precoat. However, during portions of runs with 535 whore fairly satisfactory operation was obtained for a time, filtration rate and clarity were not greatly different than observed with Hyflo and 503. In addition, Hyflo and 503 were compared with 0.10% phosphorus pentoxide treatment and under this condition also showed little difference in performance.
SECONDS PER R E V O L U T I O N
Figure 3. Effect of Drum Speed on Affination Sirup I1 with 0.10% Phosphorus Pentoxide Hyflo Super-cel 0.0025-inch cut
were found to affect the rate relatively little compared to small changes in temperature. Runs were of 2 hours' duration. The volume of filtrate and precoat thickness were observed every 10 minutes and a composite sample of the filtrate was taken every 30 minutes. Flow rates were computed for each 10-minute period using actual area existing on the filter at that time. The pH, clarity, and the color, as compared to a filtered untreated sample of the same ailination sirup, were observed on the 30-minute composite samples. This untreated sample for color comparison was a t p H 7.2 and 55' Brix and had been heated and otherwise treated in the same manner as the phosphate-treated sirup. The per cent color removal was observed a t three different wave lengths because it was found that the average of these three colors was approximately equal to the average color over all the visible range. The wave lengths used were 480,550, and 620 millimicrons. PRESSURE FILTRATION. Sirup was prepared in the same manner as for the precoat filter tests, except that the filter aid (either 0.9 or 1.8% on Brix solids) was added directly to the batch. Initial 5-pound-per-square-inch pressure was increased 1 pound per square inch per minute to a 55-pound-per-squareinch maximum a t 50 minutes, then the test continued a t this pressure for balance of a 2-hour run. TEST RESULTS
With Sirup I, EFFECT OF VARY> VQ PHOSPHATE TREATMENT. best results in general were obtained with 0.20% phosphorus pentoxide, since, the highest filtration rate was obtained with this treatment-namely, 4.08 gallons per square foot per hour-and, consequently, the lowest filter aid consumption, or 1.34% on sugar solids, and color removal of 32y0 was almost as high as the 34y0 obtained with 0.30% phosphorus pentoxide. Clarification was slightly inferior to that obtained a t a somewhat lower rate with 0.10 and 0.30% phosphorus pentoxide, although the difference was minor, Under comparable conditions with no phosphate treatment, there is no removal of color, and clarification is much inferior and flow rate lower than obtained with phosphate treatment. The 0.05% phosphorus pentoxide treatment is indicated as too low for best results although this amount is sufficient to produce a large improvement in clarification and some increase in filtration rate as compared to no phosphate treatment. Results are shown in Figure 2. Figures 3 and 4 show comparison of precoat filter filtration of phosphate-treated Sirup I1 with Hyflo combined with 0.10 and 0.20% phosphorus pentoxide treatment. There was little difference in performance between the two treatments with exception of slightly better clarification and color removal with the heavier treatment. EFFECT OF FILTER AID GRADE.The next factor investigated was grade of filter aid, using the optimum amount of phosphate
TABLE I. EFFECT OF HYFLO BODYFEEDFILTER AID Filtration of affinrttion Sirup I 0,005-inch cut 0.20% PZOS Drum speed, 95 seconds per revolution Hyflo Precoat Only, Hyflo Precoat Plus 0.50% No Body Feed Hyflo Body Feed Filtration Clarity, Filtration Clarity, rate, gal./ footrate, gal./ footMinutes sq. ft./hr. candles Minutes sq. ft./hr. candles 3.94 0-30 19.2 0-30 4.10 16.8 30-60 4.04 18.4 4.04 16.8 30-60 60-90 4.13 19.7 4.66 18.0 60-90 90-120 4.21 22.6 90-120 4.32 17.1 0-120 4.08 20.0 0-120 4.29 17.2 Filter aid consumption Filter aid Consumption on Brix solids, 1.34% on Brix solids, 1.71%
EFFECT OF FILTER AID BODYFEED. Effect of 0.50% Hyflo body feed is shown in Table I. While both flow rate and clarity were improved slightly by the body feed, the difference was not large and filter aid consumption on Brix solids was increased by 0.37% with use of body feed. EFFECT OF DRUM SPEED.The previously described tests all were run a t a constant filter drum speed of 95 seconds per revolution. The next factor investigated was the effect of increasing and decreasing this drum speed, as shown by results in Figure 6. Within the range 80 to 115 seconds per revolution, filtration rate was almost directly proportional to drum speed (inversely proportional to seconds per revolution), so that filter aid conI
,
1
I
\
F I L T E R A I D CONSUHPTION
CLARITY 60
80
DRUM SPEED
- SECONDS P E R
95
REVOLUTION
Figure 4. Effect of Drum Speed on Affination Sirup I1 with 0.20% Phosphorus Pentoxide Hyflo Super-cel 0.0025-inch cut
,
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1952
433
TABLE 11. PRESSURE FILTRATION OF AFFINATION SIRUPI1 WITH 0.90% HYFLO Minutes 0-30 30-60 60-90 90-120 30-120
No Phosphorus Pentoxide Filtration rate, Clarity, gal./sq. ft./hr. foot-candles 1.33 213
Color removal, %
1.08 0.75 0.60 0.81
43.6
0
Minutes 0-30 30-60 60-90 90-120 30-120
0.15% Phosphorus Pentoxide Filtration rate, Clarity, gal./sq. ft./hr. foot-candles
0.95 0.60 0.41 0.34 0.45
TABLE111. PRESSURE FILTRATION OF AFFINATION SIRUPI1 No Phosphorus Pentoxide Minutes 0-30 30-60 60-90 99-120 30-120
Filtration rate gal./sq. ft./hr.’ 12.80 5.37 3.00 1.96 3.44
Clarity, foot-candles 127
20.6
Color removal, %
0
Minutes 0-30 30-60 60-90 90-120 30-120
Minutes 0-30 30-60 60-90 90-120 30-120
Color removal, %
49
sumption remained practically constant, Clarificition was slightly better a t the lower rate and drum speed, although difference was small and probably within experimental error. Tests on Sirup I1 with drum speed increased to 60 seconds per revolution as compared to 95 seconds per revolution (Figures 3 and 4) show the filtration rate considerably increased a t the higher drum speed, almost in proportion to the increase in drum speed, so that the filter aid consumption on sugar solids was only very slightly increased a t the higher filtration rate. EFFECT OF DEPTH OF CUT. The 0.005-inch cut used in the initial tests was later reduced to 0.0033 inch with substantial reduction in filter aid consumption, since the flow rate was only slightly reduced. Figure 6 shows test results with the reduced cut. With Sirup I1 the technique of precoat filter opeta-
130
18.8
WITH
51
l.80Y0 HYFLO
0.15% Phosphorus Pentoxide Filtration rate, Clarity, Color regrtl./sq. ft./hr. foot-candles moval, % 1.20 45.3 0.92 0.69 0.52 0.71 18.1 49
TABLEIV. PRESSURE FILTRATION OF AFFINATIONSIRUPI1 1.8% 503 1.8% Hyflo Filtration rate Clarity gal./sq. ft./hr.’ foot-candies 1.20 45.a 0.92 0.69 0.62 0.71 18.1
Color removal, %
WITH
1.8% HYFLOAND
1.8% 503 . Filtration rate Clarity, Minutes gal./aq. ft./hr.’ foot-candles 0-30 2.11 132 30-50 1.72 60-90 1.38 90-120 0.95 30-120 1.35 27.0
Color removal, %
52
tion was further improved to reduce the knife cut t o 0.0025 inch with increase in the economy of filter aid use as shown in Figures 3 and 4. PRESSURE FILTRATION. Tables I1 and I11 show pressure filtration results’ with Sirup 11, with and without phosphate treatment, and with 0.90 and l.SOYo filter aid. Without phosphate treatment] a low filtration rate and inferior clarification were obtained with 0.90% Hyflo. With increase in Hyflo to 1.8%, however, flow rate and clarity are improved to a degree comparable to that obtained in precoat filter filtration of phosphate-treated sirup, but with the disadvantages of higher filter aid consumption, shorter cycles, and no color removal. With phosphate-treated sirup, a low filtration rate was obtained in pressure filtration with Hyflo, even with increase in amount of
I
I
80
FILTER A I D GRADE
Figure 5.
Comparison of Filter ,Aid Grades
AffinetionSirup I
0.20% phosphorus pentoxide
0.OBCinch cut D r u m speed. 95 seoonds per revolution
95
DRUM SPEED
1
115
- SECONDS PER REVOLUTION
Figure 6. Effect of Drum Speed on Affination Sirup I with 0.20% Phosphorus Pentoxide Hyflo Super-cel
0.0033-inch cut
INDUSTRIAL AND ENGINEERING CHEMISTRY
434
filter aid to 1.80%, although clarification was equal to that obtained in the precoat filter filtration. Table IV shows test results also with 1.8% Celite 503 with phosphate in pressure filtration. Filtration rate is increased as compared to Hyflo, but with inferior clarification and with relatively low filtration rate compared to precoat filter filtration of the same treated sirup. CONCLUSIONS
A favorable amount of phosphate treatment corresponded to 0.20% phosphorus pentoxide on Brix solids. \Vith one sirup there was little difference between 0.20 and 0.10% treatment, but with the other lot filtration rate and color removal were appreciably better a t 0.20% phosphorus pentoxide. Comparison of different filter aid grades showed approximately equal performance for Hyflo and for 503, with 512 giving a lower rate and 535 offering some mechanical difficulties due to coarseness (although these might be overcome in practice) without giving an increased filtration rate. Advantage for use of Hyflo body feed in the precoat filter filtration was minor and filter aid consumption was increased with use of the body feed. Filtration rate increased in proportion to drum speed from 115 to 80 seconds per revolution, then somewhat more slowly to a speed of 60 seconds per revolution. Filter aid consumption was practically constant in the 115- to 80-second-per-revolutionrange, increasing slightly a t 60 seconds per revolution. Pressure filtration tests indicated that with use of sufficient filter aid and no phosphate, clarity and flow rate equivalent to precoat filter filtration with phosphate could be obtained. The pressure filtration, however, offers the disadvantages of not removing color, of higher filter aid consumption, and shorter
Vol. 44, No. 2
cycles, although offering advantages of using lower cost e q u i p ment and the saving in cost of phosphate treatment. Pressure filtration of phosphate-treated sirup gives a low filtration rate even with use of relatively large amounts of filter aid, so that it does not appear practical. Knife cut was gradually reduced during the course of these runs to 0.0025 inch, thereby improving the economy of filter aid consumption. In practice it may be possible to reduce this cut somewhat further, although in the earlier work ( 1 ) attempt to use 0.002-inch cut was unsuccessful and the relatively high filter aid consumption in these runs was largely due to use of B 0.004-inch cut. On the basis of the present series of tests, a favorable operating condition to be recommended for larger scale runs would be the use of 0.20% phosphorus pentoxide with Hyflo with 0.0025inch cut and no body feed. Most favorable drum speed for larger equipment cannot be predicted reliably from these tests and would need to be determined, There may be other practical factors, also, in the larger scale operation that would affect performance significantly. However, the advantages of color removal, filter aid economy, and long cycles with precoat filter filtration appear of real importance and warrant consideration for plant trial. LITERATURE CITED
(1) Cummins, A. B., and Morris, D. C., Facts about Sugar, 33, 23-7 (1938). ( 2 ) Cummins, A. B., and W e y m o u t h , L. 392-8 (1942).
E., IND. ENG.CHEM.,34,
RECEIVED August 1,1951. Presented before the Division of Sugar Chemistry at the 119th Meeting of the AMERICAN CHEMICAL SOCIETY, Boston, Mass.
Film for Food Plastic films and food packaging should go well together, if statistics are a n y indication. At present 65y0 of packaging materials are used i n connection with food products. Selling point of plastics is the substantial savings t h a t may be realized b y reduction of the average 6,9'% loss i n weight (through moisture evaporation) of fresh fruit and vegetables while standing on the grocer's shelf. Cost and performance seem t o be t h e criteria when choosing plastics suitable for food packaging. I n the case of performance, oxygen permeability is of paramount importance. According t o A. L. Bayes of Linde Air Products Co., oxygen permeability for a given film is directly related t o moisture absorption properties and t o the type of plasticizer incorporated. H e concludes t h a t the relationship between moisture absorption and gas transmission may represent the key t o the development of packaging materials with low oxygen permeabilities. Bayes has obtained d a t a (Table I) on various types of commercial packaging materials and found t h a t vinylidene chloride is the only single film which exhibits extremely low oxygen permeability, as determined a t 100" F. and 7570 relative humidity. Bayes also has shown t h a t oxygen-impermeable barriers could be obtained with laminates of transparent plastic films and metal foils. R. A. Barkhuff, Jr., of Monsanto Chemical Co., indicates that plastic films must be made available a t a substantially lower price i n order t o reach forecast sales levels. He also points t o the probability t h a t polyethylene and styreneF; =3
4
isobutylene films, now produced in 1.5-mil thickness, will follow the lead of cellophane and b e available as 1-mil and thinner films (Table 11).
TABLEI. OXYGENPERMEABILITY OF COMMERCIAL PACKAGING FILMS Type of Packaging hlaterial Glassine Vinyl ohloride Polyethylene Rubber hydrochloride Cellophane Vinylidene chloride Vinylidene chloride Vinylidene chloride Modified vinylidene chloride Polyethylene coated kraft pa.per ~~~~
~~
~
~
~
Thickness of Film, Inch 0.0010
0.0010 0.0012
0.0010
0.0005 0.0015 0,0020 0.0010 0.0054
On Permeability, Cc./S Inch/24
.
IIOLI,,
0 47
0.19
2 60
0 55 0.09 0.007 0.0008
