Quartermasters Subsistence Research Laboratory, Chicago, 111 _ _ ~ ____ .I
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is moldy, dry, hxsd, tainted, infested with UiireeVilB, or eontaminated with B M'EW gas cannot be used t o ~~x~~~~ af-
ficieneg, The constant thought of this l a b o ~ a f o ~i sy that, no matter how great %HIE calorific valrxe ox-how adequate the vitamin content of the food mag be, it will riot benefit the soldier if he fails to eat it. 1% food i a allawed to spoiL, not only do we lose valunblo material that has been transported in precious ship bottoms, but thcre is a possibility of iosiarg the troops for which it was inlendecb m*d, s ~ strategic positions. It i s absolutely essential that the Army's any lives depend 0x1 Et,, fond be properly packaged, Ext,reme conditions are certain to be exacou*dered. TkBC food tho Army Quartermaster Corps buys must bc> packaged to witiistand t h e rigors of both arctic and tropical climates. It i s irnpossibie to determine whether B shipnrcnt of food, on i t s way to a port of embarkation, is p i n g to bs sent north RIP south, or shifted from one to t h e othar after initial slsipxnent. It depends upon what t h e situation at the mome:at dictates. Therefore, packaging materials must withstand t e ~ ~ for -28" to +%zoo F.or higher, and the humidities affray range from the high humidities of the tropics to t h e lower humidities of dry climates. Protection must be provided against moistme vapor, mater, odor transfer, greetse transfer, klseCt iPlfestation, and rats. BlbUe to the Plt%tUK Ob' %hah X l f & ~ $ § ~ g only ~ nthe ~ poorest ~ ~ t docks ~ and warehouses c x m be expected, Much unloading 18 earried out rrnder cover of darkness, possibly in the surf, and supplies mag be left on a beach from one night to the next, exposed to tropicd raim. Often no avarebousicg will be svailabie. Cases of food ernaey be loaded and unloaded 5everaI times on their long joumfpy and handling undeF battle conditions is anything
101 ovei-
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use does not arou&e %B very vivid picture m most minds. We usualiy 8888
ze ~ o m efood in large boxes, sitting on 8
eo the Army. No mattes q u a n t i t y of t h e f o 5 d we buyz it will be t h e troops in edible Assembly Line for A r m y Field Ration
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January, 1943
INDUSTRIAL AND ENGINEERING CHEMISTRY
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gentle. In spite of these difficulties, we require that food shall keep well for :it least a year. To accomplish this important task, the Army employs all of the major types of p a c k a g i n g . The Quartermaster Corps has specifications for metal cans, fiber cans, drums, bags, sacks, folding cartons, glass containers, kegs, and special packages.
Types of packaging Metal cans are familiar to all. In peacetimes tinned cans were normally used. These cans were manufactured of plate carrying 1.5 pounds of tin per base box. Over two years ago the possibility of a tin shortage was foreseen, and a tin replacement program undertaken. The weights of all tin coatings have now been reduced. Electrolytic tiii plate is available today. This plate carries about 0.5 pound of tin per base box, but affords greater protection than is indicated by this amount because of the method of uniform application. Enamels and lacquers are also used to increase Frozen Boneless Beef in Cartons for Overseas Shipment Compared to the protection afforded the product by Carcass Beef this plate. For overseas shipment, electrolytic plate must be enameled on the outside to protect it from corrosion. Bonderized plate is also available, and production is being seeds such as beans, peas, and rice. These products require rapidly increased. This is similar to the base plate of the tin less protection and are given less protection. can but has been chemically treated to reduce the rate of Folding cartons are specified as part of the packaging for corrosion. The use of this plate is limited, but as more such products as cereals, cornstarch, baking soda, salt, and satisfactory enamels are produced, its application will Le sugar. Inner liners or wraps are usually employed. Our D broadened. and K rations come in this category. Deoxidized steel, enameled on both sides, may also be Glass jars and bottles are specified for flavorings, extracts, employed in cans. However, its use for overseas shipment vinegar, and a few other products. However, handling is is restricted to steel drums, ends of fiber cans, or packing dry so rough in the Army that they must be well packed to prevent products that will be subjected to less severe conditions. breakage. We specify as little glass as possible. Recently At present electrolytic plate and Bonderized plate arc vinegar was removed from glass, and a search is now under authorized for packing certain dehydrated vegetables and way to replace glass further. Kegs are used for vinegar and for ends of fiber cans. Electrolytic plate may be used for some citrus concentrates. They are strong and tight, but certain canned vegetables and for the biscuit unit of the C are inconvenient as dispensers and rather wasteful of shipping space. ration. There has been ti general shift downward in the products Most of the packages mentioned have been adapted from packed in metal cans. Products formerly packed in heavily their peacetime assignments. The chief problem has been in developing special linings and closures so that a given package tinned cans are now put up in plate carrying a lesser amount of tin or in electrolytic plate. Products formerly requiring will carry a more difficult product than normal. However, a lightly tinned can are now packed in Bonderized or deto pack satisfactorily one class of food which has recently oxidized steel plate. In other words we are adapting to each come to the foreground requires a large amount of plate or product the lowest grade plate that will do the job. other critical materials. Fiber cans with untinned metal ends are specified for a number of dry products that were formerly packed in tin. Dehydrated foods The specifications prescribe a can of special construction, the body consisting of a lamination of moisture-vapor-rcAn unusually large amount of dehydrated food products sistant films employing asphalt and wax. This results in :I are being utilized for feeding the troops. These foods answer fiber can of much greater moisture-vapor-protective properthe Army’s requirements admirably in reducing weight and ties than any manufactured before the war. The liners are volume and increasing storage life. They have an average varied, depending upon the product to be packed. relative humidity of about 30 per cent a t room temperature, Enameled steel drums are utilized to replace tin in packwhereas humidities above 90 per cent are common in the ing dehydrated fruits and vegetables. However, they are tropics. Therefore, these products require considerable proused rather sparingly a t the present time since they retection against moisture vapor as well as other outside quire a little more metal and space than some other types influences. of packaging. With tin plate, black plate, rubber, aluminum foil, and other materials restricted, and waxes, cellophane, and some Cotton sheeting bags inside of five-ply multiwall paper lacquers nearing the critical list, only more or less elementary bags are employed to pack coffee, sugar, salt, and vegetable
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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
materials ieniarn tor packaging. OUI dtbsigninent has becx fairly well defined. The Quartermastel Corps has the most hgrg~oscopicfoods in histoiy t o pieseive for a year or more under the worst conditions imaginable, nith B iriajor.ity of t h e good packaging mater& resti icted fi om use. In mokt cases we ale trying to duplicate -~itYriflexible packaging Rlnii the protection originally a8orde.d by tin plate. Although \+(’ emphasize moisture-vapor protectioii, there ai? other requirements of a packaging film, A b previously stated, n e expect a packaging niateibal to afford protection against the transfer of odois, grease, and ~ i t t earid r t o pi ewxit Infestation and contamination. However, t h r i c x la tbernselveb to an eilsiex soliltion tfraii the inoistur+wpc’r question. When we 51 e7.r iwritroiitrd I\ it11 ptickitging tlelij di d e ( % vegetahles III the less csritic.al in~~t(~riaIs, it n a s necessai j to choose types ut package5 : ~ n d rriaterinla f o i tliv particulai product in Inintl. Ti1 for a su1tnhle pacllraging film, you have a numt)ei 01 basic sheets froin v l h i c 3 1 1 to choose. Glassine, Pliofilm, cellophane, and othei crlliilosr derivatives, sulfite p q r r , kraft paper’, parchmonl paper, c+., are available. Since many of these aiieeti ufier little ~ I ( J tection alone, they are uiually coated n ith a film to enhanre their moigture-~~apor-resistatit properties. M”ax CYIM one oi the first materials employed in this P ~ ~ I X E J No\+ >\e hare mmerow modified waxes, riitrocellulose colttings, resuiq, varnishes, lacquers, and other materials It followed logically to combine two of these sheets t o obtain additional moisture-vapor resistance. Sheets thus
Vol. 35
No
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c ~ n h i n e dinto it single f i i r i i art: c:xlled “1a.rnin These laminated films were often their properties further’. This gi ~iiormousnumber. of possible (;or ge of adhesives and piiistioiziuig :i,genb y offers i s considered, Tests: on
films
X yem or 80 before the war b($gari, this !a,Lor.atosy Ix:gark wii investigation of these filrns. $Qeeognizing the stra,tngicr character of snc?tala ill ~TEJ~T lime, efforta ere c:orrc~rtral~ed
Irr choosing a, rnetbotl
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dustry. HonwFer, to be effective: ii number. of ideiitiotl pieces of appltratiis lvere desirable, Ltnd they ~vcreriot a-.aail.able. Further search brotught t o light the testing equipnierit’ developed by General Foods Corporation. A half dozer1 of apparatus were then in operation, anif specifications were easily obtained. This method of testing flat sheets was ndopted sinco fairly
January, 1943
INDUSTRIAL AND ENGINEERING CHEMISTRY
reproducible results could be obtained, and the type of cabinet represented the most popular method. The test consists of inserting the film between a dry atmosphere on one side produced in a cup by anhydrous calcium chloride and a humid atmosphere on the other side of the film maintained a t 100' F. and 90-95 per cent relative humidity. After a 24-hour conditioning period, the samples are run for two 68-hour periods, the moisture pickup being measured by weighing the cup at the end of each time interval. The results are recorded as grams of moisture vapor transferred per 100 square inches per 24 hours. This test gives a comparison between films as to the protection provided by a flat undamaged sheet. However, this value may be misleading if other factors are not taken into consideration. I n forming a package, creases, sharp corners, seams, and closures are always present. These points are the most vulnerable part of any package. If the film being tested is coated or is slightly brittle, the film or coating may be cracked or damaged a t the folds and sharp corners, or the seals may be a weak point. Therefore, films that show promise in the flat should be tested as packages to ensure that they will provide the same degree of protection when holding the product. The package can either be packed with the product under consideration, or with calcium chloride to accelerate the test. Tests could be devised whereby the creased film is tested on a vapometer cup. This is being done at present, but little data are available. There is also a bit of uncertainty in interpreting this data. After a film has proved satisfactory in a packaging test, shipping tests are undertaken if possible. They usually consist of shipping an experimental pack of the product under consideration to either a fort in the United States or to the Panama Canal Zone. However, since the war started, it has been increasingly difficult to get shipments or reports back from outside the United States. The progress over the last year and a half in the development of flexible packaging materials has been slow but encouraging. The Quartermaster Corps today has several films that transfer less than one third of the moisture vapor transferred by our best sheets of a year or so ago. I n one instance of a less strategic foil, we have a film with a moisturevapor transfer rate that is a small fraction of the best previously available. Packaging presents itself as a picture of a ladder. At the top are the hermetically sealed metal cans; the other packaging materials are arranged on the ladder down to the materials offering least protection a t the bottom. Just under the metal cans is a blank area, above some of the better fiber cans and specially laminated materials. Near the middle of the scale fall most of the moisture-vapor protective films. A line is drawn through this area marking the lower limit of the protective properties which a film may possess and still be suitable for army use. A great many films in domestic use today fall below this line. It is the blank area just below metal cans in which we are interested. We are searching for materials to fill the gap between the cans and the next best protective films. Exceptionally strong shipping cases are required since the Army's food supply is expected to be transferred several times, subject to unloading a t poor docks or on a beach, and exposed to rains and high humidities. Corrugated cartons, which are so popular domestically, have no place in overseas shipments. About a year ago, a weatherproof solid fiber board was developed which has fair resistance to rain and high humidities. However, this product is none too satisfactory and is used sparingly. At present, development of a better board is underway. Recently we have experimented with fiber boxes containing asphalt barriers and
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asphalt-impregnated sheets, as well as boards that have sisal fibers embedded in an asphalt barrier. These products show considerable promise, and further investigation is being carried out. Wooden boxes and wire-bound boxes have given the most satisfactory service and are now preferred for overseas shipment.
Protection against gas The Army must be prepared a t all times for attack with toxic gases. The nonpersistent gases are unlikely to damage food since it is difficult to obtain a high enough concentration for a long enough time to have a deleterious effect. The persistent gases are the ones which cause us concern. They are chiefly mustard and lewisite. We have investigated many packaging materials for their resistance to these gases, and the Chemical Warfare Service has tested practically all types of materials for gas protection. Many products have reasonable protection in the flat condition but poor protection a t the folds, seams, and especially a t sharp corners. Films that have been found to be most resistant to mustard gas are those employing protein, regenerated cellulose, and polyvinyl alcohol. Asphalt and wax provide less protection. Because of the poor protection that many films give a t the sharp corners and folds, it has been necessary to obtain the most pliable films possible. This has been done by plasticizing the promising films. However, care must be taken that a plasticizer is not used that will dissolve mustard gas and, therefore, transfer it through the film. Considerable protection can be given from mustard gas by employing packaging materials in several layers. It is interesting to note that the large family size cereal package is quite resistant to the penetration of mustard. This package apparently provides a combination of resistance to mustard gas in the,waxed sheet and absorption of the liquid in the paperboard carton. Of course, hermetically sealed metal cans and sealed glass containers are completely resistant to mustard. At present our field rations C, D, and K are packaged so that they are resistant to contamination by war gases. Since it is difficult to obtain a single flexible film that is completely resistant to them, a combination of more than one film is required. Attention has been given to the decontamination of gassed food supplies. It is almost out of the question to use the conventional bleaching agents on all food containers that might be affected. First, liquid mustard gas would be absorbed by the shipping cases, and it would be difficult for the bleaching agent to reach them. Secondly, considerable time, labor, and chemicals are required. Thirdly, it is undesirable to get the bleaching agents mixed with the food packages. Hence, the best attack is to protect the food in the first place so that it will not be contaminated. However, when contamination does occur, it is necessary to remove the outside case and destroy it. This makes it desirable to have an inner packing case that will carry the food products for a short time until the item is consumed. If any one of the readers has or knows of a material that is being used for another purpose but might have extremely high moisture-vapor transfer resistance, the Quartermaster Corps would like to know about it. However, we feel that we have pretty well covered the present field of packaging films. We are not asking for a retest on present films or just a different combination. We are not interested in ordinary protection. We are calling on chemists for a superior product to do a stupendous job. Someone may have run across a product in the laboratory, probably in an entirely different application, that will lend itself to use as a packaging film with exceptional protective properties. That is what we want!
