11111 2.8 2 5 :; 1111/2.8 11111 2.5 l.:.i 11111 . 1.0 .~ = I.iA I~ ~"I~ 2.2 ~.OOI~ I ~ ... I~ ... I~ I:.l I.l.: ~ I~ L:: I~ .0 '"L:. u I ....'"' ~~u t.:~"'" --1.1 --1.1 -- -- --. -- ii 4 11111 L25 111111. 111111.6 111111.25111111.4111111_6 MICROCOPY RESOLUTION TEST CHART MICROCOPY RESOLUTION TEST CHART NATIONAL BUREAU OF STANDARDS-1963·A NATIONAL BUREAU OF STANDARDS-1963-A Variables Affecting Film Permeability Requirements for Modified-Atmosphere Storage of Apples Technical Bulletin No. 1422 Agricultural Research Service U.S. DEPARTMENT OF AGRICULTURE Washington, D.C. ~ued May 1971 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 • Price 60 cents CONTENTS SUInInary _________________________________________________________Page 1 Introduction ______________________________________________________ 1 General Inaterials and Inethods __ __ __ __ ___ ___ ___ _ __ __ ___ _ _ _ __ _ __ _ 2 Liners ________________________________________________________ 2 Tp.st fruits _____________________________________________________ 2 Modified atInOllpheres in liners _____ __ ___ __ __ ___ __ ___ ___ _ _ __ _ _ __ __ __ .(. Alnnospheres produced ____________ .----__________________________ 4 Pro~osed definition of liner atInosphere _____ .. ______________ .. ___ . _ _ 6 Effects of boxes on perIneability of liners _ _ _ __ _ ________ _ __ _ _ __ ____ _ 7 Ethylene in liner atInospheres _________________ .__________________ 8 VoluIne shrinkage in liners ____________________________________ • __ 9 General condition of apples stored in test liners _ _ __ _ _ __ _ __ __ _ _ _ _ 9 Storage conditions ________________________________________________ 13 Tenlperature in storage roo.ns ___________________________ . _____ ,_ 13 TeInperature in boxes of apples _____________________ • ____________ 15 AtInospheres in storage rooms __________ ,, _______________________ 18 Alpple respiration rates . __ _ __ _ _ _ ___ ____ ____ ____ __ __ __ __ ___ ___ ____ 20 Methods of IneasureInent ________________________________________ 20 Resp:retion i"ates ___________ . ________________ • __________________ 22 Effects of weight and si2"~ __ _ _ _________________________________ 23 Effects of equilibriuIn rates ______________________________________ 24 Effects of baroInetric pressures ________________________________ . 24 Alpple weights, sizes, and voluInes __________________________________ 25 Weight and sizes of individual appleD _ _ _ __ _ __ _ __ _ __ _ __ _ _ __ __ _ _ _ _ 25 Net weight of apples in boxes ___________________________________ 27 Alpple voluInes __________________________________________________ 29 Alpple-tray voluInes . _______________________________ . ___________ 30 Liner faults ______________________________________________________ 30 Initial tests ____________________________________________________ 31 Pinhole leaks ___________________________________________________ 33 SeaIn Jeaks _____ -- __________________________________________ ,, ___ 34 Twist-seal leaks .'________________________________________________ 38 Thin places in liners ___________________________________________ 39 FilIn-liner identities . " __ _ _ _ _ _ __ _ __ _ _ __ _ _ __ _ __ _ _ _ _ __ _ __ _ __ _ _ __ __ __ 41 FilIn deterioration __ __ ___ ___ ___ ______ ______ __ _____ ____ __ ___ _ _ _ 44 FilIn-liner perIneabUities ___________________________________________ 46 Materials and In\~thods __ _ ____________________________________ . 47 Al uxiliary equi pIn\.mt variables _ _ __ _ __ _ __ _ __ _ _ _ _ _ _ __ _ _ __ _ __ _ __ _ __ 50 BaroInetry variables ________________________________ - _ -- ___ . _ _ - 50 Indicator variables ___________________________________________ . _ 50 Capillary-tube variables _. _____ . _____________________ - ____ - __ ---- 51 Film-sample variables _________________________________________ ' _ 51 Film-density variables __________________________________________ . 54 Diffusion-disk variables ____________________ - ___ -- _____ - __ ------ 55 D-ring variables ____ . ___________________________________ . _ _ __ 56 Purging variables ____________________________________________ 56 Conversion variables _ .._ _ _ __ _ __ _ _ _ __ __ _ _ _ _ __ _ __ _ _ _ _ _ __ _ _ _ 57 Test-temperature variables ____________________________ . _ . _ __ _ 57 Unassessed variables _... _______________________________ .. _____ 59 Measured versus estiInated permeabilities _ _ _.. __ _ _ __ _ 60 Ratios of gas permeabilities of filIn __ _ __ __ _ _ 62 FilIn-liner design, dimensions, and tolerances __ _ __ _ __ _ __ _ _ _ _ __ _ _ _ _ __ __ 62 Materials and methods .. _ _ _ _ ____________ . _____ .. _... _ _ _. _ _ 63 Liner-design formulas ____________________ .. ______________ . ___ ._. 65 Tolerances _,. _ _• _. ___________________________________ .. 68 Practical application and importance ______________ . __ _ _ _ _ __ _ 68 Formula adaptation _ _ _ _ _ ___________ .. _. __ .. _____ . _ .. _ 68 Importance to plastics industry __ _ _ _ __ _ __ _ _ .. ____ .. __ - _ _ _ 70 Literature cited _ _ .. ____ ' __ . .. _ __ __ . __ 70 Alppendix: Examples of formulas applications __ • _________ .. _.. _ 77 II · " Variables Affecting Film Permeability Requirements for Modified-Atmosphere Storage of Apples By W. E. Tolle, research horticulturist, Market Quality Re8.earch"Division.. Agriculturo! Research Service SUMMARY In 1962, a method was published for estimating film-liner permeability requirements for the storage of apples (119) (Lit­ erature Cited,p. 70). This method necessarily was based on data from many sources that probably contained unassessed variables. The purpose of the current study was to identify such variables, to define theirimportnnce, and to discover means of limiting their effects on film specifications. Three lots of three varieties of apples from three sources were packed in five film types and stored under simulated commercial conditions for several months. Permeabilities ·of these films were mechanically measured at storage temperatures and results were compared with those computed by the RSAV6. formula. More than 50 exper,iments to reduce variance in permeability results were conducted. Only the more important of these are reported in this bulletin. These principally concerned method applications. Summaries of these experiments presented no evirlence for major changes in the basic concepts of the RSAV6. formula, but some changes in constants are suggested. Application and film­ liner design formulas are presented and illustrated. INTRODUCTION This study was conducted to determine some of the variables that may be responsible for unpredicted modified atmospheres sometimes pruduced in sealed plastic box liners containing apples. Opinions are divided what these variables are, what their rela­ tive importance is, and whether they can be sufficiently controlled to increase storage life of apples by specified beneficial atmos­ pheres within sealed packages (42,48, 75, 122).1 It is the writer's view that many of these variables relate to mechanical faults of packaging films, that some involve film permeabilities, some concern liner seals, and some are based on doubts that films can be made to meet specified atmospheric requirements. Still other variables exist in the very techniques and methods intended to J Italic figures in parentheses refer to Literature Cited, p. 70. 1 2 TECHNICAL BULLETIN 1422, U.S. DEPT. OF AGRICULTURE absolve variability. When these variables are fully identified, their complete reduction should ultimately follow. It is probable, for instance, that by'crystr..llization, cross­ linking, and rigidity combinations (76, 80, '81), by monomer vaporization techniques (14), by laminates (41, 85), by changes in lamellar anisotropy and chain mobilities in .amorphous regions (10), or by pore variations (1, 2, 4, 20, 89, 84), polymers and copolymers can be satisfactorily made to fit any need. If pad:ers and designers can know what is wanted, it is probabl€! that film specifications can be met. Many attempts have been made to define film s;Jedfications (25, 59, 60, 92, 9B, 119, 128, 126); these d\?HU.es have contrib­ uted much basic information. In commercial applications, how­ ever, the problem has many variables that interact, and no single experimellt i(:; apt to yield the final answer (17). Muny reports of experiments amenable to statistical evaluations have contributed bothexper~ l.ce and information invaluable io the basic and applied research of this problem (30, 34, 36, 42, 45, 49, 104, lOB, 111,119). This bulletin identifies the existence and incidence of certain objective and subjective variables believed to be of importance in the storing of produce in sealed films. It identifiea those that probably should be assessed more closely, It offers considerable detail and emphasis on methods, in the hope that the cited variables uitimately may be satisfactorily controlled for the bene­ fit of the produce industry. GENERAL MATERIALS AND METHODS Liners One method for the specification of film liners for the storage of apples requires only the multiplication of five selected factors (119). This formula was applied, and film manufacturers and fabricators were solicited for any film type that approximately would meet one of four gas permeability specifications. The other requirements were that the films possess, at 32° F., adequate flexi­ bility, have chemical inertness to foods, be reasonably odor free, and have sufficient strength for use as bushel-box liners. Film types, thickness, densities, and liner designs, other