Chapter2包装的功能.ppt

* * * * * * (2) The product testing should be performed at various temperatures if temperature effects are to be modeled. 2 Package Evaluation (1)For computer modeling purposes, the chief packaging characteristics are barrier properties. WVTR OTR Other Permeantion Rate Be tested in flat sheet or full package? What will happen if a system is poorly sealed? (2) The package material characteristics of sealability, printability, compatability, cost, mechanical strength, etc remain the province of the packaging engineer and are not usually incorporated into computer models. Nonbarrier parameters are not included in this discussion of shelf life. Those parameters that do affect shelf life, but are not in the model (e.g., light transmission for oxygen-sensitive products), must be considered in evaluating any computer printouts. 3 Model Fundamentals The Components which enter the package from the outside environment, and those which permeate from the inside to the outside, are identical. The transmission rate is standardized for package area, film thickness, time of measurement, and difference of partial pressure of permeant across the package. The standardized transmission rate is combined with area, thickness, and time in the model to define how much permeant can enter or leave the package. The partial-pressure-differential change with permeation is the major reason for the use of computers in shelf-life modeling. some of the permeant is absorbed by the product. (1) Computer models are usually based on a relatively simple mass transfer equation. The general models are based on a standard differential equation that describes mass transfer across a permeable barrier. This is shown in the following equation: Where: t=time W=change in weight of the critical component k=permeability coefficient for the packaging material l=thickness of the packaging material A=area of the pac