Vacuum packing tests

One simple question that can be answered by supramolecular chemistry relates to consumer safety is this food safe to eat Many methods are used to ensure that produce is fresh when sold. Freezing or vacuum packing preserve food from deterioration and sell by dates let both buyer and seller know when the food should be consumed but none of these precautions actually checks the food directly. A group led by Lavigne has tackled this problem directly by firstly determining which compounds are most closely associated with food spoilage and then by designing a colorimetric test that responds to elevated levels of these compounds [35],... 

In view of present trends it is advisable to check during this testing stage whether the package is suitable for conditions in distribution and retailing which do not approach the ideal. For example, vacuum packs of bacon in transparent printed laminates are intended for retailing in cool cabinets, and are not to be exposed for sale on a table or rack in a window. 

A column vacuum was produced with the eductor, and the operating pressure set to the desired test conditions. Water and steam flows were initiated, and the column was allowed to reach steady state. Steady state was determined by careful monitoring of column temperatures at the reboiler, mid-column, and top of column and confirmed by analysis of vapor and liquid samples drawn from the column sample ports over a 2- to 3-hour period. The height of an equivalent theoretical plate (HETF) of the packing was 19 in., as calculated from vapor and liquid sample compositions. 

The apparatus consisted of a U-shape glass volatilization pipe preheated to a designed temperature, a nose-only exposure unit containing six mice, a glass wool trap (packed with 0.5 g of glass wool fiber) that sequestered the vaporized test compound, and a vacuum system that created negative pressure and pulled the air through the... 

Finally, the electrical performance of an OFET-structure made of vacuum deposited DCNDBQT, which form a closed packed and dense molecular layer, was tested. The output characteristics of the OFET clearly show the behaviour of a p-type semiconductor. The resulting field mobilities of 10 cmWs reflect a high current density as interpreted in the framework of the ultra-thin molecular QFET structure. The sensitivity of the ultra thin material towards the environment neeessitates that in the future, the OFET has to be produced and measured under vacuum-like conditions to the exclusion of air, which may be realised by appropriate passivation processes. 

Hermetically sealed packs should not leak under normal conditions, so laboratory testing could include a vacuum/ vibration cycle, in vertical, inverted or horizontal pack modes, if relevant to the product, the market, or the distribution system (e.g. in the pressurised freight hold of an aircraft). 

In the case of multi-ply packs some plies (particularly the foil) can be perforated but, as other plies may be continuous, leakage will not be detected by a vacuum test. However, this perforation may be sufficient to affect product life. This type of leakage may have to be detected by visual means (microscope) or by careful separation of the plies by suitable solvents. The other alternative is to subject the pack to a cycling climatic test, i.e. 15°C 50% RH and 37°C 90% RH with 12 h cycles. 

Whether a pack will leak can also be checked by some form of vacuum test. The vacuum may be drawn on the pack containing the product, or a product of lower surface tension to encourage loss, or held in a dry vacuum chamber or by placing an empty pack under water (the water normally contains a dye and a wetting agent) and again applying a vacuum. In both types of test, product (or air) out or liquid in may detect a defective closure system. The level of vacuum drawn, the time it is held, and the way it is built up and released vary from company to company. 

Vacuums employed normally range from 15 to 25 inches of mercury (380-633 mm) and are held for 30 s to 10 min. Rate of vacuum release may also vary (fast, slow). In each of these tests the packs are sealed as per normal production. 

Placing packs under a positive pressure external to the pack can provide a useful indication of possible ingress. The positive pressure atmosphere may use air, water under pressure, or a concentration of any gas (or liquid) which can be pressurised (see below for further details). For tests involving combined pressure and vacuum, comments apply as for egress. 

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