46 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS compared with lower temperatures. Apart from other factors it must be remembered that any air in the package can cause stress due to expansion at high temperatures. As a generalization it can be said that temperatures up to 120øF may be useful in selected cases in all cases the results of high temperature tests should always be confirmed by longer tests at lower temperatures. We think it is fair to say that the packaging technologist is still some way from producing a ready reckoner whereby reference to produce formulation and container characteristics will give the shelf life at a glance. Since new plastic materials suitable for use in packaging are constantly appearing, it seems unlikely that, for some time at least,we shall have this type of information available in anticipation of practical use. The approach to testing outlined in this paper is therefore likely to be with us for some time to come. The authors wish to thank the Directors of The Metal Box Company Ltd. for permission to publish this paper. (Received: 1st J•dy 1960) REFERENCE • Modern Packaging Encyclopaedia, 3.21 33 136 (1960) DISCUSSION Miss L. P. TORRY: Could you tell us more about body wall collapse in plastic bottles ? MR. E. J. MACAREE: It is principally due to the creation of a vacuum inside the bottle, and this can be due to any one of three causes, the main one being loss of volatiles through the body walls of the bottle due to the permeability of the material itself. The volatile is lost at a greater rate than air can pass back into the bottle, so creating the vacuum which causes the body wall to collapse. A second cause is oxidation of components of the product, for example unsaturated oils, the oxygen from the air in the headspace being utilized. Oxidation takes place faster than air permeates into the bottle and once again a partial vacuum is obtained. The third cause, which appears least often, is that the bottle is physically swollen by the solvents in the product to such a degree that the internal volume is increased causing a partial vacuum, without any actual loss of product. Miss L. P. TORRY: I am not very satisfied with the answer because if the collapse is due to the presence of vacuum, then removal of the cap would release this and the bottle should take up its original shape. We have found that this does not happen. MR. E. J. MACAREE: You will find that if a product causes collapse within a matter of hours, such as acetone, then removal of the cap will

LABORATORY EVALUATION OF NEW PACKAGING MATERIALS 47 permit the bottle to regain its original shape. If, however, the bottle has been collapsed to an appreciable extent for three or four days then it takes up that form permanently. The same thing will happen if an empty bottle is squeezed, capped and left collapsed for an equivalent period. The bottle will also remain mis-shapen. This is a function of the material itself. MR. J. B. WILKINSON: Whilst the tests outlined give unequivocal results on one-component films, it can be that results with laminated films may be misleading. For instance, the heat seal is often stronger than the laminant (adhesive) bond and damage may be caused to the pack under conditions otherwise indicated as safe. Do you consider that any of your tests can be of particular value in indicating unusual behaviour of the laminate, the nature of which is usually unknown to the packer ? Do cycling temperatures in storage have any particular value in cases other than those where condensation effects are an issue ? MR. S. L. PALLING: On the question of cycling conditions in the absence of condensation effects, it is my experience that there is no particular virtue in carrying them out, and we do not at present include a cycling condition test in a routine testing of a pack. Some users, however, do specify that a finished pack must withstand a certain test involving cycling conditions, and in such instances we do carry them out. The tests indicated will show up the majority of faults of the laminates, it is the only way of finding out. If the inner ply has failed on a transparent package one can usually see it, and if the adhesive has been affected, then quite often you can tell that also from experience of the type of material. Mr. J. B. WILKINSON: But you do not see it unless you couple storage tests with your damage testing ? MR. S. J. PALLING: Yes you do. If a pack is going to delaminate on storage, it is quite easy to see it. Damage testing is usually carried on to complete destruction of the pack, and then no subsequent test is possible. MR. E. K. CLARKE: In your experience, is the delamination of Pliofilm containing laminates, which, it is suggested, is caused by certain perfumes, really as important as the delamination caused by its natural ageing ? MR. S. J. PALLING: Pliofilm is not affected by all essential oils, but it is affected by sunlight and this can produce a brittling effect and an ageing effect which does tend to cause delamination. I think it really depends on the perfume. If you have a perfume, or a constituent in an oil, which penetrates pliofilm and affects the laminate, then it could result in a shelf life which is shorter than the natural one, due usually to the effect of light.