44 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS by dropping a known weight from a fixed height repeatedly until the sachet bursts. A test which is often employed under factory conditions is to throw the sachet on to the floor or against the wall and then stand on it. This is convenient but not particularly reproducible. It is not usually possible to assess performance on packaging machines by tests in the laboratory but it should be borne in mind when carrying out laboratory trials that the material will eventually be packed under factory production conditions, and a machine trial should be carried out at the earliest possible moment on materials which look promising. Such tests should take into account the possibility of contamination of the seal area by the product and the subsequent effect on the seal strength. (b) Bottles and Rigid containers The seals on these containers vary considerably and the effectiveness of the closure may be checked by mechanically squeezing a filled container or by applying a vacuum on the outside and checking for visible leakage. Bursting strengths and impact strengths at various temperatures are also measured. In practice the filled containers are often packed in outer cartons which are stacked one upon another and this can induce cracking of bottles or tubes in the lower cartons. A method of testing for this effect on new designs of containers, or on established containers which are to hold a product likely to cause stress cracking, is to subject the containers to a machine which applies a top load for a short time at frequent intervals. Another test involves placing a component such as a neck of a bottle or a section of a bottle over tapered plugs and immersing these in a solution of a polyethylene glycol oxide. These sections are then examined for splitting under various degrees of strain. Thought should be given as early as possible to the form of outer package. Frequently this is considered only on its merit as a medium of presentation, ,overlooking the fact that it must protect the containers during transit. The performance of the outer plus inner containers during transport should be assessed by direct test. This may take the form of sending a number of packed cartons by rail and road over a definite circuit and an examination of the contents at the end of this journey or the cartons may be given abuse in the laboratory by machines designed to reproduce the hazards of an actual journey. 3. FUNCTIONAL SUITABILITY OF COMPLETE CONTAINERS Having decided on the grades of material which might be suitable for a particular product, a comprehensive packing test is almost always essential

LABORATORY EVALUATION OF NEW PACKAGING MATERIALS 45 with cosmetic products. This usually involves packing a number of con- tainers of each variable, storing under various conditions of temperature and humidity and checking at frequent intervals for weight changes, odour permeation and any deterioration of the container or product. Examination of the product will be related to its known properties and cannot be detailed here in view of the great variety of products to be considered. The tests to be applied should be established at the com- mencement of storage, however, to ensure that sufficient samples are put on test. Examination of sachets is usually for well-defined evidence of incom- patibility with the product, i.e. delamination, corrosion and pinholing of foil, crazing of moistureproof films, and leakage on storage, particularly in the areas of the heat seals. Bottles and tubes may be swollen by solvent, take on a different shape--often referred to as "body wall collapse"--or suffer from stress cracking. A container showing any of these faults to a serious extent would be regarded as unsuitable. The temperature/humidity conditions used for the foregoing tests can be adjusted to suit the requirements of the package but convenient con- ditions are room temperature, 70øF/65% R.H., 77øF/75% R.H., 95øF/Dry and 100øF/90% R.H. If possible, it is advisable also to use cycled con- ditions of storage, i.e. a change from one storage condition to another and, after a suitable time interval, a change back to the first. An example is 16 hours at 70øF/65% R.H. followed by 8 hours at 95øF. This would simulate conditions in a warehouse or shop where the conditions fluctuate during day and night storage. These cycled conditions induce condensation both inside and outside the package. Use of such test conditions is partly to simulate practical conditions under laboratory control, but partly also an attempt to achieve an acceler- ating effect. From this point of view it is probably fair to say that storage at 77øF/75%R.H. is twice as severe as storage at room temperature in this country. Above this, however, it is in our experience difficult to assess the relationship, as the effects of temperature and humidity give rise to different effects in different packs and products and testing for a total of at least six months is desirable for most cosmetic products. There is a current tendency to attempt to obtain considerable accelera- tion by storing at elevated temperatures, up to 150øF. It must be empha- sized that such tests are only valid provided that they simply accelerate the phenomena which are important at low temperature. If they introduce new phenomena they can be frankly misleading. For example, during experimental testing we have seen a lamination in which the adhesive was cured by storage at 150øF, with a significant improvement of properties as