DROP TESTING OF PLASTIC CONTAINERS 11 A variety of methods are used to try to make the bottles fall in a con- sistent manner. In a technique described (2), the bottles are dropped down vertically mounted guide tubes. This method introduces the danger that the bottles will bounce back and forth from the sides of the tubes. Impact testers in which a table falls away from objects placed on it, are very useful. If the bottles are being dropped on to their bases it may be possible to drop several at once. If the bottles are to be dropped in any other attitude, jigs will be necessary to hold them. These must be carefully checked to see that no rotation is imparted to the bottles as the table falls away. Some use a shaped rubber pad connected to a vacuum source. This holds the bottle in the predetermined attitude, and when the vacuum is released, the bottle should fall cleanly. Small bottles can be dropped by hand with reasonable results. If the container is held between two fingers at a point vertically above the centre of gravity it should fall with very little rotation. However, it is difficult to drop them without imparting some slight twist. Dropping surface It is considered important to drop the containers on to a smooth, massive surface. It is suggested that a steel plate at least 6 mm thick, embedded in concrete, is ideal. Plain concrete is not recommended, partly because it is of variable smoothness, and partly because it will wear badly. A steel surface as described will test the containers more rigorously than normal domestic floors. However, it is considered that it is most important that consistent results are obtained, since these can probably be correlated later with practical experience of customer complaints, etc. It might also be considered that a measure of exaggeration in a test is a useful safety factor. RESULTS A few results obtained in developing a PVC bottle for a wave set may be of interest. The bottle has a flattened shape, 90 cm 3 capacity and weigh- ing 13g. Grades PCO 634 and 747 are modified grades of PVC. PCO 638 and VZ 903 are unmodified. It is interesting to note that there is a much bigger difference between the modified and unmodified grades when tested at 10øC, than when tested at normal temperatures. The single figures given in Table VI do not, of course, give any indication

12 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table VI Difference between bottles made from various grades of PVC. Bottles dropped on to bases. Grade ICI PCO 634 ICI PCO 747 ICI PCO 638 Vybak VZ 903 Drop height in metres Room temperature 50% level 3.4 3.2 2.5 2.2 10% level 2.6 2.3 1,6 1.3 50% level 2.6 1.2 1.1 10øC 10 % level 1.4 0.6 0.8 of their variability. There is as yet not sufficient data to get a true picture of the variability of the testing since the results have been obtained during production runs when conditions are not yet considered to be optimum. This means machine settings tend to differ between runs. However as an example, the figure of 2.2 m given as the 50% level for VZ 903 at room temperature, covers results varying from 1.6 m to 2.6 m. For comparison the 50% level for a range of our standard glass bottles is from about 0.3 m to about 1 m depending on the bottle. Very small glass bottles, of course have much more strength, and a shampoo minibottle has a 50% level of about 2.5 m. On the face of it the strength of the PVC bottles quoted seems to be satisfactory compared with glass. Whether this is so will not be known until more data on customer complaints is available. After producing about three million, only txvo bottles have been returned with broken bodies. One of these appears to have been broken by excessive squeezing, the other by dropping. (Received.' 31st Janua• 7 1968) REFERENCES (1) Shell Plastics CPL/PS/4. (2) Vinatex/Dorlyl PVC bottle compounds (Vinatex Datasheet). DISCUSSION MR. W. G. BURDON: Could you tell us whether you have any experience of change of impact strength xvith time, particularly in relation to vibration during transport. Also any experience with the influence of the contents on impact strength. I believe it is well known that solids, for instance, will stand far greater heights but I wonder whether intermediate physical products, such as thick creams, will also influence the drop height.