One of the many applications of infrared spectroscopy of today is the rapid identification of plastics which eliminates time consuming organic analysis and is in many cases more reliable. As for any kind of spectrographic analysis most of the labor is involved in the preparation of the sample. So far three general methods are used: 1. The preparation of mulls which are suspensions of solid plastic powders in a high boiling paraffin oil. This suspension is then spread between rock salt plates and examined as such. The disadvantage of this method is the interference of the oil spectrum with the spectrum of the sample. The preparation of the mulls which includes the grinding of the resin is also time consuming. 2. Thin films of the plastic may be obtained by rolling the material to appropriate thicknesses and then cutting it so that it fits the rock salt window holder instead of the window itself. The disadvantages here are that special equipment is required for the rolling operation and that this operation is limited by size, form and nature of the sample received. 3. The solution technique consists in spreading solutions of the purified resin on mercury glass plates or preferably on rock salt windows. By evaporation of the solvent a solid film of the material is obtained. This method was found to be most suitable and several short cuts could be made so that qualitative analyses of a sample could be accomplished within 1 hour as compared to 1 - 2 days required by the conventional technique. These short cuts consist essentially in the fact that the whole plastic can be examined as compounded without fractionating it.
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