30 - Miscellaneous Plastics Materials

Abstract

The materials that are discussed in this chapter can be classified chemically into two groups: plastics derived from natural polymers and non-polymeric plastics whose resinous behavior stems from the colloidal complexity of a mixture of heterogeneous molecules. With the exception of some of the natural rubber derivatives, these materials were available during the first decade of this century and, together with celluloid, actually completed the range of plastics materials then in commercial use. Casein is a protein found in a number of animal and vegetable materials but only one source is of commercial interest, cow's skimmed milk. Plastics materials may be produced from casein by plasticizing with water, extrusion, and then cross-linking with formaldehyde (formulization). The resultant products have a pleasant horn-like texture and are useful for decorative purposes. Casein is the only protein that has achieved commercial significance as a plastics raw material. Many other proteins are readily available in many vegetable material residues, which arise from such processes as the extraction of oils and starches from seeds. It would be advantageous to countries possessing such residues if plastics could be successfully exploited commercially. Although plastics materials have been produced, they have failed to be of value since they are invariably dark in color and still have the water susceptibility and long curing times, both of which are severe limitations of casein. In addition to the natural protein fibers, wool and silk fibers have been produced commercially from other proteins. These materials were introduced as wool substitutes, but have little or no significance today.