Ebonite, structure

The detailed structure of ebonite is not known but it is believed that the same structures occur in the rigid material as have been suggested for vulcanised rubber. There will, however, be far more S-containing structures per unit volume and the ratios of the various structures may differ. The curing reaction is highly exothermic. 

It is now well established that synthetic materials may be prepared with mechanical properties closely resembling those of elemental metals and alloys. As a result, we have come a long way from the ebonite handles and fragile plastic toys of 30 years ago to the overwhelming occurrence of plastics in modem mechanical structures. Similarly, it is now possible to mimic the electrical properties of elemental metals... 

Fig. 4.14 TEM micrographs of sectioned industnal tire cords are prepar by the ebonite method to enhance the contrast of the various structures and to harden the adhesive and the rubber for sectioning. Fiber cross sections, two adhesive layers (RFL) and the rubber (R) are shown by TEM.

The structure of ebonite is basically similar to that of a soft vulcanizate prepared by the use of a low accelerator to sulphur ratio (see Fig. 18.2) although, of course, there are far more sulphur-containing structures per unit volume and the material is essentially saturated. When ebonite is pyrolyzed, various 2-methylthiophens are obtained this suggests that a substantial proportion of the sulphur is present in cyclic monosulphide groups attached to the tertiary carbon atom in the main chain ... 

Examination of pyrolytic fragments also yields limited information on network structure. Probably the most well-known experiment of this type was that carried out by Midgley et al. in 1932 who pyrolyzed an ebonite of empirical formula CsHsS at about 700°C and obtained a mixture of dimethyl and methyl ethyl thiophenes. From this they concluded that ebonite had the skeletal structure ... 

The study of phase size and compatibility requires that the different phases be observed, distinct from one another, and that there is minimum distortion in the polymers. However, multiphase polymers often cannot be stained or sectioned uniformly. There are composite structures that are combinations of soft rubbers, coatings and oriented fibers which caimot be stained with a single staining agent and the sections may be deformed or distorted, limiting both observation and interpretation. The ebonite method was developed by Smith and Andries [111] to stain and uniformly harden polymers. 

---