RESLNOGRAPHY 



and applied (external) stress. Starch grains 

 are natural aggregate units quite character- 

 istic of the botanical species. 



Paper sheets, woven or nonwoven fabrics, 

 roving threads, tire cords, and reclaimed 

 rubber are examples of systems of phases or 

 materials that may be only part of the fab- 



FiG. 10. An experimental fiber of polyacrylo- 

 nitrile. A positive electron micrograph of a silica 

 replica. The fiber represents a unit of Type IV. 

 The ridges of the "bark" running parallel to the 

 fiber-axis apparently contain both Types II and I 

 particles. So does the core, exposed in the upper 

 left part of the micrograph but here the particles 

 are less ordered. 



ricated whole. It may be very important to 

 recognize their areas and boundaries and to 

 determine how they may be reacted with or 

 anchored to the contiguous materials. Con- 

 versely, fibers, foils, sheets, tubes, fabrics 

 and so forth may have another resin phase 

 attached by grafting, impregnating or coat- 

 ing. 



A very important kind of Type IV is the 

 tnolded grain. This is generally supposed to 

 represent the material of the molded piece 

 and to contain the resin, fibrous and/or 

 particulate fillers, pigments, lubricants, etc. 

 Yet after molding, the original pellets of the 

 molding grains can be seen before or after 

 preferential relief polishing, etching, stain- 

 ing or breaking at grain boundaries. 



The resinographic problem can be com- 

 plicated. For instance, starch grains may be 

 incorporated into a urea-formaldehyde ad- 

 hesive binding cellulosic and metallic sheets. 

 To differentiate the starch grains from the 

 synthetic resin would one examine thin sec- 

 tions (with reflected fight) or thick sections 

 (with transmitted light) ? 



Combination with Other Materials. If 

 the resin is combined with metal the method 



//^ 



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♦- 



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Fig. 11. Commercial foil (Type IV material) manifesting three types of particles. Electron micro- 

 graphs of positive replica of rougher side, no shadowing metal. Left: Spherulitic grains (T3^pe III) com- 

 posed of crystallites (Type II). Right: Higher magnification. Apparently there are small particles (prob- 

 abl}'- Type I) arranged roughly in line within the variously oriented crystallites. 



531 



