FIBERS (TEXTILE) 



Reactions: In zinc chloroiodide the fiber Usually it is necessary to study the fibers 



turns yellow. In Millon's reagent a red color by means of longitudinal or cross sections, 



occurs. In Cuoxam it is insoluble, but turns It is advisable to assess the importance of all 



blue. divergencies and inhomogeneities by means 



Wscose jRai/on (Fig. 4b). The best medium of microtorsion, microtension and micro- 



for examining viscose rayon and copper wear tests. 



rayon is glycerin, mineral oil (n = 1.46) or In synthetic fibers the following diver- 



monobromonaphthol (n = 1.66). Striation gencies and inhomogeneities in structural 



is pronounced in longitudinal specimens. This details may occur: 



varies considerably. The cross section shows (1) Places with a lower specific bire- 



many irregular scallops. A "skin" is clearly fringence than the rest of the fiber. In both 



visible on the cross section. torsion and tensile tests these places prove to 



In Cuoxam viscose and copper rayon are be weak. Their effect on fiber characteristics 



soluble. In zinc chloroiodide the fiber colors is least if many such places occur in close 



blue to red-violet but eventually turns black, proximity. In all specimens necks form at 



With Neocarmine W viscose rayon turns red- these places, 

 violet and copper rayon blue. (2) Divergencies in birefringence caused 



Acetate Rayon (Fig. 4a). The surface of the by the skin. A skin of irregular thickness is 

 fiber is smooth. The cross section shows some found in many cases with this group of fibers, 

 round lobes visible as longitudinal ridges in Especially if the skin has a higher double 

 longitudinal specimens. In polarized light the refractivity than the medulla, an mterrup- 

 fibers are weakly double refractive. In cross tion in it may greatly affect the strength, 

 section some parts are dark and others light (3) Irregular hirefringence divergencies. 

 between crossed Nicol prisms. This can be Small places which are either more bire- 

 explained by the orientation of the elemen- fringent or less double refractive than the 

 tary micelles. rest of the fiber may greatly affect its char- 

 Acetate rayon is soluble in acetone. If acteristics. These divergencies often occur 

 Vinyon, which is also soluble, is present it is together with great or small divergencies in 

 better to use acetic acid, which leaves Vin- cross sectional shape. 



yon unaffected. With zinc chloroiodide a pro- (4) Stress concentrations. WTiere there are 



nounced yellow coloration occurs (nylon also many inclusions in the fiber, for instance in 



turns yellow!). In Cuoxam the fiber is in- the case of some large matting particles, 



soluble. Acetate rayon is also soluble in satu- stress figures occur. At such places fibrillar 



rated phenol solution (as is nylon). spHtting of the fiber may occur. 



Synthetic Fibers. Microscopic examina- (5) Spherulites. Spherulitic structures are 



tion of synthetic fibers employs practically found fairly commonly in these fibers. When 



all microscopic methods. Birefringence meas- small they nearly always cause fibrillar split - 



urements are important for detecting differ- ting. Large specimens or a number of small 



ences in specific birefringence. These differ- ones in proximity cause cross breakage. If 



ences have been partly correlated with there is a skin they cause less harm, 

 physical-mechanical characteristics. (6) Isotropic particles. On the whole the 



In addition to this birefringence deter- same applies to these as to spherulites. Fi- 



mination it is very important to judge the brillation usually follows the occurrence of 



homogeneity of the fiber with the phase con- these inhomogeneities. Their effect is great- 



trast and interference microscopes. The finer est in skinless fibers. If no stress concentra- 



structures, however, can be rendered visible tion exists around these particles they are of 



only with an electron microscope. Uttle importance. 



359 



