GE.XKK AL MICROSCOPY 



surface unevennesses cause pronounced 

 shadows which make appraisal difficult. 

 Hence this method is applied only if filler 

 dispersion cannot be appraised from sections 

 or if it is desired to know the direct cause of 

 the fracture. 



Examining Plastic in Non-Plastic Ma- 

 terials 



For investigating the presence of polymers 

 in textile or leather materials, fluorescence 

 microscopic methods are used. 



If the material containing the plastic 

 fluoresces only slightly or not at all, micro- 

 tome sections can be examined direct by 

 fluorescence microscopy. Most plastics flu- 

 oresce bright blue-white or yellow-green. 

 This method is very exact on the whole. 



Fluorescence microscopic examination of 

 plastics in natural textile fibers is not usually 

 directly possible because most natural fibers 

 have a fairly strong fluorescence of their own. 

 As these fibers generally have fairly strong 

 hydrophilic properties, however, it is very 

 simple to use fluorochromes. Staining with a 

 mixture of coriphosphine 0.1% and Rhoda- 

 mine 6 GD 0.1% for 15 minutes, thorough 

 washing in distilled water and drying, fol- 

 lowed by fluorescence microscopic examina- 

 tion, enables the plastic coating of the fibers 

 to be rendered clearly visible in nearly all 

 cases. 



J. ISINGS 



PULP AND PAPER 



Among the methods for investigating 

 pulp and paper, microscopic examination 

 occupies an important position. Microscopic 

 techniciues are used for: (a) identifying paper 

 fibers; (b) investigating coatings on paper; 

 (c) investigating sheet formation by the fi- 

 bers; (d) investigating fillers; (e) morphologi- 

 cal examination of fibers. 



In the practice of paper technology, iden- 

 tification of the various paper fibers is of 

 primary importance. As a rule it is sufficient 



to use a normal light microscope. With a 

 total magnification of (iO and 200 X stronger 

 magnification is usually superfluous. Coat- 

 ings can also be most suitably examined 

 from their cross sections with a normal light 

 microscope. These cross sections are usually 

 made with a Hardy microtome or a freezing 

 microtome. The pulp condition of the 

 various fibers can most suitably be studied 

 by examining the fibers in acjueous suspen- 

 sions with a phase contrast microscope. This 

 method has been very widely applied, espe- 

 cially in recent years. Birefringence of fibers 

 with a polarizing microscope is not deter- 

 mined; this method is usually limited to in- 

 vestigating fillers. 



The same can be said of the x-ray micro- 

 scope. Although it is possible with this 

 method to see the mutual coherence of the 

 paper fibers it is especially important for 

 examining filler distribution. Good results 

 can be achieved, particularly with the x-ray 

 projection microscope (q.v.) as there is no 

 need to make cross sections for this. The 

 fact that stereo photographs can easily be 

 made with it makes this method still more 

 attractive. 



Fluorescence microscopy is still infre- 

 quently applied for paper fiber investigation. 

 An indication of the usefulness of this 

 method is to be found in Herzog, who noted 

 a fairly pronounced difference in fluorescence 

 color between soft wood sulfite and soft wood 

 sulfate pulp. More important than the flu- 

 orescence of the pulp itself however, is the 

 method whereby the coloring of fibers with 

 fluorochromes is used. Definitive data re- 

 garding this are not available in the litera- 

 ture, although it is clear that straw and 

 esparto pulp can easily be distinguished by 

 this method. 



Lastly, electron microscopy must be men- 

 tioned as an important method of paper 

 investigation. This method is particularly 

 important for exact investigation of the 

 fibrils of pulped fibers. These can be exam- 

 ined with replica techniques under an ordi- 



394 



