PULP AND PAPER 



nary electron microscope or with thin sec- 

 tions, the contact zone between the pulped 

 fibers being chiefly examined. The reflection 

 electron microscope has also been used with 

 great success. It seems that still more results 

 can be achieved in this direction with elec- 

 tron scanning techniques. 



Paper Fiber Research 



Preparation Technitjues. The tech- 

 niques used for preparing specimens for pa- 

 per investigation are usually very simple. 

 First, fiber suspensions are investigated 

 which are obtained by shaking pulp or paper 

 in water, possibly with the application of 

 heat, after which it readily disintegrates. 

 For x-ray microscopic examination the paper 

 can remain intact, but for contact micro- 

 radiography sections about 50 microns thick 

 are used. The cross sections for examining 

 coatings are made with a Hardy microtome 

 (see Fibers (Textile) -Techniques). The speci- 

 mens are usually embedded in a mixture of 

 equal parts of water and glycerin. For the 

 electron microscope normal replica tech- 

 niques are used, while evaporated suspen- 

 sions are suitable, after shadowing, for 

 examination with a reflection microscope. 

 Full details of this can be found in Emerton. 



Staining Techniques. The main stains 

 for paper fiber iin^estigation are: 



(1) Zinc chloroiodide solution in water (see 

 Fibers (Textile) Techniques, p. 344). 



(2) Solution of iodine in potassium iodide 

 (I2-KI). Both normal staining and I2-KI 

 staining followed by treatment in glycerin- 

 sulfuric acid give good results in paper in- 

 vestigation. The formulas are given in the 

 article on Fibers (Textile) -Techniques (p. 

 346). 



(3) Staining according to Lofton and 

 Merrit wnth fuchsine and malachite green. 

 Composition of the stain: 



2 parts bj' volume of aqueous 1% fuchsine solu- 

 tion. 



1 part by volume of aqueous J^% malachite 

 green solution. 



The sohition will keep for abovit eight days. A 

 paper fiber mash is freed from water as much as 

 possible and stirred with the solution on a slide. 

 After removal of the solution the specimen is 

 treated for 10 to 30 seconds with 3 to 4 drops of 

 0.1% HCl and rinsed. Result. Unbleached sulfite 

 wood pulp: purple red; unbleached soda and sul- 

 fate wood pulp: blue with a fairly pronounced red 

 haze. Ground wood: stains like unbleached soda 

 and sulfate pulp. 



(4) Staining according to Graff (TAPPI 

 standard method). Two stains are suitable 

 for paper examination. The most widely 

 used is Stain C: 



Solution I: 40 g aluminum chloride in 100 cc wa- 

 ter S.G. 1.15 at 28°C. 

 Solution II: 100 g CaCU in 150 ml water S.G. 



1.36 at 28°C. 

 Solution III: 50 g dr\^zinc chloride in 25 ml water 



S.G. 1.80at28°C." 

 Solution IV: 0.40 g dry KI 0.65 g dry 12 in 50 ml 

 water S.G. 1.80 at 28°C. 

 The mixture for use is 20 ml of solution I, 10 ml 

 of solution II, 10 ml of solution III and 12.5 ml of 

 solution IV. A precipitate is allowed to form, the 

 clear top liquid is pipetted. Add a crystal of I2 

 and store the mi.xture in the dark. The results for 

 the various pulps are listed in Table 1. 



Paper Morphology 



The fibers used in paper manufacture are 

 of three kinds: 



(1) Rags originating from textile material. 



(2) Wood, straw, esparto, etc., pulp. 



(3) Highly lignate fibers obtained by 

 grinding wood. 



In all three cases there are unpulped and 

 pulped fibers. 



Rag Fiber. Cotton. Cotton is nearlj' always 

 very easy to identify as a fiber in jxiper. 

 Even with thorough pulping, it is hardly 

 ever possible to split all the fibers into the 

 highly d(^formed single dimensional fibrils. 

 The twisting of the ribbon-shaped fiber is a 

 clear means of identification. 



Flax and Hemp. Both flax and hemp may 

 be used as paper fiber. As they are usually 

 found in only small quantities in rag paper 

 and are, moreover, greatly deformed by 

 pulping, it is very difficult to estimate their 



395 



