294 



SAARA ASUNMAA 



Fig. 1. Ultrathin section through a contact region between 

 two perpendicularly arranged fibres in a sheet of Husum 

 sulphate pulp ol' Piniis silvestris. Arrows point to the con- 

 tact regions. Magnification • 100,000. Inset, magnitication 

 X 140,000. 



bonded fibres, not only an arrangement of contact 

 points. 



The contact region shows a tine structure; struc- 

 tural components with a width of 50-100 A ("fibril 

 strings") run between two adjacent fibre bodies. 

 Particularly in micrographs of a contact between 

 two perpendicularly arranged fibres the origin of 

 the "fibril strings'" observed can be estimated. 



Figure 1 shows detail magnifications of a contact 

 region between two perpendicularly arranged fibres 

 in a paper sheet of Husum sulphate pulp of Piniis 

 silvestris with a degree of beating 62 SR, 16,000 

 turns PFI. The electron optical magnification 25,000 

 diameters was used, an RCA EMU 2c electron micro- 

 scope was employed. 



"Fibril strings" can be followed in the plane of 

 the section, in the inset lengths of 2.5 cm, i.e. about 

 0,1 // can be measured. Several "fibril strings" are 

 marked with dark lines. The strings at the left belong 

 to the fibre I with a direction of fibre axis — *, the 

 strings at the right to the fibre II with a direction of 

 fibre axis f . The strings are observed to run parallel 

 for distances of several hundred Angstrom. 



Thus the concept of fibre-to-fibre bonding has 

 been brought one step further, to bonding between 

 structural components of the fibre, which are only 

 50-100 A wide. Distances between such structural 

 components are small enough to bring the concept 

 of fibre-to-fibre bonding into the realm of chemical 

 bonding. 



correspond to the "cellulose strings" or "fibril 

 strings" observed in suspensions of hydrolyzed fi- 

 bres and In the thallated undamaged fibre walls. 



The different layers of the fibre wall often show 

 different impregnation qualities. In hot alkalized 

 fibres the main secondary wall Is heavily impreg- 

 nated, but Its outermost part shows a very low photo- 

 graphic density (6). In beaten, metal-impregnated 

 fibres of sulphate pulp of Pinus silvestris the outer 

 secondary wall shows a higher metal content than 

 the main fibre. The outer parts of the fibre wall are 

 damaged during the mechanical treatment and are 

 easily impregnated in water solutions (2). The metal 

 Impregnation consequently gives a morphological 

 analysis of the layers of the fibre wall in electron 

 micrographs of the ultrathin fibre sections. An un- 

 evenness of the fibre surface in beaten fibres, as clearly 

 demonstrated in the electron micrographs taken by 

 means of the reflection Instrument ( 1 ), is to be seen 

 as a transit area in the sections. 



The contact region between two fibres in a fibre 

 couple of a paper sheet can be studied in ultrathin 

 sections of metal-impregnated samples. 



The real contact area as observed in the individual 

 ultrathin sections Is often small and shows a length 

 of the order of 0,1 /< up to 1 /<. According to serial 

 sections there is often a contact line between the 



The author wishes to thank Dr. O. Andersson and 

 Prof. B. Steenberg for the criticism of the manuscript 

 and for many valuable discussions. She is very indebted 

 to Dr. F. S. Sjostrand, Associate Professor of Anatomy, 

 for facilities for using the electron microscope at the 

 Laboratory for Biological Ultrastructure Research, 

 Department of Anatomy, Karolinska Institutet, Stock- 

 holm. 



References 



1. Amboss, K., Emerton, H. W., and Watts, J., Brit. 



Paper and Board Makers' Assoc, Proc. Tech. Sect. 

 35, 487 (1954). 



2. Andersson, O., Asunmaa, S., and Steenberg, B.. Svensk 



Papperstidn. (1957, to be published). 



3. Asunmaa, S., Svensk Papperstidn. 57, 367 (1954). 



4. — ibid. 58, 33 (1955). 



5. — ibid. 59, 527 (1956). 



6. — Proc. Conference on Textile and other Industrial 



Fibres, Leeds. Electron Microscopy Group, Institute 

 of Physics (1957, in press). 



7. Munkherjee, S. M., Sikorski, J., and Woods, H. J., 



/. Te.xtile Inst. 43, T 196 (1952). 



8. Ranby, B., Fine Structure and Reactions of Native 



Cellulose. Dissertation Uppsala, Stockholm, 1952. 



9. Sjostrand, F. S., E.xperientia 9, 68, 114 (1953). 



10. — /// Oster and Pollister. Physical Techniques in 



Biological Research, Vol. III. Acad. Press Inc., New 

 York, 1956. 



11. VoGEL, A., Makronwiekiilare Cheniie IL 111 (1953). 



