A Method for the Carbon Replication of Extensive Areas of 

 Very Irregular SinTaces, with Particular Application to the Study of Pulp 



Fibres, Wood, and Paper 



D. H. Page 



British Paper ami Board Inc/iisiry Research Association, St. Winifred's Laboratories, Kenley, Surrey 



The purpose of the research of which this work 

 forms a part is the study of the effect on pulp fibres 

 of the process known to the paper industry as 

 beating. Fig. 1 shows diagramatically a typical cross- 

 section of a beaten fibre that has been dried down 

 onto a glass slide. During the beating process, which 

 is one of controlled mechanical disintegration, the 

 outermost layers of the cell wall are teased out to 

 give the so-called fibrillation seen spilling away from 

 the fibre onto the substrate. Our research involves 

 an investigation of the structure of this fibrillation 

 and the surface of the fibre from which it originated. 

 It follows that replicas are required that are intact 

 over large areas. Hitherto this requirement has been 

 difficult to satisfy because of the great irregularity 

 of the fibre surface. The scale in fig. 1 gives some 

 indication of the height of the upper surface of the 

 fibre above the substrate. It commonly lies between 

 5 and 10 microns. The thickness of a conventional 

 replica is much smaller than this, plastic replicas 

 being about 800 A and carbon replicas 100 A thick. 

 For this reason a replica of such a surface is extremely 

 fragile and usually disrupts at some point in its 

 production. This problem is common to all workers 

 in the field of fibre replication and has been solved 

 by some (2, 6, 7) who partially embed their fibres in 

 a plastic. The protruding surface is then compara- 

 tively smooth and replicas are easily made. This 

 technique is not permissible in our case however 

 for much of the fine fibrillation, which may range in 

 thickness from a few hundred to a few thousand 

 Angstroms, would certainly be completely embedded 

 and not subsequently replicated. It was decided 

 therefore that a replica method was needed which, 

 while accepting the fragility of a replica made 

 without the aid of a partial embedding technique, 

 would still give consistently replicas intact over 

 large areas of the fibre and its associated fibrillation. 

 This necessitated the development of a special tech- 

 nique for handling these very fragile replicas to ensure 

 a satisfactory result. Other requirements of the 



method for our purposes were: (a) It should be 

 capable of resolving cellulosic microfibrils (100- 

 200 A thick), (b) It should be a multistage method 

 in which the first cast could be kept intact. This 

 cast could then be used for light microscopy and for 

 the production of metal solid replicas for reUcction 

 electron microscopy, a point that is considered in 

 more detail elsewhere (3). 



The stages of the method can be followed from the 

 diagram in hg. 2. A few drops of a very dilute 

 aqueous suspension of the fibres to be replicated are 

 placed on a clean glass microscope slide and allowed 

 to dry at about 60 C. During the drying process the 

 fibres are pulled into close contact with the glass 

 by surface tension forces (a). An initial cast of the 

 fibres is made in polymethyl methacrylate. Two 

 methods have been found effective. One uses metha- 

 crylate softened by chloroform, the other metha- 

 crylate softened by its monomer. The latter method, 

 which has been suggested by Heidenreich (4) for the 

 replication of metal surfaces, is the more practicable 

 and will be described here. 



A piece of commercial Perspex 1.5 mm thick and 

 cut to the size of a microscope slide is allowed to 

 stand in destabilised methacrylate monomer for one 

 to two hours. The methacrylate sheet remains on 

 the whole unaffected except for a thin surface layer 

 that is softened by this treatment to a gelatinous 

 consistency. The sheet is removed from the liquid 

 and the surplus monomer is allowed to drain from 

 it. It is then put down onto the microscope slide 

 and fibres and held to them under light pressure, 

 just sufficient to ease out any entrapped air bubbles 

 (/?). The residual catalyst in the commercial metha- 

 crylate polymerises the monomer rapidly at 70°C. 

 On splitting away the microscope slide the fibres 



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Fig. I. Diagram of cross-section of beaten pulp fibre dried 

 down onto glass slide. 



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Fig. 2. Diagram showing stages of the method. 



