X-RAY FIBRE DIAGRAM

Fig. 84. X-Ray fibre diagrams (a, b and c), cell projections of cellulose (d) and cellulose trinitrate...

According to the experiments of Andress [6] the composition of the Knecht compound after being kept under reduced pressure for some time should be denoted by the formula 2C6H10O5 HN03. Andress has demonstrated that the compound produces a characteristic X-ray fibre diagram. 

Terylene, like nylon, is thermoplastic and can have permanent pleats or shapes imposed by the action of heat with or without steam. It breaks under loads of 4-2 to 4-8 g per denier and the continuous filament has an extension of 22 to 30 per cent at the breaking point. The fibre has marked crystallinity as shown by the X-ray diffraction diagram illustrated in Fig. 2.7, and by the low moisture regain of 0-4 per cent. The closely packed and highly-orientated molecules make Terylene markedly hydrophobic and difficult to dye. Modified polyester fibres are produced with an affinity for both disperse and cationic dyes. 

This may either be done in a stenter, or a Bates Type K machine (Fig. 21.2), in which the fabric is held against electrically heated rollers by means of endless blankets. The temperature which is required for a satisfactory set is between 190° and 250°C (374° to 482°F). Heat setting is preferably carried out before dyeing. X-ray diffraction diagrams show that setting increases the crystallinity of the fibre and therefore reduces accessibility. 

A limited amount of data only is available on the crystal structures of poly(p-benzamide) and poly(p-phenylene terephthalamide). From X-ray diffraction diagrams of highly oriented examples of both fibres there appears to be a great deal of similarity between the crystal structures. 

Fig. 9. X-ray diffraction diagram for poly( p-benzamide) fibre (initial modulus 1100 g dtex ) (authors results).

The observed temperature rise in the neck has been found to be in approximate agreement with that calculated from the work done in drawing, assuming that no heat is generated due to crystallisation. In PET, X-ray diffraction diagrams of cold-drawn fibres show that very little crystallisation has occurred. 

Hess et al. [25, 8] carried out X-ray investigations of nitrocellulose during the stabilization process. In the X-ray diagrams of the nitrocotton fibres immediately after nitration, almost no interference rings were visible. They appear... 

Cave ID (1997b) Theory of X-ray measurement of microfibril angle in wood. Part 2. The diffraction diagram X-ray diffraction by materials with fibre type symmetry. Wood Science and Technology, 57(4) 225-34... 

The repeat distance b can be calculated from a fibre X-ray diagram, Fig. 2.5 (b), in the following manner ... 

As pointed out in section 2.5.1, where the reciprocal lattice is defined, it is possible to determine the shape and dimensions of any real lattice from the corresponding information about the reciprocal lattice. The spots on the /th layer line correspond to reciprocal-lattice points lying on the reciprocal-lattice plane containing all points hkl) for different h and k. The fibre diagram is in fact similar to what would be obtained if the following imaginary experiment were performed. Place the origin of a suitably scaled version of the reciprocal-lattice at the point where the incident X-ray beam would strike the film, with the normal to the planes of constant / parallel to the fibre axis and therefore to the meridian of the fibre pattern. Rotate the reciprocal lattice around the meridian and mark a point on the film every time a lattice point intersects it. To understand the difference between this pattern and a real fibre pattern it is useful to consider fig. 4.13. 

Typical orientation diagram plots obtained by X-ray diffraction for hot drawn film melt spun fibres, and cold drawn films of iso tactic polypropylene are shown in Fig. 50. It is noted that the crystal orientation change is... 

Finally, before we revert to the sorption equilibria, mention must be made of the recent discovery that cellulose II forms a true hydrate If dry fibres, whose crystalline part consists of cellulose II, are exposed to air of increasing rel. humidity, the 101 interference in the X-ray diagram shifts to another position, corresponding to an increase of the lattice spacing perpendicular to 101 from 7.32 to 7.73 A. This... 

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