Conclusions from the XRD analyses

• There is a significant difference between the XRD diffractograms for the commercial wet spun fibres and the electrospun fibres when using exactly the same grade of PAN. The electrospun fibres have a far lower crystallinity and show the presence of 3D crystallinity.

The commercial wet spun fibres only have 2D crystallinity but the electrospun have 3D crystalinity.

• There is a sharp contrast in the shape of the XRD traces for copolymer and homopolymer PAN and the conditions under which transitions occur when copper salt is added. The electrospun homopolymer PAN fibres have higher orientation and larger crystallite sizes than the electrospun copolymer fibres. For the homopolymer, the values for the coherence length vary from 14.96 nm to 6.26 nm for the wet spun and electrospun fibres respectively.

For the copolymer, the values for the coherence length vary from 12.63 nm to 5.55 nm for the wet spun and electrospun fibres respectively.

• The wet spun PAN fibres show characteristic 2D hexagonal packing as determined using the ratio of the equatorial peaks at 2 = 17° which has a d-spacing of approximately 5.25 Å, and the much weaker reflection at 2 = 29,5° which has a d-spacing of about 3.05 Å. The d-spacing is related to the inter-molecular distance of the PAN chains, and is affected by factors such as draw ratio, solvent residues, as well as temperature. The ratio of the d-spacing of the two peaks remains about √3 : 1 within an experimental accuracy, indicating pseudo-hexagonal packing. The diameter of the chain is: (2 x √3 )d(110) = 6,1 Å.

• The addition of salts to PAN fibres causes the 2 value to decrease, indicating an increase in the d-spacing due to an increase in the inter-molecular distance between the chains assumed due to the packing of Cu ions in a columnar structure between the chains.

• The addition of salts to PAN fibres causes the primary equatorial peak(s) at 2 17° to split into 2 reflections at about 2 = 16,7° and = 17.1°. The separation of the double peaks has been seen as a correlation with increasing draw ratio in wet spun PAN. The salts are thus acting as a plasticizer and effectively causing an increase in the draw ratio of the electrospinning process.

• None of the electrospun samples show the secondary equatorial peak at 2 = 29.5 , (002 lattice plane), which is visible for both homopolymer and copolymer wet spun fibres.

• The XRD data provides support for some of the less expected results presented in the preceding sub-sections of this chapter i.e. for FTIR, DSC and TGA and comparisons are discussed in Chapter 6: Conclusions.

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CHAPTER 5 – EXPERIMENTAL AND RESULTS