Figure 5.11 and Figure 5.12 below give a preliminary glimpse of merging these techniques with a comparative analysis of the different stages of cotton fibre development in relation to studying the cellulose crystallinity, hydrogen bond intensity and dyebility. In Figure 5.11, developing cotton fibres were studied with ATR FT-IR to determine the LOI, TCI and HBI. Between 10-25 dpa, the lateral order index (Figure 5.11a) was highly variable, but this variation decreased post 25 dpa. The total crystallinity index (Figure 5.11b) was also variable, but overall gradually increased, suggesting that the fibre cell wall cellulose crystallinity increases throughout development, however there were several peaks and troughs at all stages. The hydrogen bond intensity (Figure 5.11c) started off high at 10 dpa, which was also highly variable until 15 dpa, after which reduced and stayed minimal, with a few small variations at 26, 34, 42 and 52 dpa.
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Figure 5.11: ATR-FTIR analysis of untreated, developing cotton fibre samples. a) Lateral Order Index (LOI) analysis of FT-IR data. LOI is positively correlated with crystallinity (and levels of mercerisation). b) Total crystallinity Index (TCI) analysis of FT-IR data. TCI is linearly dependant on crystallinity (and mercerisation). c) Hydrogen Bond Intensity (HBI) analysis of FT-IR data. HBI relates to the degree of intermolecular regularity in cellulose and the amount of bound water in the developing cotton fibres. Data analysed as covered in (Kljun et al. 2011) and produced in collaboration with A. Kljun.
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In addition to ATR FT-IR, developing fibres with different treatments were also dyed with Direct Red 81 (Figure 5.12), a cellulose binding disazo dye. Between 10-27 dpa, there is a high level of variability between samples, with scoured samples having a low dye-efficiency, fixed samples having a gradual increase in dye-efficiency, and non-scoured samples exhibiting a large peak between 18-23 dpa. After 30 dpa, the degree of variability decreases massively, and all samples have a high dye-efficiency around 80-95% that remains stable through to maturity.
Figure 5.12: Direct Red 81 (DR81) dye efficiency absorption to developing fibres. Fibres were either scoured, non-scoured (untreated) or fixed in formaldehyde before the dyeing process. Dye treatments were done in triplicate for each dpa sample and each treatment. Produced in collaboration with A. Kljun.
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5.6 Summary
In summary,
Understanding cotton fibre maturity and development is only part of the story for fibre improvement. While these stages are important issues, if we are to improve cotton fibres at every stage, it is vital to fully understand the changes in cell wall polysaccharides during the industrial processing of cotton fibres. One crucial aspect of post harvesting modifications is to that of the cellulose crystallinity in the thick secondary cell wall, as this affects many properties including dyebility, tensile strength and uniformity (Blackburn & Burkinshaw, 2002).
Whilst X-ray diffraction and ATR-FTIR related techniques are taking measurements throughout the samples, CBMs are only binding to the outer surfaces of the fibres. An interesting aspect of the CBMs directed to crystalline cellulose (CBM3a and CBM2a) is that they are especially sensitive to modifications in the surface supramolecular structure of cotton fibre cellulose after NaOH treatments at 2.0 mol dm-3. This most likely reflects the cellulose rearrangement at the fibre surfaces – the first point of contact for the alkali treatments.
Additionally, the CBMs directed to amorphous cellulose also show sensitivity to the low concentrations of NaOH, although they have a more gradual increase in binding with the increasing alkali treatments.
These two differential recognition profiles of cellulose crystallinity are therefore significantly distinct and do not just recognise the two forms of cellulose (cellulose I and cellulose II). They have capabilities to detect a wide range of cellulose states at the surfaces of cotton fibres and man- made fibres.
Additionally, these techniques can be used to study the cellulose crystallinity and dyebility during fibre development. The peaks and troughs of developing fibre dyebility will need to be correlated with quantitatively analysed polysaccharide and glycoprotein profile changes which in turn can be used to relate to the overall fibre dyebility. One noticeable change detailed in chapter 4, was the decrease in AGP and
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extensin detection during development, which coincides with an increase in immature fibre dyebility by Direct Red 81. From this result, it could be proposed that the reduction in cell wall glycoproteins during development frees up hydroxyl groups, which in turn allow more Direct Red 81 to bind to the cotton fibre (Zollinger et al. 1991).
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Chapter 6
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The aim of this work was to provide knowledge and a better understanding of the localisation, structure and function of cell wall polysaccharides in the cotton fibre during development, maturity and processing. To achieve this,
Polysaccharide epitopes of the mature cotton fibre cell wall were characterised on the surfaces and through transverse cross sections using antibodies and carbohydrate-binding modules with specificity to a variety of cell wall components.
Polysaccharide profiles were charted throughout the developmental process using monoclonal antibodies, carbohydrate-binding modules and in vitro studies of cell wall polysaccharides of the cotton fibre. This included the four growth stages of initiation, elongation, secondary wall synthesis and maturation.
The changes in cellulose crystallinity in the fibre cell wall were charted after undergoing industrial pre-treatments of increasing alkali concentrations using Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction and carbohydrate-binding modules. Additionally, these techniques were used to investigate the changes in reconstituted cellulose.
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6.1 Characterisation of polysaccharide profiles in mature cotton