Fibre Pretreatment

This process is somewhat ambiguously referred to as pulping, but should not be confused with the chemical delignification process 

This process, when conducted as a batch operation, is known as beating , and the two terms refining and beating are sometimes used synonymously. It is common these days to consider refining as a continuous operation and beating as a batch operation, however, the two processes in terms of their mechanical effect upon the fibres are essentially the same. Details of the mechanical design of beaters and refiners can be found elsewhere, and the purpose of this chapter is to discuss the physical and chemical effects of this process on the fibre and also its effect upon ultimate sheet properties. 

Refining is the most important of all the processes to which fibres are subjected, in terms of developing pulp suspension characteristics and final sheet properties, and a great deal of research has been carried out into understanding the process more fundamentally. Whilst there is still much controversy about certain aspects of the refining process and its effects upon the fibres, a number of things are widely accepted. Firstly the primary cell wall, which does not 

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One of the earliest fibre pretreatments for improving the dyeability of cotton is of course mercerisation (section 10.5.4). However, more recent research interest in this area has been generated by environmental concerns about reactive dyeing, aiming to enhance substantivity for the modified fibre so that higher absorption and fixation are obtained. This results in less dye (hydrolysed or still active) in the effluent. A further objective is to minimise the usage of electrolyte in the application process. This area has been thoroughly reviewed [392,393]. 

In an early work by Petzold and Lunkwitz [9], this efficiency of recharging of the fibres using cationic complexes of poly(diallyldimethylammonium chloride), PDADMAC, and poly(maleic acid-co-a-methylstyrene), MS-a-MeSty, was used to flocculate cellulose fibres, but the actual adsorption of the complexes was not measured. The adsorption of anionic complexes of polyethyleneimine (PEI) and CMC on fibres pretreated with a cationic PDMDAAC has also been studied by Hubbe et al. [24]. These authors found that when the charge of the complexes was decreased there was an increase in adsorption, indicative of an electrosorption process, but the authors also detected signs of nonionic interaction although they were not able to establish the molecular reason for this behaviour. 

The hydrophobic character of the a-layer, in particular, caused by the large amount of disulfide cross-links and the bound lipid material, is the origin of the diffusion barrier, e.g. for dye molecules. Therefore, the composition and morphology of the wool surface is primarily modified in fibre pretreatment processes. 

Another important factor in wool fibre pretreatment is the enhancement of whiteness and lustre. Bleaching of wool is necessary, especially when dyeing in pastel shades is desired. Using proteolytic enzymes alone s or in combination with 11202, the degree of whiteness and the hydrophilicity of the fibres were increased compared to the sole oxidative treatment. Whiteness in wool... 

Two other major factors determining module selection are concentration polarisation control and resistance to fouling. Concentration polarisation control is a particularly important issue in liquid separations such as reverse osmosis and ultrafiltration. Hollow-fine-fibre modules are notoriously prone to fouling and concentration polarisation and can be used in reverse osmosis applications only when extensive, costly feed solution pretreatment removes all particulates. These fibres cannot be used in ultrafiltration applications at all. 

In the pretreatment and dyeing of synthetic fibres, the aminopolyphosphonates can assist in the removal of oligomers. 

In one study [90], enzyme pretreatment increased colour yield without affecting fastness properties. However, pretreatment of cellulosic fibres with cellulase lowered the subsequent fixation of homobifunctional triazine reactive dyes but did not impair the fixation of other types of reactive dyes [91]. Another study suggested that the enhanced brightness of reactive dyeings was greater with triazine dyes than with vinylsulphone types when cotton was pretreated or aftertreated with cellulase [92]. 

More controlled and efficient fixation is possible when the reactant is applied as a pretreating agent [146]. If nylon given such a pretreatment is subsequently dyed with the conventional chlorotriazine dye Cl Reactive Red 3 (7.2), the substantivity and fixation of the latter are markedly lowered because the anionic XLC residues have reacted with N-terminal amino groups in the fibre. Treatment of the modified nylon with ammonia, however, restores some degree of dyeability. Opposite effects are observed if Cl Reactive Red 3 is reacted with ethylenediamine to form an aminoalkyl derivative (7.131). This nucleophilic dye exhibits a high degree of fixation only on the modified nylon that has been pretreated with XLC. 

Interest in Fixing Agent P (7.123) has been revived in the context of nucleophilic aminoalkyl dyes of the 7.129 and 7.131 types. Nylon pretreated with this symmetrical trifunctional reactant contains residual acryloyl sites that will undergo an addition reaction with nucleophilic dye molecules [145]. Although in theory each N-terminal amino group in the fibre can give rise to two acryloyl sites (Scheme 7.73), crosslinking between two N-... 

Pretreatment for fillers. When used as a surface treatment for fillers or reinforcing materials, in which the silane is applied to the filler or fibre before incorporation into a resin matrix, the same factors as for pretreatment primers apply. In addition, the particle size and the absence/presence of water are important, and in a sense this application is only a variation on the former. It should be noted that silane treated fillers may have, or impart, different rheological properties to non-treated fillers, particularly particulates. A major disadvantage of this approach is that a general purpose silane may have to be used by a manufacturer rather than one specifically tailored to the use of a particular resin type and less than optimum properties are likely to be achieved in some cases. 

Far from the metal trace analysis, our initial studies with BCFMEs were focused on the determination of folic acid [122], In this case, the main goal was the optimisation of the electrode pretreatment for this analyte. An acidic medium (0.1M perchloric acid) was considered optimum for folic acid determination by differential pulse voltammetry. A linear range between 2.0 x HT8 and 1.0 x 10 6M with a detection limit of 1.0 x 10 8M was obtained. Nevertheless, in this work, the adsorptive properties of the folic acid on mercury were noted and the employment of mercury-coated carbon fibre UMEs for folic acid determination has been targeted as a future goal. 

The preparation of fibre for MDF uses an impact device (the refiner) to separate the fibres but this follows a thermal pretreatment that softens the lignin. Consequently separation oeeurs in the lignin-rich middle lamella between the fibres so preserving as mueh of the eellulosic fibre structure as possible. The preparation of MDF fibre is eonsidered later. 

Physical, as well as chemical, pretreatment processes have been combined with the enzyme treatment of wool. A low-temperature plasma is applied to the fibres prior to treatment with polymeric shrinkproofing agent [122]. Combined protease and heat treatment with a saturated steam [123] and the use of high frequency radiation on enzyme treated materials are reported. 

This chapter is devoted to evaluate the usefulness of measurement of different physical and chemical properties of textile fibres before and after chemcial pretreatment to provide a direct assessment of effects of different chemicals. Such information about a property that is immediately and directly affected by chemical reaction will help to optimise the process conditions, whereby the desired effects can be achieved while minimising the undesired effects such as excessive strength loss etc. 

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