Modified fibres

When modified fibres of type 5 are treated with hydroxylamine, oxime groups are also easily formed. The interaction with a protein affords a sandwich polymer22. Fibres modified in this way have enhances dyeability. When copolymer fibres are treated with diamine solutions or in acid medium with Fe+3 salts, intermolecular chemical bonds are formed, which results in a considerable increase of the temperature of zero strength and of the heat resistance of fibres. These conversions are shown in Scheme 2. 

It should be noted that fibres with high heat resistance can be also obtained by treating modified fibres of type 6, containing hydroxyimino groups, with Fe3 and Ni2+ salts, which is again explained by the formation of intermolecular chemical bonds. 

Modified PAN fibres have been obtained from copolymers containing up to 15% or ISP units using the wet spinning process30. Some properties of modified fibres are presented in Table 1. For comparison are also given the properties of fibres obtained from copolymers additionally crosslinked with conventional crosslinking agents used in the vulcanization of nitrile rubbers. 

It has been shown44 that on heating modified fibres containing ZnO at 150-170 °C, zinc chloride is formed as a result of crosslinkage by interaction of the 3-chloro-2-butenyl groups with ZnO. Under these conditions the nitrile groups of the copolymer molecules do not undergo any chemical conversions. 

The formation of such a staircase structure in the macromolecules of PAN in the process of thioamidation of PAN fibres with aqueous solutions of ammonium sulfide accounts for the significant increase of heat resistance of the modified fibres obtained. 

The same methods (chemicals, enzymes, physical treatments) can be also applied on the cell wall materials not with the aim of extracting polysaccharides but with the aim of obtaining modified fibres. New properties concerning for exemple fermentability, ratio soluble/insoluble dietary fibre, hydration., can be obtained (1). 

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]. 

Banks etal. (1995) reacted TMP fibres with glycidyl methacrylate (GMA) (Figure 6.4b), maleic anhydride or succinic anhydride and hot-pressed the modified fibres with methyl methacrylate in the presence of BPO. Infrared evidence was presented indicating that copolymerization had occurred between the bonded GMA and methyl methacrylate. However, in a later study, Qetin and Hill (1999) could find no evidence to suggest that a chemical bond had formed between the GMA and wood. 

Wirtz, S., P.R. Galle, and M.F. Neurath. 1999. Efficient gene delivery to the inflamed colon by local administration of recombinant adenoviruses with normal and modified fibre structure. Gut 44 800. 

Displacement of peak of fusion on curves DTA in area of smaller temperatures specifies that in the modified fibres crystals have mainly morphological form II (the extended circuits of polymers incorporated into crystallites) while in initial PETP crystals mainly have morphological form I (folded structure). Therefore for initial PETP it is observed endothermic effect at temperature 269°C - speaking by fusion flat folded crystallites (morphological form I). At modified PETP - fibers this effect is observed at temperature 245 - 263°C, it speaks fusion of spherallite (the morphological form II). 

Changing the relationship between the rate of diffusion and that of initiation is a powerful means of controlling the supramolecular structure of cellulose copolymers as well as the morphology of the modified fibre, i.e. the distribution of grafted chains in the bulk of the material. 

The use of reversible redox systems as initiators allows to intensify the periodic grafting process66,86 and to develop a continuous technology for the synthesis of modified fibres. For instance, when using such systems, the rate of AN grafting to viscose staple fibre (Table 5) may be as high as 70% PAN of the cellulose mass per minute. 

Most flame-retardant finished textiles are excluded from the Oko-Tex Standard 100 label. In all cases, the durability of the finish is often a problem. It is the responsibility of the fabric finisher to address these issues if commercial flame-retardant fabrics are to be produced. An alternative for the fabric designer without most of the named problems is the use of flame-resistant modified fibres, but... 

Research into controlled-release antimicrobials continues with organo-silver compounds and silver zeolites, which are promising candidates for textile finishes. Silver ions, for example, incorporated in glass ceramic, have a very low toxicity profile and excellent heat stability. These principles are also used for fibre modification, an alternative to the antimicrobial finishes with high permanence. In recent years a variety of antimicrobial modified fibres have been developed, including polyester, nylon, polypropylene and acrylic types. An example of these fibre modifications is the incorporation of 0.5-2 % of organic nitro compounds... 

One way to prevent the development of unpleasant odours that originate from the decomposition of sweat are antimicrobial finishes or bacteriostatic modified fibres. They prevent the decomposition of perspiration by bacteria to bad smelling products as described in Chapter 15. 

The other approach is to modify the cellulose chemically. Rowell et al. (1994) discussed the application of both thermal and chemical modification techniques to modify fibre used to manufacture low density fibreboards. The acetylation technique appears to offer significant improvement in the stability of panels, but the technique has not achieved significant commercial success largely because of the cost of the chemicals required. 

Determination of the fibre type, including checking of the stated fibre type, is one of the most important preliminary tests. If no IR spectrometer is available, standard fibres can be most readily identified using the characteristic reactions according to Stratmann. For modified fibres or high-performance and speciality fibres the more complicated classification on the basis of solubility groups and their subdivisions or other methods of analysis have to be used. 

It is noted here that modified fibres conserve up to 81% of strength at thermal treatment up to 290 C, whereas this value in unmodified fibre is 60% [251-252]. 

Amount of amorphous part in modified fibre decreases this will increase fibre strength and improve its mechanical characteristics, since amorphous region is the most weak for mechanical loads action and stress as it contains regions of the least degree of order in macromolecules package and in the region of defects concentration. 

High degree of crystallinity causes high fibre density, resistance to the action of chemical reagents and physico-chemical properties of polymer. Fibrillar structure of the fibre is seen in microphotoes of modified fibres, moreover introduction of hexaazocyclanes into PETP facilitates increase of regularity and density of polymer structure. All this proves that introduction of hexaazocyclanes additives increases PETP ability to crystallization. 

A study was carried out to prepare antibacterial polyamide fibres by the modification of standard monofilament yam with nitrofuiylo, to examine the liberation of biocides into water and to verify the antibacterial effects of the modified fibres by in vitro testing using Gram-positive and Gram-negative bacterial strains characteristic of hospital conditions. 22 refs. 

The ionic strength of the solution does not affect the adsorption capacity of the modified fibres up to mol l h... 

Isocyanate chemistry was also explored in order to graft long alkyl chains on the cellulose fibres and use the modified fibres as sorbent for organic pollutant... 

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