Thermoplastic fibres

As the cloth or web falls into the liquor from the winch at the back of the machine, it tends to bunch up and lie in a heap for a short time. This is no disadvantage with wool or cotton materials, but tends to cause serious creases in acetate rayons and other thermoplastic fibres. To overcome this a long shallow machine with an elliptical winch has been designed (Fig. 13.24). The elliptical shape of the roller folds the material in wide layers which are free from random creases as it falls into the dye liquor. The... 

Filter fabrics, especially nonwoven fabrics, which are produced from short staple fibres, invariably possess surfaces with protruding fibre ends. Since such protrusions may inhibit the cake release by clinging to the dust, it is a common practice to remove them. This is achieved by singeing, a process in which the fabric is passed, at relatively high speed, over a naked gas flame, or, in another technique, over a heated copper plate. The heat of the flame causes the fibres to contract to the surface of the fabric where, in the case of thermoplastic fibres, they form small hard polymer beads (Fig. 3.8). Singeing conditions (i.e. speed and gas pressure) will normally be adjusted according to polymer type and the intensity required by either the end-use application or the individual manufacturer s preference. 

The interphase in PE fibre/epoxy resin matrix composites was studied by FTIR microspectroscopy using a set-up for investigation of the matrix as close to the fibre as a few microns or less. It was shown that moisture present on the fibre surface could influence the polymerisation reaction of the epoxy/anhydride matrix in an irreversible manner. This effect was enhanced for composites from the more hydrophilic PVAl fibre. The fibre/matrix interaction in these thermoplastic fibre composites was also studied by DSC through characterisation of the fibre melting. A decreased DSC interaction parameter was found if the composition of the interphase was changed by moisture. For a composite with an epoxy/amine matrix, on the other hand, the DSC interaction parameter was unaffected by moisture from the fibre surface. 22 refs. (Pt.I, ibid, p.83-100)... 

The melt-spun thermoplastic fibres, nylon, polyester, polypropylene, show a quite different form of breakage. In undrawn fibres, which are unoriented or partially oriented, rupture occurs at the end of a long period of plastic extension at slowly increasing tension. In oriented fibres, which have been drawn, the stress-strain curve terminates in a short yield region, the residual plastic extension, before rupture occurs. Break starts as a crack, usually from a flaw but otherwise self-generated by coalescence of voids. Fig. 3a. The... 

Thermoplastic fibres often are more difficult to wet (see adsorption theory. Table 13.3). This is especially tme for the thermoplastics such as polyolefins and linear polyesters. Methods used to increase the wettability and improve adhesion include the surface treatments shown in Table 13.7. The effects of surface treatments generally decrease with time, so it is important to carry out adhesive bonding as soon as possible after surface preparation. 

It is striking that the continuous random-mat-based moulding shows essentially the same level of properties as those based on fabrics, even though these random fibres contain some 6-8 %(m/m) of a thermoplastic fibre binder. This implies that there is no reason to use fabric-based preforms in a non-oriented fibre lay-up pattern, since continuous random-based preforms are far easier to make and result in composites with comparable properties. This finding is very important for automotive applications, as it increases the likelihood of an automated process for making preforms being developed. 

The majority of nanotube/nanofibre-filled thermoplastic fibres are made by variants of melt spinning, or approximations based on sample collection from rheometers and the like, representing an optimisation of previous alignment approaches based on die designs and simple melt strand or film stretching. While conventional melt processing of the nanocomposite dope is desirable for economical reasons, initial solution-blending is often performed in the case of SWCNT-filled polymers, yet the effectiveness of this approach remains debatable. 

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