High-shrink Fibers

Charisma is a blend of high and low shrink fibers. When heat-set in the steam the yarn spun from this blend can develop considerable bulk as the high shrink fiber component contracts and moves towards the centre of the yarn cross section, whilst the low shrink fibers, the majority of the blend, concentrate outwards. Such yarns have a large area of cross section, a soft handle, and produce a much improved cover and appearance in carpets. 

The polyester fibers have high shrink properties, which make them useful in fiber applications where crimp retention or high bulk is desired. Typical applications are in carpet yams, hi-loft non-woven fabrics used as interlinings, cushioning media, and filtration media, as well as in specialty yams for weaving and knitting. The fibers have a lower melting temperature compared to PET, which makes them useful as binder fibers in non-wovens, particularly in combination with PET homopolymer fibers. 

The boiling water shrinkage of standard acrylic fibers is generally quite low, as seen in Table 12.19, but may be made intentionally high for special types of fibers. High-bulk fibers that have been stretched and cooled to retain a frozen-in strain are designed to shrink up to... 

Nonwoven Fabric. Crimped PVA staple is being used for the manufacture of dry-laid nonwoven. Also, as an example utilising the uniqueness of the fiber, a soft sheet is prepared by shrinking and pardy dissolving in hot water a nonwoven from water-soluble PVA fiber and then insoliibili ing the fabric by acetalization or similar processes. This sheet is used as car wipers, wipers for high grade furniture, and for similar purposes. 

Permanent chemical crimp can be obtained by creating an asymmetric arrangement of the skin and the core parts of the fiber cross section. Skin cellulose is more highly ordered than core cellulose and shrinks more on drying. If, during filament formation in the spin bath, the skin can be forced to burst open to expose fresh viscose to the acid, a fiber with differing shrinkage potential from side-to-side is made, and crimp should be obtained (Fig. 5a). 

The second substrate utilized was a high loft polyester, representative of material used in air filters, furniture padding, and automobile interior pads. The material used here is constructed of 1 1/2 denier fiber, weighs 1 1/2 ounces per square yard, and is relatively open in construction. Polyester as a material is water resistant and flammable. This fiber ignites at around 520°C, but melts at about 265°C. In many flame retardant tests, the polyester will melt and shrink" away from the flame, giving spurrious results. Once again, not all binders have an affinity for this substrate, and flame retardancy is affected. 

Powell in 1904 found that if wood was treated with sucrose solution and subsequently dried at a high temperature, it did not shrink. By this process Powell claimed to strengthen the fibers of the wood. Rice believes that the treatment reduces the cell spaces and stabilizes the wood, thereby minimizing shrinkage and the possibility of rot. An example of the process is as follows ... 

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