Effects of Heat and Moisture on Polymer Fibers

In Chapter 17, it was pointed out that the cross section of fibers is determined by the cross section of the spinnerette holes and the nature of the spinning process. This plays an important role in establishing the properties of the fiber. For certain applications, the spun fibers are textured after spinning. Carpet fibers, for example, are often given a heat twist and/or are crimped by passing them through a pair of gear-like rollers. 

Static electricity can be a big problem with carpets. Many carpet fibers therefore incorporate an antistatic agent (such as quaternary ammonium salts or alkyl esters of poly(ethylene glycol) to bleed off static charge. These additives are designed to bloom to the surface of the host polymer reducing the build-up of static charge. 

The polarity of the polymer also directly influences its degree of water absorption. Other things being equal, the more polar the polymer, the higher its equilibrium moisture content 

Perhaps the most important effect of moisture on polar polymers is as a plasticizer. Since fiber-forming polymers are linear, heat acts basically as a plasticizer. This explains why suits wrinkle on hot, humid days, and why the wrinkles can be removed by steam pressing. Wash-and-wear and permanent-press fabrics are produced by operations that crosshnk the fibers by reacting with functional groups on the chains, such as the hydroxyls on cellulose. The more hydrophobic polymers are inherently more wrinkle resistant because they are not plasticized by water. Wash-and-wear shirts, therefore, usually are made of blends of poly(ethylene terephthalate), a polyester, and cotton, about 65%/35%. 

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