Crease

One type of dislocation is the edge dislocation, illustrated in Fig. VII-7. We imagine that the upper half of the crystal is pushed relative to the lower half, and the sequence shown is that of successive positions of the dislocation. An extra plane, marked as full circles, moves through the crystal until it emerges at the left. The process is much like moving a rug by pushing a crease in it. 

These boiling points illus trate why we should do away with the notion that boiling points always in crease with increasing molec ular weight... 

Alcohols react with hydrogen halides to yield al kyl halides The reaction is useful as a synthesis of al kyl halides The reactivity of hydrogen halides de creases in the order HI > HBr > HCI > HF Alcohol re activity decreases in the order tertiary > secondary > primary > methyl... 

FIGURE 8 9 A polar solvent stabilizes the transition state of an SnI reaction and in creases its rate... 

FIGURE 13 18 The appear ance of the splitting pattern of two coupled protons de pends on their coupling con stant d and the chemical shift difference Av between them As the ratio Av/d de creases the doublets be come increasingly distorted When the two protons have the same chemical shift no splitting IS observed... 

Enolization (Sections 18 4 through 18 6) Aldehydes and ke tones having at least one a hydro gen exist in equilibrium with their enol forms The rate at which equilibrium is achieved is in creased by acidic or basic cata lysts The enol content of simple aldehydes and ketones is quite small p diketones however are extensively enolized... 

We tend to take the efficacy of modern drugs for granted One comparison with the not too distant past might put this view into better perspec tive Once sulfa drugs were introduced in the United States the number of pneumonia deaths alone de creased by an estimated 25 000 per year The sulfa... 

New The number of boxed essays has been in creased to 42 with the addition of... 

The wet modulus of fibers at various temperatures influences the creasing and mussiness caused by laundering. Figure 6 shows the change with temperature of the wet modulus of acetate and triacetate, and compares them with a number of other fibers (2). Acetate, triacetate, and rayon behave quite similarly, with a lower sensitivity than acryUc. 

From 1910 onward waste filament yam had been chopped into short lengths suitable for use on the machinery designed to process cotton and wool staples into spun yams. In the 1930s new plants were built specifically to supply the staple fiber markets. During World War II the production of staple matched that of filament, and by 1950, staple viscose was the most important product. The new spun-yam oudets spawned a series of viscose developments aimed at matching the characteristics of wool and cotton more closely. Viscose rayon was, after all, silk-like. Compared with wool it lacked bulk, residence, and abrasion resistance. Compared to cotton, it was weaker, tended to shrink and crease more easily, and had a rather lean, limp hand. 

High molai mass polyuiethanes weie obtained from condensation of 4,4 -(hexa luoioisopiopylidene)bis(phenylchloiofomiate) with various diamines (125). These polymers could be cast into transparent, flexible, colodess films or spun into fibers which showed promise as crease-resistant fabrics. Other polyurethanes discovered are good candidates for naval and aerospace apphcations (126). 

Textile Finishing. Polyethyleneimine-A/-methylolurea derivatives improve the crease and wear resistance of cotton (429,430). The adhesion between individual wool fibers is improved by pretreatment with amines, which leads to improved shrink resistance (431). An antimicrobial finish can be appHed to cotton by using a combination of PEI and ureas to bind zinc pyrithione to the fabric (432). After wool has been provided with a flameproof finish using fluorozirconate or fluorotitanate, the wool can be neutralized with PEI (433). Conventional neutralizing agents caimot be used for this purpose since they impair the flameproof characteristics of the impregnated fabric. 

The steps followed in the precure are repeated in the postcure process, except that after the drying step the goods are shipped to a garment manufacturer who makes garments, presses them into the desired shape with creases or pleats, and then cures the amino resin on the completed garment. 

Thus, if the fabric is flat and smooth, it will tumble dry in that configuration. On the other hand, if the fabric is cross-linked in a creased condition, as in a pleated skirt, the original pleated skirt configuration should return on laundering and tumble drying. 

Although delayed cure cotton was the primary impetus in the rise to durable-press performance, the emergence of DP blends had the effect of reducing the importance of a tme delayed cure. The industry tended to revert back to precure fabrics and the utilisation of hot-head presses to set in creases, using the thermoplastic characteristics of the synthetic components as weU as a touch of recure from the hot-head presses. 

Finishing of Wool. Wool (qv) competes for markets where warmth, wrinkle recovery, and abiUty to set in creases are important. Wool problems relate to shrinkage, particularly to its tendency to felt. This is caused by scaly stmcture, which tends toward fiber entanglement when wet and subjected to mechanical action. In order to compensate for this tendency, wool needs to be set and also made shrinkproof if it is to be laundered. 

It is generally accepted that, all other things being equal, the lower the secondary creep, the better the fiber is in terms of wear, shape retention, and crease resistance. This does not mean that glass, which has no secondary creep, is better in abrasion resistance than high tenacity viscose rayon, which has secondary creep, because the respective energy absorption capacities of these two materials, exclusive of secondary creep, are not equal. Nor does it mean that fibers that exhibit secondary creep are of no value. For fabrics to meet the requirements of wear, crease resistance, and shape retention, the load and extension yield points should not be exceeded during use. 

Grease Retention, Wrinkle Resistance, and Durable Press. On bending or creasing of a textile material, the external portion of each filament in the yam is placed under tension, and the internal portion is placed in compression. Thus, the wrinMe-recovery properties must be governed in part by the inherent, tensional elastic deformation and recovery properties of the fibers. In addition to the inherent fiber properties, the yam and fabric geometry must be considered. 

AATCC Test Method no. 66 describes measurement of recovery angle after placing a crease in a specimen. The specimen is creased by subjecting is to a prescribed load for a length of time. The recovery angle is then measured after a controlled recovery period. Recovery angles of greater than 120° are... 

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