Fiber stretch, cold

Fiber stretch, cold Pulling operation with little or no heat on fibers to increase tensile strength. 

The uniform oxidation of the cold-drawn filament results in a high overall degree of oxidation and associated backbone scission before surface deterioration reaches the level at which spontaneous restructuring and crack formation can occur. Lateral cohesion of these fibers was much greater than for the highly oriented filaments. For example, the latter could be easily peeled, whereas the cold-drawn fiber stretched rather than fibrillated after notching. 

Compression molded (150°C for 3 minutes press chilled with cold water immediately thereafter) samples of poly(trans-l,4-hexadiene) (14) and poly(5-methyl-l,4-hexadiene) were examined with a General Electric (XRD-3) X-ray unit. Transmission Laue X-ray photographs were taken using nickel filtered copper X-radiation. Samples were stretched to four times of their original lengths to obtain oriented fibers. The fiber patterns were obtained in a flat plate film holder with the specimen to film distance standardized at 5 centimeters. X-ray diffraction patterns were similarly obtained for the hydrogenated sample of poly(5-methyl-l,4-hexadiene). 

Fibers oriented by stretching to 4 x original length by cold drawing (two pulleys at different speeds) or by spin drawing as it is being cooled... 

J.J. Kim, T.S. lang, Y.D. Kwon, U.Y. Kim and S.S. Kim, Structural Study of Micro-porous Polypropylene Hollow Fiber Membranes Made by the Melt-Spinning and Cold-Stretching Method, J. Membr. Sci. 93, 209 (1994). 

This is generally termed cohesive set. When steamed or boiled in water and released in cold water stretched fibers retain much of the extension, but on immersion in boiling water this decreases rapidly at first and then more slowly over a prolonged period. The set which is lost in 1 hr is arbitrarily designated temporary set and the residual set permanent set, It is probable that several reactions occur simultaneously and the so-called permanent set continues to decrease with continued boiling of the slack fibers for several hours (Blackburn and Bindley, 1948),... 

From most solvents Ss crystallizes as orthorhombic a-Ss. Monoclinic pSg is stable above 96 °C and is usually obtained by cooling liquid sulfur slowly below the triple-point temperature of 115 °C. At 25 crystals of pSg convert to polycrystalline a-Ss in less than 1 h but are stable for several weeks at temperatures below -20 C [27]. y-S is metastable at all temperatmes and occasionally crystallizes by chance, for example from ethanolic solutions of ammonium polysulfide [28], by decomposition of copper ethybcanthate [29] or in the preparation of bis(dialkylthiophosphoryl)disulfane [30]. Smpris-ingly, y-Ss occurs also naturally as the minerd rosickyite. Fmthermore, 7-8 is a component of stretched plastic sulfur which is obtained by quenching liquid sulfur from 350 C to 20 °C (in cold water) and stretching the fibers obtained in the direction of their axes. According to an X-ray diffraction study, this fibrous sulfur consists of helical polymeric sulfur chains (S[Pg.7]

The most perfect reversible a—>0 transformation has been obtained by stretching in saturated ammonium sulfate at 90-100°C. Fibers can be stretched quite easily in this solution and show little tendency to contract when they break. The ammonium sulfate hydrates and lubricates air-dried fibers to just the right extent to facilitate transformation. There is no tendency to produce disoriented 0, but a difficulty arises during the washing away of ammonium sulfate. With the extended fibers the internal structure relaxes and 0 returns to a, so that washed but stretched fibers show a mixture of a and 0 patterns. This has been overcome to a considerable extent as follows After stretching in hot ammonium sulfate and cooling, the specimens are transferred to cold saturated solution containing about 5% formaldehyde. Left in this solution for 36-48 hours, the ammonium sulfate can be washed away,... 

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