An Entropy Stress Study of Various Textile Fibers

Dart, S. L.

doi:10.1177/004051756003000506

Cited by 14 publications

(5 citation statements)

References 12 publications

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“…A second region of recoverable strain was attributed to stretching of the helices, and a final region, found above the Tg only, could be attributed to irrecoverable flow. Dart [5] ] had previously found that above the Tg the entropy of PAN fibers decreased with an increase in length; this is consistent with he stretching of a molecular &dquo;spring&dquo; which is initially in its maximum entropy state. The &dquo;spring&dquo; concept will be used extensively in discussion of our data.…”

Section: Introductionsupporting

confidence: 56%

“…Special ' care was needed to produce acceptable fibers at the high and low extremes of the coagulation-temperature range. Normally, at high coagulation temperature ( 70-80 ° C ) macroscopic voids within the fiber become a serious problem [ 5 ] , and filament breakage in the coagulation bath is a problem at low coagulation temperatures. Cross sections of the fibers are shown in Figure 3.…”

Section: Preparation Of Fiber Samplesmentioning

confidence: 99%

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Changes in the Structure of Wet-Spun Acrylic Fibers During Processing

Bell¹,

Dumbleton²

1971

Textile Research Journal

100

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The structural changes that occur during processing of a wet-spun 93% polyacrylonitrile -7% polyvinyl acetate copolymer are discussed. Stress-strain, x-ray diffraction, shrinkage, and electron microscopy data are explained in terms of a model in which the molecules are in an irregular helical conformation in the relaxed state and can extend during deformation. The molecules are arranged in fibrils which, in turn, form a three-dimensional network. The fibrillar elements remain intact through the coagulation, hot-stretching, and drying, although network junctures break and reform.The model proposed is an extension of that used by Rosenbaum to describe the behavior of acrylic fibers after processing and is in agreement with previous work on the structural characterization of polyacrylonitrile.

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Section: Introductionsupporting

confidence: 56%

Section: Preparation Of Fiber Samplesmentioning

confidence: 99%

Changes in the Structure of Wet-Spun Acrylic Fibers During Processing

Bell¹,

Dumbleton²

1971

Textile Research Journal

100

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“…is given by force-temperature measurements which show that dry rayon has glasslike properties4 and by entropy stress studies that show wet rayon has rubberlike properties. 17 These results indicate that there is a concentration of absorbed water below which the elastic behavior of rayon is essentially glasslike and above which it is essentially rubberlike.…”

Section: Discussionmentioning

confidence: 93%

The resiliency and modulus of viscose rayon as a function of swelling and temperature

Gill¹,

Steele²

1961

J. Appl. Polym. Sci.

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Fiber resiliency and stiffness are very important factors in the crease recovery of fabrics, and the effect of water on these properties influences fabric wash-wear behavior, especially with cellulosic fibers. This paper is concerned with the effect of absorbed water on the mechanical properties of viscose rayon fibers and how this effect may be modified by chemical treatment of the rayon.Earlier studies' have shown that for a number of synthetic textile fibers there is a temperature range wherein the resiliency shows a minimum and the modulus shows a considerable decrease. These changes were believed to arise from a glass-rubber transition in the amorphous portion of the fibers. It has been shown by Bryant and Walter from tensile measurements2 and by others3 that the glass transition temperature of fibers can be lowered by absorption of water. Bryant and Walter examined different textile fibers and found that the change in T, brought about by immersion in water increased with the hydrophilic nature of the fiber. Rayon showed no minimum in resiliency in either the wet or the air-dry state over the temperature range studied. However, the resiliency of wet rayon decreased with decreasing temperature from 30 to OOC., while in the same temperature range the modulus increased. These results were interpreted by Bryant and Walter as indicating a T , of greater than 240OC. (the decomposition temperature) for the dry fiber and of less than OOC. for the wet fiber. A second-order transition has been reported for wet rayon4sS in the region of 45OC. based on force-temperature measurements, but the results are in error due to failure to apply a swelling correction.6 Transitions have also been reported for dry rayon at -2OOC. from dielectric studies' and in the region from -20 to -6OOC. from dynamic mechanical measurements,* but these are * Presented before the Fiber Society in Washington, D. C., October 28, 1960. not considered to be the primary transition. The absorption of a plasticizer by a polymer is known to reduce but a change of more than 240OC. is exceptionally large, and we considered this remarkable effect to warrant further study.It follows from Bryant and Walter's suggestion that at intermediate degrees of water absorption the T , of rayon should fall in the measurable range between 0 and 100OC. We have made resiliency and modulus measurements as a function of both water content and temperature. Control of the water content was achieved by immersing the yarn in acetone-water mixtures, in polymer-water mixtures, and in air of different relative humidities. The effects of "wet"-state and "dry"-state crosslinking of rayon on the above properties have also been determined. EXPERIMENTALAll measuremehts were made in a room maintained at 21°C. on 42-filament, 150-denier viscose yarn having 2.5 tpi of twist. The test samples had a gage length of 3 in. and their ends were glued to tabs of phenolic-impregnated paper with a coldsetting epoxide cement. Diamond-shaped holes were punched in the tabs to accommodate the hooks whic...

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“…of filament). Iff is the stress in grams per tex and p L the linear density of the filament in tex, then F = 9 8 l f p~ (7) It is convenient to use the specific heat and internal energy per unit mass (cvL and u) rather than the thermal capacity and internal energy of the entire specimen of length L . Now,…”

Section: Range Of Strain Rate For Temperature Changesmentioning

confidence: 99%

The effect of strain rate on the stress–strain curve of oriented polymers. II. The influence of heat developed during extension

Hall

1968

J of Applied Polymer Sci

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SynopsisThe temperature changes which take place in a yarn during extension are considered. From thermodynamical considerations and the heat-transfer coefficient it is shown that extension of the yarns studied will take place isothermally at strain rates below 0.04 set.-' and adiabatically at rates above 4 sec.-l. It is not possible to make an accurate estimate of the magnitude of the temperature rise during adiabatic extension, because of the lack of information on internal energy changes during irreversible extension, but by assuming these to be zero it is estimated that the temperature is likely to rise by 20-30°C. a t strains above 10%. Results from a study of the effect of strain rate on the stress-strain curves of five different yarns show in all these materials a range of strain rate in which the stress that produces a given strain increases less rapidly with strain rate than elsewhere. For viscose and poly(ethy1ene terephthalate) this effect occurs in the expected range of strain rate, and its magnitude is of the correct order for it to be attributed to the temperature rise resulting from the transition from isothermal to adiabatic extension. For the other materials the transition does not seem likely to provide a complete explanation of this effect. There is no evidence that the transition significantly affects the breaking properties.

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An Entropy Stress Study of Various Textile Fibers

Cited by 14 publications

References 12 publications

Changes in the Structure of Wet-Spun Acrylic Fibers During Processing

Changes in the Structure of Wet-Spun Acrylic Fibers During Processing

The resiliency and modulus of viscose rayon as a function of swelling and temperature

The effect of strain rate on the stress–strain curve of oriented polymers. II. The influence of heat developed during extension

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