Interactions of Nonaqueous Solvents with Textile Fibers Part III: The Dynamic Shrinkage of Polyester Yarns in Organic Solvents1

et al. 1981

The effects of an aqueous-dodecylsulfate solution buffered to pH 5 at 100°C on the structure and physical properties of an oriented semicrystalline PET yarn were measured as a function of time. Chain relaxation resulting in longitudinal shrinkage is shown to be the primary molecular event, and crystallization to be a secondary process involving the newly-relaxed amorphous chains. Four major structural events are observed: 1) longitudinal shrinkage, 2) crystallization leading to structural stabilization, 3) surface stress concentration, and 4) rapid hydrolysis and decline in molecular weight following surface cracking of the fibers to relieve surface stress concentrations. Comparison of the effects of aqueous, thermal, and solvent (dimethylformamide) treatments of PET suggests that the molecular mechanisms and kinetics of aqueous and of thermally-induced changes are similar. Solvent-induced changes are to a large extent controlled by diffusion processes. Aqueous and solvent-treated PET are similar, in that there is an increase in structural "porosity" as a result of crystallization in the swollen state.

Section: Deferential Thermal Analysis (Dta)supporting

confidence: 83%

The Effects of an Aqueous Medium on the Structure and Physical Properties of a Polyester Yarn

Knox

Scott

et al. 1981

“…The shrinkage behavior in the upper region of each curve in Figure 1 demonstrates differences in the nature and degree of interaction between polymer and solvent Shrinkage in DMF and DMAc approaches an &dquo;equilibrium&dquo; value that appears to be independent of temperature, whereas in DMSO, shrinkage and presumably also polymer-solvent interaction continue to increase with temperature [4]. The latter behavior has previously been observed in studies at TRI of the dynamic shrinkage of polyethylene terephthalate yarns in various solvents [6]. The magnitude of the shrinkage reveals that DMSO interacts more strongly with Nomex than DMAc, which shows a slightly higher degree of interaction than DMF.…”

Section: X-ray Diflraction Studiesmentioning

confidence: 53%

“…The apparatus used for the shrinkage measurements has been described previously [6]. A yarn sample (~-8 cm), from which a small weight (-150 mg) was suspended to overcome buoyancy and crimp effects, was heated in the solvent from room temperature (21 °C) at of dyebath exhaustion was measured by periodically removing aliquots of dye liquor and, after suitable dilution, determining dye concentration spectrophotometrically.…”

Section: Shrinkage Studiesmentioning

confidence: 99%

Dyeability of Nomex® Aramid Yarn

Moore

1986

Treatments in highly polar solvents, such as dimethyl formamide, dimethyl acetamide, and dimethyl sulfoxide, under suitable conditions have been found to improve the dyeability of Nomex® yam so that it can be dyed under atmospheric conditions in a reasonable length of time without the aid of a carrier. Essentially, these solvents provide chemical energy to the yam, permitting rearrangements of the polymer chains through breakage and reformation of interchain hydrogen bonding. The changes in dyeability may be attributed to orientation changes or to microvoid formation occurring in the fiber structure during treatment.Nomex*, a commercially available, thermally stable aramid fiber, is difficult to dye because of its extremely high glass transition temperature (Ta ~ 275°C). At present, the recommended method for dyeing Nomex involves relatively high concentrations of a dye carrier in the dyebath and a high dyeing temperature for a long period of time [3]. Such conditions require substantial amounts of energy to maintain dyeing temperature and for the treatment of waste dyebaths.Recent work at TRI has focused on the use of chemical energy provided by a suitable solvent to modify fiber structure and thereby improve dyeability [5,8].In our studies on Nomex, this concept was explored by modifying the Nomex structure with highly polar solvents such as dimethyl formamide, dimethyl acetamide, and dimethyl sulfoxide [4]. Characterization of the extent of interaction between these solvents and Nomex has involved a study of shrinkage phenomena under dynamic (constant heating rate) conditions. In addition, we have examined the effects of the various solvent treatments on the dyeing and mechanical properties and on the structure of Nomex. '

“…The solvent-induced shrinkage of oriented, semicrystalline polyethylene terephthalate (PET) fibers is reported in Parts I-III of this series [37][38][39]. The basic molecular mechanisms of thermal [11,12,36,41] and of solvent-induced shrinkage [3'l-39~ of oriented, semicrystalline PET fibers can be viewed similarly as a disruption of intermolecular cohesive forces in the polymer through an input of energy leading to an increase in chain mobility.…”

Section: Introductionmentioning

confidence: 99%

“…The linear relationship between final shrinkage and temperature allows one to extrapolate to a zero-.. shrinkage temperature To, the temperature below which shrinkage in a given solvent does not occur. It was suggested [38,39] that the zero-shrinkage temperature To may, as a first approximation, be equated to the To of' the given PET-solvent system. , Therefore, chain mobility in excess of that defined by the 7~ permits an internal structural rearrangement of the polymer chains into a new configuration.…”

Section: Introductionmentioning

confidence: 99%

Interactions of Nonaqueous Solvents with Textile Fibers

Knox

Scott

1975

Measurements of longitudinal shrinkage and volume swelling of polyester (PET) fibers in a wide variety of solvents were made at room temperature for time periods sufficient to establish quasiequilibrium conditions. Evaluated in terms of the solubility parameters ( & d e l t a ; ) concept, these results, together with iodine displacement studies, indicate that: (1) PET may be treated as an ( AB ) x alternating copolymer, where A is a semirigid aromatic residue —CO-C 6 H 4 — with a δ-value of 9.8, and B is a flexible aliphatic ester residue —O-CH 2 -CH 2 -O-CO— with a δ-value of 12.1 ; and (2) the preferential interaction of a solvent with either of the two PET residues provides the necessary chemical energy to disrupt intermolecular cohesive forces between the polymer chains, permitting relaxation of internal orientation forces and shrinkage of the fiber. It is shown by successively treating PET in solvents of increasing plasticizing strength that solvent-induced crystallization, a secondary process involving chain folding of the newly relaxed chains, does not inhibit shrinkage at lower temperatures. Therefore, room temperature chemical annealing is viewed as being similar to low-temperature (<175°C) thermal annealing, where small crystallites are formed which confer negligible dimensional stability on the fiber undergoing shrinkage.. ' ABSTRACT Five samples of fabric treated with a silicone resin to prevent felting were examined for the presence of fiber bonds, using optical microscopy, micromanipulation, and measurement of the force required to withdraw a single fiber from the fabric. In all cases fiber bonds were found to be present and to be responsible for the resistance to felting. A sample of similarly treated tops, which acquired very little resistance to felting as a result of the treatment, was also examined. The fibers in this sample were coated with the resin but showed no fiber bonding, and their frictional properties were similar to those of normal, untreated fibers. Stress is laid on the difficulty which may sometimes be encountered in demonstrating the presence of interfiber bonds, and on the need for examination by micromanipulation before the conclusion is reached that they are not present.