Molecular changes of PET yarns during stretching measured with rheo‐optical infrared spectroscopy and other techniques

Abstract

SYNOPSISA method has been developed for measuring infrared spectra during the mechanical deformation of yarns. This rheooptical technique was applied to study the molecular processes that take place along the stress-strain curve of PET yarns. The results were combined with data obtained from size exclusion chromatography (SEC) and tensile measurements a t elevated temperatures. The results indicate that the first modulus maximum marks the breakdown of the amorphous entanglement network and the start of molecular uncoiling by gauche + trans transitions. In addition, stress develops on the crystals and particularly on tie molecules with a short contour length in the amorphous domains. Ultimately, molecular fracture of taut-tie molecules causes the modulus to pass through a second maximum. The chain ends of broken molecules recoil by trans + gauche transitions. Local stress accumulation will lead eventually to yarn rupture. 0 1993 John Wiley & Sons, Inc.

Structure–properties relations of the drawn poly(ethylene terephthalate) filament sewing thread

“…1 When vibrating hot drawing on PET fiber is applied, it was found from temperature and intensity of relaxation transition (glass-transition) that the movements of amorphous chains are strongly inhibited. 25 With regard to the findings of Van den Heuvel et al 26 and Ajji et al, 3 we suppose that drawing increases the trans conformation in the noncrystalline molecules, because macromolecules of the taut thread's filaments above the glass transition temperature (T 1 ¼ 1208C) tend to arrange along the filament's axis when straightening. Therefore, the amount of gauche conformations diminishes and proceeds to trans conformations.…”

Assessment of static rope behavior with asymmetric damage distribution

“…Net area 1 curve considers the intact rope response curve given by the 3D FE model and the Net area 2 curve the intact rope response curve provided by a model based on the linearized strain-displacement equation for rope components that assumes that rope components only develop tensile load [24]. This distinction is necessary due to the fact that, as already stated, the analytical models (Lanteigne, M-B, and NLBM) rely on the linearization of the strain-displacement equation and uniaxial rope components behavior, neglecting friction forces and local contact deformations (assumption validated in [26]); forces and deformations considered by the 3D FE model formulation [18]. As a result, predicted intact rope strength given by the 3D FE model is overestimated in about 6% by the linearized model as shown in Fig.…”

“…The nonlinear constitutive response of the rope components is directly obtained from the experimental data reported in [10]. As such, the degradation of the mechanical properties of the PET rope components experienced when they are subjected to stretching is properly accounted for [26]. A polynomial function up to the fifth degree is used to express the normal stress r t of a generic point as a function of its normal strain e t , having the following form…”

Evaluation of creep behavior of high density polyethylene and polyethylene-terephthalate geogrids

“…The pronounced peak of the modulus curve occurs at the displacement of approximately 0.6 mm, which corresponds to a load of 0.2 kN/strap (i.e., w15% UTS) in the load/elongation curve. This peak indicates the maximum resistance to stretch the PET geogrid and is caused by the breakdown of the entanglement network in the amorphous phase as molecular conformation changes from gauche / trans transitions, i.e., from a high energy level to a low energy level in molecular arrangement (Van Den Heuvel et al, 1993;Voskamp and Retzlaff, 2006). Therefore, the elongation corresponding to the peak can be used to divide the modulus vs. elongation curve into two regions.…”