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



A 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 at elevated temperatures. The results indicate that the first modulus maximum marks the breakdown of the amorphous entanglement network and the start of molecular uncolling by gauchetrans 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 transgauche transitions. Local stress accumulation will lead eventually to yarn rupture. © 1993 John Wiley & Sons, Inc.