Trans–gauche rotational isomers in partially oriented poly(ethylene terephthalate) fibers

Abstract

The structural characterization of poly(ethy1ene terephthalate) (PET) fibers has received considerable attention in order to understand better the relationship between structure and fiber properties and because of interest in how the polymer crystallization process is influenced by parameters such as stress and temperature. In particular, the variation in structure of the as-spun fiber with increasing wind-up speed has been studied extensively.13 At relatively low (<lo00 m/mU wind-up speeds the as-spun fiber is amorphous and has little preferential molecular orientation. With increasing wind-up speed the degree of orientation is increased as evidenced by, for example, increasing birefringence3s4 until at high wind-up speeds (>4000 m/min) extensive crystallization occurs and the properties of the fibers begin to resemble those of a drawn fiber (i.e., higher breaking strength, lower elongation to break).ls3v5

Orientation and Structure of Single Electrospun Nanofibers of Poly(ethylene terephthalate) by Confocal Raman Spectroscopy

“…The population of gauche conformers follows the opposite trend. This increase in trans fraction with orientation is in agreement with studies of fibers formed at high wind-up speed 34 and of films stretched to high draw ratios. 38,44 While this method is only semiquantitative because of the approximations associated with eq 11, it demonstrates very well the capability of Raman spectroscopy to follow small structural changes in individual nanofibers.…”

“…A similar but more complicated behavior is observed for the 1096 cm –1 band which is also associated with the trans conformation . This is in agreement with the gauche -to- trans rotational isomerization of the ethylene glycol units upon orientation . These results indicate that the population of trans conformer increases with the overall orientation of the polymer chains and that their degree of orientation is extremely high in all cases.…”

“…24 This is in agreement with the gauche-to-trans rotational isomerization of the ethylene glycol units upon orientation. 34 These results indicate that the population of trans conformer increases with the overall orientation of the polymer chains and that their degree of orientation is extremely high in all cases. In contrast, the bands associated with gauche conformers 24 show the opposite behavior.…”

New Insights into the Development of Ordered Structure in Poly(ethylene terephthalate). 1. Results from External Reflection Infrared Spectroscopy

“…Bands specifically associated with the gauche conformers show low or negligible dichroism, as is generally observed. 26,[88][89][90] Perpendicular dichroism (negative peaks in Figure 3) is observed for the carbonyl band at 1727 cm -1 and the out-of-plane ring C-H bands at 873 and 729 cm -1 . Parallel dichroism is observed for the trans conformer bands at 1340 and 973 cm -1 , the C-H in-plane band at 1018 cm -1 , the weak ring bands at 1577 and 1505 cm -1 , and the main components of the complex bands around 1265 and 1110 cm -1 .…”

The Structure and Properties of Typical Melt-spun Fibres

“…In the late 1970s, the infra-redspectroscopy technique (more information on infra-red spectroscopy will be given in Section 4.2.1) was widely used by a number of workers [175][176][177][178][179][180], mainly to evaluate the orientation behaviour of crystalline and non-crystalline PET. Measurement of molecular orientation was also carried out on PET by means of laser Raman spectroscopy [181].…”