In order to verify precisely the applicability and reasonableness of the time–humidity superposition method to hydrophilic crystalline polymers, stress relaxation measurements were carried out with films of polyvinyl alcohol and nylon 6 by means of a table model Instron Tensile Tester equipped with a special glass cell to control temperature and humidity. In the case of PVA, only the time–humidity superposition is applicable at humidities higher than that at which the transition begins. For nylon 6, on the other hand, time–temperature and time–humidity superposition apply very well in the transition region and fairly well at higher temperatures and humidities. The results obtained by both the superpositions coincide very well, showing the time–humidity superposition is as reasonable as the time–temperature one. The superposed results were also compared with other existing data, and the reasonableness of the time–humidity superposition was confirmed.
The crystal structure of nylon 3 was studied, and four crystalline modifications were observed. Modification I, as determined from the x‐ray diffraction pattern of drawn fibers, is similar to the α crystal structure of nylon 6. The unit cell is monoclinic; a = 9.33 Å, b = 4.78 Å, (fiber identity period), c = 8.73 Å, and β = 60°. The theoretical density for nylon 3 with four monomeric units in the unit cell is 1.39 g/cm3, and the observed density is 1.33 g/cm3. The space group is P21. The nylon 3 chains are in the extended planar zigzag conformation. Although other odd‐numbered nylon form triclinic or pseudohexagonal crystals when oriented, drawn nylon 3 crystals are monoclinic. In addition to modification I, modifications II, III, and IV were studied. Lattice spacings of modifications II and III are equal to those of modification I. However x‐ray diffraction intensities are different. Infrared spectra of those forms indicate an extended planar zigzag conformation of the chains. Modification IV is thought to correspond to the so‐called smectic hexagonal form. No γ crystals were found, and it appears that polyamide chains with short sequences of methylene groups cannot form crystals of this type.
The time-dependence of birefringence was investigated in experiments involving relaxation at constant strain, extension at constant rate of strain, and periodically varying strain. The results of constant strain relaxation are calculated from the other two types of experiments using the linear phenomenological theory of birefringence relaxation. Strain-optical coefficient spectra are calculated for a number of low- and high-density polyethylenes and characteristics of the spectra are correlated with sample density. A simple molecular theory is presented. The time-dependence of birefringence is believed to principally arise from the finite relaxation time for crystal orientation.
The birefringence changes produced by stretching, polyethylene, polypropylene and polybutene were examined. It was found that the strain
The deformation of polybutene-1 spherulites is studied by measuring the variation of their birefringence with strain at differing angular positions within the spherulite. Results are compared with a phenomenological model for the deformation process. It is concluded that the deformation process depends upon the angular orientation within the spherulite with respect to the strain direction. In order to simplify the resolution of these processes, uniaxially crystallized films are prepared in which the lamellas are believed to be arranged parallel to each other rather than radially. The results of x-ray, birefringence, and mechanical experiments on such films are described.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.