The in-phase modulus and coefficient of diffusion of nylon 6 fibers are analyzed in terms of wide-and small-angle X-ray diffraction data. Both properties are examined in directions parallel and perpendicular to the fiber axis. The anisotropy in diffusion and mechanical coupling between the crystalline and amorphous phase reaches its maximum at relatively low draw ratios of about 2.5 to 3.0X. With increasing draw ratio the anisotropy in these properties decreases monotonically and reaches its minimum value with the fibers of the highest draw ratio (5.35X). The diffusion analysis yields a heretofore undetermined structural parameter, the separation of the microfibrils. The results indicate that increases in draw ratio lead t o an increase in the distance between the microfibrils, a decrease in the diameter to length of the crystallite, and a decrease in the diffusion constant of the permeable phase. The longitudinal structure of the microfibril is not affected significantly during this phase of drawing. These observations cannot be explained by the microfibrillar fiber model derived from studies of polyethylene and polypropylene fibers. A new structural model is proposed in which the strength, diffusion, and modulus are controlled by the densely packed matrix. The model is corroborated by transmission electron micrographs from thin fiber cross sections. be reproduced o r transmitted in any lormor by any means. electronic or mechanical, including photocopying. microfilming. and recording, or hy any information storage and retrieval system, without permission in wiling from the publisher.

synopsisTwo types of emulsion-grade polytetrafluoroethylene particles have been studied. We refer to these as ribbons and rods. The ribbons consist of very thin ribbons or lamellae folded upon themselves a number of times. In typical emulsion-grade material prepared at Allied Chemical, the unraveled ribbon measures about 3.25 p in length, 0.25 I( in width, and 60 d in thickness. The folded ribbons, which form the particles, are about 0.5 p long and 0.25 p wide. Electron diffraction shows that the ribbons are single crystals with the chain axis parallel to the long axis of the ribbons thus forming extended chain crystals. This extended-chain packing is consistent with the observed cleavage or fibrillation of the ribbons and with the molecular weight. The rods are formed in lowyield polymerizations. Electron diffraction also shows that the rods are single crystals with the chain axis parallel to the long axis of the rods. Striations parallel to the long axis are believed to result from stacking of parallel segments. Considerable bending of the long axis of rods is observed.

SynopsisThe influence of polymer structure on the orientational memory in the molten state has been studied by observing the crystallization behavior of the molten polymer through differential scanning calorimetry. It is shown that polymers with strong intermolecular forces (e.g., H-bonding) retain the orientation memory even at temperatures above their equilibrium melting temperatures. The retained orientation memory of the polymer melt is shown to influence its recrystallization rate and the morphology.

No abstract

The observation of a novel phenomenon is reported whereby the processing history of a nylon 6 leads to a memory effect which in turn affects its crystallization rate from the molten state. Differential scanning calorimetry (DSC) and optical microscopy are the primary techniques used to demonstrate that the melt‐crystallization behavior of nylon 6 can be controlled by processing variables. Characterization data is presented to show that obvious parameters such as molecular weight, impurities, monomer and oligomers, etc. are not responsible for the observed changes in crystallization behavior upon processing. It is shown that the mechanical properties and/or morphology of a nylon 6 article can depend upon the processing technique (e.g., compression or injection molding) as well as the processing history of the nylon 6 resin itself.