Deformation in lamellar and crystalline structures: in situ simultaneous small‐angle X‐ray scattering and wide‐angle X‐ray diffraction measurements on polyethylene terephthalate fibers

Abstract

Changes in the lamellar and crystalline structures were followed as a function of applied stress to understand the influence of the interactions between the crystalline and amorphous domains on the fiber properties. We observed a reversible transformation from a structure giving a four‐point small‐angle pattern to a structure giving a two‐point pattern; these structures corresponded to the lamellae with oblique and normal lamellar surfaces, respectively. The characteristics of these two structures such as the stack diameter, stack height, and tilt angle were different and were determined by the processing conditions and did not change when the fiber was elastically deformed. The structure giving a two‐point pattern was probably the load‐carrying lamellar entity in these fibers. The diameter of the lamellar stacks, tilt angle of the lamellae, and the strain in the lamellar spacing appeared to have the most influence on properties such as tenacity and dimensional stability. The long‐spacing strain, which is about the same as the fiber strain, determined the modulus at low elongation as well as ultimate elongation. These indicate that the lamellar stacks have at least as much influence as the interfibrillar chains on fiber properties. Structural features that determine the performance in semicrystalline polymers were investigated by analyzing four generations of polyethylene terephthalate fibers. Some of the fiber properties correlate with changes in the crystalline domains such as the crystalline orientation, size, and unit cell dimensions. Fibers in which the crystalline strain was large because of their strong linkages to the amorphous chains, and better load transfer, had the highest modulus and lowest ultimate elongation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1538–1553, 2003

Hydrogen bonding, mobility, and structural transitions in aliphatic polyamides

“…6(c)]. 72,82 The untilted population grows during deformation with a corresponding decrease in the tilted population, which retains its constant tilt. When the stress is released, the fiber mostly reverts back to the tilted form with some residual untilted lamellae.…”

“…Similar results have also been reported for polyester fibers. 82 A detailed study of such transformations can lead to a quantitative understanding of the linkages between the amorphous domains and the crystalline lamellae.…”

“…72,[77][78][79][80][81][82] Under stress, as the lamellae move apart, these lamellae rotate so that the lamellar surface normal aligns itself along the fiber axis, giving rise to two-point patterns. 72,82 This rearrangement is mostly reversible below the yield point of the polymer. It is pos- sible that uniaxial stress imposes stresses at the fold surface and the amorphous chains become more densely packed, and the lamellar surface becomes normal to the fiber axis.…”

Scattering techniques for structural analysis of biomaterials

“…Micellar structures present in many biopolymers such as a cellulose 37 and silk 38 can also be studied using small-angle scattering (SAS). The alternating crystalline and amorphous regions, which give rise to SAXS and SANS patterns (Plate Ic) 39,40 are affected by moisture and deformation. This makes it possible for smallangle scattering to be used to study the effect of hydration and deformation in polymers.…”

Structure-properties relationship of poly(ethylene terephthalate) wool-type fibres

“…The importance of this manmade fibre has, consequently, generated more basic research concerning the relationships between processing, morphology, and physical properties, e.g. [1][2][3][4][5][6][7][8][9][10][11][12][13][14].…”