Influence of Prereserved Shish Crystals on the Structural Evolution of Ultrahigh-Molecular Weight Polyethylene Films during the Hot Stretching Process

Abstract

Prereserved shish crystals and their influence on the macroscopic properties and structural evolution of ultrahigh-molecular weight polyethylene (UHMWPE) films during the hot stretching process were studied by in situ small-angle X-ray scattering (SAXS)/ultrasmall-angle X-ray scattering (USAXS)/wide-angle X-ray diffraction (WAXD) measurements and ex situ differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) measurements. The SEM result that the fibrous crystals in UHMWPE powder induced the formation of shish-kebab crystals in solution confirmed that the fibrous crystals were shish crystals. The initial UHMWPE films containing prereserved shish crystals were obtained by compression molding of the nascent UHMWPE powder at 135 and 138 °C. With hot stretching, a USAXS/SAXS signal representing the prereserved shish crystals and the prereserved shish-induced shish-kebab crystals appeared, which was also confirmed by ex situ SEM. This means that the presence of prereserved shish crystals made the easier epitaxial crystallization of the fragmented ordinary lamellae form shish-kebab crystals, which accelerated the evolution of ordinary lamellar crystals to shish-kebab or shish crystals. Moreover, the prereserved shish crystals induced the formation of more and longer new shish crystals, resulting in a significant increase in the relative intensity and average length of the final shish crystals. The corresponding crystallinity and the degree of orientation also increased during hot stretching. Prereserved shish crystals, which induced the formation of more shish crystals, resulted in a significant improvement in the mechanical properties of UHMWPE films.

Scanning Small-Angle X-ray Scattering of Injection-Molded Polymers: Anisotropic Structure and Mechanical Properties of Low-Density Polyethylene

“…Mechanical properties such as impact toughness were then associated with the crystalline orientation. 2 Several studies have been using small-and wide-angle X-ray scattering (SAXS/WAXS), 3 often in combination with other techniques such as scanning electron microscopy (SEM), 4 differential scanning calorimetry (DSC), 5 and mechanical testing 6,7 or a combination of them 8 in order to get an indepth understanding of the hierarchical structures in injectionmolded polymers. It has been shown that the skin layers, where the shear and cooling rates are high, often consist of so-called shish-kebab structures.…”

Disclosing the fatigue deformation mechanisms of different types of poly (ethylene terephthalate) industrial fibers on the base of the multiscale structural evolutions

“…A bundle of sample was placed on a sample holder with the fiber direction perpendicular to the x‐ray beam. Standard calculations for a long period ( L M ), lamellar diameter ( L E ), lamellar thickness ( L N ), and the lamellar tilting angle ( 𝜙 ) were conducted using X‐polar software (Precision Works Inc., NY, USA) with reference to previously reported literature 1,32–36 …”

“…Standard calculations for a long period (L M ), lamellar diameter (L E ), lamellar thickness (L N ), and the lamellar tilting angle (ϕ) were conducted using X-polar software (Precision Works Inc., NY, USA) with reference to previously reported literature. 1,[32][33][34][35][36] 3 | RESULTIS AND DISCUSSION…”

“…From the 2D SAXS patterns of samples under different fatigue stress conditions (as shown in Figure 7a), it can be observed that the HT industrial fiber pattern exhibits no significant changes, whereas the LS industrial fiber's interplanar spacing in the axial direction of crystallites decreases, indicating a more obvious variation in LS fiber's crystalline lamellar structure. Further analysis of the longitudinal and transverse integrals of the SAXS pattern axial direction of crystallite diffraction peaks enables calculation of the lamellar structural parameters, 32,44 the detailed data processing process is shown in the Figures S3 and S4. The obtained lamellar thickness, lamellar diameter, long period, and lamellar tilting angle are shown in Figure 7b-e.…”

Structural Evolution of High-Entanglement Ultrahigh Molecular Weight Polyethylene Films with Reserved Shish Crystals during the Hot Stretching Process

“…However, such research remains at the laboratory stage and has not yet met the requirements for industrial production. Currently, industrial and commercial UHMWPE resins still exist in a highly entangled state, resulting in high melt viscosity, poor flowability, and difficulties in processing and shaping during manufacturing. ,, To overcome this challenge, methods like blend modification, , gel spinning, − and compression molding ,− have been developed for UHMWPE processing. Among these, compression molding stands out as a nonflow processing method that largely reduces the limitations of poor UHMWPE flowability, making it one of the most straightforward processing techniques available .…”