Structural Evolution of UHMWPE Fibers during Prestretching Far and Near Melting Temperature: An In Situ Synchrotron Radiation Small‐ and Wide‐Angle X‐Ray Scattering Study

Abstract

Combining a homemade extension apparatus and the in situ synchrotron radiation small‐ and wide‐angle X‐ray scattering methods for measurement, the structural evolutions of gel‐spun ultrahigh molecular weight polyethylene (UHMWPE) fibers during prestretching at temperatures of 25 and 100 °C are investigated, respectively. Lamellar rotation toward the stretching direction occurs before strain hardening, while the folded‐chain crystal destruction and extended‐chain fibril formation processes occur in the strain hardening zone at 25 °C. While at 100 °C, stretching induced crystal melting before the stress plateau region and formation of fibrous crystals at the onset of the stress plateau are observed. Further stretching results in shear displacement of crystal blocks and, finally, destruction of the folded‐chain crystals and formation of extended‐chain fibrils. Prestretching UHMWPE fibers at 100 °C within a certain strain range can produce highly oriented fibrous crystals, which may provide an ideal precursor structure for the poststretching process.

The influence of formation temperatures on the crystal structure and mechanical properties of ultrahigh-molecular-weight polyethylene/high-density polyethylene-blend fibers prepared by melt spinning

“…Therefore, the crystallinity of both the U/H and U fibers increased as the hot-drawing temperature increased, and the crystallinity of the U/H blend fibers was higher than that of the U fibers. However, when the drawing temperature exceeded the optimum drawing temperature, which is 85 C for U/H blend fibers and 90 C for U fibers, a few crystalline regions of the as-spun filaments began to gradually melt, and increasing numbers of crystalline regions became strain-induced molten regions as the drawing temperature increased [30]. Moreover, as shown in Figure 9, the molecular chain orientation degree of fibers drawn at higher temperatures began to decrease, which also resulted in a reduction in the crystallinity of the fibers.…”

“…During the drawing process at a low temperature, the fibrillar structure mainly formed due to lamellar destruction. The effect of the strain-induced melting process became obvious as temperature increased [30]. If the fibers are drawn at the optimum temperature, the fibrillary structure formed by both lamellar destruction and strain-induced melting, in which the molecular chains are fully extended (as shown in Figure 9), then crystal regions form (as shown in Figure 11), crystal blocks form with the thinnest grains (as shown in Figure 15) and the orientation degree of the crystal structure is maximized (as shown in Figure 17).…”

“…Yeh et al [29] suggested that good orientation of UHMWPE molecules along the drawing direction benefits the tensile strengths and moduli of fiber specimens obtained by drawing the fiber specimens at a high temperature. Cao et al [30] proposed two distinct evolution models at stretching temperatures of 25 C and 100 C. They found that stretching-induced crystal melting occurred at 100 C but did not occur at 25 C.…”

“…Cao et al. [30] proposed two distinct evolution models at stretching temperatures of 25℃ and 100℃. They found that stretching-induced crystal melting occurred at 100℃ but did not occur at 25℃.…”

Structure and properties of gel‐spun ultra‐high molecular weight polyethylene fibers obtained from industrial production line

“…The rheological response of partially entangled UHMWPE chains both in and out of equilibrium in the tube model was also investigated by researchers 19 . The structural evolutions of gel‐spun UHMWPE fibers during prestretching at two different temperatures of 25 and 100°C were investigated by Cao et al 20 From their observations, two distinct deformation mechanisms were proposed. While transformation of folded‐chain crystals into extended‐chain fibrils in the strain‐hardened zone occurred at 25°C, formation of fibrous crystals at the onset of the stress plateau was observed during the prestretching at 100°C.…”