Structural evolution from shish-kebab to fibrillar crystals during hot-stretching process of gel spinning ultra-high molecular weight polyethylene fibers obtained from low concentration solution

Formation and evolution of shish‐kebab structure during hot stretching in gel‐spun ultra‐high molecular weight polyethylene fibers with high concentration gel solution

“…Furthermore, the final value of kebab lateral size is almost equal to the shish diameter (Table ), which means most of kebab crystals transform to fibrillar crystals. This result is the same as that of prestretched gel‐spun UHMWPE fibers from low and high concentration solutions . The increase of shish lengths (at 100°C, 110°C, and 120°C) is due to the transition of shish‐kebab crystals to shish crystals (fibrillar crystals) via melting recrystallization, and high temperature is good for proceeding melting recrystallization, which means more chain can be disentangled to form the longer shish crystals.…”

“…Figure shows the SAXS patterns, long periods, and lateral sizes of UHMWPE fibers upon heating from room temperature to 120°C, which is taken as an example to analyze the preheating process. In Figure A, the streak pattern across the beam stop in the meridian direction, suggesting the existence of microfibril structures (mainly consisting of shish crystals), while the two‐point pattern along the equatorial direction is the scattering pattern of highly oriented lamellar structures (ie, kebab structure) . With the increase of temperature, the streak pattern has no obvious change up to 120°C, but the intensity of two‐point pattern strengthens.…”

“…So the transformation of randomly oriented lamellae to shish‐kebab crystal, that is, the formation of shish‐kebab crystal, is the key precondition for the evolution of a shish‐kebab crystal to a fibrillar crystal. Moreover, we also studied the transformation of shish‐kebab crystals of gel‐spun UHMWPE fibers both were obtained from low and high concentration gel solutions, and we found that the shish‐kebab crystals formed under the same conditions could transform to microfibril structures at stretching temperatures ranging from 90 to 120°C, though the transformations of those from high spinning concentration were more difficult than those from low spinning concentration …”

Structural transformation from shish‐kebab crystals to micro‐fibrils through hot stretching process of gel‐spun ultra‐high molecular weight polyethylene fibers with high concentration solution

“…It is reasonable that the force decreases with the increasing stretching temperature. The UHMWPE fibers obtained from high concentration solution were broken at the strains ranging from 80 to 130% which are reasonable increase compared with those from low concentration solution …”

“…The final value of long period at 120 °C smaller than the initial value is due to the formation of better shish crystals after transition point with the lower degree of entanglement than that at the beginning of hot‐stretching. At the same stage, the fragmentation or melting recrystallization processes occurred after yield point of UHMWPE fibers obtained from high concentration solution are weaker than those from low concentration solution due to the high degree of entanglement, and the stress is more difficultly conducted on the lamellae and the formation of new kebab crystals is seriously affected by the chain entanglement . The analysis above corresponds to the result that the transformation from shish‐kebab crystal to the shish crystal composed mostly of extended chain crystals is easier at 120 °C comparing with the temperature of 90, 100, and 110 °C in Figure .…”