Annealing behavior of gel‐spun polyethylene fibers at temperatures lower than needed for significant shrinkage

Abstract

The annealing at 373 K of ultrastrong, gel-spun polyethylene (PE) has been studied. At this temperature, the fibers show no significant shrinkage. Still, a significant decrease in the mechanical properties is observed. The fibers have been analyzed with differential scanning calorimetry (DSC), temperature-modulated differential scanning calorimetry (TMDSC), atomic force microscopy (AFM), and small-angle X-ray scattering (SAXS). During the annealing, the glass transition of the intermediate phase is exceeded, as shown by DSC. When split for structure analysis by AFM, the annealed fibers undergo plastic deformation around the base fibrils instead of brittle fracture. The quasi-isothermal TMDSC experiments are compared to the minor structural changes seen with SAXS and AFM. The loss of performance of the PE fibers at 373 K is suggested to be caused by the oriented intermediate phase, and not by major changes in the structure or morphology. The overall metastable, semicrystalline structure is shown by TMDSC to posses local regions that can melt reversibly.

Viscoelastically generated prestress from ultra-high molecular weight polyethylene fibres

“…Thermal treatment (0.25 h) of UHMWPE fibres shows that tensile strength is unaffected, though modulus decreases and strain-to-break increases progressively with increasing temperature up to 130°C [13]. Annealing at 100°C is found to relax some of the strain in the intermediate (oriented amorphous) phase between crystals, which results in a brittle to plastic transition within these regions [14]. By considering these aspects, the annealing conditions for this work were set to 120°C for 0.5 h.…”

“…Thus recovery force must also be affected and perhaps, skin-core effects. X-ray diffraction results for Dyneema at 120°C [31] (our annealing temperature) indicate some crystalline rearrangement may have occurred, and strain relaxation within the amorphous regions can also be expected [14,33] but the optimum annealing conditions for recovery force output would require further investigation. For (ii), as indicated by Figs.…”

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

“…It can be seen that the DSC curves of final UHMWPE fibers stretched at different temperatures show two main melting peaks. In combination with 2D SAXS results, the first main melting peak located between 143°C and 146 ° C is caused by the melting of microfibrils composed mostly of shish crystals, and the second main melting peak between 149°C and 153 ° C is thought to the result of the orthorhombic‐to‐hexagonal phase transition . It can be seen that the first melting peak moves from 143.8°C to 145.4 ° C with the increase of stretching temperature, which is attributed to the fact that the microfibril structure formed at higher stretching temperature is better than at lower stretching temperature.…”

Effect of high‐temperature annealing on the microstructure and mechanical properties of polypropylene with shish kebab or spherulite structure

“…In addition, the chains in the amorphous structure are already oriented and are difficult to further stretch. This phenomenon will decrease the transfer of stress between crystalline and amorphous phases, which finally reduces the yield and impact strength . In conclusion, for spherulite or shish kebab structures, appropriate L c and X c values will likely achieve high yield and impact strength.…”