In situ SAXS/WAXS studies on the evolution of hierarchical microstructure induced by hot stretching of butene-1/ethylene copolymer filaments

Abstract

Polybutene-1 (PB-1) with form I crystals has excellent mechanical properties, creep resistance, and environmental stress crack resistance. The property of polymers is closely related to their structure, but the structure-property relationship of PB-1 filaments after hot stretching and the evolution of hierarchical microstructure is still unclear. Herein, the butene-1/ethylene copolymer with 4.3 mol% ethylene co-units (PB8220 M) filaments were used for hot stretching at different temperatures. And the effect of hot stretching on the macroscopic properties and structural evolution of the filaments were investigated by in situ small-angle X-ray scattering (SAXS)/wide-angle X-ray scattering (WAXS), combined with ex situ SAXS and differential scanning calorimetry (DSC) measurements. The results indicate that the filaments exhibit a “shish-kebab” structure for all stretching temperatures. As the hot stretching progresses, the kebab crystals (lamellae) experience partial melting, followed by recrystallization to form shish crystals under stress. And the average lengths of shish crystals at all stretching temperatures first increase and then gradually decrease with the strain due to gradual growth and subsequent fracture. Higher temperature enhances the chain mobility and accelerates the transformation of crystal structure, promoting the formation of longer shish crystals, thus improving the mechanical properties of filaments. This research can provide an important reference for optimizing the mechanical properties of PB-1 materials and expanding their application fields.