Structural Evolution of Ethylene–Octene Copolymers upon Stretching and Unloading

Abstract

Structural evolution of two ethylene−octene copolymers with different octene content during tensile deformation and recovery was investigated using the in-situ synchrotron small-angle X-ray scattering technique. Sample containing 4 mol % octene shows similar deformation mechanism as observed previously that the whole process of deformation can be regarded as a stretching of two interpenetrating networks of crystalline rigid network and entangled amorphous phase. A transition from a crystalline rigid network dominating behavior at small deformations to a stretching-induced crystalline block disaggregation− recrystallization process occurs at a critical strain where stress generated by the stretched amorphous network reaches a critical value leading to the destruction of crystalline blocks. In sample containing 8 mol % octene, this critical strain is much larger than observed in the other sample. Such a phenomenon is attributed to the fact that only crystalline lamellar stacks and bundle-like crystals with much weakened coupling can be developed in the sample. The weakened coupling between crystalline lamellar stacks is due to the existence of interstack amorphous phase which also leads to an inhomogeneous strain distribution in the system.

Microstructural evolution underlying the ternary stages of the elastic behaviors for poly(ether‐b‐amide) copolymer elastomers

“…This situation was also reported for a propylene‐based ethylene–propylene copolymer (84.3 wt % propylene content) after retarding from strain 5.0, and this may present the sum of two lamellar populations, that were, a set of tilted lamellae and a set of nontilted lamellae . It was also observed that the SAXS patterns of the ethylene–octene copolymer PEcO8 showed the same trend . Before fibrillation, the long period of PEcO8 after unloading is nearly unchanged; that is, it is fully recoverable.…”

“… are the critical strains of the so‐called “C point” for 35D and 40D, respectively, after which the PA12 crystals fibrillate (Fig. ) . The unloaded specimens of 35D ( the 17th point) and 40D ( the 17th point) were heated to 130 and 150 °C, respectively, and all specimens can return to the original length.…”

“…50 It was also observed that the SAXS patterns of the ethylene-octene copolymer PEcO8 showed the same trend. 49 Before fibrillation, the long period of PEcO8 after unloading is nearly unchanged; that is, it is fully recoverable. After fibrillation occurs, an irreversible decrease in the long period along the stretching direction is observed [ Fig.…”

“…10). 4,49 The unloaded specimens of 35D ( E P 50:62; the 17th point) and 40D ( E P 50:97; the 17th point) were heated to 130 and 150 8C, respectively, and all specimens can return to the original length. Thus, the decrease in ER can be ascribed to fibrillation.…”

Stretching‐induced phase transition of the butene‐1/ethylene random copolymer: Orientation and kinetics

“…Semicrystalline polymer is the representative substance with multilength‐scale structure covering from subnanometer to millimeter. For the polymorphic material, the macroscopic mechanical properties are closely linked with the microscopic modification and the molecular dynamics of formed crystallites . Polybutene‐1 (PB‐1) homopolymer and copolymers are the typical polymorphic polymers, which have different crystalline modifications of Forms I/I′, II, and III.…”