Tensile Deformation of Polybutene‑1 with Stable Form I at Elevated Temperature

Stretching-induced structural changes in polybutene-1 with stable crystalline modification of form I at elevated temperature was investigated by means of the in-situ synchrotron wide-angle X-ray diffraction technique. It was found that oriented metastable form II crystallites with the polymer chain aligned along the stretching direction gradually appear during tensile deformation. Based on the fact that a solid state I to II phase transition cannot take place due to the restriction in chain conformations and lattice dimensions in both phases, the observed occurrence of transition from form I to form II must proceed via a two-step process. First, those form I crystallites with their polymer chain direction tilted with respect to the stretching direction undergo a stress-induced melting process because they experience larger shear stress than the rest. Second, the freed polymer chain segments which have lost their conformational memory in stable form I recrystallize into metastable form II crystallites with their chain direction preferentially aligned along the stretching direction. This result is considered to provide a direct evidence for the stress-induced melting–recrystallization mechanism during tensile deformation of semicrystalline polymers

The evolution of microstructure of lamellae and cavities.

<p>The long period of lamellar stacks and the thickness of the cavities (top) and the master curve of the cavities strain (bottom) along the stretching direction at different strains for PB-1 samples crystallized at 50°C stretched at elevated temperatures (solid symbol) and the ones crystallized at different temperatures stretched at 100°C (hollow symbol). <i>d₀</i> denotes the linear extrapolated thickness of the cavities at zero strain.</p

The cavitation model.

<p>Schematic model of the evolution of cavitation in PB-1 during stretching. Red arrow indicates that stretching direction is horizontal.</p

Azimuthal intensity distribution of 110-reflection.

<p>The evolution of azimuthal intensity distribution of 110-reflection as a function of strain measured for PB-1 samples crystallized at 50°C stretched at 30 (top) and 100°C (middle) and the ones crystallized at 90°C stretched at 100°C (bottom).</p

Selected 2D-WAXD patterns.

<p>The 2D-WAXD patterns taken at different strains as indicated on the graph for PB-1 samples crystallized at 50°C stretched at 30 (top) and 100°C (middle), and the ones crystallized at 90°C stretched at 100°C (bottom). Stretching direction is horizontal. Arrows indicate the azimuthal angle of intensity distribution.</p

The 1D scattering intensity distribution profiles along different directions.

<p>Plots of <i>I vs q_h</i> (left) and <i>I vs q_v</i> (right) taken at different strains for PB-1 samples crystallized at 50°C stretched at 30°C (top) and 100°C (middle), and the ones crystallized at 90°C stretched at 100°C (bottom).</p

Selected 2D-USAXS patterns.

<p>The evolution of USAXS patterns of PB-1 taken at different strains. Top: PB-1 samples crystallized at 50°C and stretched at temperatures indicated on the graph. Bottom: PB-1 samples crystallized at different temperatures as indicated and stretched at 100°C. Stretching direction is horizontal. Arrows indicate the directions of integrating intensity.</p

Characteristics of Samples.

<p>Characteristics of Samples.</p

The degree of orientation of 110-reflection.

<p>The evolution of the degree of orientation of 110-reflection (<i>S₁₁₀</i>) associated with the 110-reflection as a function of strain for PB-1 samples crystallized at 50°C stretched at elevated temperatures (top) and the ones crystallized at different temperatures stretched at 100°C (bottom).</p

The 1D scattering intensity distribution profiles with Lorentz correction along stretching direction.

<p>Plots of <i>Iq_h² vs q_h</i> for PB-1 samples crystallized at 50°C at different strain at 30°C (top), and the ones crystallized at 90°C stretched at 100°C (bottom).</p