Correlation between Structure and Vapor Sorption in Semicrystalline Linear Polyethylene: One Dimensional Nano-Swelling Measured Using in Situ Vapor Sorption Small Angle Neutron Scattering (iVSANS)

Abstract

Changes in the nanoscale structure of semicrystalline polyethylene (PE) resulting from the sorption/ diffusion of hexane-d 14 vapor have been observed and quantified by in situ vapor sorption small-angle neutron scattering (iVSANS). We find a linear correlation between vapor sorption/diffusion and nanoexpansion of the amorphous phase within the lamellae confined in the spherulite domains. The expansion depends on the degree of crystallinity and spherulite perfection. We measured the structure-based sorption kinetics and isotherms of samples with two different crystalline volume fractions (φ Vc ). The low crystalline polyethylene shows a larger expansion in the long period, L, than the high crystalline polyethylene. Low crystalline PE shows a Fickian-like diffusion profile with sorption time while the high crystalline PE (φ Vc ) 78%) shows a S-shape diffusion profile (non-Fickian) at P/P°) 0.95. The diffusion coefficient increases with relative vapor pressure (P/P°) in both materials. The apparent diffusion coefficient in the low crystalline polymer is approximately a factor of 2 higher than that of the more crystalline polymer. On the other hand, effective diffusion coefficients, D eff 's, normalized with the amorphous volume fractions at each vapor activity are identical regardless of crystallinity. This indicates that amorphous volume fraction is the predominant factor that controls transport properties, at least for small diffusing molecules. Furthermore, the one-dimensional expansion is reversible during cyclic sorption and desorption processes, suggesting that the crystals were not destroyed unlike the inference of a previous study. 1

A simple constrained uniaxial tensile apparatus for in situ investigation of film stretching processing

“…This indicates that the scattering peak at large q is not the second reflection, since the first maxima is much stronger than higher order reflections. 34,35 Therefore, the second peak is attributed to scattering of new lamellar stacks with smaller long period.…”

Swelling of polyethylene particles and its relation to sorption equilibria under gas‐phase polymerization conditions

“…To investigate polymer swelling various experimental methods have been employed and reported in the literature . Most of them use a pressure cell with windows that enable the direct observation of polymer sample changes.…”

“…used a video‐microscopic apparatus to measure the swelling of PE by ethylene and 1‐hexene. Kim and Glinka studied the long period changes resulting from n ‐hexane sorption using small‐angle neutron scattering. Although their study is theoretically interesting, it was carried out at 21 °C and did not provide bulk swelling data, which may differ from the long period changes due to the possible existence of amorphous domains outside the lamellar stacks .…”

Extraction of volatile flavour compounds from butter oil in a low‐density polyethylene membrane pouch

“…A LDPE membrane is recognized for its permeability and has good tensile strength for pouch preparation. It consists of two phases, an amorphous phase and a crystalline phase or three phases, with a boundary region around the crystalline phase, hence a LDPE membrane is called a semi‐crystalline membrane . Small molecules such as volatile flavour compounds permeate through the amorphous phase to the extracting solvent while the crystalline phase acts as an impermeable region .…”