Chain Slippage Research Articles

Comparison study: effect of un-vulcanized and vulcanized NR content on the properties of two-matrix filled epoxy/natural rubber/graphene nano-platelets system

This paper focus in comparing un-vulcanized and vulcanized NR as toughening agent in epoxy resin. The incorporation of graphene nano-platelets (GNP) into two-matrix system has yield conductive materials whilst maintained their polymeric characteristics. Filled systems were prepared via magnetic stirring method and dispersion of GNP in the filled systems using ultrasonic water bath. The aim of this study is to investigate the effect of NR content on physical, mechanical, thermal and electrical performances of un-vulcanized and vulcanized filled systems. There is a great improvement in mechanical properties of vulcanized filled systems as compared to un-vulcanized filled systems. The results showed that the addition of vulcanized NR content at 5 vol% has improved flexural strength, modulus and toughness by 41.28%, 11.9% and 36.26% as compared to un-vulcanized filled system, when comparing at the same NR content. This improvement is attributed to the semi-efficient vulcanization (semi-EV) has transformed soft-like NR phases into high elastic NR phases, at which small vulcanized NR phases acted as energy dissipating center that can bear higher applied load without chain slippage. The flexured and fractured surfaces of filled systems were investigated using scanning electron microscope (SEM) technique to determine particle sizes of NR phases and its toughening mechanism. The formation of more conductive pathways in the vulcanized filled systems was agreed by the XRD analysis. Vulcanized filled systems have higher cross-link density in which implied that vulcanized NR phases are resistant to chemical penetration and cannot be easily removed.

Approaches to improve the film ductility of colorless cycloaliphatic polyimides

This study described approaches for improving the film ductility of colorless cycloaliphatic polyimides (PIs). An unexpected toughening effect was observed when a PI derived from pyromellitic dianhydride (PMDA) and 4,4′‐methylenebis(cyclohexylamine) was modified by copolymerization with a low isophoronediamine (IPDA) content of 5 to 30 mol%, despite there being no film‐forming ability in the homo PMDA/IPDA system. For example, at an IPDA content of 20 mol%, the copolymer showed significantly improved film toughness (maximum elongation at break, εb max = 57%), excellent optical transparency (light transmittance at 400 nm, T400 = 83.7%), and a high glass transition temperature (Tg = 317°C). This toughening effect can be interpreted on the basis of the concept of chain slippage. In this study, the PIs derived from bicyclo[2.2.2]octane‐2,3,5,6‐tetracarboxylic dianhydride (H‐BTA) with various diamines were also systematically investigated to evaluate the potential of H‐BTA‐derived systems. The combinations of H‐BTA with ether‐containing diamines led to highly tough PI films (εb max > 100%) with very high Tgs, strongly contrasting with the results of an earlier study. The observed excellent properties are related to the steric structure of H‐BTA. Our interest also extended to the solution processability. A copolyimide derived from H‐BTA with a sulfone‐containing diamine and an ether‐containing diamine achieved a very high optical transparency (T400 = 86.8%), a very high Tg (313°C), and good ductility (εb max = 51%) while maintaining solution processability. Thus, these approaches enabled us to dramatically improve the ductility of cycloaliphatic PI films that have, to date, been considered brittle.

Understanding the structural evolution under the oscillatory shear field to determine the viscoelastic behavior of nanorod filled polymer nanocomposites

By taking advantage of the classic coarse-grained molecular dynamics simulation, we have examined the effect of oscillatory shear strain amplitude on the viscoelastic behavior of nanorod (NR) filled polymer nanocomposites (PNCs) by tuning the interfacial interaction between polymer and NRs. We have observed the Payne effect (referred to the nonlinear viscoelastic behavior) at strong interfacial interaction. Payne-effect magnitude gradually increases with the interfacial interaction and the NR volume fraction. To understand the origin of Payne-effect, we examine the NR microstructures and their evolution during the shear field. We find that at low interfacial interaction, the probability of forming NR network is nearly unchanged with the shear strain amplitude; while at strong interfacial interaction, on the contrary the probability significantly decreases with the shear strain amplitude. We infer that various interfacial interactions change the NR network, influencing their evolution behavior under the shear flow. Meanwhile, we calculate the main cluster size and the total number of clusters for the NR network at different shear strain amplitudes, which is consistent with the probability of forming NR network. Thus, the original NR microstructure is significantly broken down under the external shear field, which can also be reflected by the number for polymer-mediated NR network bridged by glassy chains and the connected polymer beads between NRs. In addition, the polymer chains can slip on the filler surface under the shear field. As a result, the observed Payne effect comes from the slippage of the interfacial chains and breakage of the polymer-mediated NR network bridged by glassy chains at strong interfacial interaction. While at low interfacial interaction, it exhibits a weak non-linear behavior. Additionally, both reinforcement and Payne-effect magnitude exhibit a linear dependence on the inverse of the aspect ratio of the NRs. At last, different contributions to reinforcement due to hydrodynamic effects, “occluded rubber”, and “filler network” are quantified where the “filler network” is the main contribution. In summary, this work provides some interesting results to help further understand the relationship between the viscoelastic behavior and the NR network under the shear flow.

Tensile deformation of semi-crystalline polymers by molecular dynamics simulation

In this work, the microstructure evolution of semi-crystalline polymers during tensile deformation is analyzed by molecular dynamics simulation. A perfect semi-crystalline lamellar structure with crystalline/amorphous interface perpendicular to tensile direction is created with the help of coarse-grained (CG) model of poly(vinyl alcohol) (PVA). During the tensile test, two kinds of strain rates are applied to the lamellar stack to determine the stress–strain curves, yield stresses, and crystallinities. Consistent with experimental findings, two yield points were observed in the semi-crystalline sample which was corresponded to the fine and coarse crystallographic slips in the lamellar structure, where the crystal stems gradually rotated into the direction of applied stress during chain slips. After the second yielding point when the crystal stems had been rotated fully into the direction of applied stress, the lamellar structure was destroyed and it resulted in a decrease of crystallinity. In addition, the increase of the strain rate led to the acceleration of destruction of crystal structures. It is worth noting that the stress induced crystallization was observed in the interfacial region, and newly crystallized beads were belonged to the same microcrystalline domain as crystalline region due to memory effects. This work provides direct comparison of structure evolution between crystalline and amorphous region in semi-crystalline polymers during tensile deformation, and it is helpful for the design and mechanical property analysis of semi-crystalline polymers.

Ultrafine high performance polyethylene fibers

Stiff, strong and tough ultrafine polyethylene fibers that rival the best high performance fibers, but with diameters less than one micron, are fabricated for the first time by “gel-electrospinning.” In this process, solution concentration and process temperatures are chosen to induce the formation of gel filaments “in flight,” which are subsequently drawn at high rates as a consequence of the whipping instability. The resulting submicron-diameter fibers exhibited Young’s moduli of 73 ± 13 GPa, yield strengths of 3.5 ± 0.6 GPa, and toughnesses of 1.8 ± 0.3 GPa, on average. Among the smallest fibers examined, one with a diameter of 490 ± 50 nm showed a Young’s modulus of 110 ± 16 GPa, ultimate tensile strength of 6.3 ± 0.9 GPa, and toughness of 2.1 ± 0.3 GPa, a combination of mechanical properties that is unparalleled among polymer fibers to date. The correlation of stiffness, strength and toughness with fiber diameter is attributed to high crystallinity and crystallite orientation, combined with fewer defects and enhanced chain slip associated with small diameter and high specific surface area. Gel-electrospinning improves the prospects for production of such fibers at scale.

Planar granular shear flow under external vibration.

We present results from a planar shear experiment in which a two-dimensional horizontal granular assembly of pentagonal particles sheared between two parallel walls is subjected to external vibration. Particle tracking and photoelastic measurements are used to quantify both grain scale motion and interparticle stresses with and without imposed vibrations. We characterize the particle motion in planar shear and find that flow of these strongly interlocking particles consists of transient vortex motion with a mean flow given by the sum of exponential profiles imposed by the shearing walls. Vibration is applied either through the shearing surface or as bulk vertical vibration of the entire shearing region with dimensionless accelerations Γ=A(2πf)^{2}/g≈0-2. In both cases, increasing amplitude of vibration A at fixed frequency f leads to failure of the force network, reduction in mean stress, and a corresponding reduction in imposed strain. Vibration of the shearing surface is shown to induce the preferential slipping of large-angle force chains. These effects are insensitive to changes in frequency in the range studied (f=30-120 Hz), as sufficiently large displacements are required to relieve the geometrical frustration of the jammed states.

Ab initio and classical atomistic modelling of structure and defects in crystalline orthorhombic polyethylene: Twin boundaries, slip interfaces, and nature of barriers

We study the stability of twin boundaries and slip in crystalline orthorhombic polyethylene by means of density functional theory (DFT), using a nonempirical, truly nonlocal density function, and by means of classical molecular dynamics (MD). The results show that, in accordance with experimental observations, there is a clear preference to chain slip over transverse slip for all considered slip planes. The activation energy for pure chain slip lies in the range 10–20 mJ/m2 while that for transverse slip corresponds to 40–280 mJ/m2. For the (11¯0)-slip plane the energy landscape is non-convex with multiple potential energy minima, indicating the presence of stable stacking faults. This suggests that dissociation of perfect dislocations into partials may occur. For the two low-energy twin boundaries considered in this work, {110} and {310}, we find that the former is more stable than the latter, with ground state energies corresponding to 8.9 and 28 mJ/m2, respectively. We have also evaluated how well the empirical MD simulations with the all-atom optimized potential for liquid MD simulations (OPLS-AA) and the coarse-grained united atom (UA) potential concur with the DFT results. It is found that an all-atom potential is necessary to partially capture the γ-surface energy landscapes obtained from the DFT calculations. The OPLS-AA predicts chain slip activation energies comparable with DFT data, while the transverse slip energy thresholds are low in comparison, which is attributed to weak close ranged monomer repulsion. Finally, we find that the H-H interaction dominates the slip activation. While not explicitly represented in the UA potential, its key role is revealed by correlating the DFT energy landscape with changes in the electron distributions and by MD simulations in which components of the OPLS-AA intermolecular potential are selectively silenced.

Thicker Lamellae and Higher Crystallinity of Poly(lactic acid) via Applying Shear Flow and Pressure and Adding Poly(ethylene Glycol).

In this work, we explored the crystallization of poly(lactic acid) (PLA) blended with poly(ethylene glycol) (PEG) under two inevitable processing fields (i.e., flow and pressure) that coexist in almost all processing for the first time. Here, the PEG was incorporated into PLA as a molecular chain activity promoter to induce PLA crystallization. A homemade pressuring and shearing device was utilized to prepare samples and necessary characterization methods, such as differential scanning calorimetry, scanning electron microscopy, and synchrotron radiation, and were used to investigated the joint effects of PEG, pressure, and shear flow on the crystallization behaviors and morphologies of PLA/PEG samples. The results reveal that adding 3-5 wt % PEG into PLA can significantly increase the PLA crystallinity due to the efficient plasticization effect of PEG, while the PEG content reaches 10 wt %, the PLA crystallinity decreases drastically as the phase separation between PEG and PLA occurs. We also find that applying a higher pressure (∼100 MPa) can facilitate the formation of thicker lamellae with fewer defects as well as higher crystallinity under an equal degree of supercooling compared to normal pressure or a low pressure condition because the slip of molecular chains during crystallization makes the lamellae thicker under higher pressures. The PLA crystalline structure in the PLA/PEG sample is not influenced by the shear flow, yet the crystallinity is largely enhanced by applying a shear flow with an appropriate intensity (0-3.5 s-1). It is worth noting that pressure and shear flow show a synergetic effect to fabricate PLA/PEG samples with high crystallinity. These meaningful results could beyond doubt help comprehend the relationship between crystallization conditions and crystallization behaviors of PLA/PEG samples and thus provide guidance to obtain high-performance PLA/PEG products via controlling crystallization conditions.

Ultra-tough and super thermal-insulation nanocellular PMMA/TPU

Nanocellular polymers have been considered promising multifunctional materials with unique properties. The key challenge is to fabricate nanocellular polymers with adequate cell sizes and densities. Herein, we report a novel method to prepare nanocellular polymethylmethacrylate (PMMA)/thermoplastic polyurethane (TPU) with tunable structures. The nanocellular PMMA/TPU displays a ductile fracture behavior while the microcellular PMMA shows a brittle fracture behavior. The nanocellular PMMA/TPU presents a tensile toughness and an impact toughness which are respectively 180-fold and 762% higher than the microcellular PMMA. The nanocellular structure combined with the nanostructured TPU greatly promotes the movement, shear slip and nano-fibrillation of the polymer chains, thus leading to this remarkably enhanced toughness. The nanocellular PMMA/TPU with an average cell size of 205nm and an expansion ratio of 8.0 displays a thermal conductivity of 24.8mW/m·K and a high compressive strength, which is to the best of our knowledge for the first time to achieve this superinsulating performance with porous polymers. The reduced air’s thermal conductivity due to the Knudsen effect combined with the reduced polymer’s thermal conduction due to the large expansion ratio are responsible for this superinsulating performance. The multifunctional nanocellular material offers a promising solution for advanced thermal insulation applications.

Investigation of inelastic behavior of elastomeric composites during loading–unloading cycles

The inelastic responses of thermoplastic polyurethane/attapulgite (AT) elastomeric composites were studied by an elastic-testing machine combining with an infrared camera during loading–unloading cycles, in which the former detected the mechanical properties while the latter reflected the thermal effects of deformation. For both unfilled and filled polyurethanes, some significant inelastic features were noticed that in the first cycle hysteresis and most stress softening occurred, and the corresponding temperature variation was partly reversible. However, in the following cycles, the specimen approached a steady state, therefore, stress–strain curve and the corresponding temperature variation was totally reversible. It was also showed that in filled materials the inelastic effects were becoming more obvious with the increase of AT concentration. The results can be explained by chain slippage of the hard micro-domain existing in soft segments of polyurethane, which produces irreversible friction dissipation during the initial loading process.

Structure evolution and orientation mechanism of long-chain-branched poly (lactic acid) in the process of solid die drawing

Highly oriented long-chain-branched poly (lactic acid) (LCB-PLA) was prepared and the structure evolution was studied in the process of solid die drawing by compared with poly (lactic acid) (PLA). During drawing, samples underwent not only die drawing process but also free drawing process. Drawing speed presented a prominent effect on the free drawing process, while die thickness showed a more obvious influence on the die drawing process. For PLA, free drawing process mainly contributed to its final orientation degree and crystallinity, and thus the mechanical properties of PLA were greatly influenced by drawing speed. However, for LCB-PLA, die drawing process made a greater contribution to the final orientation degree and crystallinity, and its mechanical properties were mainly affected by die thickness. Under the same drawing condition, the tensile strength and modulus of LCB-PLA were always higher than those of PLA, and reached up to 228MPa and 7.2GPa, respectively, which basically met the requirement for born fixation materials. Samples which only underwent die drawing showed obvious “sandwich” structure, and the thickness of the oriented skin layer for LCB-PLA was thicker than that for PLA, suggesting that shear-induced orientation can be easily retained due to the enhanced entanglement between long branched chains. After drawing, LCB-PLA samples showed smaller lamellae size (Llateral) but larger long period (Lac) compared with PLA, suggesting that the low chain mobility restricted the motion of chain slipping of LCB-PLA and thus resulted in the fragmentation of neighboring crystal lamella by chain stretched-out.

ポリプロピレン結晶相の弾性異方性およびすべり系に関する分子動力学シミュレーション

Thermoplastic polymers are expected to be used as a matrix for fiber reinforced plastics due to their high formability and recyclability. Particularly, thermoplastic crystalline polymers have a hierarchical structure composed of crystalline phase and amorphous phase. In order to describe large deformation behavior of crystalline polymers, the polymer multiscale models considering these structures have been developed over the past few decades. However, the mechanism of plastic deformation and material parameters of crystalline phase such as anisotropic elastic coefficients, slip systems and critical resolved shear stress of each slip system have been unclear because of its difficulty of experimental measurement. In this study, we used molecular dynamics method to investigate the microscopic deformation behavior and determine the material parameters of crystalline phase of α-isotactic polypropylene (iPP). We reproduced crystalline phase of α-iPP numerically and applied various kinds of deformation. As a result, we determined thirteen anisotropic elastic coefficients. Each value was different, which means that crystalline phase of α-iPP has elastic anisotropy. Moreover observing plastic deformation behavior of molecular chain slip, we found that crystalline phase has six slip systems, i.e., longitudinal slip and transverse slip on three slip planes. We identified the critical resolved shear stress of each slip system from stress-strain responses. Finally, we performed finite element analysis on single crystal of α-iPP using the material parameters obtained by molecular dynamics simulations, which exhibited macroscopic anisotropy in elasticity and yielding.

A new model for mesomorphic-monoclinic phase transition of isotactic polypropylene

In this study, Fourier transform infrared spectroscopy, synchrotron small-angle and wide-angle X-ray scattering were employed to reveal the underlying mechanism leading to conformational reorganization during mesomorphic-monoclinic phase transition. Results indicated that conformation reorganization occurred from 50 to 130 °C, evidenced by conformational infrared bands at 800 and 841 cm−1. The conformation reorganization led to an immediate increase in the density fluctuation but not induced phase transition immediately. Only when the long period started to increase quickly from 80 °C, can phase transition occur. This indicated that intrachain conformational ordering occurred prior to crystalline ordering. Moreover, temperature dependence of long period changed before and after phase transition, implying that chain sliding was the main driven force for the phase transition rather than rewinding and translation of single stems. With the new information obtained, a two-step model for phase transition was proposed. Within a single-chain bundle, two adjacent helices with opposite handedness can interlock into double helices with higher density, and urge each other extending to entire stem during moving along opposite directions with the help of chain slipping, resulting in ordered arrangement of helical stems. Afterwards, single-chain clusters coalesce, leading to interchain crystalline ordering. The new model is helpful to understand the phenomena related to mesomorphic iPP.

Structural development of gel-spinning UHMWPE fibers through industrial hot-drawing process analyzed by small/wide-angle X-ray scattering

The ultrahigh molecular weight polyethylene (UHMWPE) fibers were obtained directly from the industrial production line. Two-step industrial hot-drawing-to-specific-drawing ratios were carried out at the temperature of 120 and 130 °C, respectively. Small-angle X-ray scattering (SAXS) measurements using synchrotron radiation were applied to study the evolution of kebab structure and the formation of shish structure. The slight increase of long period and the rapid decrease of lateral sizes indicated the destruction of original lamellae which was accomplished by chain slip resulted in the orientation of lamellae to form shish structure. The decrease of average shish length was explained that the formed new shish structure had shorter shish length than the original shish at the early stage with the high concentration of spinning solution. Wide-angle X-ray diffraction (WAXD) measurements were performed to explore the changes of the degree of orientation of the crystals. It was found that the elevated drawing temperature was benefited to the evolution of the orientational order. The DSC result confirmed the evolution of shish–kebab structure through the melting behavior.

Deformation mechanisms in ionic liquid spun cellulose fibers

Abstract The molecular deformation and crystal orientation of a range of next generation regenerated cellulose fibers, produced from an ionic liquid solvent spinning system, are correlated with macroscopic fiber properties. Fibers are drawn at the spinning stage to increase both molecular and crystal orientation in order to achieve a high tensile strength and Young’s modulus for potential use in engineering applications. Raman spectroscopy was utilized to quantify both molecular strain and orientation of fibers deformed in tension. X-ray diffraction was used to characterize crystal orientation of single fibers. These techniques are shown to provide complimentary information on the microstructure of the fibers. A shift in the position of a characteristic Raman band, initially located at ∼1095 cm −1 , emanating from the backbone structure of the cellulose polymer chains was followed under tensile deformation. It is shown that the shift rate of this band with respect to strain increases with the draw ratio of the fibers, indicative of an increase in the axial molecular alignment and subsequent deformation of the cellulose chains. A linear relationship between the Raman band shift rate and the modulus was established, indicating that the fibers possess a series aggregate structure of aligned crystalline and amorphous domains. Wide-angle X-ray diffraction data show that crystal orientation increases with an increase in the draw ratio, and a crystalline chain slip model was used to fit the change in orientation with fiber draw ratio. In addition to this a new model is proposed for a series aggregate structure that takes into better account the molecular deformation of the fibers. Using this model a prediction for the crystal modulus of a cellulose-II structure is made (83 GPa) which is shown to be in good agreement with other experimental approaches for its determination.

Entanglement network formed in miscible PLA/PMMA blends and its role in rheological and thermo-mechanical properties of the blends

The miscible amorphous/semi-crystalline polymer blends with shape memory potential has received increasing interests in recent years. In this work, the shape memory mechanism of the miscible amorphous PMMA/semi-crystalline PLA blends was investigated using thermo-mechanical and rheological approaches. With the incorporation of PMMA into PLA, a broad glass transition and increased glass transition temperature Tg were observed by differential scanning calorimetry (DSC) measurements. The broadening of glass transition is attributed to the local nanoscale heterogeneities in the miscible blend system which is related to the self-concentration of the components. The degree of molecular entanglement of the blends was derived based on the oscillatory rheological measurements, showing that the dissimilar chains are more likely to entangle with each other than the similar ones, and the entanglement density ve is enhanced with increased PMMA content up to 50% where a 100% recovery of the initial shape is yielded. After that, ve is reduced with the addition of PMMA. The mechanism underlying the shape memory property is further validated by performing the shape memory test on the PLA/PMMA blend films at respective Tg. It is evident that for the semi-crystalline blends (PLA rich), PLA crystallites and molecular entanglement provide physical cross-links for shape recording, while a negative effect of crystallinity on the shape recovery ratio is obtained due to the strain-induced crystallization and chain slippage between the crystalline and amorphous chains. In contrast, for the amorphous blends (PMMA rich), the shape recovery ratio shows a strong positive linear dependence on ve, and the entanglement network is regard as the most important factor in the shape memory performance.

Structural Interpretation of Eyring Activation Parameters for Tensile Yielding Behavior of Isotactic Polypropylene Solids

The temperature and strain rate dependence of the stress-strain curves of isotactic polypropylene were analyzed on the basis of Eyring kinetic theory. The molecular and structural basis underlying the parameters, such as activation volume and activation energy, used by the Eyring analysis were studied using the lamellar cluster theory, where a stacked lamella acts as a basic structural unit under yielding and necking deformation. It was suggested that, at lower temperatures, the activation volume corresponds to chain slippage within crystalline lamellae in the lamellar clusters whereas at higher temperature the increase in activation volume results in intralamellar slip corresponding to the α2 relaxation.

Effect of AFM probe geometry on visco-hyperelastic characterization of soft materials

Atomic force microscopy (AFM) nanoindentation is very suited for nano- and microscale mechanical characterization of soft materials. Although the structural response of polymeric networks that form soft matter depends on viscous effects caused by the relative slippage of polymeric chains, the usual assumption made in the AFM-based characterization is that the specimen behaves as a purely elastic material and viscous forces are negligible. However, for each geometric configuration of the AFM tip, there will be a limit indentation rate above which viscous effects must be taken into account to correctly determine mechanical properties. A parametric finite element study conducted on 12 geometric configurations of a blunt cone AFM tip (overall, the study included about 200 finite element analyses) allowed us to determine the limit indentation rate for each configuration. The selected tip dimensions cover commercially available products and account for changes in tip geometry caused by serial measurements. Nanoindentation rates cover typical experimental conditions set in AFM bio-measurements on soft matter. Viscous effects appear to be more significant in the case of sharper tips. This implies that, if quantitative data on sample viscosity are not available, using a rounded indenter and carrying out experiments below the limit indentation rate will allow errors in the determination of mechanical properties to be minimized.

The degree of crystalline orientation as a function of draw ratio in semicrystalline polymers: a new model based on the geometry of the crystalline chain slip mechanism

The orientation behaviour of a range of high-density polyethylenes drawn to different draw ratios has been investigated by measurements of optical birefringence and wide-angle X-ray diffraction (WAXS). Consistent with previous research, it can be concluded that birefringence relates to the overall degree of orientation of the amorphous and crystalline phases, and is described to a good approximation by the pseudo-affine deformation scheme. The WAXS results show that crystalline orientation is also related uniquely to the applied strain and moreover is independent of the characteristics of the polymer concerned. It is shown that the crystalline orientation follows a new model based on the geometry of the crystalline slip mechanism where the crystalline phase deforms affinely in the longitudinal drawing direction.

Microscopic deformation behavior of hard elastic polypropylene during cold-stretching process in fabrication of microporous membrane as revealed by synchrotron X-ray scattering

We propose a microscopic structural deformation model of hard elastic polypropylene (HEPP) during uniaxial stretching using time-resolved simultaneous wide- and small-angle X-ray scattering measurements. It is found that ‘double’ yielding point, characteristic of HEPP in the tensile deformation, corresponds to the formation of the voids with a fine chain slip within the lamellae, followed by the fragmentation of the lamellae associated with a coarse chain slip. Based on the X-ray scattering measurements, we discuss relationship between the strain in the cold stretching and air permeability of a microporous membrane prepared by hot stretching, following the cold stretching.