Linking morphology changes to barrier properties of polymeric packaging for microwave‐assisted thermal sterilized food

It is a priority to develop polymeric packaging that can withstand microwave‐assisted thermal sterilization (MATS) and maintain the quality of low‐acid foods during long‐term storage. In this study, we explored changes in the morphology of pouch films with two multi‐layer structures. The films are based on barrier layers of metal oxide‐coated poly(ethylene terephthalate) (PET) (film A) and ethylene vinyl alcohol (EVOH) (film B). A 8‐oz model food in pouches was processed with MATS (F₀ = 9.0 min) and stored at 23, 35 and 45 °C for up to 12 months. Findings reveal that the oxygen barrier of film A was influenced by the coating and crystallinity of PET. The oxygen barrier of film B was primarily affected by the moisture content of the EVOH polymer. Results also show that changes in barrier properties depended on storage temperature. Recrystallization in polymer might be an important morphological change that occurs during storages. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45481.     

Structural properties of CrF3‐ and MnCl2‐filled poly(vinyl alcohol) films

Poly(vinyl alcohol) (PVA) films filled with different amounts of CrF₃ and MnCl₂ were prepared by the casting method. Differential scanning calorimetry (DSC) and X‐ray diffraction (XRD) analysis were used to study the changes in the structure properties that occurred because of filling. The changes occurring in the measured parameters with increasing filler contents were interpreted in terms of the structural modification of the PVA matrix. All the studied samples had a main melting temperature due to the main crystalline phase of PVA. The intensity and position of this peak depended on the filling level. However, the samples of CrF₃‐filled PVA films with a filling level greater than or equal to 10 wt % revealed another melting temperature, which indicated the presence of a new crystalline phase in addition to the main crystalline phase. The changes that occurred in the degree of crystallinity of the studied samples were examined. The calculated degree of crystallinity was formulated numerically to be an exponential function of the filling level. The XRD patterns of the studied samples confirmed the DSC results. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1115–1120, 2003     

Effects of supercritical carbon dioxide treatment on the morphology of poly(l‐lactide)

Synthetic l ‐lactide random copolymers can be employed as controlled release materials when prepared using supercritical carbon dioxide (scCO₂), since they are biodegradable via hydrolysis. To determine the effects of thermal properties on polymer performance following scCO₂ processing, three types of poly(l ‐lactide) having different properties were assessed. The T_m of one poly(l ‐lactide) sample (H‐100) was found to be approximately 170 °C over the processing pressure range from 8 to 18 MPa, while a second sample (H‐440) also showed a constant value of approximately 152 °C. In contrast, the poly(l ‐lactide) REVODE exhibited a T_m of 146 °C prior to processing but a higher value of 147 °C following treatment at 8 MPa. Unlike the H‐100 and H‐440, the T_m value of the REVODE tended to decrease with increasing pressure. The T_g values increased greatly under mild conditions of 8 MPa pressure and a temperature of 40 °C. In particular, the T_g values for the H‐440 and REVODE increased by 4 °C and 5 °C, respectively. All T_g values were lowest at 12 MPa and increased with increasing processing pressure, although the effect of processing temperature was minimal. The Χ_{c DSC} of the H‐100 was 18% initially but increased to 20% upon scCO₂ processing at 40 °C and 14 MPa, and showed further increases at higher processing temperatures. Although the relationship between processing temperature and Χ_{c DSC} values for the H‐440 showed the same trend as observed with the H‐100, a different trend was seen for the REVODE. The Χ_{c XRD} values obtained from the XRD analyses differed from the values generated by DSC analysis, and showed a maximum degree of crystallinity following processing at 80 °C both with and without scCO₂ treatment. ATR FT‐IR analyses identified peaks due to semicrystalline regions in poly(l ‐lactide) samples treated with scCO₂, even when applying low temperatures. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44006.     

Investigation of the crystalline phase morphology of a β‐nucleated impact polypropylene copolymer

This study covers the preparation and the characterization of β‐nucleated impact polypropylene copolymer (NA‐IPC). Calcium stearate (CaSt), as well as pimelic (Pim) and adipic (Adi) acids, were doped into IPC as mono‐ or bicomponent nucleating agents (NAs) at varying mass ratios. Possible chemical interactions between the NAs and with IPC, as well as the effect of the NAs on the crystallization behavior and nonisothermal crystallization kinetics, were investigated. DSC and XRD results revealed that IPC nucleated with Pim and Pim‐CaSt nucleants induced up to 90% β‐crystals, whereas Adi and Adi‐CaSt formed only about 17% β‐crystals. This was associated with the strong nucleation efficiency of Pim. The nonisothermal crystallization kinetics showed that the crystallization of IPC and NA‐IPC followed a three‐dimensional growth with athermal nucleation mechanism. FTIR showed that none of the NAs chemically reacted with IPC, and the chemical structure of the polymer was thus intact during the treatment. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39923.     

Mechanical and barrier properties of edible starch–protein‐based films

The present investigation dealt with the mechanical properties, water‐vapor transmission behavior at different relative humidity conditions, and DSC thermograms of edible films formulated using various proteins (casein, gelatin, albumin) in combination with starch and nonthermal as well as intense thermal blending. Nonthermal blended film showed in the DSC thermogram a double T_g, indicating poor miscibility of the components and, hence, a poor film‐forming property. However, the DSC thermogram of all the films based on intense thermal blending showed a single T_g, indicating the complete molecular miscibility of the components. Casein‐based film showed a lower water‐vapor transmission rate, water gain at different relative humidity conditions, and higher tensile strength compared to its counterparts containing gelatin and albumin. Since the casein–starch blend gave better film properties, a blend of hydrophobic carnauba wax and casein was prepared to compare the properties of hydrophilic–hydrophilic and hydrophobic–hydrophilic blends. Both these blends compared well with respect to the water‐vapor transmission rate. Wax‐based film showed multiphased behavior in the DSC thermograms and the percent elongation was lower as compared to the casein–starch blend. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 64–71, 2003     

Characterization of biodegradable polymers by inverse gas chromatography. II. Blends of amylopectin and poly(ε‐caprolactone)

Amylopectin (AP), a potato‐starch‐based polymer with a molecular weight of 6,000,000 g/mol, was blended with poly(ε‐caprolactone) (PCL) and characterized with inverse gas chromatography (IGC), differential scanning calorimetry (DSC), and X‐ray diffraction (XRD). Five different compositions of AP–PCL blends ranging from 0 to 100% AP were studied over a wide range of temperatures (80–260°C). Nineteen solutes (solvents) were injected onto five chromatographic columns containing the AP–PCL blends. These solutes probed the dispersive, dipole–dipole, and hydrogen‐bonding interactions, acid–base characteristics, wettability, and water uptake of the AP–PCL blends. Retention diagrams of these solutes in a temperature range of 80–260°C revealed two zones: crystalline and amorphous. The glass‐transition temperature (T_g) and melting temperature (T_m) of the blends were measured with these zones. The two zones were used to calculate the degree of crystallinity of pure AP and its blends below T_m, which ranged from 85% at 104°C to 0% at T_m. IGC complemented the DSC method for obtaining the T_g and T_m values of the pure AP and AP–PCL blends. These values were unexpectedly elevated for the blends over that of pure AP and ranged from 105 to 152°C for T_g and from 166 to 210°C for T_m. The T_m values agreed well with the XRD analysis data. This elevation in the T_g and T_m values may have been due to the change in the heat capacity at T_g and the dependence of T_g on various variables, including the molecular weight and the blend composition. Polymer blend/solvent interaction parameters were measured with a variety of solutes over a wide range of temperatures and determined the solubility of the blends in the solutes. We were also able to determine the blend compatibility over a wide range of temperatures and weight fractions. The polymer–polymer interaction coefficient and interaction energy parameter agreed well on the partial miscibility of the two polymers. The dispersive component of the surface energy of the AP–PCL blends was measured with alkanes and ranged from 16.09 mJ/m² for pure AP to 38.26 mJ/m² when AP was mixed with PCL in a 50/50% ratio. This revealed an increase in the surface energy of AP when PCL was added. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3076–3089, 2006     

Effect of neutron irradiation on the structural,mechanical, and thermal properties of jute fiber

This article describes the effect of neutron irradiation on jute fiber (Corchorus olitorius). The jute fibers (4.0 tex) were irradiated by fast neutrons with an energy of 4.44 MeV at different fluences ranging from 2 × 10⁹ to 2 × 10¹³ n/cm². An important aspect of neutron irradiation is that the fast neutrons can produce dense ionization at deep levels in the materials. Structural analysis of the raw and irradiated fibers were studied by small‐angle X‐ray scattering (SAXS), X‐ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy. Thermal analysis carried out on the raw and irradiated fibers showed that the thermal stability of the fibers decreased after irradiation. The mechanical properties of the jute fibers were found to decrease after irradiation. The SAXS study showed that the average periodicity transverse to the layer decreased after irradiation, which may have been due to the shrinkage of cellulosic particles constituting the fiber. The residual compressive stress developed in the fiber after irradiation resulted in a decrease in crystallite size as supported by our XRD analysis. Observation with SEM did not indicate any change produced in the surface morphology of the fiber due to irradiation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Fabrication,characterization, and properties of poly(ethylene‐co‐vinyl acetate)/magnetite nanocomposites

Poly(ethylene‐co‐vinyl acetate) (EVA)/magnetite (Fe₃O₄) nanocomposite was prepared with different loading of Fe₃O₄ nanoparticles. The mixing and compounding were carried out on a two‐roll mixing mill and the sheets were prepared in a compression‐molding machine. The effect of loading of nanoparticles in EVA was investigated thoroughly by different characterization technique such as transmission electron microscopy (TEM), X‐ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), limiting oxygen index (LOI), and technological properties. TEM analysis showed the uniform dispersion of filler in the polymer matrix and the dispersion of filler decreased with increase in filler content. XRD of the nanocomposite revealed the more ordered structure of the polymer chain. An appreciable increase in glass transition temperature was observed owing to the restricted mobility of Fe₃O₄‐filled EVA nanocomposite. TGA and flame resistance studies indicated that the composites attain better thermal and flame resistance than EVA owing to the interaction of filler and polymer segments. Mechanical properties such as tensile strength, tear resistance, and modulus were increased for composites up to 7 phr of filler, which is presumably owing to aggregation of Fe₃O₄ nanoparticle at higher loading. The presence of Fe₃O₄ nanoparticles in the polymer matrix reduced the elongation at break and impact strength while improved hardness of the composite than unfilled EVA. The change in technological properties had been correlated with the variation of polymer–filler interaction estimated from the swelling behavior. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40116.     

Investigation of the thermal properties of novel adamantane‐modified polybenzoxazine

Two novel structures of adamantane‐modified benzoxazines were synthesized from 4‐(1‐adamantyl)‐phenol through the incorporation of adamantane as a pendant group into the polybenzoxazine backbone. Both ¹H‐NMR and Fourier transform infrared spectra were used to characterize these structures. The rigid structure of the adamantane tended to hinder the chain mobility (boat anchor effect) and substantially enhanced the thermal properties, including the glass‐transition temperature and decomposition temperature, especially for poly(6‐adamantyl‐3‐methyl‐3,4‐dihydro‐2H‐1,3‐benzoxazine). In the poly(6‐adamantyl‐3‐phenyl‐3,4‐dihydro‐2H‐1,3‐benzoxazine) system, however, the opposite result for the glass‐transition temperature was observed and it was interpreted as lower crosslinking density. The phenyl group was bulkier than the methyl group, and the movement of the molecular chain was hindered between bridging points during the curing process; this resulted in a lower crosslinking density and a lower glass‐transition temperature than those of poly(6‐adamantyl‐3‐methyl‐3,4‐dihydro‐2H‐1,3‐benzoxazine). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 932–940, 2004     

Mechanical,electrical, and dielectric properties of polyvinylidene fluoride/short carbon fiber composites with low‐electrical percolation threshold

In this investigation, polyvinylidene fluoride (PVDF)/short carbon fiber (SCF) composites have been prepared by solution casting technique to enhance electrical and dielectric properties with very low‐electrical percolation threshold (0.5 phr SCF). The effect of SCF content on mechanical, thermal and morphological properties of the composites have also been investigated. The mechanical properties of the composites are found to reduce compared to neat PVDF due to poor polymer–filler interaction which can be concluded from FESEM micrographs showing poor bonding between PVDF and SCF. The PVDF/SCF composites exhibit either positive temperature coefficient effect of resistivity or negative temperature coefficient effect of resistivity depending on the loading of SCF in the polymer matrix. The change in conductivity during heating–cooling cycle for these composites shows electrical hysteresis along with electrical set. The melting point of the composites marginally increases with the increase in fiber loading in PVDF matrix as evidenced from DSC thermograms. X‐ray diffraction analysis reveals the crystallinity of PVDF decreases with the increase in SCF loading in matrix polymer. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39866.     

Influence of diaminobenzoyl‐functionalized multiwalled carbon nanotubes on the nonisothermal curing kinetics,dynamic mechanical properties,and thermal conductivity of epoxy–anhydride composites

To obtain advanced materials with a high thermal dissipation, the addition of multiwalled carbon nanotubes containing diverse functionality groups, that is, as‐received multiwalled carbon nanotubes (AS‐MWCNTs) and diaminobenzoyl multiwalled carbon nanotubes (DA‐MWCNTs), to epoxy–anhydride composites was accomplished. According to nonisothermal differential scanning calorimetry analysis, the reactive functional groups present on the surfaces of the AS‐MWCNTs and DA‐MWCNTs accelerated the nucleophilic addition reaction of epoxy composites. Because of the difference in the reactivities of these functional groups toward epoxy groups, the distinction of fractional conversion and the reaction rate of the curing process were remarkably evident at the early stage. A suitable kinetic model was effectively elucidated with the Málek approach. The curing kinetics could best be described by a two‐parameter autocatalytic model as a truncated ?esták–Berggren model. The DA‐MWCNTs achieved effective load transfer and active heat conductive pathways; this resulted in good dynamic mechanical and thermal properties. As a result, the diglycidyl ether of bisphenol A/DA‐MWCNTs constituted an effective system with enhanced heat dissipation of materials for electronic applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43567.     

Influence of various reaction media on the thermal and rheological properties of poly(acrylamide‐co‐N‐hexadecylacrylamide)

A hydrophobically modified polyacrylamide (PAM) was synthesized by the copolymerization of acrylamide (Am) and N‐hexadecylacrylamide (hAm) through solution copolymerization in a polar organic solvent. Polymer synthesis was performed in three nonaqueous media, including dimethyl sulfoxide (DMSO), a mixture of DMSO and an anionic surfactant such as sodium dodecyl sulfate, and a mixture of DMSO and an acidic surfactant such as dodecyl benzene sulfonic acid. The obtained copolymer, poly(acrylamide‐co‐N‐hexadecylacrylamide) [poly(Am‐co‐hAm)], was characterized by ¹H‐NMR. The physical properties of poly(Am‐co‐hAm)s synthesized in different media were compared with those of PAM and with each other by viscosity measurement, X‐ray diffraction, thermogravimetric analysis, and differential scanning calorimetry. We investigated the ways in which the polymerization medium affected the hydrophobic distribution within the resulting copolymer structure. This aspect, in turn, should have altered the solution properties and the microstructure of the copolymer. For this purpose, we studied the viscometric behavior in diluted solutions, the thermal behavior and thermal stability of the copolymers, and finally, the crystalline structure of the copolymers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39939.     

Comparison of the pomegranate seed oil organogels of carnauba wax and monoglyceride

The aims of this study were to prepare organogels from pomegranate seed oil (PO) with carnauba wax (CW) and monoglyceride (MG), compare the organogels with a commercial margarine (CM) and evaluate 3 months storage stability. At 3% organogelator addition, no gels were formed, while at 7 and 10% additions, the oil binding capacities increased and were always higher in CW organogels, with crystal formation times of 8.0 to 14.0 min. Solid fat content (SFC) of the CW organogels varied between 2.96 and 8.71% at 20°C, while MG gels had 2.89–9.43%, and CM had 29.73% SFC. The peak melting temperatures of the CW organogels ranged from 74.73 to 75.74°C and MG organogels ranged from 11.09 to 50.63°C, whereas CM product exhibited 45.92°C peak melting temperature. The hardness of CW organogels was higher than that of MG organogels. The organogels showed potential as spreadable products. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41343.     

Preparation and characterization of low molecular weight silk fibroin by high‐temperature and high‐pressure method

A low molecular weight silk fibroin powder (LMSF) was prepared through high temperature (200°C) and high pressure (20 kgf/cm²), without any addition of chemicals. The carbonized adducts produced during this process were then removed by treatment with activated charcoal. The yield of LMSF by this preparation method was over 60% after the removal of carbonized adducts by using activated charcoal. Amino acid analysis showed an observable decrease in contents of serine and tyrosine in LMSF prepared by this method, as compared to those prepared by neutral salt. The molecular weight of this LMSF was also observably decreased with an increase in the reaction time. From the measurements of differential scanning calorimeter (DSC) and thermal gravimetric analyzer (TGA), thermal properties of LMSF through high temperature and high pressure were also decreased as compared to those produced by neutral salts. In addition, wide‐angle X‐ray diffraction (WAXD) patterns showed that the crystallinity of LMSF differed from that of the original silk fibroin. It can be said that the preparation method of LMSF in this study is a simple, economical, and environmentally compatible process with many advantages. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2890–2895, 2002     

Effect of 1,3,5‐trialkyl‐benzenetricarboxylamide on the crystallization of poly(lactic acid)

A series of 1,3,5‐trialkyl‐benzenetricarboxylamides (BTA‐Rs) with different side‐chain lengths of n‐alkyl are synthesized to use as nucleating agents of poly (lactic acid) (PLA). Crystallization rate of PLA is detailed discussed in nonisothermal melt‐crystallization with addition of the synthesized nucleating agents. Among these BTA‐Rs, BTA‐n‐butyl (BTA‐nBu) shows the most excellent nucleation ability for PLA. The influences of BTA‐nBu on the nonisothermal melt‐crystallization and cold‐crystallization from the glassy state, isothermal crystallization, crystalline structure, and spherulite morphology of PLA are investigated. It is found that 0.8 wt % is the optimal weight fraction of BTA‐nBu to improve the crystallization of PLA. In the case of isothermal melt‐crystallization from melt, the addition of BTA‐nBu shortens the crystallization half‐time and speeds up the crystallization rate of PLA with no discernible effect on the crystalline structure. Besides, BTA‐nBu nucleated PLA exhibits smaller spherulites size and larger nucleation density than that of pure PLA. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1328‐1336, 2013     

Low‐frequency sound absorption of organic hybrid comprised of chlorinated polyethylene and N,N′‐dicyclohexyl‐2‐benzothiazolyl sulfenamide

We investigated the sound absorption characteristics of an organic hybrid material comprised of chlorinated polyethylene (CPE) as the matrix polymer and N,N′‐dicyclohexyl‐2‐benzothiazolyl sulfenamide (DBS) as the second component of an organic low‐molecular‐weight compound. We found specific crystallites, obtained by annealing, that generated new absorption for a low‐frequency sound in a CPE/DBS blend. We observed two sound absorption peaks, around 300 and 1000 Hz, in the annealed CPE/DBS (50 : 50 w/w) blends, whereas those peaks were not observed in the untreated sample. There were two kinds of crystals with different melting points in the annealed samples. It was confirmed that the crystals with the lower melting point brought about sound absorption at a low frequency. The crystals that had the lower melting point were smaller and/or more disordered than the crystals that had the higher melting point. We calculated the fraction of these two types of crystals from differential scanning calorimetry and wide‐angle X‐ray diffraction measurements. The annealing or reannealing temperature specified the fraction of the crystal with the lower melting point, and the obtained crystal fraction characterized sound absorption frequency. Therefore, it is possible to control the sound absorption frequency of an organic hybrid by heat treatment such as annealing. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

A study of the morphology of polyurethane–polystyrene interpenetrating polymer networks by means of small angle X‐ray scattering,modulated‐temperature differential scanning calorimetry,and dynamic mechanical thermal analysis techniques

The morphology of polyurethane–polystyrene (PU‐PS) (60 : 40 by weight) interpenetrating polymer networks (IPNs), in which internetwork grafting via 2‐hydroxyethyl methacrylate resides (HEMA) (1, 2.5, and 10 wt %, respectively) in the polystyrene networks has been studied by means of small angle X‐ray scattering (SAXS), modulated‐temperature scanning calorimetry (M‐TDSC), and dynamical mechanical thermal analysis (DMTA) techniques. With increasing internetwork grafting, the average size of domains became smaller (SAXS data) and the degree of component mixing increased (M‐TDSC and DMTA results). For the PU‐PS (60 : 40 by weight) IPN with 10% HEMA, the DMTA tan δ‐temperature plot showed a single peak. This DMTA result implied that the morphology of this PU‐PS IPN is homogeneous. However, the M‐TDSC data showed that three PU‐PS (60 : 40) IPNs samples (with 1, 2.5, and 10 wt % HEMA, respectively) were phase separated. For the three IPN samples, the correlation length of the segregated phases, obtained from SAXS data based on the Debye–Bueche method, did not show distinct differences. With increasing internetwork grafting, the scattered intensity decreased. This study concluded that for these IPNs, SAXS is sensitive to the size of domains and component mixing, but no quantitative analysis was given for the component mixing. M‐TDSC is suitable to be used to quantify the degree of component mixing or the weight fraction of interphases, and DMTA is sensitive to damping behavior and to phase continuity. However, DMTA cannot provide quantitative information about the degree of component mixing or the weight (or volume) fraction of the interphases. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1958–1964, 2001     

Structural properties of CrF3‐ and MnCl2‐filled poly(vinylalcohol) films

Poly(vinylalcohol) (PVA) films filled with different filling levels of CrF₃ and MnCl₂ have been prepared by the casting method. Differential scanning calorimetry (DSC) and X‐ray diffraction (XRD) analysis were used to study the changes in structure properties that occur due to filling. The changes occurring in the measured parameters with increasing the filler content was been interpreted in terms of the structural modification of the PVA matrix. It was found that all studied samples had the main melting temperature due to the main crystalline phase of PVA. The intensity and position of this peak depended on the filling level. On the other hand, the samples of CrF₃‐filled PVA films with filling level W ≥ 10 wt % revealed another melting temperature, indicating the presence of a new crystalline phase besides the main crystalline phase. Changes occurring in the degree of crystallinity of the studied samples were discussed. The calculated degree of crystallinity was formulated numerically to be an exponential function of filling level. The X‐ray diffraction patterns of the studied samples confirmed the DSC results. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 516–521, 2003     

Influence of magnesium sulfate whiskers on the structure and properties of melt‐stretching polypropylene microporous membranes

The influence of magnesium sulfate (MgSO₄) whiskers on the structure and properties of polypropylene cast films and stretched microporous membranes was investigated. We found that for the cast films, MgSO₄ showed some nucleation effects, and the introduction of MgSO₄ led to the decrease of the orientation degree along the machine direction (MD), whereas that along the transverse direction (TD) was improved; this indicated that MgSO₄ whiskers were mainly arranged along the TD. The introduction of MgSO₄ up to 10 wt % did not induce apparent changes in the pore structure and air permeability properties of the stretched microporous membranes but improved the electrolyte absorption ability. The most pronounced change for the stretched microporous membranes was the strength along the TD. It was increased by 110% when the MgSO₄ content was 2 wt %. During the fabrication of microporous membranes, only stretching along the MD was carried out to initiate pore formation; this resulted in a lower strength along the TD. This study gave us a method for improving the mechanical properties of stretched microporous membranes along the TD. The obtained microporous membranes with better electrolyte absorption and higher mechanical strength along the TD could be used in lithium‐ion batteries as separators. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43884.     

Microstructure and melting behavior of a solution‐cast polylactide stereocomplex: Effect of annealing

The effect of annealing on the microstructure and melting behavior of a solution‐cast polylactide (PLA) stereocomplex (sc) was systematically investigated by differential scanning calorimetry and small‐angle X‐ray scattering. A preorder state, an intermediate form between the amorphous and crystalline states, was found in the solution‐cast poly(l ‐lactide)–poly(d ‐lactide) blend. When the annealing temperature (T_a) was below 220 °C, a part of the preorder state directly formed thicker sc crystallites; these corresponded to the second melting peak, which appeared around 250 °C during the heating process. Although the rest melted and became the amorphous phase, it formed a thinner lamella under the restriction of the unmelted initial sc crystallites during annealing; the melting process of this lamella was parallel to that of the new melting peak, which appeared around 220 °C. The melting of the initial crystal formed as the solvent volatilized corresponded to the range of the first melting temperature around 230 °C. When T_a was above 220 °C, the preorder state melted completely, and the initial crystal experienced perfection process. Furthermore, the highest melting temperature of PLA sc (254.1 °C, with a fusion enthalpy of 125.5 J/g) was obtained when T_a was 235 °C. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44626.