Effect of high‐temperature annealing on the microstructure and mechanical properties of polypropylene with shish kebab or spherulite structure

Various annealing temperatures below, near, or above the melting temperature were used to anneal polypropylene with oriented shish kebab and isolated spherulite structures in this work. The results showed that a high annealing temperature decreases the time needed to achieve the ideal material property. When the annealing temperature is near or above the melting temperature, the impact strength would be 1.6 times improved by partial melting and recrystallization. The crystal structure of the oriented shish kebab or isolated spherulite structures was improved when annealed at 150 °C, whereas annealing at 165 or 170 °C recombined the crystal lamellae of the structure. Moreover, the high crystallinity and thick lamellae improved the impact and yield strength values of the spherulite structure. However, excessively high crystallinity and thick lamellae in the oriented shish kebab structure did not result in good mechanical performance. Therefore, the prediction of mechanical properties for the shish kebab structure based on crystallinity and lamellar thickness is not feasible. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46465.     

Influence of annealing temperature on the lamellar and connecting bridge structure of stretched polypropylene microporous membrane

The influence of annealing temperature on the lamellar and connecting bridge structure of stretched polypropylene microporous membrane was investigated using small‐angle X‐ray scattering, temperature‐modulated differential scanning calorimetry and scanning electron microscopy. It is found that with increasing annealing temperature from 105 to 145 °C, the main lamella melting peak combines with that from connecting bridges and a uniform pore arrangement is obtained in the microporous membrane. The annealed lamella thickness is increased and lamellar structure is improved, due to the occurrence of melting and recrystallization during annealing. At the same time, more secondary crystals are formed. The melting and recrystallization and secondary crystals contribute to the appearance of an annealing peak in the differential scanning calorimetry curve of annealed film. During the following cold and hot stretching, the secondary crystals disappear and convert to initial connecting bridges. The improved lamellar structure can support the scaffold of pore structure, resulting in a uniform connecting bridge arrangement. But further increasing the temperature to 150 °C degrades the initial lamellar structure, leading to a decrease of pore arrangement in the stretched microporous membrane. Annealing leads to the difference of lamellar structure: the initial lamellar structure is improved and some weak secondary crystals are formed in the amorphous region. © 2014 Society of Chemical Industry     

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.     

A biaxial stretched β‐isotactic polypropylene microporous membrane for lithium‐ion batteries

In this article, microporous polypropylene (PP) membranes were produced with TMB‐5 as β‐crystal nucleating agent by biaxial stretching. Influences of different concentration of TMB‐5 were studied using differential scanning calorimetry and X‐ray diffraction. It was found that the highest crystallinity was reached when the nucleating agent content was 0.5 wt %. The effect of stretching temperature and stretching ratio on pore size distribution and porosity of the membranes were investigated by scanning electron microscopy and mercury porosimeter, respectively. And physical properties, such as tensile strength, permeability, and puncture resistance of the microporous membrane prepared at the optimized conditions, were evaluated. Compared with commercial PP separator membrane, the as‐prepared microporous membrane shows similar uniform pore size distribution and exhibits slightly higher porosity and ionic conductivities. When used as lithium‐ion separator, the experimental film shows more stable cycling performance than the commercial one. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45825.     

Texture and morphology of biaxially stretched poly(ethylene naphthalene‐2,6‐dicarboxylate)

The orientation of poly(ethylene naphthalene‐2,6‐dicarboxylate) (PEN) films with different morphologies were studied by wide‐angle X‐ray diffraction. Different structures were obtained by thermally treating biaxially stretched PEN samples. Virgin and thermally treated (1 h at 240, 250, and 260°C) samples of PEN bioriented films were characterized by DSC to determine the glass‐transition temperature and the crystallinity ratio. To define the orientation of crystallites in the 25 μm thick bioriented samples, pole figures were recorded for various PEN samples, as a function of their position in the transverse drawing direction. The significant result is that there is a dominant crystal population, whose c‐axis direction varies from +45° at one sample edge to ?45° at the other edge, the orientation at the center being parallel to the transverse direction. There is also a secondary population, which can be seen only near the center. DSC studies also showed that by increasing the annealing temperature the crystallinity ratio was increased and pole figures showed that the texture was modified, probably because of disorientation mainly from an annealing temperature of 260°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2224–2232, 2003     

Microporous membranes of isotactic poly(4‐methyl‐1‐pentene) from a melt‐extrusion process. II. Effects of thermal annealing and stretching on porosity

A two‐part study utilizing isotactic poly(4‐methyl‐1‐pentene) (PMP) was undertaken to investigate a three‐stage process (melt‐extrusion/annealing/uniaxial stretching) (MEAUS) utilized to produce microporous films. In this report, the thermal‐annealing (second stage) and subsequent uniaxial‐stretching (third stage) results of selected PMP films from three resins, labeled A, B, and C, are discussed. From sequential analysis of the effect each stage had on the resulting microporosity, it was discovered that the melt‐extruded precursor morphology and orientation, as a consequence of the first‐stage extrusion parameters and resin characteristics, were crucial to controlling the membrane permeability. The annealing parameters were also critical, where a temperature of 205°C applied for 20 min under no tension was the optimum annealing condition for producing highly microporous PMP films upon stretching. For the conditions studied, the stretching parameters that were found to be the optimum for producing the desired characteristics in the final film were cold‐ and hot‐stretch temperatures of 70 and 180°C, respectively. The cold‐ and hot‐stretch extension levels concluded to be the best were a cold‐stretch extension of 80%, followed by hot stretching to 90%, and, thus, a total overall extension level of 170% for the processing window studied. However, these results were only with respect to resin A films, while resin B and C samples could not be produced into microporous films via the MEAUS process. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1076–1100, 2002; DOI 10.1002/app.10395     

Preparation of poly(4‐methyl‐1‐pentene) asymmetric or microporous hollow‐fiber membranes by melt‐spun and cold‐stretch method

Poly(4‐methyl‐1‐pentene) (PMP) hollow fibers were prepared and fabricated into gas separation or microporous membranes by the melt‐spun and cold‐stretched method. PMP resin was melt‐extruded into hollow fibers with cold air as the cooling medium. The effects of take‐up speed and thermotreatment on the mechanical behavior and morphology of the fibers were investigated. Scanning electronic microscope (SEM) photos were used to reveal the geometric structure of the section and surface of the hollow fibers. It was found that the original fiber had an asymmetric structure. A “sandwich” mode was used to describe the formation of this special fine structure. And a series of PMP hollow‐fiber membranes were prepared by subsequent drawing, and it was found that there was a “skin–core” structure on the cross section of these hollow‐fiber membranes. Asymmetric or microporous PMP hollow‐fiber membranes could be obtained by controlling posttreatment conditions. The morphology of these membranes were characterized by SEM, and the gas (oxygen, nitrogen, and carbon dioxide) permeation properties of the membranes was measured. The results indicate that the annealing time of the original fiber and the stretching ratio were the key factors influencing the structure of the resulting membrane. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2131–2141, 2006     

Morphological control of porous ethylene‐vinyl acetate copolymer membrane obtained from a co‐continuous ethylene‐vinyl acetate copolymer/poly(ϵ‐caprolactone) blend

Ethylene‐vinyl acetate copolymer (EVA)/poly(?‐caprolactone) (PCL) blend (50/50 w/w) with co‐continuous morphology was prepared via melt mixing for fabricating microporous EVA membrane materials through selective solvent extraction. Shear flow and quiescent annealing techniques were employed to control co‐continuous phase size in the EVA/PCL blend, and the time‐ and temperature‐dependent relations of phase size were then evaluated theoretically. Using these techniques, microporous EVA membrane materials with various pore sizes ranging from 2 µm to more than 200 µm were obtained. In contrast to the porous EVA membrane prepared by the traditional way of solvent casting/particulate leaching, the as‐obtained microporous membrane shows a higher level of interconnectivity and much narrower pore size distribution with uniform pore structure. © 2013 Society of Chemical Industry     

Microstructure and Microfabrication Considerations for Self‐Supported On‐Chip Ultra‐Thin Micro‐Solid Oxide Fuel Cell Membranes

La_0.6Sr_0.4Co_0.8Fe_0.2O_{3 – δ} (LSCF) has been sputtered on bare Si and Si₃N₄ and yttria‐stabilised zirconia (YSZ) thin films to investigate annealing temperature‐ and thickness‐dependent microstructure and functional properties, as well as their implications for designing failure‐resistant micro‐solid oxide fuel cell (μSOFC) membranes. The LSCF thin films crystallise in the 400–450 °C range; however, after annealing in the 600–700 °C range, cracks are observed. The formation of cracks is also thickness‐dependent. High electrical conductivity, ∼520 Scm^–1 at 600 °C, and low activation energy, ∼0.13 eV, in the 400–600 °C range, are still maintained for LSCF films as thin as 27 nm. Based on these studies, a strong correlation between microstructure and electrical conductivity has been observed and an annealing temperature‐thickness design space that is complementary to temperature‐stress design space has been proposed for designing reliable membranes using sputtered LSCF thin films. Microfabrication approaches that maintain the highest possible surface and interface quality of heterostructured membranes have been carefully examined. By taking advantage of the microstructure, microfabrication and geometrical structural considerations, we were able to successfully fabricate large‐area, self‐supported membranes. These results are also relevant to conventional or grid‐supported SOFC membranes using ultrathin nanocrystalline cathodes and μSOFCs using cathode thin films other than LSCF.     

Influence of precursor film microstructure on properties of HDPE microporous membranes prepared by stretching

Oriented HDPE films having a stacked lamellar morphology were prepared to develop microporous membranes through cast film extrusion followed by stretching. Applying higher draw ratios (DR) and annealing the cast films improved crystal alignments remarkably. It was shown the improvement in c‐axis orientation upon annealing was more significant for the films prepared with lower DR. Furthermore, applying Raman spectroscopy, the amorphous mass fraction of the films was obtained. Subsequently, considering a three‐phase structure (i.e., crystal, amorphous and interphase), the interphase content of the films was also determined. A distinct DR dependence of the interphase content was noticed. It was observed that in addition to crystal perfection upon annealing, the amorphous phase fraction was also decreased due to possibly increase in free volume, promoting lamellar separation and cavitation during the subsequent stretching step. SEM images of the membranes surfaces as well as their normalized water vapor transmission rate (WVTR) values indicated a more uniform pore formation and increased permeability with DR. Furthermore, it was found that lower interphase content in the films with higher DR favors lamellar separation. However, permeability in the stretched precursor films with DR higher than a certain level (DR = 93) was not improved significantly. Moreover, crystallinity and crystal orientation of produced membranes were investigated. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44725.     

Effect of external field on the lamellar crystalline structure and properties of poly(4-methyl-1-pentene) casting film

In this work, lamellae structures of poly(4-methyl-1-pentene) casting films with different draw ratios and properties of corresponding stretched membranes were discussed. The crystalline structure was quantitatively analyzed in terms of crystallinity, long period, crystalline orientation, and lamellae lateral dimension, which were largely influenced by the draw ratio. Apparently, as draw ratio increased, the elapsed time of samples declined rapidly and porosity showed an upward tendency. In this article, these results can be used to predict the relationship between properties of casting films (such as orientation, lamellar structure, and elastic recovery) and properties of stretched membrane (average pore size, permeability, and porosity). © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47293.     

Microporous membranes of polyoxymethylene from a melt‐extrusion process: (II) Effects of thermal annealing and stretching on porosity

A two‐part study utilizing polyoxymethylene (POM) was undertaken to investigate a three‐stage process (melt‐extrusion/annealing/uniaxial‐stretching) utilized to produce microporous films. In this report, the thermal annealing (second stage) and subsequent uniaxial‐stretching (third stage) results of selected POM films from two commercial resins, labeled D & F, are discussed. Specifically, the annealing and uniaxial stretching effects on film morphology, orientation, and other pertinent film properties are addressed. Additionally, sequential analysis was performed regarding the influence each stage had on the resulting microporosity. It was found that the melt‐extruded precursor morphology and orientation, as a consequence of the first stage extrusion parameters and resin characteristics, are crucial to controlling the membrane permeability. The annealing parameters were also deemed critical, where a temperature of 145°C applied for 20 min under no tension was the optimum annealing condition for producing a highly microporous film upon stretching. For the conditions studied, the stretching parameters that were found to be optimum for producing the desired characteristics in the final film were a cold temperature of 50°C and hot stretch temperature of 100°C. The optimum extension levels were concluded to be 90% for both the cold and hot stretch steps, and thus a total overall extension level of 180%. However, these results were only with respect to resin F films. Because the resin D melt‐extruded precursors possessed twisted lamellar morphologies and relatively low crystal orientation, their samples could not be produced into microporous films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1762–1780, 2002; DOI 10.1002/app.10587     

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     

Structure and properties of bio‐based polyamide 109 treated with superheated water

The structure and properties of bio‐based polyamide 109 (PA109) after treatment with superheated water (140 °C ≤ T ≤ 280 °C) were investigated and characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, wide‐angle X‐ray diffraction, scanning electron microscopy and small‐angle X‐ray scattering. Below 170 °C, the hydrothermal treatment was considered to be a physical process, which exerted an annealing effect on PA109. It led to an increase in melting temperature, lamellar thickness and crystallinity, while the macromolecular structure, crystal structure and the order of crystalline regions were not affected. Above 170 °C, complete melting/dissolution of PA109 occurred with partial hydrolysis. Due to the high temperature and long reaction time, the hydrolysis reaction became more and more prominent, and the resin was completely hydrolyzed into oligomers at 280 °C. Also, above 170 °C, the hydrothermal treatment was accompanied by a chemical process and the melting temperature and molecular weight decreased progressively. Notably, the crystal structure was not altered, but the degree of perfection of crystals and the order of crystalline regions were broken, especially above 200 °C. The hydrolytic degradation reaction was significantly affected by temperature, while both time and the water to polyamide ratio were secondary factors which influenced it to a minor extent. The process could be considered as a typical nucleophilic substitution reaction which takes place step by step inducing the molecular weight to decrease gradually. Overall, this study provides a ‘green’ route for the processing, recycling and treatment of environmentally friendly polyamides based on hydrothermal treatment technology. © 2019 Society of Chemical Industry     

Miscibility and crystallization of biodegradable poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)/poly(vinyl phenol) blends

Miscibility and crystallization of biodegradable poly (3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHBHHx)/poly(vinyl phenol) (PVPh) blends were investigated in this work. PHBHHx is miscible with PVPh over the whole composition range as evidenced by the single composition dependent glass transition temperature and the depression of equilibrium melting point of PHBHHx in the blends. The overall crystallization rates decrease with increasing crystallization temperature for both neat PHBHHx and its blends with PVPh; moreover, the overall crystallization rates are slower in the PHBHHx/PVPh blends than in neat PHBHHx at the same crystallization temperature. Blending with PVPh may change the crystallization mechanism of PHBHHx in the blends compared with that of neat PHBHHx. Both neat PHBHHx and the PHBHHx/PVPh blends exhibit a crystallization regime II to III transition. The crystal structure of PHBHHx is not modified in the PHBHHx/PVPh blends; however, the values of crystal layer thickness, amorphous layer thickness, and long period all become larger with increasing PVPh content in the blends. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Influence of heat‐setting temperature on the properties of a stretched polypropylene microporous membrane

The influence of heat‐setting temperature on the stress–strain curves, differential scanning calorimetry (DSC) curves and properties of a stretched polypropylene microporous membrane was studied. It was found that with an increase of heat‐setting temperature, a plastic plateau region in the stress–strain curves and a melting endotherm plateau in the DSC curves became apparent. The permeability and porosity firstly increased with the temperature to 145 °C and then decreased. The pore structure arrangement showed similar changing trend. On the one hand, higher heat‐setting temperature could decrease the shrinkage of the microporous membrane. On the other hand, the crystallization of some chains around separated lamellae during heat‐setting was unfavorable to the properties of the microporous membrane. The occurrence of crystallization during heat‐setting explained the origin of the plastic plateau. For the fabrication of microporous membranes based on the melt‐stretching mechanism with good dimensional stability, heat‐setting is necessary, but too high a heat‐setting temperature can destroy the permeability. © 2013 Society of Chemical Industry     

Miscibility and crystallization behavior of biodegradable poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)/phenolic blends

Poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV)/phenolic blends are new miscible crystalline/amorphous polymer blends prepared via solution casting method in this work, as evidenced by the single composition dependent glass transition temperature. The measured T_gs can be well fitted by the Kwei equation with a q value of 13.6 for the PHBV/phenolic blends, indicating that the interaction between the two components is strong. The negative polymer–polymer interaction parameter, obtained from the melting depression of PHBV using the Nishi‐Wang equation, indicating the thermal miscibility of PHBV and phenolic. The spherulitic morphology and crystal structure of PHBV/phenolic blends were studied with polar optical microscopy and wide angle X‐ray diffraction compared with those of neat PHBV. It is found that the growth rates of PHBV in the blends are lower than that in neat PHBV at a given crystallization temperature, and the crystal structure of PHBV is not modified by the presence of phenolic in the PHBV/phenolic blends, but the crystallinity decrease with the increasing of phenolic. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Charge storage behavior of isotropic and biaxially‐oriented polypropylene films containing α‐ and β‐nucleating agents

A study on the influence of the crystal modification (α and β) of isotactic polypropylene (i‐PP) films on the resulting electret properties is presented. Two commercial nucleating agents, sodium 2,2′‐methylene‐bis(4,6‐di‐tert‐butylphenyl)‐phosphate (NA11) and N,N′‐dicyclo‐hexyl‐2,6‐naphthalene‐dicarbox‐amide (NU100), were employed in this investigation. Isothermal charge decay was measured at 90°C. In hot pressed isotropic polypropylene films, no significant differences in the charge storage properties were observed for α‐ and β‐nucleated specimens. In addition, the article presents the influence of the nucleating agents at different concentrations on the PP‐film morphology of biaxially stretched films with respect to electret features. It was possible to prepare elongated cavities with the virtually insoluble NA11 additive during stretching, even at concentrations below 0.3 wt %. These films displayed slightly improved electret properties in comparison to stretched neat PP films due to generated cavities acting as barriers for the drift of charges. Various draw ratios were also studied for i‐PP films with 0.15 wt % NA11. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 650–658, 2006     

Morphology and texture development of uniaxially stretched poly(ethylene naphthalene‐2,6‐dicarboxylate)

The texture development of PEN films with different semicrystalline morphologies have been studied by X‐ray diffraction. These different structures have been obtained by uniaxially stretching PEN amorphous films at 100 and 160°C (below and above T_g) at different drawing ratios. Samples have also been characterized by DSC to determine the crystallinity ratios, the crystallization, and melting temperatures. To define the orientation of crystallites in the oriented samples, pole figures have been constructed, as a function of temperature and drawing ratio (DR) in the range 1.5–4. In the range from DR = 2 to 4 the orientation is clearly uniplanar‐axial. At T_draw = 100°C the crystallinity shown by DSC analysis is higher than the sample stretched at 160°C. The orientation is also higher when samples are stretched at 100°C. The naphthalene rings mainly stay in the plane of the film with a lower fraction perpendicular to the plane of the film. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 395–401, 2007     

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