Influence of annealing on stress–strain behaviors and performances of β nucleated polypropylene stretched membranes

Wu, Tong; Xiang, Ming; Cao, Ya; Yang, Feng

doi:10.1007/s10965-014-0598-x

Cited by 11 publications

(3 citation statements)

References 42 publications

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“…The traditional annealing treatment consumes too much time, for example, the cast film of dry process using uniaxial stretching technique must be annealed offline for about 12 h . In order to improve the efficiency and effect of annealing in the dry process using biaxial stretching technique, we employed the first roller in the longitudinal stretching unit to heat the cast film at high temperature instantaneously . It is clear to see from Figure a that the onset melting temperatures of the cast films annealed for 10 s at 150 °C and 10 s at 155 °C were higher than that annealed conventionally at 140 °C for 2 h. In addition, the melting peaks of β crystals narrowed apparently.…”

Section: Manufacturing Technique Optimization Of Dry Process Separatomentioning

confidence: 99%

Progresses in Manufacturing Techniques of Lithium‐Ion Battery Separators in China

Wang

Xiang

et al. 2019

Chin. J. Chem.

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The lithium‐ion batteries (LIBs) have been widely used in the world since the first introduction in 1991. The microporous polyolefin separator is the key component to determine the electrical properties and safety of LIBs. In China, the LIBs separators were completely imported and expensive before 2008. We have realized the industrialization of LIBs separators by either dry or wet process successfully. Nowadays, China has become the biggest manufacturing country of LIBs separators in the world and the price is very much reduced. Among the separator processing techniques, the dry process based on biaxial stretching β nucleated polypropylene (β‐iPP) was originated from China and has the lowest manufacturing cost. However, the separator produced by this method has non‐uniform pore size distribution which limits its wider application. In this article, based on the better understanding of original crystal morphology on the pore formation during stretching, we present our recent works to improve the performance of dry process separator through the preparation of β‐spherulites, casting technique optimization, improved annealing treatment and multi‐stages longitudinal stretching. As a result, we produced the dry process separator with much more uniform pore size distribution than that made from the traditional dry process.

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Section: Manufacturing Technique Optimization Of Dry Process Separatomentioning

confidence: 99%

Progresses in Manufacturing Techniques of Lithium‐Ion Battery Separators in China

Wang

Xiang

et al. 2019

Chin. J. Chem.

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“…For example, Grant et al [24] found that the films annealed near the melting temperature of β crystal exhibited larger porosity, suggesting that annealing perfected the crystalline structure, thereby contributing to the formation of pores. In our previous work, we found that annealing could not only thicken the lamellar thickness but also narrow the lamellar thickness distribution, thus improving the performance of membranes [25]. Yang et al [26] succeeded in improving the pore size distribution by optimizing stretching temperature and tensile ratio.…”

Section: Introductionmentioning

confidence: 99%

Comparison of the Structural Evolution of β Polypropylene During the Sequential and Simultaneous Biaxial Stretching Process

Zhang

Ding

Yang

et al. 2020

Preprint

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In this paper, the lamellar structural evolution and microvoids variations of β-iPP during the processing of two different stretching methods, sequential biaxial stretching and simultaneous biaxial stretching, were investigated in detail. It was found that different stretching methods led to significantly different lamellae deformation modes, and the microporous membranes obtained from the simultaneous biaxial stretching exhibited better mechanical properties. For the sequential biaxial stretching, abundant coarse fibers originated from the tight accumulation of the lamellae parallel to the longitudinal stretching direction, whereas the lamellae perpendicular to the stretching direction were easily deformed and separated. Those coarse fibers were difficult to be separated to form micropores during the subsequent transverse stretching process, resulting in a poor micropores distribution. However, for the simultaneous biaxial stretching, the β crystal had the same deformation mode, that is, the lamellae distributed in different directions were all destroyed, forming abundant microvoids and little coarse fibers formation.

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“…The dry-stretching process was rapidly developed as a highly efficient industrial method to prepare PP microporous membranes through casting, annealing, stretching process, respectively [2][3][4]. In detail, the dry-stretching process involves three main steps [3,5,6]: (1) preparation of precursor film (cast film) with hard-elastic property (Shish-kebab microstructure [7]) via being uniaxially stretched along the machine direction; (2) thickening of the film's lamellae through annealing process [8]; and (3) stretching along the machine direction of the film at low temperature initially to create the voids and at high temperature subsequently to enlarge the voids. After step (3), the stretched films are heat-set to improve their dimensional stability [9].…”

Section: Introductionmentioning

confidence: 99%

Impact of different die draw ratio on crystalline and oriented properties of polypropylene cast films and annealed films

Zeng

Wang

et al. 2018

J Polym Res

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Four kinds of polypropylene (PP) cast films with different die draw ratios (DDR) were prepared. The impact of different DDR on the crystalline and oriented properties of PP cast films and annealed films was explored herein. Wide angle X-ray diffraction (WAXD) and fourier transform infrared (FTIR) methods were adopted to examine the orientation degree of crystalline and amorphous phases. Long period distance (L p ) of the crystalline structure was tested by small angle X-ray scattering (SAXS). Crystallization was determined by differential scanning calorimeter (DSC). The oriented and crystalline behaviors of the samples were carried out by the elastic recovery (ER) testing. Then, samples after being annealed were examined by the same methods. The influence of annealing process on the films' structures and properties was explored. Besides, the final stretched microporous membranes manufactured via stretching the annealed films along machine direction were examined by scanning electronic microscope (SEM). No matter for cast films or for annealed films, it is found that the films' orientation degree of crystalline and amorphous phases, as well as L p and crystallinity are larger at higher DDR and relatively lower at lower DDR. When the DDR is overly high (DDR = 170), both the oriented and crystalline properties will decline. Elastic recovery testing indicates that a film with better orientation of the crystalline and the amorphous phases as well as with higher crystallinity can be obtained at an appropriate DDR. SEM images show that stretched membranes with better microporous structure can be obtained when the precursor film is prepared at a proper DDR.

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Influence of annealing on stress–strain behaviors and performances of β nucleated polypropylene stretched membranes

Cited by 11 publications

References 42 publications

Progresses in Manufacturing Techniques of Lithium‐Ion Battery Separators in China

Progresses in Manufacturing Techniques of Lithium‐Ion Battery Separators in China

Comparison of the Structural Evolution of β Polypropylene During the Sequential and Simultaneous Biaxial Stretching Process

Impact of different die draw ratio on crystalline and oriented properties of polypropylene cast films and annealed films

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