Effects of melt‐extension and annealing on row‐nucleated lamellar crystalline structure of HDPE films

Lee, Sang Young; Park, Soon Yong; Song, Heon

doi:10.1002/app.25495

Cited by 21 publications

(17 citation statements)

References 15 publications

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“…After these, the heat-setting is carried out to improve the dimensional stability of stretched microporous membrane. There have been detailed works about the influence of the physical properties of raw materials, applied cast processing conditions and annealing technology on the crystalline properties and stretched pore structures [4][5][6][7][8][9][10][11][12][13] . However, as to the pore initiation process during room-temperature stretching, few works have been carried out to clarify how the initial pores are formed.…”

Section: Introductionmentioning

confidence: 99%

The study of room-temperature stretching of annealed polypropylene cast film with row-nucleated crystalline structure

Chen

Xie

et al. 2016

Polymer

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The room-temperature stretching process of polypropylene annealed film with rownucleated crystalline structure was studied by in-situ small-angle X-ray scattering (SAXS) setup and off-line wide-angle X-ray scattering (WAXS), temperature-modulated differential scanning calorimetry (TMDSC) and stress-strain curves testing. The formation process of initial connecting bridges and pores was clarified. For the annealed film, except for the initial lamellae structure, the recrystallized part formed by the melting and crystallization of imperfect crystals during annealing, tie chains connecting the lamellae structure among the amorphous region, secondary crystals from the crystallization of tie chains during annealing and daughter crystals from the special cross-hatched crystalline structure of PP coexist. It was found that 10 % stretching lead to the pronounced increase of long period and the appearance of a few initial connecting bridges. The stretching of daughter crystal and recrystallized part contributed to the formation of initial bridges. At stretching ratio of 30 %, uniform distributed connecting bridges were observed and the stretched film showed maximum structure periodicity. At this stretching ratio, except for the stretching of daughter crystal, the stretching of tie chains and secondary crystals within the amorphous region lead to the formation of more connecting bridges. At higher stretching ratios into the strain-hardening region and beyond the second yield point, except for the stretching of the above mentioned crystalline

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Section: Introductionmentioning

confidence: 99%

The study of room-temperature stretching of annealed polypropylene cast film with row-nucleated crystalline structure

Chen

Xie

et al. 2016

Polymer

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“…After these stages, the stretched films are heat‐set to improve their dimensional stability. Many works have shown that annealing is an indispensable process for obtaining microporous membranes with excellent properties . But it is still unclear as to the annealed lamellar change and the relationship between the annealed lamellar structure and connecting bridge arrangement in a stretched microporous membrane.…”

Section: Introductionmentioning

confidence: 99%

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

Cai

Shuqiu

et al. 2014

Polym. Int.

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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.

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“…This indicates that without heat setting, some stretched connecting bridges retract. This is because the annealed film with rownucleated crystalline structure shows higher hard elastic behavior and after stretching without heat setting, it will retract [9,15,16]. The existence of some connecting bridges means that these bridges are stable and they come from the crystallization of stretched tie chains during hot stretching [9].…”

Section: Resultsmentioning

confidence: 94%

“…There have been many works to build the relationship among the material characteristics, processing technology, structure and properties of stretched microporous membrane [4][5][6][7][8][9][10][11][12][13][14][15][16][17]. During the third stage, low-temperature stretching leads to the formation of initial bridges connecting the separated lamellae [18].…”

Section: Introductionmentioning

confidence: 99%

Influence of heat-treatment temperature on the structure and properties of polypropylene microporous membrane

Xie

Chen

et al. 2015

Polym. Bull.

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The polypropylene (PP) microporous membrane has been used in the Lithium battery as a separator. During the charge and discharge process, the temperature in the battery may rise. To clarify the microstructure change mechanism of membrane during the temperature increase, the PP microporous membranes were heat treated at different temperatures and the microstructure and properties were characterized using differential scanning calorimetry, scanning electron microscopy and atomic force microscopy. When the membranes were treated at temperatures lower than 130°C, no apparent dimension and microstructure changes were observed. The Gurley value (characterizing the air permeability) was kept around 240 s. When the membranes were treated at temperatures higher than 140°C, apparent dimensional shrinkage and the decrease or even disappearance of connecting bridges appeared. The corresponding Gurley value was increased to 1320 s, indicating worse air permeability property. The final heat-setting stage during the preparation of microporous membrane based on melt-stretching mechanism could stabilize the stretched connecting bridges and when the heat-treatment temperature was higher than heat-setting temperature, the crystals formed during heat setting could not support the stretched connecting bridges and resulted in the retraction or even disappearance of connecting bridges. These retracted connecting bridges were converted to new crystalline nodes sitting on both sides of separated lamellae.

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Effects of melt‐extension and annealing on row‐nucleated lamellar crystalline structure of HDPE films

Cited by 21 publications

References 15 publications

The study of room-temperature stretching of annealed polypropylene cast film with row-nucleated crystalline structure

The study of room-temperature stretching of annealed polypropylene cast film with row-nucleated crystalline structure

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

Influence of heat-treatment temperature on the structure and properties of polypropylene microporous membrane

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