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Structure and Properties of Ultra High Molecular Weight Polyethylene / High Density Polyethylene Microporous Membrane Via Thermal Induced Phase Separation

Author: GuXu
Tutor: ZhouChiXing
School: Shanghai Jiaotong University
Course: Materials Science
Keywords: Ultrahigh molecular weight polyethylene High density polyethylene Microporous membrane Thermally induced phase separation
CLC: TQ325.12
Type: Master's thesis
Year: 2012
Downloads: 152
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Abstract


The lithium-ion battery in recent years of new power technology research hotspot, the diaphragm is the important part, its main role is to provide short-circuit protection and avoid direct contact with the positive and negative. The conventional diaphragm is usually made of polyethylene (PE) and polypropylene (PP) composite diaphragm. The ultra-high molecular weight polyethylene (UHMWPE) outperforms ordinary polyethylene and polypropylene. Meanwhile, although the melting point of the UHMWPE in about 130oC, but at higher temperatures, UHMWPE melt gelatinous, it is possible to maintain the original shape unchanged, therefore expected to use UHMWPE film is used as a lithium ion battery separator. UHMWPE difficult to process, high melt strength is not conducive to the the obturator protection shorted, therefore need to be modified. UHMWPE / HDPE matrix, liquid paraffin (LP) as the solvent, HDPE join the system viscoelastic liquid - solid phase separation using thermally induced phase separation prepared UHMWPE / HDPE microporous membranes studied different process microporous membrane structure and performance of the microporous membrane were characterized. The results show that, in a solvent system of UHMWPE / LP, HDPE added to reduce the viscosity of the system, reducing the elasticity of the system, to improve the processing performance of the system. Through the study of UHMWPE / HDPE / LP ternary system of isothermal crystallization and nonisothermal crystallization process and study system liquid - solid phase separation process, we found that: Isothermal crystallization UHMWPE higher nucleation density, crystal imperfections, UHMWPE the crystallization is carried out according to the heterogeneous nucleation and is accompanied by a two-dimensional growth mechanism; while HDPE / LP binary system of a crystal nucleation density is low, the crystallization by the growth control, at higher temperatures, in accordance with the three-dimensional growth of spherulites crystals. In nonisothermal crystallization HDPE join reduce the crystallization temperature and crystallization rate. Isothermal crystallization activation energy and non-isothermal crystallization activation energy rises with HDPE to join and generate the HDPE is not conducive to the crystallization. This is also the result into a reduction of nuclear density. This paper also examines the molecular weight of UHMWPE, HDPE content, cooling rate on the pore morphology and structure. Is cooled in the slow cooling rate, the HDPE added to change the micropore shape, and pore size. Appropriate ratio and process conditions, and can be prepared in an average pore size of about 1um uniform pore size UHMWPE / HDPE microporous membrane; UHMWPE / HDPE microporous membranes at 135oC obturator, the HDPE join conducive to the occurrence of the obturator. 160oC temperature, microporous membrane film remains original shapes without collapsing, visible when used in lithium-ion battery separator, heat resistance than PP, PE diaphragm and its composite film. The study results indicate that the UHMWPE: HDPE = 80:20 ratio of microporous membrane was prepared, and is expected to replace are PP / PE / PP a three-layer structure of the microporous membrane, and used as a lithium battery separator. Its mechanical properties and heat resistance are superior to PP, PE microporous membrane, short-circuit when the temperature is too high \

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CLC: > Industrial Technology > Chemical Industry > Synthetic resins and plastics industry > Polymer resin and plastic > Polyolefin plastic > Polyethylene
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