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236839923铁杆木虫 (正式写手)
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236839923
铁杆木虫 (正式写手)
- ESEPI: 2
- 应助: 0 (幼儿园)
- 金币: 7517.3
- 散金: 499
- 红花: 3
- 帖子: 822
- 在线: 232小时
- 虫号: 561988
- 注册: 2008-05-22
- 性别: GG
- 专业: 高分子合成化学
★ ★
ksq887: 金币+2, thanks for sharing~ 2022-07-01 14:04:52
ksq887: 金币+2, thanks for sharing~ 2022-07-01 14:04:52
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continuing specific <dependecne >effect of density and crystallinity on molecular weight is shown <can be seen >in figure 5, where both properties first decrease with increasing MW, reach a minimum value at molecular weight of <about> 1*10*5, and then show the opposite dependence <on molecular weight>. As for ethylene/a-olefin copolymer containing <ethylene >of Xa mole fraction, the equilibrium melting temperature and lamellar thickness can be obtained using Flory eqution and Thomson-Gibbs eqution, respectively, the molecular weight dependence of crystallinity for copolymer with various degrees of SCB was calculated and shown in figure 6. it was proved that the crastallinity is greatly influenced by MW in the molecular weight range of A-B, and is not so much affected by the molecular weight but by the degree of SCB in that over B. the experimental results on the relationship between the molecular weight and the degree of SCB for LLDE fractions are plotted in the same figure. as the molecular weight in equation 3 is Mn ,the experimental Mw is converted into Mn using the SEC result for Mw/Mn. a concave type dependence of crystallinity on molecular weight <was obtained > by connecting the points with a dotted line. which is similar to the experimental results shown in figure 5. Though the absolute value of crystallinity is different between the experiment and theory mainly because the quenched samples were used in the experiment. this suggests that unique dependence of crystallinty on molecular weight for LLD fractions would be attributable to both of average molecular weight of a fraction and the characteristic dependence of degree of SCB on the molecular weight. |
9楼2022-05-24 18:18:41
236839923
铁杆木虫 (正式写手)
- ESEPI: 2
- 应助: 0 (幼儿园)
- 金币: 7517.3
- 散金: 499
- 红花: 3
- 帖子: 822
- 在线: 232小时
- 虫号: 561988
- 注册: 2008-05-22
- 性别: GG
- 专业: 高分子合成化学
★ ★
ksq887: 金币+2 2022-06-02 14:45:07
ksq887: 金币+2 2022-06-02 14:45:07
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On Friday, May 20th, 2022 Title: Structure distribution of Linear low density polyethylene Abstract: Molecular and crystalline structure of linear low density polyethylenes(LLD) were investigated by a series of characterization technique. Molecular structural characteristics were elucidated by temperature-rising elution fractionation(TREF) and solvent gradient elution fractionation(SGEF). A bird' eye view and a contour map of LLD obtained by a combination of TREF and size exclusion chromatography exhibited a broad and multimodal chemical composition distribution(CCD), in contrast to a sharp and single CCD of conventional high pressure of low density polyehtylene(LDPE). Short chain branching was found to decrease with increase of molecular by SGEF technque. The thermal analysis of cross-fractions proved that a characteristic broad endothermic curve of LLD is attributable to its broad and multimodal CCD. Then , using the DSC results, an indicative index(DI) which expresses the the degree of the distribution of lamellar crystal thickness is proposed. DI was found to be sensitive both to CCD and to a kind of SCB. The crystallinity and melting temperature of cross fractions having comparable molecular weights decease with increasing comonomer content in the order of octene-1=4-methyl-pentene-1>hexene-1>pentene-1>butene-1. From a statistical approach to the relationship between crystallinity and degree of SCB, the probability of exlusion of a bulky branching such as isobutyl from a crystalline lattice is considered to be twice as large as than that of ethyl branching. |
2楼2022-05-20 10:24:03
236839923
铁杆木虫 (正式写手)
- ESEPI: 2
- 应助: 0 (幼儿园)
- 金币: 7517.3
- 散金: 499
- 红花: 3
- 帖子: 822
- 在线: 232小时
- 虫号: 561988
- 注册: 2008-05-22
- 性别: GG
- 专业: 高分子合成化学
★ ★
ksq887: 金币+2 2022-06-02 14:45:17
ksq887: 金币+2 2022-06-02 14:45:17
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continuing In the past decade, interest has grown greatly in linear low density polyethylene manufacturing all over the world. LLD has gradually replaced the conventional LDPE , through the /its superior mechanical and thermal properties. Needless to say, LLD has/ short chain branching SCB derived from comonomer /units which is/are a-olefins, such as butene-, hexene-1,4-methyl-pentene-1. Hence/thus, /the/ molecular structure/ LLD/ should be investigated from view/ points/ of average comonomer content/ average content of comonomer(degree of SCB), monomer sequence distribution along the main /a polymer /chain(intramolecular distribution of SCB), /and / comonomer distribuion among polymers(intermolecular distribution of SCB ) besides the average moleduclar weight and molecular weight distribution. |
3楼2022-05-20 10:57:13
236839923
铁杆木虫 (正式写手)
- ESEPI: 2
- 应助: 0 (幼儿园)
- 金币: 7517.3
- 散金: 499
- 红花: 3
- 帖子: 822
- 在线: 232小时
- 虫号: 561988
- 注册: 2008-05-22
- 性别: GG
- 专业: 高分子合成化学
|
continuing Recently, investigations for chemical composition distribution(CCD) which is considered to have a important role in /final properties/superstructure are receiving more/increasing/ attention and its inhomogeneity was elucidated by means of various methods. but relatively little has been reported on the details of CCD and /the effect of CCD on super structure/itsinfluence on the superstructure. The authors has/already/ reported that superstructures of LLD and found /that LLD has wide distribution of the superstructure compared to LDPE/the broad distribution of superstructure. In this paper, /detail studies on CCD of LLD by fractionation techniques and its influence on lamellar crystal are considered / |
4楼2022-05-20 12:47:34
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