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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)
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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)
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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)
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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
molmolsong
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5楼2022-05-24 05:38:13
236839923
铁杆木虫 (正式写手)
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ksq887: 金币+2, thanks for sharing~ 2022-07-01 14:03:55
ksq887: 金币+2, thanks for sharing~ 2022-07-01 14:03:55
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on tuesday, may 24th , 2022. molecular weight <structural>distribution of a <whole >polymer the bird's eye view and contour map of lld is/are/ shown in figure /figures/1 and 2, respectively. theses figures clearly show that this sample is/mainly/ composed of three tops. the highest/one/ is /characterized by a very distinctive sharp perk of low scb and high molecular weight/lcomposed of a characteristic sharp peak of low scb and high molecular weight. it<this> is a common component of <all kinds of > lld produced in<with> various<polymerization> processes, <some superiorities in thermal and mechanical properties compared to ldpe are considered to be related to the presence of this component>which is related to the superior mechanical and thermal properties compared to ldpe. the middle <one>is the component having <the>average <degree of > scb and molecular weight. and the lowest <one>is the component <composed of the polymers of the highest degree of scb and the lowest molecular weight>of highest content of scb and lowest molecular weight. compared to<contrary to the lld sample> lld, ldpe <has characteristic sharp ccd composed of single top and wide mwd >shows a characteristic single sharp ccd as shown in figure 3. the sectional view of figure 2 at a definite molecular weight(mw=6.3*10^4)) gvies ccd composed of mulipeaks, each of which has been proved to follow a poisson distribution as shown in figure 4. |
6楼2022-05-24 08:18:54
236839923
铁杆木虫 (正式写手)
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ksq887: 金币+2, thanks for sharing~ 2022-07-01 14:04:00
ksq887: 金币+2, thanks for sharing~ 2022-07-01 14:04:00
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continuing As for a LDPE polymerized under uniform condition, Sb have reported that the<intermolecular distribution of SCB> SCB distribution follows Poission distribution, <too>. Though the mechanism of the occurrence of SCB is quite different <between LDPE and LLD>, this results shows <suggests >that ethylene copolymerizes with a-olefin on the basis of the <some definite> probability on each active <site> on a catalyst surface if the multi-peaks in Figure 4 reflect various active sites whose reactivities to ethylene and a-olefin differ from each other. |
7楼2022-05-24 11:23:52
236839923
铁杆木虫 (正式写手)
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ksq887: 金币+2, thanks for sharing~ 2022-07-01 14:04:07
ksq887: 金币+2, thanks for sharing~ 2022-07-01 14:04:07
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Continuing characterization of fractions of SGEF a typical result of sgef is shown in table 2. it is found that fractions having considerably narrow MWD were obtained by this fractionation technique. and the effect of methyl end group on the degree of SCB is fairly large for small molecular weight, but can be ignored for fractions <having a molecular weight higher than about >molecular weight of higher than 3*10^4, considering the experimental error. the degree of SCB decreased with increasing molecular weight, especially above<the molecular weight of > 3*10^4 as shown in Figure 5. this tendency is <was>characteristic of all kinds of LLD used in this study, and was quite different from<the results of > LDPE polymerized in <under> an uniform conditions and <those of >ehtylene/a-olefin copolymer polymerized with a soluble catalyst system such as****. In the case of the latter two polymers, the degree of SCB is known to be <almost> independent of MW in the range of high molecular weight. |
8楼2022-05-24 13:29:29
236839923
铁杆木虫 (正式写手)
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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)
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★ ★
ksq887: 金币+2, good job 2022-07-01 14:04:58
ksq887: 金币+2, good job 2022-07-01 14:04:58
|
on Wednesday, May 25th, 2022 the fraction by SGEF technique having molecular weight of <about >1*10^5 were further fractionated0 into 17-18 fractions by TREF technique. Typical results <for LLD fraction NO.10>of fraction 10 of LLD are summarized in Table 3. It is found that the fractions of LLD<LLD fraction > by SGEF is composed of various coplymer, , <whose> chemical compositions, melting temperatures, and crystallinities are <largely >different with each other . For example,<the degree of > SCB disperses in the range of 1-40(1/1000C), and melting temperature<also> disperses in the range of 60-130C. |
10楼2022-05-25 16:55:56
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