Note on the effect of γ‐irradiation on the melting behavior of polyethylene single crystals

Takamizawa, Kanichiro; Fukahori, Yoshihide; Urabe, Yoshiko

doi:10.1002/macp.1969.021280122

Cited by 25 publications

(16 citation statements)

References 16 publications

(3 reference statements)

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“…This G-value would represent only the upper limit since the decrease in 2ff/~ is caused not only by the increase in lattice enthalpy, but also by a decrease in entropy of melt due to cross-linking [30]. However, even this overestimate is substantially lower than the overal G-value of 1.5 reported for PE at moderate irradiation doses [97].…”

Section: Salovey and Kellermentioning

confidence: 60%

Radiation effects in polyethylene and n-alkanes

Ungar

1981

J Mater Sci

138

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The effect of high-energy radiation on n-alkanes and polyethylene (PE) are reviewed. The article includes a description of (a) primary radiation events, formation, spatial distribution and decay of free radicals and radical migration mechanisms, (b) formation of cross-lin ks and other sta ble products, (c) the effects of crystal linity, crystalline modifications and morphology on radiation cross-linking, and (d) radiation-induced changes in the crystal lattice and the destruction of crystallinity at high irradiation doses.An attempt is made to bring together conflicting views on various unsolved problems of the radiation physics and chemistry of these important and much studied substances. Long-chain paraffins are given considerable attention since their radiation behaviour often provides a link between that of PE and its short-chain analogues.

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Section: Salovey and Kellermentioning

confidence: 60%

Radiation effects in polyethylene and n-alkanes

Ungar

1981

J Mater Sci

138

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“…The crystals of C 160 and Cl20 from IAAC were like tree leaves, and similar to the extended chain crystals which Takamizawa et at. 10 obtained previously from low molecular weight PE fractions. Toda 11 and Frank 12 reported that roundshaped PE crystals were obtaind from solution crystallized at high temperature, and discussed the mechanism of crystallization.…”

Section: Measurementsmentioning

confidence: 99%

“…With the standard heating rate of 0.5 K min -1 , the endothermic peak of once-folded chain crystal became ambiguous, which suggests that stabilization from a metastable state of once-folded chain crystal to the extended chain crystal gradually occurs at such a slow heating rate. From this point of view, cross-linking experiment 14 for amorphous parts was made by y-ray irradiation for the purpose of inhibiting melt-recrystallization. However, this experiment was unsuccessful for C160 and C120 crystals due to the absence ofa double bonds in the parts to be crosslinked.…”

Section: Polymorphism Of Melting Process For Once-foldedmentioning

confidence: 99%

Synthesis of Ultra Pure Long Normal Alkanes to Hexacohectane, Their Crystallization and Thermal Behavior

Urabe

Tanaka

Tsuru

et al. 1997

Polym J

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ABSTRACT:Ultra pure long chain normal alkanes (abbr.: Cn, where n is the number of carbon atoms in a chain ), C80, CI02, Cl 20, Cl 60, were synthesized by Wurtz condensation. For samples of Cl20 and Cl 60, a once-folded chain crystal was formed by solution crystallization; thicknesses of the layer lamella were on an average 7.8 nm for Cl 20, and 10.0 nm for Cl 60, which equals to a half of the extended chain length for each molecular weight. In the DSC thermograms of the Cl60 crystals, an exothermic peak which indicates recrystallization to extended chain crystal following to melting of once-folded chain crystal, appeared clearly. Consequently, folding of normal alkane molecular chain was found to take place from about Cl20.KEY WORDS Higher Normal Alkane / Homologous Purity/ Gel Permeation Chromatography/ Wurtz Condensation/ Once-Folded Chain Crystal/ Extended Chain Crystal/ Hei,acohectane / Eicosahectane One remarkable characteristic of flexible polymers is that they crystallize by chain folding. Since the first report on chain folding in solution crystallization of polyethylene (PE) 1 40 years ago, many studies have been made on crystallization behavior and resulting crystal structures using well-characterized PE and also normal alkanes (abbr., n-alkanes) as model compounds. To elucidate the characteristics of the chain folding phenomenon ultra long n-alkanes such as C384 and C390 were synthesized by Wegner et al. 2 and Whiting et al., 3 respectively 1985. Unfortunetely they could not give a definite answer enough yet, owing to limited amounts of the synthesized products and insufficient homologous purity.Takamizawa et al. 4 sought solution to the same problem by stundying higher-order crystalline structure on low molecular PE fractions (Mw! Mn= 1.01-1.03) located in the transition region from extended chain crystal to folded chain crystal. The relationship between average molecular weight and X-ray long period L for PE single crystals is in Figure 1. Dotted lines show lamella thickness corresponding to the number of folding, f = 0, 1, and 2, calculated from chain length. In this calculation, contribution of the folded portions to the thickness is neglected. At the low molecular weight end, the long period linearly increases, regardless of the crystallization solvent, with the chain length, and L is nearly in accordance with the calculation shown as dotted lines. However, L suddenly decreases when the molecular weight exceeds a critical value depending on the crystallization solvent; i.e., the effects of chain folding are clearly recognized. As a whole, PE single crystals appear to have higher-order structures with integer numbers of folding following the calculated line except single crystals from fractions of 2000-2400. Takamizawa 4 printed out that this discrepancy was attributable to polydispersity of samples.It is very difficult to get a fraction with very narrow t To whom correspondence should be addressed. * Sadly passed away. Will be greatly missed. 534distribution of molecular weight from simple fract...

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“…This crystal, having a lamellar thickness of 180A, melted without reorganization at ordinary pressure and its melting temperature could be given by the intersection temperature. 23 The DTA curve at low pressure below 1.5 kbar shows a sharp, single melting peak. With increase in pressure a shoulder appears, and then the peak becomes a doublet.…”

Section: Dt a And Melting Temperature Of Folded-chainmentioning

confidence: 99%

“…3, 1975 tained at atmospheric pressure on solution-grown crystals: thick crystals gave single peak, whereas thin ones showed a multiple peak. 23 If this interpretation is correct, the higher two peaks of the three can be assigned to the melting of crystallites with different degrees of perfection formed on the heating process. There is, however, a possibility that they correlate with an appearance of the high-pressure phase proposed by Bassett and Turner 26 ' 27 and by Takemura and coworkers.…”

Section: Dt a And Melting Temperature Of Folded-chainmentioning

confidence: 99%

Effect of Pressure on Melting Temperatures of Polyethylene Fractions

Takamizawa

Ohno

Urabe

1975

Polym J

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ABSTRACT:Differential thermal analysis of polyethylene crystals was made at pressures up to 5 kbar. The crystals studied were fully extended chain crystals of two low molecular weight fractions, and a solution-grown crystal of a high molecular weight fraction. The melting curves of the former crystals were represented by the Simon equation. The latter crystal, having a lamellar thickness of 180A, showed reorganization during the heating process in the differential thermal analysis at 2.5 kbar and above. In order to determine accurately its melting temperature at 5 kbar a pressure annealing experiment was made. These results showed that the depression of the melting temperature of folded-chain crystals is considerably smaller, even at high pressures, than that reported previously. The slopes of the melting curves at atmospheric pressure are almost the same for all the crystals studied. This fact can be reasonably interpreted on the basis of a two-phase model.

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Note on the effect of γ‐irradiation on the melting behavior of polyethylene single crystals

Abstract: Polyethylene single crystals were prepared from isoamyl acetate solutions, whose thickness was 200 A. They melted without significant reorganization during the heating process

Cited by 25 publications

References 16 publications

Radiation effects in polyethylene and n-alkanes

Radiation effects in polyethylene and n-alkanes

Synthesis of Ultra Pure Long Normal Alkanes to Hexacohectane, Their Crystallization and Thermal Behavior

Effect of Pressure on Melting Temperatures of Polyethylene Fractions

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