SAXS studies of blends of high- and low-density polyethylene

Reckinger, C.; Larbi, Fatma; Rault, J.

doi:10.1080/00222348408219474

Cited by 20 publications

(7 citation statements)

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“…As r0 approaches r, the amorphous chain is compressed between the two crystalline lamellae as shown in Figure 12. The entropy of confinement of such a coil is and the free energy per unit volume of the system is AF = --AFC + L 0 KT L2 -Clca La2 (Llc)2 (31) AFC being the enthalpy of crystallization per volume, a3.…”

Section: Discussionmentioning

confidence: 99%

Origin of the long period and crystallinity in quenched semicrystalline polymers. 1

Robelin-Souffaché¹,

Rault²

1989

Macromolecules

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Section: Discussionmentioning

confidence: 99%

Origin of the long period and crystallinity in quenched semicrystalline polymers. 1

Robelin-Souffaché¹,

Rault²

1989

Macromolecules

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“…Polydisperse (p) and monodisperse (m) PE exhibit similar behavior; therefore one cannot argue that the polydispersity of the chains has an influence on the crystallization behavior of the materials (at least on the values of L and Tc). 3. In branched PE the influence of the cooling rate on L is less important than in linear PE; this effect is analyzed below.…”

Section: Slow-cooled Materialsmentioning

confidence: 99%

“…Typical SAXS curves of P3 sample (hdPE, M , = 120,000, M , = 22,000) crystallized by quenching and by slow cooling at 10.2 and O.B"C/min are shown in Figure 1. The long period of the semicrystalline state is deduced from the maximum of the SAXS curve by application of Bragg's law ( L ) or is deduced from the first maximum of the correlation function y( r ) ( Lcor): K(*) is defined by the relation K ( * ) = p ( s ) c o s ( 2 n s z ) ds (3) where I ( s ) is the SAXS intensity scattered at the angle 28 (s = sin 8 / A ) . yL and ye, the dimensionless parameters given by eq.…”

Section: Saxs Measurementsmentioning

confidence: 99%

Long periods in slow‐cooled linear and branched polyethylene: Part II

Rault

Robelin-Souffaché

1989

J Polym Sci B Polym Phys

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SynopsisIt is shown that the long periods L in slow-cooled polyethylene materials obey the general law L = Lo + ar,.,, where rw is the weight average dimension of the coil before crystallization, and Lo is a parameter of the order of I,, the crystalline core thickness, which increases as the cooling rate V decreases. a is a parameter independent of M and V but decreasing with the number of long-chain branches per molecule. The two terms in the above relation are, respectively, the contributions of crystalline and amorphous layers. For cooling rates from soO°C/min to 0.2OC/min, it is shown that the temperature T, of crystallization is constant; hence the change of morphology (long period, crystalline core thickness, crystallinity) cannot be explained by supercooling. The increase in long period and crystallite thickness in slow-cooled materials with decreasing cooling rate is interpreted in terms of annealing of the crystallized materials between the crystallization temperature T, and the secondary transition temperature Tat. Crystallization proceeds by a two-step process of solidfication and annealing. During the annealing stage, the mobility of the chains in the crystalline phase is due to defecty the kinetics of thickening is then governed by the mobility (or nucleation) of the defects appearing above Tat. In the proposed model of crystallization, the assumption that the energy of activation is proportional to T,, explains the observed laws L = 1, = log ta, where the annealing time t,, is equal to (T, -T,,)/V. The model applies also to polymers crystallized from the melt and subsequently annealed. 0 1989 John Wiley & Sons, Inc. CCC 0098-1273/89/061349-25$04.00 1350 RAULT AND ROBELIN-SOUFFACHE second term (a being a constant) represents the contribution of the amorphous phase of thickness I , .In part I4 the long periods L,, deduced from the correlation function and' L, from paracrystalline analysis were compared with the Bragg long spacing L. Similar correlations are found for the linear polymers polyethylene (PE), polytetrahydrofuran, polypropylene quenched from the melt, and for poly(ethy1ene terephthalate) crystallized from the glassy state. It is well known that the values of L,, and L, are found to be smaller than L , and this is due to the disorder of the lamellar arrangement. L,,, and L , are mostly proportional to the first moment of the distribution function of the long period, whereas L is proportional to a higher moment.In polydisperse PE the correlations between the solid and melt states are given by

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“…Figure10. log [d2/dQ(Q)] vos (Q) for 23/77 and 10/90 samples of HDPE-D/LDPE-H rapidly quenched to -78 °C.…”

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Morphology of Blends of Linear and Long-Chain-Branched Polyethylenes in the Solid State: A Study by SANS, SAXS, and DSC

Wígnall¹,

Londono²,

Lin³

et al. 1995

Macromolecules

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Differential scanning calorimetry (DSC), small-angle neutron scattering (SANS), and X-ray scattering (SAXS) have been used to investigate the solid-state morphology of blends of linear (high density) and long-chain-branched (low-density) polyethylenes (HDPE/LDPE). The blends are homogeneous in the melt, as previously demonstrated by SANS using the contrast obtained by deuterating the linear polymer. However, due to the structural and melting point differences (~20 °C) between HDPE and LDPE, the components may phase segregate on slow cooling (0.75 °C/min). For high concentrations (

0.5) of HDPE, relatively high rates of crystallization of the linear component lead to the formation of separate stacks of HDPE and LDPE lamellae, as indicated by two-peak SAXS curves. For predominantly branched blends, the difference in crystallization rate of the components becomes smaller and only one SAXS peak is observed, indicating that the two species are in the same lamellar stack. Moreover, the phases no longer consist of the pure components and the HDPE lamellae contain up to 15-20% LDPE (and vice versa). Rapid quenching into dry ice/2-propanol (-78 °C) produces only one SAXS peak (and hence one lamellar stack) over the whole concentration range. The blends show extensive cocrystallization, along with a tendency for the branched material to be preferentially located in the amorphous interlamellar regions. For high concentrations ( > 0.5) of HDPE-D, the overall scattering length density (SLD) is high and the excess concentration of LDPE between the lamellae enhances the SLD contrast between the crystalline and amorphous phases. Thus, the interlamellar spacing (long period) is clearly visible in the SANS pattern. The blend morphology is a strong function of the quenching rate, and samples quenched less rapidly (e.g., into water at 23 °C) are similar to slowly cor'ed blends. The combination of SANS, SAXS, and DSC techniques allows us to interpret morphological differences in the solid state of these blends.

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SAXS studies of blends of high- and low-density polyethylene

Cited by 20 publications

References 0 publications

Origin of the long period and crystallinity in quenched semicrystalline polymers. 1

Origin of the long period and crystallinity in quenched semicrystalline polymers. 1

Long periods in slow‐cooled linear and branched polyethylene: Part II

Morphology of Blends of Linear and Long-Chain-Branched Polyethylenes in the Solid State: A Study by SANS, SAXS, and DSC

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