A technique for monitoring the kinetics of flow-induced crystallization

McHugh, A. J.; Spěváček, Jiří

doi:10.1002/pol.1987.140250304

Cited by 15 publications

(9 citation statements)

References 2 publications

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“…The latter finding implies that those models proposed to describe the kinetics of shear-induced ("stre~s-induced"~~) crystallization, which consider the formation of solely one crystalline modification (e.g., ref. 36 and 37), should be treated with criticism in the case of iPP.…”

Section: Effects Of the Quality Of The Ippmentioning

confidence: 96%

Rules of supermolecular structure formation in sheared isotactic polypropylene melts

Varga

Karger‐Kocsis

1996

J. Polym. Sci. B Polym. Phys.

456

389

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Section: Effects Of the Quality Of The Ippmentioning

confidence: 96%

Rules of supermolecular structure formation in sheared isotactic polypropylene melts

Varga

Karger‐Kocsis

1996

J. Polym. Sci. B Polym. Phys.

456

389

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“…Video images were converted to crystallization isotherm data following the methods described in Ref. 7. In the present case, maximum and minimum fiber intensity at the center of the sample corresponded respectively to conditions of increasing intensity or fringe formation.…”

Section: Discussionmentioning

confidence: 99%

“…Similarly, the various functional forms for f ( A)21-25 along with appropriate parameters difference between T, and T,*. Thus, in constructing undercooling plots wt have used the value 78.3"C, which corresponds to a calculated melting point elevation of 0.2"C. Figure 8 shows the resulting plot of k,, versus the undercooling parameter for heterogeneous growth, which exhibits a pattern quite similar to that found in flow-induced crystallization (7). In the latter case, Avrami coefficients of 2 and 2.5 were interpreted mechanistically in terms of a one-dimensional growth process with sporadic nucleation.…”

Section: We Havementioning

confidence: 99%

“…The retardation S, is that measured from the birefringence and contains a factor for swelling (i.e., S, = Sd,/d); and the tensile stress 7 is based on the actual cross-sectional area. From the statistical network theory due to Kuhn and Griin,18 the following expression holds for the ratio of the slopes of these plots: (7) where k , is the Boltzman constant, T is temperature, no is the mean refractive index of the chain segments, and p1 and p2 are the polarizability parallel and perpendicular, respectively, to the random link backbone. The temperature dependence of C' was found to be adequately described by the above 1/T relation, which was therefore used in eq.…”

Section: Kineticsmentioning

confidence: 99%

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Strain‐induced crystallization of swollen, crosslinked polyethylene

McHugh

Yung

1989

J Polym Sci B Polym Phys

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The kinetics of strain‐induced crystallization of swollen polyethylene networks have been measured using dynamometry coupled with optical birefringence. Fibers were prepared by gel‐spinning ultrahigh‐molecular‐weight polyethylene followed by crosslinking in dicumyl peroxide and swelling in xylene. Retractive force on crystallization was monitored at various temperatures and draw ratios. Fiber visualization was achieved using optical illumination coupled with video recording and digital analysis of the in situ transformation. Avrami plots of the transformation data showed good linear fits for low draw ratios in the range α < 1.2 and moderate undercoolings (60 < Tc < 70°C). Time exponents of unity were found, indicating a one‐dimensional, heterogeneous growth mechanism whose temperature dependence could be described by a formalism similar to that recently used for flow‐induced growth.

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“…He explained that this was a result of a decreasing fraction of the amorphous phase and the resulting stress relaxation due to crystallization. The kinetics of flow‐induced crystallization in polyethylene was studied by McHugh and Spevacek34 by measuring the changes in the intensity of transmitted polarized light.…”

Section: Introductionmentioning

confidence: 99%

Online monitoring of birefringence development in heat‐setting polymer films with a fast dual‐wavelength optical technique. I. Uniaxially oriented poly(ethylene naphthalate)

Galay

Çakmak

2001

J Polym Sci B Polym Phys

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The purpose of this article is to study the fast structural changes that take place during the deformation and heat setting of uniaxially preoriented poly(ethylene 2,6‐naphthalate) films. For this purpose, an online birefringence measurement system coupled with a heat‐setting oven was used. In the online birefringence system, whose details were reported previously (H. Venkatesvaran and M. Cakmak, SPE ANTEC Tech Pap 1993, 39, 257; H. Venkatesvaran and M. Cakmak, Polym Eng Sci 2001, 41, 341), a green and red laser is passed through the films being annealed in a heat‐setting chamber; the resulting data are analyzed for the details of structural mechanisms that take place during this process. This technique is shown to be capable of detecting reversals in birefringence development; as a result, complex sequences of structural evolution can be tracked. The design of this system allows one to observe not only the increase or decrease in birefringence during the course of the heat‐setting process but also the rate dependencies on processing variables. In this study, we establish that the rate of structural rearrangement, as detected by birefringence, depends strongly on the state of the pre‐existing chain orientation and the level of crystallinity. Increased levels of preorientation in the films results in decreases in the rate of birefringence change during heat setting. This is primarily attributed to the increased levels of steric hindrance developed with the increase in orientation and crystallinity in the preoriented samples. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1107–1121, 2001

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A technique for monitoring the kinetics of flow-induced crystallization

Cited by 15 publications

References 2 publications

Rules of supermolecular structure formation in sheared isotactic polypropylene melts

Rules of supermolecular structure formation in sheared isotactic polypropylene melts

Strain‐induced crystallization of swollen, crosslinked polyethylene

Online monitoring of birefringence development in heat‐setting polymer films with a fast dual‐wavelength optical technique. I. Uniaxially oriented poly(ethylene naphthalate)

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