Some rheological properties of molten polypropylene

Adamse, J. W. C.; Janeschitz‐Kriegl, H.; Otter, J. L. den; Wales, J. L. S.

doi:10.1002/pol.1968.160060507

Cited by 28 publications

(4 citation statements)

References 20 publications

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“…Birefringence levels may vary significantly with manufacturing conditions. It is long known that birefringence levels in flowing flexible chain melts obey the Rheo-Optical law [38,39] that linearly relates birefringence to stress. The Rheo-Optical law is generally based on a linear relationship between the second moment of the orientation distribution of flexible polymer chain backbones and stress underlies the behavior.…”

Section: IVmentioning

confidence: 99%

Birefringence and Mechanical Property Development in Melt Spinning Cyclopolyolefin Filaments

Hong

White

2002

International Polymer Processing

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An experimental study of the characterization melt spinning cyclopolyolefins is presented. The shear and complex viscosities were measured and the data was found to fit the Cox-Merz relation. The birefringence of the melt-spun filaments was determined and correlated with spinline stress. These were found to be much lower than polycarbonate and polystyrene filaments melt spun under the same conditions. The birefringence was represented in terms of polymer chain orientation. The uniaxial mechanical behavior was also measured. The Young's modulus and tensile strength generally increased with spinline stress and orientation for most cyclopolyolefins. The elongation to break decreased with measured polymer chain orientation for most cyclopolyolefins. For others it was enhanced.

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Section: IVmentioning

confidence: 99%

Birefringence and Mechanical Property Development in Melt Spinning Cyclopolyolefin Filaments

Hong

White

2002

International Polymer Processing

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“…In pursuing their own argumentation the authors could calculate relaxation times which obeyed an Arrheniustype temperature dependence with an activation energy of 90 kJ/mole, which is considerably higher than activation energies known from viscosity measurements on melts ( about 46±67 kJ/mole for i-PP, see Refs. [24,25]). At about 180°C the relaxation times of the samples ± which were not identical ± appeared to be a factor of about 1000 higher than at 250°C .…”

Section: Memory Effects In Quiescent Melts Of I-ppmentioning

confidence: 99%

The physics of athermal nuclei in polymer crystallization

1999

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IntroductionStructure formation in crystallizable polymers under the in¯uences of heat transfer and¯ow is a subject of major interest in polymer processing and in the development of`t ailored resins''. The ®rst author of this paper observed in 1982 ± to his own surprise ± that no serious attempt had been made to understand the underlying processes. So it is also not surprising that the required mathematical tools had not been developed. For instance, the path was not paved for a description of the overall crystallization speed in terms of the increasing surface of the crystalline areas on which further growth takes place. In order to make use of the developments in mathematics, one needs several physical parameters, which ± if one wants to avoid speculations ± can only be determined by experiment. Traditionally, the rate of primary nucleation and the growth speed of spherulites, both as functions of temperature, were required in a wide range of temperatures for a description of structure development during solidi®cation even for the simplest case of a quiescent melt.The pertinent experimental diculties, however, are tremendous, because of the fact that the relevant undercoolings are considerable. The experiments had to be extended over quite a large temperature range of undercooling. For i-PP a range of no less than 127°C could be covered in our laboratory. In a recent review [1] the results of this extended research are compiled up to early 1995. Some more recent results were published afterwards in separate papers (growth speed measurements with four independent methods [2] and further ®ndings in shear-induced crystallization [3,4]).The reader will understand that for all these experiments, in which heat transfer problems play a dominant role, some guidelines with respect to expected phenomena are rather desirable. In other words, a classi®cation of the temperature range between the Abstract The lower temperature limit for sporadic``thermal'' nucleation, as estimated in a previous paper (Janeschitz-Kriegl (1997) Colloid Polym Sci), can be veri®ed by a variety of earlier experiments which are compiled in this paper. Below the said limit only``athermal'' nuclei are of importance in samples containing no large numbers of hetero-nuclei. The number of athermal nuclei increases tremendously (by many decades) with decreasing temperature. Why these nuclei are dormant and``awake'' only at`t heir'' temperature is explained in terms of their growth conditions, which depend on the length of the incorporated (helical) sequences. Also the sluggishness of molecular processes, occurring in the temperature range of metastable conditions, where sporadic nucleation can occur is demonstrated by some of the recalled experiments. Except for very fast industrial processes, where¯ow plays a dominant role, this sluggishness makes a noticeable in¯uence of the sporadic nucleation on structure formation very improbable.

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“…Flow birefringence is a rheooptical technique that offers an alternative and powerful approach to investigate the rheological behavior of polymeric liquids. In the 1960s and 1970s, flow birefringence was used to investigate the rheological behavior of molten homopolymers in steady-state shear flow − and in the entrance region of a rectangular or slit channel. − In recent years birefringence has been used to investigate the rheological behavior of lyotropic solutions − as well as to study the dynamics of form birefringence in block copolymer mesophases . However, very few works have specifically addressed the use of birefringence to investigate the rheological behavior of thermotropic liquid-crystalline polymers (TLCPs).…”

Section: Introductionmentioning

confidence: 99%

“…Flow birefringence is a rheooptical technique that offers an alternative and powerful approach to investigate the rheological behavior of polymeric liquids. In the 1960s and 1970s, flow birefringence was used to investigate the rheological behavior of molten homopolymers in steady-state shear flow [1][2][3] and in the entrance region of a rectangular or slit channel. [4][5][6] In recent years birefringence has been used to investigate the rheological behavior of lyotropic solutions [7][8][9] as well as to study the dynamics of form birefringence in block copolymer mesophases.…”

Section: Introductionmentioning

confidence: 99%

Optical and Mechanical Rheometry of Semiflexible Main-Chain Thermotropic Liquid-Crystalline Polymers with Varying Pendant Groups

2000

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A specially designed flow cell was used to investigate birefringence in transient shear flow, ∆n + (γ ,t), of three semiflexible main-chain thermotropic liquid-crystalline polymers (TLCPs), poly[(x)-pphenylene 1,10-decamethylenebis(4-oxybenzoate)] (PxHQ10) with varying pendant side groups (x ) oxyethyleneethoxy, tert-butyl, or phenylsulfonyl). Also, shear rheometry was used to investigate the growth of shear stress σ + (γ ,t) and first normal stress difference N1 + (γ ,t) during transient shear flow of the same TLCPs. Upon startup of shear flow, ∆n + (γ ,t) initially increases rapidly, follows two minor overshoots, and then levels off to attain a steady-state value ∆n in all three TLCPs. The steady-state value of ∆n for PSHQ10 (PxHQ10 with x ) phenylsulfonyl pendant side group) was found to be greater than that for PEHQ10 (PxHQ10 with x ) ethoxy pendant side group) and PTHQ10 (PxHQ10 with x ) tert-butyl pendant side group). This behavior is strongly correlated to the large van der Waals volume of phenylsulfonyl pendant side groups in PSHQ10 compared to that of ethoxy pendant side groups in PEHQ10 and tertbutyl pendant side groups in PTHQ10. It is also observed that N 1 + (γ ,t) exhibits a very large overshoot followed by an oscillatory decay to attain a steady-state value N1, while σ + (γ ,t) shows a very large overshoot followed by a rapid monotonic decrease to attain a steady-state value, σ. The peak values of N1 + (γ ,t) and σ + (γ ,t) for PSHQ10 were found to be 3-4 times greater than those for both PEHQ10 and PTHQ10, which we again attribute to the bulky phenylsulfonyl pendant side groups in PSHQ10. Only positive values of N1 + (γ ,t) and N1 were observed over the entire range of shear rates investigated. Variations of the ratio N1 + (γ ,t)/σ + (γ ,t) with shear strain (γ t) were found to be very similar to variations of ∆n + (γ ,t) with γ t for all three TLCPs investigated, except for that the ratio N1 + (γ ,t)/σ + (γ ,t) reached a steady state sooner than ∆n + (γ ,t). In steady-state shear flow, it is observed that the ratio N1/σ overlaps ∆n over the entire range of temperatures investigated; specifically, both the ratio N1/σ and ∆n remain constant at temperatures far below the clearing temperature (TNI), decrease gradually as the temperature approaches TNI, and drop precipitously to zero value at and near TNI.

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Some rheological properties of molten polypropylene

Cited by 28 publications

References 20 publications

Birefringence and Mechanical Property Development in Melt Spinning Cyclopolyolefin Filaments

Birefringence and Mechanical Property Development in Melt Spinning Cyclopolyolefin Filaments

The physics of athermal nuclei in polymer crystallization

Optical and Mechanical Rheometry of Semiflexible Main-Chain Thermotropic Liquid-Crystalline Polymers with Varying Pendant Groups

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