Yasuna Fujiwara

Das Doppelschmelzverhalten derβ-Phase des isotaktischen Polypropylens

ZusammenfassungWenn Proben der hexagonalenβ-Phase des isotaktischen Polypropylens über die Schmelztemperatur aufgeheizt werden, tritt gewöhnlich die Rekristallisation zur α-Phase (monoklin) mit höherer Schmelztemperatur auf. Überdies wird häufig die Erscheinung des Doppelschmelzens derβ-Phase selbst während der DSC-Messungen beobachtet. Durch die Untersuchung Über den Einfluß der Kristallisationstemperatur, der Aufheizgeschwindigkeit während DSC-Messungen, und der Aufheizunterbrechung, auf die Art des Auftretens des Doppelschmelzens kann man finden, daß diese Erscheinung aus dem Schmelzen der ursprünglichenβ-Phase und der nachfolgenden Rekristallisation zur stabileren Struktur (β′) während des Aufheizprozesses verursacht wird, wie in Fällen von anderen kristallinen Polymeren, worüber von anderen Autoren bereits berichtet worden ist.Aus der Röntgenweitwinkelbeugung wurde gefunden, daß dieβ′-Struktur das gleiche hexagonale Gitter und auch die gleicheb-Achse-Orientierung wie die ursprüngliche Probe hat.Aus der polarisationsmikroskopischen Beobachtung anβ-Phasen-Proben während des Aufheizens unter Benutzung eines mit einem Temperaturgradienten im Probefilm ausgerüsteten Heizapparates wurde gezeigt, daß dieβ′-Struktur nicht eigentlich existiert, sondern durch Rekristallisation entstanden ist, welche nach dem Schmelzen der zunächst bestehendenβ-Struktur schnell geschieht.Aus diesen Ergebnissen folgt, daß Rekristallisation zurβ′-Struktur ein nach dem Schmelzen der ursprunglichenβ-Struktur schnell fortschreitender Prozeß ist, wobei die anfängliche Kristallstruktur und Orientierung in irgendeiner Weise erhalten bleibt. Betrachtungen über die Weise, wie dies möglich sein kann, werden beschrieben.SummaryWhenβ-phase-samples (hexagonal) of isotactic polypropylene are heated beyond the melting point, recrystallization to a-phase with higher melting temperature (monoclinic) usually occurs. Besides this, the double melting phenomenon ofβ-phase itself is often observed during DSC-measurements. By investigating the influence of the crystallization temperature, heating rate during DSC-measurements, and partial scanning, upon the appearance of the double melting endotherms, it can be seen that this is caused by melting of the originalβ-phase and subsequent recrystallization to a stabler structure (β′) during scanning, similarly to the cases of other crystalline polymers which have already been reported by several authors.From wide-angle x-ray diffraction study it was found thatβ′-structure has the same hexagonal lattice and also the sameb-axis orientation as the original sample.By polarization-microscopic observation on theβ-phase-samples during heating, using a hot stage equipped with a temperature-gradient in the sample film, it was shown thatβ′-structure is not originally existing but is brought forth through recrystallization, occurring rapidly after melting of the originalβ-structure.From these results it is considered that recrystallization toβ′-structure is a process which advances rapidly after melting of originalβ-structure, inheriting the original crystal structure and orientation in some way. Speculations about the way are also described.

Plastic deformation of oriented lamellae: 1. Cold rolling of β-phase isotactic polypropylene

Abstract Isotactic polypropylene was crystallized by the oriented growth method and the oriented β-phase obtained. This has unidirectional lamellar orientation with the lamellar long axis parallel to the growth direction, the lamellae being twisted along this direction. The sample plates were cold-rolled in three orthogonal directions, and the deformation behaviour of each case was investigated chiefly by wide-angle and small-angle X-ray diffraction methods. It was revealed that deformation takes place by a different mechanism in each case, including rotation of lamellae, interlamellar slip, chain-directional and transversal chain slip. These results are discussed in connection with the anisotropic structure of these samples due to the lamellar orientation. When the β-phase samples are rolled, α-phase crystals appear with c -axis orientation and the proportion increases with draw ratio. For crystallographic reasons it is concluded in this case that by stretching the c -axis orientation is brought about not through block formation of the original β-phase lamellae and incorporation of these blocks into microfibrils, but by melting or unfolding of the original β-phase lamellae and recrystallization to the c -axis-oriented new α-phase.

II-I phase transformation of melt-crystallized oriented lamellae of polybutene-1 by shear deformation

SummaryModification II-I transformation of polybutene-1 was investigated on oriented lamellae, which were melt-crystallized in the temperature gradient. WAXS photograph of as-grown specimen showed prefered orientation of [110] to the lamellar axis, and after transformation it showed “twelve point pattern” due to dual orientation of hexagonal lattice. By shear deformation parallel or perpendicular to lamellar axis, WAXS photograph showed the appearance of “six point pattern” due to single orientation of hexagonal lattice, and also the enhancement of transformation rate. These were explained by the growth of hexagonal nuclei formed by the slip in the tetragonal crystal.

Plastic deformation of oriented lamellae: 3. Drawing behaviour of β-phase isotactic polypropylene

Abstract Specimens consisting of oriented β-phase lamellae of isotactic polypropylene, obtained by crystallization in a temperature gradient, were drawn at various temperatures. The deformation behaviour was investigated by means of stress-strain measurement, X-ray scattering and scanning electron microscopy. Drawings were carried out in two directions, parallel to the lamellar axis (parallel drawing) and perpendicular to it (perpendicular drawing). The maximum apparent stress and Youngs modulus on parallel drawing were always larger than those on perpendicular drawing. Wide-angle X-ray scattering patterns from the specimens drawn at various temperatures showed different deformation behaviours between parallel and perpendicular drawings, which may be explained by the difference of deformation mechanism at the initial stage. As a conclusion, the deformation mechanism is classified into two steps. In the initial stage of deformation, the β-phase material is deformed mainly by interlamellar slippage (the first step). Then, the β-phase crystals are destroyed by Petermann-type unfolding or local melting (the second step). The final c -axis-oriented texture is recrystallized through destruction of the β-phase material.

Über die Sphärolithstruktur von isotaktischem Polypropylen durch orientierte Kristallisation aus der Schmelze

ZusammenfassungDie Methode der orientierten Kristallisation aus der Schmelze wurde auf isotaktisches Polypropylen angewandt und orientierte Proben mit entsprechenden radialen Teilen von Einzelsphärolithen hergestellt. Die erhaltene Textur der orientierten β-Phase-entsprechend den negativen Sphärolithen-und die Textur der orientierten α-Phase-entsprechend den positiven Sphärolithen-wurden mit Röntgenweitwinkel und Röntgenkleinwinkelbeugung untersucht. Aus der ersteren Textur wird es gezeigt, daß die negativen Sphärolithe die Polyäthylen-ähnliche Lamellenstruktur mit einachsiger Orientierung haben. Aus der letzteren Textur wird geklärt, daß die zusammengesetzte Orientierung in der positiven Sphärolithe mit derPadden undKeith gezeigten Struktur der dünnen Schichten mit radialen und verzweigten Lamellen übereinstimmt. Auch das kreuzförmige Diagramm der Röntgenkleinwinkelbeugung, welches wahrscheinlich für positive Sphärolithe des Polypropylens charakteristisch ist, wird mit dieser Struktur erklärt.SummaryThe method of oriented crystallization from the melt was applied to isotactic polypropylene and oriented specimens corresponding to radial fractions of single spherulites were obtained. The obtained texture of oriented β-phase and the texture of oriented α-phase corresponding to the negative spherulite and to the positive spherulite, respectively, were investigated by x-ray wide angle and small angle diffractions. From the former texture it has been shown that the negative spherulite has the polyethylenelike lamellar structure with uniaxial orientation. From the latter texture it has been shown that the complex orientation in the positive spherulite is consistent with the structure of thin layers with radial and branched lamellae reported byPadden andKeith. The cross-shaped pattern of x-ray small angle diffraction, probably characteristic of polypropylene positive spherulites, was explained from the standpoint of this structure.

Comparison of premelting and recrystallization behaviour of β-phase isotactic polypropylene by heating and cooling at different rates

Abstract Different heat treatments (heating and subsequent cooling with quick or slow rates but up to the same temperature in the melting range) were made on β-polypropylene (β-PP), and premelting and recrystallization behaviour were compared using d.s.c. and WAXS measurements. The results suggest that, under our experimental conditions, lamellar growth during heating and cooling takes place chiefly at the expense of, or under the existence of a melt neighbouring to the lamella, and that the growth in the solid state by molecular refolding plays a minor role. The influence of the recrystallized α-phase, yielded during heating, on the growth of β-form is also discussed.

Melting behavior of the oriented β-phase polypropylene texture crystallized by the temperature slope method

Abstract Isotactic polypropylene consisting of uniaxially oriented P-phase lamellae was crystallized in a temperature gradient. The β → α transition was investigated by simultaneous measurements with differential scanning calorimetry (DSC) and X-ray diffraction using synchrotron radiation (SR). To compare the transition mechanism, the β-phase sample was deformed by rolling it along the direction of the crystallization. During rolling, the β-crystal is deformed by interlamellar and interchain slip, which induces c-axis-oriented molecules along the rolling direction. The melting behavior is changed by the rolling deformation. For the as-grown β-crystal, the DSC thermogram has three peaks: the β-melting endotherm at 150°C, an exotherm by recrystallization into the °-form, and the endotherm at 167°C caused by melting of the recrystallized α-form. After the rolling deformation, the β-endotherm is extinguished by the successive exotherm. Simultaneous X-ray measurements reveal that the β → α transition is shifte...

Enhancement of βα-recrystallization in β-form isotactic polypropylene during heating after roll deformation

Summaryβ-form isotactic polypropylene shows βα-recrystallization “behavior (recrystallization from β- to α-form) during slow heating. This is enhanced by deformation. β-form specimen with uniaxially oriented lamellae was deformed by rolling, and βα-recrystallization was studied by DSC and x-ray diffraction. The result showed that (1) βα — recrystallization is promoted with the degree of deformation. (2) Deformed specimen shows βα-recrystallization from considerably low temperature compared with the undeformed one. (3) The recrystallized α-form is c-axis-oriented along the roll direction. From these results the βα-recrystallization mechanism was discussed in view of α-nucleus formation by deformation.

CRYSTALLIZATION OF A LOW MOLECULAR WEIGHT POLYETHYLENE AND PARAFFINS UNDER A TEMPERATURE GRADIENT

A low molecular weight polyethylene (PE) and even-number paraffins were crystallized under a temperature gradient. Highly oriented crystalline textures were developed by the temperature slope crystallization. The in situ crystallizing surface was observed by an optical microscope and X-ray diffraction. Polyethylene has a b-axis orientation in which the lamellar normal and crystalline c-axis are perpendicular to the temperature gradient. On the contrary, in the even-number paraffins, both axes are parallel to the temperature gradient. The results of the in situ measurements and the crystalline orientation are compared and discussed for both cases.