Melt crystallization of polypropylene: Structure formation

Poddubny, V. I.; Lavrentyev, V. K.; Shevelev, V.A.; Михайлова, Н.В.; Sidorovich, A. V.; Баранов, В. Г.

doi:10.1007/bf00401713

Cited by 7 publications

(4 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The diffraction study of oriented polypropylene samples in the quenched form and in that with maximum crystallization has shown [9] that each of them contains two structural components: regions with three-dimensional or orientational order that can be oriented in the direction of the stretching axis and the amorphous regions in which the structure is isotropic even in samples with maximum stretching. A direct investigation of the amorphous halo possible in these samples has shown that it consists of two symmetrical bands corresponding to the pair of interplanar distances approximately coinciding with the values obtained for the melt [6]. Hence, although in crystallization and in the formation of the quenched form the inevitable redistribution of rotamers along the macromolecules takes place accompanied by the displacement of defective portions into the amorphous regions, the character of packing of these regions is retained and has the features of a smectic-like structure inherent in the stereoregularity of macromolecule.…”

Section: Structure Of Isotactic Polypropylene In the Melt And In The supporting

confidence: 79%

Pre‐transition phenomena in the crystallization and melting of flexible‐chain polymers

1986

Self Cite

View full text Add to dashboard Cite

Academy of Sciences of the USSR, Institute of Macromolecular Compounds, 199 004 Leningrad/USSRIn isotactic polypropylene both crystallization and melting are always accompanied by a transition through the states characterized by the same structure with the presence of more or less large regions having the order of the liquid crystalline type. The appearance of these metastable structures is a consequence of the chain structure initially inherent in the macromolecules and should be expected in transitions of all isotactic polymers. ifbergangseffekte oor dem Kristallisations-und dem SchmelzprozeP oon Polymeren mit flexibl, on KettenIm isotaktischen Polypropylen wird sowohl bei der Kristallisation als auch beim Schmelzen stets ein Ubergangszustand mit gleicher Struktur durchlaufen, der durch die Anwesenheit von mehr oder weniger groI3en Bereichen mit fliissigkristalliner Ordnung gekennzeichnet ist. DE~S Auftreten dieser metastabilen Strukturen ist eine Folge der Kettenstruktur der Makromolekiile und sollte bei den Ubergangen in allen isotaktischen Polymeren zu erwarten sein. npeanepexoanbse mnenua npu ?cpucmandu3ayuu u ndaenenuu a~61~0yennbtx nonwepoe B I I~O T~K T H~~C K O M nonHnponmeHe K~I I C T~J I J I H~~~H R H nnaBneHae Bcerga conpoBoxrAamTcR nepexogoM sepea COCTOFIHHFI, x a p a~~e p~3 y e~n e O A H O~ II TOB me CTPYKTYPO~, oTnwxamIqeicH HanameM 6onee H~H MeHee I I~O T R -meHHbIX 0 6 n a c~e i C IIOPRAKOM TIlIIa HcHAKOKpHCTannllreCKOrO. nOFIBJIeHHe TaKHX MeTaCTa6XJIbHbIX CTPYKTYP RBJIR-eTCR CJIeACTBHeM H3HaYaJIbHO IIpHCglrterO MaKpOMOJIeKyJIaM 4enHOI'O CTpOeHHFI, H f?rO CJIegyeT O X H A a T b npkl nepe-~~ xogax BO Bcex H~O T~K T I I~~C K H X nonaMepax.

show abstract

Section: Structure Of Isotactic Polypropylene In the Melt And In The supporting

confidence: 79%

Pre‐transition phenomena in the crystallization and melting of flexible‐chain polymers

1986

Self Cite

View full text Add to dashboard Cite

show abstract

“…The angu- For this reason i t is necessary to study the oriented samples because the superposition of scattering from two components in isotropic regions prevents even the determination of the shape of amorphous halo. On the other hand, the data obtained in the investigation of the melt characterized by the same scattering curve with two maxima indicate t h a t the structure of the amorphous phase in oriented and isotropic samples coincides [2]. It follows from the relatively narrow reflections on the layer lines and their spreading on the equator t h a t the ordered component consists of fairly large regions (domains), in which the helical fragments of PP macromolecules are organized in such a manner t h a t long-range order exists in the longitudinal direction (it is clear t h a t this is the intramolecular order) and is absent in the transverse order, i.e.…”

Section: Discussion Of Resultsmentioning

confidence: 76%

Main features of polypropylene crystallization from the quenched state

et al. 1985

Self Cite

View full text Add to dashboard Cite

Acta Polymcriu 36 (1985) Nr. 6 301 charging parameters for electrets produced by the breakdown method are 135°C > T, 2 IOO"C, t, = 5 min, U p m -2.5 kV. The thermal stability of t h e electrets produced a t about 100°C was high enough for applications. The increase in charge density for electrets charged a t higher temperatures a t the start of thermal discharge (Fig. 3) can be related with the release of charged injected bound a t room temperature by the heterocharge of electrets. The dipolar polarization frozen in was found to disappear a t lower temperature and a TSC maximum related with this process was found for copolyester IS electrets a t about 6°C . Academy of Sciences of the USSR, Institute of Macromolecular Compounds, 199004 Leningrad/USSRThe structure formation during transition from the quenched into the crystalline state has been studied for isotactic polypropylene by wide-angle X-ray scattering. Based on the temperature dependence of the shape of the curve of amorphous scattering the composition of samples with different degrees of crystallinity and different content of paracrystalline form was determined quantitatively. By means of IR spectroscopy it was shown that stretching of quenched polypropylene leads t o the freezing of the conformational array in macromolecules. This freezing hinders the transition into the crystalline state upon heating.

show abstract

“…One must thus conclude that the ordering of the preformed, imperfect helices [13] to the condis glass is a process which requires even faster thermal analysis than is at present available.…”

Section: Discussionmentioning

confidence: 96%

“…For earlier references see also references 17 and 10. It was suggested that in the melt shortsegment helices [13] are already preformed (quasi-crystalline structure of the liquid, see Ref. 21).…”

Section: Summary Of Literature and Formulation Of The Problemmentioning

confidence: 99%

Fast DSC applied to the crystallization of polypropylene

Dann

Cheng

et al. 1988

Journal of Thermal Analysis

View full text Add to dashboard Cite

In an effort to find the limit of crystallization of polypropylene, a series of quantitative and semiquantitative DSC experiments at rates up to 10,000 deg/min are described. Even at these fast rates polypropylene crystallized on cooling between 350 + 15 K and 280 :t: 6 K. No "fully amorphous" polypropylene was produced. No initial stage crystallization to the condis state could be proven by quenching after partial crystallization.The present status of scanning calorimetry permits measurements at heating rates between one and 100 K/rain without undue temperature gradient within the sample [1]. Analysis of metastable substances and the study of superheating need, however, faster thermal measurements [2]. It would also be extremely helpful if fast industrial processes such as injection molding, fiber spinning, film blowing and the various conditioning cycles could be duplicated in the scanning calorimeter. Up to the present there have been only the efforts of Hager to develop a fast foil calorimeter [3] and some experiments by us [4] to reach up to and beyond 1000 K/min. In this paper we want to discuss the problem of fast calorimetry, describe several methods for fast measurement and quenching, and apply these to the problem of polypropylene crystallization. The problem of fast calorimetryCalorimetric data can be obtained by a simple temperature measurement only as long as the temperature gradient within the sample is experimentally negligible, i.e. is less than perhaps + 0.5 K. With larger temperature gradients, measurements will only yield thermal diffusivity information. The time-dependent heat flux dQ/dt into a disc of thickness L under steady-state conditions, from the underside is given, for example, by

show abstract

Melt crystallization of polypropylene: Structure formation

Cited by 7 publications

References 6 publications

Pre‐transition phenomena in the crystallization and melting of flexible‐chain polymers

Pre‐transition phenomena in the crystallization and melting of flexible‐chain polymers

Main features of polypropylene crystallization from the quenched state

Fast DSC applied to the crystallization of polypropylene

Contact Info

Product

Resources

About