Addendum to the thermal properties of polypropylene

Abstract.We have studied crystallization behaviour of isotactic polypropylene (iPP) from mesomorphic phase in structural point of view. Time-resolved wide-angle X-ray diffraction (WAXD) measurements during a heating process have been performed using a synchrotron radiation (SR) X-ray beam line at SPring-8, Japan. The heating process was so programmed to reproduce a thermal trace of differential scanning calorimetry (DSC) with a constant heating rate (10 °C/min) in order to compare the structural change with thermal behaviour. SR-WAXD sensitively detected the crystallization behaviour and we have obtained fractions of alphacrystal, mesomorphic phase and amorphous phase as a function of temperature by analysing the data. The results showed that the crystallization from mesomorphic phase proceeds in between 60 and 120 °C (meso-alpha transition). During this process, the crystallization from amorphous hardly takes place. The crystalline fraction shows almost constant in between 120 and 140 °C; meanwhile, the mesomorphic fraction still decreases above 120 °C. The crystalline fraction starts to decrease above 140 °C and the most extensively decreases at around 165 °C (melting point). We have also determined the energy level of the mesomorphic phase (metastable state) relative to that of alpha-crystal (stable state), considering the balance among the fractions of alpha-crystal, mesomorphic phase and amorphous. IntroductionFrom a standpoint of thermal process, crystallization of bulk polymer is classified into mainly two categories; one is cooling from molten state and another is heating from "pre-quenched state". In both processes usually growth of spherulites in micrometer scale are observed, though the latter process yields more or less higher nucleus density than the former one. In those polymers "pre-quenched state" is mostly equivalent to "glassy state". However, this is not the case for isotactic polypropylene (iPP). In the heating process of pre-quenched iPP, the growth of spherulites is never observed and the macroscopic appearance is almost transparent up to the melting temperature T m . The absence of the spherulites and the transparency not necessarily imply that the pre-quenched iPP does not crystallize. The pre-quenched iPP indeed crystallizes in the heating process [1], but the higher order structure is quite different from one that is crystallized from molten state [2]. The specific behaviour of the crystallization of iPP from the pre-quenched state is considered to be due to the presence of mesomorphic phase. IPP has three well-established polymorphisms; such as alpha (monoclinic), beta

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“…As a reliable value of ΔH cryst was already reported [12], unknown parameter is only x. Figure 6 shows -d(ΔH)/dT plotted for several values of x.…”

Section: Energy Level Of Mesomorphic Phasementioning

confidence: 71%

Crystallization of isotactic polypropylene from mesomorphic phase: a constant heating rate study

Asakawa

Nishida

Matsuba

et al. 2011

J. Phys.: Conf. Ser.

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“…After heating samples above the melt temperature, a 10 C/min cooling rate was used to determine the non-isothermal crystallization onset temperature (T c ). The percent polymer crystallinity was obtained by dividing the specific enthalpy from the area associated with the crystallization part of the nonisothermal cooling curve by polymer mass fraction; this value was divided by the theoretical heat of fusion for neat PP of 207.1 J/g [97]. Nucleating efficiency (NE) was determined based on the calorimetric efficiency scale proposed by Lotz and coworkers [98].…”

Section: Characterization Of Pp/nanosilica Nanocompositesmentioning

confidence: 99%

Importance of superior dispersion versus filler surface modification in producing robust polymer nanocomposites: The example of polypropylene/nanosilica hybrids

Iyer

Torkelson

2015

Polymer

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“…Bu, Cheng, and Wunderlich[20] reviewed a large amount of literature on the melting of PP and concluded that the most reliable values are 7^ ~ 461K and AH°f ~ 8700 J/mole, but overlooked two important papers. Cox and Duswalt…”

mentioning

confidence: 98%

Crystallization of Polypropylene and Poly(Ethylene Terephthalate)

Bicerano¹

1998

Journal of Macromolecular Science, Part C: Polymer Reviews

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Addendum to the thermal properties of polypropylene

Cited by 136 publications

References 9 publications

Crystallization of isotactic polypropylene from mesomorphic phase: a constant heating rate study

Crystallization of isotactic polypropylene from mesomorphic phase: a constant heating rate study

Importance of superior dispersion versus filler surface modification in producing robust polymer nanocomposites: The example of polypropylene/nanosilica hybrids

Crystallization of Polypropylene and Poly(Ethylene Terephthalate)

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