On the crystallization of γ‐isotactic polypropylene: A high pressure study

Brückner, Sergio; Phillips, P. J.; Mezghani, Khaled; Meille, Stefano Valdo

doi:10.1002/marc.1997.030180101

Cited by 85 publications

(60 citation statements)

References 28 publications

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“…For β-iPP, although the shear condition and temperature gradient provoke the nucleation and growth of β-iPP, addition of an active β-phase nucleating agent (β-NA) is proved to be the most efficient way to obtain iPP articles with high content of β-iPP [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. For γ-iPP, it is already known that crystallization under high pressure (>200 MPa) is the main way to achieve high content of γ-iPP [25][26][27][28] in common iPP. Under atmospheric pressure, γ-iPP also can be provoked in a low molecular weight iPP [29] or PP copolymer with the presence of comonomer unit in the main chain [6,30,31], and in this condition, the relative fraction of γ-iPP is relatively smaller than that in iPP obtained under high pressure.…”

Section: Introductionmentioning

confidence: 99%

Crystallization behavior of isotactic polypropylene induced by competition action of β nucleating agent and high pressure

Yang

Chen

et al. 2011

Colloid Polym Sci

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Addition of β-form nucleating agent (β-NA) to isotactic polypropylene (iPP) can greatly induce the variation of the crystallization of matrix. Here, we introduce high pressure to the crystallization process of β-NA nucleated iPP. It is observed that there is a competition between the effect of high pressure and the nucleation effect of β-NA on crystallization of iPP. With the increasing of high pressure, both the contents of β-iPP and α-iPP decrease while the content of γ-iPP increases. A novel crystalline morphology of γ-iPP with the fragmentations of γ-spherulites regularly organized in a local region is observed. Namely, γ-spherulites grow on the lateral of β-NA needlelike structure. The dual nucleation effects of the special needlelike structure of β-NA towards β/α-iPP and the effect of high pressure which prevents the growth of β-iPP but promotes the growth of γ-iPP are the main mechanisms for the novel crystalline morphology of γ-iPP. Specifically, the mixed polymorphic β/γ-iPP can be achieved under a certain pressure. This possibly enlarges the application of iPP material.

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Section: Introductionmentioning

confidence: 99%

Crystallization behavior of isotactic polypropylene induced by competition action of β nucleating agent and high pressure

Yang

Chen

et al. 2011

Colloid Polym Sci

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“…This behavior corresponds with a movement inside of crystalline interface [41,42]. So, it is observed a displacement of α relaxation toward higher temperatures for PP from [CAT-B], due to a high molecular weight and to the presence of more isotactic chains as well as bigger crystal sizes.…”

Section: Resultsmentioning

confidence: 74%

“…Table 6 shows the position of the different maximums and the According to results obtained by DSC analysis, the melting temperatures in relation with α relaxation obtained for PP's physical mixture and hybrid catalyst were intermediate respect to PPs from individual supported catalysts although the crystallinity was the same. It is possible to observe that the polypropylene obtained by the physical mixture, where properties are governed by [CAT-A] since the activity of that catalyst is the highest, α relaxation, corresponding to the crystalline phase, appears at lower temperatures and nearby to that of [41,44]. The β relaxation increases its intensity for PP's physical mixture due to the presence of an amorphous phase with higher mobility respect to the PP's hybrid catalyst.…”

Section: [Cat-a] + [Cat-b] and [Cat-a]/[cat-b] Are Shown Inmentioning

confidence: 94%

Bimodal polypropylene through binary metallocene catalytic systems: comparison between hybrid and mixed heterogeneous catalysts

et al. 2016

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Polypropylene with wider or bimodal molecular weight distribution is required for numerous applications since low molecular weight chains improve processability and high molecular weight fraction is required to get good mechanical properties. There are several routes to achieve a bimodal resin but the use of a binary catalytic system seems to be the most attractive, particularly with metallocenes combination. From a previous work two metallocenes were selected because they lead to polypropylenes with average molecular weights that differ in one order of magnitude. Two types of binary systems have been investigated, hybrid catalysts (two metallocenes loaded on the same support) and physical mixtures (two independent supported metallocenes that are introduced to the reactor and start the polymerization together), using different ratios, i.e., 25-75, 50-50, 75-25, at three reaction temperatures, i.e., 30, 50 and 70°C. Most of the binary catalytic systems lead to bimodal molecular weight distributions. Polypropylenes produced by mixed catalysts are greatly influenced by the most active catalyst, while in PP coming from hybrid catalysts, as there is a strong interaction between both metallocenes, each one contributes according to its presence in the hybrid catalyst. Therefore, properties of obtained bimodal polypropylenes are quite influenced by the ratio between both metallocenes.

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“…[15,16] Among them, α-phase is the most stable and commonly observed modification with the nature of rigid, which is responsible for strength and modulus. The β-modification is a metastable crystalline phase exhibiting some unique characteristics such as improved toughness in comparison with the α-phase.…”

Section: Introductionmentioning

confidence: 99%

Effects of β‐nucleating agent and crystallization conditions on the crystallization behavior and polymorphic composition of isotactic polypropylene/multi‐walled carbon nanotubes composites

Kang

Chen

et al. 2014

Polymers for Advanced Techs

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In this study, the effects of crystallization conditions (cooling rate and end temperature of cooling) on crystallization behavior and polymorphic composition of isotactic polypropylene/multi-walled carbon nanotubes (iPP/MWCNTs) composites nucleated with different concentrations of β-nucleating agent (tradename TMB-5) were investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and scanning electronic microscopy (SEM). The results of DSC, WAXD and SEM revealed that the addition of MWCNTs and TMB-5 evidently elevates crystallization temperatures and significantly decreases the crystal sizes of iPP. Because of the competition between α-nucleation (provided by MWCNTs) and β-nucleation (induced by TMB-5), the β-phase crystallization takes place only when 0.15 wt% and higher concentration of TMB-5 is added. Non-isothermal crystallization kinetics study showed that the crystallization activation energy ΔE of β-nucleated iPP/MWCNTs composites is obviously higher than that of pure iPP, which slightly increases with the increase of TMB-5 concentration, accompanying with the transition of its polymorphic crystallization behavior. The results of non-isothermal crystallization and melting behavior suggested that the cooling rate and end temperature of cooling (T end ) are important factors in determining the proportion and thermal stability of β-phase: Lower cooling rate favors the formation of less amount of β-phase with higher thermal stability, while higher cooling rate encourages the formation of higher proportion of β-phase with lower thermal stability. The T end = 100°C can eliminate the β-α recrystallization during the subsequent heating and therefore enhance the thermal stability of the β-phase. By properly selecting TMB-5 concentration, cooling rate and T end , high β-phase proportion of 88.9% of the sample was obtained.

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On the crystallization of γ‐isotactic polypropylene: A high pressure study

Cited by 85 publications

References 28 publications

Crystallization behavior of isotactic polypropylene induced by competition action of β nucleating agent and high pressure

Crystallization behavior of isotactic polypropylene induced by competition action of β nucleating agent and high pressure

Bimodal polypropylene through binary metallocene catalytic systems: comparison between hybrid and mixed heterogeneous catalysts

Effects of β‐nucleating agent and crystallization conditions on the crystallization behavior and polymorphic composition of isotactic polypropylene/multi‐walled carbon nanotubes composites

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