An infrared spectroscopic approach to the polymorphic behavior of syndiotactic polypropylene and its crystal–crystal transformations during mechanical stretching

Gregoriou, Vasilis G.; Kandilioti, Georgia; Gatos, Konstantinos G.

doi:10.1016/j.vibspec.2003.08.004

Cited by 15 publications

(13 citation statements)

References 33 publications

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“…Both the opaque and transparent stripes appear to have the same thermal response. Pure sPP shows a small endothermic peak at 100°C, which owes its existences to helical form I crystalline phase [6,9]. In both opaque and transparent zones this peak is being suppressed as seen in Figure 3.…”

Section: Resultsmentioning

confidence: 87%

“…In both opaque and transparent zones this peak is being suppressed as seen in Figure 3. This can be attributed the partial transformation of helical I to the trans-planar III conformation due to mechanical drawing of the polymer [6,9]. Figure 5 shows the typical thermal behavior during heating of the 0.5 wt% montmorillonite nanocomposite stress oscillated samples.…”

Section: Resultsmentioning

confidence: 99%

“…Three repetitions were run for each different specimen. Specimen crystallinity was calculated from Equation (1) where ΔH 0 m = 190.4 J/g is the well known heat of fusion of sPP crystals [6] (Equation (1)): (1) where, x is the % of crystallinity, ΔH m and ΔH c , melt and crystallization enthalpies respectively. In order to study the internal structure of the necked area of the stress oscillated specimens samples were studied by a LEO SUPRA 35VP Field Emission (Carl Zeiss AG, Jena, Germany and a JEOL (Jeol Ltd, Tokyo, Japan) Scanning Electron Microscope.…”

Section: Methodsmentioning

confidence: 99%

“…Amorphous but crystallisable polymers like poly(ethylene terephtalate) also exhibit this effect [7]. Moreover, it was also observed in amorphous non-crystallizable polymers like polycarbonate (PC) [6]. Quite a lot of effort has been invested by different researchers, employing different approaches to interpret this phenomenon.…”

Section: Introductionmentioning

confidence: 98%

“…This stress fluctuation is accompanied by the appearance of alternating transparent/opaque zones in the necking area of the specimen [2]. The stress oscillation effect can appear either during semi-static [2] or tensile impact loading [3][4][5], spontaneously [2][3][4] or provoked [6], by an abrupt change in the specimen loading speed. It can be observed for both amorphous and semi-crystalline polymers too.…”

Section: Introductionmentioning

confidence: 99%

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Study of the stress oscillation phenomenon in syndiotactic polypropylene/montmorillonite nanocomposites

Mouzakis¹

2010

Express Polym. Lett.

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Abstract. The phenomenon of Stress Oscillation (SO) was studied in syndiotactic polypropylene and syndiotactic polypropylene nanocomposites with montmorillonite. The effect was provoked by varying the crosshead speed during tensile testing of thin stripes. The internal morphology of the stress oscillated specimens was studied by scanning electron microscopy on chemically etched samples revealing that cavitation prevails inside the opaque stripes of the yielded areas. Differential scanning calorimetry proved that there exists virtually no crystallinity differentiation between the characteristic alternating opaque/transparent stripes that mark the stress oscillation during necking. Finally a simple finite element model of the necking area of the specimens revealed non-uniform internal stress distributions of yield-point magnitudes.

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Section: Resultsmentioning

confidence: 87%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Study of the stress oscillation phenomenon in syndiotactic polypropylene/montmorillonite nanocomposites

Mouzakis¹

2010

Express Polym. Lett.

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FTIR spectroscopic investigation of thermal effects in semi‐syndiotactic polypropylene

Sevegney

Kannan

Siedle

et al. 2005

J Polym Sci B Polym Phys

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The temperature‐dependent behavior of individual components within metallocene‐catalyzed semisyndiotactic polypropylenes (semi‐sPP) with a wide range of stereoregular content (26 to 96% rr) is studied using Fourier transform infrared (FTIR) spectroscopy and temperature‐modulated differential scanning calorimetry (DSC). Changes in sensitive, high‐resolution absorbance spectra are observed as melt‐slow‐cooled thin films are subjected to stepwise temperature increases. In general, spectral bands previously identified as being sensitive to ordered structures (e.g., conformed chains, crystal morphs) appear to follow overall trends of shifting to lower wavenumbers (energies), broadening, and decreasing in peak area intensity as temperature increases. Peaks that appear due to “splitting” (observed in more stereoregular materials) show a trend toward coalescence as temperature increases; this corresponds to a gradual loss of chain conformational order. Gauche‐gauche‐trans‐trans (ggtt)n helical and all‐trans (tttt)n planar zigzag‐conformed chains that participate in the crystalline‐amorphous interfacial region (“mesophase”) appear to be more stable (i.e., they do not lose their conformational order as easily) with increasing temperature in materials with a greater degree of syndiotacticity. Moreover, IR data correspond well with modulated DSC endotherms located near 50 °C and 70 °C. At each transition temperature—thought to represent, respectively, a thermally driven chain conformation from planar zigzags to helices, and a dynamic disorder of helices marked by rapid gauche ↔ trans isomerization—the IR absorbance ratio, A978/A963, which represents the relative population of helical chains, undergoes an accelerated decrease. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 439–461, 2005

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Conformational variation and crystalline phase transformation of low syndiotactic polypropylene films in stretched and stress‐relaxed states

Zhang

Zhao

Shi

et al. 2005

J Polym Sci B Polym Phys

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Low syndiotactic polypropylene (sPP; rrrr = 80%) films were isothermally crystallized at 0 °C (sample S0) and 90 °C (sample S90) for 65 h, respectively. Fourier transform infrared spectroscopy, differential scanning calorimetry, and wide‐angle X‐ray diffraction were used to characterize the structure transformation and orientation behavior of samples S0 and S90 at both stretched and stress‐relaxed states. It was found that stretching (λ = 0–700%) induces the transformation of the chain conformation from helical to trans‐planar form for both S0 and S90 films. The stretched S0 and S90 samples show well oriented trans‐planar chains as well as partially retained helices. Simultaneously, crystalline phase transformation occurs during the stretching and relaxing processes of the investigated sPP samples, i.e., stable form I crystals can be transformed into metastable form III or mesophase by stretching samples, and vice versa. For stretched S0 sample, form III with trans‐planar conformation, which generally exists in highly stretched sPP, cannot be observed, even at higher strains. For sample S90, however, stretching might induce the formation of both the form III crystals and mesophase with trans‐planar chains; releasing the tension, form III again gets converted into trans‐planar mesophase and form I crystals. In the stretched and stress‐relaxed states of samples S0 and S90, the difference of the delicate orientation behavior and relative content of chain conformation and crystalline form can be attributed to the different heat‐treating methods of the low syndiotacticity sPP. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2924–2936, 2005

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An infrared spectroscopic approach to the polymorphic behavior of syndiotactic polypropylene and its crystal–crystal transformations during mechanical stretching

Cited by 15 publications

References 33 publications

Study of the stress oscillation phenomenon in syndiotactic polypropylene/montmorillonite nanocomposites

Study of the stress oscillation phenomenon in syndiotactic polypropylene/montmorillonite nanocomposites

FTIR spectroscopic investigation of thermal effects in semi‐syndiotactic polypropylene

Conformational variation and crystalline phase transformation of low syndiotactic polypropylene films in stretched and stress‐relaxed states

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