Structural investigation of the phase transformation in the plastic zone of a β-phase isotactic polypropylene by synchrotron radiation microdiffraction

doi:10.1016/S0032-3861(98)00278-X

Polymer

Volume 40, Issue 2, 1999, Pages 541-545

https://doi.org/10.1016/S0032-3861(98)00278-X Get rights and content

Abstract

X-ray microdiffraction with synchrotron radiation has been used to investigate the strain-induced crystalline modification transition in the plastic zone of a β-phase isotactic polypropylene (β-iPP). It was shown that the bulk β-iPP was gradually transformed into highly oriented, conformationally disordered (condis structure) α-phase iPP as the strain increased.

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Influence of nucleating agent self-assembly on structural evolution of isotactic polypropylene during uniaxial stretching
2018, Polymer
Dotlike, needlelike, and treelike morphologies of N,N′-dicyclohexyl-2,6-naphthalene dicarboxamide (NJS) are induced via self-assembly. Isotactic-polypropylene (iPP)/NJS composite with treelike NJS shows the highest β-iPP relative crystallinity (K_β). During uniaxial stretching, a higher K_β could increase the number of voids. However, the size of voids is similar regardless of the NJS morphology. The β-α phase transition takes place after void formation. During intralamellar and interlamellar slip, no obvious polymer chains orientation can be found for α-iPP. In the strain range of 0.1–0.6, the c-axis of the β-iPP crystal tends to orient perpendicular to the stretching direction. This is caused by lamellae twisting, a unique deformation mode of β-iPP lamellae. The lamellae twisting is proposed to be responsible for the intense voids formation of the composite with higher K_β. At a strain larger than 0.6, the drastic increase of orientation is mainly caused by the rotation of the residual fragmented lamellae and the orientation of the newly formed crystals.
Influence of different beta-nucleating agents on the morphology of isotactic polypropylene and their toughening effectiveness
2016, Polymer
Citation Excerpt :
The toughening effect of the beta modification has been explained by the different morphology of the spherulites and a phase transformation. Riekel et al. [17] showed that beta-iPP undergoes a transformation from beta-iPP to alpha-iPP under tensile loading, which is accompanied by the formation of microvoids and causes higher toughness of the material. Aboulfaraj et al. [18] explained the brittle failure of alpha-iPP in comparison to beta-iPP by the different ability of crystallites to glide and reorient under mechanical loading due to the different structure of the spherulites.
The influence of two 1,3,5-benzenetrisamide beta-nucleating agents in comparison to a commercial bisamide beta-nucleating agent on the morphological and mechanical properties of isotactic polypropylene (iPP) is presented. To complete the study, the neat iPP and iPP containing a 1,3,5-benzenetrisamide alpha-nucleating agent was investigated. To evaluate the effectiveness of the different supramolecular polymer additives with regard to their influence on the toughness of iPP, a difficult-to-toughen high melt flow rate (MFR) iPP grade was selected. Investigations by wide-angle X-ray scattering (WAXS) confirm that the two 1,3,5-benzenetrisamides and commercial beta-nucleating agent induce the beta crystal modification of the polymer, whereas only the alpha modification is observed for the neat polymer and the 1,3,5-benzenetrisamide alpha-nucleating agent. Scanning electron microscopy (SEM) pictures on etched samples clearly reveal a shish-kebab structure in beta-nucleated iPP with 1,3,5-benzenetrisamides. For these two samples, Charpy impact investigations show a pronounced increase in toughness, also compared to the commercial bisamide beta-nucleating agent.
Effect of cooling rate on crystal polymorphism in beta-nucleated isotactic polypropylene as revealed by a combined WAXS/FSC analysis
2016, Polymer
Citation Excerpt :
Heating of samples cooled at rates lower than about 100 K/s only show endothermic melting of crystals which were formed during cooling. Note that in these cases the glass transition can no longer be detected, which suggests that a major amount of rigid amorphous fraction formed during crystallization [63,64]. The heating curves obtained from the sample containing 500 ppm γ-quinacridone reveal a qualitatively similar dependence on the rate of prior cooling, as was discussed for non-nucleated iPP.
The efficiency of linear trans γ-quinacridone to nucleate formation of β-crystals in isotactic polypropylene (iPP) at rapid cooling conditions has been evaluated by a combination of fast scanning chip calorimetry (FSC) and microfocus wide-angle X-ray scattering (WAXS). For samples containing different amount of γ-quinacridone, FSC cooling experiments revealed information about a critical cooling rate above which the crystallization temperature decreases to below 105 °C, that is, to temperatures at which the growth rate of α-crystals is higher than that of β-crystals. Microfocus WAXS analysis was then applied to gain information about the competition of formation of β- and α-crystals in samples prepared at well-defined conditions of cooling at rates up to 1000 K/s in the FSC. For iPP containing 1 and 500 ppm γ-quinacridone, the crystallization temperature is lower than 105 °C on cooling faster about 10 and 70 K/s, respectively, which then on further increase of the cooling rate leads to a distinct reduction of the β-crystal fraction. The study may be considered as a first successful attempt to quantify and interpret β-crystal formation in iPP containing γ-quinacridone at processing-relevant cooling conditions in the shed of light of the different temperature-dependence of the growth rates of α- and β-crystals.
Influence of trisamide-based additives on the morphological and mechanical properties of isotactic polypropylene
2014, Polymer
Citation Excerpt :
The higher ductility of the beta-nucleated material has been explained in literature by the different morphology of the spherulites and a phase transformation. Riekel et al. [31] showed that beta-PP undergoes a transition from beta-PP to alpha-PP under mechanical loading, which is accompanied by the formation of microvoids. Aboulfaraj et al. [22] explained the brittle failure of alpha-PP in comparison to beta-PP by the different ability of crystallites to glide and reorient under mechanical loading.
The influence of two different trisamide-based additives on the morphological and mechanical behavior of isotactic polypropylene (PP) is investigated. Morphological investigations by wide-angle X-ray scattering (WAXS) show that only 0.04 wt.-% of one of the additives is enough to induce 80% beta modification in the crystalline part of the polymer. The materials are investigated with quasistatic (tensile testing) as well as short-time dynamic (Charpy impact strength) methods and for the first time fatigue crack growth measurements are performed on alpha- and beta-nucleated PP. In all cases a much higher toughness of the material containing the beta-nucleating agent (beta NA) can be observed. The crack growth propagation rate is one order of magnitude smaller with the use of the beta-nucleating agent compared to the alpha polymer. Scanning electron microscopy (SEM) pictures are used to support the correlation of the mechanical behavior with the morphological changes.
Deformation-induced structure evolution of oriented β-polypropylene during uniaxial stretching
2013, Polymer
Citation Excerpt :
The excellent toughness of β-iPP has been attributed to the combined effect of the peculiar lamellar morphology of β phase [14–16], and the β to α phase transformation induced by mechanical load [12,17,18]. The β to α transformation has been evidenced by different techniques [19–21] and considered as the main source for the improved toughness of β-iPP [12,17,18]. Partial melting/recrystallization and solid-to-solid martensitic-like transformation have been proposed to describe the β to α phase transformation.
β phase isotactic polypropylene (β-iPP) with the β phase lamellae oriented parallel to the melt extrusion direction, was employed to investigate the deformation-induced structure evolution at various temperatures (25, 80, 110, 130 and 140 °C). The orientation change of β phase during deformation greatly influences the β to α phase transformation and its temperature dependence. At temperatures lower than 110 °C, the orientation of β phase is almost unchanged during deformation, and void or crack forms before fragmentation and reorientation of β phase. The crystal size change of β phase is small, and the defolding of the β lamellae triggers the β to α phase transformation. As the deformation temperature rises to 130 and 140 °C, the reorientation of β phase occurs gradually upon stretching, and the size of micro-voids decreases due to the fact that less β crystal fragmentation takes place at high draw temperature than that at low temperature. The β to α phase transformation is mainly induced by intra-lamella slip, and the trend of crystal size change of β phase is larger. The chains orientation changes from perpendicular to the stretching direction in β phase to parallel to the stretching direction in α phase is achieved by the chains defolding of β phase along the stretching direction at temperatures lower than 110 °C, and it is through the chains reorientation of β phase along the stretching direction at temperatures of 130 and 140 °C. The crystal size of α phase of the deformed β-iPP during deformation depends on the dynamic balance of the breakage of existing α crystal and the formation of new crystal through phase transformation. Specially, at draw temperature of 25 °C, the slippage of β phase relieves the breakage of α phase crystal, which indicates that the high content of β phase crystal really accounts for the toughening effect on iPP.
Real time synchrotron SAXS and WAXS investigations on temperature related deformation and transitions of β-iPP with uniaxial stretching
2012, Polymer
Citation Excerpt :
The studies on deformation mechanism of β form iPP have indicated that interlamellar slippage and crazing development were the dominant modes for structure transformation. The improvement of mechanical properties during mechanical loading of β-iPP has been explained by the transition from β- to α-crystalline iPP (α-iPP), based principally on DSC experiments [1,2,25]. The metastable crystal structure can prevail under strained conditions because of the reduced entropy.
In-situ synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) were carried out to investigate the uniaxial drawing-induced deformation and structure transitions of β form isotactic polypropylene (iPP) at varying temperatures (30 °C, 60 °C, 80 °C, 100 °C and 120 °C). The WAXS results indicated that the initial strain for the strain-induced β–α transformation decreases with the tensile temperature according to the engineering stress–strain curves. The SAXS data showed that the long period increased along the direction perpendicular to the tensile force and changed little along the tensile direction with increasing strain in the elastic deformation stage before the yield point. The analysis of the obtained scattering results indicated that the angle between parent and daughter lamella rotates from initial 40° or 140° to close to 90° accounts for the lateral expansion of the samples with tension, which matches the essential auxetical behavior. A structure deformation and transition mechanism was proposed for β form iPP with uniaxial drawing. The initialization of the crystalline structure transition is after the yield point, then the mechanical loading-induced β–α transition seems to be a gradual process with lamella slippage and breaking which triggers the β–α polymorphic transition.

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Structural investigation of the phase transformation in the plastic zone of a β-phase isotactic polypropylene by synchrotron radiation microdiffraction

Abstract

Polymer

Polymer

Polymer

Polymer

Polym Eng Sci

J Appl Polym Sci

J Thermal Anal

Rev Sci Instrum

Macromolecules