From stiff plastic to elastic polypropylene: Polymorphic transformations during plastic deformation of metallocene-made isotactic polypropylene

Rosa, Claudio De; Auriemma, Finizia; Lucia, G.; Resconi, Luigi

doi:10.1016/j.polymer.2005.07.028

Cited by 74 publications

(256 citation statements)

References 54 publications

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“…The values of the degree of crystallinity of all samples of Figure 1 are reported in Figure as a function of concentration of stereodefects. For samples slowly crystallized in α and γ forms, the degree of crystallinity decreases only slightly with increasing concentration of rr defects, due to inclusion of rr defects in the defective and disordered crystals of γ form 29, 36…”

Section: Resultsmentioning

confidence: 99%

Tailoring Mechanical Properties of Isotactic Polypropylene Via Crystallization of the Mesophase and Control of Stereodefects Concentration

Rosa

Auriemma

Ballesteros

et al. 2013

Macro Chemistry & Physics

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A strategy to tailor the properties of isotactic polypropylene, based on the combination of the\ud crystallization of the mesophase and the control of the molecular structure and concentration\ud of stereodefects via polymerization with metallocene\ud catalysts, is presented. The mechanical properties can be modulated\ud through the conventional slow crystallization from\ud the melt in the α and γ forms, depending on the concentration\ud of stereodefects, or the crystallization of the mesophase\ud by melt quenching. The most stereoirregular sample with rr\ud concentration of 11% shows elastic behavior either when it is\ud slowly crystallized in the γ form or when it is crystallized in\ud the meso morphic form, but with remarkable differences in\ud the values of the modulus and tensile strength

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Section: Resultsmentioning

confidence: 99%

Tailoring Mechanical Properties of Isotactic Polypropylene Via Crystallization of the Mesophase and Control of Stereodefects Concentration

Rosa

Auriemma

Ballesteros

et al. 2013

Macro Chemistry & Physics

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“…Such a stressinduced γ-R transformation was not observed during deformation at room temperature, 21 although it was postulated in the past by other authors. 19,20 It can be inferred that both destruction of γ crystals and formation of new R crystals are associated with partial destruction of lamellae within fine shear bands reported above.…”

Section: Stress-strain and Recoverymentioning

confidence: 90%

Plastic Deformation of the γ Phase Isotactic Polypropylene in Plane−Strain Compression at Elevated Temperatures

Łężak

Bartczak

2007

Macromolecules

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Plastic deformation behavior of iPP homopolymer crystallized exclusively in the γ modification was studied. Samples of γ-iPP were obtained by isothermal crystallization under pressure of 200 MPa. Deformation experiments in plane-strain compression were performed in the temperature range of 55-100°C. Samples of γ-iPP demonstrated higher modulus, higher yield stress, and flow stress, yet slightly lower ultimate strain comparing to R-iPP in the entire range of temperature studied. During plastic deformation numerous fine shear bands, initiated by the interlamellar shear of the amorphous layers, start to develop already at the yield point. Their propagation across the sample causes a limited destruction of γ lamellae oriented perpendicularly to the direction of the band. Destroyed fragments of crystallites partially reconstruct into either mesophase (smectic) domains or crystals of R phase, depending on the deformation temperature. Mesophase is produced upon deformation at room temperature, while at 55°C and above the crystalline R phase is formed instead. With increasing strain shear bands multiply and tilt toward the flow direction. Fragmented lamellae undergo kinking and rotation, which results in formation of a chevron-like lamellar morphology. This leads also to the development of a weak crystalline texture. Both crystalline texture and lamellae orientation emerge due to the same deformation mechanism of interlamellar slip, produced by the shear within interlamellar amorphous layers. The activity of any crystallographic deformation mechanism within the crystalline component was not detected at any temperature. The interlamellar amorphous shear appears to be the primary deformation mechanism of γ-iPP. The other identified mechanisms, i.e., γ-smectic and γ-R transformations, play a supplementary role in the deformation sequence.

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“…The growth of a 1 under annealing is expected, as it reflects the improvement of structural organization of crystallites [22] . The conclusion, that the rate of inelastic deformation in the crystalline phase of iPP exceeds that of mPP, may be explained by a substantially larger size of spherulites in iPP, which weakly resist lamellar sliding.…”

Section: Discussionmentioning

confidence: 92%

“…It was demonstrated that the viscoelastic and viscoplastic responses of mPP and iPP differ noticeably. In particular, mPP reveals a novel relaxation mechanism (associated with rearrangement of chains in the mesomorphic phase [9] and rupture of small crystallites [23] ), and a unique viscoplastic behavior (attributed to deformation-induced transformation of α crystallites into the mesomorphic form [9,22] , and formation of an oriented mesomorphic phase, due to lamellae fragmentation [10] ). Investigation of the mechanical response under long-term creep [24] and ratcheting [25] shows that the time to failure under conditions of creep rupture and the number of cycles to failure under cyclic deformation, with a stress-controlled program of mPP, substantially exceeds those of iPP.…”

Section: Introductionmentioning

confidence: 99%

Effect of crystalline structure on the mechanical response of polypropylene under cyclic deformation

Drozdov¹,

Klitkou

Christiansen

2013

Journal of Polymer Engineering

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To evaluate the influence of crystalline structure on the mechanical behavior of polypropylene (PP), uniaxial tensile cyclic tests with a mixed program (oscillations between fixed maximum strains and the zero minimum stress) were performed on isotactic PP (iPP) manufactured by the Ziegler-Natta catalysis method, metallocene catalyzed PP (mPP), and annealed mPP. Although the stress-strain diagrams of iPP and mPP under tension are quite similar, their responses under unloading differ markedly. The residual strain (measured as the strain under retraction down to the zero stress) of iPP strongly exceeds that of non-annealed mPP, and annealing of mPP increases this difference. To rationalize these findings, constitutive equations are developed in cyclic viscoelasticity and viscoplasticity of semicrystalline polymers, and adjustable parameters in the stress-strain relations are found by fitting the observations. The ability of the model to describe the observed phenomenon and to predict the mechanical response in multi-cycle tensile tests, with various deformation programs, is demonstrated by numerical simulation.

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From stiff plastic to elastic polypropylene: Polymorphic transformations during plastic deformation of metallocene-made isotactic polypropylene

Cited by 74 publications

References 54 publications

Tailoring Mechanical Properties of Isotactic Polypropylene Via Crystallization of the Mesophase and Control of Stereodefects Concentration

Tailoring Mechanical Properties of Isotactic Polypropylene Via Crystallization of the Mesophase and Control of Stereodefects Concentration

Plastic Deformation of the γ Phase Isotactic Polypropylene in Plane−Strain Compression at Elevated Temperatures

Effect of crystalline structure on the mechanical response of polypropylene under cyclic deformation

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