Tensile yield of isotactic polypropylene in terms of a lamellar-cluster model

Nitta, Koh‐hei; Takayanagi, Motowo

doi:10.1002/(sici)1099-0488(20000415)38:8<1037::aid-polb4>3.0.co;2-r

Cited by 85 publications

(74 citation statements)

References 38 publications

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“…But the most striking feature of Figure 4 is that D f is temperature-dependent over the whole T d range, in contrast to L pf that no longer depends on temperature for Figure 5 for the sake of the discussion. Figure 5 shows that, at a given temperature, the D f data for the samples having the same thermal treat- [52]. Nitta's approach considers yielding as a fragmentation process, the size of the crystal fragment being basically determined by the average distance between tie chains.…”

Section: Resultsmentioning

confidence: 99%

On the strain-induced fibrillar microstructure of polyethylene: Influence of chemical structure, initial morphology and draw temperature

Xiong¹,

Lame²,

Chenal³

et al. 2016

Express Polym. Lett.

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A general feature of the morphogenesis of semicrystalline polymers is the regular stacking of chainfolded lamellar crystals alternating with amorphous layers. This stacking s characterized by an intercrystalline long period L p including the crystalline lamella and amorphous layer thicknesses. The stacking long period is in the range of a few nanometers to a few tens. When crystallization is performed from a quiescent melt, the resulting microstructure is isotropic with a spherulitic arrangement of the lamella stacks as a result of the radial growth of the crystals from a common multiple nucleus often designated as axialite [1]. The size scale of spherulites ranges from a few to several hundred microns. Upon plastic deformation at large strains, isotropic semicrystalline polymers transform into fibrillar materials that aroused a great interest from both academic and industrial standpoints owing to their remarkable mechanical performances [2-6] to be used as ropes, textile fibers for high performance tissues and fabrics, reinforcing fibers for polymer-based composites, etc. Abstract. The influence of crystalline microstructure and molecular topology on the strain-induced fibrillar transformation of semi-crystalline polyethylenes having various chemical structures including co-unit content and molecular weight and crystallized under various thermal treatments was studied by in situ SAXS at different draw temperatures. The long period of the nascent microfibrils, L pf , proved to be strongly dependent on the draw temperature but non-sensitive to the initial crystallization conditions. L pf was smaller than the initial long period. Both findings have been ascribed to the straininduced melting-recrystallization process as generally claimed in the literature. The microfibrils diameter, D f , was shown to depend on the draw temperature and initial microstructure in a different way as L pf . The evolution of D f was shown to correlate with the interfacial layer thickness that mainly depends on the chemical structure of the chains. It was concluded that, in contrast to L pf , the microfibril diameter should not be directly sensitive to the strain-induced melting-recrystallization. The proposed scenario is that after the generation of the protofibrils by fragmentation of the crystalline lamellae at yielding, the diameter of the microfibril during the course of their stabilization should be governed by the chain-unfolding and subsequent aggregation of the unfolded chains onto the lateral surface of the microfibrils. The morphogenesis of the microfibrils should therefore essentially depend on the chemical structure of the polymer that governs its crystallization ability, its chain topology and subsequently its fragmentation process at yielding. This scenario is summed up in a sketch.

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Section: Resultsmentioning

confidence: 99%

On the strain-induced fibrillar microstructure of polyethylene: Influence of chemical structure, initial morphology and draw temperature

Xiong¹,

Lame²,

Chenal³

et al. 2016

Express Polym. Lett.

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“…The present data seems to be analyzed based on the lamellar cluster theory presented by Nitta-Takayanagi. 23,24 Details of the yield process of PP samples will appear in near future.…”

Section: Deformation Mechanismmentioning

confidence: 99%

Influence of Morphological Factors on Tensile Properties in the Pre-yield Region of Isotactic Polypropylenes

Nitta

Yamaguchi

2006

Polym J

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ABSTRACT:We examined the molecular and structural variables that govern tensile properties of isotactic polypropylene forming spherulitic morphology. The polypropylenes were crystallized in such a manner as to develop as a wide range as possible in the values of the independent structural variables that describe the solid state. The initial deformations depend strongly on the amorphous regions but are independent of the spherulite size and lamellar thickness. At yield point the lamellae within spherulites were found to be fragmented and replaced by a highly oriented fibrous structure in the post-yield region. [DOI 10.1295/polymj.38.122] KEY WORDS Isotactic Polypropylene / Tensile Properties / Morphology / Spherulite / Semicrystalline polymers such as polyethylene and polypropylene contain both a liquid-like amorphous phase and an ordered crystalline phase. When solidified from the melt, these polymers show spherulitic structure, in which the crystalline lamellae composed of folded chains radiate from its center and the amorphous phases reside in the interlamellar regions in the form of tie chains, loop chains, cilia chains, and floating chains. In addition, the spherulite is filled with the lamellae in such a way that a constant long period is approximately maintained.The tensile properties of semicrystalline polymers showing spherulitic structure have been received a great deal of attention because of their scientific interest as well as practical importance. However, the molecular and structural mechanism underlying the deformation process is not well clarified yet. Essentially mechanical properties of these spherulitic materials are controlled by molecular morphology which depends largely on molecular constitution such as molecular weight and the structural regularity of the chain as well as crystallization conditions.1 The morphology of semicrystalline polymers can be simplified by various levels of hierarchy in structure such as crystalline thickness, amorphous layer thickness, the size of spherulite and the structural organization in the residual amorphous region.2 These diversity and independencies of these structural variables make it difficult to provide a molecular or structural interpretation for tensile behavior as suggested by Mandelkern et al. [2][3][4][5] In order to obtain a better understanding to the tensile behavior of semicrystalline polymers, these variables should be isolated and their individual roles assessed. Recently, this strategy has also been used in studies of tensile deformation of several polyethylenes.3,4 The present work is restricted to isotactic polypropylenes which are one of the most widely used polymers and expected to be further enhanced performance in the future. 5 The objective is to explore the structural variables that govern tensile behavior for isotactic polypropylenes with a high isotacticity. The independent structural variables are widely varied by controlling the molecular constitution and the crystallization conditions. For the purpose, the polymers studied in...

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“…Plasticity and yield of iPP have been the focus of attention in the past decade, see, e.g., ref. [1][2][3][4][5][6][7][8][9][10] This may be explained by numerous applications of poly(propylene) in industry (ranged from oriented films for packaging to nonwoven fabrics and reinforcing fibres).…”

Section: Introductionmentioning

confidence: 99%

“…Observations show that stretching of iPP specimens induces inter-lamellar separation, rotation and twist of lamellae, fine and coarse slip of lamellar blocks and their fragmentation, [3,7] chain slip through the crystals, sliding and breakage of tie chains, [9,10] and activation of the rigid amorphous fraction. At large strains, these transformations result in cavitation, formation of fibrills and stress-induced crystallization.…”

Section: Introductionmentioning

confidence: 99%

A Model for the Elastoplastic Behavior of Isotactic Poly(propylene) Below the Yield Point

Drozdov

Christiansen

2003

Macro Materials & Eng

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Observations are reported on isotactic poly(propylene) (iPP) in a series of tensile loading‐unloading tests with a constant strain rate at room temperature. A constitutive model is developed for the elastoplastic behavior of a semicrystalline polymer at isothermal uniaxial deformations with small strains. The stress‐strain relations are determined by 5 adjustable parameters which are found by fitting the experimental data. The stress σ (MPa) versus strain ε in a tensile loading‐unloading test with the maximum strain εmax = 0.09. Circles: experimental data. Solid line: results of numerical simulation.magnified imageThe stress σ (MPa) versus strain ε in a tensile loading‐unloading test with the maximum strain εmax = 0.09. Circles: experimental data. Solid line: results of numerical simulation.

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Tensile yield of isotactic polypropylene in terms of a lamellar-cluster model

Cited by 85 publications

References 38 publications

On the strain-induced fibrillar microstructure of polyethylene: Influence of chemical structure, initial morphology and draw temperature

On the strain-induced fibrillar microstructure of polyethylene: Influence of chemical structure, initial morphology and draw temperature

Influence of Morphological Factors on Tensile Properties in the Pre-yield Region of Isotactic Polypropylenes

A Model for the Elastoplastic Behavior of Isotactic Poly(propylene) Below the Yield Point

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