Oriented Overgrowths of Poly(<scp>l</scp>‐Lactide) on Oriented Isotactic Polypropylene: A Sequence of Soft and Hard Epitaxies

Guan, Guangwu; Zhang, Jie; Sun, Xiaoli; Li, Huihui; Yan, Shouke; Lotz, Bernard

doi:10.1002/marc.201800353

Cited by 17 publications

(19 citation statements)

References 44 publications

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“…It has well been confirmed that surface-induced epitaxy provides a simple and efficient way for regulating the multiscale structures of polymer thin films . It can (i) promote the nucleation and accelerate the crystallization of polymers, − (ii) regulate the molecular chain and crystal orientation, − and (iii) most importantly control the crystal modification. ,, The effective structure modulation of epitaxy on the deposit polymers is generally attributed to the crystallographic matching between depositing polymers and the underlying substrate . Taking this into account, one component of an epitaxial pair can be mutually served as a substrate for the other one.…”

Section: Introductionmentioning

confidence: 99%

Temperature-Dependent Reversibility of Epitaxy between Isotactic Polystyrene and Polypropylene

et al. 2021

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Epitaxial crystallization of isotactic polystyrene (iPS) on the oriented isotactic polypropylene (iPP) substrate and the reverse process, that is, epitaxial growth of iPP crystals on the oriented iPS film initially generated by epitaxy of it on iPP, have been investigated through transmission electron and atomic force microscopies. Epitaxy of iPS on the ordered iPP substrate was achieved by cold crystallization of an amorphous thin film at 130 °C for 2 h. The results indicate that epitaxy of iPS on the iPP substrate has parallel chain relationship. Epitaxial growth of iPP on the oriented iPS film was realized by selective melting of the iPP in the epitaxial iPP/iPS system at 190 °C for 5 min and then crystallizing at varied temperatures. It was found that oriented recrystallization of iPP on the itself-induced iPS epitaxially oriented substrate occurs at temperatures below 30 °C and produces exactly the same parallel mutual chain alignment, indicating the reversibility of epitaxy between iPP and iPS. It does, however, not happen at temperatures over 60 °C, reflecting a temperature-dependent epitaxial growth of iPP on iPS oriented films. This was explained by secondary nucleation and indicates that a larger dimension of substrate crystals than the depositing epitaxial ones is necessary for the occurrence of polymer epitaxy. This provides a theoretical basis for the substrate selection of polymer epitaxies.

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Section: Introductionmentioning

confidence: 99%

Temperature-Dependent Reversibility of Epitaxy between Isotactic Polystyrene and Polypropylene

et al. 2021

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“…As reported in ref , the PLLA grown on the PE substrate exhibits a cross-hatched lamellar morphology with the main set of lamellae arranged parallel to the chain direction of PE, that is, a perpendicular chain alignment of both polymers, while the other minor set of lamellae is oriented 64° away from the chain direction of PE. It is suggested that the perpendicular chain orientation is caused by soft epitaxial (or graphoepitaxial) crystallization of PLLA based on the surface topology of the PE substrate, which has also been found when crystallizing PLLA on the iPP substrate with a similar surface topology . The PLLA lamellae at 64° away from the PE molecular chain direction has been confirmed to be a result of hard epitaxy of PLLA on the graphoepitaxially grown PLLA lamellae, namely, homoepitaxy.…”

Section: Results and Discussionmentioning

confidence: 83%

“…It is suggested that the perpendicular chain orientation is caused by soft epitaxial (or graphoepitaxial) crystallization of PLLA based on the surface topology of the PE substrate, which has also been found when crystallizing PLLA on the iPP substrate with a similar surface topology. 32 The PLLA lamellae at 64°away from the PE molecular chain direction has been confirmed to be a result of hard epitaxy of PLLA on the graphoepitaxially grown PLLA lamellae, namely, homoepitaxy. It is further found that the occurrence of homoepitaxy depends strongly on the bulk crystallization capacity of the PLLA.…”

Section: Resultsmentioning

confidence: 94%

“…The existence of specific registration between the epitaxial pairs determines and controls the molecular chain orientation of polymers precisely. Taking poly(butylene adipate) as an example, parallel-aligned and cross-hatched lamellar structures can be produced by epitaxy on polyethylene (PE) and polypropylene (iPP), respectively. , However, recent studies on the epitaxial crystallization of poly( l -lactic acid) (PLLA) show that PLLA always exhibits a similar oriented structure, regardless of the used substrates. − This can hardly be explained simply by crystallographic matching. Therefore, we have speculated that the unusual oriented crystallization behavior of PLLA on different substrates is the result of the graphoepitaxy based on the surface topology of the substrates and the homoepitaxy of PLLA on its graphoepitaxially grown counterpart.…”

Section: Introductionmentioning

confidence: 99%

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Tacticity-Dependent Epitaxial Crystallization of Poly(l-lactic acid) on an Oriented Polyethylene Substrate

Xin

et al. 2020

Macromolecules

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The influence of tacticity on the bulk crystallization and polyethylene (PE)-induced epitaxial crystallization of poly(l-lactic acid) (PLLA) was investigated. It was found that cold-crystallization of PLLA with different tacticities from the amorphous glassy state is easier than the melt-crystallization from the isotropic melt and the cold-crystallization of PLLA at the PE surface takes place earlier than in bulk. The time-lag between the PE-induced epitaxial crystallization and bulk cold-crystallization of PLLA increases with decreasing tacticity. For example, while the cold-crystallization of the PLLA sample with 95% tacticity in the bulk and at the PE surface starts almost simultaneously, the bulk cold-crystallization of PLLA with a tacticity of 89% starts at a time point where over 90% PLLA already crystallized epitaxially on the PE substrate. The almost simultaneous start of bulk and PE-induced cold-crystallization of high tacticity PLLA enables the creation of a cross-hatched lamellar structure, which is composed of PLLA lamellae oriented along the PE chain direction and tilted ca. 64° with respect to the PE chain direction. The big time-lag between PE-induced epitaxy and bulk cold-crystallization of low-tacticity PLLA results in the disappearance of tilted PLLA lamellae. This further confirms that the PLLA lamellae aligned in the chain direction of PE are caused by PE-induced epitaxial crystallization, whereas the tilt lamellae are caused by the homoepitaxy of PLLA based on the parallelism of the helical paths.

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“…For the crystalline/crystalline polymer blends, the crystal structure and orientation of later crystallized components can be controlled by epitaxy or transcrystallization at the surface of early formed crystals [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 ], which may not reflect the effect of strain and the blending component on the later crystallized component correctly. It should be pointed out that soft epitaxy can hardly take place in crystalline/amorphous polymer blends, since it is not a common phenomenon [ 38 , 39 ]. It has been confirmed that a soft epitaxy of crystalline polymer does not happen even on oriented films of amorphous materials [ 40 ].…”

Section: Introductionmentioning

confidence: 99%

Orientation of Poly(ε-caprolactone) in Its Poly(vinyl chloride) Blends Crystallized under Strain: The Role of Strain Rate

et al. 2020

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The blends of high and low molecular weights poly(ε-caprolactone) (PCL) with poly(vinyl chloride (PVC) were prepared. The samples before and after the crystallization of PCL were uniaxially stretched to different draw ratios. The orientation features of PCL in a stretched crystalline PCL/PVC blend and crystallized from the amorphous PCL/PVC blends under varied strains were studied by wide-angle X-ray diffraction (WAXD). It was found that a uniaxial stretching of crystalline PCL/PVC blend with high molecular weight PCL results in the c-axis orientation along the stretching direction, as is usually done for the PCL bulk sample. For the stretched amorphous PCL/PVC blend samples, the crystallization of high molecular weight PCL in the blends under a draw ratio of λ = 3 with a strain rate of 6 mm/min leads to a ring-fiber orientation. In the samples with draw ratios of λ = 4 and 5, the uniaxial orientation of a-, b-, and c-axes along the strain direction coexist after crystallization of high molecular weight PCL. With a draw ratio of λ = 6, mainly the b-axis orientation of high molecular weight PCL is identified. For the low molecular weight PCL, on the contrary, the ring-fiber and a-axis orientations coexist under a draw ratio of λ = 3. The a-axis orientation decreases with the increase of draw ratio. When the λ reaches 5, only a poorly oriented ring-fiber pattern has been recognized. These results are different from the similar samples stretched at a higher strain rate as reported in the literatures and demonstrate the important role of strain rate on the crystallization behavior of PCL in its blend with PVC under strain.

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Oriented Overgrowths of Poly(l‐Lactide) on Oriented Isotactic Polypropylene: A Sequence of Soft and Hard Epitaxies

Cited by 17 publications

References 44 publications

Temperature-Dependent Reversibility of Epitaxy between Isotactic Polystyrene and Polypropylene

Temperature-Dependent Reversibility of Epitaxy between Isotactic Polystyrene and Polypropylene

Tacticity-Dependent Epitaxial Crystallization of Poly(l-lactic acid) on an Oriented Polyethylene Substrate

Orientation of Poly(ε-caprolactone) in Its Poly(vinyl chloride) Blends Crystallized under Strain: The Role of Strain Rate

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