Special Issue "Microstructure Evolutions and Mechanical Behavior of Semicrystalline Polymers"

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Crystalline Materials".

Deadline for manuscript submissions: closed (21 April 2019).

Special Issue Editor

Guest Editor
Dr. Olivier Lame

Laboratoire de Physique de la Matière Condensée et Nanostructures Université Claude Bernard Lyon, France
Website | E-Mail
Phone: +33 4 72 43 83 57
Interests: semi-crystalline polymers; relation microstructure/mechnical behaviour; in-situ X-Rays experiments; molecular dynamic simulations; polymer powder sintering

Special Issue Information

Dear Colleagues,

Reliable prediction of the mechanical behavior of semi-crystalline polymers requires microstructural characterization and an understanding of the mechanisms that link the microstructure and its evolution along the deformation with the mechanical properties.

Significant progress has been made in recent decades, particularly in the description of the elastic regime, with in-situ experimental techniques or numerical simulations. In the case of a high deformation regime or fatigue, some problems remain. More precisely, the deformation mechanisms are not fully understood at the molecular scale or at the scale of crystallite stacks and at the spherulite scale where the distribution of stress and strain remains difficult to describe.

The purpose of this Special Issue is to take stock of all experimental or theoretical contributions that may provide information on this research field in order to identify perspectives for realistically understanding and modeling mechanical behavior and life time of semi-crystalline polymers.

This Special Issue is open to any innovative contribution, even beyond this description, which could be inspiring for scientists in this field of research.

Dr. Olivier Lame
Guest Editor

Manuscript Submission Information

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Keywords

  • Semi-crystalline polymers
  • Mechanical behavior
  • Microstructural characterization
  • Modelling

Published Papers (6 papers)

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Research

Open AccessArticle
Stress Heterogeneity Leading to Void Nucleation within Spherulites for Semi-Crystalline Polymers
Crystals 2019, 9(6), 298; https://doi.org/10.3390/cryst9060298
Received: 26 April 2019 / Revised: 31 May 2019 / Accepted: 6 June 2019 / Published: 8 June 2019
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Abstract
Linking the microstructure to the mechanical properties is a key feature in the design and assessment of the durability of semi-crystalline polymers. This paper addresses the importance of a particular architecture inside spherulites. The use of the theoretical tools of continuum mechanics has [...] Read more.
Linking the microstructure to the mechanical properties is a key feature in the design and assessment of the durability of semi-crystalline polymers. This paper addresses the importance of a particular architecture inside spherulites. The use of the theoretical tools of continuum mechanics has been combined with experimental observations of the deformation of the microstructure. Microstructural heterogeneities at various scales induced critical regions in the spherulite where voiding has been reported. The local stress state has been investigated using a Finite Element code. A simple Hooke’s law was used for meshes accounting for the alternating crystalline and amorphous lamellae. This allowed a better understanding of the loci of void nucleation in the equatorial region, as well as in the “polar fans”, and were explained by using a criterion based on stress equi-triaxiality. Full article
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Open AccessArticle
The Orientation of Strain-Induced Crystallites in Uniaxially-Strained, Thin and Wide Bands Made from Natural Rubber
Crystals 2019, 9(6), 294; https://doi.org/10.3390/cryst9060294
Received: 20 April 2019 / Revised: 14 May 2019 / Accepted: 2 June 2019 / Published: 5 June 2019
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Abstract
Vulcanized natural rubber (unfilled and filled with 20 phr carbon black) is strained. We suppress the macroscopic formation of fiber symmetry by choosing strip-shaped samples ("pure-shear geometry") and investigate the orientation of the resulting crystallites by two-dimensional wide-angle X-ray diffraction (WAXD), additionally rotating [...] Read more.
Vulcanized natural rubber (unfilled and filled with 20 phr carbon black) is strained. We suppress the macroscopic formation of fiber symmetry by choosing strip-shaped samples ("pure-shear geometry") and investigate the orientation of the resulting crystallites by two-dimensional wide-angle X-ray diffraction (WAXD), additionally rotating the sample tape about the straining direction. Indications of a directed reinforcing effect of the strain-induced crystallization (SIC) in the thin strip are found. In the filled material fewer crystallites are oriented and the orientation distribution of the oriented crystallites is less perfect. The results confirm, that it is important for the evaluation of crystallinity under deformation to check, whether fiber symmetry can be assumed. This has consequences in particular on the quantitative interpretation of space-resolved scanning experiments in the vicinity of crack tips. Furthermore it raises the question, whether there is an asymmetric reinforcing effect of the SIC in the vicinity of crack tips inside natural rubber. Full article
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Open AccessArticle
Simultaneous SAXS-WAXS Experiments on Semi-Crystalline Polymers: Example of PA11 and Its Brill Transition
Crystals 2019, 9(5), 271; https://doi.org/10.3390/cryst9050271
Received: 19 April 2019 / Revised: 15 May 2019 / Accepted: 20 May 2019 / Published: 24 May 2019
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Abstract
This manuscript of the special issue “Microstructural Evolution and Mechanical Behavior of Semi-Crystalline Polymers” aims to show that Small Angle X-ray Scattering (SAXS) and Wide Angle X-ray Scattering (WAXS) experiments performed simultaneously constitute a unique tool to obtain valuable information on the hierarchical [...] Read more.
This manuscript of the special issue “Microstructural Evolution and Mechanical Behavior of Semi-Crystalline Polymers” aims to show that Small Angle X-ray Scattering (SAXS) and Wide Angle X-ray Scattering (WAXS) experiments performed simultaneously constitute a unique tool to obtain valuable information on the hierarchical structure of semi-crystalline polymers. These structural quantitative data are needed to model macroscopic properties of polymeric materials, for example their mechanical properties. To illustrate our point, we focus our study on the structure and morphology of polyamide 11. Through a simultaneous SAXS-WAXS experiment, we show that the absence of enthalpic signal in Differential Scanning Calorimetry (DSC) is not synonymous with the absence of structural and morphological evolution with temperature. The case of a thermally activated crystal–crystal transition, the Brill transition, is particularly detailed. Through this SAXS-WAXS study, we show, among other points, and for the first time, that the periodicity of crystalline lamellae (LP) changes at the transition, probably due to a modification of the amorphous phase’s free volume at the Brill transition. We also explain the crucial role of annealing to stabilize polymeric materials that may experience temperature changes over their lifetime. The influence of the annealing on the perfection of crystalline structure, morphology and mechanical behavior is more particularly studied. Full article
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Open AccessArticle
Morphological Monte Carlo Simulation for Crystallization of Isotactic Polypropylene in a Temperature Gradient
Crystals 2019, 9(4), 213; https://doi.org/10.3390/cryst9040213
Received: 4 March 2019 / Revised: 15 April 2019 / Accepted: 18 April 2019 / Published: 20 April 2019
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Abstract
Polymers are poor heat conductors, so the cooling of thick-walled shapes results in temperature gradients. Here, isotactic polypropylene (iPP) is chosen as a model polymer for the study of polymer crystallization in a temperature gradient field. The morphological Monte Carlo algorithm is applied, [...] Read more.
Polymers are poor heat conductors, so the cooling of thick-walled shapes results in temperature gradients. Here, isotactic polypropylene (iPP) is chosen as a model polymer for the study of polymer crystallization in a temperature gradient field. The morphological Monte Carlo algorithm is applied, combined with the radius growth model, to predict the growth of spherulites. Through comparison of the two numerical solutions, analytical solution and experimental data, the validity of the morphological Monte Carlo algorithm is demonstrated. In addition, the roles of central temperature, temperature gradient for the evolution of spherulites, and the conversion degree of the melt into spherulites are considered. The results of the study show that increases in central temperature and temperature gradient can increase the anisotropy of spherulites. Isothermal crystallization and crystallization in a temperature gradient field are compared, and the differences are considered. Results show that when the central temperature is below 125 °C, and when the temperature gradients are less than 15 K/mm and 27 K/mm, the differences in the conversion degree of the melt into spherulites are less than 2% and 5%, respectively. Therefore, crystallization under such temperature gradient conditions can be simplified as isothermal crystallization. Full article
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Open AccessArticle
Deformation Mechanisms of Isotactic Poly-1-Butene and Its Copolymers Deformed by Plane-Strain Compression and Tension
Crystals 2019, 9(4), 194; https://doi.org/10.3390/cryst9040194
Received: 12 March 2019 / Revised: 26 March 2019 / Accepted: 1 April 2019 / Published: 5 April 2019
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Abstract
The deformation-induced crystalline texture of isotactic poly-1-butene and its random copolymers with ethylene, developing during plane-strain compression and uniaxial tension, was investigated with X-Ray pole figures, supported by small-angle scattering (SAXS) and thermal analysis (DSC). The crystallographic (100)[001] chain slip was identified as [...] Read more.
The deformation-induced crystalline texture of isotactic poly-1-butene and its random copolymers with ethylene, developing during plane-strain compression and uniaxial tension, was investigated with X-Ray pole figures, supported by small-angle scattering (SAXS) and thermal analysis (DSC). The crystallographic (100)[001] chain slip was identified as the primary deformation mechanism, active in both compression and tension, supported by the transverse slip system and interlamellar shear. At the true strain around 0.8, lamellae fragmentation and partial destruction of the crystalline phase due to slip localization was observed, much heavier in tension than in plane-strain compression. That fragmentation brought an acceleration of the slip, which ultimately led to a common fiber texture in tensile samples, with the chain direction oriented preferentially along the drawing (flow) direction. Slightly more complicated crystal texture, reflecting triaxiality of the stress field, still with the chain direction preferentially oriented near the flow direction, was observed in compression. Additional deformation mechanism was observed at low strain in the plane-strain compression, which was either interlamellar shear operating in amorphous layers and supported by crystallographic slips or the simultaneous (110)[110] transverse slip operating on a pair of (110) planes. It was concluded that deformation proceeded similarly in both studied deformation modes, with practically the same deformation mechanisms engaged. Then, the plane-strain compression, proceeding homogeneously and preventing cavitation, seems more suitable for studies of the real deformation behavior, not obscured by any unwanted side-effects. Full article
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Open AccessArticle
On Plowing Frictional Behavior during Scratch Testing: A Comparison between Experimental and Theoretical/Numerical Results
Crystals 2019, 9(1), 33; https://doi.org/10.3390/cryst9010033
Received: 26 November 2018 / Revised: 24 December 2018 / Accepted: 8 January 2019 / Published: 11 January 2019
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Abstract
Scratch testing is a contact mechanics based nondestructive testing method that, if correctly evaluated, can give a lot of information about the material and tribological behavior of a material. In contrast to the situation with another contact-based method, indentation testing, wear characteristics can [...] Read more.
Scratch testing is a contact mechanics based nondestructive testing method that, if correctly evaluated, can give a lot of information about the material and tribological behavior of a material. In contrast to the situation with another contact-based method, indentation testing, wear characteristics can also be investigated, for example. In order to get results of practical importance from a scratch test, it is necessary to have evaluation formulae available. Indeed, such formulae exist for scratch testing but can be substantially influenced by frictional effects. For this reason, closed-form analytical relations have been suggested for the purpose of accounting for such effects during scratching and in particular the plowing frictional effect. As a major benefit, these relations can also be of assistance during material characterization through scratch testing. However, the proposed existing relations are based solely on theoretical/numerical analyses and, remembering that the scratch test of course is an experimental approach, verification by experiments is a necessity. Such a task is performed in the present study and it is shown that, based on standard contact global properties, the relations are accurate for most polymeric materials but could also be used for some metallic ones. Full article
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