Abnormal brittle-ductile transition for glassy polymers after free and constrained melt stretching: The role of molecular alignment

Qi, Yan; Xu, Tingyu; Zhang, Wenwen; Lv, Changzhu; Guo, Hang; Tian, Fucheng; Chen, Wei; Li, Liangbin

doi:10.1016/j.polymer.2021.124199

Cited by 12 publications

(13 citation statements)

References 49 publications

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“…It is well-known that brittle glassy polymers with high molecular weight, like polystyrene (PS) and poly(methyl methacrylate) (PMMA), can greatly improve their toughness by melt stretching . And previous reports suggested that melt stretching is an efficient way to work against physical aging. , Therefore, we think the ultrahigh toughness for PLA_S80 and PLA_S85 samples could be attributed to the moderate orientation of amorphous molecular chains.…”

Section: Resultsmentioning

confidence: 86%

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Enhancing Tensile Strength and Toughness via Moderate Orientation of Amorphous Molecular Chains in Biobased Biodegradable Poly(lactic acid)

et al. 2022

ACS Appl. Polym. Mater.

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The preparation of high-toughness and high-strength poly(lactic acid) (PLA) is of great significance for promoting its application in packing, construction, and medical fields. Compared to blending with polymeric elastomers, hot stretching is an effective method to improve the toughness of PLA without sacrificing its strength. However, it is still unclear which part of the structural change after hot stretching is responsible for the increased toughness of PLA. In this work, the semicrystalline structure and mechanical properties of the PLA samples stretched at different temperatures were studied. First, the semicrystalline structure of the PLA samples was studied by combining differential scanning calorimetry and wide-angle X-ray diffraction analyses. When the stretching temperature was relatively low (e.g., 65 °C), the mesophase, an intermediate phase between crystal and amorphous, was formed. Furthermore, significant stretch-induced crystallization was observed due to the enhanced chain mobility when the stretching temperature was 65−75 °C. With further increasing the stretching temperature, the crystallinity of the PLA samples decreased sharply to nearly 0 due to the rapid chain relaxation. Intriguingly, the PLA samples stretched at 85 °C showed the highest elongation at break 238.4% and high strength 75.8 MPa, which was attributed to its moderate molecular chain orientation not only hindering physical aging but also retaining the entanglement network of PLA molecular chains. The findings in this work provide an insightful understanding of the improved toughness of PLA, which will facilitate the large-scale practical application of PLA.

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Section: Resultsmentioning

confidence: 86%

“…It is well-known that brittle glassy polymers with high molecular weight, like polystyrene (PS) 41 and poly(methyl methacrylate) (PMMA), 42 can greatly improve their toughness by melt stretching. 27 And previous reports suggested that melt stretching is an efficient way to work against physical aging.…”

Section: = °Xmentioning

confidence: 99%

Enhancing Tensile Strength and Toughness via Moderate Orientation of Amorphous Molecular Chains in Biobased Biodegradable Poly(lactic acid)

et al. 2022

ACS Appl. Polym. Mater.

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“…Without any modification of the material itself, high temperature/high strain stretching (well above the glass transition temperature, T g ) has been applied to convert brittle amorphous polymers, such as PMMA, into ductile polymers, if stretched again along the same direction of pre-stretching [ 23 ]. The investigation to reveal the actual underlying mechanism of this brittle-ductile transition is still in progress [ 24 ].…”

Section: Introductionmentioning

confidence: 99%

On-Demand Tailoring between Brittle and Ductile of Poly(methyl methacrylate) (PMMA) via High Temperature Stretching

et al. 2022

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Dog-bone shaped poly(methyl methacrylate) (PMMA) samples were pre-stretched at different temperatures (within the glass transition range and slightly above) to different strains. Subsequently, these pre-stretched samples were aged at 40 °C for up to three months, and finally, all samples were uniaxially stretched to fracture. The Young’s modulus, ultimate stress and toughness of the samples were obtained and plotted as a function of the temperature, and strain in pre-stretching in the contour format. The influence of aging was revealed when the contours of different aging times were compared. One of the most interesting findings was that the toughness of this PMMA can be tailored via controlling the temperature and strain in pre-stretching. The toughness of the pre-stretched samples ranged from 1.317 MJ/m3 to 23.281 MJ/m3 (without aging) and from 1.476 MJ/m3 to 27.532 MJ/m3 (after three months of aging). Based on the results of a series of additional experiments, a mechanism was proposed to reveal the fundaments behind the influence of the temperature and strain in pre-stretching and aging.

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“…The observed behavior was correlated with results coming from structural analyses, which demonstrated an evolution from an oriented amorphous state to a highly oriented crystalline structure by increasing the drawing temperature up to 90 • C. A further increase of the drawing temperature caused a decrease of the crystallization rate and of the macromolecular orientation degree, because of the high achieved molecular motion, thus resulting in a rather brittle behavior. As briefly anticipated before, the scenario is completely different for amorphous polymers, for which an increase of the ductility upon elongation was widely observed [103,[127][128][129][130][131][132]. Figure 13 shows the variation of the elongation at break as a function of the birefringence (which is indicative of the macromolecular orientation) obtained for polystyrene filaments subjected to a spinning-like experiment [103].…”

Section: Effect Of Elongational Flow In Modifying Morphology and Mechanical Properties Of Homogeneous Polymersmentioning

confidence: 79%

Effect of the Elongational Flow on the Morphology and Properties of Polymer Systems: A Brief Review

2021

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Polymer-processing operations with dominating elongational flow have a great relevance, especially in several relevant industrial applications. Film blowing, fiber spinning and foaming are some examples in which the polymer melt is subjected to elongational flow during processing. To gain a thorough knowledge of the material-processing behavior, the evaluation of the rheological properties of the polymers experiencing this kind of flow is fundamental. This paper reviews the main achievements regarding the processing-structure-properties relationships of polymer-based materials processed through different operations with dominating elongational flow. In particular, after a brief discussion on the theoretical features associated with the elongational flow and the differences with other flow regimes, the attention is focused on the rheological properties in elongation of the most industrially relevant polymers. Finally, the evolution of the morphology of homogeneous polymers, as well as of multiphase polymer-based systems, such as blends and micro- and nano-composites, subjected to the elongational flow is discussed, highlighting the potential and the unique characteristics of the processing operations based on elongation flow, as compared to their shear-dominated counterparts.

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Abnormal brittle-ductile transition for glassy polymers after free and constrained melt stretching: The role of molecular alignment

Cited by 12 publications

References 49 publications

Enhancing Tensile Strength and Toughness via Moderate Orientation of Amorphous Molecular Chains in Biobased Biodegradable Poly(lactic acid)

Enhancing Tensile Strength and Toughness via Moderate Orientation of Amorphous Molecular Chains in Biobased Biodegradable Poly(lactic acid)

On-Demand Tailoring between Brittle and Ductile of Poly(methyl methacrylate) (PMMA) via High Temperature Stretching

Effect of the Elongational Flow on the Morphology and Properties of Polymer Systems: A Brief Review

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