Crystalline plasticity in isotactic polypropylene below and above the glass transition
temperature

Polt, Gerald; Spieckermann, Florian; Wilhelm, Harald; Fischer, Ch.‐H.; Schafler, Erhard; Bernstorff, Sigrid; Zehetbauer, M.

doi:10.3144/expresspolymlett.2015.81

Cited by 4 publications

(3 citation statements)

References 31 publications

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“…The assignment of the β-relaxation to the glass transition in PP was also confirmed by its higher activation energy when compared to that of the α-relaxation. The decrease of the dislocation density around the glass transition temperature observed in the present investigation (Figure ) can be explained by the reduction in back-stresses acting on the crystalline phase as follows: Below T g , the material remains highly strained from the rolling procedure. Quenching the sample to liquid nitrogen temperature immediatly after deformation prohibited any intermittent sample relaxation; thus, a large amount of stresses was “frozen” within the material.…”

Section: Discussionmentioning

confidence: 52%

Dislocation Movement Induced by Molecular Relaxations in Isotactic Polypropylene

Spieckermann

Polt²,

Wilhelm³

et al. 2017

Macromolecules

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The thermal stability of deformation-induced dislocations was investigated in polypropylene (PP) during annealing by means of in-situ X-ray diffraction using synchrotron radiation. The samples were cold rolled to high strains (ε = 1.2) in order to introduce a high number of dislocation lattice defects and immediately stored in liquid nitrogen afterward. Then, stepwise annealing was applied from −180 °C up to above the melting temperature (165 °C) while synchrotron X-ray diffraction patterns were recorded at each step. The resulting low noise, high angular resolution diffraction patterns were evaluated using multireflection X-ray profile analysis (MXPA), revealing parameters such as the dislocation density and the thickness of the crystalline lamellae as a function of the annealing temperature. Two significant decreases of the dislocation density were found at annealing temperatures of about 10 and 85 °C. These distinct changes in the dislocation density could be identified as the mechanisms of β- and α-relaxation, respectively, by performing additional dynamic mechanical thermal analysis (DMTA). This behavior could be attributed to an increased intrinsic mobility of the macromolecules at these temperatures accompanied by thermal activation of dislocations, resulting in their mutual annihilation or their movement into the adjacent amorphous phase. The reduction of the dislocation density at the glass transition (β-relaxation) occurs because the stabilizing effect of backstresses originating from the amorphous phase is lost. At the α-relaxation the reduction in the dislocation density is attributed to defect propagations within the crystalline lamellae as well as in the amorphous phase and the recrystallization of intralamellar mosaic blocks (i.e., grains).

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Section: Discussionmentioning

confidence: 52%

Dislocation Movement Induced by Molecular Relaxations in Isotactic Polypropylene

Spieckermann

Polt²,

Wilhelm³

et al. 2017

Macromolecules

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“…The change in melting point in iPP can be attributed to the reduction of the chain flexibility [28,37,38]. An increase of Tm introduces higher undercooling of the melt and higher size of spherulites [26,39]. POE-g-MAH was added, and the Tm was slightly reduced, it was not a significate effect.…”

Section: Thermal Behavior Of Compositesmentioning

confidence: 99%

Study of Mechanical, Thermal, and Microstructural Properties of Polypropylene/Ceramic Waste Composites

LÓPEZ-RAMIREZ¹,

FLORES-VAZQUEZ²,

CASTREJON-SANCHEZ³

et al. 2022

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In this work, the effect of reinforcement of the iPP with ceramic waste (CW), and the use of maleic anhydride compatibilizing agent grafted with polyolefin elastomer (POE-g-MAH) are studied. The composites were fabricated by extrusion and injection processes, and their morphology and microstructure, as well as fracture surface and mechanical and thermal properties were analyzed. Characterization by polarized optical microscopy showed that the ceramic waste particles were well-dispersed into the iPP matrix without the presence of agglomerates. However, the POE-g-MAH did not show good compatibility when it was added to the iPP/CW composite. Hardness Rockwell R, tensile and flexural measurements showed that the hardness, Young´s modulus, and flexural modulus increased with the incorporation of CW and without the POE-g-MAH. The ductility of the composites was several decreased with the addition of CW. POE-g-MAH affected the hardness, ductility, strength tensile, Young´s modulus, flexural modulus, and interfacial interaction in the iPP/CW composite. Analysis by X-ray diffraction showed that the CW also acted as a nucleating agent, increasing the crystallization degree, and forming the β-phase. Analysis of the Fourier transformed infrared showed transmittance bands of the iPP, CW, POE-g-MAH and composites. The bands were similar and there were no major changes in characteristic bands of composites, but CW and POE-g-MAH produced changes in the shape and intensity of band peaks of the iPP matrix. The CW addition to the iPP matrix modified the thermal properties of pure iPP, such as the degree of crystallization and melting temperature in the iPP/CW composites. The incorporation of POE-g-MAH decreased the crystallization temperature and crystallinity degree in the iPP/CW composite.

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“…Differences in the MFR resp. M W and polydispersity (M W /M N ) and chain structure (in detail, the stereoregularity and the presence of regiodefects [34][35][36]) of the matrix PP homopolymer should be kept in mind when comparing stiffness values, and some variation in the impact strength must be attributed to the differences in EPR content (see Table 4 for details). Nevertheless, one can conclude that the stiffness-toughness-balance for the SSC-based material is very different compared to the ZNC-based system, providing new opportunities for material design.…”

Section: Mechanical Propertiesmentioning

confidence: 99%

Structure-property relations of heterophasic ethylene-propylene copolymers based on a single-site catalyst

Aarnio-Winterhof¹,

Doshev²,

Seppälä³

et al. 2017

Express Polym. Lett.

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Crystalline plasticity in isotactic polypropylene below and above the glass transition temperature

Cited by 4 publications

References 31 publications

Dislocation Movement Induced by Molecular Relaxations in Isotactic Polypropylene

Dislocation Movement Induced by Molecular Relaxations in Isotactic Polypropylene

Study of Mechanical, Thermal, and Microstructural Properties of Polypropylene/Ceramic Waste Composites

Structure-property relations of heterophasic ethylene-propylene copolymers based on a single-site catalyst

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