Tensile and dynamic mechanical behaviour of polymer blends based on PVDF

Linares, A.; Acosta, J. L.

doi:10.1016/s0014-3057(96)00182-6

Cited by 68 publications

(52 citation statements)

References 21 publications

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“…This process, labelled ␣ or ␣ c , is associated with motions within the crystalline fraction, previously detected by DSC (Fig. 2) [13,14,19]. This process is also found in a variety of flexible semicrystalline polymer, including polyethylene, poly(methylene oxide), poly(ethylene oxide) and isotactic polypropylene [20,21]and its origin should be similar to the one observed in PVDF.…”

Section: Dynamic Mechanical Analysissupporting

confidence: 67%

Characterization of poled and non-poled β-PVDF films using thermal analysis techniques

2004

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Abstract␤-poly(vinylidene fluoride)-␤-PVDF-exhibits ferroelectric properties due to the special arrangement of the chain units in the crystalline phase. The ferroelectric phase can be optimised by poling the original stretched film, that tends to align the randomly organised crystallites against the applied field. In this work, polarised and non-polarised ␤-PVDF from the same batch are characterised by mechanical tests and a series of thermal analysis techniques, including DMA, TMA and DSC. The films exhibit mechanical anisotropy, and in the longitudinal direction the poled film presents larger mechanical properties, due to the higher structural organisation. Poled and non-poled show similar crystallinity levels but the melting temperature probed by DSC is higher for the non-poled film; for both films the melting peak exhibits a complex shape, indicating a heterogeneous crystalline organization. Two relaxation processes were found (␤ and ␣ c ) by dynamic mechanical analysis (DMA). The ␤ process, attributed to segmental motions in the amorphous phase, appears at the same temperature in both directions, but its intensity was found to be higher for the films tested in the longitudinal direction. For a given direction, the poled films exhibit lower peaks, due to the more organised amorphous structure. At higher temperature, the ␣ c -relaxation was related to the contraction of the films in the longitudinal direction during heating, recorded by thermal mechanical analysis (TMA). The onset of molecular mobility within the crystalline phase allows for cooperative diffusion processes in the amorphous phase, generating the randomisation of the initially oriented structure.

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Section: Dynamic Mechanical Analysissupporting

confidence: 67%

Characterization of poled and non-poled β-PVDF films using thermal analysis techniques

2004

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“…In immiscible polymer blends, the interfacial adhesion is usually not strong enough for stress to be transferred efficiently from one phase to another one during yielding or fracture, thus resulting in poor mechanical properties. 13 Therefore, the measurement of tensile properties of PEGDA/PVdF blends is another way to estimate compatibility of PEGDA with PVdF. Especially, tensile elongation at break is very sensitive to the strength of the interface and commonly measured to examine the efficiency of blend.…”

Section: Methodsmentioning

confidence: 99%

Thermally Stable Gel Polymer Electrolytes

Song

Kim

et al. 2003

J. Electrochem. Soc.

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To prepare miscible polyethylene glycol diacrylate/polyvinylidene fluoride (PEGDA/PVdF) blend gel polymer electrolytes, low molecular weight false(M=742false) liquid PEGDA oligomer was mixed with PVdF-HFP dissolved in ethylene carbonate/dimethyl carbonate/ LiPF6 liquid electrolytes, and then cured under ultraviolet irradiation. Room temperature conductivity of PEGDA/PVdF blend films was found to be comparable to that of PVdF-HFP gel polymer electrolytes, and they were electrochemically stable up to 4.6 V vs. normalLi/Li+. Scanning electron micrographs revealed that PEGDA/PVdF blend electrolytes have pore size intermediate between dense PEGDA and highly porous PVdF-HFP. It was confirmed by weight change measurement that liquid electrolyte was likely to evaporate through large pores in PVdF-HFP at 80°C, while PEGDA/PVdF blend showed better liquid electrolyte retention ability. This result was in good agreement with more stable interfacial properties of PEGDA/PVdF blend at 80°C in ac impedance analysis. Consequently, both PVdF-HFP and PEGDA/PVdF gel polymer electrolytes delivered similar discharge capacity at room temperature, but PEGDA/PVdF blend gel polymer electrolyte showed much better cycle performance than pure PVdF-HFP at 80°C. © 2003 The Electrochemical Society. All rights reserved.

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“…The elastic modulus is roughly 2 GPa at room temperature, in good agreement with published literature. 16,18 The modulus decreases gradually by 25% as the temperature is increased to 65…”

Section: Mechanical Properties Of Polyvinylidene Fluoride-carbon Blacmentioning

confidence: 99%

“…5,15 The most common polymer for battery applications is polyvinylidene fluoride, a fairly stiff semi-crystalline polymer with a Young's modulus in the range of 1.5-2.5 GPa. [16][17][18][19] The glass transition temperature of PVDF is −30…”

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confidence: 99%

Conductivity Degradation of Polyvinylidene Fluoride Composite Binder during Cycling: Measurements and Simulations for Lithium-Ion Batteries

Grillet

Humplik

Stirrup

et al. 2016

J. Electrochem. Soc.

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The polymer-composite binder used in lithium-ion battery electrodes must both hold the electrodes together and augment their electrical conductivity while subjected to mechanical stresses caused by active material volume changes due to lithiation and delithiation. We have discovered that cyclic mechanical stresses cause significant degradation in the binder electrical conductivity. After just 160 mechanical cycles, the conductivity of polyvinylidene fluoride (PVDF):carbon black binder dropped between 45-75%. This degradation in binder conductivity has been shown to be quite general, occurring over a range of carbon black concentrations, with and without absorbed electrolyte solvent and for different polymer manufacturers. Mechanical cycling of lithium cobalt oxide (LiCoO 2 ) cathodes caused a similar degradation, reducing the effective electrical conductivity by 30-40%. Mesoscale simulations on a reconstructed experimental cathode geometry predicted the binder conductivity degradation will have a proportional impact on cathode electrical conductivity, in qualitative agreement with the experimental measurements. Finally, ohmic resistance measurements were made on complete batteries. Direct comparisons between electrochemical cycling and mechanical cycling show consistent trends in the conductivity decline. This evidence supports a new mechanism for performance decline of rechargeable lithium-ion batteries during operation -electrochemically-induced mechanical stresses that degrade binder conductivity, increasing the internal resistance of the battery with cycling. Lithium-ion batteries (LIB) are an enabling energy storage technology for portable consumer electronics, electric vehicles and renewable power generation in part due to their high energy densities. The energy density is driven by not only the relatively large potential of lithium-ion chemistries, but also the ability of active materials to store large amounts of lithium.1 The most common graphitic carbon anode can absorb up to one lithium for every carbon atom. Recent research on higher capacity anodes such as silicon has highlighted an increased need for understanding the mechanics of lithium-ion batteries. As the lithium is shuttled between the anode and cathode, the active materials expand and contract to accommodate the lithium. The resulting volume changes are accentuated for high capacity materials such as silicon which can increase in volume by up to 400% during lithiation. 2Because most LIB electrodes are porous multicomponent composites, understanding the generation and impact of mechanical stresses on batteries can be difficult. The electrode is generally 50-75 vol% solid fraction with active material consisting of micron-sized particles held together by an active binder, which is itself a composite of conductive carbon particles and polymer. The performance of the battery is highly dependent on this complex structure which must allow efficient ion and electron transport through the electrode. The void space in the porous structure allows lith...

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Tensile and dynamic mechanical behaviour of polymer blends based on PVDF

Cited by 68 publications

References 21 publications

Characterization of poled and non-poled β-PVDF films using thermal analysis techniques

Characterization of poled and non-poled β-PVDF films using thermal analysis techniques

Thermally Stable Gel Polymer Electrolytes

Conductivity Degradation of Polyvinylidene Fluoride Composite Binder during Cycling: Measurements and Simulations for Lithium-Ion Batteries

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