Changes in structural and mechanical behaviour of PVDF with processing and thermomechanical treatments. 1. Change in structure

Mohajir, Badr-Eddine El; Heymans, Nicole Verheulpen

doi:10.1016/s0032-3861(01)00064-7

Cited by 239 publications

(169 citation statements)

References 11 publications

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“…nonpolar α-phase, and polar β-, γ-, and δ-phases depending on the crystallization and processing conditions [11]. The α-phase crystallizes from the melt directly, while the β-phase generates from mechanical stretching and solvent casting [14,60]. In the present study, electrospinnig can also induce -phase in pristine PVDF mat.…”

Section: Electrospun Fibrous Membranesmentioning

confidence: 56%

Novel electrospun polyvinylidene fluoride-graphene oxide-silver nanocomposite membranes with protein and bacterial antifouling characteristics

Liu¹,

Shen²,

Liao³

et al. 2018

Express Polym. Lett.

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Section: Electrospun Fibrous Membranesmentioning

confidence: 56%

Novel electrospun polyvinylidene fluoride-graphene oxide-silver nanocomposite membranes with protein and bacterial antifouling characteristics

Liu¹,

Shen²,

Liao³

et al. 2018

Express Polym. Lett.

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“…Indeed, there is one more endothermic transition at ($ 708C besides the melting peak in PVDF samples with a-modification prepared by nonisothermal crystallization by quenching from the melt. This mechanism disappears at annealing [56][57][58] (or after repeated heating cycle 57 ). The authors 56,58 consider it as an indication for the existence of upper glass transition point (T g U ), where RAP relaxation occurs.…”

Section: Resultsmentioning

confidence: 99%

Dielectric relaxation in vinylidene fluoride–hexafluoropropylene copolymers

Kochervinskiĭ

Malyshkina

Markin

et al. 2007

J of Applied Polymer Sci

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The molecular mobility in copolymers of vinylidene fluoride-hexafluoropropylene VDF/HFP of 93/7 and 86/14 ratios has been investigated by means of broadband dielectric relaxation spectroscopy (10 À1 -10 7 Hz), differential scanning calorimetry DSC (À100 to 1508C), and of wide angle X-ray diffraction WAXS. Four relaxation processes and one ferroelectric-paraelectric phase transition have been detected. The process of the local mobility b-(at temperatures below glass transition point) is not affected by chemical composition of the copolymer and the formed structure. Parameters of segmental mobility in the region of glass transition (a a -relaxation) depend on the ratio of comonomer with lower kinetic flexibility. a c -relaxation is clearly observed only in VDF/HFP 93/7 copolymer, which is characterized by a higher crystallinity and a higher perfection of crystals of a-(a p -) phase. Diffuse order-disorder relaxor type ferroelectric transition connected with the destruction of the domains in low-perfect ferroelectric phase in the amorphous regions has been detected for both copolymers. An intensive relaxation process (a-process) was observed for both copolymers in high-temperature region. DSC data shows that it falls on the broad temperature region of aphase crystals melting. It is considered to be connected with the space charge relaxation.

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“…The b form consists of parallel packing of the polymer chains in all-trans conformations, and thus, it shows a large spontaneous lattice polarization. [9][10][11] The polar b phase is the most desirable crystalline form for PVDF because it provides better pyroelectric and piezoelectric properties. Although the most common polymorph of PVDF is the a form, which is directly produced by the cooling of the melt, PVDF films consisting of b crystals are usually prepared by the drawing of samples having a crystals at temperatures below 1008C and stretching ratios of 3-5.…”

Section: Introductionmentioning

confidence: 99%

Effect of flow history on poly(vinylidine fluoride) crystalline phase transformation

Sobhani

Razavi‐Nouri

Yousefi

2007

J of Applied Polymer Sci

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This study was devoted to the effect of extensional flow during film extrusion on the formation of the b-crystalline phase and on the piezoelectric properties of the extruded poly(vinylidine fluoride) (PVDF) films after cold drawing. The PVDF films were extruded at different draw ratios with two different dies, a conventional slit die and a two-channel die, of which the latter was capable of applying high extensional flow to the PVDF melt. The PVDF films prepared with the two-channel die were drawn at different temperatures, strain rates, and strains. The optimum stretching conditions for the achievement of the maximum b-phase content were determined as follows: temperature ¼ 908C, strain ¼ 500%, and strain rate ¼ 0.083 s À1. The samples prepared from the dies were then drawn under optimum stretching conditions, and their b-phase content and piezoelectric strain coefficient (d 33 ) values were compared at equal draw ratios. Measured by the Fourier transform infrared technique, a maximum of 82% b-phase content was obtained for the samples prepared with the two-channel die, which was 7% higher than that of the samples prepared by the slit die. The d 33 value of the two-channel die was 35 pC/N, which was also 5 pC/N higher than that of the samples prepared with the slit die.

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Changes in structural and mechanical behaviour of PVDF with processing and thermomechanical treatments. 1. Change in structure

Cited by 239 publications

References 11 publications

Novel electrospun polyvinylidene fluoride-graphene oxide-silver nanocomposite membranes with protein and bacterial antifouling characteristics

Novel electrospun polyvinylidene fluoride-graphene oxide-silver nanocomposite membranes with protein and bacterial antifouling characteristics

Dielectric relaxation in vinylidene fluoride–hexafluoropropylene copolymers

Effect of flow history on poly(vinylidine fluoride) crystalline phase transformation

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