PVDF solvents

With the exception of the inorganic membranes, all of the above are solution cast or spun from a polymer solution. For the more chemically resistant polymers like PS, PAS and PVDF, solvents like dimethylformamide (DMF), di-methylsulfoxide (DMSO), or dimethylacetamide (DMAc) are required. 

Zirconium dioxide is another kind of nanoparticle that has been used for preparing a composite PVDF UF membrane (Bottino et al. 2002). The membrane performance can be varied by changing the PVDF solvent or the Zr02 concentration ratio in the ternary suspension. However, the addition of ZrOj should be well controlled as the increment of the Zr02 concentration in the PVDF m brane could lead to an increase in the permeate flux at the expense of retention (Figure 4.4). 

While fast polymerizations occurred in diethyl-, di Bu- and propylene carbonate (fcp PP = 3 - 3.3 X IQ-2 h- ), the fastest rates were provided by ethylene carbonate, HFIPA ( p PP = 5 - 7 X IQ-2 h i) and especially by dimethyl carbonate (DMC, app j jQ-i ii-i). The conversion, polymerization rate (A p PP), and PDI were largely insensitive to the amount of DMC, = 35 mL, 1 g VDF, 1-12 mL DMC), whereas the rate significantly increased with the amount of VDF pressure and monomer concentration in solution, with 1-4 g VDF, 3-12 mL DMC). These are typical features of heterogeneous polymerizations of gaseous monomers [114], reminiscent of precipitation/dispersion polymerization of PVDF in SCCO2 with [29] and without [115] iodine CTAs. However, while fluorination enhances polymer solubilization, SCCO2 is a very poor PVDF solvent [116], even at high temperatures and pressures. 

Thus, unfortunately, many of the good PVDF solvents (DMF, DMAc, ureas, etc.) act as strong CTAs and lead to no or very low conversions. However, remarkable trends are observed with carbonates, and especially with DMC, a green solvent [117]. Indeed, although DMC does not dissolve PVDF at rt, and similarly to ACN affords a heterogeneous polymerization, it provides by far the fastest reaction rates, at least thrice those obtained in ACN. Moreover, DMC consistently outperformed ACN not only for PFBI, but for all initiators tested including in polymerizations from poor initiators such as CF3—(CF2)2—CO—Cl or Cl—CF2—(CF2)6—CF2—Cl, which occurred only in DMC. Possible explanations for this trend include a photosensitizing effect or better monomer/polymer solubilization. 

Fig. 5.8 Comparison of 70 % PVDF hybrid (/e/t) and baked PVDF solvent coatings, formulated with durable inorganic pigments, after 9 years Florida exposure...

FIGURE 8.10 Binodal boundary of PVDF/solvent/water. (Data from Bottino, A. et al. Journal of Membrane Science, 57,1-20,1991. doi 10.1016/S0376-7388(00)81159-X.)... 

Suspension- and emulsion-polymerized PVDF exhibit dissimilar behavior in solutions. The suspension resin type is readily soluble in many solvents even in good solvents, solutions of the emulsion resin type contain fractions of microgel, which contain more head-to-head chain defects than the soluble fraction of the resin (116). Concentrated solutions (15 wt %) and melt rheology of various PVDF types also display different behavior (132). The Mark-Houwink relation (rj = KM°-) for PVDF in A/-methylpyrrohdinone (NMP) containing 0.1 molar LiBr at 85°C, for the suspension (115) and emulsion... 

PVDF-based microporous filters are in use at wineries, dairies, and electrocoating plants, as well as in water purification, biochemistry, and medical devices. Recently developed nanoselective filtration using PVDF membranes is 10 times more effective than conventional ultrafiltration (UF) for removing vimses from protein products of human or animal cell fermentations (218). PVDF protein-sequencing membranes are suitable for electroblotting procedures in protein research, or for analyzing the phosphoamino content in proteins under acidic and basic conditions or in solvents (219). 

The most widely used fluoroelastomers are copolymers of VDF and HFP and optionally also TFE. HFP interrupts the crystallimty of otherwise crystaUme PVDF TFE increases the fluonne content for mcreased solvent and heat resistance without raising the glass transition temperature as much as would an equivalent amount of additional HFP The dipolymer is random except that there are no contiguous HFP units and can therefore be represented as follows... 

Gozdz et al. (of Bellcore) [25] recognized that poly (vinylidene difluoride) hexafluoropropylene (PVDF HFP) copolymers could form gels with organic solvents and developed an entire battery based on this concept. Typically, the gel separator is 50 pm thick and comprises 60wt. % polymer. In the Bellcore process the separator is laminated to the electrodes under pressure at elevated temperature. The use of the PVDF HFP gelling agent increases the resistivity of the electrolyte by about five times which limits the rate capability of such batteries. 

PVDF has properties similar to PTFE but is easier to fabricate. It has good resistance to inorganic acids and alkalis, and organic solvents. It is limited to a maximum operating temperature of 140°C. 

Capacitors made of high-surface carbon with PVdF-co-HFP as a binder and filled with neat ionic liquids, without any molecular solvent, show high specific capacity, up to 180 F/g [13],... 

The electrodes were prepared by mixing graphite powder with the NMP-predissolved PVDF binder (grade KF 9306, available from KUREHA Advanced Materials Div., Tokyo, Japan) at the ratio 9/1 of C/PVDF, respectively. The viscosity of the slurry was adjusted at 5,000 cps by adding more solvent (NMP). 

The electrodes for examination were produced by smearing of suspension of active materials in the solution of binding substance -po 1 yviny 1 idcncfluoride (PVDF) - on the metal substrate by means of applicator "Doctor Blade" by Hohsen Corp. N-methyl-2-pyrrolidone was used as the solvent for the binding substance. 

For manufacturing of negative electrodes, suspensions containing 45wt% powder of the carbon material being examined, 5wt% PVDF, and 50wt% of the solvent. Copper foil with thickness of 0,02 mm was applied as substrate. 

For manufacturing of positive electrodes, pastes with the following ratio of the ingredients were applied Lithium cobaltate by Merck or by "Baltiyskaya Manufaktura" (Russia) - 42,5wt%, conductive additive (acethylene soot) - 3,5wt%, PVDF - 4wt%, solvent - the balance. Aluminium foil with the thickness of 0,02 mm was used as a current collector. 

The anodes of these two graphite samples were fabricated from a slurried mixture which contains 92 wt% of active graphite powder and 8wt% polyvinylidene difluoride (PVDF) polymer binder (Kureha 9130) and using 1 -methyl-2-pyrrolidinone (NMP) (Aldrich, >99%) as the solvent. After getting the homogenous slurry, the electrode laminates were coated on Cu current collector foil using a doctor blade in the laboratory-made laminate-coater. The laminates were then dried first at 75°C in air for 3 hrs and then the final heat treatment was carried out in a vacuum oven at 75 C for 10 hrs. Finally, the laminates were calendared to about 35% porosity in a dry room. 

PVDFs are not sensitive to most strong mineral and organic acids, oxidizing agents, aromatic and aliphatic hydrocarbons, some halogenated solvents, alcohols, bromine, metal salt solutions, or weak bases. 

Polyvinylidene fluoride (PVDF) Aqueous and/or organic samples resistant to common HPLC solvents... 

Apparently, the formation of the microporous structure within the PVdF—HFP copolymer was of critical importance to the success of Bellcore technology, and the ion conductivity was proportional to the uptake of the liquid electrolyte. To achieve the desired porosity of PVdF film, Bellcore researchers prepared the initial polymer blend of PVdF with a plasticizer dibutylphthalate (DBP), which was then extracted by low boiling solvents after film formation. Thus, a pore-memory would be left by the voids that were previously occupied by DBP. However, due to the incomplete dissolution of such high-melting DBP during the extraction process, the pore-memory could never be restored at 100% efficiency. Beside the total volume of pores thus created by the plasticizer. 

The processability of fluorine-containing polymers is improved by replacement of one or more of the fluorine atoms. Replacing one of the eight fluorine atoms with a trifluoromethyl group gives a product called FEP or Viton, actually a copolymer of tetrafluoroethylene and hexafluoropropylene (Equation 6.53). Polytrifluoromonochloroethylene (PCTFE, Kel F) (Equation 6.54), in which one fluorine atom has been replaced by a chlorine atom, has a less regular structure and is thus more easily processed. Poly(vinylidene fluoride) (PVDF, Kynar) (Equation 6.55) is also more easily processable but less resistant to solvents and corrosives. 

A composition containing at least 70 wt % of PVDF and about 30 wt % of acrylic resin has been recommended as a standard coating formulation. The recommended formulation is designed to provide coatings with optimized physical properties and a resistance to the effects of long-term environmental exposure. In addition to internal research results, a literature search was done to confirm that this composition provides the best balance of optical properties, solvent resistance, hardness, mechanical strength, and weatherability. 

Two methods, annealing and film-casting by slow solvent evaporation, have been used effectively to develop maximum crystallinity in PVDF blends. The... 

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