Flash spinning process and flash spinning fluid

Abstract

The present invention relates to (i) a spin fluid for flash spinning a polyvinylidene fluoride (PVDF) or polyvinylidene fluoride blends from a spin agent comprising dichloromethane and a cyclic hydrofluorocarbon, and (ii) to a process for the preparation of plexifilamentary fibrils of PVDF or PVDF blends using the spin fluid.

Description

[0001] TITLE

[0002] FLASH SPINNING PROCESS AND FLASH SPINNING FLUID

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to (i) a spin fluid for flash spinning a polyvinylidene fluoride (PVDF) or polyvinylidene fluoride blends from a spin agent comprising dichloromethane and a cyclic hydrofluorocarbon, and (ii) to a process for the preparation of plexifilamentary fibrils of PVDF or PVDF blends using the spin fluid.

[0005] BACKGROUND

[0006] Polyvinylidene fluoride (PVDF) is a polymer with very good chemical and temperature resistance which is of benefit in many applications, for example, in filtration applications where PVDF is frequently used in the form of fibrils. Furthermore, PVDF may exhibit useful piezoelectric properties if it is induced to adopt a crystal phase known as the p crystal phase. However, the p phase is thermodynamically unstable and can only be formed by elaborate processing steps involving heating and / or stretching the material in a strong electric field, or by precipitating PVDF polymer in a controlled manner from highly polar solvents.

[0007] Flash spinning is a process for producing fibrils that involves the following steps: (i) dissolving a polymer in a composition comprising one or more solvents (often called a spin agent), at elevated temperature and pressure to form a homogeneous solution (often called a spin fluid), (ii) reducing the pressure sufficiently below the spin fluid’s cloud point pressure (i.e., the pressure at which the spin fluid transitions from a clear solution to a cloudy, two-phase dispersion), while still maintaining sufficient pressure to prevent the spin fluid from reaching its bubble point pressure (i.e., the pressure at which the spin agent in the spin fluid begins to boil), (iii) releasing the resulting dispersion continuously through one or more orifices into a lower pressure region at or near atmospheric temperature and pressure so that the spin agent flash evaporates as it emerges from the one or more orifices, (iv) collecting the polymer which remains as a stream of fibrils, e.g., plexifilamentary fibrils, and (v) recovering the evaporated spin agent for re-use. Examples of flash spinning processes are disclosed in US 3,081 ,519 and US 3,227,794.

[0008] In a commercial flash spinning process, the spin agent’s solvent properties and physical properties are critical. In particular, the solvent properties of the spin agent determine whether and under what conditions fibrils are produced in the flash spinning process, and the spin agent’s physical properties impact the process for recovering and re-using the spin agent. The process for recovering spin agents typically involves a step in which the spin agent is condensed from the gas state to the liquid state. During this step, it is preferred that the composition of the spin agent remains essentially constant. This is inherent when spin agents comprise only one solvent but not when spin agents comprise two or more solvents, which are often required to provide the necessary solvent properties for flash spinning the desired polymer.

[0009] One example of a solvent that can be used with PVDF is dichloromethane (DCM). However, at practical operating temperatures, DCM is too strong of a solvent and cannot be used as the only component in a spin agent composition for flash spinning because it dissolves polymers at relatively low pressures. Weaker solvents such as fluorocarbons or hydrofluorocarbons can be mixed with DCM to reduce the solvent strength of the spin agent and to increase the spin fluid’s cloud point pressure such that flash spinning can be readily accomplished.

[0010] When a fluorocarbon or hydrofluorocarbon is added to DCM to form a spin agent composition, thereby reducing the solvent power of the spin agent and producing a suitable cloud point, the cloud point pressure of the spin agent composition becomes very sensitive to the amount of fluorocarbon or hydrofluorocarbon in the spin agent composition and precise control of the spin agent composition becomes of great importance. US 6,004,672 discloses that polyolefins such as polyethylene and polypropylene can be spun from a spin agent comprising DCM and the linear hydrofluorocarbon HFC-4310mee (1,1 ,1 ,2,2,3,4,5,5,5-decafluoropentane). US 7,179,413 describes that various polymers, such as polyethylene, polypropylene, and polyvinylidene fluoride (PVDF), can be spun from a spin agent comprising DCM and the linear hydrofluorocarbon PFMCP (3,3,4,4,5,5,6,6,6-nonafluoro-1-hexene). However, both documents teach that the cloud point pressure increases significantly with small increases in the amount of the linear hydrofluorocarbon in the spin agent composition.

[0011] Another important factor to be considered when selecting components for spin agents is their global warming potential (GWP), where a lower value is to be desired. Many fluorinated solvents which give suitable cloud point pressures for flash-spinning when blended with dichloromethane unfortunately have a high GWP. WO 2016 / 200873 A1 suggests mixtures of dichloromethane as a primary spin agent with 1 H,6H-perfluorohexane, 1H-perfluorohexane or 1 H-perfluoroheptane as secondary spin agent. US 7,300,968 describes flash spinning of PVDF using mixtures of DCM and HFC-365mfc (1,1 ,1 ,3,3-pentafluorobutane) as spin agent. However, using such linear hydrofluorocarbons as spin agent component has the disadvantage that these compounds often exhibit an undesirable high global warming potential (GWP) of 1000 or higher. In view of the growing concerns due to regulatory requirements there is a need for finding suitable low GWP replacements for currently used spin agents.

[0012] It is therefore an object of the present invention to provide a spin fluid for flash spinning comprising (i) PVDF or PVDF blends, and (ii) a spin agent comprising DCM and a cyclic hydrofluorocarbon, wherein the cloud point pressure of the spin fluid does not significantly increase as the amount of the hydrofluorocarbon in the spin agent composition increases, and the spin agent has a low GWP. It is a further object of the present invention to provide a spin fluid comprising PVDF or PVDF blends where the crystal phase present in the PVDF in the fibrils resulting from flash spinning is predominantly the p phase.

[0013] SUMMARY OF THE INVENTION

[0014] In one embodiment the invention is directed to a spin fluid for flash spinning comprising (a) from about 10 to about 35 weight percent of a polyvinylidene fluoride or a polyvinylidene fluoride blend, based on the total amount of the spin fluid, and (b) a spin agent, wherein the spin agent (i) comprises dichloromethane and a cyclic hydrofluorocarbon.

[0015] In a further embodiment the present invention is directed to a to a process for the preparation of plexifilamentary fibrils of polyvinylidene fluoride or polyvinylidene fluoride blend. The process comprises the steps of:

[0016] (i) generating a spin fluid comprising

[0017] (a) from 10 to 35 weight percent of a polyvinylidene fluoride or a polyvinylidene fluoride blend, based on the total amount of the spin fluid, and

[0018] (b) a spin agent, and

[0019] (ii) flash-spinning the spin fluid at a pressure that is above the vapor pressure of the spin fluid into a region of essentially atmospheric pressure to form plexifilamentary fibrils of polyvinylidene fluoride or polyvinylidene fluoride blend, wherein the spin agent comprises dichloromethane and a cyclic hydrofluorocarbon.

[0020] BRIEF DESCRIPTION OF THE FIGURES

[0021] Fig. 1 shows the cloud point pressure of spin fluids comprising 26 wt% polyvinylidene fluoride (PVDF) and different spin agents comprising DCM in combination with different linear and cyclic fluorinated compounds depending on the relative amounts of the fluorinated compound in the spin agents.

[0022] Fig. 2 shows the cloud point pressure of spin fluids comprising 26 wt% polyvinylidene fluoride (PVDF) and different spin agents comprising DCM in combination with different cyclic fluorinated compounds depending on the relative amounts of the fluorinated compound in the spin agents.

[0023] Fig. 3 shows the cloud point pressure of spin fluids comprising 26 wt% polyvinylidene fluoride (PVDF) and 12 wt% polyethylene (PE) and different spin agents comprising DCM in combination with linear and cyclic fluorinated compounds depending on the relative amounts of the fluorinated compound in the spin agent.

[0024] Fig. 4 shows the cloud point pressure of spin fluids comprising 26 wt% polyvinylidene fluoride (PVDF) and 12 wt% polyethylene (PE) and different spin agents comprising DCM in combination with different linear fluorinated compounds depending on the relative amounts of the fluorinated compound in the spin agent.

[0025] DETAILED DESCRIPTION

[0026] Definitions and Clarification of Terms

[0027] Before addressing details of embodiments, some terms and test methods are defined or clarified. Unless otherwise mentioned, all tests were carried out without preconditioning of the samples. When average values are indicated herein, this refers to the arithmetic average.

[0028] Density is determined according to the method described in ISO 1183 (Plastics - Methods for determining the density of non-cellular plastics).

[0029] Melting temperature is determined by differential scanning calorimetry, following the guidance provided in ASTM D3418 (Standard Test Method for Transition Temperatures and Enthalpies of Fusion and Crystallization of Polymers by Differential Scanning Calorimetry). For PVDF, heating and cooling is performed under inert gas at a rate of 10 °C / minute, heating the sample first from room temperature to 230 °C, then cooling the sample back to room temperature and subsequently heating the sample a second time to 230 °C. The melting point reported herein is the peak temperature of the endotherm of the second heating cycle. The melt flow rate for polyvinylidene fluoride is determined according to the method described in ASTM D1238 (Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastometer) at a temperature of 230 °C and using a mass of 3.8 kg, 5.0 kg, or 12.5 kg.

[0030] The total crystallinity index is determined as follows. A diffractometer in reflection 0-20 Bragg- Brentano geometry (htp: / / ris .mit.edu xray / oldsite / Basics%20of%20X- Ray%20Powder%20Diffraction.pdf) is fitted with a Cu-Kax-ray tube source with a wavelength of 1.54 A and a 1-dimensional detector. A parabolic mirror with a 1 / 16° fixed slit and 10mm mask is used to create a parallel incident x-ray beam while a fixed slit of 1 / 8°, Soller slits of 0.04 rad, and a nickel Cu-Kpfilter are employed on the diffracted side before the detector. Each sample is mounted onto low background, flat silicon wafer holders. The sample holder is mounted horizontally at the center of the diffractometer and normal to the scattering vector. During the measurement, the sample rotates in this plane.

[0031] PVDF can crystallize in three different crystal phases -the a, (3, and y. The different crystal phases have distinct scattering peaks (see ICDD Database ICDD PDF-4+ database - PDF - 00- 061-1403, 00-061-1404, 00-061-1406. Gates-Rector, S.; Blanton, T. The Powder Diffraction File: A Quality Materials Characterization Database. Powder Diffr. 2019, 34 (4), 352-360). The strongest intensity peaks for each phase are summarized in the following table.

[0032] The procedure as described below is used to determine the crystallinity index of the PVDF samples using MATLAB. The scattering angle 20 of the diffraction peaks can vary by about + / - .2° due to instrumental differences and sample height / texture.

[0033] 1. An empty background scan (Si wafer only) is scaled and subtracted from the sample data such that the height of the baseline (in counts) is equivalent at two points - 10° and 29° 20.

[0034] 2. A local linear background, drawn from 20 = 10° to 29° in scattering angle, is then subtracted, to bring the baseline down to zero counts.

[0035] 3. Next, based on comparison to known PVDF crystal XRD patterns, the predominant phase(s) present are chosen. Only these crystalline peaks will be fit. 4. The full pattern is fit in the range of 20 = 10° to 29° with the chosen crystalline peaks and one amorphous peak, all of Pearson VII shape. In the examples, in the current case, no scattering peak is observed for a scattering angle of 29 = 26.7-26.8°, indicating no significant portions of the a or y crystal phases are present. No significant portion means that the integrated intensity in the range of 20 = 26.7-26.8° is below 2 % of the total integrated intensity in the range of 29 = 10° to 29°. The scattering intensity is then:

[0036] 1) Amorphous peak: 18.6°, Pearson VII peak shape, lamorPhous, and

[0037] 2) p 110 / 200 superimposed peak: 20.5°, Pearson VII peak shape, lp,no / 2oo.

[0038] The amorphous peak parameters are limited to FWHM >3° and 1<M<2, while the crystalline peak parameters are limited to FWHM<2° and 1 <M<10, where FWHM is full-width at half maximum and M is the Pearson VII shape parameter.

[0039] 5. The total crystallinity index is calculated from the ratio of crystalline scattering to total scattering. The crystalline scattering is defined as the sum of the integrated intensities from the crystalline peaks of all phases present in the fit angle range. The total scattering is defined as the sum of the integrated intensity of crystalline and amorphous peaks. In this case, where no significant portions of the a or y crystal phases are found, it is justified to define a crystallinity index (Cl) as the quotient of the integrated intensity of the only crystal phase present, i.e., pure p phase, divided by the sum of the integrated intensity of the p phase and amorphous peaks: crystallinity index=C / = - P, 110 / 200 -

[0040] ‘P, 110 / 200 T 'amorphous

[0041] The term “polymer” is intended to embrace, without limitation, homopolymers, copolymers (such as for example, block, graft, random, and alternating copolymers), terpolymers, etc., and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term “polymer” shall include all possible geometrical configurations of the material. These configurations include, but are not limited to, isotactic, syndiotactic, and random symmetries.

[0042] The term “polyvinylidene fluoride” (PVDF) is intended to embrace not only homopolymers of vinylidene fluoride but also copolymers where at least 70% of the recurring units are vinylidene fluoride units.

[0043] The term “polyvinylidene fluoride blend” (PVDF blend) is intended to embrace, without limitation, polymer blends comprising from about 5 to about 95 weight percent, or from about 20 to about 80 weight percent, of PVDF and from about 95 to about 5 weight percent, or from about 80 to about 20 weight percent, of one or more polyolefins, such as polyethylene or polypropylene.

[0044] The term “polyethylene” is intended to embrace not only homopolymers of ethylene, but also copolymers and terpolymers wherein at least 85% of the recurring units are ethylene units, and the comonomer unit is, for example, propylene, butylene, hexene or octene. One useful polyethylene is high-density polyethylene that has a melting temperature of about 123 °C to about 140 °C, a density in the range of 0.94 to 0.98 grams per cubic centimeter, and a melt flow rate (ISO 1133, 190 °C / 2160 grams) of between 0.05 g / 10 min and 30 g / 10 min, preferably less than 4 g / 10 min, and / or a melt flow rate (ISO 1133, 190 °C / 21 ,600 grams) of between 1 g / 10min and 15 g / 10min.

[0045] The term “polypropylene” is intended to embrace not only homopolymers of propylene but also copolymers and terpolymers where at least 85% of the recurring units are propylene units. Furthermore, unless otherwise specifically limited, the term “polypropylene” shall include all possible geometrical configurations of the material. These configurations include, but are not limited to, isotactic, syndiotactic, and random symmetries.

[0046] The term “1 H,2H-octafluorocyclopentane” (“OFCP”) is intended to embrace, without limitation, the cis-isomer, trans-isomer, or any combination or mixture of both isomers in any ratio.

[0047] The term “plexifilamentary” refers to a three-dimensional integral network or web of a multitude of thin, ribbon-like, fibrils of random length and a median fibril width of less than about 25 microns. In plexifilamentary structures, the fibrils are generally coextensively aligned with the longitudinal axis of the structure, and they intermittently unite and separate at irregular intervals in various places throughout the length, width, and thickness of the structure to form a continuous three-dimensional network or web.

[0048] The terms “spin agent” or “spin agent composition” refers to a composition comprising one or more solvents and any additives that are used to initially dissolve the polymer(s) to form the spin fluid. Suitable additives include stabilizers, such as antioxidants or acid scavengers.

[0049] The term “spin fluid” refers to a solution for spinning in a flash spinning process comprising a polymer and a spin agent. The solution may also include one or more additives.

[0050] The term “cloud point pressure” refers to the pressure at which, at constant temperature, a clear single phase spin fluid transitions from a clear solution to a cloudy, two-phase dispersion. At the cloud point pressure, a clear spin fluid becomes turbid.

[0051] Atmospheric pressure means 101.325 kPa. Essentially atmospheric pressure means

[0052] 101.325 kPa ± 5 %. As used herein, the singular forms “a”, “an”, and “the” include the plural, and reference to a particular numerical value includes at least that particular value, unless the context clearly dictates otherwise. When a range of values is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another embodiment. All ranges are inclusive and combinable.

[0053] Spin Agents and Spin Fluids for Flash Spinning a Polyvinylidene Fluoride or a Polyvinylidene Fluoride Blend

[0054] Provided herein are spin fluids for flash spinning a polyvinylidene fluoride (PVDF) or a polyvinylidene fluoride blend (PVDF blend).

[0055] In some embodiments, the spin fluid for flash spinning a PVDF or a PVDF blend comprises (a) from about 10 to about 35 weight percent of a PVDF or a PVDF blend, based on the total amount of the spin fluid, and (b) a spin agent, wherein the spin agent comprises and a cyclic hydrofluorocarbon. In other embodiments, the spin fluid for flash spinning a PVDF or a PVDF blend comprises (a) from about 15 to about 35 weight percent of a PVDF or a PVDF blend, based on the total amount of the spin fluid, and (b) a spin agent, wherein the spin agent comprises dichloromethane and a cyclic hydrofluorocarbon, and in other embodiments, the spin fluid for flash spinning a PVDF or a PVDF blend comprises (a) from about 20 to about 30 weight percent of a PVDF or a PVDF blend, based on the total amount of the spin fluid, and (b) a spin agent, wherein the spin agent comprises dichloromethane and a cyclic hydrofluorocarbon.

[0056] In some embodiments, the spin fluid for flash spinning a PVDF or a PVDF blend comprises from about 65 to about 90 weight percent of the spin agent, based on the total amount of the spin fluid, in other embodiments from about 65 to about 85 weight percent, based on the total amount of the spin fluid, and in other embodiments from about 70 to about 80 weight percent, based on the total amount of the spin fluid.

[0057] In some embodiments the cyclic hydrofluorocarbon is 1 H , 1 H,2H-heptafluorocyclopentane. In other embodiments, the cyclic hydrofluorocarbon is 1 H, 2H-octafluorocyclopentane.

[0058] In some embodiments, the spin fluid for flash spinning comprises (a) from about 10 to about 35 weight percent of a PVDF or a PVDF blend, based on the total amount of the spin fluid, and (b) a spin agent, wherein the spin agent comprises dichloromethane and 1H,1 H,2H- heptafluorocyclopentane. In other embodiments, the spin fluid comprises (a) from about 15 to about 35 weight percent of a PVDF or a PVDF blend, based on the total amount of the spin fluid, and (b) a spin agent, wherein the spin agent comprises dichloromethane and 1H,1 H,2H- heptafluorocyclopentane, and in other embodiments, the spin fluid comprises (a) from about 20 to about 30 weight percent of a PVDF or a PVDF blend, based on the total amount of the spin fluid, and (b) a spin agent, wherein the spin agent comprises dichloromethane and 1H,1 H,2H- heptafluorocyclopentane.

[0059] In some embodiments, the spin agent comprises from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,1H,2H- heptafluorocyclopentane, in other embodiments from about 40 to about 65 weight percent dichloromethane and from about 60 to about 35 weight percent 1 H,1H,2H- heptafluorocyclopentane, and in other embodiments from about 40 to about 55 weight percent dichloromethane and from about 60 to about 45 weight percent 1 H,1H,2H- heptafluorocyclopentane. In some embodiments, the spin agent comprises from about 60 to about 80 weight percent dichloromethane and from about 40 to about 20 weight percent 1H,1 H,2H- heptafluorocyclopentane, in other embodiments from about 65 to about 80 weight percent dichloromethane and from about 35 to about 20 weight percent 1 H,1H,2H- heptafluorocyclopentane, and in other embodiments from about 70 to about 80 weight percent dichloromethane and from about 30 to about 20 weight percent 1 H,1H,2H- heptafluorocyclopentane.

[0060] In some embodiments, the spin agent consists essentially of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1H,1 H,2H- heptafluorocyclopentane, in other embodiments from about 40 to about 65 weight percent dichloromethane and from about 60 to about 35 weight percent 1 H,1H,2H- heptafluorocyclopentane, and in other embodiments from about 40 to about 55 weight percent dichloromethane and from about 60 to about 45 weight percent 1 H,1H,2H- heptafluorocyclopentane. In some embodiments, the spin agent consists essentially of from about 60 to about 80 weight percent dichloromethane and from about 40 to about 20 weight percent 1 H,1 H,2H-heptafluorocyclopentane, in other embodiments from about 65 to about 80 weight percent dichloromethane and from about 35 to about 20 weight percent 1H,1 H,2H- heptafluorocyclopentane, and in other embodiments from about 70 to about 80 weight percent dichloromethane and from about 30 to about 20 weight percent 1 H,1H,2H- heptafluorocyclopentane.

[0061] In some embodiments, the spin agent consists of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,1H,2H- heptafluorocyclopentane, in other embodiments from about 40 to about 65 weight percent dichloromethane and from about 60 to about 35 weight percent 1 H,1H,2H- heptafluorocyclopentane, and in other embodiments from about 40 to about 55 weight percent dichloromethane and from about 60 to about 45 weight percent 1 H,1H,2H- heptafluorocyclopentane. In some embodiments, the spin agent consists of from about 60 to about 80 weight percent dichloromethane and from about 40 to about 20 weight percent 1 H,1 H,2H-heptafluorocyclopentane, in other embodiments from about 65 to about 80 weight percent dichloromethane and from about 35 to about 20 weight percent 1H,1 H,2H- heptafluorocyclopentane, and in other embodiments from about 70 to about 80 weight percent dichloromethane and from about 30 to about 20 weight percent 1 H,1H,2H- heptafluorocyclopentane.

[0062] In some embodiments, the spin fluid for flash spinning comprises (a) from about 10 to about 35 weight percent of a PVDF or a PVDF blend, based on the total amount of the spin fluid, and (b) a spin agent, wherein the spin agent comprises dichloromethane and 1 H,2H- octafluorocyclopentane. In other embodiments, the spin fluid comprises (a) from about 15 to about 35 weight percent of a PVDF or a PVDF blend, based on the total amount of the spin fluid, and (b) a spin agent, wherein the spin agent comprises dichloromethane and 1 H,2H- octafluorocyclopentane, and in other embodiments, the spin fluid comprises (a) from about 20 to about 30 weight percent of a PVDF or a PVDF blend, based on the total amount of the spin fluid, and (b) a spin agent, wherein the spin agent comprises dichloromethane and 1 H,2H- octaf I uo rocy cl o pe nta ne .

[0063] In some embodiments, the spin agent comprises from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,2H-octafluorocyclopentane, in other embodiments from about 40 to about 65 weight percent dichloromethane and from about 60 to about 35 weight percent 1 H,2H-octafluorocyclopentane, and in other embodiments from about 40 to about 55 weight percent dichloromethane and from about 60 to about 45 weight percent 1 H,2H-octafluorocyclopentane. In some embodiments, the spin agent comprises from about 60 to about 80 weight percent dichloromethane and from about 40 to about 20 weight percent 1 H,2H-octafluorocyclopentane, in other embodiments from about 65 to about 80 weight percent dichloromethane and from about 35 to about 20 weight percent 1 H,2H- octafluorocyclopentane, and in other embodiments from about 70 to about 80 weight percent dichloromethane and from about 30 to about 20 weight percent 1 H,2H-octafluorocyclopentane.

[0064] In some embodiments, the spin agent consists essentially of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1H,2H- octafluorocyclopentane, in other embodiments from about 40 to about 65 weight percent dichloromethane and from about 60 to about 35 weight percent 1 H,2H-octafluorocyclopentane, and in other embodiments from about 40 to about 55 weight percent dichloromethane and from about 60 to about 45 weight percent 1 H,2H-octafluorocyclopentane. In some embodiments, the spin agent consists essentially of from about 60 to about 80 weight percent dichloromethane and from about 40 to about 20 weight percent 1 H,2H-octafluorocyclopentane, in other embodiments from about 65 to about 80 weight percent dichloromethane and from about 35 to about 20 weight percent 1 H,2H-octafluorocyclopentane, and in other embodiments from about 70 to about 80 weight percent dichloromethane and from about 30 to about 20 weight percent 1H,2H- octafluorocyclopentane.

[0065] In some embodiments, the spin agent consists of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,2H-octafluorocyclopentane, in other embodiments from about 40 to about 65 weight percent dichloromethane and from about 60 to about 35 weight percent 1 H,2H-octafluorocyclopentane, and in other embodiments from about 40 to about 55 weight percent dichloromethane and from about 60 to about 45 weight percent 1 H,2H-octafluorocyclopentane. In some embodiments, the spin agent consists of from about 60 to about 80 weight percent dichloromethane and from about 40 to about 20 weight percent 1 H,2H-octafluorocyclopentane, in other embodiments from about 65 to about 80 weight percent dichloromethane and from about 35 to about 20 weight percent 1 H,2H- octafluorocyclopentane, and in other embodiments from about 70 to about 80 weight percent dichloromethane and from about 30 to about 20 weight percent 1 H,2H-octafluorocyclopentane.

[0066] The compound 1 H,1 H,2H-heptafluorocyclopentane has a reported GWP-100 (global warming potential over a 100-year period) of 231 (IPCC 2021 report), and dichloromethane (DCM) has a reported GWP-100 of 11.2 according to the same source. Accordingly, the spin fluids combining the two compounds have a low global warming potential (GWP). In some embodiments, the compositions combining the two compounds have a GWP-100 (global warming potential over a 100-year period) of less than 150, in other embodiments of less than 115, in other embodiments of less than 90, and in other embodiments of less than 60.

[0067] The compound 1 H,2H-octafluorocyclopentane has a reported GWP-100 (global warming potential over a 100-year period) of 258 (IPCC 2021 report). Accordingly, the spin fluids combining the two compounds have a low global warming potential (GWP). In some embodiments, the compositions combining the two compounds have a GWP-100 (global warming potential over a 100-year period) of less than 160, in other embodiments of less than 125, in other embodiments of less than 100, and in other embodiments of less than 70. The spin fluid compositions as described herein have the advantage of being homogeneous compositions. For homogenous compositions, the components of the composition at ambient temperatures and pressures form a single liquid phase. This is to be contrasted with heterogeneous compositions, where, due to low miscibility of the components of the composition, the components of the composition undergo phase separation in the liquid phase. Phase separation is usually undesired since this leads to more complex and expensive processes. The homogeneous nature of the spin fluids is achievable over a broad range of practical conditions including ambient pressure and temperature.

[0068] In some embodiments, the spin fluid comprises from about 10 to about 35 weight percent of a PVDF or a PVDF blend and from about 90 to about 65 weight percent of the spin agent, each based on the total amount of the spin fluid. In another embodiment, the spin fluid comprises from about 15 to about 35 weight percent of a PVDF or a PVDF blend and from about 85 to about 65 weight percent of the spin agent, each based on the total amount of the spin fluid, and in other embodiments, the spin fluid comprises from about 20 to about 30 weight percent of a PVDF or a PVDF blend and from about 80 to about 70 weight percent of the spin agent, each based on the total amount of the spin fluid.

[0069] In some embodiments, the spin fluid comprises about 10 to about 35 weight percent of a PVDF or a PVDF blend, based on the total amount of the spin fluid, and a spin agent, wherein the spin agent consists essentially of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,1 H,2H-heptafluorocyclopentane.

[0070] In some embodiments, the spin fluid comprises about 10 to about 35 weight percent of a PVDF or a PVDF blend, based on the total amount of the spin fluid, and a spin agent, wherein the spin agent consists essentially of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1H,2H-octafluorocyclopentane.

[0071] The spin fluid may include additives, such as antioxidants or acid scavengers, in minor amounts. In some embodiments, the spin fluid comprises additives in an amount of about 1.5 weight percent or less of the total amount of the spin agent, and in other embodiments in an amount of about 0.1 weight percent or less of the total amount of the spin agent.

[0072] In some embodiments, the spin fluid comprises about 10 to about 35 weight percent of a PVDF or a PVDF blend, based on the total amount of the spin fluid, and a spin agent, wherein the spin agent consists of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,1 H,2H-heptafluorocyclopentane.

[0073] In some embodiments, the spin fluid comprises about 10 to about 35 weight percent of a PVDF or a PVDF blend, based on the total amount of the spin fluid, and a spin agent, wherein the spin agent consists of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,2H-octafluorocyclopentane.

[0074] In some embodiments, the PVDF blend comprises from about 50 to about 95 weight percent PVDF and from about 50 to about 5 weight percent polyethylene and / or polypropylene, and in other embodiments from about 50 to about 80 weight percent PVDF and from about 50 to about 20 weight percent polyethylene and / or polypropylene. In some embodiments, the PVDF blend comprises from about 5 to about 50 weight percent PVDF and from about 95 to about 50 weight percent polyethylene and / or polypropylene, and in other embodiments from about 20 to about 50 weight percent PVDF and from about 80 to about 50 weight percent polyethylene and / or polypropylene.

[0075] In some embodiments, the spin fluid comprising the spin agent as described herein exhibits a cloud point pressure in the range of about 40 to about 300 bar, in other embodiments in the range of about 50 to about 300 bar, and in other embodiments in the range of about 70 to about 300 bar. In some embodiments, the spin fluid comprising the spin agent as described herein exhibits a cloud point pressure in the range of about 45 to about 250 bar, in other embodiments in the range of about 50 to about 250 bar, and in other embodiments in the range of about 70 to about 250 bar. In some embodiments, the spin fluid comprising the spin agent as described herein exhibits a cloud point pressure in the range of about 45 to about 200 bar, in other embodiments in the range of about 50 to about 200 bar, and in other embodiments in the range of about 70 to about 200 bar. The flash spinning process must take place at an operating pressure below the spin fluid’s cloud point pressure but above the spin fluid’s bubble point pressure. If the pressure becomes lower than the spin fluid’s bubble point pressure, premature and unwanted boiling occurs. If the cloud point pressure is above about 300 bar, the flash spinning equipment must be built to withstand very high pressure which increases costs and operational constraints.

[0076] The spin fluids as described herein are advantageous for many reasons. In particular, the spin fluids comprising (i) PVDF or a PVDF blend, and (ii) a spin agent comprising DCM and a cyclic hydrofluorocarbon, utilize spin agents with relatively low GWPs, and the crystal phase present in the PVDF in the fibrils resulting from the flash spinning is predominantly the p phase. In addition, the cloud point pressure of the spin fluids comprising (i) PVDF, and (ii) a spin agent comprising DCM and a cyclic hydrofluorocarbon, does not significantly change with fluctuations in the amount of cyclic hydrofluorocarbon in the spin agent. This results in a flash spinning process which is less sensitive to fluctuations in the spin agent composition and which allows the use of higher amounts of fluorinated components, thereby reducing the volume of vaporized spin agent produced in the flash spinning process. Furthermore, the cloud point pressure with respect to PVDF of the spin fluid comprising (i) a PVDF blend, and (ii) a spin agent comprising DCM and a cyclic hydrofluorocarbon, does not change significantly as the amount of hydrofluorocarbon in the spin agent is varied, allowing for spin agent compositions which are suitable for flash spinning both PVDF and the one or more polyolefins in the PVDF blend.

[0077] Preparation of Plexifilamentary Fibrils of Polyvinylidene Fluoride or Polyvinylidene Fluoride Blend

[0078] In some embodiments, there is provided a process for the preparation of plexifilamentary fibrils of polyvinylidene fluoride (PVDF) or a polyvinylidene fluoride blend (PVDF blend). The process comprises the steps of:

[0079] (i) generating a spin fluid comprising

[0080] (a) about 10 to about 35 weight percent of a polyvinylidene fluoride or a polyvinylidene fluoride blend, based on the total amount of the spin fluid, and

[0081] (b) a spin agent, and

[0082] (ii) flash-spinning the spin fluid at a pressure that is above the vapor pressure of the spin fluid into a region of essentially atmospheric pressure to form plexifilamentary fibrils of polyvinylidene fluoride or polyvinylidene fluoride blend, wherein the spin agent comprises dichloromethane and a cyclic hydrofluorocarbon.

[0083] In some embodiments, the cyclic hydrofluorocarbon is 1 H,1 H,2H- heptafluorocyclopentane. In other embodiments, the cyclic hydrofluorocarbon is 1 H,2H- octafluorocyclopentane.

[0084] In some embodiments, the spin agent comprises or consists essentially of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,1 H,2H-heptafluorocyclopentane, in other embodiments from about 40 to about 65 weight percent dichloromethane and from about 60 to about 35 weight percent 1H,1 H,2H- heptafluorocyclopentane, and in other embodiments from about 40 to about 55 weight percent dichloromethane and from about 60 to about 45 weight percent 1 H,1H,2H- heptafluorocyclopentane. In some embodiments, the spin agent comprises or consists essentially of from about 60 to about 80 weight percent dichloromethane and from about 40 to about 20 weight percent 1 H,1 H,2H-heptafluorocyclopentane, in other embodiments from about 65 to about 80 weight percent dichloromethane and from about 35 to about 20 weight percent 1H,1 H,2H- heptafluorocyclopentane. In some embodiments, the spin agent comprises or consists essentially of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,2H- octafluorocyclopentane, in other embodiments from about 40 to about 65 weight percent dichloromethane and from about 60 to about 35 weight percent 1 H,2H-octafluorocyclopentane, and in other embodiments from about 40 to about 55 weight percent dichloromethane and from about 60 to about 45 weight percent 1 H,2H-octafluorocyclopentane. In some embodiments, the spin agent consists essentially of from about 60 to about 80 weight percent dichloromethane and from about 40 to about 20 weight percent 1 H,2H-octafluorocyclopentane, in other embodiments from about 65 to about 80 weight percent dichloromethane and from about 35 to about 20 weight pe rce nt 1 H , 2 H -octafl uorocyclopentane.

[0085] The spin fluid may include additives, such as antioxidants or acid scavengers in minor amounts. In some embodiments, the spin fluid comprises additives in an amount of about 1.5 weight percent or less, based on the total amount of the spin fluid, and in other embodiments in an amount of about 0.1 weight percent or less, based on the total amount of the spin fluid.

[0086] In some embodiments, the spin agent consists of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,1H,2H- heptafl uorocyclopentane, in other embodiments from about 40 to about 65 weight percent dichloromethane and from about 60 to about 35 weight percent 1 H,1H,2H- heptafl uorocyclopentane, and in other embodiments from about 40 to about 55 weight percent dichloromethane and from about 60 to about 45 weight percent 1 H,1H,2H- heptafl uorocyclopentane. In some embodiments, the spin agent consists of from about 60 to about 80 weight percent dichloromethane and from about 40 to about 20 weight percent 1 H,1 H,2H-heptafluorocyclopentane, in other embodiments from about 65 to about 80 weight percent dichloromethane and from about 35 to about 20 weight percent 1H,1 H,2H- heptafl uorocyclopentane.

[0087] In some embodiments, the spin agent consists of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,2H-octafluorocyclopentane, in other embodiments from about 40 to about 65 weight percent dichloromethane and from about 60 to about 35 weight percent 1 H,2H-octafluorocyclopentane, and in other embodiments from about 40 to about 55 weight percent dichloromethane and from about 60 to about 45 weight percent 1 H,2H-octafluorocyclopentane. In some embodiments, the spin agent consists of from about 60 to about 80 weight percent dichloromethane and from about 40 to about 20 weight percent 1 H,2H-octafluorocyclopentane, in other embodiments from about 65 to about 80 weight percent dichloromethane and from about 35 to about 20 weight percent 1 H,2H- octafluorocyclopentane.

[0088] In some embodiments, the flash-spinning is performed at a pressure in the range of about 40 to about 300 bar, or in the range of about 50 to about 300 bar, or in the range of about 70 to about 300 bar. In some embodiments, the flash-spinning is performed at a pressure in the range of about 45 to about 250 bar, in other embodiments in the range of about 50 to about 250 bar, and in other embodiments in the range of about 70 to about 250 bar. In some embodiments, the flash-spinning is performed at a pressure in the range of about 45 to about 200 bar, in other embodiments in the range of about 50 to about 200 bar, and in other embodiments in the range of about 70 to about 200 bar. The region of lower pressure into which flash spinning occurs is usually at or around atmospheric pressure.

[0089] In some embodiments, the spin fluid comprises from about 65 to about 90 weight percent of the spin agent, based on the total amount of the spin fluid, in other embodiments from about 65 to about 85 weight percent, based on the total amount of the spin fluid, and in other embodiments from about 70 to about 80 weight percent, based on the total amount of the spin fluid.

[0090] In some embodiments, the spin fluid comprises from about 10 to about 35 weight percent of a PVDF or a PVDF blend, and from about 90 to about 65 weight percent of the spin agent. In another embodiment, the spin fluid comprises from about 15 to about 35 weight percent of a PVDF or a PVDF blend and from about 85 to about 65 weight percent of the spin agent, and in other embodiments, the spin fluid comprises from about 20 to about 30 weight percent of a PVDF or a PVDF blend and from about 80 to about 70 weight percent of the spin agent.

[0091] In some embodiments, the spin fluid comprises about 10 to about 35 weight percent of a PVDF or a PVDF blend, based on the total amount of the spin fluid, and a spin agent, wherein the spin agent consists essentially of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,1 H,2H-heptafluorocyclopentane.

[0092] In some embodiments, the spin fluid comprises about 10 to about 35 weight percent of a PVDF or a PVDF blend, based on the total amount of the spin fluid, and a spin agent, wherein the spin agent consists essentially of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1H,2H-octafluorocyclopentane.

[0093] The spin fluid may include additives, such as antioxidants or acid scavengers, in minor amounts. In some embodiments, the spin fluid comprises additives in an amount of about 1.5 weight percent or less of the total amount of the spin agent, and in other embodiments in an amount of about 0.1 weight percent or less of the total amount of the spin agent. In some embodiments, the spin fluid comprises about 10 to about 35 weight percent of a PVDF or a PVDF blend, based on the total amount of the spin fluid, and a spin agent, wherein the spin agent consists of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,1 H,2H-heptafluorocyclopentane.

[0094] In some embodiments, the spin fluid comprises about 10 to about 35 weight percent of a PVDF or a PVDF blend, based on the total amount of the spin fluid, and a spin agent, wherein the spin agent consists of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,2H-octafluorocyclopentane.

[0095] In some embodiments, the PVDF blend comprises from about 50 to about 95 weight percent PVDF and from about 50 to about 5 weight percent polyethylene and / or polypropylene, and in other embodiments from about 50 to about 80 weight percent PVDF and from about 50 to about 20 weight percent polyethylene and / or polypropylene. In some embodiments, the PVDF blend comprises from about 5 to about 50 weight percent PVDF and from about 95 to about 50 weight percent polyethylene and / or polypropylene, and in other embodiments from about 20 to about 50 weight percent PVDF and from about 80 to about 50 weight percent polyethylene and / or polypropylene.

[0096] In some embodiments, there is provided plexifilamentary fibrils of polyvinylidene fluoride or polyvinylidene fluoride blend obtainable by the process described herein. In some embodiments, the plexifilamentary fibrils obtainable by the process described herein are characterized in that the only detectable PVDF crystal phase, i.e. , the only PVDF crystal phase having significant intensities in the range of 20 = 10° to 29°, is the p crystal phase, whereas no significant portions of the a or y crystal phases are detectable. This is advantageous in electrical applications. In some embodiments, the crystallinity index (P phase) is about 32 % or more, or 34 % or more, or 35 % or more.

[0097] The shape of the assembly of plexifilamentary fibrils of polyvinylidene fluoride or polyvinylidene fluoride blend discharged from each spin orifice may be modified by any methods known in the art. In some embodiments, the plexifilamentary fibrils of polyvinylidene fluoride or polyvinylidene fluoride blend discharged from each spin orifice may be modified by passing into a shroud such as described on US 3,387,326, in other embodiments by passing into a slotted outlet such as described in US 3,467,744 or US 5,788,993, and in other embodiments passing into a slot fan jet as described in US 8,114,325. In some embodiments, streams of fibrils from multiple orifices may exit via a common slot as described in US 3,564,088. 1 Preparation of Sheets of Nonwoven Flash-spun Plexifilamentary Fibrils by Collection, Consolidation, Bonding, Softening, and Articles Made from Sheets of Nonwoven Flash-spun Plexifilamentary Fibrils

[0098] Sheets comprising plexifilamentary fibrils of polyvinylidene fluoride or polyvinylidene fluoride blend can be formed by any method known in the art. In some embodiments, the stream of fibrils discharged from each spin orifice is directed towards a deflector device which alternately directs the stream of fibrils to the left and right onto a moving collecting device such that the fibrils accumulate in the form of a collected sheet of nonwoven flash-spun plexifilamentary fibrils, formed from fibrils oriented in an overlapping, multi-directional configuration. Deflection of the stream of fibrils may be achieved by any suitable means known in the art, including, but not limited to, those described in US 3,277,526 and US 3,387,326, US 3,169,899, US 3,497,918, US 3,456,156, US 3,593,074, US 3,851 ,023 and US 3,860,369, US 4,148,595, US 5,045,258, US 5,643,524, US 5,731 ,011 , US 5,750,152 and WO92 / 20511. The stream of fibrils may also be laid down to form a collected sheet of nonwoven flash-spun plexifilamentary fibrils without deflection as described in US 5,788,993 and US 8,114,325. The method of forming a collected sheet of nonwoven flash- spun plexifilamentary fibrils may further utilize structures in the spin cell such as those described in US 5,123,983, US 5,296,172, and WO92 / 20511.

[0099] In some embodiments, the streams of fibrils are discharged from spin orifices located on a rotating support, and the fibrils are collected on a collecting belt which surrounds the rotating arrangement circumferentially as described in US 7,118,698, US 7,621 ,731, US 7,786,034, and US 7,998,388.

[0100] In some embodiments, the collected sheet of nonwoven flash-spun plexifilamentary fibrils formed by flash-spinning as described herein may be consolidated by applying a small amount of pressure to the sheet to form a consolidated sheet of nonwoven flash-spun plexifilamentary fibrils. In some embodiments, the sheet may be passed under a roller which applies pressure to the sheet to form a consolidated sheet.

[0101] In some embodiments, a consolidated sheet as described herein is subjected to thermal or mechanical bonding as known in the art to form a thermally or mechanically bonded sheet. Bonding may also be achieved by impregnation of a consolidated sheet with a chemical bonding agent, either throughout the entire sheet, or at isolated points distributed over the sheet, or pattern-wise.

[0102] In some embodiments, the bonded sheet is subjected to a mechanical softening process to obtain a softened sheet of nonwoven flash-spun plexifilamentary fibrils. In some embodiments, an antistatic treatment is applied to the bonded or softened sheet. In some embodiments, the antistatic treatment is applied by applying a coating composition comprising an antistatic compound.

[0103] Further embodiments relate to a multilayer structure comprising at least one sheet of nonwoven flash-spun plexifilamentary fibrils as described herein, and at least one further sheet or a film. In some embodiments, the sheet of nonwoven flash-spun plexifilamentary fibrils as described herein is a collected sheet, a consolidated sheet, a bonded sheet, or a softened sheet.

[0104] The sheet of nonwoven flash-spun plexifilamentary fibrils as described herein has many uses and may be used in a variety of articles and applications, including, but not limited to, multilayer structures packaging material, filtration media, print media, tags and labels, accessories, and electronic devices such as pressure sensors, strain gauges, microphones, actuators, energy harvesters, and nanogenerators.

[0105] EXAMPLES

[0106] A study has been performed for the phase behavior and flash spinning of a polyvinylidene fluoride (PVDF) and a polyvinylidene fluoride blend (PVDF blend). The experimental procedure and results are provided below. These examples are given to illustrate exemplary embodiments of the invention and should not be interpreted as limiting in any way.

[0107] Materials Used

[0108] Dichloromethane (DCM), CAS Nr. of 75-09-2, has an atmospheric boiling point of 39.6 °C and a molecular weight of 84.93 g / mol. The dichloromethane used had a purity level above 99.5 percent by weight.

[0109] 1 H,1 H,2H-heptafluorocyclopentane (HFCP, also known as 1 , 1 ,2, 2, 3,3,4- heptafluorocyclopentane), CAS Number 15290-77-4, has a melting point of 21 °C, an atmospheric boiling point of 82.5 °C and a molecular weight of 196.07 g / mol. The 1 H,1 H,2H- heptafluorocyclopentane used had a purity level of above 99 percent by weight.

[0110] 1 H,2H-octafluorocyclopentane (OFCP, also known as 1 , 1 ,2, 2, 3, 3,4,5- octafluorocyclopentane), CAS Nr. 828-35-3, has an atmospheric boiling point of 37.5 °C and a molecular weight of 214 g / mol. The 1 H,2H-octafluorocyclopentane used was a mixture of trans- 1 H,2H-octafluorocyclopentane and cis-1 H,2H-octafluorocyclopentane and had a purity level of above 98 percent by weight. 2H,3H-decafluoropentane (HFC-4310-mee), CAS Nr. 138495-42-8, has an atmospheric boiling point of 55 °C and a molecular weight of 252.05 g / mol. The 2H,3H-decafluoropentane used had a purity level above 99.5 percent by weight.

[0111] Perfluoro-N-methylmorpholine, CAS Number 382-28-5, has an atmospheric boiling point of 50 °C and a molecular weight of 299 g / mol. The perfluoro-N-methylmorpholine used was obtained from 3M, under the trade name PF5052, and had a purity level of above 98 percent by weight.

[0112] Perfluoro(methylcyclohexane) (PFMCH, also known as trifluoromethylundecafluorocyclohexane), CAS Nr. 355-02-2, has an atmospheric boiling point of 76 °C and a molecular weight of 350.05 g / mol. No analysis was performed for the purity.

[0113] The polyvinylidene fluoride (PVDF) used was Kynar® 720 grade or Kynar® 740 grade from Arkema. The Kynar® 720 has a melt flow rate of 5.0-26.5 g / 10 min (ASTM D1238, 230 °C / 3.8 kg) and a melting point of 165-172 °C. The Kynar® 740 has a melt flow rate of 1.5 - 3.0 g / 10 min (ASTM D1238, 230 °C / 5 kg) and a melting point of 165-172 °C.

[0114] The polyethylene (PE) used was a polyethylene having a density of 0.957 g / cm3(ISO 1183), and melt flow rates of 0.75 g / 10min (ISO 1133 condition D, 190 “C / 2.16 kg) and 22 g / 10min (ISO 1133 condition G, 190 °C / 21.6 kg).

[0115] All polymers were dried during a minimum of 8 hours in a vacuum oven at about 45-50 °C before use.

[0116] Spinning Equipment

[0117] The apparatus used consisted of two high pressure cylindrical chambers, each equipped with a piston which was adapted to apply pressure to the contents of the vessel. The cylinders had an inside diameter of 1.0 inch (25.4 mm) and each had an internal capacity of 50 cubic centimeters. The cylinders were connected to each other at one end through a 3 / 32 inch (2.3 mm) diameter channel and a mixing chamber containing a series of fine mesh screens was used as a static mixer. In the channel, a Type J thermocouple was in contact with the spin fluid to record the temperature. Mixing was accomplished by forcing the contents of the vessel back and forth between the two cylinders through the static mixer. A spinneret assembly with a quick-acting means for opening the orifice was attached to the channel through a tee. The spinneret assembly consisted of a lead hole with a diameter of 0.25 inch (6.3 mm) and a length of about 2.0 inch (50.8 mm), and a spinneret orifice with a diameter of 0.030 inch (0.762 mm) and a length of 0.030 inch (0.762 mm). A pressure transmitter calibrated at the spin temperature was mounted in the lead hole to measure the pressure of the spin fluid. The pistons were driven by a high-pressure hydraulic system.

[0118] In operation, the apparatus was charged with polymer pellets and spin agent and a pressure of at least 50 bar was applied to the pistons to compress the charge and avoid the spin fluid from boiling during subsequent heating. The contents were then heated to mixing temperature and held at that temperature for about 30 to 45 minutes during which time a differential pressure was alternatively established between the two cylinders to repeatedly force the contents through the mixing channel from one cylinder to the other to provide mixing and effective formation of a spin fluid. The spin fluid temperature was then increased to the final spin temperature and held there for about 10 to 20 minutes to equilibrate. The pressure of the spin fluid was kept above the cloud point pressure during mixing and during the increase in temperature from the mixing temperature to the spin temperature. Mixing was continued throughout this period. At the end of the mixing cycle, the accumulator was set to the pressure desired for spinning. Next, the valve between the accumulator and the twin piston assembly was opened to reduce the pressure of the spin fluid to the desired spin pressure, and about two to five seconds later, the spinneret orifice was opened to release the spin fluid into conditions of atmospheric pressure. The delay of about two to five seconds corresponds to the residence time in the letdown chamber in a continuous spinning process. The resultant stream of flash-spun fibrils was collected in a stainless-steel open mesh screen basket. During spinning, the spin pressure was recorded just upstream of the spinneret.

[0119] For cloud point pressure determination, the spinneret assembly was replaced with a view cell assembly containing a 1 / 2 inch (12.3 mm) diameter high-pressure sight glass, through which the contents of the cell could be viewed as they flow through the channel. The window was lit by means of a fiber optic light guide, while the view through the sight glass was displayed using a digital camera. In the cell, a Type J thermocouple was located about 5 mm behind the high- pressure sight glass. The Type J thermocouple and a pressure measuring device located in close proximity to the window measured the pressure and temperature inside the view cell behind the sight glass and the pressure and temperature were continuously monitored by a computer. When, after a period of mixing, a clear, homogeneous spin fluid was established, the temperature was held constant and the differential pressure applied to the pistons was equalized so that the pistons stopped moving. Then, the pressure applied to the spin fluid in the view cell was gradually decreased until phase separation was observed through the sight glass, as the initially clear, homogeneous spin fluid became cloudy in appearance. The temperature and pressure were recorded when the thermocouple became no longer visible. This pressure was the phase separation pressure or cloud point pressure for that spin fluid at that temperature. The pressure was then increased until the spin fluid returned to its transparent state, i.e., until the insoluble phase redissolved, and in this way, two or three repeat cloud point measurements could be made at an approximately constant temperature. Once this data was recorded, mixing was resumed while the spin fluid was heated to the next temperature at which the cloud point pressure was to be measured.

[0120] Results

[0121] Example 1: Cloud point study of PVDF in DCM - HFCP

[0122] Measurements of cloud point pressures using the equipment described above were performed for spin fluids comprising 26 wt% of Kynar® 740 and spin agents of dichloromethane and 1 H,1 H,2H-heptafluorocyclopentane (HFCP) with different compositions in ratios by weight of from 80:20 to 55:45. The cloud point pressures for a temperature of 215 °C are shown in Figures

[0123] 1 , 2, and 3.

[0124] Example 2: Cloud point study of PVDF in DCM - OFCP

[0125] Measurements of cloud point pressures using the equipment described above were performed for spin fluids comprising 26 wt% of Kynar® 740 and spin agents of dichloromethane and 1 H,2H-octafluorocyclopentane (OFCP) with different compositions in ratios by weight of from 80:20 to 43:57. The cloud point pressures for a temperature of 215 °C are shown in Figures 1 and

[0126] 2.

[0127] Comparative Examples 1 and 2: Cloud point studies of PVDF in DCM - ZONYL® PFBE (comparative example 1) and of PVDF in DCM - H FC-4310-mee (comparative example 2)

[0128] Cloud point pressure data at a temperature of 215 °C for spin fluids comprising 12 wt% of Kynar® 760 and spin agents of dichloromethane and 3,3,4,4,5,5,6,6,6-nonafluoro-1-hexene (Zonyl® PFBE) with three different compositions in ratios by weight of 90:10, 85:15, and 80:20 were taken from Figure 5 of US 7,179,413 and are shown in Figures 1 and 4.

[0129] Measurements of cloud point pressures using the equipment described above were performed for spin fluids comprising 12 wt% of Kynar® 740 and spin agents of dichloromethane and 2H,3H-decafluoropentane (HFC-4310-mee) with two different compositions in ratios by weight of 85:15 and 75:25. The cloud point pressures for a temperature of 215 °C are shown in Figures 1 and 3.

[0130] Comparative Examples 3 and 4: Cloud point studies of PVDF in DCM - PFMCH (comparative example 3) and of PVDF in DCM - PF5052 (comparative example 4)

[0131] Measurements of cloud point pressures using the equipment described above were performed for spin fluids comprising 26 wt% of Kynar® 740 and spin agents of dichloromethane and perfluoro(methylcyclohexane) (PFMCH) with two different compositions in ratios by weight of 80:20 and 70:30. The cloud point pressures for a temperature of 215 °C are shown in Figure 2 and 4.

[0132] Measurements of cloud point pressures using the equipment described above were performed for spin fluids comprising 26 wt% of Kynar® 740 and spin agents of dichloromethane and perfluoro-N-methylmorpholine (PF5052) with two different compositions in ratios by weight of 85:15 and 80:20. The cloud point pressures for a temperature of 215 °C are shown in Figure 2.

[0133] Comparative Examples 5 to 6: Cloud point studies of PE in DCM - ZONYL® PFBE (comparative example 5) and of DCM - H FC-4310-mee (comparative example 6)

[0134] Cloud point pressure data at a temperature of 215 °C for spin fluids comprising 12 wt% polyethylene (PE) and spin agents of dichloromethane and 3,3,4,4,5,5,6,6,6-nonafluoro-1-hexene (Zonyl® PFBE) with two different compositions in ratios by weight of 85:15 and 80:20 were taken from Figure 9 of US 7,179,413 and are shown in Figure 4.

[0135] Cloud point pressure data at a temperature of 215 °C for spin fluids comprising 12 wt% polyethylene (PE) and spin agents of dichloromethane and 2H,3H-decafluoropentane (HFC- 4310-mee) with four different compositions in ratios by weight of 90:10, 85:15, 80:20, and 75:25 were taken from Figure 2 of US 6,004,672 and are shown in Figure 3.

[0136] Comparative Examples 7 to 8: Cloud point studies of PE in DCM - PFMCH (comparative example 7) and DCM - HFCP (comparative example 8)

[0137] Measurements of cloud point pressures using the equipment described above were performed for spin fluids comprising 14 wt% of polyethylene (PE) and spin agents of dichloromethane and perfluoro(methylcyclohexane) (PFMCH) with three different compositions in ratios by weight of 75:25, 72.5:27.5, and 70:30. The cloud point pressures for a temperature of 215 °C are shown in Figure 4. Measurements of cloud point pressures using the equipment described above were performed for spin fluids comprising 14 wt% of polyethylene (PE) and spin agents of dichloromethane and 1 H,1 H,2H-heptafluorocyclopentane (HFCP) with three different compositions in ratios by weight of 80:20, 75:25 and 70:30. The cloud point pressures for a temperature of 215 °C are shown in Figure 3.

[0138] Table 1 : Summary of the cloud point studies of Examples 1 and 2 and Comparative Examples 1 to 8.

[0139] (1 ) The PVDF used was Kynar® 740

[0140] The cloud point pressures of the spin fluids comprising PVDF-Kynar® 740 and the spin agents of dichloromethane and 1 H,1 H,2H-heptafluorocyclopentane (E1) or of dichloromethane and 1 H,2H-octafluorocyclopentane (E2) do not substantially increase with increasing amounts of the fluorinated spin agent component in the spin agents. The slope of the cloud point pressures is only about 8.3 bar for an increase in the HFCP concentration of 10 wt% and only about 16.5 bar for an increase in the OFCP concentration of 10 wt%.

[0141] In contrast, for spin agents comprising the linear fluorinated compounds 3, 3, 4, 4, 5, 5, 6, 6, 6- nonafluoro-1-hexene (Zonyl® PFBE) or 2H,3H-decafluoropentane (HFC-4310-mee) in combination with dichloromethane, the cloud point pressures of the spin fluids comprising PVDF- Kynar® 760 / 740 and the spin agents significantly increases with increasing amounts of the fluorinated spin agent component in the spin agents. The slope of the cloud point pressures is about 45 bar for an increase in the Zonyl® PFBE concentration of 10 wt%, and about 42 bar for an increase in the HFC-4310-mee concentration of 10 wt%. For spin agents comprising the cyclic fluorinated compounds perfluoro(methylcyclohexane) (PFMCH) or perfluoro-N-methylmorpholine (PF5052) in combination with dichloromethane, the cloud point pressures of the spin fluids comprising PVDF-Kynar® 740 and the spin agents increase even more with increasing amounts of the fluorinated spin agent component in the spin agent. The slope of the cloud point pressure is about 125 bar for an increase in the PFMCH concentration of 10 wt% and about 124 bar for an increase in the PF5052 concentration of 10 wt%.

[0142] In addition, when flash-spinning polyethylene (PE) instead of polyvinylidene fluoride (PVDF) using spin fluids comprising dichloromethane in combination with fluorinated compounds, the cloud point pressures of the spin fluids comprising polyethylene and the spin agents again increases significantly with increasing amounts of the fluorinated spin agent component in the spin agents. The slope of the cloud point pressures is about 80 bar for an increase in the Zonyl® PFBE concentration of 10 wt%, about 90 bar for an increase in the HFC-4310-mee concentration of 10 wt%, about 182 bar for an increase in the PFMCH concentration of 10 wt% and about 54 bar for an increase in the HFCP concentration of 10 wt%.

[0143] Therefore, the inventive spin fluids as described herein comprising PVDF and spin agents of dichloromethane and 1 H,1 H,2H-heptafluorocyclopentane or of dichloromethane and 1H,2H- octafluorocyclopentane show a surprisingly advantageous cloud point behavior in that the cloud point pressure does not significantly increase with increasing amount of the fluorinated component in the spin agent. This results in a process which is less sensitive to fluctuations in spin agent composition, and in a reduction in the volume of vaporized spin agent produced in the flash spinning process through the use of higher amounts of the fluorinated component.

[0144] In addition, the inventive spin fluids comprising PVDF and spin agents of dichloromethane and the cyclic hydrofluorocarbon 1H,1H,2H-heptafluorocyclopentane, or PVDF and spin agents of dichloromethane and the cyclic hydrofluorocarbon 1H,2H-octafluorocyclopentane tend to exhibit lower cloud point pressures at 215°C compared to spin agents of dichloromethane in combination with other fluorinated compounds. This allows the efficient preparation of plexifilamentary fibrils under more gentle pressure conditions.

[0145] Finally, mixtures of dichloromethane and 1 H,1 H,2H-heptafluorocyclopentane or dichloromethane and 1 H,2H-octafluorocyclopentane exhibit a desirable low GWP value of below 200. This makes them suitable as replacements for currently used spin agents. Examples 3 to 10: Flash spinning of PVDF in DCM - HFCP

[0146] Flash spinning was performed on the equipment described in the above at different spin pressures, temperatures, and concentrations of polyvinylidene fluoride (PVDF - Kynar® 740) in a spin agent of DCM and 1 H,1 H,2H-heptafluorocyclopentane in a 60:40 ratio by weight.

[0147] The spinning conditions and fibril properties are reported in Table 3 below.

[0148] Table 3: Summary of the flash spinning experiments of Examples 3 to 10.

[0149] (1 ) The PVDF used was Kynar® 740

[0150] The above examples illustrate that the inventive spin fluids as described herein comprising PVDF and spin agents of dichloromethane and 1 H,1H,2H-heptafluorocyclopentane (HFCP) can be used for the flash spinning of PVDF at different polymer concentrations, spin temperatures, and spin pressures. This allows an efficient preparation of plexifilamentary fibrils of PVDF. In addition, the obtained fibrils contain high amounts of crystals in the p phase. This is advantageous in electrical applications.

[0151] Examples 11 to 13: Flash spinning of PVDF in DCM - OFCP

[0152] Flash spinning was performed on the equipment described in the above for a spin fluid comprising 26 wt% polyvinylidene fluoride (PVDF - Kynar® 720) and spin agents of DCM and trans-1 H,2H-octafluorocyclopentane in different ratios by weight and at different spin temperatures and pressures.

[0153] The spinning conditions and fibril properties are reported in Table 4 below.

[0154] Table 4: Summary of the flash spinning experiments of Examples 11 to 13.

[0155] | Example |

[0156]

[0157] (1 ) The PVDF used was Kynar® 720

[0158] The above examples illustrate that the inventive spin fluids as described herein comprising PVDF and spin agents of dichloromethane and 1 H,2H-octafluorocyclopentane (OFCP) can be used for the flash spinning of PVDF at different polymer concentrations, spin temperatures, and spin pressures. This allows an efficient preparation of plexifilamentary fibrils of PVDF. In addition, the obtained fibrils contain high amounts of crystals in the [3 phase. This is advantageous in electrical applications.

[0159] Example 14: Flash spinning of PE - PVDF blend in DCM - HFCP

[0160] Flash spinning was performed on the equipment described in the above for a spin fluid comprising 18 wt% polymer blend (80 wt% PE and 20 wt% PVDF - Kynar® 720) and a spin agent of DCM and 1 H,1 H,2H-heptafluorocyclopentane in an 80:20 ratio by weight at a spin temperature of about 205 °C and a spin pressure of about 68 bar.

[0161] The spinning conditions are reported in Table 5 below.

[0162] Table 5: Summary of the flash spinning experiments of Example 14. Example 15: Flash spinning of PVDF - PE blend in DCM - HFCP

[0163] Flash spinning was performed on the equipment described in the above for a spin fluid comprising 14 wt% polymer blend (95 wt% Kynar® 720 - 5 wt% PE) and a spin agent of DCM and 1 H,1 H,2H-heptafluorocyclopentane in a 70:30 ratio by weight at a spin temperature of about 215 °C and a spin pressure of about 65 bar.

[0164] The spinning conditions are reported in Table 6 below.

[0165] Table 6: Summary of the flash spinning experiments of Example 15.

[0166] Examples 14 and 15 illustrate that the inventive spin fluids as described herein comprising a PVDF blend and spin agents of dichloromethane and 1 H,1 H,2H-heptafluorocyclopentane (HFCP) can be used for flash spinning PVDF blends. An efficient preparation of plexifilamentary fibrils of PE / PVDF is possible because the spin agent compositions are suitable for flash spinning both PVDF and PE.

[0167] Example 16: Flash spinning of PP - PVDF blend in DCM - HFCP

[0168] Flash spinning was performed on the equipment described in the above for a spin fluid comprising 10 wt% polymer blend (70 wt% PP and 30 wt% PVDF - Kynar® 720) and a spin agent of DCM and 1 H,1 H,2H-heptafluorocyclopentane in a 45:55 ratio by weight at a spin temperature of about 200 °C and a spin pressure of about 57 bar.

[0169] The spinning conditions are reported in Table 7 below.

[0170] Table 7: Summary of the flash spinning experiments of Example 16.

[0171] The above example illustrates that the inventive spin fluids as described herein comprising a PVDF blend and a spin agent of dichloromethane and 1 H,1 H,2H-heptafluorocyclopentane (HFCP) can be used for flash spinning PVDF blends. An efficient preparation of plexifilamentary fibrils of PP / PVDF is possible because the spin agent compositions are suitable for flash spinning both PVDF and PP.

[0172] OTHER EMBODIMENTS

[0173] 1. In some embodiments, the present application provides a spin fluid for flash spinning comprising

[0174] (a) from about 10 to about 35 weight percent of a polyvinylidene fluoride or a polyvinylidene fluoride blend, based on the total amount of the spin fluid, and

[0175] (b) a spin agent, wherein the spin agent comprises dichloromethane and a cyclic hydrofluorocarbon.

[0176] 2. The spin fluid of embodiment 1 comprising from about 15 to about 35 weight of a polyvinylidene fluoride or a polyvinylidene fluoride blend, based on the total amount of the spin fluid, or from about 20 to about 30 weight of a polyvinylidene fluoride or a polyvinylidene fluoride blend, based on the total amount of the spin fluid.

[0177] 3. The spin fluid of embodiment 1 or 2 comprising from about 65 to about 90 weight percent of the spin agent, based on the total amount of the spin fluid, or from about 65 to about 85 weight percent of the spin agent, based on the total amount of the spin fluid, or from about 70 to about 80 weight percent of the spin agent, based on the total amount of the spin fluid.

[0178] 4. The spin fluid of any one of embodiments 1 to 3 wherein the cyclic hydrofluorocarbon is 1 H , 1 H ,2H-heptafluorocyclopentane. 5. The spin fluid of embodiment 4 wherein the spin agent comprises from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1H,1 H,2H- heptafluorocyclopentane, or from about 40 to about 65 weight percent dichloromethane and from about 60 to about 35 weight percent 1 H,1H,2H-heptafluorocyclopentane, or from about 40 to about 55 weight percent dichloromethane and from about 60 to about 45 weight percent 1 H , 1 H ,2H-heptafluorocyclopentane.

[0179] 6. The spin fluid of embodiment 5 wherein the spin agent consists essentially of or consists of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,1H,2H-heptafluorocyclopentane, or from about 40 to about 65 weight percent dichloromethane and from about 60 to about 35 weight percent 1 H,1H,2H- heptafluorocyclopentane, or from about 40 to about 55 weight percent dichloromethane and from about 60 to about 45 weight percent 1 H,1 H,2H-heptafluorocyclopentane.

[0180] 7. The spin fluid of embodiment 4 wherein the spin agent comprises from about 60 to about 80 weight percent dichloromethane and from about 40 to about 20 weight percent 1H,1 H,2H- heptafluorocyclopentane, or from about 65 to about 80 weight percent dichloromethane and from about 35 to about 20 weight percent 1 H,1H,2H-heptafluorocyclopentane, or from about 70 to about 80 weight percent dichloromethane and from about 30 to about 20 weight percent 1 H , 1 H ,2H-heptafluorocyclopentane.

[0181] 8. The spin fluid of embodiment 7 wherein the spin agent consists essentially of or consists of from about 60 to about 80 weight percent dichloromethane and from about 40 to about 20 weight percent 1 H,1H,2H-heptafluorocyclopentane, or from about 65 to about 80 weight percent dichloromethane and from about 35 to about 20 weight percent 1 H,1H,2H- heptafluorocyclopentane, or from about 70 to about 80 weight percent dichloromethane and from about 30 to about 20 weight percent 1 H,1 H,2H-heptafluorocyclopentane.

[0182] 9. The spin fluid of any one of embodiments 1 to 3 wherein the cyclic hydrofluorocarbon is 1 H,2H-octafluorocyclopentane.

[0183] 10. The spin fluid of embodiment 9 wherein the spin agent comprises from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,2H- octafluorocyclopentane, or from about 40 to about 65 weight percent dichloromethane and from about 60 to about 35 weight percent 1 H,2H-octafluorocyclopentane, or from about 40 to about 55 weight percent dichloromethane and from about 60 to about 45 weight percent 1H,2H- octaf I uo rocy cl o pe nta ne .

[0184] 11. The spin fluid of embodiment 10 wherein the spin agent consists essentially of or consists of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,2H-octafluorocyclopentane, or from about 40 to about 65 weight percent dichloromethane and from about 60 to about 35 weight percent 1 H,2H-octafluorocyclopentane, or from about 40 to about 55 weight percent dichloromethane and from about 60 to about 45 weight percent 1H,2H-octafluorocyclopentane.

[0185] 12. The spin fluid of embodiment 9 wherein the spin agent comprises from about 60 to about 80 weight percent dichloromethane and from about 40 to about 20 weight percent 1 H,2H- octafluorocyclopentane, or from about 65 to about 80 weight percent dichloromethane and from about 35 to about 20 weight percent 1 H,2H-octafluorocyclopentane, or from about 70 to about 80 weight percent dichloromethane and from about 30 to about 20 weight percent 1H,2H- octaf I uo rocy cl o pe nta ne .

[0186] 13. The spin fluid of embodiment 12 wherein the spin agent consists essentially of or consists of from about 60 to about 80 weight percent dichloromethane and from about 40 to about 20 weight percent 1 H,2H-octafluorocyclopentane, or from about 65 to about 80 weight percent dichloromethane and from about 35 to about 20 weight percent 1 H,2H-octafluorocyclopentane, or from about 70 to about 80 weight percent dichloromethane and from about 30 to about 20 weight percent 1H,2H-octafluorocyclopentane.

[0187] 14. The spin fluid of any of the preceding embodiments comprising from about 10 to about 35 weight percent of a PVDF or a PVDF blend and from about 90 to about 65 weight percent of the spin agent, each based on the total amount of the spin fluid, or comprising from about 15 to about 35 weight percent of a PVDF or a PVDF blend and from about 85 to about 65 weight percent of the spin agent, each based on the total amount of the spin fluid, or comprising from about 20 to about 30 weight percent of a PVDF or a PVDF blend and from about 80 to about 70 weight percent of the spin agent, each based on the total amount of the spin fluid. 15. The spin fluid of any of the preceding embodiment comprising from about 10 to about 35 weight percent of a PVDF or a PVDF blend, based on the total amount of the spin fluid, and a spin agent, wherein the spin agent comprises, consists essentially of, or consists of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,1 H,2H-heptafluorocyclopentane or wherein the spin agent comprises, consists essentially of, or consists of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,2H-octafluorocyclopentane.

[0188] 16. The spin fluid of any of the preceding embodiments, wherein the spin agent additionally comprises an additive, selected from antioxidants, acid scavengers, and blends thereof.

[0189] 17. The spin fluid of any of embodiments 1 to 16 wherein the PVDF blend comprises from about 50 to about 95 weight percent PVDF and from about 50 to about 5 weight percent polyethylene and / or polypropylene, or from about 50 to about 80 weight percent PVDF and from about 50 to about 20 weight percent polyethylene and / or polypropylene.

[0190] 18. The spin fluid of any of embodiments 1 to 16 wherein the PVDF blend comprises from about 5 to about 50 weight percent PVDF and from about 95 to about 50 weight percent polyethylene and / or polypropylene, or from about 20 to about 50 weight percent PVDF and from about 80 to about 50 weight percent polyethylene and / or polypropylene.

[0191] 19. In some embodiments, the present application provides a process for the preparation of plexifilamentary fibrils of polyvinylidene fluoride or polyvinylidene fluoride blend which comprises the steps of:

[0192] (i) generating a spin fluid comprising

[0193] (a) from about 10 to about 35 weight percent of a polyvinylidene fluoride or a polyvinylidene fluoride blend, based on the total amount of the spin fluid, and

[0194] (b) a spin agent, and

[0195] (ii) flash spinning the spin fluid at a pressure that is above the vapor pressure of the spin fluid into a region of essentially atmospheric pressure to form plexifilamentary fibrils of the polyvinylidene fluoride or polyvinylidene fluoride blend, wherein the spin agent comprises dichloromethane and a cyclic hydrofluorocarbon. 20. The process of embodiment 19 wherein the spin fluid comprises from about 15 to about 35 weight a polyvinylidene fluoride or a polyvinylidene fluoride blend, based on the total amount of the spin fluid or from about 20 to about 30 weight a polyvinylidene fluoride or a polyvinylidene fluoride blend, based on the total amount of the spin fluid.

[0196] 21. The process of embodiment 19 or 20 wherein the spin fluid comprises from about 65 to about 90 weight percent of the spin agent, based on the total amount of the spin fluid, or from about 65 to about 85 weight percent of the spin agent, based on the total amount of the spin fluid, or from about 70 to about 80 weight percent of the spin agent.

[0197] 22. The process of any one of embodiments 19 to 21 wherein the cyclic hydrofluorocarbon is 1 H , 1 H ,2H-heptafluorocyclopentane.

[0198] 23. The process of embodiment 22 wherein the spin agent comprises from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1H,1 H,2H- heptafluorocyclopentane, or from about 40 to about 65 weight percent dichloromethane and from about 60 to about 35 weight percent 1 H,1H,2H-heptafluorocyclopentane, or from about 40 to about 55 weight percent dichloromethane and from about 60 to about 45 weight percent 1 H , 1 H ,2H-heptafluorocyclopentane.

[0199] 24. The process of embodiment 23 wherein the spin agent consists essentially of or consists of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,1H,2H-heptafluorocyclopentane, or from about 40 to about 65 weight percent dichloromethane and from about 60 to about 35 weight percent 1 H,1H,2H- heptafluorocyclopentane, or from about 40 to about 55 weight percent dichloromethane and from about 60 to about 45 weight percent 1 H,1 H,2H-heptafluorocyclopentane.

[0200] 25. The process of embodiment 22 wherein the spin agent comprises from about 60 to about 80 weight percent dichloromethane and from about 40 to about 20 weight percent 1H,1 H,2H- heptafluorocyclopentane, or from about 65 to about 80 weight percent dichloromethane and from about 35 to about 20 weight percent 1 H,1H,2H-heptafluorocyclopentane, or from about 70 to about 80 weight percent dichloromethane and from about 30 to about 20 weight percent 1 H , 1 H ,2H-heptafluorocyclopentane. 26. The process of embodiment 25 wherein the spin agent consists essentially of or consists of from about 60 to about 80 weight percent dichloromethane and from about 40 to about 20 weight percent 1 H,1H,2H-heptafluorocyclopentane, or from about 65 to about 80 weight percent dichloromethane and from about 35 to about 20 weight percent 1 H,1H,2H- heptafluorocyclopentane, or from about 70 to about 80 weight percent dichloromethane and from about 30 to about 20 weight percent 1 H,1 H,2H-heptafluorocyclopentane.

[0201] 27. The process of any one of embodiments 19 to 21 wherein the cyclic hydrofluorocarbon is 1 H,2H-octafluorocyclopentane.

[0202] 28. The process of embodiment 27 wherein the spin agent comprises from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,2H- octafluorocyclopentane, or from about 40 to about 65 weight percent dichloromethane and from about 60 to about 35 weight percent 1 H,2H-octafluorocyclopentane, or from about 40 to about 55 weight percent dichloromethane and from about 60 to about 45 weight percent 1H,2H- octaf I uo rocy cl o pe nta ne .

[0203] 29. The process of embodiment 28 wherein the spin agent consists essentially of or consists of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,2H-octafluorocyclopentane, or from about 40 to about 65 weight percent dichloromethane and from about 60 to about 35 weight percent 1 H,2H-octafluorocyclopentane, or from about 40 to about 55 weight percent dichloromethane and from about 60 to about 45 weight percent 1H,2H-octafluorocyclopentane.

[0204] 30. The process of embodiment 27 wherein the spin agent comprises from about 60 to about 80 weight percent dichloromethane and from about 40 to about 20 weight percent 1 H,2H- octafluorocyclopentane, or from about 65 to about 80 weight percent dichloromethane and from about 35 to about 20 weight percent 1 H,2H-octafluorocyclopentane, or from about 70 to about 80 weight percent dichloromethane and from about 30 to about 20 weight percent 1H,2H- octaf I uo rocy cl o pe nta ne .

[0205] 31. The process of embodiment 30 wherein the spin agent consists essentially of or consists of from about 60 to about 80 weight percent dichloromethane and from about 40 to about 20 weight percent 1 H,2H-octafluorocyclopentane, or from about 65 to about 80 weight percent dichloromethane and from about 35 to about 20 weight percent 1 H,2H-octafluorocyclopentane, or from about 70 to about 80 weight percent dichloromethane and from about 30 to about 20 weight percent 1H,2H-octafluorocyclopentane.

[0206] 32. The process of any of the preceding embodiments wherein the spin fluid comprises from about 10 to about 35 weight percent of a PVDF or a PVDF blend and from about 90 to about 65 weight percent of the spin agent, each based on the total amount of the spin fluid, or comprises from about 15 to about 35 weight percent of a PVDF or a PVDF blend and from about 85 to about 65 weight percent of the spin agent, each based on the total amount of the spin fluid, or comprises from about 20 to about 30 weight percent of a PVDF or a PVDF blend and from about 80 to about 70 weight percent of the spin agent, each based on the total amount of the spin fluid.

[0207] 33. The process of any of the preceding embodiment wherein the spin fluid comprises from about 10 to about 35 weight percent of a PVDF or a PVDF blend, based on the total amount of the spin fluid, and a spin agent, wherein the spin agent comprises, consists essentially of, or consists of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1 H,1 H,2H-heptafluorocyclopentane or wherein the spin agent comprises, consists essentially of, or consists of from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1H,2H-octafluorocyclopentane.

[0208] 34. The process of any of the preceding embodiments, wherein the spin agent additionally comprises an additive, selected from antioxidants, acid scavengers, and blends thereof.

[0209] 35. The process of any of embodiments 19 to 34 wherein the PVDF blend comprises from about 50 to about 95 weight percent PVDF and from about 50 to about 5 weight percent polyethylene and / or polypropylene, or from about 50 to about 80 weight percent PVDF and from about 50 to about 20 weight percent polyethylene and / or polypropylene.

[0210] 36. The process of any of embodiments 19 to 34 wherein the PVDF blend comprises from about 5 to about 50 weight percent PVDF and from about 95 to about 50 weight percent polyethylene and / or polypropylene, or from about 20 to about 50 weight percent PVDF and from about 80 to about 50 weight percent polyethylene and / or polypropylene. 37. The process of any of embodiments 19 to 36, wherein the flash-spinning is performed at a pressure in the range of about 40 to about 300 bar, or in the range of about 50 to about 300 bar, or in the range of about 70 to about 300 bar.

[0211] 38. The process of embodiment 37, wherein the flash-spinning is performed at a pressure in the range of about 45 to about 250 bar, or in the range of about 50 to about 250 bar, or in the range of about 70 to about 250 bar.

[0212] 39. The process of embodiment 38, wherein the flash-spinning is performed at a pressure in the range of about 45 to about 200 bar, or in the range of about 50 to about 200 bar, or in the range of about 70 to about 200 bar.

[0213] 40. In some embodiments, the present application provides a use of the spin fluid of any of embodiments 1 to 18 for preparing plexifilamentary fibrils of polyvinylidene fluoride or polyvinylidene fluoride blend by flash spinning.

[0214] 41. The plexifilamentary fibrils of polyvinylidene fluoride or polyvinylidene fluoride blend obtainable or obtained by the process of any one of embodiments 19 to 39.

[0215] 42. The plexifilamentary fibrils of polyvinylidene fluoride or polyvinylidene fluoride blend of embodiment 41 wherein the only detectable PVDF crystal phase is the p crystal phase whereas no significant portions of the a or y crystal phases are detectable.

[0216] 43. The plexifilamentary fibrils of polyvinylidene fluoride or polyvinylidene fluoride blend of embodiment 42 having a crystallinity index (P phase) of about 32 % or more, or about 34 % or more, or about 35 % or more.

[0217] 44. A sheet of nonwoven flash-spun plexifilamentary fibrils comprising plexifilamentary fibrils of polymer of any of embodiments 41 to 43.

[0218] 45. The sheet of embodiment 44, wherein the sheet is a collected sheet, a consolidated sheet, a bonded sheet, or a softened sheet. 46. A bonded sheet obtainable by thermally or mechanically bonding the consolidated sheet of embodiment 45.

[0219] 47. A softened sheet obtainable by softening the consolidated sheet of embodiment 45 or by softening the bonded sheet of embodiment 46.

[0220] 48. An article comprising plexifilamentary fibrils of polymer of any of embodiments 41 to 43 and / or a sheet of any one of embodiments 44 to 47.

[0221] 49. The article of embodiment 48 which is selected from packaging material, filtration media, print media, tags and labels, accessories, and electronic devices such as pressure sensors, strain gauges, microphones, actuators, energy harvesters, and nanogenerators.

[0222] While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant art(s) that various changes in form and detail can be made therein without departing from the spirit and scope of the present invention. Thus, it should be appreciated that, while the invention has been described with reference to the above exemplary embodiments, other embodiments are within the scope of the claims. Moreover, it should be understood that the exemplary embodiments described herein may be combined to form other embodiments. After reading the above description, it will be apparent to one skilled in the relevant art(s) how to implement the invention in alternative embodiments. Thus, the present invention should not be limited by any of the above-described exemplary embodiments.

Claims

CLAIMS1. A spin fluid for flash spinning comprising(a) from about 10 to about 35 weight percent of a polyvinylidene fluoride or a polyvinylidene fluoride blend, based on the total amount of the spin fluid, and(b) a spin agent, wherein the spin agent comprises dichloromethane and a cyclic hydrofluorocarbon.

2. The spin fluid of claim 1 wherein the cyclic hydrofluorocarbon is 1H,1 H,2H- heptafluorocyclopentane or 1 H,2H-octafluorocyclopentane.

3. The spin fluid of claim 1 or 2 wherein the spin agent comprises from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1H,1 H,2H- heptafluorocyclopentane.

4. The spin fluid of claim 1 or 2 wherein the spin agent comprises from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1H,2H- octafluorocyclopentane.

5. The spin fluid of any one of claims 1 to 4, wherein the spin fluid comprises from about 90 to about 65 weight percent of the spin agent, based on the total amount of the spin fluid, or from about 85 to about 65 weight percent of the spin agent, based on the total amount of the spin fluid.

6. A process for the preparation of plexifilamentary fibrils of polyvinylidene fluoride or polyvinylidene fluoride blend which comprises the steps of:(i) generating a spin fluid comprising(a) from about 10 to about 35 weight percent of a polyvinylidene fluoride or a polyvinylidene fluoride blend, based on the total amount of the spin fluid, and(b) a spin agent, and(ii) flash spinning the spin fluid at a pressure that is above the vapor pressure of the spin fluid into a region of essentially atmospheric pressure to form plexifilamentary fibrils of the polyvinylidene fluoride or polyvinylidene fluoride blend; wherein the spin agent comprises dichloromethane and a cyclic hydrofluorocarbon.

7. The process of claim 6 wherein the cyclic hydrofluorocarbon is 1 H,1H,2H- heptafluorocyclopentane or 1 H,2H-octafluorocyclopentane.

8. The process of claim 6 or 7 wherein the spin agent comprises from about 40 to about 80 weight percent dichloromethane and from about 60 to about 20 weight percent 1H,1 H,2H- heptafluorocyclopentane.

9. The process of claim 6 or 7 wherein the spin agent comprises from about 40 to about 80 weight percent dichloromethane and from about 60 to 20 weight percent 1 H,2H- octafluorocyclopentane.

10. The process of any one of claims 6 to 8 wherein the spin fluid comprises from 90 to 65 weight percent of the spin agent, based on the total amount of the spin fluid, or from about 85 to about 65 weight percent of the spin agent, based on the total amount of the spin fluid.

11. Use of the spin fluid of any one of claims 1 to 5 for preparing plexifilamentary fibrils of polyvinylidene fluoride or polyvinylidene fluoride blend by flash spinning.

12. Plexifilamentary fibrils of polyvinylidene fluoride or polyvinylidene fluoride blend obtainable by the process of any one of claims 6 to 10.

13. The plexifilamentary fibrils of polyvinylidene fluoride or polyvinylidene fluoride blend of claim 12 wherein the only detectable PVDF crystal phase is the crystal phase whereas no significant portions of the a or y crystal phases are detectable.

14. A sheet of nonwoven flash-spun plexifilamentary fibrils comprising plexifilamentary fibrils of polyvinylidene fluoride or polyvinylidene fluoride blend of claim 12 or 13.

15. An article comprising the plexifilamentary fibrils of polyvinylidene fluoride or polyvinylidene fluoride blend of claim 12 or 13 and / or the sheet of claim 14.

16. The article of claim 15 which is selected from packaging material, filtration media, print media, tags and labels, accessories, and electronic devices such as pressure sensors, strain gauges, microphones, actuators, energy harvesters, and nanogenerators.

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