WO2025240715A1

WO2025240715A1 - Azeotropic and azeotrope-like compositions comprising dichloromethane and 2-methylpentane or 3-methylpentane and use of the compositions as flash spinning agents

Info

Publication number: WO2025240715A1
Application number: PCT/US2025/029520
Authority: WO
Inventors: Jan VAN MEERVELD; Martin Schiller; Noel Stephen Brabbs
Original assignee: DuPont Safety and Construction Inc
Current assignee: DuPont Safety and Construction Inc
Priority date: 2024-05-17
Filing date: 2025-05-15
Publication date: 2025-11-20
Anticipated expiration: 2026-11-17

Abstract

The present invention relates to (i) an azeotropic or azeotrope-like composition comprising (1) dichloromethane and 2-methylpentane, or comprising (2) dichloromethane and 3-methylpentane, (ii) a spin fluid for flash spinning comprising these azeotropic or azeotrope-like compositions and a polyvinylidene fluoride (PVDF), and (iii) a process for the preparation of plexifilamentary fibrils of PVDF using the spin fluid.

Description

TITLE

AZEOTROPIC AND AZEOTROPE-LIKE COMPOSITIONS COMPRISING DICHLOROMETHANE AND 2-METHYLPENTANE OR 3-METHYLPENTANE

AND USE OF THE COMPOSITIONS AS FLASH SPINNING AGENTS

FIELD OF THE INVENTION

The present invention relates to (i) an azeotropic or azeotrope-like composition comprising (1 ) dichloromethane and 2-methylpentane, or comprising (2) dichloromethane and 3-methylpentane, (ii) a spin fluid for flash spinning comprising these azeotropic or azeotrope-like compositions and a polyvinylidene fluoride (PVDF), and (iii) a process for the preparation of plexifilamentary fibrils of PVDF using the spin fluid.

BACKGROUND

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 β crystal phase. However, the β 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.

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. 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 reusing 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, and it is preferred that the composition of the spin agent remains essentially constant during this step. This is inherent when spin agents comprise only one solvent but not when they comprise two or more solvents, which are often required to provide the necessary solvent properties for flash spinning the desired polymer. Accordingly, when using a spin agent that comprises two or more solvents, it is advantageous to use a composition that is azeotropic or azeotrope-like which behaves similarly to a spin agent with only one solvent.

One example of a solvent that can be used with polymers such as polyvinylidene fluoride (PVDF) is dichloromethane (DCM). At practical operating temperatures, DOM 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. In particular, because DCM dissolves polymers at relatively low pressures, the cloud point pressure of a spin fluid using a spin agent with only this chlorinated solvent is so close to the bubble point pressure that use of such spin agent is not feasible. Weaker solvents such as hydrofluorocarbons can be mixed with DCM to reduce the solvent strength of the spin agent and increase the spin fluid’s cloud point pressure such that flash spinning can be readily accomplished.

WO 2016/200873 A1 suggests spin agent compositions of dichloromethane with 1 H,6H-perfluorohexane, 1 H-perfluorohexane, or 1 H-perfluoroheptane. However, use of such linear hydrofluorocarbons in combination with DCM results in spin agents that often exhibit undesirably high global warming potential (GWP). In view of the growing concerns regarding climate change and increasing regulatory requirements, there is a need to find suitable low GWP replacements for spin agent compositions disclosed in the prior art. Such spin agent compositions should also form a homogeneous liquid phase at ambient temperatures and pressures, rather than a heterogeneous liquid phase where, due to low miscibility of the components of the spin agent composition, a liquid-liquid phase separation occurs. Compositions forming heterogeneous liquid phases are usually undesired since processes involving such compositions are more complex and expensive due to the liquidliquid phase separation.

Where an azeotrope forms between a chlorinated solvent component and a nonchlorinated component in the spin agent, it is beneficial if this is a positive azeotrope because the boiling point of the azeotrope is then lower than that of either individual component of the spin agent composition. This allows the low-pressure region into which flash spinning takes place (i.e., the spin-cell) to be maintained at a lower temperature without risking the spin agent composition condensing inside it. This also reduces the need for spin-cell heating and provides a more comfortable environment for operators working near the spin-cell. On the other hand, a negative azeotrope, which has a higher boiling point than that of either individual component of the spin agent composition, could require spin-cell heating which would lead to increased equipment and operating costs.

Accordingly, there is a need for, and the present inventors have discovered, low GWP azeotropic and azeotrope-like compositions of a chlorinated solvent and a non-cyclic hydrocarbon that (I) form a positive homogenous azeotrope with a boiling temperature below 50 °C, (ii) simplify the spin agent recovery and re-use process, and (iii) provide suitable cloud point pressures for flash spinning PVDF. It is a further object of the present invention to provide a spin fluid comprising PVDF where the crystal phase present in the PVDF in the fibrils resulting from flash spinning is predominantly the p phase.

SUMMARY OF THE INVENTION

In one embodiment the invention is directed to an azeotropic or azeotrope-like composition comprising

(1) dichloromethane and 2-methylpentane, or

(2) dichloromethane and 3-methylpentane.

In one embodiment the invention is directed to an azeotropic or azeotrope-like composition comprising dichloromethane and 2-methylpentane.

In a further embodiment the invention is directed to an azeotropic or azeotrope-like composition comprising dichloromethane and 3-methylpentane.

In a further 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, based on the total amount of the spin fluid, and (b) a spin agent, wherein the spin agent comprises (1) an azeotropic or azeotrope-like composition comprising dichioromethane and 2- methylpentane, or (2) an azeotropic or azeotrope-like composition comprising dichioromethane and 3-methylpentane.

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

(I) generating a spin fluid comprising

(a) from about 10 to about 35 weight percent of a polyvinylidene fluoride, 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, wherein the spin agent comprises

(1) an azeotropic or azeotrope-like composition comprising dichloromethane and 2-methylpentane, or

(2) an azeotropic or azeotrope-like composition comprising dichloromethane and 3-methylpentane.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 shows the calculated vapor-liquid equilibrium (VLE) for the compositions of dichloromethane (DCM) and 2-methylpentane (2-MP) at 40°C.

Fig. 2 shows the calculated vapor-liquid equilibrium (VLE) for the compositions of dichloromethane (DCM) and 3-methylpentane (3-MP) at 40°C.

Fig. 3 shows the cloud point pressure curve of a spin fluid comprising 25 wt% polyvinylidene fluoride (PVDF) and a spin agent of dichloromethane (DCM) and 2- methylpentane in a 93:7 ratio by weight, the cloud point pressure curve of a spin fluid comprising 30 wt% polyvinylidene fluoride (PVDF) and a spin agent of dichloromethane (DCM) and 2-methylpentane (2-MP) in a 87:13 ratio by weight, and the cloud point pressure curve of a spin fluid comprising 22 wt% polyvinylidene fluoride (PVDF) and a spin agent of dichloromethane (DCM) and 2-methylpentane (2-MP) in a 97:3 ratio by weight.

Fig. 4 shows the cloud point pressure curve of a spin fluid comprising 28 wt% polyvinylidene fluoride (PVDF) and a spin agent of dichloromethane (DCM) and 3-methylpentane (3-MP) in a 91 :9 ratio by weight.

DETAILED DESCRIPTION

Definitions and Clarification of Terms

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.

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

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 polyvinyl id ene 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.

The total crystallinity index is determined as follows. A diffractometer in reflection θ-2θ Bragg-Brentano geometry is fitted with a Cu-K_a x-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°, Seller slits of 0.04 rad, and a nickel Cu-Kp filter 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.

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.

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 +/- 0.2° due to instrumental differences and sample height/texture. 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° 29.

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.

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 29 = 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 20 = 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 20 = 10° to 29°. The scattering intensity is then:

1 ) Amorphous peak: 18.6°, Pearson VII peak shape and

2) p 110/200 superimposed peak: 20.5°, Pearson VII peak shape

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 fullwidth at half maximum and M is the Pearson VII shape parameter.

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:

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. 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. The PVDF may contain up to 10 weight percent or up to 5 weight percent of other polymers, such as polyolefins.

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.

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.

The terms “spin agent” or “spin agent composition" refer 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.

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.

The term “dew point pressure" refers to the pressure at which, at constant temperature, liquid starts condensing from a vapor, vapor mixture, or vapor-gas mixture.

The term “bubble point pressure" refers to the pressure at which, at constant temperature, a liquid, liquid mixture, or liquid-solution begins to boil.

The term “azeotropic composition" refers to a composition comprising two or more fluids wherein the bubble point pressure equals the dew point pressure. An azeotropic composition boils without change of the composition and behaves as a single substance. The azeotropic compositions described herein comprising dichloromethane are determined in a temperature range of -20 °C to 100 °C and expressed in mass fractions.

The term “azeotrope-like composition" refers to a composition comprising two or more fluids which exhibit only small differences between the dew point pressure and the bubble point pressure, i.e., the dew point pressure is different by 5% or less from the bubble point pressure (both expressed in absolute pressure). An azeotrope-like composition boils without substantial change of the composition and behaves substantially as a single substance. The azeotrope-like compositions described herein are determined in a temperature range of -20 °C to 100 °C and expressed in mass fractions.

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.

Atmospheric pressure means 101.325 kPa. Essentially atmospheric pressure means 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.

Azeotropic or Azeotrope-like Compositions

Azeotropic or azeotrope-like compositions comprising dichloromethane and 2 -methylpentane

Provided herein are azeotropic or azeotrope-like compositions comprising dichloromethane and 2-m ethyl pentane.

In some embodiments, the azeotropic or azeotrope-like compositions comprise from about 73 to about 99 weight percent dichloromethane and from about 27 to about 1 weight percent 2-methylpentane, or from about 75 to about 99 weight percent dichloromethane and from about 25 to about 1 weight percent 2-methylpentane. These azeotropic or azeotrope-like compositions boil at a temperature of about -20 °C to about 100 °C and at a boiling pressure of about 6 kPa to about 591 kPa. In other embodiments, the azeotropic or azeotrope-like compositions comprise from about 73 to about 99 weight percent dichloromethane and from about 27 to about 1 weight percent 2-methylpentane, or from about 75 to about 99 weight percent dichloromethane and from about 25 to about 1 weight percent 2-methylpentane. These azeotropic or azeotrope-like compositions boil at a temperature of about -20 °C to about 60 °C and at a boiling pressure of about 6 kPa to about 202 kPa. In other embodiments, the azeotropic or azeotrope-like compositions comprise from about 73 to about 99 weight percent dichloromethane and from about 27 to about 1 weight percent 2-methylpentane, or from about 75 to about 99 weight percent dichloromethane and from about 25 to about 1 weight percent 2-methylpentane. These azeotropic or azeotrope-like compositions boil at a temperature of about -20 °C to about 40 °C and at a boiling pressure of about 6 kPa to about 105 kPa.

In some embodiments, the azeotropic or azeotrope-like compositions consist essentially of from about 73 to about 99 weight percent dichloromethane and from about 27 to about 1 weight percent 2-methylpentane, or from about 75 to about 99 weight percent dichloromethane and from about 25 to about 1 'weight percent 2-methylpentane. These azeotropic or azeotrope-like compositions boil at a temperature of about -20 °C to about 100 °C and at a boiling pressure of about 6 kPa to about 591 kPa. In other embodiments, the azeotropic or azeotrope-like compositions consist essentially of from about 73 to about

99 weight percent dichloromethane and from about 27 to about 1 weight percent 2- methylpentane, or from about 75 to about 99 weight percent dichloromethane and from about 25 to about 1 weight percent 2-methylpentane. These azeotropic or azeotrope-like compositions boil at a temperature of about -20 °C to about 60 °C and at a boiling pressure of about 6 kPa to about 202 kPa. In other embodiments, the azeotropic or azeotrope-like compositions consist essentially of from about 73 to about 99 weight percent dichloromethane and from about 27 to about 1 weight percent 2-methylpentane, or from about 75 to about 99 weight percent dichloromethane and from about 25 to about 1 weight percent 2-methylpentane. These azeotropic or azeotrope-like compositions boil at a temperature of about -20 °C to about 40 °C and at a boiling pressure of about 6 kPa to about 105 kPa.

In some embodiments, the azeotropic or azeotrope-like compositions consist of from about 73 to about 99 weight percent dichloromethane and from about 27 to about 1 weight percent 2-methylpentane, or from about 75 to about 99 weight percent dichloromethane and from about 25 to about 1 weight percent 2-methylpentane. These azeotropic or azeotrope-like compositions boil at a temperature of about -20 °C to about

100 °C and at a boiling pressure of about 6 kPa to about 591 kPa. In other embodiments, the azeotropic or azeotrope-like compositions consist of from about 73 to about 99 weight percent dichloromethane and from about 27 to about 1 weight percent 2-methylpentane, or from about 75 to about 99 weight percent dichloromethane and from about 25 to about 1 weight percent 2-methylpentane. These azeotropic or azeotrope-like compositions boil at a temperature of about -20 °C to about 60 °C and at a boiling pressure of about 6 kPa to about 202 kPa. In other embodiments, the azeotropic or azeotrope-like compositions consist of from about 73 to about 99 weight percent dichloromethane and from about 27 to about 1 weight percent 2-methylpentane, or from about 75 to about 99 weight percent dichioromethane and from about 25 to about 1 weight percent 2-methylpentane. These azeotropic or azeotrope-like compositions boil at a temperature of about -20 °C to about 40 °C and at a boiling pressure of about 6 kPa to about 105 kPa. In some embodiments, the composition comprising dichloromethane and 2- methylpentane is azeotropic.

In some embodiments, the azeotropic composition consists essentially of from about 80 to about 94.5 weight percent dichloromethane and from about 20 to about 5.5 weight percent 2-methylpentane. In some embodiments, the azeotropic composition consists of from about 80 to about 94.5 weight percent dichloromethane and from about 20 to about 5.5 weight percent 2-methylpentane. These azeotropic compositions boil at a temperature of about -20 °C to about 100 °C and at a boiling pressure of about 7 kPa to about 591 kPa.

In some embodiments, the azeotropic composition consists essentially of about 80.0 weight percent dichloromethane and about 20.0 weight percent 2-methylpentane at a pressure of about 7.1 kPa and at a boiling temperature of about -20 °C. In some embodiments, the azeotropic composition consists of about 80.0 weight percent dichloromethane and about 20.0 weight percent 2-methylpentane at a pressure of about 7.1 kPa and at a boiling temperature of about -20 °C.

In some embodiments, the azeotropic composition consists essentially of about

84.5 weight percent dichloromethane and about 15.5 weight percent 2-methylpentane at a pressure of about 49.2 kPa and at a boiling temperature of about 20 °C. In some embodiments, the azeotropic composition consists of about 84.5 weight percent dichloromethane and about 15.5 weight percent 2-methylpentane at a pressure of about 49.2 kPa and at a boiling temperature of about 20 °C.

In some embodiments, the azeotropic composition consists essentially of about 87.0 weight percent dichloromethane and about 13.0 weight percent 2-methylpentane at a pressure of about 104.8 kPa and at a boiling temperature of about 40 °C. In some embodiments, the azeotropic composition consists of about 87.0 weight percent dichloromethane and about 13.0 weight percent 2-methylpentane at a pressure of about 104.8 kPa and at a boiling temperature of about 40 °C.

In some embodiments, the azeotropic composition consists essentially of about 89.0 weight percent dichloromethane and about 11.0 weight percent 2-methylpentane at a pressure of about 202 kPa and at a boiling temperature of about 60 °C. In some embodiments, the azeotropic composition consists of about 89.0 weight percent dichloromethane and about 11.0 weight percent 2-methylpentane at a pressure of about 202 kPa and at a boiling temperature of about 60 °C.

In some embodiments, the azeotropic composition consists essentially of about

94.5 weight percent dichloromethane and about 5.5 weight percent 2-methylpentane at a pressure of about 591 kPa and at a boiling temperature of about 100 °C. In some embodiments, the azeotropic composition consists of about 94.5 weight percent dichioromethane and about 5.5 weight percent 2-methylpentane at a pressure of about 591 kPa and at a boiling temperature of about 100 °C.

In some embodiments, the azeotropic composition consists essentially of about 86.8 weight percent dichioromethane and about 13.2 weight percent 2-methylpentane at a pressure of about 101.3 kPa and at a boiling temperature of about 38.9 °C. In some embodiments, the azeotropic composition consists of about 86.8 weight percent dichioromethane and about 13.2 weight percent 2-methylpentane at a pressure of about 101.3 kPa and at a boiling temperature of about 38.9 °C.

Azeotropic or azeotrope-like compositions comprising dichioromethane and 3-methylpentane

Provided herein are azeotropic or azeotrope-like compositions comprising dichioromethane and 3-methylpentane.

In some embodiments, the azeotropic or azeotrope-like compositions comprise from about 75 to about 99 weight percent dichioromethane and from about 25 to about 1 weight percent 3-methylpentane, or from about 79 to about 99 weight percent dichioromethane and from about 21 to about 1 weight percent 3-methylpentane. These azeotropic or azeotrope-like compositions boil at a temperature of about -20 °C to about 100 °C and at a boiling pressure of about 6 kPa to about 590 kPa. In other embodiments, the azeotropic or azeotrope-like compositions comprise from about 75 to about 99 weight percent dichioromethane and from about 25 to about 1 weight percent 3-methylpentane, or from about 79 to about 99 weight percent dichioromethane and from about 21 to about 1 weight percent 3-methylpentane. These azeotropic or azeotrope-like compositions boil at a temperature of about -20 °C to about 60 °C and at a boiling pressure of about 6 kPa to about 200 kPa. In other embodiments, the azeotropic or azeotrope-like compositions comprise from about 76 to about 99 weight percent dichioromethane and from about 24 to about 1 weight percent 3-methylpentane, or from about 80 to about 99 weight percent dichioromethane and from about 20 to about 1 weight percent 3-methylpentane. These azeotropic or azeotrope-like compositions boil at a temperature of about -20 °C to about 40 °C and at a boiling pressure of about 6 kPa to about 104 kPa.

In some embodiments, the azeotropic or azeotrope-like compositions consist essentially of from about 75 to about 99 weight percent dichioromethane and from about 25 to about 1 weight percent 3-methylpentane, or from about 79 to about 99 weight percent dichioromethane and from about 21 to about 1 weight percent 3-methylpentane. These azeotropic or azeotrope-like compositions boil at a temperature of about -20 °C to about 100 °C and at a boiling pressure of about 6 kPa to about 590 kPa. In other embodiments, the azeotropic or azeotrope-like compositions consist essentially of from about 75 to about

99 weight percent dichloromethane and from about 25 to about 1 weight percent 3- methylpentane, or from about 79 to about 99 weight percent dichloromethane and from about 21 to about 1 weight percent 3-methylpentane. These azeotropic or azeotrope-like compositions boii at a temperature of about -20 °C to about 60 °C and at a boiling pressure of about 6 kPa to about 200 kPa. In other embodiments, the azeotropic or azeotrope-iike compositions consist essentially of from about 76 to about 99 weight percent dichioromethane and from about 24 to about 1 weight percent 3-methylpentane, or from about 80 to about 99 weight percent dichioromethane and from about 20 to about 1 weight percent 3-methylpentane. These azeotropic or azeotrope-like compositions boil at a temperature of about -20 °C to about 40 °C and at a boiling pressure of about 6 kPa to about 104 kPa.

In some embodiments, the azeotropic or azeotrope-like compositions consist of from about 75 to about 99 weight percent dichioromethane and from about 25 to about 1 weight percent 3-methylpentane, or from about 79 to about 99 weight percent dichioromethane and from about 21 to about 1 weight percent 3-methylpentane. These azeotropic or azeotrope-like compositions boil at a temperature of about -20 °C to about

100 °C and at a boiling pressure of about 6 kPa to about 590 kPa. In other embodiments, the azeotropic or azeotrope-iike compositions consist of from about 75 to about 99 weight percent dichioromethane and from about 25 to about 1 weight percent 3-methylpentane, or from about 79 to about 99 weight percent dichioromethane and from about 21 to about 1 weight percent 3-methylpentane. These azeotropic or azeotrope-iike compositions boil at a temperature of about -20 °C to about 60 °C and at a boiling pressure of about 6 kPa to about 200 kPa. In other embodiments, the azeotropic or azeotrope-iike compositions consist of from about 76 to about 99 weight percent dichioromethane and from about 24 to about 1 weight percent 3-methylpentane, or from about 80 to about 99 weight percent dichioromethane and from about 20 to about 1 weight percent 3-methylpentane. These azeotropic or azeotrope-iike compositions boil at a temperature of about -20 °C to about 40 °C and at a boiling pressure of about 6 kPa to about 104 kPa.

In some embodiments, the composition comprising dichioromethane and 3- methylpentane is azeotropic.

In some embodiments, the azeotropic composition consists essentially of from about 85 to about 95 weight percent dichioromethane and from about 15 to about 5 weight percent 3-methylpentane. In some embodiments, the azeotropic composition consists of from about 85 to about 95 weight percent dichioromethane and from about 15 to about 5 weight percent 3-methylpentane. These azeotropic compositions boil at a temperature of about -20 °C to about 100 °C and at a boiling pressure of about 6 kPa to about 590 kPa. In some embodiments, the azeotropic composition consists essentially of about 85.0 weight percent dichloromethane and about 15.0 weight percent 3-methyipentane at a pressure of about 6.9 kPa and at a boiling temperature of about -20 °C. In some embodiments, the azeotropic composition consists of about 85.0 weight percent dichloromethane and about 15.0 weight percent 3-methylpentane at a pressure of about 6.9 kPa and at a boiling temperature of about -20 °C.

In some embodiments, the azeotropic composition consists essentially of about 88.5 weight percent dichloromethane and about 11 .5 weight percent 3-methylpentane at a pressure of about 48.3 kPa and at a boiling temperature of about 20 °C. In some embodiments, the azeotropic composition consists of about 88.5 weight percent dichloromethane and about 11.5 weight percent 3-methyipentane at a pressure of about

48.3 kPa and at a boiling temperature of about 20 °C.

In some embodiments, the azeotropic composition consists essentially of about 90.0 weight percent dichloromethane and about 10.0 weight percent 3-methylpentane at a pressure of about 103.7 kPa and at a boiling temperature of about 40 °C. In some embodiments, the azeotropic composition consists of about 90.0 weight percent dichloromethane and about 10.0 weight percent 3-methylpentane at a pressure of about 103.7 kPa and at a boiling temperature of about 40 °C.

In some embodiments, the azeotropic composition consists essentially of about 92.0 weight percent dichloromethane and about 8.0 weight percent 3-methylpentane at a pressure of about 201 kPa and at a boiling temperature of about 60 °C. In some embodiments, the azeotropic composition consists of about 92.0 weight percent dichloromethane and about 8.0 weight percent 3-methyipentane at a pressure of about 201 kPa and at a boiling temperature of about 60 °C.

In some embodiments, the azeotropic composition consists essentially of about 95.0 weight percent dichloromethane and about 5.0 weight percent 3-methylpentane at a pressure of about 590 kPa and at a boiling temperature of about 100 °C. In some embodiments, the azeotropic composition consists of about 95.0 weight percent dichloromethane and about 5.0 weight percent 3-methylpentane at a pressure of about 590 kPa and at a boiling temperature of about 100 °C.

In some embodiments, the azeotropic composition consists essentially of about 90.2 weight percent dichloromethane and about 9.8 weight percent 3-methylpentane at a pressure of about 101.3 kPa and at a boiling temperature of about 39.2 °C. In some embodiments, the azeotropic composition consists of about 90.2 weight percent dichloromethane and about 9.8 weight percent 3-methylpentane at a pressure of about

101 .3 kPa and at a boiling temperature of about 39.2 °C. Properties of the azeotropic or azeotrope-like compositions

The compound dichloromethane (DCM) has a reported GWP-100 of 11.2 (IPCC 2021 report). While no specific data is available for 2-methylpentane and 3-methylpentane, values reported for hydrocarbons with up to four carbon atoms show a rapid decline in GWP-100 as the number of carbon atoms increases, so it is reasonable to assume a GWP- 100 of at or close to zero for these compounds.

Accordingly, the azeotropic or azeotrope-like compositions combining the two compounds dichloromethane and 2-methylpentane or the two compounds dichloromethane and 3-methylpentane have a very low global warming potential (GWP). In some embodiments, the azeotropic or azeotrope-like compositions comprising dichloromethane and either 2-methylpentane or 3-methylpentane have a GWP-100 (global warming potential over a 100-year period) of less than about 12 or of less than about 10.

The azeotropic or azeotrope-like compositions as described herein have the advantage of being homogeneous azeotropic or azeotrope-like compositions. For homogenous azeotropic or azeotrope-like compositions, the components of the composition at ambient temperatures and pressures form a single liquid phase. This is to be contrasted with heterogeneous azeotropic or azeotrope-like 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 processes involving the composition are more complex and expensive. The homogeneous nature of the azeotropic or azeotrope-like compositions is achievable over a broad range of practical conditions including ambient pressure and temperature.

The azeotropic or azeotrope-like compositions are useful in a wide range of applications. In some embodiments, the azeotropic or azeotrope-like compositions are used as spin agents for flash spinning, in other embodiments as cleaning agents, and in other embodiments as solvents.

Spin Agents and Spin Fluids for Flash Spinning

In some embodiments, the azeotropic or azeotrope-like compositions are spin agents within spin fluids for flash spinning.

In some embodiments, the spin fluid comprises (a) from about 10 to about 35 weight percent of a polyvinylidene fluoride, based on the total amount of the spin fluid, and (b) a spin agent, wherein the spin agent comprises or consists essentially of the azeotropic or azeotrope-like composition comprising dichloromethane and 2-methylpentane, or the azeotropic or azeotrope-like composition comprising dichloromethane and 3- methylpentane. In other embodiments, the spin fluid comprises (a) from about 15 to about 35 weight percent of a polyvinylidene fluoride, based on the total amount of the spin fluid, and (b) a spin agent, wherein the spin agent comprises or consists essentially of the azeotropic or azeotrope-like composition comprising dichloromethane and 2- methylpentane, or the azeotropic or azeotrope-like composition comprising dichloromethane and 3-methylpentane. In other embodiments, the spin fluid comprises (a) from about 20 to about 30 weight percent of a polyvinylidene fluoride, based on the total amount of the spin fluid, and (b) a spin agent, wherein the spin agent comprises or consists essentially of the azeotropic or azeotrope-like composition comprising dichloromethane and 2-methylpentane, or the azeotropic or azeotrope-like composition comprising dichioromethane and 3-methylpentane.

In some embodiments, the spin fluid for flash spinning a PVDF 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.

In some embodiments, the spin agent consists essentially of from about 84 to about 98 weight percent dichioromethane and from about 16 to about 2 weight percent

2-methylpentane, in other embodiments from about 88 to about 98 weight percent dichioromethane and from about 12 to about 2 weight percent 2-methylpentane, and in other embodiments from about 92 to about 97 weight percent dichioromethane and from about 8 to about 3 weight percent 2-methylpentane. In some embodiments, the spin agent consists essentially of from about 84 to about 92 weight percent dichioromethane and from about 16 to about 8 weight percent 2-methylpentane.

3-methylpentane, in other embodiments from about 88 to about 98 weight percent dichioromethane and from about 12 to about 2 weight percent 3-methylpentane, and in other embodiments from about 92 to about 97 weight percent dichioromethane and from about 8 to about 3 weight percent 3-methylpentane. in some embodiments, the spin agent consists essentially of from about 84 to about 92 weight percent dichioromethane and from about 16 to about 8 weight percent 3-methylpentane.

The spin fluid may include additives, such as antioxidants or acid scavengers in minor amounts, provided that their presence does not interfere with the azeotropic or azeotrope-like nature of the compositions of dichioromethane and 2-methylpentane, or dichioromethane and 3-methylpentane described herein, 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 agent consists of from about 84 to about 98 weight percent dichloromethane and from about 16 to about 2 weight percent 2-methylpentane, in other embodiments from about 88 to about 98 weight percent dichloromethane and from about 12 to about 2 weight percent 2-methylpentane, and in other embodiments from about 92 to about 97 weight percent dichloromethane and from about 8 to about 3 weight percent

2-methylpentane. In some embodiments, the spin agent consists of from about 84 to about 92 weight percent dichloromethane and from about 16 to about 8 weight percent 2- methylpentane.

In some embodiments, the spin agent consists of from about 84 to about 98 weight percent dichloromethane and from about 16 to about 2 weight percent 3-methylpentane, in other embodiments from about 88 to about 98 weight percent dichloromethane and from about 12 to about 2 weight percent 3-methylpentane, and in other embodiments from about 92 to about 97 weight percent dichloromethane and from about 8 to about 3 weight percent

3-methylpentane. In some embodiments, the spin agent consists of from about 84 to about 92 weight percent dichloromethane and from about 16 to about 8 weight percent 3- methylpentane.

In some embodiments, the spin fluid comprising the azeotropic or azeotrope-like composition as described herein exhibits a cloud point pressure in the range of about 45 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 azeotropic or azeotrope-like composition 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 azeotropic or azeotrope-like composition 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 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.

When used as a spin agent, the homogeneous azeotropic or azeotrope-like compositions have the advantage that in the spin agent recovery process, upon condensation of the spin agent, no phase separation occurs. Furthermore, the azeotropic or azeotrope-like compositions described herein result in spin fluids with a cloud point pressure at or close to the azeotrope. This then makes it easy to condense the used spin agent into a liquid with the same or substantially the same composition so that it can be reused.

Preparation of Plexifilamentary Film-fibril Strands of Polyvinylidene Fluoride

In some embodiments, there is provided a process for the preparation of plexifilamentary fibrils of polyvinylidene fluoride. The process comprises the steps of:

(i) generating a spin fluid comprising

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

(b) a spin agent, and

(ii) flash spinning the spin fluid at a pressure above the vapor pressure of the spin fluid into a region of essentially atmospheric pressure to form plexifilamentary fibrils of the polyvinylidene fluoride; wherein the spin agent comprises or consists essentially of

In some embodiments, the flash-spinning is performed at a pressure in the range of about 45 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.

In some embodiments, the spin fluid comprises (a) from about 15 to about 35 weight percent of a polyvinylidene fluoride, based on the total amount of the spin fluid, and (b) a spin agent, wherein the spin agent comprises or consists essentially of the azeotropic or azeotrope-like composition comprising dichloromethane and 2-methylpentane, or the azeotropic or azeotrope-like composition comprising dichloromethane and 3- methylpentane. In other embodiments, the spin fluid comprises (a) from about 20 to about 30 weight percent of a polyvinylidene fluoride, based on the total amount of the spin fluid, and (b) a spin agent, wherein the spin agent comprises or consists essentially of the azeotropic or azeotrope-like composition comprising dichloromethane and 2- methylpentane, or the azeotropic or azeotrope-like composition comprising dichloromethane and 3-methylpentane.

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.

In some embodiments, the spin agent consists essentially of from about 84 to about 98 weight percent dichloromethane and from about 16 to about 2 weight percent

2-methylpentane, in other embodiments from about 88 to about 98 weight percent dichloromethane and from about 12 to about 2 weight percent 2-methylpentane, and in other embodiments from about 92 to about 97 weight percent dichloromethane and from about 8 to about 3 weight percent 2-methylpentane. In some embodiments, the spin agent consists essentially of from about 84 to about 92 weight percent dichloromethane and from about 16 to about 8 weight percent 2-methylpentane.

3-methylpentane, in other embodiments from about 88 to about 98 weight percent dichloromethane and from about 12 to about 2 weight percent 3-methylpentane, and in other embodiments from about 92 to about 97 weight percent dichloromethane and from about 8 to about 3 weight percent 3-methylpentane. In some embodiments, the spin agent consists essentially of from about 84 to about 92 weight percent dichloromethane and from about 16 to about 8 weight percent 3-methylpentane.

The spin fluid may include additives, such as antioxidants or acid scavengers in minor amounts, provided that their presence does not interfere with the azeotropic or azeotrope-like nature of the compositions of dichloromethane and 2-methylpentane, or dichloromethane and 3-methylpentane described herein. 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 agent consists of from about 84 to about 98 weight percent dichloromethane and from about 16 to about 2 weight percent 2-methylpentane, in other embodiments from about 88 to about 98 weight percent dichloromethane and from about 12 to about 2 weight percent 2-methylpentane, and in other embodiments from about 92 to about 97 weight percent dichloromethane and from about 8 to about 3 weight percent 2-methylpentane. In some embodiments, the spin agent consists of from about 84 to about 92 weight percent dichloromethane and from about 16 to about 8 weight percent 2- methylpentane.

In some embodiments, the spin agent consists of from about 84 to about 98 weight percent dichloromethane and from about 16 to about 2 weight percent 3-methylpentane, in other embodiments from about 88 to about 98 weight percent dichloromethane and from about 12 to about 2 weight percent 3-methylpentane, and in other embodiments from about 92 to about 97 weight percent dichloromethane and from about 8 to about 3 weight percent 3-methylpentane. In some embodiments, the spin agent consists of from about 84 to about 92 weight percent dichloromethane and from about 16 to about 8 weight percent 3- methylpentane.

In some embodiments, there is provided plexifilamentary fibrils of polyvinylidene fluoride 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 29 = 10° to 29°, is the |3 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.

The shape of the assembly of plexifilamentary fibrils of polyvinylidene fluoride discharged from each spin orifice may be modified by any methods known in the art. In some embodiments, the plexifilamentary fibrils of polyvinylidene fluoride 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.

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

Sheets comprising plexifilamentary fibrils of polyvinylidene fluoride (PVDF) 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 plexifiiamentary 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 plexifiiamentary 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.

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.

In some embodiments, the collected sheet of nonwoven flash-spun plexifiiamentary 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 plexifiiamentary fibrils. In some embodiments, the sheet may be passed under a roller which applies pressure to the sheet to form a consolidated sheet.

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.

In some embodiments, the bonded sheet is subjected to a mechanical softening process to obtain a softened sheet of nonwoven flash-spun plexifiiamentary 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.

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

The sheet of nonwoven flash-spun plexifiiamentary 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.

EXAMPLES

A study has been performed for the phase behavior and flash spinning of a polyvinyiidene fluoride (PVDF). 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.

Materials Used

Dichloromethane (DCM), CAS Number 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.

2-Methylpentane (2-MP), CAS Number 107-83-5, has an atmospheric boiling point of 60 °C and a molecular weight of 86.18 g/mol. The 2-methylpentane used had a purity level above 99 %.

3-Methylpentane (3-MP), CAS Number 96-14-0, has an atmospheric boiling point of 64 °C and a molecular weight of 86.18 g/mol. The 3-methylpentane used had a purity level above 99 %.

The polyvinyiidene 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.

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

Spinning Equipment

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 0.020 inch (0.508 mm) and a length of 0.020 inch (0.508 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.

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.

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.

Results

Example 1: Vapor liquid equilibrium for the composition of dichloromethane and 2-methylpentane

Figure 1 shows the calculated vapor liquid equilibrium for the composition of dichloromethane and 2-methylpentane. The azeotropic composition of dichloromethane and 2-methylpentane at 40°C corresponds to about 87.0 wt% dichloromethane and about 13.0 wt% 2-methylpentane. The bubble point pressure for the azeotropic composition is equal to about 104.8 kPa. The azeotropic-like composition of dichloromethane and 2- methylpentane at a 5% deviation from the azeotrope point was found to be from about 73:27 wt% to about 99:1 wt%.

Example 2: Vapor liquid equilibrium for the composition of dichloromethane and 3-methylpentane

Figure 2 shows the calculated vapor liquid equilibrium for the composition of dichloromethane and 3-methylpentane. The azeotropic composition of dichloromethane and 3-methylpentane at 40°C corresponds to about 90.0 wt% dichloromethane and about 10.0 wt% 3-methylpentane. The bubble point pressure for the azeotropic composition is equal to about 103.7 kPa. The azeotropic-like composition of dichloromethane and 3- methylpentane at a 5% deviation from the azeotrope point was found to be from about 76:24 wt% to about 99:1 wt%.

Examples 3, 4 and 5: Cloud point study of polyvinylidene fluoride

Figure 3 shows the cloud point pressure curves of three different spin fluids comprising PVDF at different concentrations and a spin agent of dichloromethane and 2- methylpentane in different ratios by weight. Example 3 concerns the cloud point pressure curve of a spin fluid comprising 25 wt% PVDF (Kynar® 740) and a spin agent of dichloromethane and 2-methylpentane in a 87:13 ratio by weight.

Example 4 concerns the cloud point pressure curve of a spin fluid comprising 30 wt% PVDF (Kynar® 740) and a spin agent of dichloromethane and 2-methylpentane in a 93:7 ratio by weight.

Example 5 concerns the cloud point pressure curve of a spin fluid comprising 22 wt% PVDF (Kynar® 740) and a spin agent of dichloromethane and 2-methylpentane in a 97:3 ratio by weight.

These spin fluids comprising from 22 wt% to 30 wt% PVDF show a cloud point pressure curve suitable for flash spinning.

Example 6: Cloud point study of polyvinyl idene fluoride

Figure 4 shows the cloud point pressure curve of a spin fluid comprising 28 wt% PVDF (Kynar® 740) and a spin agent of dichloromethane and 3-methylpentane in a 91 :8 ratio by weight. This spin fluid comprising 28 wt% PVDF shows a cloud point pressure curve suitable for flash spinning.

Examples 7, 8, and 9: Flash spinning performance of polyvinylidene fluoride

Flash spinning of was performed on the equipment described in the above for different spin fluids. The Table 1 below shows the conditions for flash spinning PVDF from spin fluids comprising PVDF in different concentrations and different spin agents at different temperatures.

Table 1 : Summary of the flash spinning experiments of Examples 7, 8, and 9.

* assuming a GWP of 11 .2 for the dichloromethane and a GWP of about zero for the 2- methyl pentane, and the 3-methylpentane

** based on the intensity level in the range 28 = 26.7° - 26.8°

The above examples illustrate that the azeotropic or azeotrope-like compositions of dichloromethane and 2-methylpentane, and azeotropic or azeotrope-like compositions of di chloromethane and 3-methylpentane can be used as a spin agent for the flash spinning process 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.

In addition, the azeotropic or azeotrope-like compositions exhibit a desirably low GWP value of less than 12, or less than 10. This makes these compositions suitable as replacement for spin agent disclosed in the prior art.

Furthermore, the azeotropic or azeotrope-like compositions form positive homogenous azeotropes with an advantageously low boiling temperature below 50 °C. Such low boiling temperatures correlate to a pressure around (or only slightly above) atmospheric pressure.

The azeotrope-like compositions which are centered around the azeotrope point exhibit only small differences between the bubble point pressure and the dew point pressure. This has the advantage that the azeotropic or azeotrope-like compositions do not change significantly during the different steps of the spin agent recovery process and thus allow the spin agent to be re-used/recycled in a commercial process.

OTHER EMBODIMENTS

1. In some embodiments, the present application provides an azeotropic or azeotropelike composition comprising

(1) dichloromethane and 2-methylpentane; or

(2) dichioromethane and 3-methylpentane. 2. The azeotropic or azeotrope-like composition of embodiment 1 comprising from about 73 to about 99 weight percent dichloromethane and from about 27 to about 1 weight percent 2-methylpentane.

3. The azeotropic or azeotrope-like composition of embodiment 2 consisting essentially of or consisting of from about 73 to about 99 weight percent dichloromethane and from about 27 to about 1 weight percent 2-methylpentane.

4. The azeotropic or azeotrope-like composition of any one of embodiments 2 to 3 comprising from about 75 to about 99 weight percent dichloromethane and from about 25 to about 1 weight percent 2-methylpentane.

5. The azeotropic or azeotrope-like composition of embodiment 4 consisting essentially of or consisting of from about 75 to about 99 weight percent dichloromethane and from about 25 to about 1 weight percent 2-methylpentane.

6. The azeotropic or azeotrope-like composition of any one of embodiments 2 to 5 boiling at a temperature of about -20 °C to about 100 °C at a pressure of about 6 kPa to about 591 kPa.

7. The azeotropic or azeotrope-like composition of any one of embodiments 2 to 5 boiling at a temperature of about -20 °C to about 60 °C at a pressure of about 6 kPa to about 202 kPa.

8. The azeotropic or azeotrope-like composition of any one of embodiments 2 to 5 boiling at a temperature of about -20 °C to about 40 °C at a pressure of about 6 kPa to about 105 kPa.

9. The azeotropic composition of any one of the embodiments 2 to 8 consisting essentially of or consisting of from about 80 to about 94.5 weight percent dichloromethane and from about 20 to about 5.5 weight percent 2-methylpentane.

10. The azeotropic composition of embodiment 9 boiling at a temperature of about -20 °C to about 100 °C at a pressure of about 7 kPa to about 591 kPa. 11. The azeotropic composition of any one of the embodiments 2 to 10 consisting essentially of or consisting of about 80.0 weight percent dichloromethane and about 20.0 weight percent 2-methylpentane.

12. The azeotropic composition of embodiment 11 boiling at a temperature of about -20 °C at a pressure of about 7.1 kPa.

13. The azeotropic composition of any one of the embodiments 2 to 10 consisting essentially of or consisting of about 84.5 weight percent dichloromethane and about 15.5 weight percent 2-methylpentane.

14. The azeotropic composition of embodiment 13 boiling at a temperature of about 20 °C at a pressure of about 49.2 kPa.

15. The azeotropic composition of any one of the embodiments 2 to 10 consisting essentially of or consisting of about 87.0 weight percent dichloromethane and about 13.0 weight percent 2-methylpentane.

16. The azeotropic composition of embodiment 15 boiling at a temperature of about 40 °C ata pressure of about 104.8 kPa.

17. The azeotropic composition of any one of the embodiments 2 to 10 consisting essentially of or consisting of about 89.0 weight percent dichloromethane and about 11.0 weight percent 2-methylpentane.

18. The azeotropic composition of embodiment 17 boiling at a temperature of about 60 °C at a pressure of about 202 kPa.

19. The azeotropic composition of any one of the embodiments 2 to 10 consisting essentially of or consisting of about 94.5 weight percent dichloromethane and about 5.5 weight percent 2-methylpentane.

20. The azeotropic composition of embodiment 19 boiling at a temperature of about 100 °C at a pressure of about 591 kPa. 21. The azeotropic composition of any one of the embodiments 2 to 10 consisting essentially of or consisting of about 86.8 weight percent dichioromethane and about 13.2 weight percent 2-methylpentane.

22. The azeotropic composition of embodiment 21 boiling at a temperature of about 38.9 °C at a pressure of about 101.3 kPa.

23. The azeotropic or azeotrope-like composition of embodiment 1 comprising from about 75 to about 99 weight percent dichloromethane and from about 25 to about 1 weight percent 3-methylpentane.

24. The azeotropic or azeotrope-like composition of embodiment 23 consisting essentially of or consisting of from about 75 to about 99 weight percent dichloromethane and from about 25 to about 1 weight percent 3-methylpentane.

25. The azeotropic or azeotrope-like composition of embodiment 23 or 24 comprising from about 79 to about 99 weight percent dichloromethane and from about 21 to about 1 weight percent 3-methylpentane.

26. The azeotropic or azeotrope-like composition of embodiment 25 consisting essentially of or consisting of from about 79 to about 99 weight percent dichioromethane and from about 21 to about 1 weight percent 3-methylpentane.

27. The azeotropic or azeotrope-like composition of any one of embodiments 23 to 26 boiling at a temperature of about -20 °C to about 100 °C at a pressure of about 6 kPa to about 590 kPa.

28. The azeotropic or azeotrope-like composition of any one of embodiments 23 to 26 boiling at a temperature of about -20 °C to about 60 °C at a pressure of about 6 kPa to about 200 kPa.

29. The azeotropic or azeotrope-like composition of any one of embodiments 23 to 28 comprising from about 76 to about 99 weight percent dichioromethane and from about 24 to about 1 weight percent 3-methylpentane. 30. The azeotropic or azeotrope-like composition of embodiment 29 consisting essentially of or consisting of from about 76 to about 99 weight percent dichioromethane and from about 24 to about 1 weight percent 3-methy!pentane.

31. The azeotropic or azeotrope-like composition of embodiment 29 or 30 comprising from about 80 to about 99 weight percent dichioromethane and from about 20 to about 1 weight percent 3-methylpentane.

32. The azeotropic or azeotrope-like composition of embodiment 31 consisting essentially of or consisting of from about 80 to about 99 weight percent dichioromethane and from about 20 to about 1 weight percent 3-methyipentane.

33. The azeotropic or azeotrope-like composition of any one of embodiments 29 to 32 boiling at a temperature of about -20 °C to about 40 °C at a pressure of about 6 kPa to about 104 kPa.

34. The azeotropic composition of any one of the embodiments 23 to 33 consisting essentially of or consisting of from about 85 to about 95 weight percent dichioromethane and from about 15 to about 5 weight percent 3-methylpentane.

35. The azeotropic composition of embodiment 34 boiling at a temperature of about - 20 °C to about 100 °C at a pressure of about 6 kPa to about 590 kPa.

36. The azeotropic composition of any one of the embodiments 23 to 33 consisting essentially of or consisting of about 85.0 weight percent dichioromethane and about 15.0 weight percent 3-methylpentane.

37. The azeotropic composition of embodiment 36 boiling at a temperature of about - 20 °C at a pressure of about 6.9 kPa.

38. The azeotropic composition of any one of the embodiments 23 to 33 consisting essentially of or consisting of about 88.5 weight percent dichioromethane and about 11.5 weight percent 3-methylpentane.

39. The azeotropic composition of embodiment 38 boiling at a temperature of about 20 °C at a pressure of about 48.3 kPa. 40. The azeotropic composition of any one of the embodiments 23 to 33 consisting essentially of or consisting of about 90.0 weight percent dichloromethane and about 10.0 weight percent 3-methylpentane.

41. The azeotropic composition of embodiment 40 boiling at a temperature of about 40 °C ata pressure of about 103.7 kPa.

42. The azeotropic composition of any one of the embodiments 23 to 33 consisting essentially of or consisting of about 92.0 weight percent dichloromethane and about 8.0 weight percent 3-methylpentane.

43. The azeotropic composition of embodiment 42 boiling at a temperature of about 60 °C at a pressure of about 201 kPa.

44. The azeotropic composition of any one of the embodiments 23 to 33 consisting essentially of or consisting of about 95.0 weight percent dichloromethane and about 5.0 weight percent 3-methylpentane.

45. The azeotropic composition of embodiment 44 boiling at a temperature of about 100 °C at a pressure of about 590 kPa.

46. The azeotropic composition of any one of the embodiments 23 to 33 consisting essentially of or consisting of about 90.2 weight percent dichloromethane and about 9.8 weight percent 3-methylpentane.

47. The azeotropic composition of embodiment 46 boiling at a temperature of about 39.2 °C at a pressure of about 101.3 kPa.

48. in some embodiments, the present application provides a spin fluid for flash spinning comprising

(b) a spin agent, wherein the spin agent comprises or consists essentially of an azeotropic or azeotrope-like composition comprising

(1) dichloromethane and 2-methylpentane, or

(2) dichloromethane and 3-methylpentane. 49. The spin fluid of embodiment 48 comprising from about 15 to about 35 weight percent of a polyvinyiidene fluoride, based on the total amount of the spin fluid, or from about 20 to about 30 weight percent of a polyvinyiidene fluoride, based on the total amount of the spin fluid.

50. The spin fluid of embodiment 48 or 49 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.

51 . The spin fluid of any one of embodiments 48 to 50, wherein the spin agent consists essentially of or consists of from about 84 to about 98 weight percent dichloromethane and from about 16 to about 2 weight percent 2-methylpentane, or from about 88 to about 98 weight percent dichloromethane and from about 12 to about 2 weight percent 2- methylpentane, or from about 92 to about 97 weight percent dichloromethane and from about 8 to about 3 weight percent 2-methylpentane.

52. The spin fluid of any one of embodiments 48 to 51, wherein the spin agent consists essentially of or consists of from about 84 to about 92 weight percent dichloromethane and from about 16 to about 8 weight percent 2-methylpentane.

53. The spin fluid of any one of embodiments 48 to 50, wherein the spin agent consists essentially of or consists of from about 84 to about 98 weight percent dichloromethane and from about 16 to about 2 weight percent 3-methylpentane, or from about 88 to about 98 weight percent dichloromethane and from about 12 to about 2 weight percent 3- methylpentane, or from about 92 to about 97 weight percent dichloromethane and from about 8 to about 3 weight percent 3-methylpentane.

54. The spin fluid of any one of embodiments 48 to 50, or 53, wherein the spin agent consists essentially of or consists of from about 84 to about 92 weight percent dichloromethane and from about 16 to about 8 weight percent 3-methylpentane.

55. In some embodiments, the present application provides a process for the preparation of plexifilamentary fibrils of polyvinyiidene fluoride comprising the steps of:

(i) generating a spin fluid comprising (a) about 10 to about 35 weight percent of a polyvinyiidene fluoride, based on the total amount of the spin fluid, and

(b) a spin agent, and

(ii) flash spinning the spin fluid at a pressure above the vapor pressure of the spin fluid into a region of essentially atmospheric pressure to form plexifilamentary fibrils of the polyvinyiidene fluoride; wherein the spin agent comprises or consists essentially of

(1 ) an azeotropic or azeotrope-like composition comprising dichioromethane and 2-methylpentane, or

(2) an azeotropic or azeotrope-like composition comprising dichioromethane and 3-methylpentane.

56. The process of embodiment 55 wherein the spin fluid comprises from about 15 to about 35 weight percent of a polyvinyiidene fluoride, based on the total amount of the spin fluid, or from about 20 to about 30 weight percent of a polyvinyiidene fluoride, based on the total amount of the spin fluid.

57. The process of embodiment 55 or 56 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, based on the total amount of the spin fluid.

58. The process of any one of embodiments 55 to 57, wherein the spin agent consists essentially of or consists of from about 84 to about 98 weight percent dichloromethane and from about 16 to about 2 weight percent 2-methylpentane, or from about 88 to about 98 weight percent dichioromethane and from about 12 to about 2 weight percent 2- methylpentane, or from about 92 to about 97 weight percent dichioromethane and from about 8 to about 3 weight percent 2-methyipentane.

59. The process of any one of embodiments 55 to 58, wherein the spin agent consists essentially of or consists of from about 84 to about 92 weight percent dichioromethane and from about 16 to about 8 weight percent 2-methylpentane.

60. The process of any one of embodiments 55 to 57, wherein the spin agent consists essentially of or consists of from about 84 to about 98 weight percent dichioromethane and from about 16 to about 2 weight percent 3-methylpentane, or from about 88 to about 98 weight percent dichloromethane and from about 12 to about 2 weight percent 3- methylpentane, or from about 92 to about 97 weight percent dichloromethane and from about 8 to about 3 weight percent 3-methylpentane.

61. The process of any one of embodiments 55 to 57, or 60, wherein the spin agent consists essentially of or consists of from about 84 to about 92 weight percent dichloromethane and from about 16 to about 8 weight percent 3-methylpentane.

62. In some embodiments, the present application provides a use of the spin fluid of any of embodiments 48 to 54 for preparing plexifilamentary fibrils of polyvinylidene fluoride by flash spinning.

63. The plexifilamentary fibrils of polyvinylidene fluoride obtainable or obtained by the process of any one of embodiments 55 to 61.

64. The plexifilamentary fibrils of polyvinylidene fluoride of embodiment 62 wherein the only detectable PVDF crystal phase is the β crystal phase whereas no significant portions of the a or y crystal phases are detectable.

65. The plexifilamentary fibrils of polyvinyiidene fluoride of embodiment 64 having a crystallinity index (p phase) of about 32 % or more, or about 34 % or more, or about 35 % or more.

66. A sheet of nonwoven flash-spun plexifilamentary fibrils comprising plexifilamentary fibrils of polymer of any of embodiments 63 to 65.

67. The sheet of embodiment 66, wherein the sheet is a collected sheet, a consolidated sheet, a bonded sheet, or a softened sheet.

68. A bonded sheet obtainable by thermally or mechanically bonding the consolidated sheet of embodiment 67.

69. A softened sheet obtainable by softening the consolidated sheet of embodiment 67 or by softening the bonded sheet of embodiment 68.

70. An article comprising plexifilamentary fibrils of polyvinylidene fluoride of any of embodiments 63 to 65 and/or a sheet of any one of embodiments 66 to 69. 71. The article of embodiment 70 which is selected from packaging material, filtration media, print media, tags and labels, accessories, and electronic devices.

72. The article of embodiment 71, wherein the electronic devices are selected from pressure sensors, strain gauges, microphones, actuators, energy harvesters, and nanogenerators.

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

1. An azeotropic or azeotrope-like composition comprising

(1) dichloromethane and 2-methylpentane, or

(2) dichloromethane and 3-methylpentane.

2. The azeotropic or azeotrope-like composition of claim 1 comprising from about 73 to about 99 weight percent dichloromethane and from about 27 to about 1 weight percent

2-methylpentane.

3. The azeotropic composition of any one of claims 1 or 2 consisting essentially of from about 80 to about 94.5 weight percent dichloromethane and from about 20 to about 4.5 weight percent 2-methylpentane.

4. The azeotropic composition of claim 3 boiling at a temperature of about -20 °C to about 100 °C at a pressure of about 7 kPa to about 591 kPa.

5. The azeotropic or azeotrope-like composition of claim 1 comprising from about 75 to about 99 weight percent dichloromethane and from about 25 to about 1 weight percent

3-methylpentane.

6. The azeotropic composition of any one of claims 1 or 5 consisting essentially of from about 85 to about 95 weight percent dichloromethane and from about 15 to about 5 weight percent 3-methylpentane.

7. The azeotropic composition of claim 6 boiling at a temperature of about -20 °C to about 100 °C at a pressure of about 6 kPa to about 590 kPa.

8. A spin fluid for flash spinning comprising

(a) from about 10 to about 35 weight percent of a poly vinylidene fluoride, based on the total amount of the spin fluid, and

(b) a spin agent, wherein the spin agent comprises an azeotropic or azeotrope-like composition comprising

(1) dichloromethane and 2-methylpentane, or

(2) dichloromethane and 3-methylpentane.

9. The spin fluid of claim 8 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.

10. The spin fluid of any one of claims 8 or 9, wherein the spin agent comprises an azeotropic or azeotrope-like composition which

(1) consists essentially of or consists of from about 84 to about 98 weight percent dichioromethane and from about 16 to than about 2 weight percent 2-methylpentane, or

(2) consists essentially of or consists of from about 84 to about 98 weight percent dichioromethane and from about 16 to about 2 weight percent 3-methylpentane.

11. A process for the preparation of plexifilamentary fibrils of polyvinylidene fluoride which comprises the steps of:

(i) generating a spin fluid comprising

(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; wherein the spin agent comprises an azeotropic or azeotrope-like composition comprising dichioromethane and 2-methylpentane, or wherein the spin agent comprises an azeotropic or azeotrope-like composition comprising dichioromethane and 3-methylpentane.

12. The process of claim 11 , 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, based on the total amount of the spin fluid.

13. The process of any one of claims 11 or 12, wherein the spin agent comprises an azeotropic or azeotrope-like composition which

(1) consists essentially of or consists of from about 84 to about 98 weight percent dichioromethane and from about 16 to than about 2 weight percent 2-methyfpentane or (2) consists essentialiy of or consists of from about 84 to about 98 weight percent dichloromethane and from about 16 to about 2 weight percent 3-methylpentane.

14. Use of the spin fluid of any one of claims 8 to 10 for preparing of plexifilamentary fibrils of polyvinylidene fluoride by flash spinning.

15. Plexifilamentary fibrils of polyvinylidene fluoride obtainable by the process of any one of claims 11 to 13.

16. The plexifilamentary fibrils of polyvinylidene fluoride of claim 15 wherein the only detectable PVDF crystal phase is the 0 crystal phase whereas no significant portions of the a or y crystal phases are detectable.

17. A sheet of nonwoven flash-spun plexifilamentary fibrils comprising plexifilamentary fibrils of polyvinylidene fluoride of claim 15 or 16.

18. An article comprising the plexifilamentary fibrils of polyvinylidene fluoride of claim 15 or 16 and/or the sheet of claim 17.

19. The article of claim 18 which is selected from packaging material, filtration media, print media, tags and labels, accessories, and electronic devices.