PVDF Of Fluorocarbon Family

November 03, 2024

Fluorine resin family of PVDF crystalline form, basic properties, synthesis method, application areas and major manufacturers

I. Introduction of PVDF

Polyvinylidene fluoride (PVDF) resin is an important fluoropolymer product, and is the second largest production and use of fluorine-containing plastics.PVDF resin is made from homopolymerization or copolymerization of vinylidene fluoride (VDF), with a relative molecular mass of (40~2) million.PVDF resin combines the characteristics of fluorine resins and general-purpose resins, and has excellent processing performance, weather resistance, corrosion resistance, insulation, piezoelectricity and dielectricity, etc. PVDF resin is also widely used in the manufacture of fluorine resins, and is widely used in the manufacture of fluorine resins, PVDF resin has excellent processability, weatherability, corrosion resistance, insulation, piezoelectricity and dielectricity.

The main chain of PVDF has an alternating CH2- and CF2- group structure, which influences PVDF to have some of the excellent properties of polyethylene (-CH2-CH2-)n and polytetrafluoroethylene (-CF2-CF2-)n, etc. Some commercially available grades of PVDF resin are available in a wide range of sizes. Some commercially available grades of PVDF are copolymers of VDF and a small amount of other fluorine-containing monomers (generally less than 6%), the use of fluorine-containing monomers such as HFP, CTFE and TFE, etc., the addition of copolymerization monomers so that the polymer has some different properties from homopolymers, such as to improve the softness of the PVDF, so that it is more suitable for wire and cable processing.

Second, the crystalline form of PVDF

Polyvinylidene fluoride (PVDF) homopolymers are semi-crystalline polymers whose degree of crystallinity varies from 50% to 70% depending on the production method and thermodynamic history of the process. The degree of crystallinity greatly affects the rigidity, mechanical strength and impact resistance of PVDF polymers. Other factors affecting the properties of PVDF include molecular weight and its distribution, irregularities in the polymer's carbon-carbon chains, and crystalline morphology. Similar to other linear polyolefins, the crystalline form of PVDF polymers consists of layered lattices and spherical forms. The difference in size and distribution between the two for different sizes of PVDF products is determined by the method of polymerization.

The crystallization of PVDF exhibits a complex homogeneous polycrystalline phenomenon not seen in other known polymers. There are four different crystalline forms: α, β, γ, and δ. Five crystalline forms have also been reported in the literature, namely α, β, γ, δ, and ε. These crystalline forms are present in different ratios, and factors affecting the ratio of these crystalline structures include: pressure, electric field strength, controlled melt crystallization, precipitation from solvents, and the presence or absence of crystalline species during crystallization. α and β are the most common crystalline forms in practical situations. morphology. Usually, the α crystalline state is formed during normal melt processing, the β crystalline state grows from mechanical deformation of the melt-processed sample, the γ crystalline state is generated under special conditions, and the δ crystalline state is caused by distortion of one phase under a high electric field. The density of PVDF is 1.98 g/cm3 for all α-crystalline cases, and 1.68 g/cm3 for amorphous PVDF, so that when the density of a typical commercially available PVDF product is 1.75 to 1.78 g/cm3, this indicates that its degree of crystallinity is about 40%.

Third, the basic performance of PVDF

(1) Mechanical properties

PVDF has excellent mechanical properties. Compared with perfluorocarbon polymers, the elastic deformation under load (i.e. creep resistance) is much better, the life of repeated flexing is longer, and the aging resistance is also improved. Mechanical strength is significantly improved by directional treatment. Filling a small amount of glass beads or carbon fibers can improve the strength of the base polymer.PVDF mechanical properties are as follows.

PVDF (polyvinylidene fluoride) has excellent mechanical properties, and its mechanical property parameters are as follows:

Tensile Strength: The tensile strength of PVDF is up to 50MPa, almost twice that of PTFE (polytetrafluoroethylene)1.

Tensile Modulus: At a tensile rate of 5mm/min, the tensile modulus of PVDF is 2280MPa2.

Tensile Yield Strength: At a tensile rate of 50mm/min, the tensile yield strength of PVDF is 59MPa2.

Elongation at break: At a tensile rate of 50mm/min, the elongation at break of PVDF is 60%2.

Flexural strength: the flexural strength of PVDF is between 48 and 62 MPa3.

Flexural modulus of elasticity: the flexural modulus of PVDF is between 1.4 and 1.8 GPa3.

Compression strength: The compression strength of PVDF is between 69 and 103 MPa3.

Impact strength: The impact strength of PVDF is 211J-m-¹3.

Performances	60Hz	10-3 Hz	10-6Hz	10-9Hz
Dielectric constant (25°C)	9~10	8~9	8~9	3~4
Dielectric loss	0.03~0.05	0.005~0.02	0.03~0.05	0.09~0.11
Volume resistance/Ω.m				2x10-12
Dielectric strength Thickness/0.003175m Thichness/0.000203m				260 1300

(2) Electrical properties

The values of electrical properties of PVDF homopolymer without any filler and untreated are listed in Table 2, where the values vary considerably with cooling and post-treatment, which determine the polymer to have different crystalline forms. For specimens that were treated under various conditions at very high electric field strengths (polarization) oriented to obtain a directionally polarized crystalline morphology, dielectric constants as high as 17 were measured.

The unique dielectric properties of PVDF and the homogeneous polycrystalline phenomenon give this polymer high piezoelectric and thermoelectric activity. The relationship between the ferroelectric phenomena of PVDF, including piezoelectric and thermoelectric properties, and other electrical properties has been specifically discussed in the references. The high dielectric constant structure obtained and the complex homogeneous polycrystalline phenomena along with the high dielectric loss factor make it impossible to use PVDF as an insulating material for conductors exposed to high-frequency currents, since the insulating material would heat up in this case and may even melt. On the other hand, PVDF can be easily melted by means of radiofrequency or electrolyte heating, and this feature is used in certain processes or connections. High-energy irradiation cross-links PVDF, thereby increasing its mechanical strength. This property is also unique among polyolefin polymers, as other polymers degrade when exposed to high energy irradiation.

(3) Chemical properties

PVDF also has excellent chemical properties and is resistant to most inorganic acids, weak bases, halogens and oxidizing agents even at high temperatures, as well as to organic aliphatic and aromatic compounds and chlorinated solvents. However, strong bases, amines, esters and ketones can cause PVDF to swell, soften or even dissolve depending on the conditions. Certain esters and ketones can be used as co-solvents to dissolve PVDF. Such a system allows the molten coating to dissolve as the temperature rises, resulting in a good lamination.

PVDF is one of the few semi-crystalline polymers that is compatible with other polymers, particularly acrylic and methacrylic resins. The crystalline form, properties and performance of these blended polymers are dependent on the structure and composition of the added polymers, as well as the composition of the PVDF. For example, ethyl polyacrylate is completely miscible with PVDF, whereas isopropyl polyacrylate and its congeners are not. When selecting a match, it is important to have a strong dipole effect to obtain compatibility with PVDF, whereas polyvinyl fluoride is not compatible with polyvinylidene fluoride.

Author:

Ms. Tina

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sales@honyplastic.com

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