CN103146101B - Preparation method of high-crystallinity polyvinylidene fluoride (PVDF) - Google Patents

Abstract

The invention discloses a preparation method of high-crystallinity polyvinylidene fluoride (PVDF), which comprises the following steps: adding a microsphere expanding agent of which the thermal expansion coefficient is far higher than that of PVDF in the preparation of the PVDF material, wherein when the temperature rises from room temperature to the melting temperature of the PVDF, the microsphere sharply expands, and the volume of the microsphere is increased by about 10-20 times in comparison with the situation at room temperature; and then, cooling the PVDF from the melting temperature to room temperature to ensure that the PVDF is gradually solidified and crystallized, wherein in the cooling process, the microsphere sharply shrinks, so that uniform tensile stress can be formed in the PVDF in the solidification process, and the tensile stress can improve the crystallinity of a beta phase in the PVDF. For the PVDF prepared by the method, the crystallinity of the beta phase is obviously improved; and the pyroelectric property of the material is superior to that of the PVDF material prepared by a common method. The PVDF organic ferroelectric material prepared by the invention has high beta-phase crystallinity and spontaneous polarization rate and favorable pyroelectric property, and conforms to the use requirements of ferroelectric organic materials.

Description

A kind of preparation method of high-crystallinity polyvinylidene difluoride (PVDF)

Technical field

The invention belongs to the technology of preparing of high-performance organic functional material, specifically, relate to the preparation method of high-crystallinity polyvinylidene difluoride (PVDF).

Background technology

In various materials, ferroelectric material, because having good dielectric, piezoelectricity and pyroelectric property, is widely used in preparing large value capacitor, electric energy storing device, energy harvester, pressure transmitter and non-refrigerated infrared detector etc.

Ferroelectric material can be divided into inorganic iron electric material and the large class of Organic Iron electric material two.Inorganic iron electric material (as the potteries such as barium titanate, Pb-based lanthanumdoped zirconate titanates and monocrystalline) ferroelectricity is good, widely applies.But the shortcoming of inorganic iron electric material is that preparation cost is high, complicated process of preparation, material brittle, do not there is snappiness, opaque and follow-up use processing difficulties.In addition, the ferroelectric material of larger area or volume be prepared, also special main equipment and technique must be adopted.Compare with inorganic iron electric material, Organic Iron electric material has softness, transparent, low cost of manufacture, technique is simple and be easy to the features such as processing.The Organic Iron electric material of larger area or volume also can be manufactured by common equipment and technique.

In numerous organism materials, polyvinylidene difluoride (PVDF) (PVDF) is the most noticeable.The degree of crystallinity of PVDF is high, its unique molecular chain structure makes can form the β phase crystallization with higher spontaneous polarizability in its body, and spontaneous polarizability is to weigh the ferroelectric important indicator of material, therefore the ferroelectricity of PVDF is better than other organic materialss, and the size of material spontaneous polarizability also becomes the important indicator of weighing its β phase degree of crystallinity.Yet generally,, except having good ferroelectric β phase crystal formation, PVDF also can follow in preparation process does not have ferroelectric alpha-crystal form growth (spontaneous polarizability of α phase is 0).Therefore the degree of crystallinity that how to improve β phase crystal formation is the key of preparation high-performance PVDF Organic Iron electric material.

For improving the content of β phase crystal formation in PVDF, a lot of methods are used.Adopt crystal pulling method, in the process of setting of PVDF, it is applied to tension stress, can effectively improve β phase degree of crystallinity, but the method requires high, complex process to Preparation equipment, is not suitable for a large amount of production; In PVDF, add three fluorine ethylenes (TrFE), form polyvinylidene difluoride (PVDF)-tri-fluorine ethylenes (P (VDF-TrFE)) Ferroelectric Copolymers, also can improve the degree of crystallinity of material beta phase, but (P (VDF-TrFE)) multipolymer is expensive; In PVDF, adding muriate, as bismuth chloride etc., is also the method for conventional raising material beta phase content, and the method is simple to operation, but undesirable to the raising effect of β phase degree of crystallinity.

Although PVDF has the unrivaled softness of inorganic iron electric material, transparent, low cost of manufacture, technique is simple and be easy to the features such as processing, and ferroelectricity is better than other organic materialss, make PVDF be used widely, the further raising that needs of its ferroelectricity.Therefore, the method for the raising PVDF material beta phase degree of crystallinity that research and development is simple effective and with low cost, has stronger realistic meaning, is to make PVDF obtain the key of further widespread use.

Summary of the invention

The object of the present invention is to provide a kind of preparation method of simple and effective high-crystallinity polyvinylidene difluoride (PVDF), the method can improve PVDF material beta phase degree of crystallinity.

The preparation method of a kind of polyvinylidene difluoride (PVDF) provided by the invention, its step comprises:

(1) PVDF is mixed with acrylic resin microballoon swelling agent for 99: 1 in mass ratio～80: 20, ball milling evenly mixes it;

(2) dry and obtain mixed powder;

(3) powder is heated to 175 ℃～200 ℃, makes PVDF melting, simultaneously at the pressure that axially applies 2MPa～8MPa;

(4) insulation is 10～60 minutes, then cooling;

(5) when temperature is down to 100 ℃～80 ℃, shed pressure, be cooled to room temperature.

The method of raising PVDF material beta phase degree of crystallinity provided by the invention is by adding thermal expansivity much larger than the microballoon swelling agent of PVDF in the preparation of PVDF material, when temperature rises to the melt temperature (approximately 185 ℃) of PVDF from room temperature, microballoon sharply expands, and the volume of microballoon is compared with increasing approximately 10～20 times in room temperature situation.After this PVDF is lowered the temperature, from melt temperature, be cooled to the process of room temperature, PVDF is solidification and crystallization gradually.In this course, microballoon sharply shrinks, and makes PVDF in process of setting, in body, form uniform tension stress, and tension stress can improve the degree of crystallinity of β phase in PVDF.The PVDF that utilizes the method to prepare, its β phase degree of crystallinity obviously improves, and material pyroelectric property (pyroelectric coefficient) is better than PVDF material prepared by usual way.

In a word, PVDF Organic Iron electric material prepared by the present invention has higher β phase degree of crystallinity, spontaneous polarizability and good pyroelectric property, meets ferroelectric organic materials service requirements.Its performance is as table 1.

Accompanying drawing explanation

Fig. 1 is the section electron scanning micrograph that adds the PVDF material of preparing after microballoon swelling agent.

Embodiment

The preparation method of a kind of high-crystallinity polyvinylidene difluoride (PVDF) provided by the invention, its step comprises:

(1) PVDF is mixed with acrylic resin microballoon swelling agent for 99: 1 in mass ratio～80: 20, after this take pure water as medium ball milling, PVDF is evenly mixed with microballoon;

(2) oven drying at low temperature obtains the even mixed powder of PVDF and microspheres;

(3) powder is placed in to hot pressing furnace and carries out hot pressing.Powder is heated to 175 ℃～200 ℃, makes PVDF melting (at this temperature, microballoon is still in globular solids).Simultaneously at the pressure that axially applies 2MPa～8MPa;

(4) to sample insulation 20 minutes, after this cooling naturally;

(5) when temperature is down to 100 ℃～80 ℃, shed pressure, after this make sample naturally be cooled to room temperature;

(6) by the polishing of PVDF sample, cleaning after preparation.

As the improvement of technique scheme, (1) the middle microballoon swelling agent using median size is at room temperature 6 μ m～20 μ m.

Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described further.At this, it should be noted that, for the explanation of these embodiments, be used for helping to understand the present invention, but do not form limitation of the invention.In addition,, in each embodiment of described the present invention, involved technical characterictic just can not combine mutually as long as do not form each other conflict.

Example 1:

By particle diameter under room temperature, be the acrylic resin microballoon swelling agent of 10 μ m and PVDF according to the quality of 90: 10 than weighing, after this take pure water as medium ball milling, PVDF is evenly mixed with microballoon.Even mixed slurry is dried under the environment of 50 ℃, obtain the even mixed powder of PVDF and microspheres.Powder is placed in to hot pressing furnace and carries out hot pressing.Powder is heated to 175 ℃, makes PVDF melting, simultaneously at the pressure that axially applies 2MPa.To sample insulation 20 minutes, after this cooling naturally.When temperature is down to 100 ℃, shed pressure, after this make sample naturally be cooled to room temperature.By the polishing of PVDF sample, cleaning after preparation.

Its performance is in Table 3.

Example 2-5:

Microspheres and PVDF compare weighing according to the quality of 99: 1,95: 5,85: 15 and 80: 20.All the other are with example 1.Processing parameter is in Table 2, and its performance is in Table 3.

Example 6-7

The hot pressing temperature of powder is respectively 190 ℃ and 200 ℃, and all the other are with example 1.Processing parameter is in Table 2, and its performance is in Table 3.

Example 8-9

The hot pressing pressure of material is distributed as 5MP and 8MP, and all the other are with example 1, and processing parameter is in Table 2.Its performance is in Table 3.

Example 10-12

The acrylic resin microballoon swelling agent adding at room temperature particle diameter is 6 μ m, 15 μ m and 20 μ m, and all the other are with example 1, and processing parameter is in Table 2.Its performance is in Table 3.

Example 13

Temperature-fall period sheds pressure when sample temperature is down to 80 ℃, and all the other are with example 1.Processing parameter is in Table 2, and its performance is in Table 3.

The above is preferred embodiment of the present invention, but the present invention should not be confined to the disclosed content of this embodiment and accompanying drawing.So every, do not depart from the equivalence completing under spirit disclosed in this invention or revise, all falling into the scope of protection of the invention.

The performance perameter of table 1 high-crystallinity PVDF

Degree of crystallinity (%)	65
		Spontaneous polarizability (C/m 2)	0.035
Pyroelectric coefficient (nC/cm 2℃)	≥8.0

Table 2 different technical parameters table

The performance perameter of the PVDF material of table 3 Different Preparation

Claims (1)

1. a preparation method for polyvinylidene difluoride (PVDF), its step comprises:

(1) by PVDF and acrylic resin microballoon swelling agent in mass ratio 99:1～80:20 mix, ball milling evenly mixes it; Described acrylic resin microballoon swelling agent median size is at room temperature 6 μ m～20 μ m;

(2) dry and obtain mixed powder;

(3) powder is heated to 175 ℃～200 ℃, makes PVDF melting, simultaneously at the pressure that axially applies 2MPa～8MPa;

(4) insulation is 10～60 minutes, then cooling;

(5) when temperature is down to 100 ℃～80 ℃, shed pressure, be cooled to room temperature.