WO2014135539A1

WO2014135539A1 - Method for modifying a fluorinated semi-crystalline polymer surface

Info

Publication number: WO2014135539A1
Application number: PCT/EP2014/054177
Authority: WO
Inventors: Jean-François COULON; Fabienne Poncin Epaillard; Patrice GLARIS
Original assignee: Association Pour Les Transferts De Technologies Du Mans; Ecam Rennes - Louis De Broglie; Universite Du Maine
Priority date: 2013-03-04
Filing date: 2014-03-04
Publication date: 2014-09-12
Also published as: FR3002749A1; FR3002749B1

Abstract

The present invention concerns a method for modifying the surface of a preformed material comprising a free surface made from fluorinated semi-crystalline polymer comprising: a) a step of heating to a temperature higher than or equal to the melting temperature of the fluorinated semicrystalline polymer and lower than the decomposition temperature of same, b) keeping the material at the reached temperature for a defined time; and c) a step of cooling the material to a temperature higher than the vitreous transition temperature (Tg), whereby the free fluorinated semi-crystalline polymer surface is modified by the spontaneous formation of nano- or micro-objects. It also concerns the material obtained in this way and the use thereof for preparing medical devices, in particular disposable medical devices, for bacteriological analysis and in the field of food.

Description

Surface modification method of fluorinated semi-crystalline polymer

The present invention relates to a method for increasing the hydrophobicity and / or oleophobicity of a low surface-tension semicrystalline polymer surface, as well as a material obtainable by this process and its uses.

The hydrophobic and / or oleophobic materials are of great interest for many applications that require limiting the wetting of liquids, especially aqueous or oily liquids, on materials, such as coatings, impermeable materials, self-cleaning surfaces, protections eyepieces, etc.

Materials based on semi-crystalline polymers of low surface tension, such as fluorinated polymers, especially polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (PFE) or polyvinylidene fluoride (PVDF), have anti-corrosive properties. interesting adhesives and can thus be used for the manufacture of materials as described above.

In particular, polytetrafluoroethylene (PTFE), marketed under the trademark Teflon, is a white semi-crystalline thermoplastic polymer highly valued for its anti-adhesive properties and its high chemical inertness. Today, with an annual production of 20,000 tons, it represents more than 90% of the production of fluoropolymers and finds applications in many fields, particularly in the food and medical fields. It has the advantage of having a low surface energy (19-20 mJ.m- ² ) which results in a very limited wetting of its surface by a liquid. "Wetting" refers to the degree of spreading. liquid on the surface.

It is known that the surface properties of a material substantially affect its behavior at the interface with another material. If it is possible to modify the surface properties of a material by modifying the chemical composition of its extreme surface, the physical modification of the surface can also lead to new behaviors of the material.

It is thus known to modify the surface properties of PTFE, in particular its roughness, in order to accentuate its intrinsic wetting properties and to reinforce its hydrophobic character, possibly to make it super hydrophobic. This state has already been observed at the end of the texturing of PTFE by techniques such as plasma etching (Shiu et al., "Fabrication of tunable superhydrophobic surfaces", Smart materials III (2004)), the polymer blend ( Luo et al., Various curing conditions for controlling PTFE micro / nano-fiber texture of a bionic superhydrophobic coating surface ", Materials Chemistry and Physics 19 (2010) 40-47 and Song et al.," Superhydrophobic PEEK / PTFE Composite Coating ", Applied Physics A (2008)) or hot printing (Jucius et al., "Hot Embossing of PTFE: Superhydrophobic Surface Towards", Applied Surface Science 257 (201 1) 2353-2360). The term "texturing" here designates a treatment process that creates on the surface of the material repetitive patterns whose period and depth have a scale of the order of a micrometer and / or nanometer.

Nevertheless, certain techniques implemented for modifying the surface properties of semi-crystalline low surface tension polymer materials can be complex to implement or require the polymer of interest to be mixed with another polymer. Thus, there is a need for a method for modulating the hydrophobic and / or oleophobic nature of surfaces of fluorinated semicrystalline polymers, which is simple to implement and low cost and which does not affect the properties. at the heart of the material.

It is an object of the present invention to provide a process for increasing the hydrophobicity and / or oleophobicity of a low surface tension semicrystalline material which is simple and inexpensive.

The present invention also aims to provide a material for various applications, including medical and food, obtainable by such a method.

In fact, the process of the invention makes it possible, by a simple and inexpensive thermal treatment, to significantly reduce the affinity of semi-crystalline low surface tension surface, especially fluorinated, surfaces. Thus, a PTFE surface treated according to the process of the invention may have a water contact angle of 120 ° to 170 °, advantageously 150 ° to 165 ° and / or a contact angle of diiodomethane of 90 to 120 °, advantageously 100 to 1 15 °

Thus, the present invention relates to a method of surface modification of a preformed material comprising a fluorinated semicrystalline polymer free surface comprising:

a) a heating step at a temperature greater than or equal to the melting temperature of the fluorinated semicrystalline polymer and below its decomposition temperature,

b) the maintenance of the material at the temperature reached during a determined period; and c) a step of cooling the material to a temperature above the glass transition temperature (Tg),

whereby the free surface of the fluorinated semicrystalline polymer is modified by spontaneous formation of excrescences.

The surface of a material thus obtained can then be described as "textured".

In the context of the present invention, the term "textured" characterizes a surface having patterns whose period and depth have a scale of the order of a micrometer and / or nanometer. These patterns may in particular be excrescences formed on the surface of the material. Among these excrescences, there are in particular two types, namely the spherical growths and oblong growths protrusions. The first, also called "warts", generally have a diameter of the order of 0.1 to 10 μηι, and usually between 0.5 and 5 μηι, or even 0.5 to 3.5 μηι. The seconds, called "dendrites", generally have a diameter of the order of 0.05 to 1 μηι, and more particularly of 0.1 to 0.6 μηι, and a length of 0.1 to 5 μηι, most often 0 , 5 and 5 μηι, or even 0.5 to 3.5 μηι. Their presence on the surface can be detected in particular by scanning electron microscopy (SEM).

Furthermore, the term "low surface voltage" means a surface tension less than or equal to 25 mJ.m- ² , advantageously between 5 mJ.m- ² and 20 mJ.m- ² .

The term "preformed" refers to a material having undergone one or more shaping steps, for example under the effect of stress and / or heat.

The term "free surface" refers to a surface in contact with the air. Finally, the term "semi-crystalline polymer" denotes a polymer having crystalline zones and amorphous zones and whose degree of crystallinity, as determined for example by differential scanning calorimetry, varies between 10 and 80%.

Most often, the low surface-tension semi-crystalline polymer is a fluoropolymer.

In the context of the present invention, the term "fluoropolymer" is intended to denote a polymer comprising fluorine atoms. A polymer in which all the hydrogen atoms are substituted with fluorine atoms is called perfluorinated. Thus, the fluorinated polymers of the invention include both monofluorinated polymers, polyfluorinated polymers and fully fluorinated or perfluorinated polymers.

Preferably, the fluoropolymer is a perfluorinated polymer. Advantageously, the fluorinated polymer is chosen from polytetrafluoroethylene (or PTFE), fluorinated ethylene propylene (PFE) and polyvinylidene fluoride (or PVDF).

The fluorinated polymer is, for example, PTFE.

A fluoropolymer material may be partially or completely fluorinated polymer. According to one embodiment, the method according to the invention implements a preformed material consisting of solid fluorinated semicrystalline polymer. The polymer may also contain other polymers, additives or fillers. Alternatively, the material used comprises at least a portion of the surface is coated with a layer of said fluorinated semi-crystalline polymer.

It has been observed that the process of the invention makes it possible to texture the fluorinated semi-crystalline polymers, preferably the fluorinated polymers, in particular such as PTFE, FEP and PVDF, and thus to further reduce the wetting of a liquid on their surface.

The material resulting from the process of the invention comprises, on its free surface, growths, in particular of the "warts" and / or "dendrites" type, and this surface has increased hydrophobicity and / or oleophobicity.

For the purpose of the present invention, the term "hydrophobic" is used to describe a compound which has no affinity for water and which avoids being in contact with water. More specifically, a hydrophobic compound is a compound that does not establish hydrogen bonds and electrostatic interactions with water. The hydrophobicity of a material can be evaluated by measuring the contact angle of the water on the surface of the material. By "contact angle" is meant the angle between the tangent to a drop at the point of contact and the surface of the material. A drop of water deposited on the surface of a hydrophobic material will therefore have a high contact angle. More precisely, a material will be qualified as hydrophobic if the angle of contact of the water on this material is greater than or equal to 90 °.

By "state of super-hydrophobicity" is meant a state in which the hydrophobicity of the material is such that the contact angle of the water is greater than 150 °, or even greater than 160 °. A drop of water deposited on a super-hydrophobic material no longer adheres to the surface of the material and slides.

Similarly, the term "oleophobic" refers to a compound which has no affinity for fats, oils and fats and which avoids being in contact with these compounds. The oleophobicity of a material can be evaluated by measuring the contact angle of low polarity compounds such as diiodomethane on the surface of the material. A drop of diiodomethane deposited on the surface of an oleophobic material will therefore have a high contact angle. More precisely, a material will be qualified as oleophobic if the contact angle of the diiodomethane on this material is greater than or equal to 90 °. Thus, the process of the invention makes it possible to reinforce the hydrophobic and / or oleophobic nature of the fluorinated semi-crystalline polymer.

According to the invention, the method comprises a step of annealing the material comprising at the surface a fluorinated semicrystalline polymer.

For the purposes of the present invention, the term "annealing" means a heating cycle comprising a temperature rise step (step a) at a temperature above the melting temperature, followed by a maintenance step at this point. temperature (step (b)), and a cooling step (step (c)) at a temperature above the glass transition temperature (Tg).

As indicated above, the annealing leads to the formation of surface excrescences of the fluorinated semicrystalline polymer, in particular "dendrites" and "warts".

Typically, the heating of step a) is carried out by introducing the sample into the heated enclosure. According to the invention, the heating step a) is carried out so as to heat the material to a temperature greater than or equal to the melting point of the fluorinated semi-crystalline polymer, but below its degradation temperature. Indeed, on the one hand, the temperature must be higher than the melting temperature of the fluorinated semi-crystalline polymer so that the annealing can take place, and secondly, when the temperature exceeds the degradation temperature, the semi-crystalline polymer -crystalline fluorine begins to be degraded. This temperature is called "annealing temperature".

The annealing temperature is preferably 10 to 50 ° C, preferably 20 to 40 ° C above the melting point of the fluoropolymer. The further this temperature is from the melting temperature, the faster the growths are formed.

According to one embodiment, the heating step a) is carried out in a preheated oven. Preferably, the oven is preheated for a period of 3h to 20h prior to step a).

Typically, step a) of heating the material comprising the fluorinated semicrystalline polymer is carried out in an oven preheated to the annealing temperature overnight. The step b) of maintaining the annealing temperature induces in particular the spontaneous formation on the surface of the fluorinated semicrystalline polymer of spheroid-shaped growths, of the "wart" type. Indeed, it has been observed that at this stage of the process, it is excrescences of this type that appear in a privileged manner.

Furthermore, it has been observed that "wart" growths are preferentially formed on solid fluorinated semicrystalline polymer materials.

The appearance of these excrescences is not immediate, however, and may take, depending on the chosen annealing temperature, and its distance from the polymer melting temperature, minutes to hours.

Step (b) is therefore preferably carried out for a time sufficient for the spontaneous formation of spheroid-shaped growths on the free surface.

Moreover, the spontaneous formation of growths is progressive. Indeed, after the number of growths increases with the continuation of annealing, before reaching a plateau beyond which the surface is not further modified.

As an indication, the annealing step b) can be carried out for a period of 5 min to 160 min, advantageously 90 min to 140 min. Generally, an annealing time of 120 minutes satisfactorily increases the hydrophobic and / or oleophobic properties of the polymer.

Generally, the protuberances of spheroidal shape have a diameter of 0.5 μηι to 3.5 μηι and more particularly a diameter of 1 to 2 μηι.

Since the "wart" growths formed predominantly at this stage contribute in particular to increasing the hydrophobicity, the duration of the annealing in step b) thus makes it possible to modulate the hydrophobicity of the surface of the treated material.

It has been observed that the cooling step c) preferentially gives rise to the spontaneous formation of oblong, "dendrite" type growths.

Tests have shown that the formation of these oblong growths is affected by the cooling rate. More specifically, in the case of slow cooling, the "dendrite" growths have time to form and are long and wide. On the contrary, in the case of rapid cooling, these dendrites have only very little time to form and therefore have smaller dimensions.

Also, the cooling step (c) is preferably carried out for a predetermined period of time depending on the desired size of the oblong shaped protuberances formed on the free surface.

It is assumed at this stage that these excrescences are derived from a recrystallization on the surface of the material. The effect of cooling rate on the morphology of However, growths have been observed only in the vicinity of the melting temperature and, in any event, above the glass transition temperature. Indeed, the mobility of the polymer chains drops rapidly with temperature,

Conveniently, the cooling step c) can be carried out by inertia of the furnace or by quenching with liquid nitrogen.

The cooling can in particular be done slowly by simply stopping the heating of the oven or on the contrary well in a fast manner, by quenching with liquid nitrogen at the exit of the oven.

These two types of cooling generally lead to different textures of the material.

The cooling rate may for example be between 1.5 ° C / min at 3.5 ° C / min, preferably equal to 2.5 ^q C / min.

Typically, such a cooling rate is obtained by stopping the oven. Thus, when the cooling step c) is done by inertia of the furnace, it is typically implemented for a period of 1 h 30 to 3 h 30, preferably 1 h 45 to 2 h 15, preferably about 2 h, depending on the speed of cooling the oven.

Alternatively, the cooling step c) can be carried out so as to pass from the melting temperature to the glass transition temperature Tg of the fluorinated semicrystalline polymer in a period of at least 10 minutes, and preferably at least 20 minutes, for example by quenching in ambient air or in nitrogen.

This duration is then called "cooling time".

Generally, the protuberances of oblong shape formed have a length of 0.5 μηι to 3.5 μηι and a diameter of 0.1 μηι to 0.6 μηι.

In the context of the invention, the process can be applied to a solid fluorinated semi-crystalline polymer material or a material of which at least a portion of the free surface is coated with a layer of fluorinated semicrystalline polymer.

The term "solid" means a material whose composition between the surface and the heart is homogeneous.

The coating is a layer deposited on the surface of a solid material. The thickness of the layer can vary to a large extent, since the surface modification process essentially involves phenomena occurring in close proximity to the surface.

The process can therefore be carried out with a material coated with a fluorinated semi-crystalline polymer having a minimum thickness of 10, or even approximately 5 μηι. More specifically, the process of the invention can be carried out on a solid block made from granular semi-crystalline polymer or on a coating or film made from dispersions of fluorinated semi-crystalline polymer.

In the particular case of PTFE, solid granular PTFE-based blocks, for example, can be prepared by molding at room temperature using a hydraulic press (pressure of 15 to 70 MPa), followed by sintering. 380 ° C with a slow rise in temperature and in stages, usually in the open air, then a decrease in temperature that follows the same pattern as the rise to ensure good recrystallization.

One method of preparing the PTFE coatings and thin films is to spray a PTFE dispersion in one or more layers and then sinter it at a temperature above the melting point, for example at 380 ° C. .

For other types of polymers, a suspension may also be used. It is deposited on the surface of the material to be treated. Then the solvent of the suspension is evaporated, leaving the polymer particles on the surface of the treated material. The whole is then heated beyond the melting temperature of the polymer in suspension to coalesce the particles and thus create a film on the surface of the material.

The texturing observed following the implementation of the process may differ between a solid material and a coating. Indeed, for the PTFE for example, in the case of massive block, growths of "wart" type appear on the surface of the material, in addition to those of type "dendrite". The texturing of a PTFE coated material is only on a scale since it is observed that the formation of "dendrite" type growths.

This difference in texturing could be explained by the manufacturing difference, especially in terms of stress relaxation. More precisely, the massive block of PTFE is melted under stress, linked to the lack of homogeneity, in particular of the temperature and pressure at the core of the material during its implementation, while the coating is not, or much less so.

Thus, the method of the invention makes it possible, by modifying the roughness of the surface of the fluorinated semicrystalline polymer, to increase the hydrophobicity and the oleophobicity of the fluorinated semi-crystalline polymer, and even to reach a state of super -hydrophobie.

As explained above, the surface texturing of the fluorinated semicrystalline polymer increases its hydrophobicity and oleophobia due to the creation of particular growths, of the "dendrite" and / or "wart" type on the surface of the material. In the particular case of PTFE, the contact angle of the initial water, before annealing, is generally around 1 15 °, thus indicating that PTFE is a relatively hydrophobic material, even without being treated. Following the implementation of the method of the invention, this contact angle can increase to more than 150 ° or more than 160 °, thus demonstrating that the material can become super-hydrophobic at the end of the process.

Likewise, the contact angle of the diiodomethane of untreated PTFE is about 85 °, close to the limit indicated above for an oleophobic material. After treatment according to the process of the invention, the contact angle of the diiodomethane can increase up to 100 ° or even more than 110 °, demonstrating that the process makes it possible to significantly increase the oleophobic character of a surface of this polymer.

The subject of the present invention is also a fluorinated semi-crystalline polymer material of modified surface that can be obtained by the method of the invention.

As indicated above, this material is characterized in particular by the presence on the surface of spheroid-shaped growths, of the "wart" and / or oblong, of the "dendrite" type. These surface excrescences cause a change in the roughness which affects the properties of the material, in particular its hydrophobicity and / or oleophobia, as shown by the increase in contact angles measured for water and diiodomethane.

Preferably, the material that can be obtained thus has a modified surface characterized by greater hydrophobicity and / or oleophobia than that of the untreated fluorinated semicrystalline polymer, in particular by a state of super-hydrophobicity.

Moreover, the material obtainable by the process of the invention advantageously has a modified fluorinated semi-crystalline polymer surface having a contact angle with water greater than 120 °, in particular from 120 to 170 °, and most preferably from 150 to 165 ° and / or an angle of contact with diiodomethane greater than 90 ° and in particular from 100 to 115 °.

The present invention also relates to the use of a material according to the invention or obtainable by the method of the invention, for the preparation of medical devices, in particular disposable.

The present invention also relates to the use of a material according to the invention or obtainable by the method of the invention for bacteriological analysis.

The present invention also relates to the use of a material according to the invention sceptible to be obtained by the method of the invention in the food field. The invention will be better understood on reading the description which follows, given solely by way of example, and with reference to the appended drawings, in which:

FIG. 1 is a graph showing the inertia cooling curve of the ERSCEM oven used for the treatment of the samples in Example 2;

- Figure 2 is a photograph taken under a scanning electron microscope (SEM) of a control sample PTFE (untreated) from a solid block, magnification x3000;

Figure 3 is a graph showing the DSC curve of the control PTFE sample; the ordinate axis corresponding to the thermal power values in mW;

- Figure 4 shows the SEM photographs of a PTFE sample from a massive block, annealed at 350 ^< € (A and B) and 400 ° C (C and D), x6000 magnitudes (A and C) and x3000 (B and D);

FIG. 5 is a graph showing the evolution of the measured contact angle of the water (diamonds) and diiodomethane (squares) in degrees (°) as a function of the annealing time in minutes;

FIG. 6 shows the evolution of the length (A) and the width (B) in micrometers of the dendrites observed as a function of the annealing time in minutes;

- Figure 7 shows the photographs taken at SEM of a PTFE sample from a solid block, annealed for 30 min (A), 1 h15 (B) and 2h (C) at magnification x3000;

FIG. 8 shows the photographs taken at the SEM of a PTFE sample from a solid block, annealed in air (A) and under nitrogen (B), at x3000 magnification;

FIG. 9 is a graph showing the evolution of the measured contact angle of the water (diamonds) and diiodomethane (squares) in degrees (°) as a function of the cooling time in minutes, before quenching at air (A) and before nitrogen quenching (B);

FIG. 10 shows SEM photographs of a sample of PTFE from a solid block, subjected to nitrogen quenching immediately at the furnace outlet (A) and after 30 minutes of cooling (B), at x6000 magnification;

FIG. 11 shows the SEM photographs of a sample of PTFE resulting from an untreated coating (A) and after annealing for 2 hours at 350 ° C. (slow cooling down to 150 ° C.), at x3000 magnification; and

Figure 12 shows the photographs taken at the SEM of an untreated PVDF sample (A) and after annealing for 20 to 30 minutes at 200 ° C (B), at x 6000 magnification. EXAMPLES

Example 1: Preparation of PTFE Samples

PTFE samples of 1.8 cm and 0.4 cm thickness were prepared by cutting a 4 mm thick PTFE plate supplied by Maceplast.

Example 2: Treatment of PTFE Samples

In the following study, the samples were all polished beforehand in an identical manner in order to distinguish phenomena related to the process of the invention from those related to the initial surface state of the material. This step is not however required to carry out the process of the invention.

The PTFE samples prepared in Example 1 were therefore polished and washed, and then treated according to the process of the invention. A. Polishing

Polishing reduced the roughness to about one micrometer. It was done on a VAGO machine from ESCIL.

First, a pre-polishing was performed by abrasive paper 800 polishing up to total loss of friction. This pre-polishing was followed by a MD Largo ™ fabric polishing (Struers) coupled with a diamond suspension (9 μηι diameter) and a blue lubricant (DP Lubricant Blue from Struers) and the operation was repeated several times to visually obtain homogeneity of the surface. It was followed by a DP Mol fabric (Struers) coupled to a diamond suspension (3 μηι in diameter) and a yellow lubricant and a DP Nap (Struers) fabric coupled to a diamond suspension (1 μηι in diameter) and a pink lubricant (DP Lubricant Pink from Struers

Between each step, the sample was rinsed with water and ethanol so as not to transfer the abraded PTFE chips to the next tissue.

B. The washing

The samples were blown with compressed air for one minute, rinsed with deionized water, passed to the ultrasonic bath for 15 minutes and dried for one hour in an oven at 60 ^<C.

Following these polishing and washing steps, the surface of the PTFE samples was extremely smooth and clean, as shown by the SEM image (see Figure 2). C. Annealing

The samples were annealed in an ERSCEM oven (muffle furnace) which had been preheated to the desired temperature overnight. The samples were placed on a ceramic cup. The cooling was done by simply stopping the heating. It was defined beforehand according to the curve of Figure 1.

D. The washing

The annealed PTFE samples were washed according to the protocol indicated in paragraph B (before the annealing step).

Example 3: Methods of Analysis of Treated PTFE Samples

In general, the samples were not reused after the measurements.

A. The anchorage

Five measurements were made according to the sessile drop technique, by deposition of 3.5 μί drops of water on the sample, and five others were carried out by deposition of 3.5 μί diiodomethane drops. This technique makes it possible not to deform the drop by its own weight and by a drop inertia of the latter.

The deposits were made close to the edge so that the focal length could be adjusted correctly, but not too much to avoid edge effects. The surface of the sample was not dried with a cloth so as not to load the surface with static electricity. The contact angles being high, the inclination of the sample was generally sufficient to remove the deposited drops. B. Differential Scanning Calorimetry (DSC) (on Perkin Elmer Pyris6)

The DSC made it possible to determine the enthalpy of melting of the material. Two types of measures were carried out through it.

Firstly, simulations of the annealing operations were carried out. For this, samples of a few micrograms (5-12 mg) of unannealed PTFE were cut, accurately weighed and then encapsulated.

A first rapid rise in temperature to 100 ° C. was carried out to bring the sample to temperature, then a 3-minute isotherm was applied because there is an inertia between the set temperature and the temperature of the sample. . A further increase in temperature was initiated up to the annealing temperature, this time controlled at 10 ° C / min. Once the annealing temperature was reached, an isotherm of duration corresponding to the desired annealing was programmed, the annealing was then simulated. carried out in the oven. The material was cooled to the furnace exit temperature (150 ° C) at a rate of 3 ° C / min (determined by the furnace cooling curve), this step thus simulated the cooling time of the samples after annealed in the oven. Again, a 5-minute isotherm was performed to account for the inertia of the samples. A new rise was then restarted up to the temperature of 350 ° C. (higher than the melting temperature) to observe the melting after annealing. Five measurements were taken to determine an average and a standard deviation.

In a second step, to observe the melting of the PTFE samples after annealing, a few micrograms were prepared in the same manner as previously (cut, weighed and encapsulated). Five samples were prepared. The method used for the DSC has this time been a simple set temperature to the ^"OO 'C (always with an isothermal 3 min) followed by a rise to 350 ^ 10 ° C / min.

DSC curves were thus obtained showing the endothermic melting peak of the material.

C. Scanning Electron Microscopy (SEM) (on Hitachi S-3200N)

SEM allowed to observe the surface of the PTFE annealed samples.

The observed texture has been measured to characterize its evolution as a function of the various variables (annealing time, cooling time, annealing temperature). However, the PTFE is not conductive, so the electrons from which it is bombarded do not escape from the surface thus creating interference. The samples were metallized with a gold-palladium alloy to allow their observation.

The annealed samples were cut into squares approximately 0.5 cm apart so that several of them could be placed on the SEM sample holder. The images taken were then used to measure the length and width of the patterns observed on the PTFE surface.

Example 4: Results of Analysis of PTFE Samples Treated

A. The witness

The control sample (cut, polished and washed but not annealed) was measured using direction-finding angles. The results were obtained after 5 deposits of sessile drops of water, then of diiodomethane. They are collated in Table 1 below.

Table 1: Contact Angles Sample Sample

Its surface condition was observed at SEM x3000 (Figure 2). It is found that the surface has a homogeneous and smooth appearance, free of texturing.

A DSC analysis was performed to determine its melting temperature and its enthalpy of fusion. A warm-up there was thus carried out at 150 ° C and then isothermally at that temperature for 3 minutes, and finally a simple rise in temperature to the ^"O ^ / min up to 400 ^ to fuse the sample.

From the graph of this analysis it is deduced that the melting is carried out towards 331 'Ό endothermically with an enthalpy of 31.7 ± 2 J / g, as indicated in FIG.

B. Influence of the annealing temperature

Annealing was carried out at two temperatures, namely 350 ° C. and 400 ° C., and for 90 minutes and 60 minutes. The cooling of the samples was done according to the cooling curve of the oven (Figure 1) up to Ι δΟ 'Ό, the temperature at which the samples were taken out of the oven and quenched in the air.

Wetting measures were performed, always with 5 drops of water deposits and 5 drops of diiodomethane. They are summarized in Table 2 below. Table 2: Contact angles as a function of time and annealing temperature

Over a 90-minute annealing time, the contact angles obtained with the water are equivalent for the two annealing temperatures tested. In both cases, there is an increase in the angles which goes in the direction of a reduction of the surface energy. Over an annealing time of 60 min, the angles obtained are higher for the annealing at 400 ° C. They increase little compared to the control in the case of annealing at 350 ° C.

The contact angle of the water is therefore higher for an annealing time of 90 min and for an annealing temperature of 400 ° C.

The results for an annealing time of one hour at 400 ° C show a faster progression to the values reached for a 90-minute annealing time, which seems to indicate that a value of 90 minutes is reached. threshold. The annealed samples observed at SEM at magnification show great similarities. Figure 4 shows snapshots taken at 350 ° C (A and B) and at 400 ° C (C and D), at magnifications x6000 (top) and x3000 (bottom).

Given the risk of degradation at 400 ° C, the following tests were carried out at 350 ° C to avoid any degradation, with 2h annealing to be sure to reach the maximum values of contact angles and on a cooling time of 3:30 by inertia of the oven, allowing to go down to 150 ° C, the temperature at which the samples are taken out of the oven in the ambient air.

C. Influence of the annealing time

The influence of the annealing time was studied by testing an annealing time ranging from 0 minutes to 2 hours, in steps of 15 minutes, and a cooling time of 3:30 inside the oven off, until 150 ° C, then to ambient air.

Measurements of contact angles of water and diiodomethane were made as indicated above. The graph shown in Figure 5 shows the average angles of the five deposits and their standard deviations as a function of the annealing time.

Figure 5 clearly shows an increase in contact angles as a function of the annealing time, the contact angle of the water (diamonds) increasing from 1 16 ° for unannealed PTFE to an angle of 160 ° or more for PTFE annealed for 1 hour or more

Similarly, it is found that the contact angle of the diiodomethane increases by 85 ° for unannealed PTFE to 100 to 115 ° for an annealing of 30 minutes or more.

These results show that, whatever the phenomenon involved, an annealing of 2h makes it possible to achieve high hydrophobic and / or oleophobic properties.

In order to evaluate whether this evolution could be correlated with the surface condition of the samples, SEM observations of samples annealed for 30 minutes, 1 hr and 2 h were carried out at x3000 magnification (see Figure 7). Measurements were taken from the plates to determine the length and width of the "dendrite" growths of the texturing. The results, summarized on the graphs of Figure 6 do not seem to present significant evolution. On average, lengths of 2.2 μηι and widths of 0.35 μηι are obtained.

On the other hand, it is found that the number of "wart" type growths on the surface increases with the annealing time, as shown by the photos taken at x3000 magnification on annealing of respectively 30 minutes, 1 hr and 2 h (Figure 8).

D. Influence of the annealing atmosphere

The effect of annealing under nitrogen was investigated using a tubular furnace under the following conditions: annealing temperature of 400 ° C, annealing time of 90 minutes, slow cooling to 150 ° C.

The contact angles of water and diiodomethane were measured. The results are summarized in Table 3 below.

Table 3: Contact angles after annealing under nitrogen

These values of measured contact angles are greater than those of the control sample, but lower than those obtained by annealing under air (approximately 162 ° for water and 1 ° 10 ° for diiodomethane). Air annealing therefore leads to a more hydrophobic and more oleophobic material.

SEM observations at x1000, x3000 and x6000 magnifications showed texturing similar to that obtained with air annealing. Figure 8 illustrates the appearance of the samples obtained under air (A) and under nitrogen (B).

Under nitrogen, we obtain a different texturing although still composed of dendrites and warts. The dendrites, with respect to a sample annealed under the same conditions with the exception of the atmosphere, are nevertheless thinner and separated by non-textured interstices. E. Influence of cooling time

The influence of the cooling time was studied by leaving more or less rapidly the samples of the oven left in free cooling. The quenching was carried out initially in ambient air and in a second time in liquid nitrogen in order to try to stop in a clear way any recrystallization phenomenon after the desired cooling time.

Contact angle measurements were performed as described above. The results are shown in Figure 9, with air quenching (Figure 9A) and quenching with nitrogen (Figure 9B).

For both air and nitrogen quenching, no significant changes in contact angles are observed as a function of the cooling time. Indeed, by taking the samples out of the furnace at the end of the 2h annealing, we find the same maximum measured values (about 162 ° for water and 1 10 ° for diiodomethane) that in the case of a long cooling of 3:30.

SEM observations were performed at x1000, x3000, x6000 and x10 000 magnifications.

Figure 10 shows the snapshots of a sample taken at 0 min (Fig. 10 A) and at 30 min (Fig. 10 B) for cooling and then quenched with nitrogen.

These images show an increase in the width of the "dendrite" growths, confirmed by the measurements presented in Table 4 below.

Table 4: Width of excrescences as a function of cooling time

It is clear that on rapid quenching, the growths of the type

"Dendrite" are less wide and more so with quenching with liquid nitrogen. We note that from 45 minutes, we reach the final width of the dendrites (about 0.35 μηι).

Thus, cooling by inertia of the furnace or by quenching with nitrogen does not seem to significantly modify the wetting properties of the material.

F. Influence of PTFE type

Tests were carried out on a pan with a PTFE coating. To this end, a non-used commercial stove was cut into samples of a few centimeters on the side, which were subjected to washing as indicated above. However, we did not polish because the coating was too thin and the roughness of the pan was too high. Polishing would have removed the coating. The prepared sample was annealed for 2 hours at 350 ^ and allowed to cool for 3:30 to 150 ^<C. In order to see if the application of the method of the invention to an industrial object implementation and different formulation modified the surface properties, contact angle measurements were made.

The angles measured before annealing are shown in Table 5 below.

Table 5: Contact angles according to the type of PTFE

These results show that contact angles increase with annealing. This increase in contact angles led to comparing the surface area of our samples with the x3000 magnification to SEM.

In Figure 11 (A), it is observed that the unannealed control sample has a slight texturing corresponding to the lighter areas.

In FIG. 11 (B), it can be seen that the annealed sample has "dendrite" growths but no "wart" growths.

These results demonstrate that the application of the method of the invention to a PTFE film applied to a pan also allows to texturize and increase its hydrophobicity and oleophobia significantly. Example 4 Study of the Treatment of PVDF Samples

A. Preparation of PVDF samples

PVDF samples were prepared by cutting out a commercially unvarnished commercial PDVF plate.

The control PVDF sample undergoes no treatment besides washing. The other samples were treated according to the method of the invention as follows: heating in an oven at 200 ° C. for 30 minutes, then cooling in the oven.

B. Analysis of processed PVDF samples

A comparison to the SEM of the untreated and treated sample surface was performed.

In Figure 12 (A), it is observed that the surface of the unprocessed PVDF sample has no texturing except for a slight micron scale roughness.

In Figure 12 (B), it is observed that the treated sample surface has dendrite-like patterns. Texturing of the PVDF has therefore been performed.

Measurements of contact angles of water and diiodomethane show that the process of the invention makes it possible to significantly reduce the affinity of fluoropolymers with respect to water and oily compounds.

Claims

1. A method of surface modification of a preformed material comprising a fluorinated semicrystalline polymer free surface comprising:

(a) a heating step at a temperature greater than or equal to the melting temperature of the fluorinated semicrystalline polymer and below its decomposition temperature,

(b) maintaining the material at the temperature reached for a specified period; and

(c) a step of cooling the material to a temperature above the glass transition temperature (Tg),

The method of claim 1, wherein the preformed material is solid fluorinated semicrystalline polymer.

The method of claim 1 or 2, wherein the preformed material is a material of which at least a portion of the surface is coated with a layer of said fluorinated semicrystalline polymer.

4. Method according to one of claims 1 to 3, wherein the fluoropolymer is a perfluorinated polymer.

5. Method according to any one of claims 1 to 4, wherein the fluoropolymer is selected from polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (PFE) and polyvinylidene fluoride (PVDF).

The method of any one of claims 2, 4 and 5, wherein the step

(b) is carried out for a time sufficient for the spontaneous formation of spheroid-shaped growths on the free surface.

7. The method of claim 6, wherein the spheroid-shaped growths have a diameter of 0.5 μηι to 3.5 μηι.

8. Process according to any one of claims 1 to 7, wherein oblong shaped growths are formed.

9. A method according to any one of claims 1 to 8, wherein the step (c) of cooling is carried out for a determined time according to the desired size of oblong shaped protrusions formed on the free surface.

10. The method of claim 8 or 9, wherein the protrusions of oblong shape have a length of 0.5 μηι to 3.5 μηι and a diameter of 0.1 μηι to 0.6 μηι.

1 1. A modified fluorinated semicrystalline polymer free surface material obtainable by the process of any one of claims 1 to 10.

12. Material according to claim 1 1, wherein the modified surface obtained is characterized by a higher hydrophobicity and / or oleophobia of the fluorinated semi-crystalline polymer, preferably by a state of super-hydrophobicity.

13. The material of claim 1 1 or 12, wherein the fluorinated semicrystalline polymer modified surface has a water contact angle greater than 120 ° and / or a contact angle with the CH ₂ I ₂ greater than 90 °.

14. Use of a material according to any one of claims 1 1 to 13, for the preparation of medical devices, including disposable.

15. Use of a material according to any one of claims 1 1 to 13 for bacteriological analysis.

16. Use of a material according to any one of claims 1 1 to 13 in the food field.