This invention is related to activation of an inert polymeric material, especially made from fluoropolymers and subsequently with the functionalization of the activated polymeric material.

The term "inert polymer" refers to any polymer that maintains its structural integrity after exposure to a strong effect of various parameters such as ozone, plasma treatment, UV radiation, gamma rays or electron beam for a period of time between few minutes and several hours. Functionalization is a process leading to the change and/or improvement of the properties of polymeric material by chemical modification

In the scientific literature (e.g., Bottino, A. et al. J. Membrane Sci. 166 (2000) 23-29; B. Onal- Ulusoy, J. Food Qual. 38 (2015) 1745-4557; M. Baghbanzadeh et al. Desalination 369 (2015) 75-84 H. Sun et al. J. Appl. Polym. Sci. 132 (2015) 42080 (1-9); G.J. Ross et al. Polymer 41 (2000) 1685-1696; T. Daqing et al., Sep. Purif. Technol. 157 (2016) 1-8 F. Liu et al. J. Membr. Sci. 375 (2011) 1-27), there is known a process of activation and functionalization of PVDF (polyvinylidene fluoride) material focused on the application of harsh conditions. The activation process was accomplished by heating the polymer in KOH / MeOH mixture at 60 °C followed by reaction with concentrated (98%) sulfuric acid at 80 °C for 48 hours. The reason to use such conditions was to oxidize and to introduce hydroxyl and carboxylic groups. This procedure severely affects material properties including strength, texture, color, and integrity.

More recently, a mixture of sulfuric acid and hydrogen peroxide was used with limited success (Al Gharabli S. et al. J. Membr Sci. 541 (2017) 567-579; S. Al-Gharabli et al J. Mater Res. 32 (2017) 4219-4231 ; S. Al.-Gharabli et al. Eur. Pol. J. 96 (2017) 414-428). The presented and available methods in the literature are characterized by low efficiency, a small number of generated hydroxyl groups, material degradation, limited and random distribution of OH groups on the surface (very often agglomerates are formed).

These disadvantages have been largely eliminated in the method according to the presented invention.

The core of the invention is to activate inert polymers including fluoropolymers by direct treatment with base Piranha (aqueous solution of NH ₄ OH and H ₂ O ₂ ). The mixture of activator can be used in the range of concentration between 5 and 50 wg. % and within the ratio of components from 1 :2 to 5:1, during 1- 20 minutes. Preferably, the concentration of activator mixture should be 20 wt.% in the ratio of 3:1 (NH ₄ OH : H ₂ O ₂ )

Furthermore, the principal of the invention is that activated by base Piranha material can be subsequently functionalized. Functionalization described herein can be by grafting any chemical compound or moiety e.g. but not limited to: alkylsilanes, perfluoroalkylsilanes, epoxides, cyanate, isocyanate, carbon-based materials - carbon nanotubes, peptides, proteins, antibodies, mono and polysaccharide, anti-inflammatory, drug release, anti-fouling agents, and biofunctional compounds.

During the activation, the high oxidizing power of Piranha reagent is able to break the C-F bonds in PVDF and generate C-OH or COOF1 to turn the inert character of the polymer to labile one. The new material having high number of functional groups is ready for a further chemical, stable modification by generating covalent bonds by standard chemical procedures. The inert fluoropolymers possess a unique property by building up the physicochemical nature from the blank. The nontoxic nature of fluoropolymers enables the integration of biologically active compound into the material with high activity, selectivity, and biocompatibility. The starting polymeric material can be as powders, films, membranes, coating, devices surfaces, or implant surfaces.

Inert polymers can be any material which does not undergo uncontrolled reactions or alter material integrity by exposure to base piranha at different conditions. Some examples of inert polymers includes but not limited to fluoropolymers, poly(vinylidene fluoride), poly(vinylidene fluoride-co-hexafluoropropylene), poly(vinyl fluoride), poly(ethylene), poly(propylene) and polydimethylsiloxane.

The functionalized, new type of polymeric material can be used in water purification processes (e.g., membrane distillation, pervaporation, filtration), biocompatible materials, coatings, as well as device, implant or stent material or coating of material.

The invention is illustrated in the non-limiting example embodiments.

Example 1

PVDF membrane was activated by base Piranha (20 wt.% aqueous solution of NH ₄ OH and IT O in the ratio of 3:1) during 1 min. Subsequently, the prepared membrane was used in the separation of water-ethanol. Fig. 1. Improvement of separation (A) and transport (B) properties in air-gap membrane distillation process for removal of the volatile organic compound - here ethanol, of the piranha activated PVDF membrane in comparison to pristine one.

Example 2

PVDF membrane was activated by base Piranha (20 wt.% aqueous solution of NH OH and H O in the ratio of 3: 1) during 1 min. Subsequently, the prepared membrane was used in the osmotic membrane distillation process.

Fig. 2. Shows the plots illustrating an improvement of transport and separation properties in osmotic membrane distillation process used for juice concentration and fouling study. The evidence of significant improvement of antifouling ability for the piranha-activated membrane.

Example 3

PVDF membrane was activated by base Piranha (20 wt.% aqueous solution of NH ₄ OH and H O in the ratio of 3: 1) during 1 min. Subsequently, the prepared membrane was functionalized by soaking the membrane 3h in grafting solution (3- Aminopropyl)triethoxysilane (0.1M prepared in toluene). The functionalization process was done at 50°C. In the next step, the functionalized membrane was washed consecutively in toluene, methanol and distilled water. Finally, the functionalized membrane was dried at 60°C for 12h. As a result, membrane first rich in hydroxyl groups (after activation) and then in amino groups (NH ₂ ) after functionalization was obtained.

Fig. 3 showed the scheme of membrane modification and improvement of water resistance of activated (PVDF-OH) and functionalized (PVDF-NFf) polymeric materials.

Example 4

Firstly, the membrane rich in amine groups was prepared according to the protocol presented in Example 3. Subsequently, carbon-based material - carbon nanotubes (CNT) were covalently attached to the surface. The modification followed by immersing the membrane with NH groups in the solution containing anhydrous dichloromethane and CNT (mixed previously during 10 min under sonication at room temperature). Then, TBTU (2-(lH-benzotriazole-l-yl)- 1,1,3,3-tetramethylaminium tetrafluoroborate) and DIPEA (N,N-diisopropylethylamine) were added to the mixture to generate connection of CNT with the membrane by active ester. The process was done during 3h of continues mixing under sonication at room temperature. The membrane was washed consecutively in dichloromethane, ethanol and distilled water. Finally, the functionalized membrane was dried at 60°C for 12h.

Fig. 4 present the scheme of activation and functionalization of CNT on the surface of PVDF activated the material.

Fig. 5 PVDF (upper left side) microscopic image from SEM of the pristine membrane; (bottom left side) results from atomic force microscope - roughness and cross section for 2 selected lines.

Fig. 5 PVDF-CNT (upper right side) microscopic image from SEM of the activated and then functionalized membrane; (bottom right side) results from atomic force microscope - roughness and cross section for 2 selected lines. Visible changes of the material after functionalization with CNT, and differences in the roughness of the material. 3x increase of roughness parameter. Fig. 6. Images form TEM transmission electron microscope - PVDF (left, upper side) pristine material, CNT (upper, right side) CNT used to the functionalization process, PVDF-CNT (both bottom images) effect of the PVDF functionalization - CNT connected to the polymeric material. Images prepared at various magnification.

Fig. 6. (right side) Raman spectra for pristine PVDF (A), PVDF with chemically attached CNT (B), and pure CNT (C).