WO2009019567A2

WO2009019567A2 - Process for the functionalisation of polymeric materials and functionalized polymeric materials so obtained

Info

Publication number: WO2009019567A2
Application number: PCT/IB2008/002030
Authority: WO
Inventors: Joao Cortez; Enrico Fatarella; Solitario Nesti; Vanja Kokol; Marc Schroeder
Original assignee: Next Technology Tecnotessile Societa' Nazionale Diricerca R.L.; The University Of Maribor - Faculty Of Mechanical Engineering
Priority date: 2007-08-03
Filing date: 2008-08-01
Publication date: 2009-02-12
Also published as: ITMI20071611A1; WO2009019567A8; WO2009019567A3

Abstract

The present invention relates to a process for functionalising polymer materials, comprising a first step wherein the polymer material is grafted, by means of high energy irradiation, with a functionalised monomer having at least one first functional group and at least one olefinic end group, and a second step wherein the so-treated polymer material is reacted with a functionalised organic compound having at least one second functional group reactive with respect to said first functional group, in the presence of an enzymatic catalyst. The coupled functionalised compound is able to impart specific properties to the polymer matrix, such as antibacterial or flame retardant properties, or can be employed to produce biocomposites to be used, for instance, in the biomedical field, or in the food, construction, packaging or textile industries.

Description

PROCESS FOR FUNCTIONALISING POLYMER MATERIALS AND FUNCTIONALISED POLYMER MATERIALS SO OBTAINED

The present invention relates to a process for functionalising polymer materials and to the functionalised polymer materials so obtained. More particularly, the present invention relates to a process for functionalising polymer materials and to the functionalised polymer materials so obtained, wherein unsaturated monomers are grafted onto the polymer material by irradiation and subsequently, in the presence of an enzymatic catalyst, by means of the grafted unsaturated monomers, functionalised compounds are coupled which are able to modify the properties of the polymer material itself.

In the textile industry, to modify the properties of natural or synthetic fibres, wet finishing methods are widely applied. These methods show some drawbacks, mainly tied to the use of harmful chemicals and to the need for large amounts of water and energy, which give rise to problems of high environmental impact.

Technologies have been also developed to carry out functionalisation reactions on substrates of various types catalysed by enzymes, which offer several advantages compared to conventional techniques. Enzymes are generally safe from an environmental point of view because they are biodegradable, their action can be easily controlled - unlike that of traditional chemical products - and they operate under mild conditions of temperature (usually in the range of from 37 to 60°C), pH (usually from 4 to 8) and pressure (atmospheric). Their efficiency is very high, albeit selective, since enzymes need specific substrates in order to act. This selectivity represents an advantage for the interactions between molecules and substrate, but it may also constitute a limit from an application viewpoint, since the enzyme can only work on substrates containing the groups that are involved in the enzymatic reaction.

The Applicants have faced the problem of developing a process for the functionalisation of a wide range of polymer materials, of both natural and synthetic origin, which uses techniques with a low environmental impact and makes it possible to obtain materials that have improved properties and may feature some specific functionalities not available in the original polymer matrix.

The Applicants have found that it is possible to obtain this result by means of a process comprising two steps, a first step wherein the surface of the polymer material is functionalised by means of unsaturated monomers grafted thereto using irradiation, and a second step wherein enzymatic catalysis is used in order to couple functionalised compounds onto the polymer material so modified. These functionalised compounds are able to impart specific properties to the polymer matrix, for instance antibacterial or flame retardant properties; or they can be employed in the production of bio-composites and/or bio-laminates to be used, for instance, in the biomedical field, or in the packaging, construction, food or textile industries.

According to a first aspect, therefore, this invention refers to a process for functionalising polymer materials, which comprises:

(i) placing the polymer material into contact with a functionalised monomer having at least one first functional group and at least one olefinic end group;

(ii) treating the polymer material with high-energy irradiation, such as to generate radicals on the polymer material surface so as to graft said functionalised monomer onto said surface;

(iii) reacting the so treated polymer material with a functionalised organic compound, comprising also a protein material, having at least one second functional group reactive with respect to said first functional group, in the presence of an enzymatic catalyst.

According to a second aspect, the present invention refers to a polymer material whose surface is functionalised by grafting thereto a functionalised monomer having at least one first functional group and at least one olefinic end group, and subsequently by coupling a functionalised organic compound having at least one second functional group reactive with respect to said first functional group.

The process according to the present invention allows a stable bond of a covalent type to be obtained between the polymer material and the functionalised organic compound, and it may be applied on a wide range of polymer substrates, even substrates that do not have reactive sites on their surface, e.g. a polyolefin. In fact grafting by irradiation generates on the surface of the polymer substrate a large quantity of active sites, which are available for subsequent enzyme-aided coupling of functionalised compounds. Furthermore the irradiation treatment, plasma irradiation in particular, allows the water- repellence of the polymer substrate to be reduced, thus increasing its wettability. In particular, the process according to the present invention may be applied to the following polymer materials:

(i) polymers of natural origin, such as polysaccharides, in particular cellulose (e.g. cotton, linen or hemp fibres, paper or wood pulp, or even lignocellulosic materials) or proteins (e.g. wool or silk fibres or leather); (ii) polyolefins, e.g. polypropylene or polyethylene; (iii) polyacrylates (e.g. polymethyl methacrylate), polyamides (e.g. nylon), polyesters (e.g. polyethylene terephthalate), polyurethanes, polyaramides (e.g. Kevlar™), polysiloxanes; (iv) cellulose derivatives, e.g. viscose, acetates, triacetates, chitosan;

(v) silica materials and titanium alloys.

The polymer material may be used in different forms, e.g. in the form of fibres, fabrics, nonwovens and films.

As regards the functionalised monomer to be grafted onto the polymer material, it contains at least one olefinic end group and at least one first functional group. Said first functional group can be selected, for instance, from: amino group -NR₁R₂ where R₁ and R₂, equal to or different from each other, are hydrogen or C₁-C₄ alkyl groups; hydroxyl group -OH; carboxyl group -COOH; thiol group - SH; epoxy group, carboxyamide group or phenol group. The olefinic end group is preferably:

CH₂=CR - where R is hydrogen or a Cj-C₄ alkyl group, preferably a methyl or ethyl group. Particularly preferred functionalised monomers are: 2-aminoethyl methacrylate, hydroxyethyl methacrylate, thio methacrylate, acrylic acid, allyl alcohol and glycidyl methacrylate.

The functionalised monomer can be applied as such or, preferably, diluted with a suitable solvent such as water, alcohol, chloroform and the like, or a mixture thereof.

The concentration of the functionalised monomer in the solution is normally in the range of from 5 to 50% wt, preferably from 10 to 40% wt. Irradiation of the polymer material placed in contact with the functionalised monomer can be achieved with high energy radiations by applying well known technologies, so as to generate radicals on the surface of the polymer material. In particular, plasma, electron beam, or ultraviolet (UV) irradiation technologies can be applied. Irradiation promotes the generation of macroradicals on the polymer material surface and these are able to react with the functionalised monomer by means of an addition reaction of the olefϊnic double bond so as to produce a stable covalent linkage. The most preferable technology is plasma irradiation, which can be performed using well-known methods. The plasma can be generated using a non- polymerising gas, in particular a noble gas such as argon. Applying a potential difference across the gas by means of two electrodes promotes the generation of electrically active species (ions and electrons). The electrons within the electric field are accelerated and can collide with the gas molecules present in the reaction chamber, thus exciting them and generating other active species that sustain the plasma. The applied power is selected in the range of from 100 W to 5000 W, preferably from 200 to 3000 W. The potential difference between the two electrodes is usually in the range of from 300 to 20000 V, preferably from 500 V to 1000 V. The irradiation treatment usually lasts for a time of from 10 to 500 seconds, preferably from 30 to 300 seconds.

After irradiation, the polymer material grafted with the functionalised monomer is reacted with the functionalised organic compound that is intended to change the properties of the polymer material itself and which contains at least one second functional group capable of reacting with the first functional group. Before proceeding with this step, it is recommended to wash the polymer material with a suitable solvent (for instance the same used to dissolve the functionalised monomer) in order to remove the unreacted monomer. The presence of unreacted monomer on the polymer substrate could negatively affect the subsequent grafting step of the functionalised organic compound and in particular it could significantly reduce the enzymatic activity.

After washing, the grafted polymer material is preferably dried to remove any residual solvent.

The grafted polymer material is then placed in contact with the functionalised organic compound in the presence of the enzymatic catalyst. Since the process involves an enzymatic reaction, the reaction conditions have to be carefully controlled in terms of pH and temperature. For this reason, the functionalised polymer is incubated in a buffer solution at a substantially constant temperature in order to achieve a proper enzymatic activity, usually selected in the range of from 0.1 to 3000 nkat, preferably from 0.4 to 6 nkat. The pH of the buffer solution is selected according to the specific enzyme, usually within a range of from 4.0 to 8.0, preferably from 5.0 to 7.0. The most suitable temperature likewise depends on the specific selected enzyme, and is usually selected in the range of from 15° to 8O⁰C, preferably from 20° to 6O⁰C. The organic compound is usually added in an amount such as to obtain a concentration of from 0.5 to 1,000 mM, preferably from 1 to 10 mM. The duration of the treatment is generally of from 5 to 1000 minutes, preferably from 20 to 500 minutes.

At the end of incubation, the enzymatic reaction is preferably stopped by adding a compound that inhibits the activity of the enzymatic catalyst, e.g. a solution of sodium fluoride. The so-functionalised polymer material is then usually washed in order to eliminate the unreacted organic compound and enzymatic catalyst, so as to stabilise the material.

The functionalised organic compound to be coupled onto the grafted polymer material may be selected from a wide range of products containing at least one second functional group capable of reacting with the first functional group present on the material thanks to the previous grafting step. Some examples of this second functional group are: hydroxyl group -OH; amine group -NR₁R₂, wherein Ri and R₂, equal to or different from each other, are hydrogen or Ci-C₄ alkyl groups; carboxyl group -COOH; phenol groups; silica groups; carboxyamide groups, including amino-acids and proteins.

The functionalised organic compound generally displays a specific activity, which is imparted to the polymer material following implementation of the process of the present invention, for instance:

(a) compounds having antibacterial or bacteriostatic properties (e.g. guaiacol and its derivatives or quinone compounds),

(b) compounds having fiame-retardant properties (e.g. phenol compounds);

(c) compounds having thermal regulation properties for the manufacture of fabrics able to maintain a constant body temperature;

(d) compounds having adhesive properties, e.g. for promoting adhesion of protein coatings to analytical plates and/or other materials used in the biomedical sector;

(e) compounds having coupling properties, e.g. for fixing protein matrices that increase cell adhesion and growth for biomedical devices;

(f) compounds that improve biocompatibility, e.g. for use in biomedical devices; (g) compounds that are able to enhance mechanical properties of the polymer substrate;

(h) compounds that are able to promote crosslinking of different products (e.g. collagen) on the polymer substrate; (i) colouring agents, absorbers of ultraviolet radiation, reflecting agents, scented agents.

As organic compounds protein substrates (proteins or peptides) can also be used, which, once coupled onto the surface of the polymer material, may generate composite materials suitable for different applications, e.g. for the production of technical textile materials, such as synthetic fabrics with enhanced technical properties including, for instance, good breathability in contact with human skin thanks to the biological protein component. Such protein substrates will improve the biocompatibility of the polymer materials and improve cell adhesion and promote cell growth. As regards the enzymatic catalyst, it can be selected according to the specific reaction to be catalysed, as well as, of course, based on its cost and availability on the market. Preferably, the enzymatic catalyst is selected from: transglutaminase, tyrosinase, laccase, oxidase, peroxidase, protease, transferase, amylase, glycosidase, hydrolase, oxidoreductase, esterase, lipase, and the like. The present invention will be now explained through some practical examples given solely for illustrative purposes, without limiting the scope of the invention.

The figures annexed to the present description show: Fig. 1 : FT-IR spectra of polypropylene fibres as such (spectrum (a)) and plasma treated (spectrum (b)); Fig. 2: FT-IR spectra of polypropylene fibres as such (spectrum (a)), after being plasma pre-treated with AEMA and then incubated with guaiacol sulphonate in the absence of enzymatic catalysts (spectrum (b)), and after being plasma pre- treated with AEMA and then incubated with guaiacol sulphonate in the presence of laccase (spectrum (c));

Fig. 3: FT-IR spectra of cellulose fibres as such (spectrum (a)) and plasma treated (spectrum (b)).

EXAMPLE l :

(A) AEMA grafting onto polypropylene nonwoven fabric. 10 x 10 cm samples of polypropylene nonwoven fabric were impregnated with an aqueous solution containing 20% wt. of 2-aminoethyl methacrylate (AEMA):

as hydrochloride, by means of conventional padding technologies.

The samples were irradiated at different powers with argon plasma for a fixed treatment time of 1 SO s.

A capacitive cold plasma source (LTGD plasma) with a radiofrequency of 13.56 kHz was used. The distance -between the electrodes used in the experimental step was 80 mm and the samples to be irradiated were placed on a metallic grid positioned in the middle of the two electrodes. Treated samples were washed with distilled water and dried in a ventilated oven at 105 °C for 4 h.

The grafting of the functionalised monomer onto the fibre surface was verified by means of a FT-IR (Fourier Transform Infra-Red) technique, operating in the Horizontal Attenuated Total Reflettance (HATR) mode, using a Perkin Elmer Spectrum One spectrophotometer equipped with a zinc selenide crystal and applying a mean of 16 scans and a resolution of 4 cm^'1. The area of the characteristic bands of the functionalised monomer was measured and compared with the characteristic peak of the fibre. In Figure 1 the two infrared spectra of the polypropylene fibre as such (spectrum (a)) are compared with the fibre following the plasma treatment described above (spectrum (b)). It is evident that, as a consequence of the plasma treatment, the characteristic carbonyl stretching band (C=O) appears in the infrared spectrum at a wavelength of approximately 1720 cm^"1 typical of the ester groups.

The efficiency of the plasma-aided grafting of functional groups onto the nonwoven surface in terms of homogeneity of distribution was evaluated by measuring the distribution correlation of the mean spectrum of the modified substrate on its surface. This analysis showed that following the plasma irradiation, AEMA was efficiently grafted across the entire surface of the sample.

Spectroscopic analysis further shows that following the treatment, AEMA is covalently bonded to the fabric surface with a quite good yield. An analysis of the adsorption ratio between the carbonyl stretching band at 1720 cm^"1 (typical of AEMA) and the bending of the C-H group at 1440 cm^"1 (typical of polyolefms) confirmed the substantial homogeneity in the monomer distribution across the entire sample. (B) Grafting of guaiacol sulphate by means of laccase onto the polypropylene fibres grafted with AEMA. Polypropylene nonwoven textile samples grafted using the procedure previously described were tempered for 10 minutes at 50 °C and then incubated in a buffer at a pH of 5.0 and at a temperature of 50 °C with laccase at a value of enzymatic activity equal to 6.0 nkat, in the presence of guaiacol sulphonate, a phenolic compound with antiseptic properties:

After an incubation of 2 h, the enzymatic reaction was stopped by adding 1 ml of a sodium fluoride solution. The fibres were then washed with distilled water and dried. The functionalisation catalysed by the enzymatic system is characterised by means of the following techniques:

(a) Infra-Red Spectroscopy (FT-IR) using a Perkin Elmer Spectrum One spectrophotometer (HATR mode) equipped with a zinc selenite crystal and applying a mean of 16 scans with a resolution of 4 cm^'1. The areas of the characteristic bands of the functional molecule were measured and compared with the characteristic peak of the fibre.

Figure 2 shows FT-IR spectra obtained from a sample of polypropylene fibres as such (spectrum (a)), after being plasma pre-treated with AEMA and then incubated with guaiacol sulphonate in the absence of enzymatic catalysts (spectrum (b)), and after being plasma pre-treated with AEMA and then incubated with guaiacol sulphonate in the presence of laccase (spectrum (c)). Spectrum (c) shows the characteristic bands of the aromatic molecule (e.g. the band at 1049 cm^"1 typical of aromatic sulphate stretching and the band of the quinone peak at 1640 cm^"1), which do not appear when the combined enzyme/plasma process is not carried out (spectrum (b)).

(b) XPS (X-ray Photoelectron Spectroscopy) using a PHI TF-XPS apparatus equipped with an Al monochromator as the X-ray source, with an energy resolution of 0.6 eV. Charge compensation was provided by a neutralizer.

10 The untreated polypropylene shows a very simple XPS spectrum containing essentially three different peaks indicating the presence of three different atomic species: the oxygen peak (Ols) at 533 eV, the carbon peak (CIs) at 2S6 eV and the nitrogen peak (NIs) at 401 eV.

Table 1

I₅ atomic ratio

Sample

O/C N/C s/c

Untreated polypropylene 0.030 0.005 -

Polypropylene + Guaiacol 0.090 0.027 0.001 sulphonate + laccase

Plasma-treated polypropylene + 0.153 0.052 0.001

Guaiacol sulphonate

Plasma-treated polypropylene + 0.328 0.072 0.013

Guaiacol sulphonate + laccase

The substrate as such, since it does not contain amino and/or hydroxyl groups able to interact with the enzymatic system (laccase), does not show a substantial presence of the functional molecule on the fibre surface as a substantial increase0 of the sulphur groups detectable on the inoculated fibre is not observed. Analogously, the plasma-treated sample placed in contact with the functional molecule without the catalytic system, though showing a variation in the amount of O and N atoms, induced by the presence of the mediator molecule (AEMA), does not show the presence of the functional molecule on the surface, as demonstrated by the absence of sulphur except for small absorbed quantities.

Conversely, when the plasma-pretreated textile substrate is incubated with guaiacol sulphonate in the presence of the enzymatic catalyst (laccase), a good yield is achieved for the coupling reaction of the functional molecule on the textile surface. This outcome confirms that the plasma pretreatment combined with the enzymatic catalyst enables the coupling of functionalised molecules onto the polyolefin matrix. EXAMPLES 2-4

Example 1 was repeated using the same materials and the same operative conditions as reported above, except that, instead of guaiacol sulphonate, the polypropylene fibres grafted with AEMA were treated with: ferulic acid (4-hydroxy-3-methoxycinnamic acid) (Example 2); methyl-3-hydroxy-4-methoxybenzoate (Example 3)

2,6-dibromophenol (Example 4).

The samples thus obtained were analysed in terms of antibacterial properties and flame retardant properties. The results are reported in Table 2 (in comparison with the polypropylene fibre as such): Table 2

The flame retardant properties were determined according to AATCC TM 34

(1969) standard. The antibacterial properties were determined according to AATCC 100-2004 standard, as described in the paper by M. Schroeder et al, published in

Biotechnology Journal, 2007-2, p. 1 -8.

EXAMPLE 5.

(A) AEMA grafting onto cotton fibres. 100% raw cotton fibres samples were treated as described in Example 1 in order to graft AEMA, using the same amounts and the same operating conditions.

By means of FT-IR it was verified that, following the plasma treatment, the characteristic carbonyl stretching band typical of ester compounds appears in the spectrum around 1720 cm^"1 (see Figure 3, where spectrum (a) regards untreated cellulosic fibre, while spectrum (b) regards cellulosic fibre after plasma treatment).

A grafting yield of the monomer of 3% wt was achieved as computed by measuring the band ratio between the carboxylic stretching peak at about 1730 cm^"1 and the stretching peak of the ether group typical of cellulose at 1250 cm^"1. (B) Fluorescent protein grafting by means of microbial transglutaminase onto cellulose fibres grafted with AEMA. Following the same procedure as reported in Example 1, cellulosic fibres grafted with AEMA were incubated with a fluorescent protein (FITC-TVQQEL) for 1 hour at 37°C, in the presence of 100 mg/1 of microbial transglutaminase at pH 7 in a phosphate buffer. Some samples with the same characteristics as the previous ones but without microbial transglutaminase were prepared for comparison purposes. The treated samples were then washed five times at pH 7.4 in methanol and distilled water, and then they were characterised by means of laser cofocal microscopy. With this technique it was possible to verify that ^' the fluorescent protein was coupled onto the treated fibres only when transglutaminase was applied; in the absence of the enzyme, the fluorescent protein did not bond to any appreciable extent.

Claims

1. A process for functionalising polymer materials, which comprises:

(iii) reacting the so treated polymer material with a functionalised organic compound having at least one second functional group reactive with respect to said first functional group, in the presence of an enzymatic catalyst.

2. Process according to claim 1, wherein the polymer material is cellulose or a derivative thereof.

3. Process according to claim 1, wherein the polymer material is a protein or a mixture of proteins.

4. Process according to claim 1, wherein the polymer material is a polyolefϊn.

5. Process according to claim 1, wherein the polymer material is selected from: polyacrylates, polyamides, polyesters, polyurethanes, polyaramides, polysiloxanes.

6. Process according to any one of the preceding claims, wherein the polymer material is in the form of a fibre, a fabric, a nonwoven or a film.

7. Process according to any one of the preceding claims, wherein the functionalised monomer has at least one first functional group selected from: amino group -NRiR₂ wherein Ri and R₂, equal to or different from each other, are hydrogen or C₁-C₄ alkyl groups; hydroxyl group -OH; carboxyl group - COOH; thiol group -SH; epoxy group, carboxyamide group, phenol group.

8. Process according to any one of the preceding claims, wherein the functionalised monomer comprises an olefinic end group: CH₂=CR - where R is hydrogen or a C₁-C₄ alkyl group, preferably methyl or ethyl groups.

9. Process according to any one of the preceding claims, wherein the functionalised monomer is selected from: 2-aminoethyl methacrylate, hydroxyethyl methacrylate, thio methacrylate, acrylic acid, alfyl alcohol and glycidyl methacrylate.

10. Process according to any one of the preceding claims, wherein the functionalised monomer is placed into contact with the pol}τner material in the form of a solution, preferably having a concentration of from 5 to 50% wt, more preferably from 10 to 40% wt.

11. Process according to any one of the preceding claims, wherein the irradiation is plasma irradiation.

12. Process according to claim 11, wherein the plasma irradiation is carried out with a power in the range of from 100 W to 5000 W, preferably from

200 to 3000 W.

13. Process according to claim 11 or 12, wherein the plasma irradiation is carried out with an irradiation time in the range of from 10 to 500 seconds, preferably from 30 to 300 seconds.

14. Process according to any one of claims from 1 to 10, wherein the irradiation is electron beam irradiation.

15. Process according to any one of claims from 1 to 10, wherein the irradiation is ultraviolet (UV) irradiation.

16. Process according to any one of the preceding claims, wherein after step (ii) and before step (iii) the polymer material is washed with a solvent in order to remove the unreacted monomer.

17. Process according to any one of the preceding claims, wherein step (iii) is carried out under conditions such as to achieve an enzymatic activity in the range of from 0.1 to 3000 nkat, preferably from 0.4 to 6 nkat.

18. Process according to any one of the preceding claims, wherein step (iii) is carried out at a pH in the range of from 4.0 to 8.0, preferably from 5.0 to 7.0.

19. Process according any one of the preceding claims, wherein step (iii) is carried out at a temperature in the range of from 15° to 80⁰C, preferably

20. Process according to any one of the preceding claims, wherein the organic compound is added at a concentration of from 0.5 to 1000 mM, preferably from 1 to 10 mM.

21. Process according to any one of the preceding claims, wherein the functionalised organic compound contains at least one second functional group reactive with respect to the first functional group selected from: hydroxyl group -OH; amino group -NRiR₂ where Ri and R₂, equal to or different from each other, are hydrogen or Ci-C₄ alkyl groups; carboxyl group -COOH; glycosyl groups; amide groups; thiol groups; phenol groups.

22. Process according to any one of the preceding claims, wherein the functionalised organic compound is a protein.

23. Process according to any one of the preceding claims, wherein the enzymatic catalyst is selected from: transglutaminase, tyrosinase, laccase, oxidase, peroxidase, protease, transferase, amilase, glycosidase, hydrolase, oxidoreductase, esterase, lipase, and the' like.

24. Polymer material whose surface is functionalized by grafting thereto a functionalised monomer having at least one first functional group and at least one olefinic end group, and subsequently by coupling a functionalised organic compound having at least one second functional group reactive with respect to said first functional group.

25. Polymer material functionalised according to claim 24, produced according to a process according to any one of the claims from 1 to 23.