A degradable biofilm additive and its preparation method and application

Abstract

The present invention provides a degradable biofilm auxiliary agent and a preparation method and application thereof, and relates to the technical field of organic synthesis. The degradable biofilm auxiliary agent provided by the present invention contains a benzophenone structure (which can absorb ultraviolet rays) and a piperidinol structure (which can capture free radicals), and the whole exists in the form of an oligomer. When the benzophenone ultraviolet absorber exists in the degradable biofilm in the form of an oligomer, the long chain of the oligomer can form a strong interaction with the main chain of the degradable biofilm polymer, so that the added ultraviolet absorber can be stably present in the degradable biofilm for a long time to avoid migration. In addition, the oligomer itself is a plasticizer, so that the mechanical properties of the degradable biofilm are improved. The auxiliary agent provided by the present invention can effectively absorb ultraviolet light, and the free radicals generated by ultraviolet light irradiation can be captured by piperidinol to prevent continued oxidation of other degradable biofilm molecular chains, and therefore, the anti-photooxidation aging ability of the degradable biofilm can be effectively enhanced.

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis, and in particular to a degradable biofilm additive and a preparation method and application thereof. Background Art

[0002] The degradable biofilm that is being vigorously developed now is made of biological materials and has the characteristics of being degradable, pollution-free and green and environmentally friendly. It is gradually used to replace some difficult-to-degrade polyethylene plastic materials and is widely used in food packaging, greenhouse film, ground film and other fields. However, degradable bioplastic film has many problems such as poor thermal stability, weak mechanical properties, weak anti-aging ability, and weak water vapor barrier ability. It is difficult to meet the needs in practical applications. Therefore, adding additives with specific functions to degradable plastic films is an effective way to solve these functional deficiencies.

[0003] At present, some UV absorbers, such as benzophenone UV absorbers, are often added to plastic films to enhance the mechanical properties and anti-oxidation and aging properties of plastics. However, pure benzophenone UV absorbers have small molecular weight, insufficient thermal stability, and are easy to migrate out. At the same time, their ability to resist light oxidation and aging needs to be further improved. Summary of the invention

[0004] The purpose of the present invention is to provide a degradable biofilm additive and its preparation method and application. The additive provided by the present invention can improve the compatibility and thermal stability with the degradable bioplastic film, and effectively enhance the mechanical properties and anti-photooxidation aging ability of the film.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a degradable biofilm adjuvant, characterized in that it has a structure shown in Formula 1:

[0007]

[0008] The relative molecular weight of the degradable biofilm additive is 5000-7000.

[0009] The present invention provides a method for preparing the degradable biofilm additive described in the above scheme, comprising the following steps:

[0010] Compound 1, compound 2, a chain initiator and N,N-dimethylformyl are mixed and copolymerized to obtain a degradable biofilm adjuvant having a structure shown in Formula 1;

[0011]

[0012] The molar ratio of the compound 1 to the compound 2 is 1:0.5-2.

[0013] Preferably, the copolymerization reaction is carried out at a temperature of 70 to 100° C. and for a time of 12 to 24 hours; and the copolymerization reaction is carried out under a protective atmosphere.

[0014] Preferably, the chain initiator is one or more of azobisisobutyronitrile, azobisisoheptanenitrile and dimethyl azobisisobutyrate; the molar ratio of the chain initiator to compound 1 is 1:20-50.

[0015] Preferably, the preparation method of the compound 1 comprises the following steps: mixing 2,4-dihydroxybenzophenone, propylene bromide, an inorganic base catalyst and N,N-dimethylformamide, and performing an electrophilic substitution reaction to obtain compound 1;

[0016] The molar ratio of the 2,4-dihydroxybenzophenone to allyl bromide is 1:1-2.

[0017] Preferably, the inorganic base catalyst includes one or more of K2CO3, NaOH and KOH; the molar ratio of the 2,4-dihydroxybenzophenone to the inorganic base catalyst is 1:1.5-2.

[0018] Preferably, the temperature of the electrophilic substitution reaction is 80-100° C. and the time is 24-48 hours; the electrophilic substitution reaction is carried out under a protective atmosphere.

[0019] Preferably, the preparation method of the compound 2 comprises the following steps: dissolving pentamethylpiperidinol and an organic base catalyst in a polar organic solvent to obtain a pentamethylpiperidinol solution;

[0020] dissolving acryloyl chloride in a polar organic solvent to obtain an acryloyl chloride solution;

[0021] In an ice bath and under a protective atmosphere, the acryloyl chloride solution is added dropwise to the pentamethylpiperidinol solution to carry out an esterification reaction to obtain compound 2;

[0022] The molar ratio of pentamethylpiperidinol to acryloyl chloride is 1:1-2.

[0023] Preferably, the organic base catalyst includes one or more of triethylamine, piperidine and diethylamine.

[0024] The present invention provides the use of the degradable biofilm auxiliary agent described in the above scheme or the degradable biofilm auxiliary agent prepared by the preparation method described in the above scheme in a degradable biofilm.

[0025] The present invention provides a degradable biofilm auxiliary agent, having a structure shown in Formula 1, wherein the repeating unit contains a benzophenone structure (absorbable ultraviolet light) and a piperidinol structure (capable of capturing free radicals), and the whole exists in the form of an oligomer. In the present invention, when the benzophenone ultraviolet absorber exists in the degradable biofilm in the form of an oligomer, the long chain of the oligomer can form a strong interaction with the main chain of the degradable biofilm polymer, such as being entangled with each other, so that the added ultraviolet absorber can be stably present in the degradable biofilm for a long time to avoid migration. In addition, the oligomer itself is a plasticizer, and a certain amount of ultraviolet absorbers and free radical scavengers can play a plasticizing role, so that the mechanical properties of the degradable biofilm are improved. The auxiliary agent provided by the present invention can effectively absorb ultraviolet light because it contains ultraviolet absorbers and free radical scavengers at the same time, and the free radicals generated by ultraviolet irradiation can be captured by piperidinol to prevent the continued oxidation of other degradable biofilm molecular chains, and therefore, the anti-photooxidation aging ability of the degradable biofilm can be effectively enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the infrared spectrum of the degradable biofilm additive prepared in Example 1;

[0027] Figure 2 TG-DSC graph of the degradable biofilm additive prepared in Example 1;

[0028] Figure 3 The gel permeation chromatogram of the degradable biofilm aid prepared in Example 1;

[0029] Figure 4 The gel permeation chromatogram of the degradable biofilm aid prepared in Example 2;

[0030] Figure 5 The gel permeation chromatogram of the degradable biofilm aid prepared in Example 3;

[0031] Figure 6 The ultraviolet diffuse reflection absorption spectra of pure degradable biofilm PBAT and the degradable biofilm adjuvant prepared in Example 1 in the degradable biofilm PBAT;

[0032] Figure 7 Thermogravimetric analysis results of pure biodegradable biofilm PBAT and the additive prepared in Example 1 in the biodegradable biofilm PBAT;

[0033] Figure 8 Mechanical properties of pure biodegradable biofilm PBAT and PBAT doped with different additives before and after light aging. DETAILED DESCRIPTION

[0034] The present invention provides a degradable biofilm additive having a structure shown in Formula 1:

[0035]

[0036] The relative molecular weight of the degradable biofilm additive is 5000-7000.

[0037] The degradable biofilm auxiliary agent provided by the present invention has a repeating unit containing a benzophenone structure (absorbable ultraviolet light) and a piperidinol structure (capture free radicals), and the whole exists in the form of an oligomer. In the present invention, when the benzophenone ultraviolet absorber exists in the degradable biofilm in the form of an oligomer, the long chain of the oligomer can form a stronger interaction with the main chain of the degradable biofilm polymer, such as being entangled with each other, so that the added ultraviolet absorber can be stably present in the degradable biofilm for a long time, avoiding migration. In addition, the oligomer itself is a plasticizer, and a certain amount of ultraviolet absorbers and free radical trapping agents can play a plasticizing effect, so that the mechanical properties of the degradable biofilm are improved. The auxiliary agent provided by the present invention can effectively absorb ultraviolet light because it contains ultraviolet absorbers and free radical trapping agents at the same time, and the free radicals generated by ultraviolet irradiation can be captured by piperidinol, preventing the continued oxidation of other degradable biofilm molecular chains, and therefore, the anti-photooxidation aging ability of the degradable biofilm can be effectively enhanced.

[0038] The present invention provides a method for preparing the degradable biofilm additive described in the above scheme, comprising the following steps:

[0039] Compound 1, compound 2, a chain initiator and N,N-dimethylformyl are mixed and copolymerized to obtain a degradable biofilm adjuvant having a structure shown in Formula 1;

[0040]

[0041] The molar ratio of the compound 1 to the compound 2 is 1:0.5-2.

[0042] In the present invention, unless otherwise specified, the raw materials used are commercially available products well known in the art.

[0043] The following first describes compound 1.

[0044] In the present invention, the preparation method of the compound 1 preferably comprises the following steps: mixing 2,4-dihydroxybenzophenone, allyl bromide, an inorganic base catalyst and N,N-dimethylformamide, and conducting an electrophilic substitution reaction to obtain compound 1.

[0045] In the present invention, the molar ratio of the 2,4-dihydroxybenzophenone to allyl bromide is 1:1-2, preferably 1:1.2-1.8.

[0046] In the present invention, the inorganic base catalyst preferably includes one or more of K2CO3, NaOH and KOH; the molar ratio of the 2,4-dihydroxybenzophenone to the inorganic base catalyst is preferably 1:1.5-2, more preferably 1:1.6-1.8.

[0047] In the present invention, the N,N-dimethylformamide (DMF) is used as a solvent. The present invention has no special requirements on the amount of the N,N-dimethylformamide used, as long as it can completely dissolve 2,4-dihydroxybenzophenone and allyl bromide.

[0048] In the present invention, the temperature of the electrophilic substitution reaction is preferably 80-100°C, more preferably 85-95°C, and further preferably 90°C; the time of the electrophilic substitution reaction is preferably 24-48h, more preferably 30-40h, and further preferably 34-38h. In the present invention, the electrophilic substitution reaction is preferably carried out under a protective atmosphere; the protective atmosphere is preferably a nitrogen atmosphere.

[0049] In the present invention, when K2CO3 is used as a catalyst, the equation of the electrophilic substitution reaction is as follows:

[0050]

[0051] After the electrophilic substitution reaction is completed, the present invention preferably performs post-treatment on the obtained reaction solution, and the post-treatment preferably includes: after the reaction solution is cooled to room temperature, water is added to the reaction solution to dissolve the inorganic base catalyst, and then the reaction solution is extracted with ethyl acetate, and the upper organic phase is concentrated by rotary evaporation, and the obtained product is purified by column chromatography to obtain compound 1. In the present invention, the eluent used for column chromatography purification is preferably ethyl acetate / petroleum ether; the volume ratio of ethyl acetate to petroleum ether is preferably 1:40.

[0052] Next, Compound 2 is described.

[0053] In the present invention, the preparation method of the compound 2 preferably comprises the following steps: dissolving pentamethylpiperidinol and an organic base catalyst in a polar organic solvent to obtain a pentamethylpiperidinol solution;

[0054] dissolving acryloyl chloride in a polar organic solvent to obtain an acryloyl chloride solution;

[0055] In an ice bath and under a protective atmosphere, the acryloyl chloride solution was added dropwise to the pentamethylpiperidinol solution to carry out an esterification reaction to obtain compound 2.

[0056] The invention dissolves pentamethylpiperidinol and an organic base catalyst into a polar organic solvent to obtain a pentamethylpiperidinol solution.

[0057] In the present invention, the organic base catalyst preferably includes one or more of triethylamine, piperidine and diethylamine; the molar ratio of pentamethylpiperidinol to the organic base catalyst is preferably 1:1.5-2.5, more preferably 1:1.7-2.2.

[0058] In the present invention, the polar organic solvent preferably includes dichloromethane, tetrahydrofuran, chloroform or acetone. The present invention has no special requirements on the amount of the polar organic solvent, as long as it can completely dissolve pentamethylpiperidinol and the organic base catalyst.

[0059] In the present invention, acryloyl chloride is dissolved in a polar organic solvent to obtain an acryloyl chloride solution. In the present invention, the types of the polar organic solvent have been discussed above and will not be repeated here.

[0060] The present invention has no special requirement on the amount of the polar organic solvent, as long as it can completely dissolve the acryloyl chloride.

[0061] After obtaining the pentamethylpiperidinol solution and the acryloyl chloride solution, the present invention drips the acryloyl chloride solution into the pentamethylpiperidinol solution under an ice bath and a protective atmosphere to carry out an esterification reaction to obtain compound 2.

[0062] In the present invention, the molar ratio of pentamethylpiperidinol in the pentamethylpiperidinol solution to acryloyl chloride in the acryloyl chloride solution is preferably 1:1-2, more preferably 1:1.2-1.8, and further preferably 1:1.4-1.6. The present invention has no special requirements for the dripping rate, and the dripping rate well known in the art can be used.

[0063] In the present invention, the protective atmosphere is preferably a nitrogen atmosphere.

[0064] In the present invention, the esterification reaction time is preferably 3 to 5 hours, more preferably 4 hours.

[0065] In the present invention, when triethylamine is used as a catalyst and dichloromethane is used as a solvent, the equation for the esterification reaction is as follows:

[0066]

[0067] After the esterification reaction is completed, the present invention preferably washes the obtained reaction solution with water, allows the layers to stand, and takes the organic phase for rotary evaporation and concentration. The concentrated product is purified by column chromatography using ethyl acetate / petroleum ether as an eluent to obtain compound 2. In the present invention, the volume ratio of ethyl acetate to petroleum ether in the eluent is preferably 1:30.

[0068] After obtaining compound 1 and compound 2, the present invention mixes compound 1, compound 2, a chain initiator and N,N-dimethylformyl to carry out copolymerization reaction to obtain a degradable biofilm adjuvant having a structure shown in formula 1;

[0069]

[0070] In the present invention, the molar ratio of compound 1 to compound 2 is 1:0.5-2, preferably 1:1-1.5.

[0071] In the present invention, the chain initiator is preferably one or more of azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (ABVN) and dimethyl azobisisobutyrate (AIBME); the molar ratio of the chain initiator to compound 1 is preferably 1:20 to 50, more preferably 1:25 to 45, and further preferably 1:30 to 40.

[0072] The present invention has no special requirement on the amount of N,N-dimethylformyl used, as long as it can completely dissolve compound 1 and compound 2.

[0073] In the present invention, the copolymerization reaction temperature is preferably 70-100°C, more preferably 80-90°C; the copolymerization reaction time is preferably 12-24h, more preferably 16-20h. In the present invention, the copolymerization reaction is preferably carried out under a protective atmosphere, and the protective atmosphere is preferably a nitrogen atmosphere.

[0074] In the present invention, the copolymerization reaction equation is as follows:

[0075]

[0076] After the copolymerization reaction is completed, the present invention preferably pours the obtained reaction solution into an aqueous solution to precipitate a polymer, washes the precipitated polymer with water, and then vacuum-dries it to obtain a degradable biofilm additive.

[0077] The present invention provides the use of the degradable biofilm auxiliary agent described in the above scheme or the degradable biofilm auxiliary agent prepared by the preparation method described in the above scheme in a degradable biofilm.

[0078] The degradable biofilm additive provided by the present invention, its preparation method and application are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0079] Example 1

[0080] Step 1: Add 2,4-dihydroxybenzophenone (25mmol, 5.356g) and propylene bromide (25mmol, 3.025g) to the reaction bottle, and add the catalyst K2CO3 (37.5mmol, 5.183g), dissolve them in N,N-dimethylformamide solution (200mL), the reaction temperature is 80℃, the reaction time is 24h, and the reaction is completed under N2 protection. After the reaction is completed, cool to room temperature, add a certain amount of water to the reaction solution to mix and dissolve K2CO3, then extract the reaction solution with ethyl acetate, and concentrate the upper organic phase by rotary evaporation. The obtained product is purified by column chromatography, ethyl acetate / petroleum ether (v / v=1:40) as the eluent, and finally a yellow-green solid, that is, compound 1 (4.50g, yield 70.8%) is obtained.

[0081] The reaction formula of step 1 is:

[0082]

[0083] Step 2: Add pentamethylpiperidinol (40mmol, 6.851g) and catalyst triethylamine (88mmol, 8.905g) to the reaction bottle, dissolve them in dichloromethane (120mL) to obtain pentamethylpiperidinol solution; dissolve acryloyl chloride (40mmol, 3.621g) in dichloromethane (100mL) to obtain acryloyl chloride solution; use a dropping funnel to slowly drop the acryloyl chloride solution into the pentamethylpiperidinol solution. The entire reaction was carried out at 0°C and under N2 gas protection for 4h. After the reaction was completed, a certain amount of water was added to wash off the triethylamine in the reaction solution, and the stratification was allowed to stand, and the upper organic phase was concentrated by rotary evaporation. The concentrated product was purified by column chromatography, ethyl acetate / petroleum ether (v:v=1:30) as the eluent, and finally a light yellow liquid was obtained, i.e., compound 2 (5.95g, yield 66%).

[0084] The reaction formula of step 2 is:

[0085]

[0086] Step 3: Add compound 1 (5 mmol, 1.272 g) obtained in the first step and compound 2 (5 mmol, 1.127 g) obtained in the second step in a molar ratio of 1:1 in a reaction bottle, and add chain initiator AIBN (0.15 mmol, 0.025 g), use N, N-dimethylformamide (20 mL) as solvent, N2 protection and absolute anhydrous, and react at a reaction temperature of 70°C for 24 hours. After the reaction is completed, pour the reaction solution into an aqueous solution to precipitate the polymer, wash the precipitated polymer with water, and then vacuum dry to obtain a degradable biofilm additive (1.1 g).

[0087] The reaction formula of step three is:

[0088]

[0089] Example 2

[0090] The only difference from Example 1 is that the molar ratio of Compound 1 to Compound 2 is 1:2.

[0091] Example 3

[0092] The only difference from Example 1 is that the molar ratio of Compound 1 to Compound 2 is 1:0.5.

[0093] Structure and performance characterization:

[0094] Figure 1 The infrared spectrum of the degradable biofilm additive prepared in Example 1 is shown in FIG. Figure 1 It can be seen that it has the structure shown in Formula 1.

[0095] Figure 2 This is the TG-DSC diagram of the degradable biofilm additive prepared in Example 1. Figure 2 It can be seen that the oligomer has a relatively high thermal decomposition temperature, with an initial decomposition temperature of 185°C, which can meet the requirements for thermal stability as an auxiliary agent in subsequent processing, such as the granulation temperature of the degradable bioplastic film PBAT at about 180°C and the blowing temperature at about 160°C. In these processing processes, the oligomer of the present invention can maintain structural stability. In addition, the glass transition temperature of the oligomer is about 60°C, which can ensure that it is mixed evenly with PBAT during granulation and plastic film blowing.

[0096] Figure 3 This is the gel permeation chromatogram of the degradable biofilm aid prepared in Example 1. Figure 3 It can be seen that the relative molecular weight of the degradable biofilm additive prepared in Example 1 is 6558, which is an oligomer.

[0097] Figure 4 This is the gel permeation chromatogram of the degradable biofilm aid prepared in Example 2. Figure 4 It can be seen that the relative molecular weight of the degradable biofilm additive prepared in Example 2 is 5016, which is an oligomer.

[0098] Figure 5 This is the gel permeation chromatogram of the degradable biofilm aid prepared in Example 3. Figure 5 It can be seen that the relative molecular weight of the degradable biofilm additive prepared in Example 3 is 5658, which is an oligomer.

[0099] The additive prepared by the present invention was applied to the degradable biofilm to conduct performance tests:

[0100] Specifically, taking 0.25wt% of the oligomer of Example 1 as an additive doped into PBAT as an example, the preparation process is as follows: 1kg of commercial PBAT masterbatch, 20g of talcum powder, and 250mg of the oligomer of Example 1 are mechanically mixed uniformly; then the mixture is added to a granulator for granulation: the temperature of the granulator is set at 180°C, and the screw speed is set at 170rpm; the obtained PBAT masterbatch containing additives is used for film blowing: the temperature of the film blowing machine is set at 160°C, and the screw speed is 40 rpm, to obtain a PBAT film doped with additives. Using the same method, other PBAT films containing additives are obtained.

[0101] Figure 6 The UV diffuse reflection absorption spectra of pure biodegradable biofilm PBAT and the biodegradable biofilm additive prepared in Example 1 in the biodegradable biofilm PBAT. Figure 6 It can be seen that the ultraviolet absorption range of the degradable biofilm containing additives becomes wider, and there is strong absorption in the wavelength range of 320-400 nm, which is consistent with the absorption range of benzophenone, indicating that the presence of oligomer additives effectively improves the ultraviolet absorption capacity of the PBAT film.

[0102] Figure 7 Thermogravimetric analysis results of pure biodegradable biofilm PBAT and the additive prepared in Example 1 in the biodegradable biofilm PBAT. As can be seen from the figure, the addition of low-content oligomers does not affect the thermal stability of the PBAT film, and it still maintains a high thermal stability.

[0103] Figure 8 The mechanical properties of pure biodegradable biofilm PBAT and PBAT doped with different additives before and after light aging. Figure 8 It can be seen that the mechanical properties of the PBAT film doped with the prepared oligomer additive are better than those of the pure PBAT film and the PBAT doped with pure benzophenone, whether before or after light aging, which confirms the good plasticizing function of the new oligomer additive. Sample No. 1: pure PBAT; 2: PBAT + 0.25wt% benzophenone; 3: PBAT + 0.5wt% benzophenone; 4: PBAT + 0.25wt% oligomer of Example 1; 5: PBAT + 0.5wt% benzophenone.

[0104] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A degradable biofilm additive, characterized in that: It has the structure shown in formula 1: The relative molecular weight of the degradable biofilm additive is 5000-7000.

2. The method for preparing the degradable biofilm additive according to claim 1, characterized in that: The following steps are involved: Compound 1, compound 2, a chain initiator and N,N-dimethylformyl are mixed and copolymerized to obtain a degradable biofilm additive having a structure shown in Formula 1; The molar ratio of the compound 1 to the compound 2 is 1:0.5-2.

3. The preparation method according to claim 2, characterized in that: The copolymerization reaction is carried out at a temperature of 70 to 100° C. and for a time of 12 to 24 hours; the copolymerization reaction is carried out under a protective atmosphere.

4. The preparation method according to claim 2, characterized in that: The chain initiator is one or more of azobisisobutyronitrile, azobisisoheptanenitrile and dimethyl azobisisobutyrate; the molar ratio of the chain initiator to compound 1 is 1:20-50.

5. The preparation method according to claim 2, characterized in that: The preparation method of the compound 1 comprises the following steps: mixing 2,4-dihydroxybenzophenone, propylene bromide, an inorganic base catalyst and N,N-dimethylformamide, and performing an electrophilic substitution reaction to obtain the compound 1; The molar ratio of the 2,4-dihydroxybenzophenone to allyl bromide is 1:1-2.

6. The preparation method according to claim 5, characterized in that: The inorganic base catalyst includes one or more of K2CO3, NaOH and KOH; the molar ratio of the 2,4-dihydroxybenzophenone to the inorganic base catalyst is 1:1.5-2.

7. The preparation method according to claim 5 or 6, characterized in that: The temperature of the electrophilic substitution reaction is 80-100° C., and the time is 24-48 hours; the electrophilic substitution reaction is carried out under a protective atmosphere.

8. The preparation method according to claim 2, characterized in that: The preparation method of the compound 2 comprises the following steps: dissolving pentamethylpiperidinol and an organic base catalyst in a polar organic solvent to obtain a pentamethylpiperidinol solution; dissolving acryloyl chloride in a polar organic solvent to obtain an acryloyl chloride solution; In an ice bath and under a protective atmosphere, the acryloyl chloride solution is added dropwise to the pentamethylpiperidinol solution to carry out an esterification reaction to obtain compound 2; The molar ratio of pentamethylpiperidinol to acryloyl chloride is 1:1-2.

9. The preparation method according to claim 8, characterized in that: The organic base catalyst includes one or more of triethylamine, piperidine and diethylamine.

10. Use of the degradable biofilm aid according to claim 1 or the degradable biofilm aid prepared by the preparation method according to any one of claims 2 to 9 in degradable biofilm.

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