MXPA98003857A - Entrelazados poly (aminoacidos) and supreparac method - Google Patents

Abstract

The present invention relates to an interlaced poly (amino acid), having the stoichiometric formula: [A] x [B] and where A represents repeat units of the skeleton polymer structure [1] and B represents entanglement units of the structures [2] and [3], distributed randomly between the units of the polymer structure [1], through the formation of ester bonds with a carboxylate group of the radical R, (1) (2) and (3) , where x represents the weight percentage of units A and y represents the percentage by weight of units B, based on the weight of the combined units A and B, where x is 80 to 99.9 percent by weight and is from 0.1 to 20 weight percent, m is 0, 1 or 2, n is from 20 to 20,000, R is a radical selected from one or more of -C (= O) OM, CH2C (= O) OM and CH2CH2C (= O) OM, and M is selected from one or more of H, alkali metal ions and alkaline earth metal ions, X is O, S N N, R1 is a residue of a di-, tri- or tetrafunctional group , selected from the alkylene (C1-C4), aryl, arylalkyl and methylene ether of a polyphenol (C6-C15), alkanopolyol (C2-C6) or poly (alkylene glycol), each R2 is H when X is OOS, and each R2 is, independently, H or (C1-C3) alkyl when X is N, R3 is a di-tri- or tetra-propionate residue of alkanopolyol (C2-C6), a is 0-1, and b is 1.2.

Description

POL [(AMLNOÁCIDOS) INTERLACED AND METHOD FOR PREPARATION BACKGROUND 5 This invention relates to entangled poly (amino acids) and improved methods for preparing these entangled poly (amino acids). In particular, this invention relates to the use of polyaziridines and polyepoxides as ** __________ > interleavers for poly (amino acids), to produce superabsorbent polymers under aqueous conditions, without handling hydrogel intermediates. The superabsorbent polymers are capable of absorbing large amounts of water and aqueous solutions, in particular physiological saline solutions, and have final in a variety of applications, including, for example, sanitary products, hygienic materials, r retaining agents and controlled release vehicles. The superabsorbent polymers are generally water soluble polymers, which have become insoluble by a process of entanglement, resulting in an inflatable polymer capable of many times absorbing its original weight in water or aqueous solutions, typically at least 20 times the original weight of the superabsorbent polymer. These superabsorbent polymers are generally polyanionic and the The hydration of the charged parts in the entangled polymer provides the driving force for the absorbent properties. Conventional superabsorbent polymers include, for example, polycarboxylic acids, such as poly (acrylic acids), hydrolyzed acrylonitrile polymers, poly (vinyl alcohols) and starch graft polymers and acrylic acid. The U.A. Patent Nos. 4,541,871 and 4,645,789 disclose the use of polyepoxide and polyaziridinyl compounds, respectively, to provide water-absorbing polyelectrolytes based on acrylic acid. However, water-absorbing polymers based on the chemistry of the acrylic acid skeleton have the disadvantage of not being easily biodegradable and thus contribute to charge the environment when they are discarded or released into the effluent streams. Attempts to provide biodegradable superabsorbent polymers include entanglement of the polysuccinimide (hereinafter referred to as PSI), followed by hydrolysis, where the reaction of the PSI with the crosslinking agent typically requires a non-aqueous solvent, and hydrolysis of the PSI partially intertwined with amino acid derivatives imply special handling procedures for hydrogel intermediates (for example, the patent of E. U. A., No. 5,525,682). The U.A. Patent No. 5,284,936 discloses the preparation of poly (amino acids) entangled by thermal entanglement. of polyaspartate with aspartate and lysine and subsequent hydrolysis to supply superabsorbent polymers. The present invention is directed to overcoming the problems associated with prior art processes, used to prepare superabsorbent entangled poly (amino acids), which are biodegradable, by providing an efficient entanglement process, without implying special stages of handling of the intermediate hydrogel products.

EXPOSITION OF THE INVENTION The present invention provides an interlaced poly (amino acid), having the stoichiometric formula of [A] x [B] y, where A "represents repeating units of the skeleton polymer structure [1] and B represents units of entanglement of the structures [2] and [3], distributed randomly between the units of the polymer structure [1], through the formation of ester bonds with a carboxylate group of the radical R, - (NH-CH- (CH2) m-CO-) n- (1) R - I I [-CH2CH- (R1) a- (CHCH2) b-] (2.) [-CH2CH2NH- (R3) - (NHCH2CH2) b-] (3) where x represents the weight percentage of the units A e "and represents the percentage by weight of the units B, based on the weight of the combined units A and B; wherein x is from 80 to 99.9 weight percent e and is from 0.1 to 20 weight percent; m is 0, 1 or 2; n is from 20 to 20,000; R is a radical selected from one or more of -C (= 0) 0M, -CH C (= 0) ÓM and CH CH C (= 0) OM, and M is selected from one or more of H, metal ions alkaline and alkaline earth metal ions; X is O, ~ S or N; R is a residue of a di-, tri- or tetrafunctional group, selected from the alkylene (C1-C4), aryl, arylalkyl and methylene ether of a polyphenol (C5-C15), alkanopolyol (C2-Cg) or poly- ( alkylene glycol); each R2 is H, when X is O or S, and each R2 is, independently, H or (C1-C3) alkyl when X is N; R3 is an ester residue of di-tri- or tetrapropionate of alkanopolyol (C2-Cg); a is 0 or 1; and b is 1, 2 03. The present invention further provides a "method for preparing entangled poly (amino acids), which comprises: (a) contacting an aqueous solution of the poly (amino acid) with 0.1 to 20 weight percent of the interleaver, based on the weight of the poly (amino acid), in a reaction mixture, at a pH of 3 to 7, where this poly (amino acid) is selected from one or more of the poly (aspartic acid) and poly (acid) glutamic acid and this crosslinker is selected from one or more crosslinkers of the formulas (4) and (5) X1 X1 / \ / \ 10 C CHH2o - CCHH - ((RR aa-- • [[CCHH - CCHH2]] hb (4) CH2 CH2 / \ / \ CH2 - N - (3) - [N - CH2] b (5) where X1 = O, S or NR2; R1, R2, R3, a and b have the definitions described above; (b) removing the water from the reaction mixture, (c) subjecting this reaction mixture to a * 'thermal treatment and (d) recovering the poly (amino acid 20) entangled as a solid.

DETAILED DESCRIPTION The entangled poly (amino acids) of the present invention are water insoluble polymers, which are capable of absorbing significant amounts of water, biological fluids or physiological saline solutions. Preferably, the entangled poly (amino acids) have a polyanionic backbone, such as poly (aspartic acid) or poly (glutamic acid), with the remainder of the polymer including crosslinking elements attached to the backbone polymer by means of the reaction with the groups side chain carboxy. In addition, the entangled poly (amino acids) may contain minor amounts of optional amino acid residue backbones, selected from one or more of the glycine, alanine, valine, leucine, isoleucine, phenylalanine, proline, asparagine, glutamine, tyrosine, serine. and threonine, Typically the optional amino acid units represent less than 10 percent and preferably less than 5 percent by weight, based on the weight of the interlaced poly (amino acid) product. Other optional amino acid residues that can be included in the interlaced poly (amino acid) in minor amounts include, for example, cysteine, lysine, methionine, histidine, tryptophan and arginine. As used herein, all percentages mentioned will express percentages (%) by weight, unless otherwise specified. The phrase "aqueous composition" or "solution" means herein aqueous-based compositions or solutions, which are substantially aqueous, ie, solvents in addition to water, such as alcohols, may be present, so long as they are compatible with, or miscible with, the composition or aqueous solution.

Generally, the desired degree of entanglement will be sufficient to render the polymer substantially insoluble in water, while still allowing a sufficient macromolecular flexibility of the interlaced polymer matrix, to absorb aqueous solutions, especially saline solutions, in an amount of at least 3 times, preferably 10 times, more preferably -20 times and especially preferred at least 30 times, the weight of the polymer. The entanglement reaction occurs between the carboxylate groups of the side chain of the backbone polymer and the reactive end groups of the crosslinking agent. The amount of the entanglement units in the entangled poly (amino acids) of the present invention is typically from 0.1 to 20%, preferably from 0.2 to 10%, more preferably from 0.5 to 5% and especially preferred from 1 to 13%, with based on the total weight of the interlaced poly (amino acid). The absorbency properties and the degree of entanglement are controlled by the appropriate selection of temperature, time and pH parameters, used in the preparation of the entangled poly (amino acids). For example, the process of the present invention uses temperatures of 80 to 220 ° C, preferably 100 to 200 ° C and more preferably 100 to 180 ° C, for the crosslinking reaction, which are typically less than those disclosed in prior art using conventional interleavers (e.g., the conditions described in U.S. Patent No. 5,284,936, which involve basic amino acid crosslinkers). Furthermore, the times of the crosslinking reaction in the process of the present invention are reduced (10 minutes to 3 hours, preferably 15 minutes to 2 hours and more preferably 15 minutes to 1 hour), compared with those described in prior art (for example, 12 to 24 hours in the U.S. Patent No. 5,284,936). The control of the pH during the interlacing reaction is an important fa in achieving the desired degree of entanglement and the resulting absorbency properties. Typically, the pH is from 3 to 7, preferably from 4.0 to 6.5, more preferably from 5.0 to 6.5 and especially preferred from 5.5 to 6.0. While we do not wish to be bound by theory, we believe that, in the case of . the present invention, the described range of pH allows the protonation of the heteroatom in the 3-member ring of the linker, thus activating the ring towards nucleophilic ring-opening attack by the side chain carboxylate group of the amino acid polymer of the backbone; furthermore, the described pH range provides an environment where a sufficient fraction of the side chain carboxylic acid group exists in the carboxylate form, which is required for the nucleophilic ring opening reaction, with the crosslinker, while, at the same time time, minimizes the competitive hydrolysis of the 3-membered ring in the aqueous environment. The entangled poly (amino acids) of the present invention can be conveniently prepared without the process of the hydrpgel intermediates. An aqueous solution of one or more polymers of poly (amino acid) backbones, adjusted to a desired pH range, is placed in a reaction vessel and the aqueous solution of the crosslinking agent is added to the reaction mixture, with stirring, at room temperature (about 20 ° C) to 80 ° C (step (a)). After brief agitation, the reaction mixture is then transferred to a drying apparatus, for example an oven or a freeze-drying system, to remove the volatile components (step (b)). Typically, the reaction mixture is frozen with a mixture of acetone and solid carbon dioxide (dry ice) (at about -30 ° C) and subjected to vacuum (less than 7 pascals, which corresponds to 50 microns or 0.05 millimeters (mm) ) of Hg), during 2 to 24 hours, to remove the volatiles during which the temperature begins to approach the ambient temperature. The solid reaction product is then broken into small particles, preferably to a powder, and heat treated at 100 to 200 ° C, preferably at 100 to 180 ° C, for 15 to 90 minutes, to complete the crosslinking reaction (step (c)). The interlaced poly (amino acid) is then cooled to room temperature and recovered; The solid can be ground to a powder, if convenient. Alternatively, the reaction mixture can be placed in a furnace (forced air flow) to simultaneously dry and interlock the polymer (combination of steps (b) and (c)). In this case, the heat treatment is typically for 30 minutes to 2 hours, preferably 30 to 90 minutes, at a temperature of 120 to 220 ° C, preferably 150 to 200 ° C, depending on the surface area of the mixture and the air flow rate of the furnace. The process of the present invention does not involve separate steps of hydrolysis, such as those frequently encountered in prior art processes. For example, hydrolysis is often required in conventional processes to "activate" or "reopen" the cyclic structures of the imide, which are formed during entanglement or are initially present in the starting materials (e.g., PSI); unless the hydrolysis is used to unfold these imide structures, the absorbency properties of the polymers are decreased due to the reduction in the available carboxylate sites during hydration. The process of the present invention does not use "imide-containing" starting materials in the entanglement process, thus, there is no need for reactivation of the carboxylate sites by hydrolysis. The entangled poly (amino acids) of the present invention are polymers comprising a backbone having repeating units of amino acid monomers of structure (1), which have been randomly entangled with the «* Reactive materials of formulas (4) and (5). The The materials of the formulas (4) and (5) are entangled by the reaction with the carboxylate sites in the R groups of structure (1). Suitable crosslinkers include polyepoxides and polyaziridines soluble or dispersible in water. As used here, the term "water soluble", as applied to the interleavers, indicates that the interleaver has a solubility of at least * approximately 1 gram (g) of interlacing per- 100 g of water. The solubility or dispersibility of the crosslinkers in an aqueous composition is necessary to allow the interleaver access to the poly (amino acid), otherwise, the rate and degree of entanglement will be insufficient for practical use. Suitable interlacing agents useful in preparing the interlaced poly (amino acids) of the present invention, include the polyglycidyl ethers of the alkane polyols (C2-Cg) and poly (alkylene glycols), such as, for example, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether , glycerin diglycidyl ether, and triglycidyl ether, propylene glycol, diglycidyl ether and butanediol diglycidyl ether Additional crosslinking agents of this type include, for example, the pliglicidyl ethers of erythritol, trimethylolethane and trimethylolpropane. Suitable additional entanglements include diepoxyalkanes (C4-C8) and diepoxyaralkanes, such as, for example, 1,2,3,4-diepoxybutane, 1,2,4,5-diepoxypentane, 1, 2, 5, 6-diepoxyhexane, 1, 2, 7, 8-diepoxyoctane, 1,4- and 1,3-di-inylbenzene-diepoxides; polyphenol ethers (Cg-Q._ t_) -polyglycidyl, such as, for example, 4-diepoxyhexane; , 4'- isopropylidenediphenol-diglycidyl ether (bisphenol A-diglycidyl ether) and hydroquinone diglycidyl ether. Previous relaxance results in the entanglement structure (2), where R is, for example, the bis-(C1-C4) alkane, 1,4-phenyl, 1,3-phenyl, di (methylene) -ether of ethylene- glycol, di (methylene) -ether of hydroquinone or di (methylene) -ether of 4,4 '-isopropylidenediphenol. Another class of suitable entanglement agents include the polyaziridinyl derivatives of alkane polyols (C2-Cg), such as, for example, pentaerythritol-tris- [β- (N-aziridinyl) propionate], trimethylolpropan-tris- [β- (N-aziridinyl) propionate], pentaerythritol-bis- [β-] (N-aziridinyl) -propionate] and trimethylolpropan-bis- [ß- (N-aziridinyl) -propionate]. Of particular use are the polyaziridinyl derivatives of esters of erythritol propionate, pentaerythritol, trimethylol etol and trimethylolpropane, which are prepared by the addition of the aziridine to the corresponding acrylate esters of the polyols. The polyaziridinyl derivatives of the polypropionate esters of pentaerythritol, trimethylolethane and trimethylolpropane are represented by structure (6), where w = 2, 3 or 4; R 4 = methyl or ethyl; z = 0 or 1, and w + z = a maximum of 4.

CH2 / \ 15 - [CH2-N-CH2CH2C (== 0) OCH2] w-C (R4) z (CH2OH) 4_ (w + z) (6) - When the interlayers of the formulas "(4) or (5) are brought into contact with the skeleton polymers of the structure (1), the resulting ester interlacing can be represented by the structures (2A) or (3A), respectively. Only two binding sites are shown in the * structures (2A) and (3A) for the interlacing part; however, it will be understood that many binding sites, such as 3 or 4, can occur by interlacing, depending on the The nature of the groups R1 and R3 (see formulas (4) and (5)).

XR2 XR2 I I [-C (= 0) OCH2CH- (R1) a- (CHCH2OC (= 0) -] (2A) [-C (= 0) OCH2CH2NH- (R3) - (NHCH2CH2OC (= 0) -] (3) Preferred crosslinkers are ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, 1,2,3,4-diepoxybutane, 4,4'-isopropylidenediphenol diglycidyl ether, hydroquinone diglycidyl ether, pentaerythritol tris - [ß- (N-aziridinyl) propionate and trimethylolpropan-tris [ß-N-aziridinyl) propionate; more preferred are ethylene glycol diglycyl ether and pentaerythritol tris [β- (N-aziridinyl) propionate. Preferred poly (amino acids), used to prepare the superabsorbents of the entangled poly (amino acids) of the present invention, are poly (aspartic acid) and poly (glutamic acid); the poly (amino acids) are preferably used in the salt form of an alkali metal, for example sodium or potassium salts (M = Na or K in structure (1)). The number average molecular weights (Mn) of the poly (amino acids) used in the preparation of the entangled superabsorbent polymers are typically from 3,000 to 2,000,000, preferably from 15,000 to 1,000,000 and more preferably from 40,000 to 500,000. Corresponding weight average molecular weights (Mw) are typically from 6,000 to 4,000,000, preferably from 30,000 to 2,000,000 and more preferably from 60,000 to 1,000,000. Molecular weights are determined by aqueous phase gel permeation chromatography ("GPC"), using a TosoHaas GMP XL column with 0.05M sodium acetate, as the mobile phase, with a refractive index detector. Correspondingly, the value of n in structure (1) is typically from 20 to 20,000, preferably from 100 to 10,000 and more preferably from 200 to 5,000. The abbreviations used in the Examples and Tables are listed below with the corresponding descriptions. The PETAP interleaver is represented by the structure (7), which corresponds to the structure (6), where w = 3, z = 0. SPA = sodium polyaspartate EGDGE = Ethylene glycol diglycidyl ether PETAP = Pentaerythritol-tris [ß- (N-aziridinyl) propionate].

CH2 / \ [CH2-N-CH2CH2C (= 0) OCH2] 3-CCH2OH (7) Some embodiments of the invention are described in detail in the following Examples. All ratios, parts and percentages (%) are expressed by weight, unless specified otherwise and all reagents used are of good commercial quality, unless otherwise specified.

Example 1 General Method for Preparing Poly (amino acids) Interlaced To 29.6 milliliter (1 fluid ounce) flasks containing a magnetic stir bar, 10.0 grams (g) of an aqueous solution of sodium polyaspartate was added.

(SPA, approximately 10% solids) at a pH of from 5 to 6.5. Each of the bottles was then treated with various amounts of interlayer (50% aqueous solution) while stirring the mixture. The interleavers were added in drops, using a Pasteur pipette (0.5-5% PETAP or EGDGE, based on the weight of the SPA) and the mixtures were shaken vigorously for 5 minutes. The contents of each flask were transferred to a bottle dried by freezing and the samples were frozen using a mixture of acetone and solid carbon dioxide (dry ice). The samples were then dried by placing in a freeze-drying system (Labconco Freze Dry System / Lyph Lock 4.5) and the volatiles were removed using a 24 hour vacuum treatment. The samples were then ground into powders, heat-treated for 30 minutes, at 180 ° C, allowed to cool under vacuum or an inert atmosphere (nitrogen) and tested on the absorbency (in 0.9% aqueous sodium chloride) using the test method described in Example 16.

Examples 2 to 15 In the manner described in Example 1, different interlayers (XL) and different levels of interlacing (% XL) were mixed with SPA and the resulting polymers were evaluated 5 in the absorbency, according to the method described in Example 16. A summary of the reaction parameters used in the SPA interlaces (XL,% XL, pH, Mw) and the corresponding absorbency performance are presented in Table 1. Commercially available superabsorbents, 10 based in the interlaced poly (acrylic acid), they typically have absorbances of 15 seconds and 10 minutes of 20-40 / 9 and 40-60 g / g, respectively.

Example 16 The interlaced SPA (0.2 g) of Examples 2 to 15, were uniformly distributed in a "tea bag") (5 centimeters x 5 cm) of non-woven fabric and heat sealed. The bag was immersed in a solution of 0.9% aqueous sodium chloride (physiological saline) for 15 seconds, followed by 1 minute of drip drying and then weighed. The The tea bag was then re-immersed in the saline solution for 2 minutes and 45 seconds, followed by 1 minute of drip-drying and reweighing. A final immersion for 7 minutes, followed by drip drying and weighing back generates absorbency properties for different poly (amino acids) interlaced, corresponding to values of 15 seconds, 3 minutes and 10 minutes., Respectively. The same general procedure was repeated for the tea bag alone (without the sample), to determine a "reference" value, which is to be subtracted from the weight of the soaked tea bag containing the sample. Absorbency was expressed as the grams of saline solution absorbed per gram of the interlaced poly (amino acid), based on the following equation: absorbency (g / g) = [(weight of the wet tea bag with the treated sample) - (weight of the wet tea bag without the sample)] / [sample weight]. The absorbance data are presented in Table 1 for several interlaced poly (amino acids); Absorbency data seconds give an indication of the regime at which the interlaced poly (amino acids) are capable of absorbing the aqueous solutions (kinetic absorbency) values for 10 minutes estimates the ability of the interlaced poly (amino acids) to absorb aqueous solutions (equilibrium absorbency) .

Table 1

Claims (8)

to CLAIMS

1. An interlaced poly (amino acid), having the stoichiometric formula: [A] x [B] y 5 where A represents repeating units of the skeletal polymer structure [1] and B represents entanglement units of the structures [2] and [3], randomly distributed between the units of the polymer structure [1], through the formation of ester bonds 10 with a carboxylate group of the radical R, - (NH-CH- (CH2) m-CO-) n- (1) R 15 XR2 XR: H [-CH2CH- (R1) a- (CHCH2) b-] () 20 [-CH2CH2NH- (R3) - (NHCH2CH2) b-] O) where x represents the weight percentage of the units A and 25 and represents the percentage by weight of the units B, based on the weight of the combined units A and B; where x is from 80 to 99. 9 weight percent e and is from 0.1 to 20 weight percent; m is 0, 1 or 2; n is from 20 to 20,000; R is a radical selected from one or more of -C (= 0) OM, -CH2C (= 0) 0M and CH2CH2C (= 0) OM, and M is selected from one or more of H, alkali metal ions and ions of alkaline earth metals; X is O, S or N; R1 is a residue of a di-, tri- or tetrafunctional group selected from the alkylene (C ^ -Cq.), Aryl, arylalkyl and methylene ether of a polyphenol (Cg-C ^), alkanopolyol (C2 ~ C) or poly- (alkylene glycol); each R2 is H when X is O or S, and each R2 is, independently, H or (C1-C3) alkyl when X is N; R ^ is an ester residue of di-tri- or tetrapropionate of alkanopolyol (C2 ~ C); a is 0 or 1; and b is 1, 2 or 3.

2. The interlaced poly (amino acid) of claim 1, wherein R1 is selected from one or more of the bis (C1-C4) alkylene, 1,4-phenyl, 1,3-phenyl, ethylene di (methylene) ether glycol, di (methylene) -ether of hydroquinone and di (methylene) -ether of 4,4'-isopropylidenediphenol.

3. A process for preparing entangled poly (amino acids), which comprises: (a) contacting an aqueous solution of the poly (amino acid) with 0.1 to 20 weight percent of the interlayer, based on the weight of the poly (amino acid) , in a reaction mixture, at a pH of 3 to 7, where this poly (amino acid) is selected from one or more of the poly (aspartic acid) and poly (glutamic acid) and this interleaver is selected from one or more crosslinkers of the formulas (4) and (5) X1 X1 / \ / \ CH2 - CH (Rx) a- CCH "CH2] b (4) CH2 CH2 / \ / \ ^^ 10 CCHH22 - NN - (R3) - [N - CH2] b (5) where X1 = O, S or NR2; R1 = a residue of a di-, tri- or tetrafunctional group, selected from the alkylene (C1-C4), aryl, arylalkyl and methylene ether of a polyphenol (C -C ^ s), alkanopolyol (C2-Cg) or poly- (alkylene glycol); _ ^ R2 = H or (C1-C3) alkyl R3 = a residue of di-tri- or tetrapropionate ester of alkanepolyol (C2-Cg); a = 0 or 1; and b = 1, 2 or 3. (b) removing the water from the reaction mixture, (c) subjecting this reaction mixture to a thermal treatment and (d) recovering the poly (amino acid) as a solid.

4. The process, according to claim 3, wherein the pH is from 5 to 6.5.

5. The process according to claim 3, wherein the interlayer is selected from one or more of the ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, 1,2,4,4-diepoxybutane, 4, 4'-isopropylidene-diphenol, diglycidyl ether, hydroquinone diglycidyl ether, pentaerythritol-tris [ß- (N-aziridinyl) propionate and trimethylol-propan-tris [ß- (N-aziridinyl) propionate.

6. The method, according to claim 3, wherein the water is removed from the reaction mixture by freeze-drying, followed by a heat treatment, performed at 100 to 200 ° C, for 15 to 90 minutes, before recovery of the interlaced poly (amino acid).

7. The method, according to claim 3, wherein steps (b) and (c) are combined in one step by heating the reaction mixture in an oven at 120 to 220 ° C, for 30 minutes up to 2 hours , before the recovery of the interlaced poly (amino acid).

8. The method, according to claim 3, wherein the percentage by weight of the interlayer is from 0.5 to 5 percent, based on the weight of the poly (amino acid).