EP0807704A1 - Recovery of fibres from bonded nonwovens - Google Patents

Abstract

A method for removing a polymer binder containing carboxylate groups cross-linked via alkaline earth metal ions from impregnated nonwovens comprises: (1) the nonwoven is treated with an aqueous alkali salt solution so that the alkali salt anions combine with the alkaline earth metal cations to form a poorly soluble salt or chelate; and (2) the binder-free fibres are separated. Preferably a phase transfer catalyst, preferably an alkyl phenol ethoxylate, fatty alcohol ethoxylate, oxo alcohol ethoxylate or quat. organic ammonium salt, is used in the alkali salt solution. Calcium ions are the cations present. The binder comprises a radical-polymerised polymer containing 0.1-30 wt.% carboxylate groups, of which 50-100 wt.% are present as salts containing alkaline earth metal cations. The alkali salt solution has a temperature of 10-100 degrees C. The nonwoven is added to the alkali salt solution, which is then optionally stirred before separating the fibres 1-60 minutes later.

Description

The invention relates to a method for recovering fibers from nonwoven fabrics. Nonwovens can be consolidated by coating or impregnation with a binder.

Basically, there is a desire for recyclable nonwovens in which the fibers can be recovered after use. For this purpose, the binder must be removed from the consolidated nonwoven. Correspondingly, according to JP 5 384 189 and the unpublished German patent application P 19 535 792.3 (0050/46241), non-crosslinked binders were used for the consolidation of nonwovens, which are soluble in water by converting carboxyl groups into carboxylate groups and can thus be separated from the fibers again.

In order to obtain nonwoven fabrics with good strength, binders are used which crosslink after application to the nonwoven fabric. For crosslinking, the binders can be monomers with several ethylenically unsaturated groups or monomers with other reactive groups, e.g. Methylol groups. Crosslinking via metal salt groups, e.g. crosslinking via Ca carboxylate groups is e.g. known from EP 442 370. It is also desirable to recover fibers from nonwovens bonded with crosslinked binders.

The object of the present invention was therefore a process for the recovery of fibers from nonwoven fabrics bonded or solidified with crosslinked binders.

• die Faservliese mit einem Polymerbindemittel mit Carboxylatgruppen gebunden sind, wobei die Carboxylatgruppen über Erdalkalikationen vernetzt sind
• die Faservliese mit einer wäßrigen Lösung eines Alkalisalzes behandelt werden, wobei das Anion des Alkalisalzes mit den Erdalkalikationen ein schwerlösliches Salz oder Komplex bildet und anschließend
• die vom Bindemittel befreiten Fasern abgetrennt werden.

The object was achieved by a method for detaching binders from nonwoven fabrics bound with these binders, characterized in that

• the nonwoven fabrics are bound with a polymer binder with carboxylate groups, the carboxylate groups being crosslinked via alkaline earth metal cations
• the nonwoven fabrics are treated with an aqueous solution of an alkali salt, the anion of the alkali salt forming a poorly soluble salt or complex with the alkaline earth metal cations and then
• the fibers freed from the binder are separated.

Nonwovens made from a wide variety of fibers can be used for the method according to the invention.

For example, synthetic fibers such as viscose, polyester, polyamide, polypropylene, polyacrylonitrile, carbon fibers or fibers of homo- and copolymers of vinyl chloride or tetrafluoroethylene or fibers of natural origin such as cellulose, cellulose, cellulose, cotton or wood fibers or also glass, ceramic or mineral fibers or mixtures thereof.

The fibers are folded into non-woven fabrics and then solidified with a binding agent, for which purpose the binding agent e.g. is brought onto the fibers by impregnation, spraying, cracking, dipping or printing. This is generally followed by drying to remove the solvent, generally water. In this manner known to those skilled in the art, a bound, i.e. get consolidated nonwoven.

The nonwoven fabrics thus produced find e.g. Use as carrier materials for roofing membranes or floor coverings. As binders, polymers are generally used which are built up from ethylenically unsaturated monomers.

The polymers contain carboxylate groups which are crosslinked via alkaline earth metal ions, i.e. they are cross-linked with metal salts.

The polymers preferably contain 0.1 to 30 wt.%, Particularly preferably 0.5 to 25 wt.% And very particularly preferably 5 to 20 wt.

The carboxylate groups are preferably 50 to 100%, particularly preferably 80 to 100%, as a salt with alkaline earth metal cations.

Preferred alkaline earth metal cations are Ca ²⁺ and Ba ²⁺ , Mg ²⁺ . Ca ²⁺ is particularly preferred.

The metal salt-crosslinked polymers can be obtained, for example, from polymers with carboxylic acid or carboxylic anhydride groups by adding an alkaline earth metal salt, for example an oxide, hydroxide, carbonate or hydrogen carbonate, for example for the aqueous dispersion or solution of the polymer, as described in EP-A-442 370.

The metal salt-crosslinked polymer is preferably composed of the following monomers A), B) and C):

Monomers A)

Monomers A) are monomers with at least one carboxylic acid or carboxylic anhydride group, which can be converted into the metal salt groups. Particularly noteworthy are acrylic acid, methacrylic acid, itaconic acid, maleic acid, maleic anhydride.

The amount of these monomers results from the desired content of carboxylate groups crosslinked with alkaline earth metal cations.

Monomers B)

Main monomers B) selected from C ₁ -C ₂₀ -alkyl (meth) acrylates, vinyl esters of carboxylic acids containing up to 20 C atoms, vinyl aromatics with up to 20 C atoms, ethylenically unsaturated nitriles, vinyl halides are of particular technical importance. Vinyl ethers of alcohols containing 1 to 10 carbon atoms, aliphatic hydrocarbons with 2 to 8 carbon atoms and 1 or 2 double bonds or mixtures of these monomers.

Examples include (meth) acrylic acid alkyl esters with a C ₁ -C ₁₀ alkyl radical, such as methyl methacrylate, methyl acrylate, n-butyl acrylate, ethyl acrylate and 2-ethylhexyl acrylate.

Mixtures of the (meth) acrylic acid alkyl esters are also particularly suitable.

Vinyl esters of carboxylic acids with 1 to 20 C atoms are e.g. Vinyl laurate, stearate, vinyl propionate, vinyl versatic acid and vinyl acetate.

Suitable vinyl aromatic compounds are vinyl toluene, α- and p-methylstyrene, α-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene and preferably styrene. Examples of nitriles are acrylonitrile and methacrylonitrile.

The vinyl halides are chlorine, fluorine or bromine-substituted ethylenically unsaturated compounds, preferably vinyl chloride and vinylidene chloride.

Examples of vinyl ethers include Vinyl methyl ether or vinyl isobutyl ether. Vinyl ethers of alcohols containing 1 to 4 carbon atoms are preferred.

Butadiene, isoprene and chloroprene may be mentioned as hydrocarbons with 2 to 8 carbon atoms and two olefinic double bonds.

Monomers C)

In addition to these main monomers, other monomers C), for example monomers containing hydroxyl groups, in particular C ₁ -C ₁₀ -hydroxyalkyl (meth) acrylates or (meth) acrylamide, can be used in the polymer.

Customary polymers generally consist of at least 40, preferably at least 60, particularly preferably at least 80% by weight of the above main monomers B).

The polymerization can be carried out by conventional polymerization methods, e.g. by substance, emulsion, suspension, dispersion, precipitation and solution polymerization. The polymerization processes mentioned are preferably carried out in the absence of oxygen, preferably in a stream of nitrogen. The usual equipment is used for all polymerization methods, e.g. Stirred tanks, stirred tank cascades, autoclaves, tubular reactors and kneaders. The method of solution, emulsion, precipitation or suspension polymerization is preferably used. The methods of solution and, in particular, emulsion polymerization are particularly preferred. The polymerization can be carried out in solvents or diluents, e.g. Toluene, o-xylene, p-xylene, cumene, chlorobenzene, ethylbenzene, technical mixtures of alkyl aromatics, cyclohexane, technical aliphate mixtures, acetone, cyclohexanone, tetrahydrofuran, dioxane, glycols and glycol derivatives, polyalkylene glycols and their derivatives, diethyl ether, tert-ether, tert-ether Methyl acetate, isopropanol, ethanol, water or mixtures such as Isopropanol / water mixtures can be run. Water is preferably used as the solvent or diluent, if appropriate with proportions of up to 60% by weight of alcohols or glycols. Water is particularly preferably used.

The metal-crosslinked polymers are generally applied to the nonwovens in the form of their aqueous solution or dispersion. After drying, the nonwovens are bound, ie solidified. The non-woven fabrics then generally contain 1 to 40 parts by weight, preferably 5 to 30 parts by weight, of the metal-crosslinked binder, based on 100 parts by weight of fibers.

After the later use of the bonded nonwoven fabrics, the fibers can be recovered according to the method of the invention by removing the blinding agent from the nonwoven fabric, i.e. is separated from the fibers.

For this purpose, the nonwoven fabric is treated with an aqueous solution of a salt (hereinafter referred to as "soluble salt"), the anion of which forms a salt which is poorly soluble in water with the alkaline earth metal.

The soluble salt can be an inorganic or organic salt.

In particular, it is an alkali metal salt.

The anion of the soluble salt can e.g. are oxalate or carbonate, which e.g. form a sparingly soluble salt with the calcium cation.

The anion of the soluble salt can also be an organic anion, for example, which forms a poorly soluble complex with the alkaline earth metal, for example Ca ²⁺ . EDTA is particularly worth mentioning here.

The soluble salt contained in the aqueous solution preferably has a solubility of at least 10 g / · l water at 23 ° C.

The aqueous solution preferably contains the salt in amounts of 0.02 to 15 parts by weight, particularly preferably in amounts of 0.1 to 10 parts by weight, very particularly preferably 0.5 to 2.5 parts by weight , based on 100 parts by weight of water.

In contrast, the solubility of the sparingly soluble alkaline earth metal salt formed when treating the nonwoven fabric is preferably less than 0.5 g / l of water at 23 ° C.

In addition to the soluble salt, the aqueous solution preferably also contains a phase transfer catalyst.

Suitable phase transfer catalysts are, for example, in Chimia 34 (1980) No. 1, pages 12 to 20. Examples of phase transfer catalysts are, for example, polyalkylene glycols, which is commercially available, for example, under the name Pluriol® or quaternary, organic Ammonium salts, which are commercially available, for example, under the name lutensite.

genannt, worin R¹-R⁴ unabhängig voneinander für einen organischen Rest, bevorzugt einen Kohlenwasserstoffrest mit 1 bis 12 C-Atomen, bevorzugt 1 bis 6 C-Atomen stehen und X^⊖ für ein Anion, bevorzugt ein anorganisches Anion z.B. Cl^-, Br^⊖ steht.Quaternary organic ammonium salts include, in particular, those of the formula I.

mentioned, wherein R ¹ -R ⁴ independently of one another are an organic radical, preferably a hydrocarbon radical having 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms and X ^{⊖ is} an anion, preferably an inorganic anion, for example Cl ^- , Br ^⊖ stands.

Particularly preferred phase transfer catalysts are those with alkoxy groups, preferably with 2 to 20 alkoxy groups, e.g. Alkylphenol ethoxylates (e.g. Lutensole® AP, emulsifier 825 fatty alcohol ethoxylates (e.g. Lutensol A8) and oxo alcohol ethoxylates (e.g. Lutensol AO7, Lutensol ON80).

By alkoxylation of alkylphenols, fatty alcohols or oxoalcohols with alkylene oxides, preferably ethylene oxide, these phase transfer catalysts contain alkoxy groups.

The content of the phase transfer catalyst in the aqueous solution is preferably 0.01 to 1 part by weight, particularly preferably 0.08 to 0.5 part by weight, based on 100 parts by weight of water.

In addition, e.g. bases, in particular sodium hydroxide solution, are also added in order to increase the proportion of alkali cations.

The temperature of the aqueous solution can e.g. 10 to 100 ° C, in particular 15 to 80 ° C and particularly preferably 20 to 50 ° C. Temperatures above 30 ° C., in particular above 40 ° C., are advantageous in order to achieve an even better and, above all, faster detachment of the binder from the nonwoven fabric.

The nonwoven fabric can be fed to the method according to the invention as a whole or in comminuted form.

The nonwoven fabric is preferably chopped into parts with an edge length of 1 to 10 cm.

For treatment with the aqueous solution, the nonwoven fabric is preferably added to the aqueous solution. The amount of the nonwoven is preferably 1 to 200 g, particularly preferably 5 to 150 g and very particularly preferably 10 to 80 g per liter of solution. The treatment time can be shortened by intensive stirring. Generally, the time required is 5 minutes to 1 hour. With vigorous stirring, however, less than 30 minutes, in particular less than 20 minutes, are sufficient to detach at least 80% by weight of the binder from the fiber and to recover the fibers.

Examples

Polyester spunbonded fabrics from Hoechst, Bobingen were impregnated with Acronal® DS 2324x (binder application of 20% by weight ± 2 (solid / solid). Acronal DS 2324X is an aqueous dispersion of a metal salt-crosslinked polymer (crosslinking of the carboxylate groups of the polymer with Ca ²⁺ cations) on an acrylate basis, the drying was carried out at 5 minutes at 200 ° C. in a Mathis laboratory dryer, after which the approximately A-4 sized fleece sheets were cut into pieces of about 1 cm ² .

A cold saturated sodium oxalate solution (approx. 3% by weight) and in each case a 10% by weight solution of soda or Na ₄ EDTA (Trilon B) in water were prepared. In each 250 g of the solution obtained, the amounts of the phase transfer catalyst indicated in the table and optionally sodium hydroxide solution were added.

In order to recover the binder-free fibers from the nonwovens, pieces of the comminuted nonwoven (see above) were placed in 250 g of the solution. The temperature of the solution and the amount of the nonwoven is shown in the table.

The fleece pieces were stirred for about 24 hours using a laboratory stirrer for 15 minutes at 2000 rpm.

The fibers were then filtered off through a 60 μ sieve, dried at 130 ° C. for 2 h and weighed back.

The degree of recycling R given in the table is calculated in accordance with $$\text{R =}\frac{\text{Nonwoven before recycling in g - weighed fibers in g}}{\text{Content of bid in the nonwoven before recycling in g}}\text{100\%}$$

In the event that the weighed fibers are completely free of binders, the degree of recycling is 100%. Values above 100% in the table can be explained by the fact that when the fibers were filtered off, very fine fibers were possibly not retained by the sieve and the weight of the fibers after recycling was too low.

Claims (7)

Process for detaching binders from nonwoven fabrics bound with these binders, characterized in that - The nonwoven fabrics are bound with a polymer binder with carboxylate groups, the carboxylate groups being crosslinked via alkaline earth metal cations - The nonwoven fabrics are treated with an aqueous solution of an alkali salt, the anion of the alkali salt forming a poorly soluble salt or complex with the alkaline earth metal cations and then - The fibers freed from the binder are separated. A method according to claim 1, characterized in that the aqueous solution additionally contains a phase transfer catalyst. A method according to claim 1 or 2, characterized in that the phase transfer catalyst is selected from the group of alkylphenol ethoxylates, fatty alcohol ethoxylates, oxo alcohol ethoxylates and quaternary, organic ammonium salts. Method according to one of claims 1 to 3, characterized in that the alkaline earth metal ^cations are Ca ²⁺ . Method according to one of claims 1 to 4, characterized in that the polymer binder to which the nonwoven is bonded is a free-radically polymerized polymer having a carboxylate group content of 0.1 to 30% by weight, based on the polymer, acts and 50 to 100 wt .-% of the carboxylate groups are present as a salt with an alkaline earth metal. Process according to one of claims 1 to 5, characterized in that the aqueous solution of the alkali salt has a temperature of 10 to 100 ° C. Method according to one of claims 1 to 6, characterized in that the nonwoven fabric is added to the aqueous solution of the alkali salt, the aqueous solution is optionally stirred and after 1 to 60 minutes the fibers freed from the binder are separated.