DE4421239A1 - Process for the recycling of high-molecular-weight nylon 6, and repolymer prepared by this process - Google Patents

Abstract

The invention relates to a process for the recycling of high-molecular-weight nylon 6 (polyamide 6), to the repolymer prepared by this process, and to a process for recycling high-molecular-weight nylon 6 or used plastic parts made from nylon 6 using a common depolymerisation step in the presence of caprolactam, water and acid to give a defined viscosity level of the melt, from which, after removal of the component which is insoluble in the low-viscosity melt, the remaining material is repolymerised or degraded to give a repolymer which can be further processed or to give caprolactam.

Description

The invention relates to the subject matter specified in the claims.

The invention particularly relates to a method for processing high molecular polyamide 6 or used plastic parts made of poly amide 6 and repolymer prepared by this process.

Polyamide 6 also includes glass fiber, glass balls or carbon fibers reinforced or filled with minerals and flame retardant Products to be understood, the above and below still listed led modifications implemented individually or in any combination could be.

Such products also represent modifications of polyamide 6 in which a small part, d. H. a maximum of about 10 mol% of the caproamide units other monomer units made from amide-forming components - such as monoami nen, diamines, monocarboxylic acids, dicarboxylic acids and / or lactams or the corresponding - aminocarboxylic acids with more than 6 carbon atoms - replaced is.

Finally, the polyamide 6 can be added by adding other thermoplastics be modified, e.g. B. those based on polyolefins or copolyolefins, the u. a. used to improve the toughness of the product in question become. Such polymers are described, for example, in US Patent publications 4 174 358 and 4 537 929.

A long-known process for the preparation of polyamide-6-Ab cases from any production processes or used polyamide-6 Plastic objects whose shape z. B. by injection molding, Ex trudging or spinning and further processing or processing steps that have taken place is degradation to caprolactam. Often one serves the hydrolytic degradation of polyamide 6 at higher temperatures ren in the presence of phosphoric acid as a catalyst. In the U.S. patent  5 169 870, for example, is one such method in connection with the Recovery of caprolactam from polyamide 6 carpets described.

Instead of acidic catalysts, basic sub punching are used, such as the German Offenlegungsschrift 4 211 609 can be taken.

One method for partial depolymerization of high molecular weight polyamides is Subject of DD 2 64 119. For this purpose, for. B. from the poly amid-6 fiber production derived high molecular weight polyamide 6 waste in a share of 10 to 70% in liquid caprolactam at temperatures from 250 to 280 ° C up to a degradation of 10 to 50%, based on the average degree of polymerization of the starting product, partial depolymerized and the caprolactam used polymerized. According to the DD 2 64 119 is in the presence of 2% water and in another case with small amounts of benzoic acid - obviously as chains length limiter - worked. The procedure according to DD 2 64 119 ent speaks of the well-known hydrolytic polymerization of caprolactam. Here the goal of DD 2 64 119 is the transfer of Polyamide waste in polycondensates, the quality of which for a Further processing in the injection molding sector are suitable. The procedure of the DD 2 64 119 leads to products with relative solution viscosities, but not are filterable.

Another method of utilizing used polyamide 6 art Fabric parts consist of grinding these parts and the subsequent part len addition of the ground material to fresh granulate. It has been shown that such grist for z. B. injection molding applications can be. Due to heat, UV radiation and other external influences Damage caused by used polyamide 6 parts has namely in the generally proven to be much less than the duration of use of the Parts would be expected. This mechanical-thermal process has  however, in so far as the cycle of use and processing and cannot be repeated any number of times. As a result of repeated Ge these materials will eventually need and repeated damage placed in a state where they meet the application requirements are no longer enough.

Then the old parts must either be disposed of in a suitable manner or by means of the above chemical methods to caprolactam are elaborated.

The object of the invention is therefore to develop a method with the help of high-molecular polyamide 6 or used polyamide-6 Objects are brought into a shape

• a) immediately used again in the next process step finished polyamide 6 can be obtained,
• b) in the case of reinforced / filled and / or insoluble additives modified polyamide 6 grades a separation of the reinforcement medium, fillers and insoluble additives and
• c) from the - if necessary after separation of those mentioned under b) Components using suitable separation methods - by application chemical processes, such as hydrolytic degradation in the presence catalytically effective amounts of phosphoric acid at higher temperatures ren caprolactam can be recovered.

This object is achieved by the method according to claim 1 solved. Two preferred main variants of the method according to the invention are described in claims 12 and 13.

Advantageous embodiments of the invention are in the subclaims contain.  

The invention therefore relates in particular to a method in which the high molecular weight polyamide or the polyamide objects (A) - optionally after the removal of adhering impurities and / or parts consisting of other materials - as regrind or in another suitable reduction form
along with
20-85 parts by weight, in particular 30 to 85 parts by weight, caprolactam (B)
5-30 parts by weight, especially 10 to 25 parts by weight, water (C) and
0-10 parts by weight, in particular 0 to 3 parts by weight, of an organic or inorganic acid (D),
in a closed stirred autoclave or another suitable reaction vessel (depolymerization reactor) at a temperature of 150 to 210 ° C and a pressure determined essentially by the temperature and the amount of water from 1.5 to 15 bar within 1 to 12 hours to a homogeneous Polyamide 6 melt with a realistic solution viscosity of 1.05 to 1.5 (measured on a 0.5% solution in m-cresol according to DIN 53727) are depolymerized.

It has been shown that this procedure called the task conditions met:

The depolymerizate obtained in the manner according to the invention can be given if necessary after separation of glass fibers and / or mineral fillers and / or other components insoluble in the melt by means of con continuous or discontinuous, carried out in one or more stages Filtration in the depolymerization reactor or a second, behind the front direction for filtration of the melt attached reactor according to known Processes at temperatures from 240 to 290 ° C and pressures from 0.001 to Polymerized 20 bar to polyamide 6 with a solution viscosity greater than 1.55  and processed into ready-to-use polyamide 6 granules, where to achieve lower caprolactam and oligomer contents than approx. 10% by weight a treatment of the polyamide 6 melt downstream in a reactor Extruder or thin film apparatus possibly under reduced pressure Presence of an entrainer or the polyamide-6 Granulate is subjected to hot water extrusion.

But if one with reinforcing agents, fillers or other insoluble ones Additives modified polyamide is used in the depolymerization and a separation of the insoluble constituents is provided, it is for Relief of filtration advantageous, the solution viscosity of the depolymer sat by a suitable choice of depolymerization conditions on one low value from approx. 1.06 to approx. 1.3.

If no filtration is necessary, the solution viscosity of the Depoly merisats can be set to higher values. This procedure is preferably on unreinforced, unfilled and otherwise not insoluble use modified polyamide 6 items.

Finally, the depolymerizate can also be carried out in a further reactor known methods under the influence of superheated steam and in Presence of 0.3 to 10 wt .-% phosphoric acid - based on the amount of the depolymerizate - completely in at temperatures of 230 to 330 ° C Caprolactam are cleaved back, which is then after going through the usual oxidation and preconcentration to pure caprolactam is distilled.

Complete hydrolytic degradation in the presence of phosphoric acid can can be applied to any depolymerizate, but presupposes that Reinforcing agents, fillers and other insoluble components beforehand largely separated. In the separation of these substances should deeply viscous and correspondingly easily filterable depolymers  be what by appropriate choice of depolymerization conditions can be ensured.

In contrast to the DD 2 64 119 described above, the Depoly runs merization of polyamide 6 to low viscosity material according to the Invention appropriate process at low temperatures and in the presence of the speci embellished amounts of water at high speed, which in the sense of Invention for the subsequent processing stages of great use is.

With regard to high dissolution rates of polyamide 6 in Caprolac tam and short depolymerization times it has proven to be particularly favorable proven to depolymerize at temperatures from 170 to 185 ° C and Pressures from 2 to 8 bar in lactam / water mixtures, which based on the total amount of polyamide 6 and caprolactam approx. Contain 20% water.

The following examples illustrate the invention. The specified relative Solution viscosities were determined in accordance with DIN 53727 on 0.5% solutions of relevant samples measured in m-cresol at 20 ° C. Measuring the Melt Volume indices (MVI) at 185 ° C and a load of 21.6 N was according to DIN 53735 performed.

Example 1

This example demonstrates the behavior of a caprolactam / polyamide-6 Mixture during the depolymerization in the presence of 2% by weight of water analogous to DD 2 64 119 and a temperature that corresponds to the mode of operation of the corresponds to the inventive method. The initial viscosity of ver polyamide 6 used was 1.89.

The results show that with the water used according to DD 2 64 119 amount of depolymerization is sluggish, and the system when over at all, only after very long reaction times in the desired low viscous state passes.

Example 2

This example demonstrates the behavior of polyamide-6 / caprolactam Solutions under depolymerization conditions, i.e. H. in the presence of Water.

For this purpose, in a stirrable double-jacket steel autoclave Bottom drain valve and the necessary measuring equipment solutions made of poly amide 6 (relative solution viscosity = 1.83), caprolactam and water poses. It turned out depending on the temperature and the amount of water a certain pressure.

Samples were taken at regular intervals through the bottom drain valve taken, which were characterized on the basis of their solution viscosities. The results show that after a few hours only a slight change in the quality of the respective depolymerizates occurs.

The MVI of the material at the end of experiment 2.2. (8 hours) was 2000 g / 10 minutes.

Claims (14)

1. Process for the preparation of high molecular weight polyamide 6, in which

• (a) crushing the high molecular weight polyamide 6 (A),
• (b) freed of contaminants and metal parts if necessary,
• (c) 10 to 50 parts by weight of the high molecular weight polyamide 6 (A) with
  • (B): 20 to 85 parts by weight of caprolactam,
  • (C): 5 to 30 parts by weight of water and
  • (D): 0 to 10 parts by weight of at least one organic or inorganic acid or mixtures thereof,
• (d) subject to depolymerization in a closed reactor at a temperature of at least 165 to 195 ° C. and a pressure of at least 1.5 bar within at least 1 hour,
• (e) if appropriate, the resulting depolymerizate is subsequently freed from the insoluble components in the melt,
• (f) optionally repolymerized at temperatures of 240 to 290 ° C. and pressures of 0.001 to 20 bar to give polyamide 6 with a relative solution viscosity greater than 1.55,
• (g) if appropriate, the melt is further treated in a reactor under reduced pressure and, if appropriate, in the presence of an entrainer known per se while reducing the lactam and oligomer content, and
• (h) discharges the melt for further processing.

2. The method according to claim 1, characterized in that the depo Lymerization in a first depolymerization step to a homogeneous NEN melt with a relative solution viscosity of 1.05 to 1.5 (measured on a 0.5% solution in m-cresol according to DIN 53727) to be led. 3. The method according to claims 1 or 2, characterized in that that the depolymerization in a second depolymerization step in known manner in the presence of a total of 0.3 to 10 wt .-% phosphorus acid - based on the amount of the depolymerizate - at temperatures from 230 to 330 ° C completely up to the caprolactam and this is discharged or distilled off if necessary. 4. The method according to claims 1 or 2, characterized in that that the plastic parts A with 30 to 90 parts by weight of caprolactam, 10 up to 25 parts by weight of water and 0 to 3 parts by weight of at least one organic or inorganic acid mixed and depolymerized become. 5. The method according to claims 1 to 4, characterized in that 35 to 50 parts by weight (A), 40 to 65 parts by weight (B), 15 to 25 Parts by weight (C) and 0 to 3 parts by weight (D) are used. 6. The method according to claims 1 or 2, characterized in that that the depolymerization takes place at 170 to 185 ° C. 7. The method according to claims 1 or 2, characterized in that that the depolymerization at 1.5 to 15 bar, preferably at 2 to 8 bar he follows. 8. The method according to claims 1 or 2, characterized in that that the depolymerization in 1 to 12 hours, preferably in 2 to 10 Hours.   9. The method according to claims 1 or 2, characterized in that that the depolymerizate of the first depolymerization step before Repolymerization or the second depolymerization step from the components which are insoluble in the melt are freed and filtered. 10. The method according to claims 1 to 9, characterized in that the components insoluble in the melt are glass fibers, Glasku gels, mineral fillers and / or inorganic pigments. 11. The method according to claims 1 to 10, characterized in that that the separation of the components insoluble in the melt is at least one-stage filtration. 12. The method according to claims 1, 2 or 4, characterized in net that the four components (A + B + C + D) in one closed NEN autoclave or other suitable reaction vessel (Depolymerization reactor) at a temperature of 165 to 195 ° C and a pressure of 1.5 to 15 bar, being 170 to 185 ° C and 2 to 8 bar is particularly preferred for mixtures with 20% by weight of water (D) are within 1 to 1 2 hours to a homogeneous polyamide-6 Melt with a relative solution viscosity of 1.05 to 1.5 depo be lymerized, and the resulting depolymerizate is then - after separation of glass fibers and / or mineral fillers and / or other components insoluble in the melt continuous or discontinuous, single or multi-stage through guided filtration - in the depolymerization reactor or a second, behind the device for filtration of the melt attached reactor according to known methods at temperatures of 240 to 290 ° C and Pressures from 0.001 to 20 bar to polyamide 6 with a relative solution solution viscosity polymerized greater than 1.55, the melt is fully discharged and ready-to-use polyamide 6 granules with a residual gel hold on caprolactam and oligomers from 0.2 to 12 wt .-% up is working, possibly to achieve lower Caprolac  tam and oligomer contents as approx. 10% by weight a treatment of Polyamide 6 melt in an extruder downstream of the reactor or thin film apparatus under reduced pressure and possibly in Presence of an entrainer or the poly amide-6 granules are subjected to hot water extraction. 13. The method according to claims 1 to 4, characterized in that the four components (A + B + C + D) in a closed Stirred autoclaves or another suitable reaction vessel (Depo polymerization reactor) at a temperature of 165 to 195 ° C and a pressure of 1.5 to 15 bar within 1 to 12 hours a homogeneous polyamide 6 melt with a relative solution viscosity from 1.05 to 1.5 can be depolymerized, and so get ne sepolymer afterwards - after separation of glass fibers and / or mineral fillers and / or others in the melt insoluble components by means of continuous or discontinuous Filtration carried out in one or more stages in another Reactor according to likewise known processes under the influence of superheated steam and in the presence of a total of 0.3 to 10 wt .-% phosphoric acid - based on the amount of depolymer sats - completely in caprolactam at temperatures from 230 to 330 ° C is split back, which then after going through the usual Oxidation and preconcentration stage to pure caprolactam is gated. 14. Repolymer, prepared by the process according to one of the An sayings 1, 2 or 4 to 12, characterized in that there is a relative solution viscosity of at least 1.55 and maximum 10% of the insoluble com originally present in the melt contains components.