DE3107732A1 - Process for removing residual monomers from polymers - Google Patents

Abstract

A process for removing residual monomers from polymers by mixing the polymers with carboxylic acid hydrazides at above the glass transition temperature of the polymer and the decomposition temperature of the carboxylic acid hydrazides. The degassed polymers obtainable by the process of the invention are valuable starting materials for numerous applications of plastics, in particular for plastics in contact with foodstuffs, for example in packaging.

Description

Process for removing residual monomers from polymers

The invention relates to a method for removing residual monomers from polymers by mixing the polymers with carboxylic acid hydrazides above the Glass transition temperature of the polymer and the decomposition temperature of the carboxylic acid hydrazides.

Thermoplastic polymers such as polystyrene, impact-resistant polystyrene (HIPS), impact-resistant acrylonitrile (SAN), acrylonitrile / butadiene / styrene (ABS) polymers, Polymethyl methacrylate, styrene-maleic anhydride (S-MA) copolymers, polyamides, Acrylonitrile polymers of the barrier type (Ullmann's Encyclopedia of Technical Chemie, Volume 19, page 275, Verlag Chemie, Weinheim, 1980) are in separate Degassing steps for unreacted monomers and auxiliaries, such as Solvents, exempt.

It is generally irrelevant which polymerization process is used the polymers were produced. With all conventional methods, such as mass, Solution, bulk / suspension, emulsion or precipitation polymerization must have the residual monomers still contained are removed.

Very different paths are being taken to achieve this. The usual The method is degassing using single or multi-stage degassing units, as described, for example, in US Pat. No. 2,727,884, US Pat. No. 2,941,935. However, the thermoplastic resins produced by these methods contain Often there are still residual amounts of monomers that could be used, for example, in the packaging sector for Food or in articles that are exposed to long-term food contact are, do not allow.

It has therefore already been proposed to remove the residual monomers in these To remove polymers by irradiation with electrons. The residual monomers are thereby reduced, at the same time 9, however, a noticeable yellow coloration occurs and a partial crosslinking of the polymers. The investment for the plant and the energy consumption for operating the plant are also very high.

In US Pat. No. 4,124,658, chemical post-degassing is discussed of styrene polymers with sulfonic acid hydrazides. This procedure has however, the decisive disadvantage that the residual monomers are not actually removed but are withdrawn from the detection by a hydrogenation. As shown sulfonic acid hydrazides decompose during thermolysis with the formation of sulfonic acid and diimine (S. Hünig et. al. Angew. Chem. 77, (1965) 368). The diimine is used as a hydrogenation reagent known and widely used. When degassing SAN according to US Pat. No. 4,124 658 styrene and not actually removed, but in ethylbenzene or propionitrile converted. These low boilers also migrate in the event of long-term contact with food into the contact medium.

The object of the present invention was therefore to provide polymers with a produce reduced residual monomer content without the need for additional degassing units are necessary. The process should degas down to such low residual monomer contents allow the polymers without any risk of contamination for food packaging can be used.

By removing the residual monomers, the properties of the polymers are not changed.

It has now been found that residual monomers are advantageously removed from polymers if polymers are used together with carboxylic acid hydrazides of the general formula where R1 denotes an aliphatic or aromatic radical, x denotes 0 or 1, R1 furthermore, when x denotes 0, also denotes the radical -NH-NH2, the radical R2 denotes -NH-, in which R2 denotes a hydrogen atom, an aliphatic or aromatic atom R1 denotes the radical -NH-R3-NH-, where R3 denotes an aromatic radical, also when x is 1, intensively mixed with one another at temperatures above the glass transition temperature of the polymer and the decomposition temperature of the carboxylic acid hydrazides .

It has also been found that the process is carried out advantageously if the mixing is done on an extruder.

It has also been found that the process is carried out advantageously if the mixing is carried out with residence times of 0.2 to 20 minutes.

It has also been found that the process is carried out advantageously when 0.1 to 3 mol of carboxylic acid hydrazide, based on 1 mol of residual monomer, is used will.

Furthermore, it has been found that the process is carried out advantageously if the polymers used are styrene polymers, styrene copolymers, acrylonitrile polymers, Acrylonitrile copolymers, methacrylic acid ester polymers, methacrylic acid ester copolymers, Acrylic ester polymers, acrylic ester copolymers can be used.

Compared to the known methods, the method delivers of the invention polymers with a far lower residual monomer amount. Therefore, they are according to the invention treated polymers are well suited for food packaging. It finds a distance and there is no chemical change in the residual monomers. With the help of the invention Process succeeds in drastically reducing the residual monomer content of polymers, without additional degassing units being necessary for this, and without in the process, the polymers yellow or crosslink. All of these beneficial results are surprising in view of the state of the art.

Preferred carboxylic acid hydrazides are those in whose formulas x 0 or 1 denotes, R1, if x denotes 0, denotes an alkyl or alkenyl radical each 4 to 18 carbon atoms or one unsubstituted or with each 1 to 5, in particular 1 to 3, substituents, preferably 1 to 5, in particular 1 to 3 alkyl groups with 1 to 9 carbon atoms, polyethoxy groups of the formula - (OCH2-CH2) n-OCH2-CH3, where n denotes an integer, in particular from 1 to 18, and / or hydroxyl-substituted phenyl radical, the radical -NH-NH2, the radical R 2-NH-, where R2 is a hydrogen atom, an alkyl radical with 1 to 18 carbon atoms, one unsubstituted or one with 1 to 5, in particular 1 to 3, substituents, preferably 1 to 5, in particular 1 to 3 alkyl groups each with 1 to 9 carbon atoms, Polyethoxy groups of the formula - (OCH2-CH2) n-OCH2-CH3, in which n is an integer, in particular denotes from 1 to 18, and / or denotes phenyl radical substituted by hydroxyl groups, means that R1 also, when x denotes 1, denotes an alkylene radical or alkenylene radical 4 to 18 carbon atoms each, or one unsubstituted or each with 1 to 5, in particular 1 to 3, substituents, preferably 1 to 5, in particular 1 to 3 alkyl groups with 1 to 9 carbon atoms, polyethoxy groups of the formula - (OCH2-CH2) n -OCH2-CH3, wherein n is an integer, especially from 1 to 18 denotes, and / or hydroxyl-substituted phenylene radical or the The radical -NH-R3-NH- denotes in which R3 is an unsubstituted or in each case with 1 to 5, especially 1 to 3 substituents, preferably 1 to 5, especially 1 to 3 alkyl groups each having 1 to 9 carbon atoms, polyethoxy groups of the formula - (OCH, -CH2) -OCH -CH3, where n denotes an integer, in particular from 1 to 18, and / or hydroxyl-substituted phenylene radical denotes.

The hydrazides listed in the examples are particularly preferred, Phthalic acid dihydrazide, terephthalic acid dihydrazide, nonylbenzoic acid hydrazide, isophthalic acid dihydrazide, Octadecanecarboxylic acid hydrazide, linoleic acid hydrazide, benzene-1,4-bis-semicarbazide, tolylene-1,4-bis-semicarbazide, Nonylphenyl semicarbazide and carbodihydrazide.

Mixing is preferred in an extruder - expediently single-shaft or twin-screw extruder - carried out. However, other mixing units can also be used, which allow intensive mixing can be used, such as static mixers with Kenics or Sulzer mixing elements as well as dynamic pin mixers.

The residence time in mixing the polymers and carboxylic acid hydrazides can expediently vary between 0.2 and 20 minutes, depending on the quality of the mixing in the respective mixing units. When using extruders, this is advantageous the residence times between 20 to 180 seconds, the melt viscosity of the Polymer determines the necessary mixing time. By varying the temperature the residence time spectrum according to the invention can be adjusted.

Mixing is preferably carried out at temperatures which on the one hand above the glass transition temperature of the polymer lie and on the other hand lie above the decomposition point of the carboxylic acid hydrazides. Regarding the definition For the glass temperature, we refer to Ullmann's Encyclopedia of Technical Chemistry, Volume 18, pages 594 and 595. Very particularly preferred are temperatures which are 50 up to 1500C above the decomposition temperature of the carboxylic acid hydrazides. Carboxylic acid hydrazides, which are particularly suitable for the process according to the invention are those whose The decomposition temperature is above 1000C, advantageously above 1200C. Appropriate leads the decomposition at temperatures of 50 to 2000C, in particular 80 to 1500C is above the glass temperature of the respective polymer, without pressure or under pressure, continuously or discontinuously.

The carboxylic acid hydrazides are expediently amounts of 0.2 to 3 mol, based on 1 mole of residual monomers, used. In the preferred embodiment 0.3 to 1 mole of carboxylic acid hydrazide is used per mole of residual monomers, particularly advantageously are amounts of 0.5 to 0.6 moles of carboxylic acid hydrazide.

Amounts of more than 1 mole of carboxylic acid hydrazide are not essential Decrease in the residual monomer content more. Lower amounts above 3 moles of carboxylic acid hydrazide the residual monomer content no longer decreases.

Practically all thermoplastic resins and can be used as polymers modified polymers are used, the residual monomer content of which are reduced target. But it can also be relatively low molecular weight polymers, regardless of whether they in substance, solution or as a dispersion, with the aid of the carboxylic acid hydrazides be post-degassed. The method is particularly used for modified and unmodified polystyrene, for styrene polymers such as SAN, S-MSA, S-MMA copolymers, for ABS, ASA, ACS and MBS resins, impact modified S-MSA copolymers, impact modified Polymethyl methacrylates, polyamides and highly acrylic Phitrile-containing Barrier plastics.

The degassed polymers obtainable by the process of the invention are valuable starting materials for numerous plastic applications, in particular for plastics that come into contact with food, e.g. in packaging.

The parts given in the following examples are parts by weight.

Example 1 The following substances are intensified on a twin-screw extruder mixed with one another and then discharged -styrene-acrylonitrile copolymer; Mw (average molecular weight) = 1.6 105; AN content 25%. Residual monomer content 4,500 ppm styrene, 500 ppm acrylonitrile carbodihydrazide 0.1%, based on the SAN polymer.

Mixing is carried out at 2500 ° C. and a residence time of 4 minutes.

After extrusion, the SAN copolymer has a styrene content of 2,300 ppm and 129 ppm acrylonitrile reduced residual monomer content. The SAN copolymer is not yellowed and completely soluble. The mechanical properties correspond the source material.

Example 2 The polymer described in Example 1 is used 0.45% carbodihydrazide under appropriate conditions (= 250 ° C, residence time 5 minutes) scheduled. After the extrusion, 1,450 ppm of styrene and 70 ppm of acrylonitrile are still found. The other- Renal properties of the SAN copolymers are again not changes.

Comparative Example 1 The copolymer is made analogously to US Pat. No. 4,124,658 Example 1 with 0.45% p-toluenesulfonic acid hydrazide at 2500C and a residence time of Extruded for 4 minutes through the single-screw extruder used in Example 1. The copolymer contains, as Table 1 shows, reduced proportions of residual monomers, but this occurs Ethylbenzene and propionitrile. The copolymer is also very yellowed.

Table 1 Residual Monomers (ppm) Styrene Acrylonitrile Ethylbenzene Propionitrile SAN copolymer 4,500,500 - before treatment Example 1 2 300 129 - Example 2 1 450 70 Comparative Example 1 2 100 320 1 700 120 Comparative Example 2 4 100 410 Comparative Example 2 2,6-Di-tert-butylphenol is used in an amount of 0.45 percent by weight with the Polymers described in Example 1 mixed according to the conditions of Example 1. The extruded polymer contains the amounts of residual monomers listed in Table 1. It's also yellowed.

Example 3 The following components are used on a pen mixer Dwell time of 7 minutes and mixed temperatures of 26,000: - styrene-MA copolymer; M3 = 1.4. 105; MSA content 13%; Residual monomer content 5,300 ppm styrene - 0.4% tolylene-1,4-bis-semicarbazide After extrusion, the polymer still contains 1,900 ppm of styrene. Other low boilers are not found by gas chromatography. The polymer is not yellowed and soluble.

Example 4 The following components are made on a single-screw extruder mixed at 230 ° C and residence time of 1.5 minutes: - Polystyrene, Mw = 2.2. 105, Residual monomer content 8 200 ppm styrene, 400 ppm ethylbenzene - 0.5% terephthalic acid dihydrazide After the extrusion, 2,800 ppm of styrene and 370 ppm of ethylbenzene are still found. That Polymers is colorless.

Example 5 On a single-screw extruder, at 220.degree. C. and residence time of 3 minutes - HIPS, 10% by weight of polybutadiene as the rubber component, Mw of the hard component 1.2. 105; Residual monomer content 7,200 ppm styrene, 250 ppm ethylbenzene - Carbodihydrazide (0.3 wt.%) Formulated. The polymer still contains 2,100 ppm Styral and 210 ppm ethylbenzene. The mechanical properties correspond to the starting polymer.

Example 6 On a single-screw extruder, at 2400C and residence time of 3 minutes - ASA polymer: 17.5% by weight of polybutyl acrylate, based on the ASA polymer, as a soft component, SAN copolymer with 25% by weight of AN, based on the SAN copolymer, and Mw = 1.3 105 as the hard component and a residual monomer content of 1,900 ppm Styrene and 45 ppm acrylonitrile - 0.1% isophthalic acid dihydrazide formulated. That The polymer still contains 630 ppm styrene and 5 ppm acrylonitrile. The mechanical Properties are unchanged.

Example 7 On a single-screw extruder, at 2300C and residence time of 4 minutes - SAN copolymer with 70% acrylonitrile, M = 1.4 '105; w residual monomer content made up of 120 ppm acrylonitrile and 190 ppm styrene - 0.05% carbodihydrazide. The barrier plastic has after the con- refinement one Residual monomer content of 21 ppm acrylonitrile and 90 ppm styrene.

Example 8 On a twin screw extruder were at 21,000 and residence time from 4 minutes - styrene-methyl methacrylate copolymer, MMA content 50%; Mw = 1.2 e 105; Residual monomer content 1,900 ppm styrene, 820 ppm methyl methacrylate - 0.2% 2,4 (dihydroxy) phenyl semicarbazide ~ assembled. The copolymer still contained 820 ppm styrene and 410 ppm methyl methacrylate.

Example 9 On a pin mixer was at 2000C and residence time of 5 minutes - polymethyl methacrylate, Mw = 2.2 z 105; Residual monomer content 3 700 ppm MMA - 0.1% phthalic acid dihydrazide mixed. The resulting polymer had a residual monomer content of 920 ppm MMA.

Claims (4)

Claims 1. A process for removing residual monomers from polymers, characterized in that polymers are used together with carboxylic acid hydrazides of the general formula in which R denotes an aliphatic or aromatic radical, x denotes 0 or 1, R1 furthermore, if x denotes 0, also denotes the radical -NH-NH2, the radical R 2-NH-, in which R² denotes a hydrogen atom, an aliphatic or denotes aromatic radical, R1 also, when x is 1, denotes the radical -NH-R3-NH-, in which R3 denotes an aromatic radical, intensively with one another at temperatures above the glass transition temperature of the polymer and the decomposition temperature of the carboxylic acid hydrazides mixed. 2. The method according to claim 1, characterized in that the mixing is made on an extruder. 3. The method according to claim 1, characterized in that the mixing is carried out with residence times of 0.2 to 20 minutes. 4. The method according to claim 1, characterized in that 0.1 to 3 mol of carboxylic acid hydrazide, based on 1 mol of residual monomer, can be used. Process according to claim 1, characterized in that the polymers Styrene polymers, styrene copolymers, acrylonitrile polymers, acrylonitrile copolymers, Methacrylic acid ester polymers, methacrylic acid ester copolymers, acrylic acid ester polymers, Acrylic ester copolymers are used.