Vinyl aromatic/diene-block copolymers having good organoleptic properties

Abstract

The invention relates to a vinyl aromatic/diene-block copolymer A, obtained by an anionic polymerization of a monomer composition, comprising: Al: 60-95 wt.-% of at least one vinyl aromatic monomer, and A2:5-40 wt.-% of at least one diene monomer, wherein the vinyl aromatic/diene-block copolymer A in total comprises less than 10 parts per million (ppm) of acetaldehyde, methacrolein and styrene based on the total amount of vinyl aromatic/diene-block copolymer A; the vinyl aromatic/diene-block copolymer A has improved orgnoleptic properties and is in particular suitable for producing food packaging materials.

Claims

1. A method for processing a vinyl aromatic/diene-block copolymer A, obtained by an anionic polymerization of a monomer composition, comprising: A1: 60-95 wt.-%, based on the total weight of the monomer composition, of at least one vinyl aromatic monomer, and A2: 5-40 wt.-%, based on the total weight of the monomer composition, of at least one diene monomer, or a polymer composition P comprising at least one vinyl aromatic/diene-block copolymer A and at least one styrene homopolymer or styrene copolymer; wherein a polymer melt is formed from the vinyl aromatic/diene-block copolymer A or the polymer composition P and water is dosed to the polymer melt during the processing; wherein the vinyl aromatic/diene-block copolymer A in total comprises less than 10 parts per million (ppm) of acetaldehyde, methacrolein, and styrene based on the total amount of vinyl aromatic/diene-block copolymer A; and the vinyl aromatic/diene-block copolymer A further comprises at least one stabilizer, selected from a phenol-based stabilizer or a phosphite-based stabilizer; and wherein the oxygen concentration of the ambient air in contact with the polymer melt is reduced.

2. The method according to claim 1, wherein the vinyl aromatic/diene-block copolymer A in total comprises less than 400 ppm, based on the total amount of vinyl aromatic/diene-block copolymer A, of the following volatile organic compounds: acetaldehyde, isobutene, ethanol, acroleine, propanal, methacroleine, 2-methylpentane, 3-methalpentane, 2-methyl-2-butanol, methylcyclopentane, 4-vinylcyclohexene, ethylbenzene, phenylacetylene, styrene, o-xylene, isopropylbenzene, allylbenzene, n-propylbenzene, α-methylstyrene, cyclohexane, and n-hexane.

3. The method according to claim 1, wherein the vinyl aromatic/diene-block copolymer A in total comprises less than 100 ppm, based on the total amount of vinyl aromatic/diene-block copolymer A and disregarding the presence of cyclohexane and n-hexane, of the following volatile organic compounds: acetaldehyde, isobutene, ethanol, acroleine, propanal, methacroleine, 2-methylpentane, 3-methalpentane, 2-methyl-2-butanol, methylcyclopentane, 4-vinylcyclohexene, ethylbenzene, phenylacetylene, styrene, o-xylene, isopropylbenzene, allylbenzene, n-propylbenzene, and α-methylstyrene.

4. The method according to claim 1, wherein the at least one vinyl aromatic monomer is selected from styrene, α-methyl styrene, and mixtures thereof and the at least one diene monomer is selected from 1,3-butadiene and 2-methyl-1,3-butadiene.

5. The method according to claim 1, wherein the polymer melt is provided in a polymer melt discharge device and the oxygen concentration compared to ambient air is reduced by providing the polymer melt discharge device with a sealing.

6. The method according to claim 5, wherein the sealing of the polymer melt discharge device is obtained by continuously feeding of the polymer melt to the polymer melt discharge device.

7. The method according to claim 1, wherein a chemically inert fluid, selected from at least one chemical inert solvent and at least one chemical inert gas, is fed to the polymer melt discharge device.

8. The method according to claim 1, wherein the vinyl aromatic/diene-block copolymer A in total comprises less than 5 ppm of acetaldehyde, methacrolein, and styrene.

9. The method according to claim 1, wherein the vinyl aromatic/diene-block copolymer A in total comprises less than 2 ppm of acetaldehyde, methacrolein, and styrene.

10. The method according to claim 2, wherein the vinyl aromatic/diene-block copolymer A in total comprises less than 200 ppm, based on the total amount of vinyl aromatic/diene-block copolymer A, of the following volatile organic compounds: acetaldehyde, isobutene, ethanol, acroleine, propanal, methacroleine, 2-methylpentane, 3-methalpentane, 2-methyl-2-butanol, methylcyclopentane, 4-vinylcyclohexene, ethylbenzene, phenylacetylene, styrene, o-xylene, isopropylbenzene, allylbenzene, n-propylbenzene, α-methylstyrene, cyclohexane, and n-hexane.

11. The method according to claim 3, wherein the vinyl aromatic/diene-block copolymer A in total comprises less than 50 ppm, based on the total amount of vinyl aromatic/diene-block copolymer A and disregarding the presence of cyclohexane and n-hexane, of the following volatile organic compounds: acetaldehyde, isobutene, ethanol, acroleine, propanal, methacroleine, 2-methylpentane, 3-methalpentane, 2-methyl-2-butanol, methylcyclopentane, 4-vinylcyclohexene, ethylbenzene, phenylacetylene, styrene, o-xylene, isopropylbenzene, allylbenzene, n-propylbenzene, and α-methylstyrene.

12. The method according to claim 3, wherein the vinyl aromatic/diene-block copolymer A in total comprises less than 30 ppm, based on the total amount of vinyl aromatic/diene-block copolymer A and disregarding the presence of cyclohexane and n-hexane, of the following volatile organic compounds: acetaldehyde, isobutene, ethanol, acroleine, propanal, methacroleine, 2-methylpentane, 3-methalpentane, 2-methyl-2-butanol, methylcyclopentane, 4-vinylcyclohexene, ethylbenzene, phenylacetylene, styrene, o-xylene, isopropylbenzene, allylbenzene, n-propylbenzene, and α-methylstyrene.

13. The method according to claim 7, wherein the at least one chemical inert solvent is a liquid hydrocarbon and the at least one chemical inert gas is CO.sub.2, nitrogen, and/or argon.

Description

SHORT DESCRIPTION OF THE FIGURES

(1) FIG. 1a shows samples of commercial SBC granules which were heated to 230° C. under air.

(2) FIG. 1b shows samples of commercial SBC granules which were heated to 230° C. under argon atmosphere.

(3) FIGS. 2a and 2b show the results of a headspace GC-MS chromatography of commercial SBC granules which were heated to 120° C. in an air-tight vial.

(4) FIGS. 3a and 3b show the results of a headspace GC-MS chromatography of commercial SBC granules which were degassed at 45° C. and then heated to 120° C. in an air-tight vial.

(5) FIGS. 4a and 4b show the results of a headspace GC-MS chromatography of commercial SBC granules which were degassed at 45° C., re-granulated at 220-240° C. in a conventional process and then heated to 120° C. in an air-tight vial.

(6) FIG. 5 shows the effect of increased water injection to the extruder on the formation of volatile organic compounds during the processing of SBC granules.

(7) FIG. 6 shows the effect of different stabilizers on the formation of volatile organic compounds during the processing of SBC granules.

(8) The following examples, Figures and claims further illustrate the invention.

EXAMPLES

(9) Various, commercially available styrene/butadiene-block copolymers (hereinafter also referred to as SBC) were used to carry out the examples and comparative examples below. The following were selected:

(10) TABLE-US-00001 (A) Styrolux ® 693D, Ineos Styrolution Group GmbH (B) Styrolux ® 684D, Ineos Styrolution Group GmbH (C) Styroclear ® GH 62, Ineos Styrolution Group GmbH (D) K-Resin ® KX40, Ineos Styrolution Group GmbH (E) K-Resin ® KR03, Ineos Styrolution Group GmbH (F) Finaclear ® 520, Total Petrochemicals (G) Asafex ™ 810, Asahi Kasei Corporation (H) Styroflex ® BX 6425, Ineos Styrolution Group GmbH (I) Styroflex ® 2G66, Ineos Styrolution Group GmbH

(11) Testing of Organoleptic Properties

(12) First, the organoleptic behavior of various SBCs was investigated. For this purpose, about 50 g of SBC granules each were introduced into Erlenmeyer flasks and were each doused with about 200 ml of boiling, demineralized water. As reference, an Erlenmeyer flask without SBC, which also contains about 200 ml of boiling water is used. The flasks were sealed with a glass cover and allowed to cool over a period of about 4 minutes. Odor samples of the gas space of the respective flasks were evaluated by a group (up to 10 persons) according to the following classification:

(13) 1=neutral, no odor compared to reference sample

(14) 2=slight but acceptable odor

(15) 3=more disagreable odor

(16) 4=very akward odor

(17) The commercially available SBC granules were subjected to various pretreatments prior to carrying out the described evaluation process. The first evaluation with SBC granule samples taken directly from the commercially available package of the respective SBC granules typically received a rating of 1.2 to 2.2. Carefully degassing the SBC granules at 45° C. in a vacuum dryer for 48 hours typically resulted in a significant improvement in organoleptic assessment. Re-processing the degassed material at a temperature of 220-240° C. (recommended process parameters) in a lab twin-screw extruder resulted in a third evaluation of the re-granulated polymer to a typical rating of 1.9. The results are summarized in Table 1.

(18) TABLE-US-00002 TABLE 1 Example 1 Example 2 Example 3 Untreated After After re- SBC sample (as supplied) degassing processing (A) 1.9 1.6 2.7 (A) 1.8 1.5 2.6 (B) 1.7 1.2 2.6 (B) 1.7 1.4 2.7 (C) 2 1.3 2.8 (D) 1.2 1.2 2.3 (E) 1.5 1.4 2.4 (F) 2.2 1.4 2.3 (G) 2 2.1 2.9 (H) 1.6 1.2 1.9 (I) 2 1.5 3.3

(19) These results show that organoleptically flawless granules also develop a distinct, unpleasant odor during processing. The processing of the SBC granules thus adversely affects the organoleptic properties of the polymer.

(20) Investigation of the Influence of Oxygen

(21) Fresh commercial SBC granules were heated either under air or under argon atmosphere and held at about 230° C. for 20-30 min. It was observed that in the presence of oxygen a strong new formation of the organoleptically perceptible substances and a clear yellow coloration of the polymer melt occurs. The samples are shown in FIG. 1a.

(22) In the samples heated under argon atmosphere, only a small new formation of organoleptically perceptible substances and no yellow coloration were observed. The samples are shown in FIG. 1b.

(23) Determination of Organoleptically Perceptible Substances

(24) The organoleptically perceptible substances, which are contained in the individual commercially available SBC granules, were measured using headspace gas chromatography mass spectrometry (GC-MS).

(25) The GC machine has the following characteristics:

(26) GC machine: HP 5700A Detector: FID

(27) Column: Sil 5 (length=25 m, ID=0.15; film thickness: 1.2 μm)

(28) The following temperature program is used:

(29) Start—2 min at 40° C.—10° C./min ramp till 240° C.—8 min at 240° C.—End

(30) Sample Preparation:

(31) 5 g of the respective granules were placed in a sealed, air-tight vial and heated to 120° C. for 1 h. Samples were taken from the headspace and injected to the separating column of the GC device.

(32) The volatile organic compounds were detected by a flame ionization detector and identified by a quadrupole mass spectrometer. The following compounds of Table 2 were detected:

(33) TABLE-US-00003 (a) Acetaldehyde (b) Isobutene (c) Ethanol (d) Acroleine (e) Propanal (f) Methacroleine (g) 2-methylpentane (h) 3-methalpentane (i) n-hexane (j) 2-methyl-2-butanol (k) Methylcyclopentane (l) Cyclohexane (m) 4-vinylcyclohexene (n) Ethylbenzene (o) Phenylacetylene (p) Styrene (q) o-xylene (r) Isopropylbenzene (s) Allylbenzene (t) n-propylbenzene (u) α-methylstyrene (v) not identified

(34) The exact measured values in μg/kg (i.e. parts per billion, ppb) are graphically shown in FIGS. 2a and 2b.

(35) The commercially SBC granules were then carefully degassed at 45° C. in a vacuum dryer for 48 hours. The organoleptically perceptible substances, which are contained in the degassed SBC granules, were measured again using headspace GC-MS. The measured values are graphically shown in FIGS. 3a and 3b. It is evident from these results that degassing of the commercially SBC granules signifacanity decreases the amounts of volatile organic compounds in the polymers. The exact measured values are graphically shown in FIGS. 3a and 3b.

(36) The headspace GC-MS measurements were repeated after the degassed SBC granules were re-granulated at 220-240° C. in a conventional process. The exact measured values are graphically shown in FIGS. 4a and 4b. As the content of most of the volatile organic compounds is dramatically increased upon re-granulation.

(37) Effect of Water Injection During Polymer Processing

(38) The effect of water injection during polymer processing was further investigated. A SBC sample comprising 1350 ppm Iragnox® 1010, 1350 ppm Sumilizer® GS and 1800 ppm Irgaphos® 168 was introduced to a degassing extruder after polymerization. Water was injected to the polymer melt discharge device of the extruder. Water was injected between the second and the third degassing dome and between the third and the fourth degassing dome of the extruder in a continuous fashion. Two different levels of water injection (normal, indicated as W.sub.n, and increased, indicated as W.sub.i) were applied. The normal settings are around 30 liter/hour for each injection point for around 13 m.sup.3/hour polymer resin passing through the extruder. The increased amount of water was increased by 10-60 wt.-% of the normal settings.

(39) It was found that increased water injection results in an overall decreased amount of acetaldehyde, methacrolein and styrene. The results are shown in FIG. 5. The amounts are given in percent (%) relative to the process with normal water injection W.sub.n set as 100%

(40) Effect of Stabilizer

(41) The effect of stabilizer addition was further investigated. A reaction mixture comprising Styroclear® GH 62 in cyclohexane as obtained from the polymerization process was admixed with different stabilizing agents. The compositions are indicated in the following Table 3:

(42) TABLE-US-00004 Designa- tion Composition (C) Styroclear ® GH 62 (S1) (S3) + (S4) + (S5) in ratio 1:1:1.33 (1350 ppm:1350 ppm:1800 ppm) (S2) (S3) + (S4) + (S5) in ratio 1:1:1 (S3) pentaerythritol-tetrakis(3-(3,5-di-tert-butyl-4-hydroxy- phenyl)propionate (commercially available as IRGANOX ® 1010) (S4) 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert- pentylphenylacrylate (commercially available SUMILIZER ® GS) (S5) tris(2,4-di-t-butylphenyl)phosphite (commercially available as IRGAFOS ® 168) (S6) octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (commercially available as IRGANOX ® 1076)

(43) The resulting mixture was introduced to an extruder after polymerization and the organoleptically perceptible substances were measured again using headspace GC-MS after processing was completed.

(44) The results are shown in FIG. 6. As can be seen, the addition of stabilizers results in overall reduced formation of volatile organic compounds, in particular methacroleine.