Stabilising Composition

Abstract

The invention concerns a stabilising composition, comprising: at least one antioxidant comprising one or more of: a phenolic antioxidant, a phosphite antioxidant, a sulphur-containing antioxidant, and an aminic antioxidant; and at least one buffering agent, wherein the buffering agent has the capacity to buffer in aqueous solution at a pH range from 4 to 8.

Claims

1-25. (canceled)

26. A method of stabilising a polyolefin or a hot melt adhesive to provide a stabilised polymeric composition, the method comprising: adding a stabilising composition to the polyolefin or the hot melt adhesive, wherein the stabilising composition comprises: a. at least one antioxidant comprising one or more of: i. a phenolic antioxidant; ii. a phosphite antioxidant; iii. a sulphur-containing antioxidant; and iv. an aminic antioxidant; and b. at least one buffering agent, wherein the buffering agent has the capacity to buffer in aqueous solution at a pH range from 4 to 8, and wherein the buffering agent is a solid at a temperature of 50° C. or lower.

27. The method according to claim 26, wherein the buffering agent is a solid at a temperature of 40° C. or lower and 1 atmosphere pressure.

28. The method according to claim 26, wherein the buffering agent has a molecular weight of less than 500.

29. The method according to claim 26, wherein the buffering agent comprises one or more metal phosphates and/or metal pyrophosphates.

30. The method according to claim 26, wherein the buffering agent comprises a mixture of two or more metal phosphates and/or metal pyrophosphates.

31. The method according to claim 26, wherein the buffering agent comprises a mixture of at least one monobasic alkali metal phosphate and at least one dibasic alkali metal phosphate.

32. The method according to claim 26, wherein the buffering agent comprises one or more amino acids and/or alkali metal salts thereof.

33. The method according to claim 26, wherein the buffering agent is present in an amount of from 1% to 50% by weight of the stabilising composition.

34. The method according to claim 26, wherein the stabilising composition additionally comprises a secondary inorganic antioxidant.

35. The method according to claim 34, wherein the secondary inorganic antioxidant comprises one or more of a metal hypophosphite, a metal thiosulphate, a metal bisulphite, a metal metabisulphite and/or a metal hydrosulphite.

36. The method according to claim 35, wherein the metal of the metal hypophosphite, the metal thiosulphate, the metal bisulphite, the metal metabisulphite and/or the metal hydrosulphite is an alkali metal and/or an alkaline earth metal.

37. The method according to claim 35, wherein the metal hypophosphite is an anhydrous or hydrated metal hypophosphite.

38. The method according to claim 34, wherein the ratio of the buffering agent to the secondary inorganic antioxidant is from 5:95 to 95:5.

39. The method according to claim 26, wherein the phenolic antioxidant comprises a semi-hindered or a hindered phenolic antioxidant.

40. The method according to claim 26, wherein the phenolic antioxidant is present in an amount of from 1% to 50% by weight of the stabilising composition.

41. The method according to claim 26, wherein the phosphite antioxidant comprises an organophosphite antioxidant.

42. The method according to claim 26, wherein the phosphite antioxidant is present in an amount of from 20% to 90% by weight of the stabilising composition.

43. The method according to claim 26, wherein the sulphur-containing antioxidant comprises one or more thioether groups and one or more ester groups.

44. The method according to claim 26, wherein the sulphur-containing antioxidant is present in an amount of from 1% to 50% by weight of the stabilising composition.

45. The method according to claim 26, wherein the antioxidant comprises a phenolic antioxidant and a phosphite antioxidant.

46. The method according to claim 26, wherein the antioxidant comprises a phenolic antioxidant, a phosphite antioxidant, and a sulphur-containing antioxidant.

47. The method according to claim 26, wherein the stabilising composition is present in an amount of from 0.01% to 5% by weight of the stabilised polymeric composition.

48. The method according to claim 26, wherein the stabilising composition is added to the polyolefin.

49. The method according to claim 26, wherein the stabilising composition is added to the hot melt adhesive.

50. A stabilised polymeric composition comprising a polymeric base material and a stabilising composition, wherein the polymeric base material comprises a polyolefin or a hot melt adhesive; the stabilising composition comprises: a. at least one antioxidant comprising one or more of: i. a phenolic antioxidant; ii. a phosphite antioxidant; iii. a sulphur-containing antioxidant; and iv. an aminic antioxidant; and b. at least one buffering agent, wherein the buffering agent has the capacity to buffer in aqueous solution at a pH range from 4 to 8, and wherein the buffering agent is a solid at a temperature of 50° C. or lower.

51. The stabilised polymeric composition according to claim 50, wherein the stabilising composition is present in an amount of from 0.01% to 5% by weight of the stabilised polymeric composition.

Description

EXAMPLES

[0147] 1. Stabilisation of a Hot Melt Adhesive

Preparing the Stabilised Composition

[0148] A hot melt adhesive was prepared from the appropriate amounts of metallocene polyolefin polymer base material, tackifier resin, wax and oil.

[0149] Numerous stabilising compositions were prepared.

[0150] Table 1 shows the different components that were used in the stabilising compositions.

TABLE-US-00001 TABLE 1 Component Shorthand Type ANOX ™ 20 A20 Phenolic antioxidant ALKANOX ™ 240 A240 Phosphite antioxidant NAUGARD ™ 412S N412S Sulphur-containing antioxidant Monosodium glutamate MSG Buffering agent Cysteine Cys Buffering agent Cystine Cystine Buffering agent Methionine Met Buffering agent Arginine Arg Buffering agent Histidine His Buffering agent Tyrosine Tyr Buffering agent Potassium acetate KOAc Acid scavenger Potassium carbonate K.sub.2CO.sub.3 Acid scavenger 1:1 NaH.sub.2PO.sub.4:Na.sub.2HPO.sub.4 Na P Buffering agent 1:1 KH.sub.2PO.sub.4/K.sub.2HPO.sub.4 K P Buffering agent

[0151] Table 2 shows the various stabilising compositions that were prepared. The % amounts shown in the table are % by weight of the overall hot melt adhesive composition. Samples 1, 12 and 13 were comparative samples.

TABLE-US-00002 TABLE 2 Buffering Agent/Acid A20 A240 N412S Scavenger Total Sample (%) (%) (%) Identity % (%)  1 (Comp) 0.500 — — — — 0.500  2 0.050 0.400 — Cys 0.050 0.500  3 0.050 0.400 0.025 Cys 0.025 0.500  4 0.050 0.375 0.050 MSG 0.025 0.500  5 0.050 0.400 — Cystine 0.050 0.500  6 0.050 0.400 — Met 0.050 0.500  7 0.050 0.375 0.050 Arg 0.025 0.500  8 0.050 0.375 0.050 His 0.025 0.500  9 0.050 0.375 0.050 Tyr 0.025 0.500 10 0.050 0.375 0.050 MSG 0.025 0.500 11 0.050 0.350 0.050 MSG 0.050 0.500 12 (Comp) 0.050 0.350 0.050 KOAc 0.050 0.500 13 (Comp) 0.050 0.350 0.050 K.sub.2CO.sub.3 0.050 0.500 14 0.050 0.350 0.050 Na P 0.050 0.500 15 0.050 0.350 0.050 K P 0.050 0.500

[0152] Each of the above-identified stabilising compositions were added to a sample of the hot melt adhesive in an amount of 0.5% by weight of the hot melt adhesive.

[0153] The mixture was then heated at 170° C. for 30 minutes to melt the mixture before being heated in an oil bath at 160° C. for 30 minutes whilst stirring with an overhead stirrer to ensure intimate mixing of the hot melt adhesive with the stabilising composition.

[0154] Colour Retention and Dynamic Viscosity

[0155] Approximately 10 g of the molten hot melt adhesive mixture was poured into each of six test tubes. One test tube was retained as the T=0 hours condition i.e. with no heat aging. The remaining five test tubes were heated in a fan oven (Thermo OMH180 with fan speed 1) at 170° C. A test tube was removed from the oven after 24 hours, 48 hours, 72 hours, 96 hours and 120 hours, and the colour of the sample assessed at 180° C. in a Lovibond™ Comparator 3000 using the Gardner Colour Scale.

[0156] Overall, the colour development of each sample was assessed over five days heat aging. Sample 1 represents an industry standard control antioxidant.

[0157] The results are shown in Table 3 below.

TABLE-US-00003 TABLE 3 T = T = T = T = T = T = Sample 0 h 24 h 48 h 72 h 96 h 120 h  1 (Comp) <1 2.5 4.5 6.5 10.0 11.5  2 <1 3.0 5.0 7.5 11.5 12.0  3 <1 2.5 4.5 5.5 8.5 11.0  4 <1 1.5 2.5 3.0 3.0 4.0  5 <1 3.0 8.0 13.0 13.5 14.5  6 <1 2.0 6.0 11.5 12.0 12.5  7 <1 3.5 4.5 5.0 8.0 12.0  8 <1 3.0 3.0 4.0 4.5 5.5  9 <1 3.5 4.0 4.5 5.5 7.0 10 <1 2.0 3.0 3.0 4.0 4.5 11 <1 2.5 3.0 3.0 4.5 4.0 12 (Comp) <1 2.0 3.0 3.5 4.0 4.0 13 (Comp) <1 3.0 4.0 4.0 4.0 3.5 14 <1 <1 <1 1.0 2.0 2.5 15 <1 2.0 2.0 2.0 2.5 4.0

[0158] The above results show the performance of the sample stabilising compositions during a prolonged period of heat aging. The lower the number recorded for colour development, the better the heat aging performance of the stabilising composition.

[0159] Sample 1 acted as a typical industry standard antioxidant. As can be seen from the results, the stabilising compositions in accordance with the present invention performed comparably or showed an improvement over the industry standard sample.

[0160] In particular, samples 4, 8 to 11, 14 and 15 all showed a significant improvement in heat aging performance over the industry standard sample. Sample 14 showed extremely good heat aging performance, with no discernible colour formation up to 48 hours.

[0161] For each of the samples, the retention in dynamic viscosity was also assessed. Measurements of dynamic viscosity were taken at T=0 hours and T=120 hours using a Brookfield LV DV2T at a temperature of 160° C. via a single point test. The retention in dynamic viscosity was then calculated as the % ratio of the viscosity at T=120 divided by the viscosity at T=0

[0162] The results are shown in Table 4 below.

TABLE-US-00004 TABLE 4 Sample Dynamic Viscosity retained after T = 120 h (%)  1 (Comp) 97.7  2 99.8  3 101.8  4 100.1  5 100.2  6 102.1  7 112.5  8 103.7  9 98.7 10 119.0 11 107.8 12 (Comp) 105.5 13 (Comp) 99.7 14 112.2 15 114.2

[0163] The above results show the retention of dynamic viscosity of the sample stabilising compositions after a prolonged period of heat aging. A reduction in dynamic viscosity i.e. a value of less than 100%, is indicative of oxidative degradation in the sample. This may be detrimental to the performance of the hot melt adhesive. An increase in dynamic viscosity is not considered detrimental to the performance of the hot melt adhesive.

[0164] Sample 1 acted as a typical industry standard antioxidant. As can be seen from the results, the stabilising compositions in accordance with the present invention performed comparably or showed an improvement over the industry standard sample. In particular, samples 3 to 8, 10, 11, 14 and 15 all showed an improvement in dynamic viscosity retention over the industry standard sample.

[0165] 2. Stabilisation of a Polyolefin

Preparing the Stabilised Composition

[0166] The polyolefin base material was polypropylene.

[0167] Numerous stabilising compositions were prepared.

[0168] Table 5 shows the different components that were used in the stabilising compositions.

TABLE-US-00005 TABLE 5 Component Shorthand Type ANOX ™ 20 A20 Phenolic antioxidant ALKANOX ™ 240 A240 Phosphite antioxidant ULTRANOX ™ 626 U626 Phosphite antioxidant Calcium stearate CaSt Acid scavenger Dihydrotalcite DHT Acid scavenger Sodium hypophosphite Na Hyp Secondary inorganic antioxidant (anhydrous) 1:1 NaH.sub.2PO.sub.4:Na.sub.2HPO.sub.4 Na P Buffering agent

[0169] Table 6 shows the various stabilising compositions that were prepared. The % amounts shown in the table are % by weight of the overall polypropylene composition. Samples 16, 20 and 21 were comparative samples.

TABLE-US-00006 TABLE 6 Na Na A20 A240 U626 CaSt DHT Hyp P Total Sample (%) (%) (%) (%) (%) (%) (%) (%) 16 (Comp) 0.04 0.08 — 0.03 — — — 0.15 17 0.04 0.08 — — — 0.01 0.02 0.15 18 0.04 0.08 — — —  0.015  0.015 0.15 19 0.04 0.08 — — — 0.02 0.01 0.15 20 (Comp) 0.04 0.08 — — 0.018 — — 0.138 21 (Comp) 0.08 — 0.08 — — — — 0.16 22 0.08 — 0.08 — —  0.015  0.015 0.19

[0170] Each of the samples was compounded with the polypropylene base material in an extruder at 230° C. under nitrogen to form a polypropylene composition.

[0171] Colour Stability and Melt Flow Rate

[0172] Each of the polypropylene compositions was multi-passed through the extruder at 260° C. under air. The discolouration of the compositions was measured in terms of Yellowness Index (YI) using a colorimeter. YI values were taken following compounding (pass 0) and after pass 1, 3 and 5. The lower the YI value, the less discolouration of the composition. The results are shown in Table 7.

TABLE-US-00007 TABLE 7 YI Value Sample Pass 0 Pass 1 Pass 3 Pass 5 16 (Comp) 0.138 0.438 3.025 4.498 17 −0.680 0.005 1.095 2.280 18 −1.073 −0.670 0.158 1.020 19 −0.825 −0.363 0.845 2.215 20 (Comp) −0.885 0.335 2.120 3.580 21 (Comp) −0.845 0.338 1.705 2.875 22 −0.893 0.165 0.918 1.333

[0173] The stabilising composition of Sample 16 represents an industry standard involving a calcium stearate acid scavenger. The stabilising composition of Sample 20 represents an industry standard which does not utilise a stearate acid scavenger (instead using DHT). The stabilising composition of Sample 21 contains no acid scavenger.

[0174] From the results, it can be seen that the polypropylene samples stabilised with the stabilising compositions in accordance with the present invention (samples 17, 18, 19 and 22) show less discolouration than the polypropylene samples stabilised with the industry standard stabilising compositions.

[0175] The melt flow rate of the polypropylene composition of Sample 16, Sample 18, Sample 21 and Sample 22 was determined in accordance with standard test method ASTM D1238L using a CEAST™ 7026 Melt Flow Tester (230° C., 2.16 kg, 2.095 mm die). The melt flow rate was determined following compounding (pass 0) and after pass 5. An increase in the melt flow rate value is indicative of degradation of the sample. The results are shown in Table 8.

TABLE-US-00008 TABLE 8 Melt Flow Rate (g/10 min) Sample Pass 0 Pass 5 16 (Comp) 1.83 5.34 18 1.99 4.59 21 (Comp) 2.37 4.87 22 2.06 4.48

[0176] From the results it can be seen that the polypropylene stabilised using the stabilising composition according to the present invention (Sample 18) retained its melt flow rate better than the polypropylene stabilised using an industry standard stabilising composition (Sample 16). Sample 16 shows a 292% increase in melt flow rate after 5 passes through the extruder whereas Sample 18 only shows a 231% increase. This corresponds to a significant improvement in melt flow rate retention on heat aging for Sample 18.

[0177] For Samples 21 and 22, it can be seen that the polypropylene sample stabilised in accordance with the present invention (Sample 22) exhibited a comparable melt flow rate to the polypropylene sample stabilised with the industry standard stabilising composition (Sample 21).

[0178] 3. Stabilisation of a Polyolefin-Anhydrous Vs. Monohydrate Hypophosphite

Preparing the Stabilised Composition

[0179] The polyolefin base material was polypropylene.

[0180] Table 9 shows the different components that were used in the stabilising compositions.

TABLE-US-00009 TABLE 9 Component Shorthand Type ANOX ™ 20 A20 Phenolic antioxidant ALKANOX ™ 240 A240 Phosphite antioxidant Anhydrous sodium Na Hyp (an) Secondary inorganic hypophosphite antioxidant Monohydrate sodium Na Hyp (mono) Secondary inorganic hypophosphite antioxidant 1:1 NaH.sub.2PO.sub.4:Na.sub.2HPO.sub.4 Na P Buffering agent

[0181] Table 10 shows details of the polypropylene compositions that were prepared.

TABLE-US-00010 TABLE 10 PP Na Na Base Hyp Hyp Na Polymer A20 A240 (an) (mono) P Total Sample (g) (g) (g) (g) (g) (g) (g) 23 599.100 0.240 0.480 0.090 0 0.090 600.000 24 599.082 0.240 0.480 0 0.108 0.090 600.000 25 (Comp) 599.280 0.240 0.480 0 0 0 600.000

[0182] Each of the samples was formed by compounding all of the components in an extruder at 230° C. under nitrogen to form a polypropylene composition.

[0183] It should be noted that a slightly greater amount of monohydrate sodium hypophosphite was used in Sample 24 compared to the anhydrous sodium hypophosphite used in Sample 23. This was done to ensure that the phosphorous loading of the samples was the same.

[0184] Colour Stability

[0185] Each of the polypropylene compositions was multi-passed through the extruder at 260° C. under air. The discolouration of the compositions was measured in terms of Yellow Index (YI) using a colorimeter. YI values were taken following compounding (pass 0) and after pass 1, 3 and 5. The lower the YI value, the less discolouration of the composition. The results are shown in Table 11.

TABLE-US-00011 TABLE 11 YI Value Sample Pass 0 Pass 1 Pass 3 Pass 5 23 0.43 1.92 3.33 5.65 24 −0.06 1.50 2.86 4.08 25 (Comp) 0.08 1.44 3.85 8.61

[0186] These results are displayed graphically in FIG. 1.

[0187] The stabilising composition of Sample 25 represents an industry standard having no acid scavenger.

[0188] From the results, it can be can be seen that the polypropylene samples stabilised in accordance with the present invention (samples 23 and 24) show less discolouration than the polypropylene sample stabilised with the industry standard stabilising composition (Sample 25).

[0189] In addition, it can be seen that the sample containing the monohydrate sodium hypophosphite (Sample 24) performed slightly better than the sample containing the anhydrous sodium hypophosphite (Sample 23) with respect to discolouration of the polypropylene composition.

[0190] Melt Flow Rate

[0191] The melt flow rate of the polypropylene compositions was determined in accordance with standard test method ASTM D1238L using a CEAST™ 7026 Melt Flow Tester (230° C., 2.16 kg, 2.095 mm die). The melt flow rate was determined following compounding (pass 0) and after pass 5. An increase in the melt flow rate value is indicative of degradation of the sample. The results are shown in Table 12.

TABLE-US-00012 TABLE 12 Melt Flow Rate (g/10 min) Sample Pass 0 Pass 5 23 7.74 12.50 24 6.83 13.04 25 (Comp) 7.57 12.95

[0192] The results are displayed graphically in FIG. 2.

[0193] From the results it can be seen that the polypropylene samples stabilised in accordance with the present invention (samples 23 and 24) exhibited comparable melt flow rates to the polypropylene sample stabilised with the industry standard stabilising composition (Sample 25).

[0194] Additionally, it can be seen that the polypropylene sample containing the monohydrate sodium hypophosphite (Sample 24) exhibited a comparable melt flow rate to the sample containing the anhydrous sodium hypophosphite (Sample 23).

[0195] Overall, the results show that at equal phosphorous loadings, there is no detrimental effect to colour stability or melt flow rate when using monohydrate sodium hypophosphite compared to when using anhydrous sodium hypophosphite. In fact, a slight improvement in colour stability was observed when using the monohydrate sodium hypophosphite