USE OF HYDROGEN PEROXIDE IN SOLID FORM TO MODIFY THE RHEOLOGY OF A THERMOPLASTIC POLYMER WHEN MELTED

Abstract

The invention relates to the use of at least one hydrogen peroxide in solid form to modify the rheology of a thermoplastic polymer when melted, specifically a polyolefin and particularly a polymer comprising at least one unit from propylene and, more particularly, polypropylene. The invention also relates to a method for modifying the rheology of a thermoplastic polymer when melted, specifically reducing viscosity when melted.

Claims

1-20. (canceled)

21. A process for modifying the melt rheology of a thermoplastic polymer comprising at least one step of mixing said polymer and hydrogen peroxide in solid form.

22. The process of claim 21, wherein modifying the melt rheology of the thermoplastic polymer comprises modifying one or more melt rheological properties of the thermoplastic polymer.

23. The process of claim 22, wherein the one or more melt rheological properties are chosen from the group consisting of the melt flow index (MFI), the melt viscosity, the molecular weight, the molecular weight distribution and the polydispersity index.

24. The process of claim 21, wherein the thermoplastic polymer is a polymer comprising at least one unit derived from propylene.

25. The process of claim 21, wherein the thermoplastic polymer is chosen from the group consisting of polypropylene and propylene copolymers comprising in their structure at least 50 mol % of units derived from propylene and at least one unit derived from an ethylenically unsaturated monomer other than propylene.

26. The process of claim 21, wherein the thermoplastic polymer is polypropylene.

27. The process of claim 21, wherein the hydrogen peroxide in solid form is chosen from the group consisting of sodium percarbonate (2Na.sub.2CO.sub.3.3H.sub.2O.sub.2), urea-hydrogen peroxide (H.sub.2O.sub.2—CO(NH.sub.2).sub.2), hydrogen peroxide adsorbed on a solid support and mixtures thereof.

28. The process of claim 21, wherein the hydrogen peroxide in solid form is sodium percarbonate (2Na.sub.2CO.sub.3.3H.sub.2O.sub.2).

29. The process of claim 21, wherein the solid hydrogen peroxide is used without a water-soluble catalyst.

30. The process of claim 21, wherein the solid hydrogen peroxide is used at a temperature ranging from 50° C. to 350° C.

31. The process as claimed in claim 21 for visbreaking the thermoplastic polymer.

32. The process as claimed in claim 21, wherein the hydrogen peroxide in solid form represents from 0.001% to 15% by weight of the thermoplastic polymer.

33. The process as claimed in claim 21, wherein the mixing step further comprises at least one organic peroxide.

34. The process as claimed in claim 33, wherein the at least one organic peroxide is a dialkyl peroxide and the dialkyl peroxide is chosen from the group consisting of 2,5-dimethyl-2,5-di(tert-butylperoxy)hex-3-yne, di-tert-butyl peroxide, di-tert-amyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, tert-butyl cumyl peroxide, di(tert-butylperoxyisopropyl)benzene, dicumyl peroxide and mixtures thereof.

35. The process as claimed in claim 33, wherein the organic peroxide represents from 0.001% to 15% by weight of the thermoplastic polymer.

36. The process as claimed in claim 21, wherein the mixing step is an extrusion step.

37. A composition comprising at least one hydrogen peroxide in solid form and at least one organic peroxide.

38. A premix composition comprising: at least one thermoplastic polymer, at least one hydrogen peroxide in solid form, and optionally at least one organic peroxide.

Description

EXAMPLES

Example of Preparation of the Polymer Compositions

[0204] In the examples below, various additives were tested in order to modify the melt rheology, in particular by reducing the melt viscosity, of polypropylene (PP).

[0205] The polymer compositions, described below, were thus produced by mixing polypropylene (PP) with an additive chosen from: [0206] an organic peroxide (95% pure 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane sold under the trade name Luperox® 101 by Arkema), [0207] hydrogen peroxide in liquid form (aqueous 35% by weight hydrogen peroxide solution sold under the name Albone® 35 by ARKEMA), [0208] sodium percarbonate (sold under the trade name ALDRICH and having an equivalent of hydrogen peroxide of 28.5% by weight), [0209] a mixture of these additives.

[0210] The various compositions are prepared in a powder mixer (Caccia CP0010G) at a temperature not exceeding 45° C. at a mixing speed of 2300±200 rpm for a time of 5 to 10 minutes.

[0211] The additive concentrations are given in ppm for the organic peroxide or as a weight percentage of pure hydrogen peroxide, or as a percentage of sodium percarbonate (with the equivalent of pure hydrogen peroxide as a weight percentage) relative to the polypropylene.

[0212] A process for visbreaking the compositions, described below, is then carried out.

[0213] After mixing, the powder obtained is then extruded in the form of granules on a counter-rotating twin-screw extruder of the Brabender KDSE type with a material temperature at the die of 230° C. and a throughput of 7 kg/h.

[0214] Melt Flow Index (MFI) Test

[0215] The melt flow index (MFI) is measured according to standard ISO 1133 at a temperature of 190° C. under a load of 2160 grams. The die has a length of 8 mm and an internal diameter of 2.095 mm

[0216] The temperature for carrying out the test at 190° C. was supplemented in the results tables by a measurement at a temperature of 230° C. (the other test conditions remaining identical).

[0217] The higher the melt flow index (MFI), the lower the melt viscosity.

Example 1

[0218] The melt flow index (MFI) was determined for the following compositions at a temperature of 190° C. and 230° C. in accordance with standard ISO 1133.

[0219] The results are grouped together in the table below:

TABLE-US-00001 TABLE 1 Comparison of the melt flow indices with hydrogen peroxide or organic peroxide. MFI MFI (g/10 min) (g/10 min) Compositions 190° C. 230° C. 1 PP alone 0.9 2 2 PP + 507 ppm Luperox ® 101 7 ± 2 19 ± 3 3 PP + 1% Albone ® 35 2 ± 3 21 ± 7 (0.35% hydrogen peroxide) 4 PP + 3% Albone ® 35 5 ± 3 17 ± 7 (1.05% hydrogen peroxide)

[0220] During the extrusion of compositions 3 and 4, phenomena of bubbles and released gases were observed and also an extrudability irregularity (unstable hopper feeding).

[0221] Results—Discussion

[0222] It is found that a large amount of aqueous hydrogen peroxide is necessary to achieve the same performance level, measured by the MFI value of the polypropylene, as in the presence of the organic peroxide.

[0223] Furthermore, it is observed that the melt index fluctuates significantly with the aqueous hydrogen peroxide. This phenomenon is due to the irregularity in feeding the polypropylene in the presence of aqueous hydrogen peroxide.

Example 2

[0224] The melt flow index (MFI) was determined for the following compositions at a temperature of 190° C. and 230° C. in accordance with standard ISO 1133.

[0225] The results are grouped together in the table below:

TABLE-US-00002 TABLE 2 Comparison of the hot melt flow indices with organic peroxide alone or in the presence of sodium percarbonate. MFI MFI (g/10 min) (g/10 min) Compositions 190° C. 230° C. 5 PP alone 0.9 2 6 PP + 507 ppm Luperox ® 101  7 ± 2 19 ± 3 7 PP + 1013 ppm Luperox ® 101 14 ± 2 42 ± 3 8 PP + 507 ppm Luperox ® 101 + 10 ± 2 32 ± 3 0.2% sodium percarbonate (+0.057% hydrogen peroxide) 9 PP + 507 ppm Luperox ® 101 + 13 ± 2 45 ± 3 0.4% sodium percarbonate (+0.114% hydrogen peroxide) 10 PP + 1.2% sodium percarbonate 14 ± 2 81 ± 3 (+0.34% hydrogen peroxide)

[0226] By comparing the melt flow indices (MFI) of compositions 10 and 3, it is found that sodium percarbonate is more effective than aqueous hydrogen peroxide.

[0227] Indeed, composition 10 has a significantly higher and more stable melt flow index (MFI) than composition 3 at a temperature of 190° C. and 230° C. Consequently, composition 10 also has a lower melt viscosity than composition 3 at these temperatures.

[0228] Furthermore, composition 10 has a melt flow index (MFI) that is identical to composition 7 at a temperature of 190° C. and higher at a temperature of 230° C.

[0229] It also results from table 2 that the MFI measurements have the same reproducibility whether in the presence of organic peroxide alone or in the presence of a mixture of organic peroxide and sodium percarbonate.

[0230] Composition 9 has a melt flow index similar to composition 7 using half the organic peroxide which was replaced by an amount of solid hydrogen peroxide in the form of sodium percarbonate much lower than the amount required in the example 10.

[0231] Thus the use of sodium percarbonate makes it possible to reduce the amount of organic peroxide to be used to obtain a thermoplastic polymer having a similar viscosity.

[0232] Furthermore, the mixture of organic peroxide and sodium percarbonate has the advantage of reducing bubbles in the extruded polypropylene, which makes it possible to minimize the number of degassing operations during the extrusion.

Example 3

[0233] The amount of volatile organic compounds (in μgC/g) in the following compositions was determined after the visbreaking process.

[0234] The content of volatile organic compounds was measured under the analytical conditions used for GC/MS and GC/FID analyses and correspond to those described in detail in standard VDA 277.

[0235] The chromatographic conditions used are as follows: [0236] Column: ZB-WAX plus, 30 m×0.25 mm, 0.25 μm [0237] Temperature programming: 50° C. (3 minutes) then 12° C./min up to a temperature of 200° C. (19.5 min) [0238] Carrier gas (helium) flow rate: 1 ml/min [0239] Split: 20 ml/min

[0240] An amount of 2.6 grams of each sample is placed in a headspace type sampling vial which is then crimped. The samples are then heated for a period of 5 hours at a temperature of 120° C.

[0241] The headspaces of the samples are drawn off then analyzed by GC/MS or GC/FID. The analyses are carried out twice for each sample.

[0242] The results are grouped together in the table below:

TABLE-US-00003 TABLE 3 Measurements of the volatile matter according to VDA 277 Volatiles Compositions (μgC/g) 5 PP alone 110 6 PP + 507 ppm Luperox ® 101 320 7 PP+ 1013 ppm Luperox ® 101 475 8 PP + 507 ppm Luperox ® 101 + 290 0.2% sodium percarbonate (+0.057% hydrogen peroxide) 9 PP + 507 ppm Luperox ® 101 + 280 0.4% sodium percarbonate (+0.114% hydrogen peroxide) 10 PP + 1.2% sodium percarbonate 135 (+0.34% hydrogen peroxide)

[0243] Composition 9 has a similar melt flow index to composition 7 using half the organic peroxide and also has the advantage of generating a significantly lower volatile matter content.

[0244] The results show that the composition according to the invention makes it possible both to increase the melt flow index at temperatures of 190° C. and 230° C. while significantly reducing the content of residual volatile organic compounds in the polypropylene.

[0245] For an identical melt flow index level, the composition of the invention also makes it possible to considerably reduce the amount of hydrogen peroxide of use compared to a composition comprising only aqueous hydrogen peroxide.